Journal articles on the topic 'Long-range weather forecasting Africa, Southern'

Abstract. Subsistence farming in southern Africa is vulnerable to extreme weather conditions. The yield of rain-fed agriculture depends largely on rainfall-related factors such as total seasonal rainfall, anomalous onsets and lengths of the rainy season and the frequency of occurrence of dry spells. Livestock, in turn, may be seriously impacted by climatic stress with, for example, exceptionally hot days, affecting condition, reproduction, vulnerability to pests and pathogens and, ultimately, morbidity and mortality. Climate change may affect the frequency and severity of extreme weather conditions, impacting on the success of subsistence farming. A potentially interesting adaptation measure comprises the timely forecasting and warning of such extreme events, combined with mitigation measures that allow farmers to prepare for the event occurring. This paper investigates how the frequency of extreme events may change in the future due to climate change over southern Africa and, in more detail, the Limpopo Basin using a set of climate change projections from several regional climate model downscalings based on an extreme climate scenario. Furthermore, the paper assesses the predictability of these indicators by seasonal meteorological forecasts of the European Centre for Medium-Range Weather Forecasts (ECMWF) seasonal forecasting system. The focus is on the frequency of dry spells as well as the frequency of heat stress conditions expressed in the temperature heat index. In areas where their frequency of occurrence increases in the future and predictability is found, seasonal forecasts will gain importance in the future, as they can more often lead to informed decision-making to implement mitigation measures. The multi-model climate projections suggest that the frequency of dry spells is not likely to increase substantially, whereas there is a clear and coherent signal among the models of an increase in the frequency of heat stress conditions by the end of the century. The skill analysis of the seasonal forecast system demonstrates that there is a potential to adapt to this change by utilizing the weather forecasts, given that both indicators can be skilfully predicted for the December–February season, at least 2 months ahead of the wet season. This is particularly the case for predicting above-normal and below-normal conditions. The frequency of heat stress conditions shows better predictability than the frequency of dry spells. Although results are promising for end users on the ground, forecasts alone are insufficient to ensure appropriate response. Sufficient support for appropriate measures must be in place, and forecasts must be communicated in a context-specific, accessible and understandable format.

Abstract Seasonal multimodel forecasts from the Development of a European Multimodel Ensemble System for Seasonal-to-Interannual Prediction (DEMETER) project are used to drive a malaria model and create reforecasts of malaria incidence for Botswana, in southern Africa, in a unique integration of a fully dynamic, process-based malaria model with an ensemble forecasting system. The forecasts are verified against a 20-yr malaria index and compared against reference simulations obtained by driving the malaria model with data from the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-40). Performance assessment reveals skill in the DEMETER-driven malaria forecasts for prediction of low (below the lower tercile), above-average (above the median), and high (above the upper tercile) malaria events, with the best results obtained for low malaria events [relative operating characteristics (ROC) area = 0.84, 95% confidence interval = 0.63–1.0]. For high malaria events, the DEMETER-driven malaria forecasts are skillful, but the forecasting system performs poorly for those years that it predicts the highest probabilities of a high malaria event. Potential economic value analysis demonstrates the potential value for the DEMETER-driven malaria forecasts over a wide range of user cost-loss ratios, which is primarily due to the ability of the system to save on the cost of action in low malaria years.

Abstract. Subsistence farming in Southern Africa is vulnerable to extreme weather conditions. The yield of rain-fed agriculture depends largely on rainfall-related factors such as total seasonal rainfall, anomalous onsets and lengths of the rainy season and the frequency of occurrence of dry spells. Livestock, in turn, may be seriously impacted by climatic stress with, for example, exceptionally hot days, affecting condition, reproduction, vulnerability to pests and pathogens and, ultimately, morbidity and mortality. Climate change may affect the frequency and severity of extreme weather conditions, impacting on the success of subsistence farming. A potentially interesting adaptation measure comprises the timely forecasting and warning of such extreme events, combined with mitigation measures that allow farmers to prepare for the event occurring. This paper investigates how the frequency of extreme events may change in the future due to climate change over southern Africa and, in more detail, the Limpopo basin using a set of climate change projections from several regional climate model downscalings. Furthermore the paper assesses the predictability of these indicators by seasonal meteorological forecasts of the European Centre for Medium-range Weather Forecasts (ECMWF) seasonal forecasting system. The focus is on the frequency of dry spells as well as the frequency of heat stress conditions expressed in the Temperature Heat Index. In areas where their frequency of occurrence increases in the future and predictability is found, seasonal forecasts will gain importance in the future as they can more often lead to informed decision making to implement mitigation measures. The multi-model climate projections suggest that the frequency of dry spells is not likely to increase substantially, whereas there is a clear and coherent signal among the models, of an increase in the frequency of heat stress conditions by the end of the century. The skill analysis of the seasonal forecast system demonstrates that there is a potential to adapt to this change by utilizing the weather forecasts given that both indicators can be skilfully predicted for the December-to-February season, at least two months ahead of the wet season. This is particularly the case for predicting above-normal and below-normal conditions. The frequency of heat stress conditions shows better predictability than the frequency of dry spells. Although results are promising for end users on the ground, forecasts alone are insufficient to ensure appropriate response. Sufficient support for appropriate measures must be in place, and forecasts must be communicated in a context-specific, accessible and understandable format.

Abstract. Aerosol-aware microphysics parameterisation schemes are increasingly being introduced into numerical weather prediction models, allowing for regional and case-specific parameterisation of cloud condensation nuclei (CCN) and cloud droplet interactions. In this paper, the Thompson aerosol-aware microphysics scheme, within the Weather Research and Forecasting (WRF) model, is used for two fog cases during September 2017 over Namibia. Measurements of CCN and fog microphysics were undertaken during the AErosols, RadiatiOn and CLOuds in southern Africa (AEROCLO-sA) field campaign at Henties Bay on the coast of Namibia during September 2017. A key concept of the microphysics scheme is the conversion of water-friendly aerosols to cloud droplets (hereafter referred to as CCN activation), which could be estimated from the observations. A fog monitor 100 (FM-100) provided cloud droplet size distribution, number concentration (Nt), liquid water content (LWC), and mean volumetric diameter (MVD). These measurements are used to evaluate and parameterise WRF model simulations of Nt, LWC, and MVD. A sensitivity analysis was conducted through variations to the initial CCN concentration, CCN radius, and the minimum updraft speed, which are important factors that influence droplet activation in the microphysics scheme of the model. The first model scenario made use of the default settings with a constant initial CCN number concentration of 300 cm−3 and underestimated the cloud droplet number concentration, while the LWC was in good agreement with the observations. This resulted in droplet size being larger than the observations. Another scenario used modelled data as CCN initial conditions, which were an order of magnitude higher than other scenarios. However, these provided the most realistic values of Nt, LWC, MVD, and droplet size distribution. From this, it was concluded that CCN activation of around 10 % in the simulations is too low, while the observed appears to be higher reaching between 20 % and 80 %, with a mean (median) of 0.55 (0.56) during fog events. To achieve this level of activation in the model, the minimum updraft speed for CCN activation was increased from 0.01 to 0.1 m s−1. This scenario provided Nt, LWC, MVD, and droplet size distribution in the range of the observations, with the added benefit of a realistic initial CCN concentration. These results demonstrate the benefits of a dynamic aerosol-aware scheme when parameterised with observations.

Abstract. Mineral dust plays an important role in the climate of the Tibetan Plateau (TP) by modifying the radiation budget, cloud macro- and microphysics, precipitation, and snow albedo. Meanwhile, the TP, with the highest topography in the world, can affect intercontinental transport of dust plumes and induce typical distribution characteristics of dust at different altitudes. In this study, we conduct a quasi-global simulation to investigate the characteristics of dust source contribution and transport over the TP at different altitudes by using a fully coupled meteorology–chemistry model, the Weather Research and Forecasting model with chemistry (WRF-Chem), with a tracer-tagging technique. Generally, the simulation reasonably captures the spatial distribution of satellite-retrieved dust aerosol optical depth (AOD) at different altitudes. Model results show that dust particles are emitted into atmosphere through updrafts over major desert regions and then transported to the TP. The East Asian dust (mainly from the Gobi and Taklamakan deserts) is transported southward and is lifted up to the TP, contributing a mass loading of 50 mg m−2 at a height of 3 km and 5 mg m−2 at a height of 12 km over the northern slope of the TP. Dust from North Africa and the Middle East are concentrated over both of the northern and southern slopes below 6 km, where mass loadings range from 10 to 100 and 1 to 10 mg m−2 below 3 km and above 9 km, respectively. As the dust is transported to the north and over the TP, mass loadings are 5–10 mg m−2 above a height of 6 km. The dust mass flux carried from East Asia to the TP is 7.9 Tg yr−1, mostly occurring at heights of 3–6 km. The dust particles from North Africa and the Middle East are transported eastward following the westerly jet and then are carried into the TP at the west side with dust mass fluxes of 7.8 and 26.6 Tg yr−1, respectively. The maximum mass flux of the North African dust mainly occurs at 0–3 km (3.9 Tg yr−1), while the Middle Eastern dust occurs at 6–9 km (12.3 Tg yr−1). The dust outflow occurs on the east side (−17.89 Tg yr−1) and south side (−11.22 Tg yr−1) of the TP, with a peak value (8.7 Tg yr−1) at 6–9 km. Moreover, the dust (by mass) is concentrated within the size range of 1.25–5.0 µm and the dust (by particle number) is concentrated in the size range of 0.156–1.25 µm. Compared with other aerosols, the dust contributes to more than 50 % of the total AOD over the TP. The direct radiative forcing induced by the dust is −1.28 W m−2 at the top of the atmosphere (cooling), 0.41 W m−2 in the atmosphere (warming), and −1.68 W m−2 at the surface (cooling). Our quantitative analyses of the dust contributions from different source regions and the associated radiative forcing can help us to better understand the role of dust on the climate over the TP and surrounding regions.

Abstract. Characterising the dynamics of landscape scale wildfires at very high temporal resolutions is best achieved using observations from Earth Observation (EO) sensors mounted onboard geostationary satellites. As a result, a number of operational active fire products have been developed from the data of such sensors. An example of which are the Fire Radiative Power (FRP) products, the FRP-PIXEL and FRP-GRID products, generated by the Land Surface Analysis Satellite Applications Facility (LSA SAF) from imagery collected by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on-board the Meteosat Second Generation (MSG) series of geostationary EO satellites. The processing chain developed to deliver these FRP products detects SEVIRI pixels containing actively burning fires and characterises their FRP output across four geographic regions covering Europe, part of South America and northern and southern Africa. The FRP-PIXEL product contains the highest spatial and temporal resolution FRP dataset, whilst the FRP-GRID product contains a spatio-temporal summary that includes bias adjustments for cloud cover and the non-detection of low FRP fire pixels. Here we evaluate these two products against active fire data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS), and compare the results to those for three alternative active fire products derived from SEVIRI imagery. The FRP-PIXEL product is shown to detect a substantially greater number of active fire pixels than do alternative SEVIRI-based products, and comparison to MODIS on a per-fire basis indicates a strong agreement and low bias in terms of FRP values. However, low FRP fire pixels remain undetected by SEVIRI, with errors of active fire pixel detection commission and omission compared to MODIS ranging between 9–13 and 65–77% respectively in Africa. Higher errors of omission result in greater underestimation of regional FRP totals relative to those derived from simultaneously collected MODIS data, ranging from 35% over the Northern Africa region to 89% over the European region. High errors of active fire omission and FRP underestimation are found over Europe and South America, and result from SEVIRI's larger pixel area over these regions. An advantage of using FRP for characterising wildfire emissions is the ability to do so very frequently and in near real time (NRT). To illustrate the potential of this approach, wildfire fuel consumption rates derived from the SEVIRI FRP-PIXEL product are used to characterise smoke emissions of the 2007 Peloponnese wildfires within the European Centre for Medium-Range Weather Forecasting (ECMWF) Integrated Forecasting System (IFS), as a demonstration of what can be achieved when using geostationary active fire data within the Copernicus Atmosphere Monitoring System (CAMS). Qualitative comparison of the modelled smoke plumes with MODIS optical imagery illustrates that the model captures the temporal and spatial dynamics of the plume very well, and that high temporal resolution emissions estimates such as those available from geostationary orbit are important for capturing the sub-daily variability in smoke plume parameters such as aerosol optical depth (AOD), which are increasingly less well resolved using daily or coarser temporal resolution emissions datasets. Quantitative comparison of modelled AOD with coincident MODIS and AERONET AOD indicates that the former is overestimated by ∼ 20–30%, but captures the observed AOD dynamics with a high degree of fidelity. The case study highlights the potential of using geostationary FRP data to drive fire emissions estimates for use within atmospheric transport models such as those currently implemented as part of the Monitoring Atmospheric Composition and Climate (MACC) programme within the CAMS.

