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Esmaili, Rebekah, Christopher Barnet, Jason Dunion, Michael Folmer, and Jonathan Zawislak. "Evaluating Satellite Sounders for Monitoring the Tropical Cyclone Environment in Operational Forecasting." Remote Sensing 14, no. 13 (2022): 3189. http://dx.doi.org/10.3390/rs14133189.
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Tropical cyclones can form over open ocean where in situ observations are limited, so forecasters rely on satellite observations to monitor their development and track. We explore the utility of an operational satellite sounding product for tropical forecasting by characterizing the products retrieval skill during research flights. Scientists from both the NOAA-Unique Combined Atmospheric Processing System (NUCAPS) research team and tropical cyclone communities collaborated to target relevant tropical cyclones during the campaign. This effort produced 130 dropsondes that are well-timed with satellite sounder overpasses over three different tropical cyclones and one Saharan Air Layer outbreak. For the combined infrared and microwave retrieval, the NUCAPS temperature has a root mean square error (RMSE) of 1.2 K near the surface (1000–600 mb) and 0.8 K in the mid-troposphere (600–300 mb), which is in line with global product requirements. The water vapor mixing ratio RMSE was 26% near the surface and 46% in the mid-troposphere. NUCAPS microwave-only retrievals can also be useful for cloudy scenes, with surface RMSE values of 4 K (temperature) and 23% (water vapor). Using information content analysis, we estimated that the vertical resolution near the surface was 1.7 km for the temperature retrievals and 2.2 km for the water vapor retrievals in this study. We discuss the feasibility of implementing NUCAPS in an operational forecasting setting, which requires rapid data delivery to forecaster software tools.
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Croad, Hannah L., John Methven, Ben Harvey, Sarah P. E. Keeley, and Ambrogio Volonté. "The role of boundary layer processes in summer-time Arctic cyclones." Weather and Climate Dynamics 4, no. 3 (2023): 617–38. http://dx.doi.org/10.5194/wcd-4-617-2023.
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Abstract. Arctic cyclones are the most energetic weather systems in the Arctic, producing strong winds and precipitation that present major weather hazards. In summer, when the sea ice cover is reduced and more mobile, Arctic cyclones can have large impacts on ocean waves and sea ice. While the development of mid-latitude cyclones is known to be dependent on boundary layer (BL) turbulent fluxes, the dynamics of summer-time Arctic cyclones and their dependence on surface exchange processes have not been investigated. The purpose of this study is to characterise the BL processes acting in summer-time Arctic cyclones and understand their influence on cyclone evolution. The study focuses on two cyclone case studies, each characterised by a different structure during growth in the Arctic: (A) low-level-dominant vorticity (warm-core) structure and (B) upper-level-dominant vorticity (cold-core) structure, linked with a tropopause polar vortex. A potential vorticity (PV) framework is used to diagnose the BL processes in model runs from the ECMWF Integrated Forecasting System model. Both cyclones are associated with frictional Ekman pumping and downward sensible heat fluxes over sea ice. However, a third process, the frictional baroclinic generation of PV, acts differently in A and B due to differences in their low-level temperature structures. Positive PV is generated in Cyclone A near the bent-back warm front, like in typical mid-latitude cyclones. However, the same process produces negative PV tendencies in B, shown to be a consequence of the vertically aligned axisymmetric cold-core structure. This frictional process also acts to cool the lower troposphere, reducing the warm-core anomaly in A and amplifying the cold-core anomaly in B. Both cyclones attain a vertically aligned cold-core structure that persists for several days after maximum intensity, which is consistent with cooling from frictional Ekman pumping, frictional baroclinic PV generation, and downward sensible heat fluxes. This may help to explain the longevity of isolated cold-core Arctic cyclones with columnar vorticity structure.
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DAS, G. K., S. K. MIDYA, G. C. DEBNATH, and S. N. ROY. "The relationship between geopotential height and movement & landfall of tropical cyclone in the Bay of Bengal region." MAUSAM 63, no. 3 (2022): 469–74. http://dx.doi.org/10.54302/mausam.v63i3.1214.
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In this paper a simple relationship is employed to investigate relative impacts on the movement and landfall of tropical cyclone in the Bay of Bengal region when geopotential height of different troposphere levels is used as an input. Five tropical cyclone during pre-monsoon and post-monsoon season over the Bay of Bengal region has been selected for the study. The RS/RW data of coastal stations namely Kolkata (Dumdum), Dhaka, Agartala, Bhubaneswar, Visakhapatnam, Machlipatnam, Chennai and Karaikal has been collected for the period of the cyclones under study. The geopotential height of different standard levels has been plotted against the time for the stations for every cyclone. The study suggests that the cyclone moves towards and cross near the station having relatively steeper decrease in geopotential height upto mid tropical level followed by increased in geopotential height.
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Zhang, Shuqin, Yuan Tang, Liwen Zhang, Qinghua Liao, and Tianyu Zhang. "Variations in Key Factors at Different Explosive Development Stages of an Extreme Explosive Cyclone over the Japan Sea." Atmosphere 14, no. 9 (2023): 1327. http://dx.doi.org/10.3390/atmos14091327.
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Explosive cyclones (ECs) occur frequently over the Japan Sea. The most rapidly intensifying EC over the Japan Sea during the 44-year period 1979–2022, in the cold season (October–April), was examined to reveal the variations in the key factors at different explosive development stages. The EC deepened at a maximum deepening rate of 3.07 bergerons and explosive development lasted for 15 h. At the initial moment of explosive development, the EC had distinctive low-level baroclinicity, the low-level water vapor convergence was weak, and mid-level cyclonic vorticity advection was far away from the EC’s center. At the moment at which the EC reached the maximum deepening rate, the low-level water vapor convergence and mid-level cyclonic vorticity advection increased distinctly and approached the EC’s center. A diagnostic analysis using the Zwack–Okossi equation showed that the main contributor to the initial explosive development was warm-air advection. Through the evolutionary process of the explosive development, the non-key factors of the cyclonic vorticity advection and diabatic heating at the initial explosive development stage increased quickly and became key factors contributing to the maximum explosive development. The key factors contributing to the explosive development varied with the stage of explosive development. The cross-section and vertical profile of each term suggested that the cyclonic vorticity advection was enhanced in the upper troposphere and diabatic heating increased in the middle troposphere.
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Nicholls, M. E., and M. T. Montgomery. "An examination of two pathway to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model." Atmospheric Chemistry and Physics Discussions 13, no. 1 (2013): 765–825. http://dx.doi.org/10.5194/acpd-13-765-2013.
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Abstract. Simulations are conducted with a cloud-resolving numerical model to examine the transformation of a weak incipient mid-level cyclonic vortex into a tropical cyclone. Results demonstrate that two distinct pathways are possible and that development along a particular pathway is sensitive to model physics and initial conditions. One pathway involves a steady increase of the surface winds to tropical cyclone strength as the radius of maximum winds gradually decreases. A notable feature of this evolution is the creation of small-scale lower tropospheric cyclonic vorticity anomalies by deep convective towers and subsequent merger and convergence by the low-level secondary circulation. The second pathway also begins with a strengthening low-level circulation, but eventually a significantly stronger mid-level circulation develops. Cyclogenesis occurs subsequently when a small-scale surface concentrated vortex forms abruptly near the center of the larger-scale circulation. The small-scale vortex is warm core throughout the troposphere and results in a local surface pressure fall of a few millibars. It usually develops rapidly, undergoing a modest growth to form a small tropical cyclone. Many of the simulated systems approach or reach tropical cyclone strength prior to development of a prominent mid-level vortex so that the subsequent formation of a strong small-scale surface concentrated vortex in these cases could be considered intensification rather than genesis. Experiments are performed to investigate the dependence on the inclusion of the ice phase, radiation, the size and strength of the incipient mid-level vortex, the amount of moisture present in the initial vortex, and the sea surface temperature. Notably, as the sea surface temperature is raised, the likelihood of development along the second pathway is increased. This appears to be related to an increased production of ice. The sensitivity of the pathway taken to model physics and initial conditions revealed by these experiments raise the possibility that the solution to this initial value problem is near a bifurcation point. Future improvements to model parameterizations and more accurate observations of the transformation of disturbances to tropical cyclones should clarify the conditions that favor a particular pathway when starting from a mid-level vortex.
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Nicholls, M. E., and M. T. Montgomery. "An examination of two pathways to tropical cyclogenesis occurring in idealized simulations with a cloud-resolving numerical model." Atmospheric Chemistry and Physics 13, no. 12 (2013): 5999–6022. http://dx.doi.org/10.5194/acp-13-5999-2013.
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Abstract. Simulations are conducted with a cloud-resolving numerical model to examine the transformation of a weak incipient mid-level cyclonic vortex into a tropical cyclone. Results demonstrate that two distinct pathways are possible and that development along a particular pathway is sensitive to model physics and initial conditions. One pathway involves a steady increase of the surface winds to tropical cyclone strength as the radius of maximum winds gradually decreases. A notable feature of this evolution is the creation of small-scale lower tropospheric cyclonic vorticity anomalies by deep convective towers and subsequent merger and convergence by the low-level secondary circulation. The second pathway also begins with a strengthening low-level circulation, but eventually a significantly stronger mid-level circulation develops. Cyclogenesis occurs subsequently when a small-scale surface concentrated vortex forms abruptly near the center of the larger-scale circulation. The small-scale vortex is warm core throughout the troposphere and results in a fall in local surface pressure of a few millibars. It usually develops rapidly, undergoing a modest growth to form a small tropical cyclone. Many of the simulated systems approach or reach tropical cyclone strength prior to development of a prominent mid-level vortex so that the subsequent formation of a strong small-scale surface concentrated vortex in these cases could be considered intensification rather than genesis. Experiments are performed to investigate the dependence on the inclusion of the ice phase, radiation, the size and strength of the incipient mid-level vortex, the amount of moisture present in the initial vortex, and the sea surface temperature. Notably, as the sea surface temperature is raised, the likelihood of development along the second pathway is increased. This appears to be related to an increased production of ice. The sensitivity of the pathway taken to model physics and initial conditions revealed by these experiments raise the possibility that the solution to this initial value problem is near a bifurcation point. Future improvements to model parameterizations and more accurate observations of the transformation of disturbances to tropical cyclones should clarify the conditions that favor a particular pathway when starting from a mid-level vortex.
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Evstigneev, Vladislav P., Valentina A. Naumova, Dmitriy Y. Voronin, Pavel N. Kuznetsov, and Svetlana P. Korsakova. "Severe Precipitation Phenomena in Crimea in Relation to Atmospheric Circulation." Atmosphere 13, no. 10 (2022): 1712. http://dx.doi.org/10.3390/atmos13101712.
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The increase in the frequency and intensity of hazardous hydrometeorological phenomena is one of the most dangerous consequences of climate instability. In this study, we summarize the data on severe weather phenomena using the data from 23 meteorological stations in Crimea from 1976 to 2020. Particular attention was paid to the precipitation phenomena descriptions. For the last 45 years, a significant positive trend of interannual variability of the annual occurrence of severe weather phenomena was estimated to be +2.7 cases per decade. The trend for severe precipitation phenomena was estimated to be +1.3 cases per decade. The probable maximum annual daily precipitation as a quantitative indicator of hazardous events was estimated for each station by using both the stationary and the non-stationary GEV models. For at least half of the meteorological stations, a non-stationary GEV model was more appropriate for the estimation of the precipitation extremes. An analysis of the main synoptic processes that drive severe weather phenomena of precipitation was carried out. The greatest contribution to the formation of severe precipitation was made by Mediterranean–Black Sea cyclones. At the same time, half of all of the cases of extreme precipitation were caused by cyclones generated over the Black Sea only, in all seasons apart from winter. In the mid-troposphere, four types of meridional circulation were identified depending on the location of troughs and ridges, with respect to the Black Sea region. More than 42% of severe precipitation phenomena were accompanied by an isolated high-altitude cyclone in the mid-troposphere over the Black Sea region. The main recommendation that can be drawn from this study is that long-term climatic non-stationarity should be taken into account whenever the risk assessment or hazard analysis is to be carried out. The results can also favor the designing of drainage and sewerage systems in urban areas. The findings of atmospheric patterns can be used for the improvement of extreme precipitation forecasts.
