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1
Donohoe, Aaron, e David S. Battisti. "The Seasonal Cycle of Atmospheric Heating and Temperature". Journal of Climate 26, n. 14 (12 luglio 2013): 4962–80. http://dx.doi.org/10.1175/jcli-d-12-00713.1.
Testo completoAbstract (sommario):
Abstract The seasonal cycle of the heating of the atmosphere is divided into a component due to direct solar absorption in the atmosphere and a component due to the flux of energy from the surface to the atmosphere via latent, sensible, and radiative heat fluxes. Both observations and coupled climate models are analyzed. The vast majority of the seasonal heating of the northern extratropics (78% in the observations and 67% in the model average) is due to atmospheric shortwave absorption. In the southern extratropics, the seasonal heating of the atmosphere is entirely due to atmospheric shortwave absorption in both the observations and the models, and the surface heat flux opposes the seasonal heating of the atmosphere. The seasonal cycle of atmospheric temperature is surface amplified in the northern extratropics and nearly barotropic in the Southern Hemisphere; in both cases, the vertical profile of temperature reflects the source of the seasonal heating. In the northern extratropics, the seasonal cycle of atmospheric heating over land differs markedly from that over the ocean. Over the land, the surface energy fluxes complement the driving absorbed shortwave flux; over the ocean, they oppose the absorbed shortwave flux. This gives rise to large seasonal differences in the temperature of the atmosphere over land and ocean. Downgradient temperature advection by the mean westerly winds damps the seasonal cycle of heating of the atmosphere over the land and amplifies it over the ocean. The seasonal cycle in the zonal energy transport is 4.1 PW. Finally, the authors examine the change in the seasonal cycle of atmospheric heating in 11 models from phase 3 of the Coupled Model Intercomparison Project (CMIP3) due to a doubling of atmospheric carbon dioxide from preindustrial concentrations. The seasonal heating of the troposphere is everywhere enhanced by increased shortwave absorption by water vapor; it is reduced where sea ice has been replaced by ocean, which increases the effective heat storage reservoir of the climate system and thereby reduces the seasonal magnitude of energy fluxes between the surface and the atmosphere. As a result, the seasonal amplitude of temperature increases in the upper troposphere (where atmospheric shortwave absorption increases) and decreases at the surface (where the ice melts).
2
Kong, Debing, Guicai Ning, Shigong Wang, Jing Cong, Ming Luo, Xiang Ni e Mingguo Ma. "Clustering diurnal cycles of day-to-day temperature change to understand their impacts on air quality forecasting in mountain-basin areas". Atmospheric Chemistry and Physics 21, n. 19 (30 settembre 2021): 14493–505. http://dx.doi.org/10.5194/acp-21-14493-2021.
Testo completoAbstract (sommario):
Abstract. Air pollution is substantially modulated by meteorological conditions, and especially their diurnal variations may play a key role in air quality evolution. However, the behaviors of temperature diurnal cycles along with the associated atmospheric condition and their effects on air quality in China remain poorly understood. Here, for the first time, we examine the diurnal cycles of day-to-day temperature change and reveal their impacts on winter air quality forecasting in mountain-basin areas. Three different diurnal cycles of the preceding day-to-day temperature change are identified and exhibit notably distinct effects on the day-to-day changes in atmospheric-dispersion conditions and air quality. The diurnal cycle with increasing temperature obviously enhances the atmospheric stability in the lower troposphere and suppresses the development of the planetary boundary layer, thus deteriorating the air quality on the following day. By contrast, the diurnal cycle with decreasing temperature in the morning is accompanied by a worse dispersion condition with more stable atmosphere stratification and weaker surface wind speed, thereby substantially worsening the air quality. Conversely, the diurnal cycle with decreasing temperature in the afternoon seems to improve air quality on the following day by enhancing the atmospheric-dispersion conditions on the following day. The findings reported here are critical to improve the understanding of air pollution in mountain-basin areas and exhibit promising potential for air quality forecasting.
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WALKER, J. C. G. "Atmospheric Evolution: The Carbon Cycle and Atmospheric CO2." Science 230, n. 4722 (11 ottobre 1985): 163–64. http://dx.doi.org/10.1126/science.230.4722.163-a.
Testo completo
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Alexandrov, G. A. "Explaining the seasonal cycle of the globally averaged CO<sub>2</sub> with a carbon-cycle model". Earth System Dynamics 5, n. 2 (21 ottobre 2014): 345–54. http://dx.doi.org/10.5194/esd-5-345-2014.