Abstract. Characterising the dynamics of landscape-scale wildfires at very high temporal resolutions is best achieved using observations from Earth Observation (EO) sensors mounted onboard geostationary satellites. As a result, a number of operational active fire products have been developed from the data of such sensors. An example of which are the Fire Radiative Power (FRP) products, the FRP-PIXEL and FRP-GRID products, generated by the Land Surface Analysis Satellite Applications Facility (LSA SAF) from imagery collected by the Spinning Enhanced Visible and Infrared Imager (SEVIRI) onboard the Meteosat Second Generation (MSG) series of geostationary EO satellites. The processing chain developed to deliver these FRP products detects SEVIRI pixels containing actively burning fires and characterises their FRP output across four geographic regions covering Europe, part of South America and Northern and Southern Africa. The FRP-PIXEL product contains the highest spatial and temporal resolution FRP data set, whilst the FRP-GRID product contains a spatio-temporal summary that includes bias adjustments for cloud cover and the non-detection of low FRP fire pixels. Here we evaluate these two products against active fire data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) and compare the results to those for three alternative active fire products derived from SEVIRI imagery. The FRP-PIXEL product is shown to detect a substantially greater number of active fire pixels than do alternative SEVIRI-based products, and comparison to MODIS on a per-fire basis indicates a strong agreement and low bias in terms of FRP values. However, low FRP fire pixels remain undetected by SEVIRI, with errors of active fire pixel detection commission and omission compared to MODIS ranging between 9–13 % and 65–77 % respectively in Africa. Higher errors of omission result in greater underestimation of regional FRP totals relative to those derived from simultaneously collected MODIS data, ranging from 35 % over the Northern Africa region to 89 % over the European region. High errors of active fire omission and FRP underestimation are found over Europe and South America and result from SEVIRI's larger pixel area over these regions. An advantage of using FRP for characterising wildfire emissions is the ability to do so very frequently and in near-real time (NRT). To illustrate the potential of this approach, wildfire fuel consumption rates derived from the SEVIRI FRP-PIXEL product are used to characterise smoke emissions of the 2007 "mega-fire" event focused on Peloponnese (Greece) and used within the European Centre for Medium-Range Weather Forecasting (ECMWF) Integrated Forecasting System (IFS) as a demonstration of what can be achieved when using geostationary active fire data within the Copernicus Atmosphere Monitoring Service (CAMS). Qualitative comparison of the modelled smoke plumes with MODIS optical imagery illustrates that the model captures the temporal and spatial dynamics of the plume very well, and that high temporal resolution emissions estimates such as those available from a geostationary orbit are important for capturing the sub-daily variability in smoke plume parameters such as aerosol optical depth (AOD), which are increasingly less well resolved using daily or coarser temporal resolution emissions data sets. Quantitative comparison of modelled AOD with coincident MODIS and AERONET (Aerosol Robotic Network) AOD indicates that the former is overestimated by ~ 20–30 %, but captures the observed AOD dynamics with a high degree of fidelity. The case study highlights the potential of using geostationary FRP data to drive fire emissions estimates for use within atmospheric transport models such as those implemented in the Monitoring Atmospheric Composition and Climate (MACC) series of projects for the CAMS.

Abstract Periods of low convective activity over southern Africa during the peak rainy season from December to February are known to be due to the northeastward displacement of the tropical temperate trough (TTT) systems from the landmass. In this study, using Interim European Centre for Medium-Range Weather Forecasts (ECMWF) Re-Analysis (ERA-Interim) data, the authors show that the displacement of the TTT systems during long periods of low convective activity has origins in the Northern Hemisphere. Using standardized area-averaged outgoing longwave radiation (OLR) daily anomalies over southern Africa, long periods of low convective activity are defined as periods of positive OLR anomalies lasting consecutively for 5 or more days with a standard deviation of 1 or more. An eddy streamfunction anomaly composite of the periods of low convective activity shows an upper-level anomalous wave originating in the Northern Hemisphere and extending to southern Africa from the eastern Pacific and displacing the tropical–extratropical cloud bands from the southern African landmass into the southwestern Indian Ocean. The wave train is also seen to generate an anticyclonic anomaly over southern Africa, resulting in suppressed convective activity. Understanding the causes of the long periods of low convective activity will help in improving their predictability and also the predictability of seasonal rainfall over southern Africa.

The main objective of this paper is to implement Polar WRF model for the Maitri (Lat. 70° 45 S, Long. 11° 44 E) region at the horizontal resolution of 15 km using initial and boundary conditions of the Global Forecast System T-382 operational at the India Meteorological Department (IMD). The study evaluates the performance of the model using the conventional approach of case studies. The results of the case studies illustrated in this paper reveal that the model is capable of capturing synoptic and meso-scale weather systems. Forecast fields are consistent with the corresponding analysis fields. Synoptic charts of mean sea level pressure prepared by the Weather Service of South Africa at Pretoria are used for the model validation. The model derived meteograms of mean sea level pressure are compared against the corresponding observations. The study demonstrates the usefulness of the forecast products for short range forecasting of weather over the Maitri region. The forecast outputs are made available in the real-time mode in the national web site of IMD www.imd.gov.in. The study is expected to benefit weather forecasters at Maitri.

AbstractLong-term variations in fire weather conditions are examined throughout Australia from gridded daily data from 1950 to 2016. The McArthur forest fire danger index is used to represent fire weather conditions throughout this 67-yr period, calculated on the basis of a gridded analysis of observations over this time period. This is a complementary approach to previous studies (e.g., those based primarily on model output, reanalysis, or individual station locations), providing a spatially continuous and long-term observations-based dataset to expand on previous research and produce climatological guidance information for planning agencies. Long-term changes in fire weather conditions are apparent in many regions. In particular, there is a clear trend toward more dangerous conditions during spring and summer in southern Australia, including increased frequency and magnitude of extremes, as well as indicating an earlier start to the fire season. Changes in fire weather conditions are attributable at least in part to anthropogenic climate change, including in relation to increasing temperatures. The influence of El Niño–Southern Oscillation (ENSO) on fire weather conditions is found to be broadly consistent with previous studies (indicating more severe fire weather in general for El Niño conditions than for La Niña conditions), but it is demonstrated that this relationship is highly variable (depending on season and region) and that there is considerable potential in almost all regions of Australia for long-range prediction of fire weather (e.g., multiweek and seasonal forecasting). It is intended that improved understanding of the climatological variability of fire weather conditions will help lead to better preparedness for risks associated with dangerous wildfires in Australia.

Abstract Early indication of an increased risk of extremely warm conditions could help alleviate some of the consequences of severe heat waves on human health. This study focuses on boreal spring heat wave events over West Africa and the Sahel and examines the long-range predictability and forecast quality of these events with two coupled forecasting systems designed at Météo-France, both based on the CNRM-CM coupled global climate model: the operational seasonal forecasting System 5 and the experimental contribution to the World Weather Research Programme/World Climate Research Programme (WWRP/WCRP) subseasonal-to-seasonal (S2S) project. Evaluation is based on past reforecasts spanning 22 years, from 1993 to 2014, compared to reference data from reanalyses. On the seasonal time scale, skill in reproducing interannual anomalies of heat wave duration is limited at a gridpoint level but is significant for regional averages. Subseasonal predictability of daily humidity-corrected apparent temperature drops sharply beyond the deterministic range. In addition to reforecast skill measures, the analysis of real-time forecasts for 2016, both in terms of anomalies with respect to the reforecast climatology and using a weather-type approach, provides additional insight on the systems’ performance in giving relevant information on the possible occurrence of such events.

Antarctic precipitation estimations derived from several new sources are examined in comparison to results found previously. The availability of analyzed atmospheric datasets has been a significant and beneficial tool for atmospheric and climate research for a broad range of research interests. This is particularly true for the polar regions, where the observational arrays are sparsely distributed. in high southern latitudes, a comprehensive assimilation of all available observations, including satellite data, is necessary for an accurate depiction of the atmospheric circulation. Recent st udies have found the operational analyses of the European Centre for Medium-range Weather Forecasts to be superior to those of other weather-forecasting centers in depicting the large-scale atmospheric circulation patterns over Antarctica. “Re-analysis” programs at major weather-forecasting centers have produced atmospheric numerical analyses using a “frozen” data-assimilation system. These projects have also derived precipitation and evaporation fields using an ensemble of short-term forecasts. From these new sources, Antarctic Ρ - E (precipitation minus evaporation/sublimation) is compared and evaluated against the long-term glaciological synthesis, as well as results from previous studies. The comparisons indicate significant regional disagreements exist between P — E from the re-analysis forecasts and the glaciological data. For the ensemble forecasting method, the continental-average evaporation is the largest area of uncertainty and differs by an order of magnitude between the rc-analysis datasets. This finding supports the use of the atmospheric moisture budget for determining P — E collectively in atmospheric diagnostic studies for Antarctica.

The finite resolution of general circulation models of the coupled atmosphere–ocean system and the effects of sub-grid-scale variability present a major source of uncertainty in model simulations on all time scales. The European Centre for Medium-Range Weather Forecasts has been at the forefront of developing new approaches to account for these uncertainties. In particular, the stochastically perturbed physical tendency scheme and the stochastically perturbed backscatter algorithm for the atmosphere are now used routinely for global numerical weather prediction. The European Centre also performs long-range predictions of the coupled atmosphere–ocean climate system in operational forecast mode, and the latest seasonal forecasting system—System 4—has the stochastically perturbed tendency and backscatter schemes implemented in a similar way to that for the medium-range weather forecasts. Here, we present results of the impact of these schemes in System 4 by contrasting the operational performance on seasonal time scales during the retrospective forecast period 1981–2010 with comparable simulations that do not account for the representation of model uncertainty. We find that the stochastic tendency perturbation schemes helped to reduce excessively strong convective activity especially over the Maritime Continent and the tropical Western Pacific, leading to reduced biases of the outgoing longwave radiation (OLR), cloud cover, precipitation and near-surface winds. Positive impact was also found for the statistics of the Madden–Julian oscillation (MJO), showing an increase in the frequencies and amplitudes of MJO events. Further, the errors of El Niño southern oscillation forecasts become smaller, whereas increases in ensemble spread lead to a better calibrated system if the stochastic tendency is activated. The backscatter scheme has overall neutral impact. Finally, evidence for noise-activated regime transitions has been found in a cluster analysis of mid-latitude circulation regimes over the Pacific–North America region.

Abstract. Biomass burning (BB) in southern Africa is the largest emission source of CO and O3 precursors within Africa during the West African Monsoon (WAM) between June and August. The long range transport and chemical processing of such emissions thus has the potential to exert a dominant influence on the composition of the tropical troposphere over Equatorial Africa (EA) and the Tropical Atlantic Ocean (TAO). We have performed simulations using a three-dimensional global chemistry-transport model (CTM) to quantify the effect that continental transport of such BB plumes has on the EA region. BB emissions from southern Africa were found to exert a significant influence over the TAO and EA between 10° S–20° N. The maximum concentrations in CO and O3 occur between 0–5° S near the position of the African Easterly Jet – South as placed by the European Centre for Medium range Weather Forecasts (ECMWF) meteorological analysis data. By comparing co-located model output with in-situ measurements we show that the CTM fails to capture the tropospheric profile of CO in southern Africa near the main source region of the BB emissions, as well as the "extreme" concentrations of both CO and O3 seen between 600–700 hPa over EA around 6° N. For more northerly locations the model exhibits high background concentrations in both CO and O3 related to BB emissions from southern Africa. By altering both the temporal resolution and the vertical distribution of BB emissions in the model we show that changes in temporal resolution have the largest influence on the transport of trace gases near the source regions, EA, and in the outflow towards the west of Central Africa. Using a set of trajectory calculations we show that the performance of the CTM is heavily constrained by the ECMWF meteorological fields used to drive the CTM, which transport biomass burning plumes from southern Africa into the lower troposphere of the TAO rather than up towards the middle troposphere at 650 hPa. Similar trajectory simulations repeated using an updated meteorological dataset, which assimilates additional measurement data taken around EA, show markedly different origins for pollution events and highlight the current limitations in modelling this tropical region.