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Yang, Y. Q., Q. Hou, C. H. Zhou, H. L. Liu, Y. Q. Wang, and T. Niu. "Sand/dust storms over Northeast Asia and associated large-scale circulations in spring 2006." Atmospheric Chemistry and Physics Discussions 7, no. 3 (2007): 9259–81. http://dx.doi.org/10.5194/acpd-7-9259-2007.
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Abstract. This paper presents a study on the meteorological conditions that accompany the sand/dust storms (SDS) of East Asia in spring 2006, based on the SDS data collected both by WMO during 2000–2006 and by 2456 Chinese surface stations, and on the meteorological reanalysis data from NCEP-NCAR . The evolution of 3-D structures of the general circulations prevailed in both winter and spring as well as their annual anomalies were investigated by comparing the years having most and least occurrences of SDS between 2000 and 2006. It is found that spring 2006 featured a noticeably increased occurrence of SDS, compared with previous years. The general circulations prevailed through both winter and spring, especially the 3-D structure of the polar circulation, show the significant anomalies compared to a normal year. This produced a range of corresponding weather phenomena, including circumpolar vortices at the upper troposphere, mid-level westerly jets, and lower zonal winds, which all favored the SDS production and transport in 2006. The study also reveals a fact that comparing with a normal year, the transitional period from the winter of 2005 to the spring of 2006 has witnessed a fast-developed high center at the upper troposphere of the northern hemisphere and the circumpolar vortex area, which pushes the area dominated by the circumpolar vortices further to mid-latitudes. The circumpolar vortices shifted southwards, and prevailed over an extensive area across the northeast hemisphere for a sustained period. The mid-high latitude areas that sit in the south of the circumpolar vortices in Asia have experienced significantly abnormal westerly jets at the mid-level of troposphere. Zonal winds prevailed at the mid and lower levels of troposphere. Sea level pressure registered an abnormal high at 4–10 hPa, compared with a normal year. The above-mentioned 3-D structures of general circulation have created thermal and dynamic conditions that favor the repeated genesis and momentous development of the Mongolian cyclones, which in turn contributes to the frequent occurrences and long distance transport of SDS.
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Xu, Li, and Zi-Liang Li. "Impacts of the Wave Train along the Asian Jet on the South China Sea Summer Monsoon Onset." Atmosphere 12, no. 9 (2021): 1227. http://dx.doi.org/10.3390/atmos12091227.
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The South China Sea (SCS) summer monsoon (SCSSM) onset signifies the commencement of large-scale summer monsoon over East Asia and the western North Pacific (WNP). Previous studies on the influencing factors of the SCSSM onset mainly focus on the tropical systems, such as El Niño-Southern Oscillation (ENSO). This study reveals that the wave train along the Asian jet could act as an extratropical factor to modulate the SCSSM onset, and it is largely independent of ENSO. The SCSSM onset tends to be earlier during the positive phase of the wave train (featured by northerly anomalies over Central Iran plateau and eastern China, southerly anomalies over Arabian Peninsula, eastern Indian subcontinent, and eastern Bonin islands). The wave train affects the SCSSM onset mainly via modulating the WNP subtropical high. The wave train during the positive phase can induce negative geopotential height anomalies in the mid-troposphere and anomalous cyclones in the lower-troposphere over the SCS and the Philippine Sea, leading to the weakening of the WNP subtropical high. Specifically, the anomalous ascending motions associated with the low-level cyclone are favorable for the increased rainfall over the SCS, and the anomalous westerly on the south of the anomalous cyclone is conducive to the transition of the zonal wind (from easterly to westerly). The above circulation anomalies associated with the positive phase of the wave train provide a favorable environment for the advanced SCSSM onset.
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Lu, Ren, and Xiaodong Tang. "Relationship between Early-Stage Features and Lifetime Maximum Intensity of Tropical Cyclones over the Western North Pacific." Atmosphere 12, no. 7 (2021): 815. http://dx.doi.org/10.3390/atmos12070815.
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The relationship between early-stage features and lifetime maximum intensity (LMI) of tropical cyclones (TCs) over the Western North Pacific (WNP) was investigated by ensemble machine learning methods and composite analysis in this study. By selecting key features of TCs’ vortex attributes and environmental conditions, a two-step AdaBoost model demonstrated accuracy of about 75% in distinguishing weak and strong TCs at genesis and a coefficient of determination (R2) of 0.30 for LMI estimation from the early stage of strong TCs, suggesting an underlying relationship between LMI and early-stage features. The composite analysis reveals that TCs with higher LMI are characterized by lower latitude embedded in a continuous band of high low-troposphere vorticity, more compact circulation at both the upper and lower levels of the troposphere, stronger circulation at the mid-troposphere, a higher outflow layer with stronger convection, a more symmetrical structure of high-level moisture distribution, a slower translation speed, and a greater intensification rate around genesis. Specifically, TCs with greater “tightness” at genesis may have a better chance of strengthening to major TCs (LMI ≥ 96 kt), since it represents a combination of the inner and outer-core wind structure related to TCs’ rapid intensification and eyewall replacement cycle.
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Ohtake, Hideaki, Fumichika Uno, Takashi Oozeki, Yoshinori Yamada, Hideaki Takenaka, and Takashi Nakajima. "Outlier Events of Solar Forecasts for Regional Power Grid in Japan Using JMA Mesoscale Model." Energies 11, no. 10 (2018): 2714. http://dx.doi.org/10.3390/en11102714.
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To realize the safety control of electric power systems under high penetration of photovoltaic power systems, accurate global horizontal irradiance (GHI) forecasts using numerical weather prediction models (NWP) are becoming increasingly important. The objective of this study is to understand meteorological characteristics pertaining to large errors (i.e., outlier events) of GHI day-ahead forecasts obtained from the Japan Meteorological Agency, for nine electric power areas during four years from 2014 to 2017. Under outlier events in GHI day-ahead forecasts, several sea-level pressure (SLP) patterns were found in 80 events during the four years; (a) a western edge of anticyclone over the Pacific Ocean (frequency per 80 outlier events; 48.8%), (b) stationary fronts (20.0%), (c) a synoptic-scale cyclone (18.8%), and (d) typhoons (tropical cyclones) (8.8%) around the Japanese islands. In this study, the four case studies of the worst outlier events were performed. A remarkable SLP pattern was the case of the western edge of anticyclone over the Pacific Ocean around Japan. The comparison between regionally integrated GHI day-ahead forecast errors and cloudiness forecasts suggests that the issue of accuracy of cloud forecasts in high- and mid-levels troposphere in NWPs will remain in the future.
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Liu, Xiaobo, Hai Chu, Jun Sun, Wei Zhao, and Qingtao Meng. "A Numerical Simulation of the Development Process of a Mesoscale Convection Complex Causing Severe Rainstorm in the Yangtze River Delta Region behind a Northward Moving Typhoon." Atmosphere 13, no. 3 (2022): 473. http://dx.doi.org/10.3390/atmos13030473.
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In recent years, due to the influence of global warming, extreme weather events occur frequently, such as the continuous heavy precipitation, regional high temperature, super typhoon, etc. Tropical cyclones make frequent landfall, heavy rains and flood disasters caused by landfall typhoons have a huge impact, and typhoon rainstorms are often closely related to mesoscale and small-scale system activities. The application 2020 NCEP (National Centers for Environmental Prediction) final operational global analysis data and WRF (Weather Research and Forecasting model, version 3.9) mesoscale numerical prediction model successfully simulates the evolution characteristics of the mesoscale convective complex (MCC) that caused an extreme rainstorm in the Yangtze River delta region behind a northwards typhoon in this article. The results show that a meso-β-scale vortex existed in the mid- to upper troposphere in the region where the MCC occurred; accompanied by the occurrence of the meso-β-scale vortex, the convective cloud clusters developed violently, and its shape is a typical vortex structure. The simulation-sensitive experiment shows that the development of the meso-β-scale cyclonic vortex is the main reason for the enhancement of MCC. The occurrence and development of the MCC is manifested as a vertical positive vorticity column and a strong vertical ascending motion region in the dynamic field. In the development and maturity stage of the MCC, the vorticity and vertical rising velocity in the MCC area are significantly greater than those in the weakened typhoon circulation, which shows significant mesoscale convective system characteristics. The diagnostic analysis of the vorticity equation shows that the positive vorticity advection caused by the meso-β-scale cyclonic vortex in the mid- to upper troposphere plays important roles in the development of the MCC. Enhanced low-level convergence enhances vertical ascending motion. The convective latent heat release also plays an important role on the development of the MCC, changes the atmospheric instability by heating, enhances the upward movement, and delivers positive vorticity to the upper level, making the convection develop higher, forming a positive feedback mechanism between low-level convergence and high-level divergence. The simulation-sensitive experiment also shows that the meso-β-scale cyclonic vortex formation in this process is related to convective latent heat release.
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Lim, Young-Kwon, Siegfried D. Schubert, Oreste Reale, Myong-In Lee, Andrea M. Molod, and Max J. Suarez. "Sensitivity of Tropical Cyclones to Parameterized Convection in the NASA GEOS-5 Model." Journal of Climate 28, no. 2 (2015): 551–73. http://dx.doi.org/10.1175/jcli-d-14-00104.1.
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Abstract The sensitivity of tropical cyclones (TCs) to changes in parameterized convection is investigated to improve the simulation of TCs in the North Atlantic. Specifically, the impact of reducing the influence of the Relaxed Arakawa–Schubert (RAS) scheme-based parameterized convection is explored using the Goddard Earth Observing System version 5 (GEOS-5) model at 0.25° horizontal grid spacing. The years 2005 and 2006, characterized by very active and inactive hurricane seasons, respectively, are selected for simulation. A reduction in parameterized deep convection results in an increase in TC activity (e.g., TC number and longer life cycle) to more realistic levels compared to the baseline control configuration. The vertical and horizontal structure of the strongest simulated hurricane shows the maximum wind speed greater than 60 m s−1 and the minimum sea level pressure reaching ~940 mb, which are never achieved by the control configuration. The radius of the maximum wind of ~50 km, the location of the warm core exceeding 10°C, and the horizontal compactness of the hurricane center are all quite realistic without any negatively affecting the atmospheric mean state. This study reveals that an increase in the threshold of minimum entrainment suppresses parameterized deep convection by entraining more dry air into the typical plume. This leads to cooling and drying at the mid to upper troposphere, along with the positive latent heat flux and moistening in the lower troposphere. The resulting increase in conditional instability provides an environment that is more conducive to TC vortex development and upward moisture flux convergence by dynamically resolved moist convection, thereby increasing TC activity.
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Yamasaki, Masanori. "A Study on the Effects of the Ice Microphysics on Tropical Cyclones." Advances in Meteorology 2013 (2013): 1–13. http://dx.doi.org/10.1155/2013/573786.