Testo completoAbstract (sommario):
Abstract. The seasonal changes in the globally averaged atmospheric carbon-dioxide concentrations reflect an important aspect of the global carbon cycle: the gas exchange between the atmosphere and terrestrial biosphere. The data on the globally averaged atmospheric carbon-dioxide concentrations, which are reported by Earth System Research Laboratory of the US National Oceanic & Atmospheric Administration (NOAA/ESRL), could be used to demonstrate the adequacy of the global carbon-cycle models. However, it was recently found that the observed amplitude of seasonal variations in the atmospheric carbon-dioxide concentrations is higher than simulated. In this paper, the factors that affect the amplitude of seasonal variations are explored using a carbon-cycle model of reduced complexity. The model runs show that the low amplitude of the simulated seasonal variations may result from underestimated effect of substrate limitation on the seasonal pattern of heterotrophic respiration and from an underestimated magnitude of the annual gross primary production (GPP) in the terrestrial ecosystems located to the north of 25° N.
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Reinhard, Christopher T., Stephanie L. Olson, Sandra Kirtland Turner, Cecily Pälike, Yoshiki Kanzaki e Andy Ridgwell. "Oceanic and atmospheric methane cycling in the cGENIE Earth system model – release v0.9.14". Geoscientific Model Development 13, n. 11 (20 novembre 2020): 5687–706. http://dx.doi.org/10.5194/gmd-13-5687-2020.
Testo completoAbstract (sommario):
Abstract. The methane (CH4) cycle is a key component of the Earth system that links planetary climate, biological metabolism, and the global biogeochemical cycles of carbon, oxygen, sulfur, and hydrogen. However, currently lacking is a numerical model capable of simulating a diversity of environments in the ocean, where CH4 can be produced and destroyed, and with the flexibility to be able to explore not only relatively recent perturbations to Earth's CH4 cycle but also to probe CH4 cycling and associated climate impacts under the very low-O2 conditions characteristic of most of Earth's history and likely widespread on other Earth-like planets. Here, we present a refinement and expansion of the ocean–atmosphere CH4 cycle in the intermediate-complexity Earth system model cGENIE, including parameterized atmospheric O2–O3–CH4 photochemistry and schemes for microbial methanogenesis, aerobic methanotrophy, and anaerobic oxidation of methane (AOM). We describe the model framework, compare model parameterizations against modern observations, and illustrate the flexibility of the model through a series of example simulations. Though we make no attempt to rigorously tune default model parameters, we find that simulated atmospheric CH4 levels and marine dissolved CH4 distributions are generally in good agreement with empirical constraints for the modern and recent Earth. Finally, we illustrate the model's utility in understanding the time-dependent behavior of the CH4 cycle resulting from transient carbon injection into the atmosphere, and we present model ensembles that examine the effects of atmospheric pO2, oceanic dissolved SO42-, and the thermodynamics of microbial metabolism on steady-state atmospheric CH4 abundance. Future model developments will address the sources and sinks of CH4 associated with the terrestrial biosphere and marine CH4 gas hydrates, both of which will be essential for comprehensive treatment of Earth's CH4 cycle during geologically recent time periods.
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Bengtsson, Lennart. "The global atmospheric water cycle". Environmental Research Letters 5, n. 2 (9 aprile 2010): 025202. http://dx.doi.org/10.1088/1748-9326/5/2/025202.
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Philip, Sjoukje, e Geert Jan van Oldenborgh. "Significant Atmospheric Nonlinearities in the ENSO Cycle". Journal of Climate 22, n. 14 (15 luglio 2009): 4014–28. http://dx.doi.org/10.1175/2009jcli2716.1.
Testo completoAbstract (sommario):
Abstract The nonlinearities that cause El Niño events to deviate more from the mean state than La Niña events are still not completely understood. This paper investigates the contribution of one candidate mechanism: ENSO nonlinearities originating from the atmosphere. The initially linear intermediate complexity model of the equatorial Pacific Ocean, in which all couplings were fitted to observations, describes the ENSO cycle reasonably well. In this linear model, extra terms are systematically introduced in the atmospheric component: the nonlinear response of mean wind stress to SST anomalies, the skewness of the driving noise term in the atmosphere, and the relation of this noise term to the background SST or the ENSO phase. The nonlinear response of mean wind stress to SST in the ENSO region is found to be the dominant term influencing the ENSO cycle. However, this influence is only visible when noise fields are used that are fitted to observed patterns of prescribed standard deviation and spatial decorrelation. Standard deviation and skewness of noise do have a dependence on the ENSO phase, but this has a relatively small influence on the ENSO cycle in this model. With these additional nonlinearities in the representation of the atmosphere, a step forward has been made toward building a realistic reduced complexity model for ENSO.