Improved climate forecasting has the potential to increase the ability of farm managers to cope with a variable climate. In this study a simulation model of a breeding ewe flock was used to make a preliminary assessment of the value of climate forecasting for wool-producing enterprises in Victoria. Stocking and selling policies were modified in response to long-range forecasts of weather conditions. The effects on pasture cover, sheep welfare and financial returns were compared with those of a traditional management policy for a period of 25 years. These comparisons were made at two locations, Hamilton and Rutherglen, and at two stocking rates. The effects of different levels of accuracy of the weather forecast on the value of the changes in stocking and selling policies were also evaluated. Altering the stocking and selling policies using an accurate forecast of seasonal conditions resulted in a reduction in the death rate of adult ewes and their progeny. Timely action when adverse conditions were imminent resulted in an increase in both pasture cover during autumn and winter and minimum liveweight of the sheep. Gross returns were increased on average by more than 5%. Much of this increase was contributed by higher wool returns associated with the increase in size of the flock during favourable conditions. Expenditure on sheep purchases was lower for the traditionally managed farms; however, knowledge of forthcoming conditions did allow stock numbers to be reduced before pasture reserves were depleted in poor seasons which in turn reduced the requirement for supplementary feed. The total cash costs tended to be lower on the traditionally managed farm, but this difference was not significant. Both the cash operating surplus and net cash income were significantly increased by altering stocking and selling policies using an accurate forecast of seasonal conditions at Hamilton, but, although the same trends were evident, the effect of using the forecast at Rutherglen was not significant. Where the forecast was accurate in only 8 years in 10 or 6 years in 10, the benefits of altering the stocking and selling policies were reduced, but even at the lower level of accuracy the average cash operating surplus for the 25 years of the analysis was higher than that achieved using the traditional management regime. However, in individual years, inappropriate policies adopted due to an incorrect forecast resulted in reductions in financial returns of up to 64%. Accurate forecasts can improve land care and animal welfare by changing pasture and animal management, particularly by reducing stock numbers. However, since the profitability of sheep enterprises in Victoria is highly dependent on the choice of stocking rate, recommendations to reduce stock numbers without considering the financial viability of sheep enterprises may go unheeded. Hence, in the short-term at least, it can be difficult to achieve improvements in land care and animal welfare while at the same time maintaining profitability. This study indicated that the financial benefits for wool producers of reliable seasonal outlooks in southern Australia are probably substantially less than generally anticipated, at least for the strategies investigated. Furthermore, the accuracy of seasonal forecasting in southern Australia is such that the benefits from correct forecasts can be partly offset in other years from decisions which have been made on the basis of incorrect forecasts. The study also highlighted a number of important issues that need to be considered in evaluating climate forecasts.

The Long-Rains wet season of March–May (MAM) over Kenya in 2018 was one of the wettest on record. This paper examines the nature, causes, impacts, and predictability of the rainfall events, and considers the implications for flood risk management. The exceptionally high monthly rainfall totals in March and April resulted from several multi-day heavy rainfall episodes, rather than from distinct extreme daily events. Three intra-seasonal rainfall events in particular resulted in extensive flooding with the loss of lives and livelihoods, a significant displacement of people, major disruption to essential services, and damage to infrastructure. The rainfall events appear to be associated with the combined effects of active Madden–Julian Oscillation (MJO) events in MJO phases 2–4, and at shorter timescales, tropical cyclone events over the southwest Indian Ocean. These combine to drive an anomalous westerly low-level circulation over Kenya and the surrounding region, which likely leads to moisture convergence and enhanced convection. We assessed how predictable such events over a range of forecast lead times. Long-lead seasonal forecast products for MAM 2018 showed little indication of an enhanced likelihood of heavy rain over most of Kenya, which is consistent with the low predictability of MAM Long-Rains at seasonal lead times. At shorter lead times of a few weeks, the seasonal and extended-range forecasts provided a clear signal of extreme rainfall, which is likely associated with skill in MJO prediction. Short lead weather forecasts from multiple models also highlighted enhanced risk. The flood response actions during the MAM 2018 events are reviewed. Implications of our results for forecasting and flood preparedness systems include: (i) Potential exists for the integration of sub-seasonal and short-term weather prediction to support flood risk management and preparedness action in Kenya, notwithstanding the particular challenge of forecasting at small scales. (ii) We suggest that forecasting agencies provide greater clarity on the difference in potentially useful forecast lead times between the two wet seasons in Kenya and East Africa. For the MAM Long-Rains, the utility of sub-seasonal to short-term forecasts should be emphasized; while at seasonal timescales, skill is currently low, and there is the challenge of exploiting new research identifying the primary drivers of variability. In contrast, greater seasonal predictability of the Short-Rains in the October–December season means that greater potential exists for early warning and preparedness over longer lead times. (iii) There is a need for well-developed and functional forecast-based action systems for heavy rain and flood risk management in Kenya, especially with the relatively short windows for anticipatory action during MAM.

In West Africa (WA), interest in solar energy development has risen in recent years with many planned and ongoing projects currently in the region. However, a major drawback to this development in the region is the intense cloud cover that reduces the incoming solar radiation when present and causes fluctuations in solar power production. Therefore, understanding the occurrence of clouds and their link to the surface solar radiation in the region is important for making plans to manage future solar energy production. In this study, we use the state-of-the-art European Centre for Medium-range Weather Forecasts ReAnalysis (ERA5) dataset to examine the occurrence and persistence of cloudy and clear-sky conditions in the region. Then, we investigate the effects of cloud cover on the quantity and variability of the incoming solar radiation. The cloud shortwave radiation attenuation (CRASW↓) is used to quantify the amount of incoming solar radiation that is lost due to clouds. The results showed that the attenuation of incoming solar radiation is stronger in all months over the southern part of WA near the Guinea Coast. Across the whole region, the maximum attenuation occurs in August, with a mean CRASW↓ of about 55% over southern WA and between 20% and 35% in the Sahelian region. Southern WA is characterized by a higher occurrence of persistent cloudy conditions, while the Sahel region and northern WA are associated with frequent clear-sky conditions. Nonetheless, continuous periods with extremely low surface solar radiation were found to be few over the whole region. The analysis also showed that the surface solar radiation received from November to April only varies marginally from one year to the other. However, there is a higher uncertainty during the core of the monsoon season (June to October) with regard to the quantity of incoming solar radiation. The results obtained show the need for robust management plans to ensure the long-term success of solar energy projects in the region.

Abstract The Weather Research and Forecasting (WRF) model version 3.0.1 is used in both short-range (days) and long-range (years) simulations to explore the California wintertime model wet bias. California is divided into four regions (the coast, central valley, mountains, and Southern California) for validation. Three sets of gridded surface observations are used to evaluate the impact of measurement uncertainty on the model wet bias. Short-range simulations are driven by the North American Regional Reanalysis (NARR) data and designed to test the sensitivity of model physics and grid resolution to the wet bias using eight winter storms chosen from four major types of large-scale conditions: the Pineapple Express, El Niño, La Niña, and synoptic cyclones. Control simulations are conducted with 12-km grid spacing (low resolution) but additional experiments are performed at 2-km (high) resolution to assess the robustness of microphysics and cumulus parameterizations to resolution changes. Additionally, long-range simulations driven by both NARR and general circulation model (GCM) data are performed at low resolution to gauge the impact of the GCM forcing on the model wet bias. These short- and long-range simulations show that low-resolution runs tend to underpredict precipitation in the coast region and overpredict it elsewhere in California. The sensitivity test of WRF physics in short-range simulations indicates that model precipitation depends most strongly on the microphysics scheme, though convective parameterization is also important, particularly near the coast. In contrast, high-resolution (2 km) simulation increases model precipitation in all regions. As a result, it improves the forecast bias in the coast region while it downgrades the model performance in the other regions. It is also found that the choice of validation dataset has a significant impact on the model wet bias of both short- and long-range simulations. However, this impact in long-range simulations appears to be a secondary contribution as compared to its counterpart from the GCM forcing.

Abstract. We investigated the effects of fire-induced plume-rise on the simulation of carbon monoxide (CO) over Africa and its export during SAFARI 2000 using the NCAR Community Atmosphere Model (CAM) with a CO tracer and a plume-rise parameterization scheme. The plume-rise parameterization scheme simulates the consequences of strong buoyancy of hot gases emitted from biomass burning, including both dry and cloud-associated (pyro-cumulus) lofting. The current implementation of the plume-rise parameterization scheme into the global model provides an opportunity to examine the effect of plume-rise on long-range transport. The CAM simulation with the plume-rise parameterization scheme seems to show a substantial improvement of the agreements between the modeled and aircraft-measured vertical distribution of CO over Southern Africa biomass-burning area. The plume-rise mechanism plays a crucial role in lofting biomass-burning pollutants to the middle troposphere. In the presence of deep convection we found that the plume-rise mechanism results in a decrease of CO concentration in the upper troposphere. The plume-rise depletes the boundary layer, and thus leaves lower concentrations of CO to be lofted by the deep convection process. The effect of the plume-rise on free troposphere CO concentration is more important for the source area (short-distance transport) than for remote areas (long-distance transport). A budget analysis of CO burden over Southern Africa reveals the plume-rise process to have a similar impact as the chemical production of CO by OH and CH4. In addition, the plume-rise process has an minor impact on the regional export. These results further confirm and extend previous findings in a regional model study. Effective lofting of large concentration of CO by the plume-rise mechanism also has implications for local air quality forecasting in areas affected by other fire-related pollutants.

Abstract. Atmospheric lidar measurements were carried out at Elandsfontein measurement station, on the eastern Highveld approximately 150 km east of Johannesburg in South Africa (SA) throughout 2010. The height of the planetary boundary layer (PBL) top was continuously measured using a~Raman lidar, PollyXT (POrtabLe Lidar sYstem eXTended). High atmospheric variability together with a large surface temperature range and significant seasonal changes in precipitation were observed, which had an impact on the vertical mixing of particulate matter (PM), and hence, on the PBL evolution. The results were compared to radio soundings, CALIOP (Cloud–Aerosol Lidar with Orthogonal Polarization) space-borne lidar measurements and three atmospheric models that followed different approaches to determine the PBL top height. These models included two weather forecast models operated by ECMWF (European Centre for Medium-range Weather Forecasts) and SAWS (South African Weather Service) and one mesoscale prognostic meteorological and air pollution regulatory model TAPM (The Air Pollution Model). The ground-based lidar used in this study was operational for 4935 h during 2010 (49% of the time). The PBL top height was detected 86% of the total measurement time (42% of the total time). Large seasonal and diurnal variations were observed between the different methods utilised. Comparison of lidar measurements to the models indicated that the ECMWF model agreed the best with mean absolute difference of 15.4%, while the second best correlation was with the SAWS model with corresponding difference of 20.1%. TAPM was found to have a tendency to underestimate the PBL top height. The wind speeds in SAWS operated and TAPM models were strongly underestimated which probably led to underestimation of the vertical wind and turbulence and thus underestimation of the PBL top height. High variation was found when lidar measurements were compared to radiosonde measurements. This could be partially due to the distance between the lidar measurements and the radiosondes, which were 120 km apart. Comparison between ground-based and satellite lidar shows good agreement with a correlation coefficient of 0.88. On average the daily maximum PBL top height in October (spring) and June (winter) were 2260 m and 1480 m, respectively. To our knowledge, this study is the first long term study of PBL top heights and PBL growth rates in the Southern Hemisphere. Only a few studies have been performed in Europe and Asia, most of them with less data coverage.