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The effects of the ice microphysical processes on the development of weak vortices and tropical cyclones (TCs) are examined by numerical experiments with a nonhydrostatic model. Since it has been understood that the ice phase generally enhances the eyewall circulation in strong TCs because of additional heat release and insignificant effect of rainwater evaporation, this study focuses on the development of relatively weak vortices and TCs. Some past studies showed that the development is slower by the effects of the ice phase through cooling due to the melting of snow and graupel, whereas this study indicates that cooling due to evaporation of rainwater in the subcloud layer plays a much more important role in the slower development, and much more solid substances in the mid-troposphere, which are produced through the ice phase processes, contribute to more rainwater evaporation in the subcloud layer. The relative importance of many processes of the ice microphysics is also examined as a basis for future improvements of parameterization of the microphysical processes.
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Knowland, K. E., R. M. Doherty, and K. I. Hodges. "The effects of springtime mid-latitude storms on trace gas composition determined from the MACC reanalysis." Atmospheric Chemistry and Physics Discussions 14, no. 19 (2014): 27093–141. http://dx.doi.org/10.5194/acpd-14-27093-2014.
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Abstract. The relationship between springtime air pollution transport of ozone (O3) and carbon monoxide (CO) and mid-latitude cyclones is explored for the first time using the Monitoring Atmospheric Composition and Climate (MACC) reanalysis for the period 2003–2012. In this study, the most intense spring storms (95th percentile) are selected for two regions, the North Pacific (NP) and the North Atlantic (NA). These storms (~60 storms over each region) often track over the major emission sources of East Asia and eastern North America. By compositing the storms, the distributions of O3 and CO within a "typical" intense storm are examined. We compare the storm-centered composite to background composites of "average conditions" created by sampling the reanalysis data of the previous year to the storm locations. Mid-latitude storms are found to redistribute concentrations of O3 and CO horizontally and vertically throughout the storm. This is clearly shown to occur through two main mechanisms: (1) vertical lifting of CO-rich and O3-poor air isentropically from near the surface to the mid- to upper-troposphere in the region of the warm conveyor belt; and (2) descent of O3-rich and CO-poor air isentropically in the vicinity of the dry intrusion, from the stratosphere toward the mid-troposphere. This can be seen in the composite storm's life cycle as the storm intensifies, with area-averaged O3 (CO) increasing (decreasing) between 200 and 500 hPa. At the time of maximum intensity, area-averaged O3 around the storm center at 300 hPa is enhanced by 50 and 36% for the NP and NA regions respectively, compared to the background, and by 11 and 7.6% at 500 hPa. In contrast, area-averaged CO at 300 hPa decreases by 12% for NP and 5.5% for NA, and at 500 hPa area-averaged CO decreases by 2.4% for NP while there is little change over the NA region at 500 hPa. From the mid-troposphere, O3-rich air is clearly seen to be transported toward the surface but the downward transport of CO-poor air is not discernible due to the high levels of CO in the lower troposphere. Area-averaged O3 is slightly higher at 1000 hPa (3.5 and 1.8%, for the NP and NA regions, respectively). There is an increase of CO at 1000 hPa for the NP region (3.3%) relative to the background composite and a slight decrease in area-averaged CO for the NA region at 1000 hPa (−2.7%).
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Knowland, K. E., R. M. Doherty, and K. I. Hodges. "The effects of springtime mid-latitude storms on trace gas composition determined from the MACC reanalysis." Atmospheric Chemistry and Physics 15, no. 6 (2015): 3605–28. http://dx.doi.org/10.5194/acp-15-3605-2015.
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Abstract. The relationship between springtime air pollution transport of ozone (O3) and carbon monoxide (CO) and mid-latitude cyclones is explored for the first time using the Monitoring Atmospheric Composition and Climate (MACC) reanalysis for the period 2003–2012. In this study, the most intense spring storms (95th percentile) are selected for two regions, the North Pacific (NP) and the North Atlantic (NA). These storms (∼60 storms over each region) often track over the major emission sources of East Asia and eastern North America. By compositing the storms, the distributions of O3 and CO within a "typical" intense storm are examined. We compare the storm-centered composite to background composites of "average conditions" created by sampling the reanalysis data of the previous year to the storm locations. Mid-latitude storms are found to redistribute concentrations of O3 and CO horizontally and vertically throughout the storm. This is clearly shown to occur through two main mechanisms: (1) vertical lifting of CO-rich and O3-poor air isentropically, from near the surface to the mid- to upper-troposphere in the region of the warm conveyor belt; and (2) descent of O3-rich and CO-poor air isentropically in the vicinity of the dry intrusion, from the stratosphere toward the mid-troposphere. This can be seen in the composite storm's life cycle as the storm intensifies, with area-averaged O3 (CO) increasing (decreasing) between 200 and 500 hPa. The influence of the storm dynamics compared to the background environment on the composition within an area around the storm center at the time of maximum intensity is as follows. Area-averaged O3 at 300 hPa is enhanced by 50 and 36% and by 11 and 7.6% at 500 hPa for the NP and NA regions, respectively. In contrast, area-averaged CO at 300 hPa decreases by 12% for NP and 5.5% for NA, and area-averaged CO at 500 hPa decreases by 2.4% for NP while there is little change over the NA region. From the mid-troposphere, O3-rich air is clearly seen to be transported toward the surface, but the downward transport of CO-poor air is not discernible due to the high levels of CO in the lower troposphere. Area-averaged O3 is slightly higher at 1000 hPa (3.5 and 1.8% for the NP and NA regions, respectively). There is an increase of CO at 1000 hPa for the NP region (3.3%) relative to the background composite and a~slight decrease in area-averaged CO for the NA region at 1000 hPa (-2.7%).
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Wang, Danyang, and Yanluan Lin. "Size and Structure of Dry and Moist Reversible Tropical Cyclones." Journal of the Atmospheric Sciences 77, no. 6 (2020): 2091–114. http://dx.doi.org/10.1175/jas-d-19-0229.1.
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Abstract The size and structure of tropical cyclones (TCs) are investigated using idealized numerical simulations. Three simulations are conducted: a pure dry TC (DRY), a moist reversible TC (REV) with fallout of hydrometeors in the atmosphere disallowed, and a typical TC (CTL). It was found that the width of the eyewall ascent region and the radius of maximum wind rm are much larger in DRY and REV than those in CTL. This is closely related to the deep inflow layer (~4 km) in DRY and REV associated with a different entropy restoration mechanism under the subsidence region. With the wide ascents, the close link between rm and the outer radius in DRY and REV can be well predicted by the Emanuel and Rotunno (ER11) model. The magnitude of subsidence, mainly controlled by the vertical gradient of entropy in the mid- and upper troposphere, is nearly one order greater in DRY and REV than that in CTL. This study demonstrates that the falling nature of hydrometeors poses a strong constraint on the size and structure of real world TCs via the entropy distribution in the subsidence region. The wide ascent, self-stratification in the outflow, and decently reproduced wind profile in DRY and REV suggest that DRY and REV behave like a prototype of the ER11 model with CTL being an extreme type.
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Grams, C. M., H. Binder, S. Pfahl, N. Piaget, and H. Wernli. "Atmospheric processes triggering the central European floods in June 2013." Natural Hazards and Earth System Sciences 14, no. 7 (2014): 1691–702. http://dx.doi.org/10.5194/nhess-14-1691-2014.
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Abstract. In June 2013, central Europe was hit by a century flood affecting the Danube and Elbe catchments after a 4 day period of heavy precipitation and causing severe human and economic loss. In this study model analysis and observational data are investigated to reveal the key atmospheric processes that caused the heavy precipitation event. The period preceding the flood was characterised by a weather regime associated with cool and unusual wet conditions resulting from repeated Rossby wave breaking (RWB). During the event a single RWB established a reversed baroclinicity in the low to mid-troposphere in central Europe with cool air trapped over the Alps and warmer air to the north. The upper-level cut-off resulting from the RWB instigated three consecutive cyclones in eastern Europe that unusually tracked westward during the days of heavy precipitation. Continuous large-scale slantwise ascent in so-called "equatorward ascending" warm conveyor belts (WCBs) associated with these cyclones is found as the key process that caused the 4 day heavy precipitation period. Fed by moisture sources from continental evapotranspiration, these WCBs unusually ascended equatorward along the southward sloping moist isentropes. Although "equatorward ascending" WCBs are climatologically rare events, they have great potential for causing high impact weather.
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Grams, C. M., H. Binder, S. Pfahl, N. Piaget, and H. Wernli. "Atmospheric processes triggering the Central European floods in June 2013." Natural Hazards and Earth System Sciences Discussions 2, no. 1 (2014): 427–58. http://dx.doi.org/10.5194/nhessd-2-427-2014.
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Abstract. In June 2013 Central Europe was hit by a century flood affecting the Danube and Elbe catchments after a 4 day period of heavy precipitation and causing severe human and economic loss. In this study model analysis and observational data are investigated to reveal the key atmospheric processes that caused the heavy precipitation event. The period preceeding the flood was characterised by a weather regime associated with cool and unusual wet conditions resulting from repeated Rossby wave breaking (RWB). During the event a single RWB established a reversed baroclinicity in the low to mid troposphere in Central Europe with cool air trapped over the Alps and warmer air to the North. The upper-level cut-off resulting from the RWB instigated three consecutive cyclones in eastern Europe that unusually tracked westward during the days of heavy precipitation. Continuous large-scale slantwise ascent in so-called "upside down" warm conveyor belts (WCBs) associated with these cyclones is found as the key process that caused the 4 day heavy precipitation period. Fed by moisture sources from continental evapotranspiration, these WCBs unusually ascended equatorward along the southward sloping moist isentropes. Although "upside down" WCBs are climatologically rare events, they have great potential for causing high impact weather.
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Yamashita, Yousuke, Masayuki Takigawa, Kentaro Ishijima, et al. "Resolution Dependency of Numerically Simulated Stratosphere-to-Troposphere Transport Associated with Mid-Latitude Closed Cyclones in Early Spring around Japan." SOLA 13 (2017): 186–91. http://dx.doi.org/10.2151/sola.2017-034.
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Zien, A. W., A. Richter, A. Hilboll, A. M. Blechschmidt, and J. P. Burrows. "Systematic analysis of tropospheric NO<sub>2</sub> long-range transport events detected in GOME-2 satellite data." Atmospheric Chemistry and Physics Discussions 13, no. 11 (2013): 30945–1012. http://dx.doi.org/10.5194/acpd-13-30945-2013.
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Abstract. Intercontinental long-range transport (LRT) events of NO2 relocate the effects of air pollution from emission regions to remote, pristine regions. We detect transported plumes in tropospheric NO2 columns measured by the GOME-2/MetOp-A instrument with a specialized algorithm and trace the plumes to their sources using the HYSPLIT lagrangian transport model. With this algorithm we find 3808 LRT events over the ocean for the period 2007 to 2011. LRT events occur frequently in the mid-latitudes, emerging usually from coastal high-emission regions. In the free troposphere, plumes of NO2 can travel for several days to the polar oceanic atmosphere or to other continents. They travel along characteristic routes and originate from both continuous anthropogenic emission and emission events such as bush fires. Most NO2 LRT events occur during autumn and winter months, when meteorological conditions and emissions are most favorable. The evaluation of meteorological data shows that the observed NO2 LRT is often linked to cyclones passing over an emission region.
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Zien, A. W., A. Richter, A. Hilboll, A. M. Blechschmidt, and J. P. Burrows. "Systematic analysis of tropospheric NO<sub>2</sub> long-range transport events detected in GOME-2 satellite data." Atmospheric Chemistry and Physics 14, no. 14 (2014): 7367–96. http://dx.doi.org/10.5194/acp-14-7367-2014.
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Abstract. Intercontinental long-range transport (LRT) events of NO2 relocate the effects of air pollution from emission regions to remote, pristine regions. We detect transported plumes in tropospheric NO2 columns measured by the GOME-2/MetOp-A instrument with a specialized algorithm and trace the plumes to their sources using the HYSPLIT Lagrangian transport model. With this algorithm we find 3808 LRT events over the ocean for the period 2007 to 2011. LRT events occur frequently in the mid-latitudes, emerging usually from coastal high-emission regions. In the free troposphere, plumes of NO2 can travel for several days to the polar oceanic atmosphere or to other continents. They travel along characteristic routes and originate from both continuous anthropogenic emission and emission events such as bush fires. Most NO2 LRT events occur during autumn and winter months, when meteorological conditions and emissions are most favorable. The evaluation of meteorological data shows that the observed NO2 LRT is often linked to cyclones passing over an emission region.
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Ryoo, J. M., D. E. Waliser, and E. J. Fetzer. "Trajectory analysis on the origin of air mass and moisture associated with Atmospheric Rivers over the west coast of the United States." Atmospheric Chemistry and Physics Discussions 11, no. 4 (2011): 11109–42. http://dx.doi.org/10.5194/acpd-11-11109-2011.
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Abstract. The origins and pathways of air masses leading to heavy rainfall over the west coast of the United States are examined by computing the back-trajectories in a Lagrangian quasi-isentropic trajectory model. Extreme precipitation over the west coast of the United States often coincides with transport in a deep and narrow corridor of concentrated water vapor band from the ocean, commonly referred to as Atmospheric Rivers (ARs). They also occur in conjunction with moisture plumes emanating from the tropics, or along the mid-latitude storm track. However, the actual moisture sources and the dynamic and thermodynamic processes of the moisture transport, are still unclear. Trajectories are found to be insensitive to the reanalysis data set used; we examined NCEP, GMAO MERRA, and ECMWF ERA-Interim. Reconstructed water vapor mixing ratios along trajectories are in generally good agreement among the reanalysis datasets in most of the subtropics and extratropics, indicating that the large-scale circulation is a primary control for moisture transport over those regions. Clustering and pdf (probability density function) analyses illustrate that trajectories over the west coast of United States have different origins. One group of trajectories (cluster 1) originates in the warm part of extratropical cyclones in the low level. The other group of trajectories (cluster 2) originates in the cold and dry regions in the mid-level (pressures less than 600 hPa) over northeastern Asia, then cross the Pacific Ocean. This study demonstrates that the quasi-isentropic Lagrangian trajectory model and clustering analysis (that have been typically used to analyze trajectories in the upper troposphere and higher altitudes) can be used to examine sources of air masses and moisture, and also associated transport processes in the lower troposphere.
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Hegarty, J., H. Mao, and R. Talbot. "Winter- and summertime continental influences on tropospheric O<sub>3</sub> and CO observed by TES over the western North Atlantic Ocean." Atmospheric Chemistry and Physics 10, no. 8 (2010): 3723–41. http://dx.doi.org/10.5194/acp-10-3723-2010.
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Abstract. The distributions of tropospheric ozone (O3) and carbon monoxide (CO), and the synoptic factors regulating these distributions over the western North Atlantic Ocean during winter and summer were investigated using profile retrievals from the Tropospheric Emission Spectrometer (TES) for 2004–2006. Seasonal composites of TES retrievals, reprocessed to remove the influence of the a priori on geographical and seasonal structure, exhibited strong seasonal differences. At the 681 hPa level during winter months of December, January and February (DJF) the composite O3 mixing ratios were uniformly low (~45 ppbv), but continental export was evident in a channel of enhanced CO (100–110 ppbv) flowing eastward from the US coast. In summer months June, July, and August (JJA) O3 mixing ratios were variable (45–65 ppbv) and generally higher due to increased photochemical production. The summer distribution also featured a channel of enhanced CO (95–105 ppbv) flowing northeastward around an anticyclone and exiting the continent over the Canadian Maritimes around 50° N. Offshore O3-CO slopes were generally 0.15–0.20 mol mol−1 in JJA, indicative of photochemical O3 production. Composites for 4 predominant synoptic patterns or map types in DJF suggested that export to the lower free troposphere (681 hPa level) was enhanced by the warm conveyor belt airstream of mid-latitude cyclones while stratospheric intrusions increased TES O3 levels at 316 hPa. A major finding in the DJF data was that offshore 681 hPa CO mixing ratios behind cold fronts could be enhanced up to >150 ppbv likely by lofting from the surface via shallow convection resulting from rapid destabilization of cold air flowing over much warmer ocean waters. In JJA composites for 3 map types showed that the general export pattern of the seasonal composites was associated with a synoptic pattern featuring the Bermuda High. However, weak cyclones and frontal troughs could enhance offshore 681 hPa CO mixing ratios to >110 ppbv with O3-CO slopes >0.50 mol mol−1 south of 45° N. Intense cyclones, which were not as common in the summer, enhanced export by lofting of boundary layer pollutants from over the US and also provided a possible mechanism for transporting pollutants from boreal fire outflow southward to the US east coast. Overall, for winter and summer the TES retrievals showed substantial evidence of air pollution export to the western North Atlantic Ocean with the most distinct differences in distribution patterns related to strong influences of mid-latitude cyclones in winter and the Bermuda High anticyclone in summer.
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Korty, Robert L., Suzana J. Camargo, and Joseph Galewsky. "Variations in Tropical Cyclone Genesis Factors in Simulations of the Holocene Epoch." Journal of Climate 25, no. 23 (2012): 8196–211. http://dx.doi.org/10.1175/jcli-d-12-00033.1.
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Abstract The thermodynamic factors related to tropical cyclone genesis are examined in several simulations of the middle part of the Holocene epoch when the precession of Earth’s orbit altered the seasonal distribution of solar radiation and in one transient simulation of the millennium preceding the industrial era. The thermodynamic properties most crucial for genesis display a broad stability across both periods, although both orbital variations during the mid-Holocene (MH) 6000 years ago (6ka) and volcanic eruptions in the transient simulation have detectable effects. It is shown that the distribution of top-of-the-atmosphere radiation 6ka altered the Northern Hemisphere seasonal cycle of the potential intensity of tropical cyclones in addition to slightly increasing the difference between middle tropospheric and boundary layer entropy, a parameter that has been related to the incubation period required for genesis. The Southern Hemisphere, which receives more solar radiation during its storm season today than it did 6ka, displays slightly more favorable thermodynamic properties during the MH than in the preindustrial era control. Surface temperatures over the ocean in both hemispheres respond to radiation anomalies more slowly than those in upper levels, altering the thermal stability. Volcanism produces a sharp but transient temperature response in the last-millennium simulation that strongly reduces potential intensity during the seasons immediately following a major eruption. Here, too, the differential vertical temperature response is key: temperatures in the lower and middle troposphere cool, while those near the tropopause rise. Aside from these deviations, there is no substantial variation in thermodynamic properties over the 1000-yr simulation.
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Milrad, Shawn M., Eyad H. Atallah, John R. Gyakum, Rachael N. Isphording, and Jonathon Klepatzki. "The Extreme Precipitation Index (EPI): A Coupled Dynamic–Thermodynamic Metric to Diagnose Midlatitude Floods Associated with Flow Reversal." Weather and Forecasting 34, no. 5 (2019): 1257–76. http://dx.doi.org/10.1175/waf-d-18-0156.1.
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Abstract The extreme precipitation index (EPI) is a coupled dynamic–thermodynamic metric that can diagnose extreme precipitation events associated with flow reversal in the mid- to upper troposphere (e.g., Rex and omega blocks, cutoff cyclones, Rossby wave breaks). Recent billion dollar (U.S. dollars) floods across the Northern Hemisphere midlatitudes were associated with flow reversal, as long-duration ascent (dynamics) occurred in the presence of anomalously warm and moist air (thermodynamics). The EPI can detect this potent combination of ingredients and offers advantages over model precipitation forecasts because it relies on mass fields instead of parameterizations. The EPI’s dynamics component incorporates modified versions of two accepted blocking criteria, designed to detect flow reversal during the relatively short duration of extreme precipitation events. The thermodynamic component utilizes standardized anomalies of equivalent potential temperature. Proof-of-concept is demonstrated using four high-impact floods: the 2013 Alberta Flood, Canada’s second costliest natural disaster on record; the 2016 western Europe Flood, which caused the worst flooding in France in a century; the 2000 southern Alpine event responsible for major flooding in Switzerland; and the catastrophic August 2016 Louisiana Flood. EPI frequency maxima are located across the North Atlantic and North Pacific mid- and high latitudes, including near the climatological subtropical jet stream, while secondary maxima are located near the Rockies and Alps. EPI accuracy is briefly assessed using pattern correlation and qualitative associations with an extreme precipitation event climatology. Results show that the EPI may provide potential benefits to flood forecasters, particularly in the 3–10-day range.
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Luan, Y., and L. Jaeglé. "Composite study of aerosol export events from East Asia and North America." Atmospheric Chemistry and Physics Discussions 12, no. 8 (2012): 21977–2022. http://dx.doi.org/10.5194/acpd-12-21977-2012.
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Abstract. We use satellite observations of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectrometer (MODIS) together with the GEOS-Chem global chemical transport model to contrast export of aerosols from East Asia and North America during 2004–2010. The GEOS-Chem model reproduces the spatial distribution and temporal variations of Asian aerosol outflow generally well, although a low bias (−30%) is found in the model fine mode AOD. We use the model to identify 244 aerosol pollution export events from E. Asia and 251 export events from N. America over our 7-yr study period. When these events are composited by season, we find that the AOD in the outflow is enhanced by 50–100% relative to seasonal mean values. The composite Asian plume splits into one branch going poleward towards the Arctic, with the other crossing the Pacific in 6–8 days. A fraction of the aerosols is trapped in the subtropical Pacific High. The N. American plume travels to the northeast Atlantic, reaching Europe after 4–5 days. Part of the composite plume turns anticyclonically in the Azores High, where it slowly decays. Both the Asian and N. American export events are favored by a dipole structure in sea-level pressure anomalies, associated with mid-latitude cyclone activity over the respective source regions. The observed AOD in the E. Asian outflow exhibits stronger seasonality, with a spring maximum, than the N. American outflow, with a weak summer maximum. The large spring AOD in the Asian outflow is the result of enhanced sulfate and dust aerosol concentrations, but is also due to a larger export efficiency of sulfate and SO2 from the Asian boundary layer relative to the N. American boundary layer. While the N. American sulfate outflow is mostly found in the lower troposphere (1–3 km altitude), the Asian sulfate outflow occurs at higher altitudes (2–6 km). In the Asian outflow 42–59% of the sulfate column is present above 2 km altitude, with only 24–35% in the N. American outflow. We link this to the factor of 2–5 lower precipitation in the warm conveyor belts (WCB) of midlatitude cyclones over E. Asia compared to N. America. This relative lack of precipitation makes Asian WCB very efficient for injecting aerosols in the middle troposphere.
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Joos, Hanna, Michael Sprenger, Hanin Binder, Urs Beyerle, and Heini Wernli. "Warm conveyor belts in present-day and future climate simulations – Part 1: Climatology and impacts." Weather and Climate Dynamics 4, no. 1 (2023): 133–55. http://dx.doi.org/10.5194/wcd-4-133-2023.