Abstract. This paper presents atmosphere-only and coupled climate model configurations of the European Centre for Medium-Range Weather Forecasts Integrated Forecasting System (ECMWF-IFS) for different combinations of ocean and atmosphere resolution. These configurations are used to perform multi-decadal ensemble experiments following the protocols of the High Resolution Model Intercomparison Project (HighResMIP) and phase 6 of the Coupled Model Intercomparison Project (CMIP6). These experiments are used to evaluate the sensitivity of major biases in the atmosphere, ocean, and cryosphere to changes in atmosphere and ocean resolution. All configurations successfully reproduce the observed long-term trends in global mean surface temperature. Furthermore, following an adjustment to account for drift in the subsurface ocean, coupled configurations of ECMWF-IFS realistically reproduce observation-based estimates of ocean heat content change since 1950. Climatological surface biases in ECMWF-IFS are relatively insensitive to an increase in atmospheric resolution from ∼ 50 to ∼ 25 km. However, increasing the horizontal resolution of the atmosphere while maintaining the same vertical resolution enhances the magnitude of a cold bias in the lower stratosphere. In coupled configurations, there is a strong sensitivity to an increase in ocean model resolution from 1 to 0.25°. However, this sensitivity to ocean resolution takes many years to fully manifest and is less apparent in the first year of integration. This result has implications for the ECMWF coupled model development strategy that typically relies on the analysis of biases in short ( < 1 year) ensemble (re)forecast data sets. The impacts of increased ocean resolution are particularly evident in the North Atlantic and Arctic, where they are associated with an improved Atlantic meridional overturning circulation, increased meridional ocean heat transport, and more realistic sea-ice cover. In the tropical Pacific, increased ocean resolution is associated with improvements to the magnitude and asymmetry of El Niño–Southern Oscillation (ENSO) variability and better representation of non-linear sea surface temperature (SST)–radiation feedbacks during warm events. However, increased ocean model resolution also increases the magnitude of a warm bias in the Southern Ocean. Finally, there is tentative evidence that both ocean coupling and increased atmospheric resolution can improve teleconnections between tropical Pacific rainfall and geopotential height anomalies in the North Atlantic.

Abstract A new radiation package, “McRad,” has become operational with cycle 32R2 of the Integrated Forecasting System (IFS) of the European Centre for Medium-Range Weather Forecasts (ECMWF). McRad includes an improved description of the land surface albedo from Moderate Resolution Imaging Spectroradiometer (MODIS) observations, the Monte Carlo independent column approximation treatment of the radiative transfer in clouds, and the Rapid Radiative Transfer Model shortwave scheme. The impact of McRad on year-long simulations at TL159L91 and higher-resolution 10-day forecasts is then documented. McRad is shown to benefit the representation of most parameters over both shorter and longer time scales, relative to the previous operational version of the radiative transfer schemes. At all resolutions, McRad improves the representation of the cloud–radiation interactions, particularly in the tropical regions, with improved temperature and wind objective scores through a reduction of some systematic errors in the position of tropical convection as a result of a change in the overall distribution of diabatic heating over the vertical plane, inducing a geographical redistribution of the centers of convection. Although smaller, the improvement is also seen in the rmse of geopotential in the Northern and Southern Hemispheres and over Europe. Given the importance of cloudiness in modulating the radiative fluxes, the sensitivity of the model to cloud overlap assumption (COA) is also addressed, with emphasis on the flexibility that is inherent to this new RT approach when dealing with COA. The sensitivity of the forecasts to the space interpolation that is required to efficiently address the high computational cost of the RT parameterization is also revisited. A reduction of the radiation grid for the Ensemble Prediction System is shown to be of little impact on the scores while reducing the computational cost of the radiation computations. McRad is also shown to decrease the cold bias in ocean surface temperature in climate integrations with a coupled ocean system.

SUMMARYRainfall variability, both within and between seasons, is reflected in highly variable crop growth and yields in rainfed agriculture in sub-Saharan Africa and results in varying degrees of weather-induced risk associated with a wide range of crop, soil and water management innovations. In addition there is both growing evidence and concern that changes in rainfall patterns associated with global warming may substantively affect the nature of such risk. Eighty-nine years of daily rainfall data from a site in southern Zambia are analysed. The analyses illustrate approaches to assessing the extent of possible trends in rainfall patterns and the calculation of weather-induced risk associated with the inter- and intra-seasonal variability of the rainfall amounts. Trend analyses use monthly rainfall totals and the number of rain days in each month. No simple trends were found. The daily data were then processed to examine important rain dependent aspects of crop production such as the date of the start of the rains and the risk of a long dry spell, both following planting and around flowering. The same approach is used to assess the risk of examples of crop disease in instances when a ‘weather trigger’ for the disease can be specified. A crop water satisfaction index is also used to compare risks from choices of crops with different maturity lengths and cropping strategies. Finally a different approach to the calculations of these risks fits a Markov chain model to the occurrence of rain, with results then derived from this model. The analyses shows the relevance of this latter approach when relatively short daily rainfall records are available and is illustrated through a comparison of the effects of El Niño, La Niña and Ordinary years on rainfall distribution patterns.

Abstract. Lightning is the major cause of the natural ignition of wildfires worldwide and produces the largest wildfires in some regions. Lightning strokes produce about 5 % of forest fires in the Mediterranean Basin and are one of the most important precursors of the largest forest fires during the summer. Lightning-ignited wildfires produce significant emissions of aerosols, black carbon, and trace gases, such as CO, SO2, CH4, and O3, affecting air quality. Characterization of the meteorological and cloud conditions of lightning-ignited wildfires in the Mediterranean Basin can serve to improve fire forecasting models and to upgrade the implementation of fire emissions in atmospheric models. This study investigates the meteorological and cloud conditions of lightning-ignited wildfires (LIWs) and long continuing current (LCC) lightning flashes in the Iberian Peninsula and Greece. LCC lightning and lightning in dry thunderstorms with a low precipitation rate have been proposed to be the main precursors of the largest wildfires. We use lightning data provided by the World Wide Lightning Location Network (WWLLN), the Earth Networks Total Lightning Network (ENTLN), and the Lightning Imaging Sensor (LIS) on board the International Space Station (ISS), together with four databases of wildfires produced in Spain, Portugal, southern France, and Greece, respectively, in order to produce a climatology of LIWs and LCC lightning over the Mediterranean Basin. In addition, we use meteorological data provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA5 reanalysis data set and by the Spanish State Meteorological Agency (AEMET), together with the Cloud Top Height product (CTHP) derived from Meteosat Second Generation (MSG) satellites measurements to investigate the meteorological conditions of LIWs and LCC lightning. According to our results, LIWs and a significant amount of LCC lightning flashes tend to occur in dry thunderstorms with weak updrafts. Our results suggest that LIWs tend to occur in clouds with a high base and with a vertical content of moisture lower than the climatological value, as well as with a higher temperature and a lower precipitation rate. Meteorological conditions of LIWs from the Iberian Peninsula and Greece are in agreement, although some differences possibly caused by the highly variable topography in Greece and a more humid environment are observed. These results show the possibility of using the typical meteorological and cloud conditions of LCC lightning flashes as proxy to parameterize the ignition of wildfires in atmospheric or forecasting models.

Abstract This paper examines the effect of topographically phase-locked convection on the motion of typhoons across the island of Taiwan. Data for 84 typhoons that reached Taiwan’s eastern coast from 1960 to 2010 are analyzed, with motions compared to the long-term average overland translation speed. For 61 continuous-track typhoons among all cases, 77% of the slow-moving tropical cyclones (TCs) made landfall on the northern end of Taiwan’s eastern coast, while 60% of the fast storms had southeastern coastal landfalls. This geographic asymmetry with respect to typhoon translation speeds widened after landfall, as the slow movers typically decelerated during the overland period, whereas the faster TCs sped up. In particular, the average overland duration was 16 h for the slow class, compared to only 3 h for the fast-moving typhoons. The combination of slower translation with longer duration for the northern class of TCs led to large rainfall on the southwestern slope of the island’s Central Mountain Range. Weather Research and Forecasting model experiments are used to study the effect of convection on storm motion over a mountainous island resembling Taiwan. The authors find that the topographically phase-locked convection acts to slow down (speed up) the northern (southern) landfalling typhoons. The model results also suggest that a positive feedback mechanism exists for the slow storms, in which the convective heating pattern forced by topography acts to reduce the TC motion, leading to even more prolonged precipitation and heating, yielding further speed reductions.

In Australia, and particularly in the northern part of the grain belt, wheat is grown in an extremely variable climate. The wheat crop manager in this region is faced with complex decisions on choice of planting time, varietal development pattern, and fertiliser strategy. A skilful seasonal forecast would provide an opportunity for the manager to tailor crop management decisions more appropriately to the season. Recent developments in climate research have led to the development of a number of seasonal climate forecasting systems. The objectives of this study were to determine the value of the capability in seasonal forecasting to wheat crop management, to compare the value of the existing forecast methodologies, and to consider the potential value of improved forecast quality. We examined decisions on nitrogen (N) fertiliser and cultivar maturity using simulation analyses of specific production scenarios at a representative location (Goondiwindi) using long-term daily weather data (1894-1989). The average profit and risk of making a loss were calculated for the possible range of fixed (i.e. the same every year) and tactical (i.e. varying depending on seasonal forecast) strategies. Significant increase in profit (up to 20%) and/or reduction in risk (up to 35%) were associated with tactical adjustment of crop management of N fertiliser or cultivar maturity. The forecasting system giving greatest value was the Southern Oscillation Index (SOI) phase system of Stone and Auliciems (1992), which classifies seasons into 5 phases depending on the value and rate of change in the SOI. The significant skill in this system for forecasting both seasonal rainfall and frost timing generated the value found in tactical management of N fertiliser and cultivar maturity. Possible impediments to adoption of tactical management, associated with uncertainties in forecasting individual years, are discussed. The scope for improving forecast quality and the means to achieve it are considered by comparing the value of tactical management based on SO1 phases with the outcome given perfect prior knowledge of the season. While the analyses presented considered only one decision at a time, used specific scenarios, and made a number of simplifying assumptions, they have demonstrated that the current skill in seasonal forecasting is sufficient to justify use in tactical management of crops. More comprehensive studies to examine sensitivities to location, antecedent conditions, and price structure, and to assumptions made in this analysis, are now warranted. We have examined decisions related only to management of wheat. It would be appropriate to pursue similar analyses in relation to management decisions for other crops, cropping sequences, and the whole farm enterprise mix.

Abstract. On 13 June 2015, the London Volcanic Ash Advisory Centre (VAAC) warned the Buenos Aires VAAC about a possible volcanic eruption from the Nevados Ojos del Salado volcano (6879 m), located in the Andes mountain range on the border between Chile and Argentina. A volcanic ash cloud was detected by the SEVIRI instrument on board the Meteosat Second Generation (MSG) satellites from 14:00 UTC on 13 June. In this paper, we provide the first comprehensive description of this event through observations and numerical simulations. Our results support the hypothesis that the phenomenon was caused by wind remobilization of ancient pyroclastic deposits (ca. 4.5 ka Cerro Blanco eruption) from the Bolsón de Fiambalá (Fiambalá Basin) in northwestern Argentina. We have investigated the spatiotemporal distribution of aerosols and the emission process over complex terrain to gain insight into the key role played by the orography and the condition that triggered the long-range transport episode. Numerical simulations of windblown dust were performed using the ARW (Advanced Research WRF) core of the WRF (Weather Research and Forecasting) model (WRF-ARW) and FALL3D modeling system with meteorological fields downscaled to a spatial resolution of 2 km in order to resolve the complex orography of the area. Results indicate that favorable conditions to generate dust uplifting occurred in northern Fiambalá Basin, where orographic effects caused strong surface winds. According to short-range numerical simulations, dust particles were confined to near-ground layers around the emission areas. In contrast, dust aerosols were injected up to 5–6 km high in central and southern regions of the Fiambalá Basin, where intense ascending airflows are driven by horizontal convergence. Long-range transport numerical simulations were also performed to model the dust cloud spreading over northern Argentina. Results of simulated vertical particle column mass were compared with the MSG-SEVIRI retrieval product. We tested two numerical schemes: with the default configuration of the FALL3D model, we found difficulties to simulate transport through orographic barriers, whereas an alternative configuration, using a numerical scheme to more accurately compute the horizontal advection in abrupt terrains, substantially improved the model performance.

This study focuses on the ability of the global Land Data Assimilation System, LDAS-Monde, to improve the representation of land surface variables (LSVs) over Burkina-Faso through the joint assimilation of satellite derived surface soil moisture (SSM) and leaf area index (LAI) from January 2001 to June 2018. The LDAS-Monde offline system is forced by the latest European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis ERA5 as well as ERA-Interim former reanalysis, leading to reanalyses of LSVs at 0.25° × 0.25° and 0.50° × 0.50° spatial resolution, respectively. Within LDAS-Monde, SSM and LAI observations from the Copernicus Global Land Service (CGLS) are assimilated with a simplified extended Kalman filter (SEKF) using the CO2-responsive version of the ISBA (Interactions between Soil, Biosphere, and Atmosphere) land surface model (LSM). First, it is shown that ERA5 better represents precipitation and incoming solar radiation than ERA-Interim former reanalysis from ECMWF based on in situ data. Results of four experiments are then compared: Open-loop simulation (i.e., no assimilation) and analysis (i.e., joint assimilation of SSM and LAI) forced by either ERA5 or ERA-Interim. After jointly assimilating SSM and LAI, it is noticed that the assimilation is able to impact soil moisture in the first top soil layers (the first 20 cm), and also in deeper soil layers (from 20 cm to 60 cm and below), as reflected by the structure of the SEKF Jacobians. The added value of using ERA5 reanalysis over ERA-Interim when used in LDAS-Monde is highlighted. The assimilation is able to improve the simulation of both SSM and LAI: The analyses add skill to both configurations, indicating the healthy behavior of LDAS-Monde. For LAI in particular, the southern region of the domain (dominated by a Sudan-Guinean climate) highlights a strong impact of the assimilation compared to the other two sub-regions of Burkina-Faso (dominated by Sahelian and Sudan-Sahelian climates). In the southern part of the domain, differences between the model and the observations are the largest, prior to any assimilation. These differences are linked to the model failing to represent the behavior of some specific vegetation species, which are known to put on leaves before the first rains of the season. The LDAS-Monde analysis is very efficient at compensating for this model weakness. Evapotranspiration estimates from the Global Land Evaporation Amsterdam Model (GLEAM) project as well as upscaled carbon uptake from the FLUXCOM project and sun-induced fluorescence from the Global Ozone Monitoring Experiment-2 (GOME-2) are used in the evaluation process, again demonstrating improvements in the representation of evapotranspiration and gross primary production after assimilation.

Abstract. Droughts are widespread natural hazards and in many regions their frequency seems to be increasing. A finer-resolution version (0.05° × 0.05°) of the continental-scale hydrological model PCRaster Global Water Balance (PCR-GLOBWB) was set up for the Limpopo River basin, one of the most water-stressed basins on the African continent. An irrigation module was included to account for large irrigated areas of the basin. The finer resolution model was used to analyse hydrological droughts in the Limpopo River basin in the period 1979–2010 with a view to identifying severe droughts that have occurred in the basin. Evaporation, soil moisture, groundwater storage and runoff estimates from the model were derived at a spatial resolution of 0.05° (approximately 5 km) on a daily timescale for the entire basin. PCR-GLOBWB was forced with daily precipitation and temperature obtained from the ERA-Interim global atmospheric reanalysis product from the European Centre for Medium-Range Weather Forecasts. Two agricultural drought indicators were computed: the Evapotranspiration Deficit Index (ETDI) and the Root Stress Anomaly Index (RSAI). Hydrological drought was characterised using the Standardized Runoff Index (SRI) and the Groundwater Resource Index (GRI), which make use of the streamflow and groundwater storage resulting from the model. Other more widely used meteorological drought indicators, such as the Standardized Precipitation Index (SPI) and the Standardized Precipitation Evaporation Index (SPEI), were also computed for different aggregation periods. Results show that a carefully set-up, process-based model that makes use of the best available input data can identify hydrological droughts even if the model is largely uncalibrated. The indicators considered are able to represent the most severe droughts in the basin and to some extent identify the spatial variability of droughts. Moreover, results show the importance of computing indicators that can be related to hydrological droughts, and how these add value to the identification of hydrological droughts and floods and the temporal evolution of events that would otherwise not have been apparent when considering only meteorological indicators. In some cases, meteorological indicators alone fail to capture the severity of the hydrological drought. Therefore, a combination of some of these indicators (e.g. SPEI-3, SRI-6 and SPI-12 computed together) is found to be a useful measure for identifying agricultural to long-term hydrological droughts in the Limpopo River basin. Additionally, it was possible to undertake a characterisation of the drought severity in the basin, indicated by its time of occurrence, duration and intensity.

Abstract Clouds and precipitation play critical roles in wet removal of aerosols and soluble gases in the atmosphere, and hence their accurate prediction largely influences accurate prediction of air pollutants. In this study, the impacts of clouds and precipitation on wet scavenging and long-range transboundary transport of pollutants are examined during the 2016 Korea–United States Air Quality (KORUS-AQ) field campaign using the Weather Research and Forecasting Model coupled with chemistry. Two simulations—one in which atmospheric moisture is constrained and one in which it is not—are performed and evaluated against surface and airborne observations. The simulation with moisture constraints is found to better reproduce precipitation as well as surface PM2.5, whereas the areal extent and amount of precipitation are overpredicted in the simulation without moisture constraints. As a results of overpredicted clouds and precipitation and consequently overpredicted wet scavenging, PM2.5 concentration is generally underpredicted across the model domain in the simulation without moisture constraints. The effects are significant not only in the precipitating region (upwind region, southern China in this study) but also in the downwind region (South Korea) where no precipitation is observed. The difference in upwind precipitation by 77% on average between the two simulations leads to the difference in PM2.5 by ∼39% both in the upwind and downwind regions. The transboundary transport of aerosol precursors, especially nitric acid, has a considerable impact on ammonium-nitrate aerosol formation in the ammonia-rich downwind region. This study highlights that skillful prediction of atmospheric moisture can have ultimate potential to skillful prediction of aerosols across regions.

Abstract In this study, the role of the Saharan air layer (SAL) is investigated in the development and intensification of tropical cyclones (TCs) via modifying environmental stability and moisture, using multisensor satellite data, long-term TC track and intensity records, dust data, and numerical simulations with a state-of-the-art Weather Research and Forecasting model (WRF). The long-term relationship between dust and Atlantic TC activity shows that dust aerosols are negatively associated with hurricane activity in the Atlantic basin, especially with the major hurricanes in the western Atlantic region. Numerical simulations with the WRF for specific cases during the NASA African Monsoon Multidisciplinary Analyses (NAMMA) experiment show that, when vertical temperature and humidity profiles from the Atmospheric Infrared Sounder (AIRS) were assimilated into the model, detailed features of the warm and dry SAL, including the entrainment of dry air wrapping around the developing vortex, are well simulated. Active tropical disturbances are found along the southern edge of the SAL. The simulations show an example where the dry and warm air of the SAL intruded into the core of a developing cyclone, suppressing convection and causing a spin down of the vortical circulation. The cyclone eventually weakened. To separate the contributions from the warm temperature and dry air associated with the SAL, two additional simulations were performed, one assimilating only AIRS temperature information (AIRST) and one assimilating only AIRS humidity information (AIRSH) while keeping all other conditions the same. The AIRST experiments show almost the same simulations as the full AIRS assimilation experiments, whereas the AIRSH is close to the non-AIRS simulation. This is likely due to the thermal structure of the SAL leading to low-level temperature inversion and increased stability and vertical wind shear. These analyses suggest that dry air entrainment and the enhanced vertical wind shear may play the direct roles in leading to the TC suppression. On the other hand, the warm SAL temperature may play the indirect effects by enhancing vertical wind shear; increasing evaporative cooling; and initiating mesoscale downdrafts, which bring dry air from the upper troposphere to the lower levels.

Abstract. The Pearl River Delta (PRD) region in southern China has been subject to severe ozone (O3) pollution during daytime and anomalous nocturnal O3 increase (NOI) during nighttime. In this study, the spatiotemporal variation of NOI events in the PRD region from 2006 to 2019 is comprehensively analysed, and the role of vertical transport in the occurrence of NOI events is quantified based on observed surface and vertical O3 and the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis (ERA5) dataset. The results show that the average annual frequency of NOI events in the whole PRD region during the 14 year period is estimated to be 53 ± 16 d yr−1, with an average of 58 ± 11 µg m−3 for the nocturnal O3 peak (NOP) concentration. Low-level jets (LLJs) are the main meteorological processes triggering NOI events, explaining on average 61 % of NOI events. Annual NOI events exhibit an upward trend before 2011 (4.70 d yr−1) and a downward trend thereafter (−0.72 d yr−1), which is consistent with the annual variation of LLJs (r=0.88, p<0.01). Although the contribution of convective storms (Conv) to NOI events is relatively small with an average value of 11 %, Conv-induced NOI events steadily increased at a rate of 0.26 d yr−1 during this 14 year period due to the impact of urbanisation. Seasonally, a relatively higher frequency of NOI events is observed in spring and autumn, which is consistent with the seasonal pattern of LLJs and maximum daily 8 h average (MDA8) O3. Spatially, NOI events are frequent in the eastern PRD, which agrees well with the spatial distribution of the frequency of LLJs and partially overlaps with the distribution of MDA8 O3 concentration, suggesting that vertical transport plays a more important role in NOI events than daytime O3 concentration. The Weather Research and Forecasting (WRF) model coupled with the Community Multiscale Air Quality (CMAQ) model and the observed vertical O3 profiles are further applied to illustrate the mechanisms of NOI formation caused by LLJs and Conv. The results confirm that both LLJs and Conv trigger NOI events by inducing downdrafts with the difference being that LLJs induce downdrafts by wind shear, while Conv by compensating downdrafts. Through observational and modelling analysis, this study presents the long-term (2006–2019) trends of NOI events in the PRD region and quantifies the contribution of meteorological processes for the first time, emphasising the importance of vertical transport, as well as daytime O3 concentration for the occurrence of NOI events.

Abstract. The performance of the Weather Research and Forecasting regional model with chemistry (WRF-Chem) in simulating the spatial and temporal variations in aerosol mass, composition, and size over California is quantified using the extensive meteorological, trace gas, and aerosol measurements collected during the California Nexus of Air Quality and Climate Experiment (CalNex) and the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted during May and June of 2010. The overall objective of the field campaigns was to obtain data needed to better understand processes that affect both climate and air quality, including emission assessments, transport and chemical aging of aerosols, aerosol radiative effects. Simulations were performed that examined the sensitivity of aerosol concentrations to anthropogenic emissions and to long-range transport of aerosols into the domain obtained from a global model. The configuration of WRF-Chem used in this study is shown to reproduce the overall synoptic conditions, thermally driven circulations, and boundary layer structure observed in region that controls the transport and mixing of trace gases and aerosols. Reducing the default emissions inventory by 50% led to an overall improvement in many simulated trace gases and black carbon aerosol at most sites and along most aircraft flight paths; however, simulated organic aerosol was closer to observed when there were no adjustments to the primary organic aerosol emissions. We found that sulfate was better simulated over northern California whereas nitrate was better simulated over southern California. While the overall spatial and temporal variability of aerosols and their precursors were simulated reasonably well, we show cases where the local transport of some aerosol plumes were either too slow or too fast, which adversely affects the statistics quantifying the differences between observed and simulated quantities. Comparisons with lidar and in situ measurements indicate that long-range transport of aerosols from the global model was likely too high in the free troposphere even though their concentrations were relatively low. This bias led to an over-prediction in aerosol optical depth by as much as a factor of 2 that offset the under-predictions of boundary-layer extinction resulting primarily from local emissions. Lowering the boundary conditions of aerosol concentrations by 50% greatly reduced the bias in simulated aerosol optical depth for all regions of California. This study shows that quantifying regional-scale variations in aerosol radiative forcing and determining the relative role of emissions from local and distant sources is challenging during `clean' conditions and that a wide array of measurements are needed to ensure model predictions are correct for the right reasons. In this regard, the combined CalNex and CARES data sets are an ideal test bed that can be used to evaluate aerosol models in great detail and develop improved treatments for aerosol processes.