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Abstract. This study investigates how warm conveyor belts (WCBs) will change in a future climate. WCBs are strongly ascending airstreams in extratropical cyclones that are responsible for most of their precipitation. In conjunction with the cloud formation, latent heat is released, which has an impact on the potential vorticity distribution and therefore on the atmospheric circulation in the middle and upper troposphere. Because of these and other impacts of WCBs, it is of great importance to investigate changes in their frequencies, regions of occurrence, and physical characteristics in a warmer climate. To this aim, future climate simulations (Representative Concentration Pathway 8.5 – RCP8.5 – scenario; 2091–2100) are performed with the Community Earth System Model version 1 (CESM1) and compared to present-day climate (1991–1999). Trajectories are calculated based on 6-hourly 3D wind fields, and WCBs are identified as trajectories that ascend at least 600 hPa in 2 d. WCBs are represented reasonably well in terms of location and occurrence frequency compared to WCBs in the ERA-Interim reanalyses. In a future climate, WCB inflow regions in the North Pacific are systematically shifted northward in winter, which is in agreement with the northward shift of the storm track in this region. In the North Atlantic, increased frequencies are discernible in the southwest and there is a decrease to the south of Iceland. Finally, in the Southern Hemisphere, WCB frequencies increase in the South Atlantic in both seasons and to the east of South Africa and the Indian Ocean in June–July–August (JJA). These changes are partly consistent with corresponding changes in the occurrence frequencies of extratropical cyclones, i.e. the driving weather systems of WCBs. Changes are also found in the WCB characteristics, which have implications for WCB impacts in a future climate. The increase in inflow moisture in the different regions and seasons – ∼23 %–33 % (∼14 %–20 %) in winter (summer) – leads to (i) an increase in WCB-related precipitation – ∼13 %–23 % (∼7 %–28 %) in winter (summer) – especially in the upper percentiles and thus a possible increase in extreme precipitation related to WCBs, (ii) a strong increase in diabatic heating – ∼20 %–27 % (∼17 %–33 %) in winter (summer) – in the mid-troposphere, and (iii) a higher outflow level – ∼10 K (∼10–16 K) in winter (summer) – which favours WCBs more strongly interacting with the upper-level Rossby waveguide. In summary, by investigating a distinct weather system, the WCB, and how it changes in its occurrence frequency and characteristics in a future climate, this study provides new insights into the dynamics and impacts of climate change in the extratropical storm track regions.
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Papritz, Lukas, David Hauswirth, and Katharina Hartmuth. "Moisture origin, transport pathways, and driving processes of intense wintertime moisture transport into the Arctic." Weather and Climate Dynamics 3, no. 1 (2022): 1–20. http://dx.doi.org/10.5194/wcd-3-1-2022.
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Abstract. A substantial portion of the moisture transport into the Arctic occurs in episodic, high-amplitude events with strong impacts on the Arctic's climate system components such as sea ice. This study focuses on the origin of such moist-air intrusions during winter and examines the moisture sources, moisture transport pathways, and their linkage to the driving large-scale circulation patterns. For that purpose, 597 moist-air intrusions, defined as daily events of intense (exceeding the 90th anomaly percentile) zonal mean moisture transport into the polar cap (≥70∘ N), are identified. Kinematic backward trajectories combined with a Lagrangian moisture source diagnostic are then used to pinpoint the moisture sources and characterize the airstreams accomplishing the transport. The moisture source analyses show that the bulk of the moisture transported into the polar cap during these moist-air intrusions originates in the eastern North Atlantic with an uptake maximum poleward of 50∘ N. Trajectories further reveal an inverse relationship between moisture uptake latitude and the level at which moisture is injected into the polar cap, consistent with ascent of poleward-flowing air in a baroclinic atmosphere. Focusing on intrusions in the North Atlantic (424 intrusions), we find that lower tropospheric moisture transport is predominantly accomplished by two types of airstreams: (i) cold, polar air warmed and moistened by surface fluxes and (ii) air subsiding from the mid-troposphere into the boundary layer. Both airstreams contribute about 36 % each to the total transport. The former accounts for most of the moisture transport during intrusions associated with an anomalously high frequency of cyclones east of Greenland (218 intrusions), whereas the latter is more important in the presence of atmospheric blocking over Scandinavia and the Ural Mountains (145 events). Long-range moisture transport, accounting for 17 % of the total transport, dominates during intrusions with weak forcing by baroclinic weather systems (64 intrusions). Finally, mid-tropospheric moisture transport is invariably associated with (diabatically) ascending air and moisture origin in the central and western North Atlantic, including the Gulf Stream front, accounting for roughly 10 % of the total transport. In summary, our study shows that moist-air intrusions into the polar atmosphere result from a combination of airstreams with predominantly high-latitude or high-altitude origin, whose relative importance is determined by the underlying driving weather systems (i.e., cyclones and blocks).
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Deng, Kaiqiang, Song Yang, Mingfang Ting, Chundi Hu, and Mengmeng Lu. "Variations of the Mid-Pacific Trough and Their Relations to the Asian–Pacific–North American Climate: Roles of Tropical Sea Surface Temperature and Arctic Sea Ice." Journal of Climate 31, no. 6 (2018): 2233–52. http://dx.doi.org/10.1175/jcli-d-17-0064.1.
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The mid-Pacific trough (MPT), occurring in the upper troposphere during boreal summer, acts as an atmospheric bridge connecting the climate variations over Asia, the Pacific, and North America. The first (second) mode of empirical orthogonal function analysis of the MPT, which accounts for 20.3% (13.4%) of the total variance, reflects a change in its intensity on the southwestern (northeastern) portion of the trough. Both modes are significantly correlated with the variability of tropical Pacific sea surface temperature (SST). Moreover, the first mode is affected by Atlantic SST via planetary waves that originate from the North Atlantic and propagate eastward across the Eurasian continent, and the second mode is influenced by the Arctic sea ice near the Bering Strait by triggering an equatorward wave train over the northeast Pacific. A stronger MPT shown in the first mode is significantly linked to drier and warmer conditions in the Yangtze River basin, southern Japan, and the northern United States and wetter conditions in South Asia and northern China, while a stronger MPT shown in the second mode is associated with a drier and warmer southwestern United States. In addition, an intensified MPT (no matter whether in the southwestern or the northeastern portion) corresponds to more tropical cyclones (TCs) over the western North Pacific (WNP) and fewer TCs over the eastern Pacific (EP) in summer, which is associated with the MPT-induced ascending and descending motions over the WNP and the EP, respectively.
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Luan, Y., and L. Jaeglé. "Composite study of aerosol export events from East Asia and North America." Atmospheric Chemistry and Physics 13, no. 3 (2013): 1221–42. http://dx.doi.org/10.5194/acp-13-1221-2013.
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Abstract. We use satellite observations of aerosol optical depth (AOD) from the Moderate Resolution Imaging Spectrometer (MODIS) together with the GEOS-Chem global chemical transport model to contrast export of aerosols from East Asia and North America during 2004–2010. The GEOS-Chem model reproduces the spatial distribution and temporal variations of Asian aerosol outflow generally well, although a low bias (−30%) is found in the model fine mode AOD, particularly during summer. We use the model to identify 244 aerosol pollution export events from E. Asia and 251 export events from N. America over our 7-year study period. When these events are composited by season, we find that the AOD in the outflow is enhanced by 50–100% relative to seasonal mean values. The composite Asian plume splits into one branch going poleward to the Arctic in 3–4 days, with the other crossing the Pacific Ocean in 6–8 days. A fraction of the aerosols is trapped in the subtropical Pacific High during spring and summer. The N. American plume travels to the northeast Atlantic, reaching Europe after 4–5 days. Part of the composite plume turns anticyclonically in the Azores High, where it slowly decays. Both the Asian and N. American export events are favored by a dipole structure in sea-level pressure anomalies, associated with mid-latitude cyclone activity over the respective source regions. This dipole structure during outflow events is a strong feature for all seasons except summer, when convection becomes more important. The observed AOD in the E. Asian outflow exhibits stronger seasonality, with a spring maximum, than the N. American outflow, with a broad spring/summer maximum. The large spring AOD in the Asian outflow is the result of enhanced sulfate and dust aerosol concentrations, but is also due to a larger export efficiency of sulfate and SO2 from the Asian boundary layer relative to the N. American boundary layer. While the N. American sulfate outflow is mostly found in the lower troposphere (1–3 km altitude), the Asian sulfate outflow occurs at higher altitudes (2–6 km). In the Asian outflow 42–59% of the sulfate column is present above 2 km altitude, with only 24–35% in the N. American outflow. We link this to the factor of 2–5 lower precipitation in the warm conveyor belts (WCB) of midlatitude cyclones over E. Asia compared to N. America. This relative lack of precipitation makes Asian WCB very efficient for injecting aerosols in the middle troposphere.
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SURESH, R., S. K. KUNDU, A. K. BHATNAGAR, and R. C. BHATIA. "On forecasting tracks of tropical disturbances using ATOVS data over Bay of Bengal." MAUSAM 57, no. 4 (2021): 609–18. http://dx.doi.org/10.54302/mausam.v57i4.500.
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lkj &,d m".kdfVca/kh; vonkc ds thou pØ ds vkadMs+ rFkk nks m".kdfVca/kh; pØokrh rwQkuksa ds o"kZ 2002&03 dh vof/k ds vkadMs+ mPp Vh- vks- oh- ,l- ¼,- Vh- vks- oh- ,l-½ /kzqod{kh; mixzgksa ,u- vks- ,- , 15 rFkk 16] ftuesa mPp lw{e rjaxh; ifjKkiu bdkbZ ¼,- ,e- ,l- ;w½ yxh gqbZ gaS ls izkIr fd, x, gSa ftudk fo’ys"k.k bu rwQkuksa ds ekxZ dk iwokZuqeku djus ds fy, fd;k x;k gSA bu ekSle fo{kksHkksa ds 700&400 gsDVkikLdy ¼gs-ik-½ Lrj esa e/; {kksHkeaMyh; m".krk e/; Lrjh ckfgokZg ds dkj.k gksrh gS tks rwQku ds 200&700 fd-eh- vkxs rd foLrkfjr gksrh gS rFkk fo{kksHkksa dh xfr’khyrk dk djhc 6 ls 24 ?kaVs igys iwokZuqeku djus esa iwoZ ladsrd dk dk;Z djrh gSA ;g fo{kksHk yxHkx mlh v{k dks vuqxeu djrk gS tks e/; {kksHkeaMy esa foLrkfjr ¼vkxs c<s+ gq,½ ftg~okdkj m".k {ks= dks dsUnz ls tksM+rk gSA e/;e rhozrk okys nks HkweaMyh; pØokrksa dh fLFkfr esa tc 7º ls 13º lsfYl;l rkieku dk m"edksj Åijh {kksHkeaMyh; Lrj ¼250&200 gs-ik-½ ds djhc dsafnzr jgk ml le; vonkc dh fLFkfr esa fdlh fo’ks"k m".krk dk irk ugha pyk gSA
 Advanced TOVS (ATOVS), comprising the Advanced Microwave Sounding Unit (AMSU), data obtained from polar orbiting satellites NOAA 15 and 16 during the life cycle of a tropical depression and two tropical cyclonic storms during 2002-03 have been analysed to predict the track of these disturbances. The mid-tropospheric warming due to altostratus outflow from these weather disturbances in the layer 700 – 400 hPa which protrudes about 200 -700 km ahead the storm acts as a pre-cursor to predict the movement of the disturbances with a lead time of about 6 to 24 hours. The disturbance almost follows the axis connecting the centre with the warm tongue that protrudes ahead of the disturbance in the mid-troposphere. While warm core of 7 to 13° C is centered around the upper tropospheric level (250 – 200 hPa) in the case the two moderate intensity tropical cyclones, no significant warmness could be seen in the depression stage. 
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Soldatenko. "Estimated Impacts of Climate Change on Eddy Meridional Moisture Transport in the Atmosphere." Applied Sciences 9, no. 23 (2019): 4992. http://dx.doi.org/10.3390/app9234992.
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Research findings suggest that water (hydrological) cycle of the earth intensifies in response to climate change, since the amount of water that evaporates from the ocean and land to the atmosphere and the total water content in the air will increase with temperature. In addition, climate change affects the large-scale atmospheric circulation by, for example, altering the characteristics of extratropical transient eddies (cyclones), which play a dominant role in the meridional transport of heat, moisture, and momentum from tropical to polar latitudes. Thus, climate change also affects the planetary hydrological cycle by redistributing atmospheric moisture around the globe. Baroclinic instability, a specific type of dynamical instability of the zonal atmospheric flow, is the principal mechanism by which extratropical cyclones form and evolve. It is expected that, due to global warming, the two most fundamental dynamical quantities that control the development of baroclinic instability and the overall global atmospheric dynamics—the parameter of static stability and the meridional temperature gradient (MTG)—will undergo certain changes. As a result, climate change can affect the formation and evolution of transient extratropical eddies and, therefore, macro-exchange of heat and moisture between low and high latitudes and the global water cycle as a whole. In this paper, we explore the effect of changes in the static stability parameter and MTG caused by climate change on the annual-mean eddy meridional moisture flux (AMEMF), using the two classical atmospheric models: the mid-latitude f-plane model and the two-layer β-plane model. These models are represented in two versions: “dry,” which considers the static stability of dry air alone, and “moist,” in which effective static stability is considered as a combination of stability of dry and moist air together. Sensitivity functions were derived for these models that enable estimating the influence of infinitesimal perturbations in the parameter of static stability and MTG on the AMEMF and on large-scale eddy dynamics characterized by the growth rate of unstable baroclinic waves of various wavelengths. For the base climate change scenario, in which the surface temperature increases by 1 °C and warming of the upper troposphere outpaces warming of the lower troposphere by 2 °C (this scenario corresponds to the observed warming trend), the response of the mass-weighted vertically averaged annual mean MTG is -0.2 ℃ per 1000 km. The dry static stability increases insignificantly relative to the reference climate state, while on the other hand, the effective static stability decreases by more than 5.4%. Assuming that static stability of the atmosphere and the MTG are independent of each other (using One-factor-at-a-time approach), we estimate that the increase in AMEMF caused by change in MTG is about 4%. Change in dry static stability has little effect on AMEMF, while change in effective static stability leads to an increase in AMEMF of about 5%. Thus, neglecting atmospheric moisture in calculations of the atmospheric static stability leads to tangible differences between the results obtained using the dry and moist models. Moist models predict ~9% increase in AMEMF due to global warming. Dry models predict ~4% increase in AMEMF solely because of the change in MTG. For the base climate change scenario, the average temperature of the lower troposphere (up to ~4 km), in which the atmospheric moisture is concentrated, increases by ~1.5 ℃. This leads to an increase in specific humidity of about 10.5%. Thus, since both AMEMF and atmospheric water vapor content increase due to the influence of climate change, a rather noticeable restructuring of the global water cycle is expected.
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Riemer, M., and M. T. Montgomery. "Simple kinematic models for the environmental interaction of tropical cyclones in vertical wind shear." Atmospheric Chemistry and Physics 11, no. 17 (2011): 9395–414. http://dx.doi.org/10.5194/acp-11-9395-2011.
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Abstract. A major impediment to the intensity forecast of tropical cyclones (TCs) is believed to be associated with the interaction of TCs with dry environmental air. However, the conditions under which pronounced TC-environment interaction takes place are not well understood. As a step towards improving our understanding of this problem, we analyze here the flow topology of a TC immersed in an environment of vertical wind shear in an idealized, three-dimensional, convection-permitting numerical experiment. A set of distinct streamlines, the so-called manifolds, can be identified under the assumptions of steady and layer-wise horizontal flow. The manifolds are shown to divide the flow around the TC into distinct regions. The manifold structure in our numerical experiment is more complex than the well-known manifold structure of a non-divergent point vortex in uniform background flow. In particular, one manifold spirals inwards and ends in a limit cycle, a meso-scale dividing streamline encompassing the eyewall above the layer of strong inflow associated with surface friction and below the outflow layer in the upper troposphere. From the perspective of a steady and layer-wise horizontal flow model, the eyewall is well protected from the intrusion of environmental air. In order for the environmental air to intrude into the inner-core convection, time-dependent and/or vertical motions, which are prevalent in the TC inner-core, are necessary. Air with the highest values of moist-entropy resides within the limit cycle. This "moist envelope" is distorted considerably by the imposed vertical wind shear, and the shape of the moist envelope is closely related to the shape of the limit cycle. In a first approximation, the distribution of high- and low-θe air around the TC at low to mid-levels is governed by the stirring of convectively modified air by the steady, horizontal flow. Motivated by the results from the idealized numerical experiment, an analogue model based on a weakly divergent point vortex in background flow is formulated. The simple kinematic model captures the essence of many salient features of the manifold structure in the numerical experiment. A regime diagram representing realistic values of TC intensity and vertical wind shear can be constructed for the point-vortex model. The results indicate distinct scenarios of environmental interaction depending on the ratio of storm intensity and vertical-shear magnitude. Further implications of the new results derived from the manifold analysis for TCs in the real atmosphere are discussed.
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Riemer, M., M. T. Montgomery, and M. E. Nicholls. "A new paradigm for intensity modification of tropical cyclones: thermodynamic impact of vertical wind shear on the inflow layer." Atmospheric Chemistry and Physics Discussions 9, no. 3 (2009): 10711–75. http://dx.doi.org/10.5194/acpd-9-10711-2009.
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Abstract. An important roadblock to improved intensity forecasts for tropical cyclones (TCs) is our incomplete understanding of the interaction of a TC with the environmental flow. In this paper we re-visit the classical idealised numerical experiment of tropical cyclones (TCs) in vertical wind shear on an f-plane. We employ a set of simplified model physics – a simple bulk aerodynamic boundary layer scheme and "warm rain" microphysics – to foster better understanding of the dynamics and thermodynamics that govern the modification of TC intensity. A suite of experiments is performed with intense TCs in moderate to strong vertical shear. In all experiments the TC is resilient to shear but significant differences in the intensity evolution occur. The ventilation of the TC core with dry environmental air at mid-levels and the dilution of the upper-level warm core are two prevailing hypotheses for the adverse effect of vertical shear on storm intensity. Here we propose an alternative and arguably more effective mechanism how cooler and drier (lower θe) air – "anti-fuel" for the TC power machine – can enter the core region of the TC. Strong and persistent downdrafts flux low θe air from the lower and middle troposphere into the boundary layer, significantly depressing the θe values in the storm's inflow layer. Air with lower θe values enters the eyewall updrafts, considerably reducing eyewall θe values in the azimuthal mean. When viewed from the perspective of an idealised Carnot-cycle heat engine a decrease of storm intensity can thus be expected. Although the Carnot cycle model is – if at all – only valid for stationary and axisymmetric TCs, a strong correlation between the downward transport of low θe into the boundary layer and the intensity evolution offers further evidence in support of our hypothesis. The downdrafts that flush the inflow layer with low θe air are associated with a quasi-stationary region of convective activity outside the TC's eyewall. We show evidence that, to zero order, the formation of the convective asymmetry is driven by the balanced dynamical response of the TC vortex to the vertical shear forcing. Thus a close link is provided between the thermodynamic impact in the near-core boundary layer and the balanced dynamics governing the TC vortex evolution.
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Qiu, Wenyu, Liguang Wu, and Fumin Ren. "Monsoonal Influences on Offshore Rapid Intensification of Landfalling Typhoons in a Sheared Environment over the South China Sea." Weather and Forecasting 35, no. 2 (2020): 623–34. http://dx.doi.org/10.1175/waf-d-19-0134.1.
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Abstract Tropical cyclones (TCs) formed in the western North Pacific and South China Sea can undergo rapid intensification (RI) shortly before making landfall in China. Forecasting such offshore RI is a great challenge in operations. In this study the offshore RI events in a sheared environment are examined for TCs that made landfall in China during 1979–2017. It is found that there were only three offshore RI events in a sheared environment, all of which occurred to the south of Hainan Island within the monsoon trough in early to mid-July, coinciding with the termination of the mei-yu season. The specific geographic location and timing of the occurrence of the offshore RI in the sheared environment is associated with the adjustment of the East Asia summer monsoon system when the mei-yu season terminates in the Yangtze River valley. In addition to the adjustment favorable for TC intensification by enhancing the TC–trough interaction in the upper troposphere, this study suggests that two environmental factors also contribute to the offshore RI over the South China Sea in a sheared environment. One is the intrusion of dry air associated with the western North Pacific subtropical high (WNPSH) and the other is the penetration of the water vapor flux associated with the monsoon surge. The adjustment of the East Asia summer monsoon system allows the water vapor flux of the monsoon surge to penetrate the TC circulation and prevents the dry air of the WNPSH from intruding into the TC circulation.
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Moreno-Ibáñez, Marta, René Laprise, and Philippe Gachon. "Analysis of the Development Mechanisms of a Polar Low over the Norwegian Sea Simulated with the Canadian Regional Climate Model." Atmosphere 14, no. 6 (2023): 998. http://dx.doi.org/10.3390/atmos14060998.
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Polar lows (PLs) are maritime mesoscale cyclones associated with severe weather. They develop during marine cold air outbreaks near coastlines and the sea ice edge. Unfortunately, our knowledge about the mechanisms leading to PL development is still incomplete. This study aims to provide a detailed analysis of the development mechanisms of a PL that formed over the Norwegian Sea on 25 March 2019 using the output of a simulation with the sixth version of the Canadian Regional Climate Model (CRCM6/GEM4), a convection-permitting model. First, the life cycle of the PL is described and the vertical wind shear environment is analysed. Then, the horizontal wind divergence and the baroclinic conversion term are computed, and a surface pressure tendency equation is developed. In addition, the roles of atmospheric static stability, latent heat release, and surface heat and moisture fluxes are explored. The results show that the PL developed in a forward-shear environment and that moist baroclinic instability played a major role in its genesis and intensification. Baroclinic instability was initially only present at low levels of the atmosphere, but later extended upward until it reached the mid-troposphere. Whereas the latent heat of condensation and the surface heat fluxes also contributed to the development of the PL, convective available potential energy and barotropic conversion do not seem to have played a major role in its intensification. In conclusion, this study shows that a convection-permitting model simulation is a powerful tool to study the details of the structure of PLs, as well as their development mechanisms.
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Hong, Tang-Xun, Ching-Yuang Huang, Chen-Yang Lin, Guo-Yuan Lien, Zih-Mao Huang, and Shu-Ya Chen. "Impacts of GNSS RO Data on Typhoon Forecasts Using Global FV3GFS with GSI 4DEnVar." Atmosphere 14, no. 4 (2023): 735. http://dx.doi.org/10.3390/atmos14040735.