Abstract. The Weather Research and Forecasting Model with chemistry (WRF-Chem model) was used to investigate a typical dust storm event that occurred from 18 to 23 March 2010 and swept across almost all of China, Japan, and Korea. The spatial and temporal variations in dust aerosols and the meteorological conditions over East Asia were well reproduced by the WRF-Chem model. The simulation results were used to further investigate the details of processes related to dust emission, long-range transport, and radiative effects of dust aerosols over the Taklimakan Desert (TD) and Gobi Desert (GD). The results indicated that weather conditions, topography, and surface types in dust source regions may influence dust emission, uplift height, and transport at the regional scale. The GD was located in the warm zone in advance of the cold front in this case. Rapidly warming surface temperatures and cold air advection at high levels caused strong instability in the atmosphere, which strengthened the downward momentum transported from the middle and low troposphere and caused strong surface winds. Moreover, the GD is located in a relatively flat, high-altitude region influenced by the confluence of the northern and southern westerly jets. Therefore, the GD dust particles were easily lofted to 4 km and were the primary contributor to the dust concentration over East Asia. In the dust budget analysis, the dust emission flux over the TD was 27.2 ± 4.1 µg m−2 s−1, which was similar to that over the GD (29 ± 3.6 µg m−2 s−1). However, the transport contribution of the TD dust (up to 0.8 ton d−1) to the dust sink was much smaller than that of the GD dust (up to 3.7 ton d−1) because of the complex terrain and the prevailing wind in the TD. Notably, a small amount of the TD dust (PM2.5 dust concentration of approximately 8.7 µg m−3) was lofted to above 5 km and transported over greater distances under the influence of the westerly jets. Moreover, the direct radiative forcing induced by dust was estimated to be −3 and −7 W m−2 at the top of the atmosphere, −8 and −10 W m−2 at the surface, and +5 and +3 W m−2 in the atmosphere over the TD and GD, respectively. This study provides confidence for further understanding the climate effects of the GD dust.

Abstract. The performance of the Weather Research and Forecasting regional model with chemistry (WRF-Chem) in simulating the spatial and temporal variations in aerosol mass, composition, and size over California is quantified using measurements collected during the California Nexus of Air Quality and Climate Experiment (CalNex) and the Carbonaceous Aerosol and Radiative Effects Study (CARES) conducted during May and June of 2010. The extensive meteorological, trace gas, and aerosol measurements collected at surface sites and along aircraft and ship transects during CalNex and CARES were combined with operational monitoring network measurements to create a single dataset that was used to evaluate the one configuration of the model. Simulations were performed that examined the sensitivity of regional variations in aerosol concentrations to anthropogenic emissions and to long-range transport of aerosols into the domain obtained from a global model. The configuration of WRF-Chem used in this study is shown to reproduce the overall synoptic conditions, thermally-driven circulations, and boundary layer structure observed in region that controls the transport and mixing of trace gases and aerosols. However, sub-grid scale variability in the meteorology and emissions as well as uncertainties in the treatment of secondary organic aerosol chemistry likely contribute to errors at a primary surface sampling site located at the edge of the Los Angeles basin. Differences among the sensitivity simulations demonstrate that the aerosol layers over the central valley detected by lidar measurements likely resulted from lofting and recirculation of local anthropogenic emissions along the Sierra Nevada. Reducing the default emissions inventory by 50% led to an overall improvement in many simulated trace gases and black carbon aerosol at most sites and along most aircraft flight paths; however, simulated organic aerosol was closer to observed when there were no adjustments to the primary organic aerosol emissions. The model performance for some aerosol species was not uniform over the region, and we found that sulfate was better simulated over northern California whereas nitrate was better simulated over southern California. While the overall spatial and temporal variability of aerosols and their precursors were simulated reasonably well, we show cases where the local transport of some aerosol plumes were either too slow or too fast, which adversely affects the statistics regarding the differences between observed and simulated quantities. Comparisons with lidar and in-situ measurements indicate that long-range transport of aerosols from the global model was likely too high in the free troposphere even though their concentrations were relatively low. This bias led to an over-prediction in aerosol optical depth by as much as a factor of two that offset the under-predictions of boundary-layer extinction resulting primarily from local emissions. Lowering the boundary conditions of aerosol concentrations by 50% greatly reduced the bias in simulated aerosol optical depth for all regions of California. This study shows that quantifying regional-scale variations in aerosol radiative forcing and determining the relative role of emissions from local and distant sources is challenging during "clean" conditions and that a wide array of measurements are needed to ensure model predictions are correct for the right reasons. In this regard, the combined CalNex and CARES datasets are an ideal testbed that can be used to evaluate aerosol models in great detail and develop improved treatments for aerosol processes.

Abstract. In 2016–2018, the ObseRvations of Aerosols above CLouds and their intEractionS (ORACLES) project undertook 3-month-long deployments to the southeastern (SE) Atlantic Ocean using research aircraft to better understand the impact of biomass burning (BB) aerosol transport to the SE Atlantic Ocean on climate. In this (part 1 of the meteorological overview) paper, the climatological features at monthly timescales are investigated. The southern African easterly jet (AEJ-S), defined as the zonal easterlies over 600–700 hPa exceeding 6 m s−1 around 5–15∘ S, is a characteristic feature of the mid-level circulation over southern Africa that was also during the deployment months of August 2017, September 2016, and October 2018. Climatologically, the AEJ-S develops at lower altitudes (∼ 3 km; 700 hPa) between 5–10∘ S in August, while it develops at around 4 km (∼ 600 hPa) and further south (5–15∘ S) in September and October, largely driven by the strong sensible heating over the African plateau. Notable meteorological anomalous characteristics during the 3 deployment months, compared to climatology (2000–2018), include the following: (1) during August 2017, the AEJ-S was weaker than the climatological mean, with an additional anomalous upper-level jet aloft (∼ 6 km) around 10∘ S. August 2017 was also drier over the SE Atlantic at 600–700 hPa than climatology, with a stronger Benguela low-level jet (LLJ) at 925–950 hPa along the Namibian coast of the SE Atlantic. Consistent with this, the southern Atlantic anticyclone was also stronger and closer to the coast than the August climatological mean. (2) During September 2016, the AEJ-S intensity was similar to the climatological mean, although the heat low and vertical motion over the land was slightly stronger compared to the September climatology. The LLJ and the large-scale southern Atlantic anticyclone were stronger than the climatological mean. (3) During October 2018, the AEJ-S was slightly weaker compared to the climatological mean, as was the LLJ and the southern Atlantic anticyclone. October 2018 was wetter over the Benguela coastal region at 600 hPa than the climatological mean. During all the deployment months, the sea surface temperatures (SST) over the SE Atlantic were warmer than the climatological means, but the monthly mean low cloud fraction was only noticeably reduced in August 2017. A weak August 2017 AEJ-S can explain low offshore black carbon (BC) mixing ratios within the European Centre for Medium-Range Weather Forecasts (ECMWF) Copernicus Atmosphere Monitoring Service (CAMS) reanalysis, although the BC peak altitude, at 2–3 km, is below that of the AEJ-S. The upper-level wave disturbance and the associated anomalous circulation also explain the weakening of AEJ-S through the reduction of the strength of the heat low over the land during August 2017.

Numerical weather prediction (NWP) models have been increasing in skill and their capability to simulate weather systems and provide valuable information at convective scales has improved in recent years. Much effort has been put into developing NWP models across the globe. Representation of physical processes is one of the critical issues in NWP, and it differs from one model to another. We investigated the performance of three regional NWP models used by the South African Weather Service over southern Africa, to identify the model that produces the best deterministic forecasts for the study domain. The three models – Unified Model (UM), Consortium for Small-scale Modelling (COSMO) and Weather Research and Forecasting (WRF) – were run at a horizontal grid spacing of about 4.4 km. Model forecasts for precipitation, 2-m temperature, and wind speed were verified against different observations. Snow was evaluated against reported snow records. Both the temporal and spatial verification of the model forecasts showed that the three models are comparable, with slight variations. Temperature and wind speed forecasts were similar for the three different models. Accumulated precipitation was mostly similar, except where WRF captured small rainfall amounts from a coastal low, while it over-estimated rainfall over the ocean. The UM showed a bubble-like shape towards the tropics, while COSMO cut-off part of the rainfall band that extended from the tropics to the sub-tropics. The COSMO and WRF models simulated a larger spatial coverage of precipitation than UM and snow-report records.

Abstract Patterns of freshwater availability — its variability and distribution — are already shifting as a function of global climate change and climate variability. High resolution global gridded reanalyses products present an important tool to understand the already observed changes, and thereby improve future scenarios as the climate evolves. A historical 100-year long district rainfall dataset and a unique set of highly detailed rainfall data from the highveld of South Africa spanning a 10-year period provides an opportunity to independently evaluate the European Centre for Medium Range Weather Forecasting ERA5 reanalysis product. Evaluation is challenged by the episodic nature of significant rainfall events of southern Africa as well as differences in spatial and temporal resolution between model output and surface precipitation data. Here we present a convergent methodology spanning annual to event timescales and regional to gauge-level spatial scales in order to identify the characteristics of systematic biases in variability and amount of rain as well as timing of events. We find that ERA5 is consistently wetter than observed in ways that affect the timing of individual events, while performing well on metrics associated with large scale trends and seasonal variability. Errors are associated with both stratiform and convective rainfall types, but the timing of onset of convective rainfall is a challenge that is critical in this summer rainfall dominated region.

Southern Africa is highly vulnerable to drought because of its dependence on climate-sensitive sectors of agriculture, hydroenergy and fisheries. Recurring droughts continue to impact rural livelihoods and degrade the environment. Drought severity in southern Africa is exacerbated by poor levels of preparedness and low adaptive capacity. Whilst weather extremes and hazards are inevitable, the preparedness to manage such hazards determines their impact and whether they become disasters. Southern Africa is often caught unprepared by drought as existing early warning systems lack the drought forecastingcomponent, which often results in reactionary interventions as opposed to well-planned and proactive response mechanisms. This study assesses the spatio-temporal changes of rainfall and aridity in southern Africa through an analysis of long-term precipitation and evaporation trends from 1960 to 2007. Stakeholder consultation was conducted in Madagascar, Malawi, Zambia and Zimbabwe during the peak of the 2015/16 drought, focusing on overall drought impacts, current water resource availability, existing early warning systems, adaptation mechanisms and institutional capacity to mitigate and managedroughts as part of overall disaster risk reduction strategies. Average rainfall has decreased by 26% in the region between 1960 and 2007, and aridity has increased by 11% between 1980 and 2007. The absence of drought forecasting and lack of institutional capacity to mitigate drought impede regional drought risk reduction initiatives. Existing multi-hazard early warning systems in the region focus on flooding and drought monitoring and assessment. Drought forecasting is often not given due consideration, yet it is a key component of early warning and resilience building. We propose a regional drought early warning framework, emphasising the importance of both monitoring and forecasting as being integral to a drought early warning system and building resilience to drought.

Severe weather events associated with strong winds and flooding can cause fatalities, injuries and damage to property. Detailed and accurate weather forecasts that are issued and communicated timeously, and actioned upon, can reduce the impact of these events. The responsibility to provide such forecasts usually lies with government departments or state-owned entities; in South Africa that responsibility lies with the South African Weather Service (SAWS). SAWS is also a regional specialised meteorological centre and therefore provides weather information to meteorological services within the Southern African Development Community (SADC). We evaluated SAWS weather information using near real-time observations and models on the nowcasting to short-range forecasting timescales during two extreme events. These are the Idai tropical cyclone in March 2019 which impacted Mozambique, Zimbabwe and Malawi resulting in over 1000 deaths, and the floods over the KwaZulu-Natal (KZN) province in April 2019 that caused over 70 deaths. Our results show that weather models gave an indication of these systems in advance, with warnings issued at least 2 days in advance in the case of Idai and 1 day in advance for the KZN floods. Nowcasting systems were also in place for detailed warnings to be provided as events progressed. Shortcomings in model simulations were shown, in particular on locating the KZN flood event properly and over/underestimation of the event. The impacts experienced during the two events indicate that more needs to be done to increase weather awareness, and build disaster risk management systems, including disaster preparedness and risk reduction.

Sea surface temperature (SST) variability plays a key role in the global weather and climate system, with phenomena such as El Niño-Southern Oscillation (ENSO) regarded as a major source of interannual climate variability at the global scale. The ability to make long-range forecasts of SST variations and extreme marine heatwave events have potentially significant economic and societal benefits, especially in a warming climate. We have developed a deep learning time series prediction model (Unet-LSTM), based on more than 70 years (1950–2021) of ECMWF ERA5 monthly mean SST and 2-m air temperature data, to predict global 2-dimensional SSTs up to a 24-month lead. Model prediction skills are high in the equatorial and subtropical Pacific. We have assessed the ability of the model to predict SST anomalies in the Niño3.4 region, an ENSO index in the equatorial Pacific, and the Blob marine heatwave events in the northeast Pacific in detail. An assessment of the predictions of the 2019–2020 El Niño and the 2016–2017 and 2017–2018 La Niña show that the model has skill up to 18 months in advance. The prediction of the 2015–2016 extreme El Niño is less satisfactory, which suggests that subsurface ocean information may be crucial for the evolution of this event. Note that the model makes predictions of the 2-d monthly SST field and Nino 3.4 is just one region embedded in the global field. The model also shows long lead prediction skills for the northeast Pacific marine heatwave, the Blob. However, the prediction of the marine heatwaves in the southeast Indian Ocean, the Ningaloo Niño, shows a short lead prediction. These results indicate the significant potential of data-driven methods to yield long-range predictions of SST anomalies.