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The FORMOSAT-7/COSMIC-2 satellites were launched in 2019, which can provide considerably larger amounts of radio occultation (RO) observations than the FORMOSAT-3/COSMIC satellites. The radio signals emitted from the global navigation satellites system (GNSS) are received by these low Earth orbit (LEO) satellites to provide the so-called bending angle accounting for bending of the rays after penetrating through the atmosphere. Deeper RO observations can be retrieved from FORMOSAT-7/COSMIC-2 for use in RO data assimilation to improve forecasts of tropical cyclones. This study used the global model FV3GFS with the finest grid resolution of about 25 km to simulate five selected typhoons over the western North Pacific, including Hagibis in 2019, Maysak and Haishen in 2020, and Kompasu and Rai in 2021. For each case, two experiments were conducted with and without assimilating FORMOSAT-7/COSMIC-2 RO bending angle. The RO data were assimilated by the GSI 4DEnVar data assimilation system for a total period of 4 days (with 6 h assimilation window) before the typhoon genesis time, followed by a forecast length of 120 h. The RO data assimilation improved the typhoon track forecasts on average of 42 runs. However, no significantly positive impacts, in general, were found on the typhoon intensity forecasts, except for Maysak. Analyses for Maysak attributed the improved intensity forecast mainly to the improved analyses for wind, temperature, and moisture in the mid-upper troposphere after data assimilation. Consequently, the RO data largely enhanced the evolving intensity of the typhoon at a more consistent movement as explained by the wavenumber-one vorticity budget analysis. On the other hand, a noted improvement on the wind analysis, but still with degraded temperature analysis above the boundary layer, also improved track forecast at some specific times for Hagibis. The predictability of typhoon track and intensity as marginally improved by use of the large RO data remains very challenging to be well explored.
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Reid, J. S., N. D. Lagrosas, H. H. Jonsson, et al. "Observations of the temporal variability in aerosol properties and their relationships to meteorology in the summer monsoonal South China Sea/East Sea: the scale-dependent role of monsoonal flows, the Madden–Julian Oscillation, tropical cyclones, squall lines and cold pools." Atmospheric Chemistry and Physics 15, no. 4 (2015): 1745–68. http://dx.doi.org/10.5194/acp-15-1745-2015.
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Abstract. In a joint NRL/Manila Observatory mission, as part of the Seven SouthEast Asian Studies program (7-SEAS), a 2-week, late September 2011 research cruise in the northern Palawan archipelago was undertaken to observe the nature of southwest monsoonal aerosol particles in the South China Sea/East Sea (SCS/ES) and Sulu Sea region. Previous analyses suggested this region as a receptor for biomass burning from Borneo and Sumatra for boundary layer air entering the monsoonal trough. Anthropogenic pollution and biofuel emissions are also ubiquitous, as is heavy shipping traffic. Here, we provide an overview of the regional environment during the cruise, a time series of key aerosol and meteorological parameters, and their interrelationships. Overall, this cruise provides a narrative of the processes that control regional aerosol loadings and their possible feedbacks with clouds and precipitation. While 2011 was a moderate El Niño–Southern Oscillation (ENSO) La Niña year, higher burning activity and lower precipitation was more typical of neutral conditions. The large-scale aerosol environment was modulated by the Madden–Julian Oscillation (MJO) and its associated tropical cyclone (TC) activity in a manner consistent with the conceptual analysis performed by Reid et al. (2012). Advancement of the MJO from phase 3 to 6 with accompanying cyclogenesis during the cruise period strengthened flow patterns in the SCS/ES that modulated aerosol life cycle. TC inflow arms of significant convection sometimes span from Sumatra to Luzon, resulting in very low particle concentrations (minimum condensation nuclei CN < 150 cm−3, non-sea-salt PM2.5 < 1 μg m−3). However, elevated carbon monoxide levels were occasionally observed suggesting passage of polluted air masses whose aerosol particles had been rained out. Conversely, two drier periods occurred with higher aerosol particle concentrations originating from Borneo and Southern Sumatra (CN > 3000 cm−3 and non-sea-salt PM2.5 10–25 μg m−3). These cases corresponded with two different mechanisms of convection suppression: lower free-tropospheric dry-air intrusion from the Indian Ocean, and large-scale TC-induced subsidence. Veering vertical wind shear also resulted in aerosol transport into this region being mainly in the marine boundary layer (MBL), although lower free troposphere transport was possible on the western sides of Sumatra and Borneo. At the hourly time scale, particle concentrations were observed to be modulated by integer factors through convection and associated cold pools. Geostationary satellite observations suggest that convection often takes the form of squall lines, which are bowed up to 500 km across the monsoonal flow and 50 km wide. These squall lines, initiated by cold pools from large thunderstorms and likely sustained by a veering vertical wind shear and aforementioned mid-troposphere dry layers, propagated over 1500 km across the entirety of the SCS/ES, effectively cutting large swaths of MBL aerosol particles out of the region. Our conclusion is that while large-scale flow patterns are very important in modulating convection, and hence in allowing long-range transport of smoke and pollution, more short-lived phenomena can modulate cloud condensation nuclei (CCN) concentrations in the region, resulting in pockets of clean and polluted MBL air. This will no doubt complicate large scale comparisons of aerosol–cloud interaction.
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Wang, Yuan, Lifeng Zhang, Jun Peng, and Saisai Liu. "Mesoscale Horizontal Kinetic Energy Spectra of a Tropical Cyclone." Journal of the Atmospheric Sciences 75, no. 10 (2018): 3579–96. http://dx.doi.org/10.1175/jas-d-17-0391.1.
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A high-resolution cloud-permitting simulation with the Weather Research and Forecasting (WRF) Model is performed to investigate the mesoscale horizontal kinetic energy (HKE) spectra of a tropical cyclone (TC). The spectrum displays an arc-like shape in the troposphere and a quasi-linear shape in the lower stratosphere for wavelengths below 500 km during the mature period of the TC, while they both develop a quasi −5/3 slope. The total HKE spectrum is dominated by its rotational component in the troposphere but by its divergent component in the lower stratosphere. Further spectral HKE budget diagnosis reveals a generally downscale cascade of HKE, although a local upscale cascade gradually forms in the lower stratosphere. However, the mesoscale energy spectrum is not only governed by the energy cascade, but is evidently influenced also by other physical processes, among which the buoyancy effect converts available potential energy (APE) to HKE in the mid- and upper troposphere and converts HKE to APE in the lower stratosphere, the vertically propagating inertia–gravity waves transport the HKE from the upper troposphere to lower and higher layers, and the vertical transportation of convection always transports HKE upward.
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Prieto, Raidel Báez, and Mateus Da Silva Teixeira. "ANÁLISIS SINÓPTICO DE UN EVENTO EXTREMO Y PERSISTENTE DE LLUVIA SOBRE EL ESTADO DE RÍO GRANDE DO SUL, BRASIL, EN MAYO DE 2004." Ciência e Natura 38, no. 2 (2016): 1010. http://dx.doi.org/10.5902/2179460x21265.
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Between 04 to 09 May 2004, part of the state of Rio Grande do Sul (RS), Brazil; have recorded rainfall above 300mm. The east region of this state, mainly on the coast, had the highest rainfall accumulation occurred. A synoptic analysis of this period has shown a persistent trough west of RS in high and middle levels of troposphere, in the first three days of this event. This trough started a cyclonic vortice in the mid-low-tropospheric levels in the following days. The upward movement associated with this trough stayed semi-stationary over the state of RS and acted in almost entire tropospheric layer during great part of this period. In addition, it was observed that this tropospheric layer had high values of relative humidity from surface up to 300 hPa, over the state of RS – greater than 70%. In 09 May 2004, the cyclonic vortice has lost their configuration and has distanced from RS. The state of RS was dominated by an anticyclonic circulation and by a drier tropospheric layer, what disfavors rainfall occurrence in this region. During all analyzed period, it could be observed that the configuration in the middle troposphere has extended up to higher levels, but the same does not occurred to the surface. Also, a cyclonic circulation in 850 hPa was observed over the state of RS, but any cyclogenesis has occurred at surface. A surface cyclogenesis was observed over the coast of the state of Sao Paulo (SP), in 05 May. This cyclone has moved to south, approaching the coast of the states of RS e Santa Catarina (SC), in 08 May. A comparison of the atmospheric behavior with the rainfall recorded in the state of RS between 03 and 09 May suggest that this low-pressure center has no direct influence in the cumulative rainfall observed in this period. In addition, in 08 and 09 May, this low-pressure center weakened and move away from the coast of the states of RS and SC. Therefore, although the weak low-level temperature advection and low-level moisture flux convergence observed over this region, a persistent mid-low-tropospheric trough, what favor persistent upward movement, together with a deep and very humid layer, seems to be the main responsible to the great amounts of rainfall registered in the state of RS.
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Fudeyasu, Hironori, and Yuqing Wang. "Balanced Contribution to the Intensification of a Tropical Cyclone Simulated in TCM4: Outer-Core Spinup Process*." Journal of the Atmospheric Sciences 68, no. 3 (2011): 430–49. http://dx.doi.org/10.1175/2010jas3523.1.
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Abstract The balanced contribution to the intensification of a tropical cyclone simulated in the three-dimensional, nonhydrostatic, full-physics tropical cyclone model version 4 (TCM4), in particular the spinup of the outer-core circulation, is investigated by solving the Sawyer–Eliassen equation and by computing terms in the azimuthal-mean tangential wind tendency equation. Results demonstrate that the azimuthal-mean secondary circulation (radial and vertical circulation) and the spinup of the midtropospheric outer-core circulation in the simulated tropical cyclone are well captured by balance dynamics. The midtropospheric inflow develops in response to diabatic heating in mid–upper-tropospheric stratiform (anvil) clouds outside the eyewall in active spiral rainbands and transports absolute angular momentum inward to spin up the outer-core circulation. Although the azimuthal-mean diabatic heating rate in the eyewall is the largest, its contribution to radial winds and thus the spinup of outer-core circulation in the middle troposphere is rather weak. This is because the high inertial stability in the inner-core region resists the radial inflow in the middle troposphere, limiting the inward transport of absolute angular momentum. The result thus suggests that diabatic heating in spiral rainbands is the key to the continued growth of the storm-scale circulation.
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Wang, Xiaokang, Xiquan Dong, Yi Deng, Chunguang Cui, Rong Wan, and Wenjun Cui. "Contrasting Pre-Mei-Yu and Mei-Yu Extreme Precipitation in the Yangtze River Valley: Influencing Systems and Precipitation Mechanisms." Journal of Hydrometeorology 20, no. 9 (2019): 1961–80. http://dx.doi.org/10.1175/jhm-d-18-0240.1.
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Abstract The mei-yu season over the Yangtze–Huai Rivers basin, typically occurring from mid-June to mid-July, is one of three heavy-rainfall periods over China and can contribute 50% of the annual precipitation. In this study, the first and second heaviest daily precipitation events at the Wuhan station have been selected to represent typical mei-yu and pre-mei-yu precipitation events where the differences in the atmospheric thermodynamic characteristics, precipitation nature, influencing systems, and mechanisms are investigated. During the mei-yu case, moist air mainly came from the South China Sea. Precipitation occurred south of the mei-yu front where abundant moisture and favorable thermodynamic conditions were present. The main influencing systems include a stable blocking pattern and strong and stable western Pacific subtropical high in the midtroposphere, and a small yet intense mesoscale cyclonic vortex in the low troposphere. Rainfall in Wuhan was continuous, caused by a well-organized convective line. A heavy rainband was located along the narrow band between the elongated upper-level jet (ULJ) and the low-level jet (LLJ) where the symmetric instability was found in the midtroposphere near Wuhan. Quite differently, for the pre-mei-yu precipitation case, moist air primarily came from the Beibu Gulf and the Bay of Bengal. Precipitation happened in the low-level convective instability region, where a short-wave trough in the midtroposphere and a mesoscale cyclonic vortex in the low-troposphere were found. Precipitation in Wuhan showed multiple peaks associated with independent meso-β-scale convective systems. A rainstorm occurred at the exit of the LLJ and the right entrance of the ULJ, where convective instability exited in the mid- to low troposphere.
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Zhu, Jinyao, Xin Jin, Chunhua Shi, and Dan Chen. "The Troposphere-to-Stratosphere Transport Caused by a Rossby Wave Breaking Event over the Tibetan Plateau in Mid-March 2006." Remote Sensing 15, no. 1 (2022): 155. http://dx.doi.org/10.3390/rs15010155.
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Based on reanalysis data, satellite ozone concentration observations, and a Lagrangian trajectory simulation, a Rossby wave breaking (RWB) event and its effect on stratosphere–troposphere exchange (STE) over the Tibetan Plateau in mid-March 2006 were investigated. Results showed that the increased eddy heat flux from the subtropical westerly jet magnified the amplitude of the Rossby wave, which contributed to the occurrence of the cyclonic RWB event. The quasi-horizontal cyclonic motion of the isentropic potential vorticity in the RWB cut the tropical tropospheric air mass into the extratropical stratosphere, completing the stratosphere–troposphere mass exchange. Meanwhile, the tropopause folding zone extended polewards by 10° of latitude and the tropospheric air mass escaped from the tropical tropopause layer into the extratropical stratosphere through the tropopause folding zone. The particles in the troposphere-to-stratosphere transport (TST) pathway migrated both eastwards and polewards in the horizontal direction, and shifted upwards in the vertical direction. Eventually, the mass of the TST particles reached about 3.8 × 1014 kg, accounting for 42.2% of the particles near the tropopause in the RWB event. The rest of the particles remained in the troposphere, where they moved eastwards rapidly along the westerly jet and slid down in the downstream upper frontal zone.
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BHAGAT, D. K. U. R. "Absolute angular momentum generation & its vertical transport in the field of mid-tropospheric cyclones." MAUSAM 56, no. 4 (2022): 759–64. http://dx.doi.org/10.54302/mausam.v56i4.1025.
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A quasi-stationary synoptic system is usually seen on the weather charts during southwest monsoon period over the north-east Arabian Sea and adjoining area of Gujarat and north Konkan. The transport of absolute angular momentum, for the atmospheric weather systems, plays a significant role during the southwest monsoon period.
 In this paper, the mean absolute angular momentum and its vertical transport associated with MTC have been discussed. The expected accumulation of momentum throughout the troposphere upto 800 km around the centre of MTC has been calculated and displayed. The transport of angular momentum to the underlying surface and momentum loss or gain has also been discussed. Estimates have been made of surface stress by means of angular momentum transferred.
 The study reveals that the flux of angular momentum found to be dominated mostly between surface and 500 hPa and the values of shearing stress are positive from the centre of MTC to 500 km.
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Wang, Huiping, Chunhua Shi, and Dong Guo. "The Different Characteristics of the Mass Transport between the Stratosphere and the Troposphere in Two Types of Cyclonic Rossby Wave-Breaking Events." Remote Sensing 15, no. 13 (2023): 3286. http://dx.doi.org/10.3390/rs15133286.
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Using the ERA5 reanalysis data and trajectory analysis provided by Hysplit4, a comparative analysis was conducted on the primary pathways of air particles and the dominant weather systems in two distinct cases of equatorward and poleward cyclonic Rossby wave-breaking (CWB) events. Subsequently, the characteristics of mass exchange between the stratosphere and troposphere in both CWBs were estimated and discussed. CWB events are frequently associated with the development of an upper front in subtropics and a ridge or blocking in mid-latitudes, leading to a tropopause anomaly characterized by a downward depression in the subtropics and an upward bulge in the mid-latitudes. High potential vorticity (PV) particles exhibit negligible vertical motion and are instead controlled by the circulation of the ridge or blocking, leading to a significant poleward transport. In contrast, low PV particles display noticeable vertical motion, with approximately one fourth of them ascending on the north side of the upper-level jet exit region. After CWB occurrence, approximately 25% of low PV particles moved southward and sank below 500 hPa with the downstream trough’s cold air. Most high PV particles remained in the stratosphere, and low PV particles predominantly remained in the troposphere. Only a small proportion (2% to 6%) of particles underwent stratosphere–troposphere exchange (STE). In equatorward CWB, STE manifested as transport from stratosphere to troposphere, occurring mainly in 24–48 h post breaking with a maximum mass transport of approximately 1.54 × 1013 kg. In poleward CWB, STE involved transport from troposphere to stratosphere, occurring mainly within 0–18 h post breaking with a maximum mass transport of approximately 1.48 × 1013 kg.
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Wimmer, Meryl, Gwendal Rivière, Philippe Arbogast, et al. "Diabatic processes modulating the vertical structure of the jet stream above the cold front of an extratropical cyclone: sensitivity to deep convection schemes." Weather and Climate Dynamics 3, no. 3 (2022): 863–82. http://dx.doi.org/10.5194/wcd-3-863-2022.
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Abstract. The effect of deep convection parameterisation on the jet stream above the cold front of an explosive extratropical cyclone is investigated in the global numerical weather prediction model ARPEGE, operational at Météo-France. Two hindcast simulations differing only in the deep convection scheme used are systematically compared with each other, with (re)analysis datasets and with NAWDEX airborne observations. The deep convection representation has an important effect on the vertical structure of the jet stream above the cold front at 1-d lead time. The simulation with the less active scheme shows a deeper jet stream, associated with a stronger potential vorticity (PV) gradient in the middle troposphere. This is due to a larger deepening of the dynamical tropopause on the cold air side of the jet and a higher PV destruction on the warm air side, near 600 hPa. To better understand the origin of this stronger PV gradient, Lagrangian backward trajectories are computed. On the cold air side of the jet, numerous trajectories undergo a rapid ascent from the boundary layer to the mid-levels in the simulation with the less active deep convection scheme, whereas they stay at mid-levels in the other simulation. This ascent explains the higher PV noted on that side of the jet in the simulation with the less active deep convection scheme. These ascending air masses form mid-level ice clouds that are not observed in the microphysical retrievals from airborne radar-lidar measurements. On the warm air side of the jet, in the warm conveyor belt ascending region, the Lagrangian trajectories with the less active deep convection scheme undergo a higher PV destruction due to a stronger heating occurring in the lower and middle troposphere. In contrast, in the simulation with the most active deep convection scheme, both the heating and PV destruction extend further up into the upper troposphere.
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Brennan, Michael J., and Gary M. Lackmann. "The Influence of Incipient Latent Heat Release on the Precipitation Distribution of the 24–25 January 2000 U.S. East Coast Cyclone." Monthly Weather Review 133, no. 7 (2005): 1913–37. http://dx.doi.org/10.1175/mwr2959.1.
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Abstract The role of a diabatically produced lower-tropospheric potential vorticity (PV) maximum in determining the precipitation distribution of the 24–25 January 2000 U.S. East Coast cyclone is investigated. Operational numerical weather prediction (NWP) models performed poorly with this storm, even within 24 h of the event, as they were unable to properly forecast the westward extent of heavy precipitation over the Carolinas and mid-Atlantic. The development of an area of incipient precipitation (IP) around 0600 UTC 24 January over the southeastern United States prior to rapid cyclogenesis was also poorly forecasted by the operational NWP models. It is hypothesized that the lower-tropospheric diabatic PV maximum initially produced by the IP was important to subsequent inland moisture transport over the Carolinas and mid-Atlantic. A PV budget confirms that latent heat release in the midtroposphere associated with the IP led to the initial formation of a PV maximum in the lower troposphere that propagated eastward in association with the IP to the Atlantic coast late on 24 January. The impact of this PV maximum on the westward moisture transport was quantified by piecewise Ertel PV inversion. Results from the inversion show that the balanced flow associated with this evolving cyclonic PV maximum contributed substantially to the onshore moisture flux into the Carolinas and Virginia. The balanced flow associated with the PV anomaly also contributed to quasigeostrophic forcing for ascent in the region. These findings suggest that accurate numerical prediction of the precipitation distribution in this event requires adequate representation of the IP and its associated impacts on the PV distribution.
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Rogers, Robert F., Paul D. Reasor, Jonathan A. Zawislak, and Leon T. Nguyen. "Precipitation Processes and Vortex Alignment during the Intensification of a Weak Tropical Cyclone in Moderate Vertical Shear." Monthly Weather Review 148, no. 5 (2020): 1899–929. http://dx.doi.org/10.1175/mwr-d-19-0315.1.
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Abstract The mechanisms underlying the development of a deep, aligned vortex, and the role of convection and vertical shear in this process, are explored by examining airborne Doppler radar and deep-layer dropsonde observations of the intensification of Hurricane Hermine (2016), a long-lived tropical depression that intensified to hurricane strength in the presence of moderate vertical wind shear. During Hermine’s intensification the low-level circulation appeared to shift toward locations of deep convection that occurred primarily downshear. Hermine began to steadily intensify once a compact low-level vortex developed within a region of deep convection in close proximity to a midlevel circulation, causing vorticity to amplify in the lower troposphere primarily through stretching and tilting from the deep convection. A notable transition of the vertical mass flux profile downshear of the low-level vortex to a bottom-heavy profile also occurred at this time. The transition in the mass flux profile was associated with more widespread moderate convection and a change in the structure of the deep convection to a bottom-heavy mass flux profile, resulting in greater stretching of vorticity in the lower troposphere of the downshear environment. These structural changes in the convection were related to a moistening in the midtroposphere downshear, a stabilization in the lower troposphere, and the development of a mid- to upper-level warm anomaly associated with the developing midlevel circulation. The evolution of precipitation structure shown here suggests a multiscale cooperative interaction across the convective and mesoscale that facilitates an aligned vortex that persists beyond convective time scales, allowing Hermine to steadily intensify to hurricane strength.
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Diab, R. D., A. Raghunandan, A. M. Thompson, and V. Thouret. "Classification of tropospheric ozone profiles over Johannesburg based on MOZAIC aircraft data." Atmospheric Chemistry and Physics Discussions 3, no. 1 (2003): 705–32. http://dx.doi.org/10.5194/acpd-3-705-2003.
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Abstract. Each ozone profile is a unique response to the photochemical and dynamic processes operating in the troposphere and hence is critical to our understanding of processes and their relative contributions to the tropospheric ozone budget. Traditionally, mean profiles, together with some measure of variability, averaged by season or year at a particular location have been presented as a climatology. However, the mean profile is difficult to interpret because of the counteracting influences present in the micro-structure. On the other hand, case study analysis, whilst revealing, only applies to isolated conditions. In a search for pattern and order within ozone profiles, a classification based on a cluster analysis technique has been applied in this study. Ozone profiles are grouped according to the magnitude and altitude of ozone concentration. This technique has been tested with 56 ozone profiles at Johannesburg, South Africa, recorded by aircraft as part of the MOZAIC (Measurement of Ozone and Water Vapor aboard Airbus In-service Aircraft) program. Six distinct groups of ozone profiles have been identified and their characteristics described. The widely recognized spring maximum in tropospheric ozone is identified through the classification, but a new summertime mid-tropospheric enhancement due to the penetration of tropical air masses from continental regions in central Africa has been identified. Back trajectory modeling is used to provide evidence of the different origins of ozone enhancements in each of the classes. Continental areas over central Africa are shown to be responsible for the low to mid-tropospheric enhancement in spring and the mid-tropospheric peak in summer, whereas the winter low-tropospheric enhancement is attributed to local sources. The dominance of westerly winds through the troposphere associated with the passage of a mid-latitude cyclone gives rise to reduced ozone values.