While climate information from General Circulation Models (GCMs) are usually too coarse for climate impact modelers or decision makers from various disciplines (e.g., hydrology, agriculture), Regional Climate Models (RCMs) provide feasible solutions for downscaling GCM output to finer spatiotemporal scales. However, it is well known that the model performance depends largely on the choice of the physical parameterization schemes, but optimal configurations may vary e.g., from region to region. Besides land-surface processes, the most crucial processes to be parameterized in RCMs include radiation (RA), cumulus convection (CU), cloud microphysics (MP), and planetary boundary layer (PBL), partly with complex interactions. Before conducting long-term climate simulations, it is therefore indispensable to identify a suitable combination of physics parameterization schemes for these processes. Using the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis product ERA-Interim as lateral boundary conditions, we derived an ensemble of 16 physics parameterization runs for a larger domain in Northern sub-Saharan Africa (NSSA), northwards of the equator, using two different CU-, MP-, PBL-, and RA schemes, respectively, using the Weather Research and Forecasting (WRF) model for the period 2006–2010 in a horizontal resolution of approximately 9 km. Based on different evaluation strategies including traditional (Taylor diagram, probability densities) and more innovative validation metrics (ensemble structure-amplitude-location (eSAL) analysis, Copula functions) and by means of different observation data for precipitation (P) and temperature (T), the impact of different physics combinations on the representation skill of P and T has been analyzed and discussed in the context of subsequent impact modeling. With the specific experimental setup, we found that the selection of the CU scheme has resulted in the highest impact with respect to the representation of P and T, followed by the RA parameterization scheme. Both, PBL and MP schemes showed much less impact. We conclude that a multi-facet evaluation can finally lead to better choices about good physics scheme combinations.

Weather and climate information trigger early action and facilitate better disaster preparedness. Decision-driven and people-centered weather and climate information are pivotal for the effective uptake. The challenge of early responses in preparing for drought hazard is growing in the dry savannah of tropical sub-Saharan African countries. This paper analyzed user needs for weather and climate information in fostering drought risk preparedness in Central-Southern Nigeria. Stratified, snowball, and simple random samplings were used to obtain a sample of 397 respondents across the agro-ecological zones of Edo State. Structured questionnaire was used to collect farm-level household data across communities. Eight focus group discussions and 11 key informants' interviews were conducted, targeting contact farmers and other agricultural stakeholders in selected key economic sectors of Edo State, Central-Southern Nigeria. Results show that non-users of weather and climate information are more than users in the savannah area. Heckman probit results explained that male gender, farmers' experience, income, and persistent incidence of erratic rainfall have more propensity to facilitate use of WCI in taking critical decisions while group membership or associations and distance of meteorological station prevent stakeholders from developing interest in using WCI for drought preparedness and response. Multi-criteria decision-making indicated that rainfall amount, onset and cessation rainfall dates, and rainfall distributions are the most useful WCI needed by end users in their decision response plan in agriculture; rainfall intensity, rainfall cessation date, rainfall distributions, and length of dry season are ranked as the most useful WCI for water resource management while heat intensity, rainstorms, and drought alerts were ranked as most appropriate for users in the disaster risk reduction in fostering resilience toward anticipated future drought hazard. Subseasonal-to-seasonal (S2S) and medium (4–10 days) timescales information are the most highly rated to facilitate resource planning for efficient utilization and management in all the economic sectors. The users' most preferred delivery method of receiving WCI are mobile telephone, radio, agricultural extension officers, farmers' groups, and contact farmers/specialist for efficiency and convenient criteria in enhancing users' decision capacity to uptake WCI. There is a need for a policy drive to build synergy that will make WCI forecasting systems include impact-based forecast estimates and response advisory across a wide range of natural hazards. A seamless collaborative effort in bringing scientific outputs and users' needs together will increase the utility of WCI through systematic efforts. NiMet should improve on its engagement with the stakeholders, the agricultural extension and planning office, water management authorities, and disaster risk reduction and emergency response personnel as partner institutions. These policy actions would provide a robust collaborative framework for co-producing useable WCI based on user needs in managing decision points against extreme events and mainstream preparedness into existing decision-making apparatus of rural communities in Central-Southern Nigeria.

AbstractThis paper presents an introduction to the Southern hemisphere high altitude experiment on particle nucleation and growth (SALTENA). This field campaign took place between December 2017 and June 2018 (wet to dry season) at Chacaltaya (CHC), a GAW (Global Atmosphere Watch) station located at 5240 m a.s.l. in the Bolivian Andes. Concurrent measurements were conducted at two additional sites in El Alto (4000 m a.s.l.) and La Paz (3600 m a.s.l.). The overall goal of the campaign was to identify the sources, understand the formation mechanisms and transport, and characterize the properties of aerosol at these stations. State-of-the-art instruments were brought to the station complementing the ongoing permanent GAW measurements, to allow a comprehensive description of the chemical species of anthropogenic and biogenic origin impacting the station and contributing to new particle formation. In this overview we first provide an assessment of the complex meteorology, air mass origin, and boundary layer – free troposphere interactions during the campaign using a 6-month high-resolution WRF (Weather Research and Forecasting) simulation coupled with FLEXPART (FLEXible PARTicle dispersion model). We then show some of the research highlights from the campaign, including i) chemical transformation processes of anthropogenic pollution while the air masses are transported to the CHC station from the metropolitan area of La Paz/El Alto, ii) volcanic emissions as an important source of atmospheric sulfur compounds in the region, iii) the characterization of the compounds involved in new particle formation, and iv) the identification of long-range transported compounds from the Pacific or the Amazon basin. We conclude the article with a presentation of future research foci. The SALTENA dataset highlights the importance of comprehensive observations in strategic high-altitude locations, especially the undersampled Southern Hemisphere.

IntroductionTasmania hangs from the map of Australia like a drop in freefall from the substance of the mainland. Often the whole state is mislaid from Australian maps and logos (Reddit). Tasmania has, at least since federation, been considered peripheral—a region seen as isolated, a ‘problem’ economically, politically, and culturally. However, Tasmania not only cleaves to the ‘north island’ of Australia but is also subject to the gravitational pull of an even greater land mass—Antarctica. In this article, we upturn the political conventions of map-making that place both Antarctica and Tasmania in obscure positions at the base of the globe. We show how a changing global climate re-frames Antarctica and the Southern Ocean as key drivers of worldwide environmental shifts. The liquid and solid water between Tasmania and Antarctica is revealed not as a homogenous barrier, but as a dynamic and relational medium linking the Tasmanian archipelago with Antarctica. When Antarctica becomes the focus, the script is flipped: Tasmania is no longer on the edge, but core to a network of gateways into the southern land. The state’s capital of Hobart can from this perspective be understood as an “Antarctic city”, central to the geopolitics, economy, and culture of the frozen continent (Salazar et al.). Viewed from the south, we argue, Tasmania is not a problem, but an opportunity for a form of ecological, cultural, economic, and political sustainability that opens up the southern continent to science, discovery, and imagination.A Centre at the End of the Earth? Tasmania as ParadoxThe islands of Tasmania owe their existence to climate change: a period of warming at the end of the last ice age melted the vast sheets of ice covering the polar regions, causing sea levels to rise by more than one hundred metres (Tasmanian Climate Change Office 8). Eleven thousand years ago, Aboriginal people would have witnessed the rise of what is now called Bass Strait, turning what had been a peninsula into an archipelago, with the large island of Tasmania at its heart. The heterogeneous practices and narratives of Tasmanian regional identity have been shaped by the geography of these islands, and their connection to the Southern Ocean and Antarctica. Regions, understood as “centres of collective consciousness and sociospatial identities” (Paasi 241) are constantly reproduced and reimagined through place-based social practices and communications over time. As we will show, diverse and contradictory narratives of Tasmanian regionality often co-exist, interacting in complex and sometimes complementary ways. Ecocritical literary scholar C.A. Cranston considers duality to be embedded in the textual construction of Tasmania, writing “it was hell, it was heaven, it was penal, it was paradise” (29). Tasmania is multiply polarised: it is both isolated and connected; close and far away; rich in resources and poor in capital; the socially conservative birthplace of radical green politics (Hay 60). The weather, as if sensing the fine balance of these paradoxes, blows hot and cold at a moment’s notice.Tasmania has wielded extraordinary political influence at times in its history—notably during the settlement of Melbourne in 1835 (Boyce), and during protests against damming the Franklin River in the early 1980s (Mercer). However, twentieth-century historical and political narratives of Tasmania portray the Bass Strait as a barrier, isolating Tasmanians from the mainland (Harwood 61). Sir Bede Callaghan, who headed one of a long line of federal government inquiries into “the Tasmanian problem” (Harwood 106), was clear that Tasmania was a victim of its own geography:the major disability facing the people of Tasmania (although some residents may consider it an advantage) is that Tasmania is an island. Separation from the mainland adversely affects the economy of the State and the general welfare of the people in many ways. (Callaghan 3)This perspective may stem from the fact that Tasmania has maintained the lowest Gross Domestic Product per capita of all states since federation (Bureau of Infrastructure Transport and Regional Economics 9). Socially, economically, and culturally, Tasmania consistently ranks among the worst regions of Australia. Statistical comparisons with other parts of Australia reveal the population’s high unemployment, low wages, poor educational outcomes, and bad health (West 31). The state’s remoteness and isolation from the mainland states and its reliance on federal income have contributed to the whole of Tasmania, including Hobart, being classified as ‘regional’ by the Australian government, in an attempt to promote immigration and economic growth (Department of Infrastructure and Regional Development 1). Tasmania is indeed both regional and remote. However, in this article we argue that, while regionality may be cast as a disadvantage, the island’s remote location is also an asset, particularly when viewed from a far southern perspective (Image 1).Image 1: Antarctica (Orthographic Projection). Image Credit: Wikimedia Commons, Modified Shading of Tasmania and Addition of Captions by H. Nielsen.Connecting Oceans/Collapsing DistanceTasmania and Antarctica have been closely linked in the past—the future archipelago formed a land bridge between Antarctica and northern land masses until the opening of the Tasman Seaway some 32 million years ago (Barker et al.). The far south was tangible to the Indigenous people of the island in the weather blowing in from the Southern Ocean, while the southern lights, or “nuyina”, formed a visible connection (Australia’s new icebreaker vessel is named RSV Nuyina in recognition of these links). In the contemporary Australian imagination, Tasmania tends to be defined by its marine boundaries, the sea around the islands represented as flat, empty space against which to highlight the topography of its landscape and the isolation of its position (Davies et al.). A more relational geographic perspective illuminates the “power of cross-currents and connections” (Stratford et al. 273) across these seascapes. The sea country of Tasmania is multiple and heterogeneous: the rough, shallow waters of the island-scattered Bass Strait flow into the Tasman Sea, where the continental shelf descends toward an abyssal plain studded with volcanic seamounts. To the south, the Southern Ocean provides nutrient-rich upwellings that attract fish and cetacean populations. Tasmania’s coast is a dynamic, liminal space, moving and changing in response to the global currents that are driven by the shifting, calving and melting ice shelves and sheets in Antarctica.Oceans have long been a medium of connection between Tasmania and Antarctica. In the early colonial period, when the seas were the major thoroughfares of the world and inland travel was treacherous and slow, Tasmania’s connection with the Southern Ocean made it a valuable hub for exploration and exploitation of the south. Between 1642 and 1900, early European explorers were followed by British penal colonists, convicts, sealers, and whalers (Kriwoken and Williamson 93). Tasmania was well known to polar explorers, with expeditions led by Jules Dumont d’Urville, James Clark Ross, Roald Amundsen, and Douglas Mawson all transiting through the port of Hobart. Now that the city is no longer a whaling hub, growing populations of cetaceans continue to migrate past the islands on their annual journeys from the tropics, across the Sub-Antarctic Front and Antarctic circumpolar current, and into the south polar region, while southern species such as leopard seals are occasionally seen around Tasmania (Tasmania Parks and Wildlife). Although the water surrounding Tasmania and Antarctica is at times homogenised as a ‘barrier’, rendering these places isolated, the bodies of water that surround both are in fact permeable, and regularly crossed by both humans and marine species. The waters are diverse in their physical characteristics, underlying topography, sea life, and relationships, and serve to connect many different ocean regions, ecosystems, and weather patterns.Views from the Far SouthWhen considered in terms of its relative proximity to Antarctic, rather than its distance from Australia’s political and economic centres, Tasmania’s identity undergoes a significant shift. A sign at Cockle Creek, in the state’s far south, reminds visitors that they are closer to Antarctica than to Cairns, invoking a discourse of connectedness that collapses the standard ten-day ship voyage to Australia’s closest Antarctic station into a unit comparable with the routinely scheduled 5.5 hour flight to North Queensland. Hobart is the logistical hub for the Australian Antarctic Division and the French Institut Polaire Francais (IPEV), and has hosted Antarctic vessels belonging to the USA, South Korea, and Japan in recent years. From a far southern perspective, Hobart is not a regional Australian capital but a global polar hub. This alters the city’s geographic imaginary not only in a latitudinal sense—from “top down” to “bottom up”—but also a longitudinal one. Via its southward connection to Antarctica, Hobart is also connected east and west to four other recognized gateways: Cape Town in South Africa, Christchurch in New Zealand; Punta Arenas in Chile; and Ushuaia in Argentina (Image 2). The latter cities are considered small by international standards, but play an outsized role in relation to Antarctica.Image 2: H. Nielsen with a Sign Announcing Distances between Antarctic ‘Gateway’ Cities and Antarctica, Ushuaia, Argentina, 2018. Image Credit: Nicki D'Souza.These five cities form what might be called—to adapt geographer Klaus Dodds’ term—a ‘Southern Rim’ around the South Polar region (Dodds Geopolitics). They exist in ambiguous relationship to each other. Although the five cities signed a Statement of Intent in 2009 committing them to collaboration, they continue to compete vigorously for northern hemisphere traffic and the brand identity of the most prominent global gateway. A state government brochure spruiks Hobart, for example, as the “perfect Antarctic Gateway” emphasising its uniqueness and “natural advantages” in this regard (Tasmanian Government, 2016). In practice, the cities are automatically differentiated by their geographic position with respect to Antarctica. Although the ‘ice continent’ is often conceived as one entity, it too has regions, in both scientific and geographical senses (Terauds and Lee; Antonello). Hobart provides access to parts of East Antarctica, where the Australian, French, Japanese, and Chinese programs (among others) have bases; Cape Town is a useful access point for Europeans going to Dronning Maud Land; Christchurch is closest to the Ross Sea region, site of the largest US base; and Punta Arenas and Ushuaia neighbour the Antarctic Peninsula, home to numerous bases as well as a thriving tourist industry.The Antarctic sector is important to the Tasmanian economy, contributing $186 million (AUD) in 2017/18 (Wells; Gutwein; Tasmanian Polar Network). Unsurprisingly, Tasmania’s gateway brand has been actively promoted, with the 2016 Australian Antarctic Strategy and 20 Year Action Plan foregrounding the need to “Build Tasmania’s status as the premier East Antarctic Gateway for science and operations” and the state government releasing a “Tasmanian Antarctic Gateway Strategy” in 2017. The Chinese Antarctic program has been a particular focus: a Memorandum of Understanding focussed on Australia and China’s Antarctic relations includes a “commitment to utilise Australia, including Tasmania, as an Antarctic ‘gateway’.” (Australian Antarctic Division). These efforts towards a closer relationship with China have more recently come under attack as part of a questioning of China’s interests in the region (without, it should be noted, a concomitant questioning of Australia’s own considerable interests) (Baker 9). In these exchanges, a global power and a state of Australia generally classed as regional and peripheral are brought into direct contact via the even more remote Antarctic region. This connection was particularly visible when Chinese President Xi Jinping travelled to Hobart in 2014, in a visit described as both “strategic” and “incongruous” (Burden). There can be differences in how this relationship is narrated to domestic and international audiences, with issues of sovereignty and international cooperation variously foregrounded, laying the ground for what Dodds terms “awkward Antarctic nationalism” (1).Territory and ConnectionsThe awkwardness comes to a head in Tasmania, where domestic and international views of connections with the far south collide. Australia claims sovereignty over almost 6 million km2 of the Antarctic continent—a claim that in area is “roughly the size of mainland Australia minus Queensland” (Bergin). This geopolitical context elevates the importance of a regional part of Australia: the claims to Antarctic territory (which are recognised only by four other claimant nations) are performed not only in Antarctic localities, where they are made visible “with paraphernalia such as maps, flags, and plaques” (Salazar 55), but also in Tasmania, particularly in Hobart and surrounds. A replica of Mawson’s Huts in central Hobart makes Australia’s historic territorial interests in Antarctica visible an urban setting, foregrounding the figure of Douglas Mawson, the well-known Australian scientist and explorer who led the expeditions that proclaimed Australia’s sovereignty in the region of the continent roughly to its south (Leane et al.). Tasmania is caught in a balancing act, as it fosters international Antarctic connections (such hosting vessels from other national programs), while also playing a key role in administering what is domestically referred to as the Australian Antarctic Territory. The rhetoric of protection can offer common ground: island studies scholar Godfrey Baldacchino notes that as island narratives have moved “away from the perspective of the ‘explorer-discoverer-colonist’” they have been replaced by “the perspective of the ‘custodian-steward-environmentalist’” (49), but reminds readers that a colonising disposition still lurks beneath the surface. It must be remembered that terms such as “stewardship” and “leadership” can undertake sovereignty labour (Dodds “Awkward”), and that Tasmania’s Antarctic connections can be mobilised for a range of purposes. When Environment Minister Greg Hunt proclaimed at a press conference that: “Hobart is the gateway to the Antarctic for the future” (26 Apr. 2016), the remark had meaning within discourses of both sovereignty and economics. Tasmania’s capital was leveraged as a way to position Australia as a leader in the Antarctic arena.From ‘Gateway’ to ‘Antarctic City’While discussion of Antarctic ‘Gateway’ Cities often focuses on the economic and logistical benefit of their Antarctic connections, Hobart’s “gateway” identity, like those of its counterparts, stretches well beyond this, encompassing geological, climatic, historical, political, cultural and scientific links. Even the southerly wind, according to cartoonist Jon Kudelka, “has penguins in it” (Image 3). Hobart residents feel a high level of connection to Antarctica. In 2018, a survey of 300 randomly selected residents of Greater Hobart was conducted under the umbrella of the “Antarctic Cities” Australian Research Council Linkage Project led by Assoc. Prof. Juan Francisco Salazar (and involving all three present authors). Fourteen percent of respondents reported having been involved in an economic activity related to Antarctica, and 36% had attended a cultural event about Antarctica. Connections between the southern continent and Hobart were recognised as important: 71.9% agreed that “people in my city can influence the cultural meanings that shape our relationship to Antarctica”, while 90% agreed or strongly agreed that Hobart should play a significant role as a custodian of Antarctica’s future, and 88.4% agreed or strongly agreed that: “How we treat Antarctica is a test of our approach to ecological sustainability.” Image 3: “The Southerly” Demonstrates How Weather Connects Hobart and Antarctica. Image Credit: Jon Kudelka, Reproduced with Permission.Hobart, like the other gateways, activates these connections in its conscious place-branding. The city is particularly strong as a centre of Antarctic research: signs at the cruise-ship terminal on the waterfront claim that “There are more Antarctic scientists based in Hobart […] than at any other one place on earth, making Hobart a globally significant contributor to our understanding of Antarctica and the Southern Ocean.” Researchers are based at the Institute for Marine and Antarctic Studies (IMAS), the Commonwealth Scientific and Industrial Research Organisation (CSIRO), and the Australian Antarctic Division (AAD), with several working between institutions. Many Antarctic researchers located elsewhere in the world also have a connection with the place through affiliations and collaborations, leading journalist Jo Chandler to assert that “the breadth and depth of Hobart’s knowledge of ice, water, and the life forms they nurture […] is arguably unrivalled anywhere in the world” (86).Hobart also plays a significant role in Antarctica’s governance, as the site of the secretariats for the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) and the Agreement on the Conservation of Albatrosses and Petrels (ACAP), and as host of the Antarctic Consultative Treaty Meetings on more than one occasion (1986, 2012). The cultural domain is active, with Tasmanian Museum and Art Gallery (TMAG) featuring a permanent exhibit, “Islands to Ice”, emphasising the ocean as connecting the two places; the Mawson’s Huts Replica Museum aiming (among other things) to “highlight Hobart as the gateway to the Antarctic continent for the Asia Pacific region”; and a biennial Australian Antarctic Festival drawing over twenty thousand visitors, about a sixth of them from interstate or overseas (Hingley). Antarctic links are evident in the city’s natural and built environment: the dolerite columns of Mt Wellington, the statue of the Tasmanian Antarctic explorer Louis Bernacchi on the waterfront, and the wharfs that regularly accommodate icebreakers such as the Aurora Australis and the Astrolabe. Antarctica is figured as a southern neighbour; as historian Tom Griffiths puts it, Tasmanians “grow up with Antarctica breathing down their necks” (5). As an Antarctic City, Hobart mediates access to Antarctica both physically and in the cultural imaginary.Perhaps in recognition of the diverse ways in which a region or a city might be connected to Antarctica, researchers have recently been suggesting critical approaches to the ‘gateway’ label. C. Michael Hall points to a fuzziness in the way the term is applied, noting that it has drifted from its initial definition (drawn from economic geography) as denoting an access and supply point to a hinterland that produces a certain level of economic benefits. While Hall looks to keep the term robustly defined to avoid empty “local boosterism” (272–73), Gabriela Roldan aims to move the concept “beyond its function as an entry and exit door”, arguing that, among other things, the local community should be actively engaged in the Antarctic region (57). Leane, examining the representation of Hobart as a gateway in historical travel texts, concurs that “ingress and egress” are insufficient descriptors of Tasmania’s relationship with Antarctica, suggesting that at least discursively the island is positioned as “part of an Antarctic rim, itself sharing qualities of the polar region” (45). The ARC Linkage Project described above, supported by the Hobart City Council, the State Government and the University of Tasmania, as well as other national and international partners, aims to foster the idea of the Hobart and its counterparts as ‘Antarctic cities’ whose citizens act as custodians for the South Polar region, with a genuine concern for and investment in its future.Near and Far: Local Perspectives A changing climate may once again herald a shift in the identity of the Tasmanian islands. Recognition of the central role of Antarctica in regulating the global climate has generated scientific and political re-evaluation of the region. Antarctica is not only the planet’s largest heat sink but is the engine of global water currents and wind patterns that drive weather patterns and biodiversity across the world (Convey et al. 543). For example, Tas van Ommen’s research into Antarctic glaciology shows the tangible connection between increased snowfall in coastal East Antarctica and patterns of drought southwest Western Australia (van Ommen and Morgan). Hobart has become a global centre of marine and Antarctic science, bringing investment and development to the city. As the global climate heats up, Tasmania—thanks to its low latitude and southerly weather patterns—is one of the few regions in Australia likely to remain temperate. This is already leading to migration from the mainland that is impacting house prices and rental availability (Johnston; Landers 1). The region’s future is therefore closely entangled with its proximity to the far south. Salazar writes that “we cannot continue to think of Antarctica as the end of the Earth” (67). Shifting Antarctica into focus also brings Tasmania in from the margins. As an Antarctic city, Hobart assumes a privileged positioned on the global stage. This allows the city to present itself as central to international research efforts—in contrast to domestic views of the place as a small regional capital. The city inhabits dual identities; it is both on the periphery of Australian concerns and at the centre of Antarctic activity. Tasmania, then, is not in freefall, but rather at the forefront of a push to recognise Antarctica as entangled with its neighbours to the north.AcknowledgementsThis work was supported by the Australian Research Council under LP160100210.ReferencesAntonello, Alessandro. “Finding Place in Antarctica.” Antarctica and the Humanities. Eds. Peder Roberts, Lize-Marie van der Watt, and Adrian Howkins. London: Palgrave Macmillan, 2016. 181–204.Australian Government. 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