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Thum, Tea, Julia E. M. S. Nabel, Aki Tsuruta, Tuula Aalto, Edward J. Dlugokencky, Jari Liski, Ingrid T. Luijkx et al. "Evaluating two soil carbon models within the global land surface model JSBACH using surface and spaceborne observations of atmospheric CO<sub>2</sub>". Biogeosciences 17, n. 22 (23 novembre 2020): 5721–43. http://dx.doi.org/10.5194/bg-17-5721-2020.
Testo completoAbstract (sommario):
Abstract. The trajectories of soil carbon in our changing climate are of the utmost importance as soil is a substantial carbon reservoir with a large potential to impact the atmospheric carbon dioxide (CO2) burden. Atmospheric CO2 observations integrate all processes affecting carbon exchange between the surface and the atmosphere and therefore are suitable for carbon cycle model evaluation. In this study, we present a framework for how to use atmospheric CO2 observations to evaluate two distinct soil carbon models (CBALANCE, CBA, and Yasso, YAS) that are implemented in a global land surface model (JSBACH). We transported the biospheric carbon fluxes obtained by JSBACH using the atmospheric transport model TM5 to obtain atmospheric CO2. We then compared these results with surface observations from Global Atmosphere Watch stations, as well as with column XCO2 retrievals from GOSAT (Greenhouse Gases Observing Satellite). The seasonal cycles of atmospheric CO2 estimated by the two different soil models differed. The estimates from the CBALANCE soil model were more in line with the surface observations at low latitudes (0–45∘ N) with only a 1 % bias in the seasonal cycle amplitude, whereas Yasso underestimated the seasonal cycle amplitude in this region by 32 %. Yasso, on the other hand, gave more realistic seasonal cycle amplitudes of CO2 at northern boreal sites (north of 45∘ N) with an underestimation of 15 % compared to a 30 % overestimation by CBALANCE. Generally, the estimates from CBALANCE were more successful in capturing the seasonal patterns and seasonal cycle amplitudes of atmospheric CO2 even though it overestimated soil carbon stocks by 225 % (compared to an underestimation of 36 % by Yasso), and its estimations of the global distribution of soil carbon stocks were unrealistic. The reasons for these differences in the results are related to the different environmental drivers and their functional dependencies on the two soil carbon models. In the tropics, heterotrophic respiration in the Yasso model increased earlier in the season since it is driven by precipitation instead of soil moisture, as in CBALANCE. In temperate and boreal regions, the role of temperature is more dominant. There, heterotrophic respiration from the Yasso model had a larger seasonal amplitude, which is driven by air temperature, compared to CBALANCE, which is driven by soil temperature. The results underline the importance of using sub-annual data in the development of soil carbon models when they are used at shorter than annual timescales.
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Bala, G., K. Caldeira, A. Mirin, M. Wickett e C. Delire. "Multicentury Changes to the Global Climate and Carbon Cycle: Results from a Coupled Climate and Carbon Cycle Model". Journal of Climate 18, n. 21 (1 novembre 2005): 4531–44. http://dx.doi.org/10.1175/jcli3542.1.
Testo completoAbstract (sommario):
Abstract A coupled climate and carbon (CO2) cycle model is used to investigate the global climate and carbon cycle changes out to the year 2300 that would occur if CO2 emissions from all the currently estimated fossil fuel resources were released to the atmosphere. By the year 2300, the global climate warms by about 8 K and atmospheric CO2 reaches 1423 ppmv. The warming is higher than anticipated because the sensitivity to radiative forcing increases as the simulation progresses. In this simulation, the rate of emissions peaks at over 30 Pg C yr−1 early in the twenty-second century. Even at the year 2300, nearly 50% of cumulative emissions remain in the atmosphere. Both soils and living biomass are net carbon sinks throughout the simulation. Despite having relatively low climate sensitivity and strong carbon uptake by the land biosphere, these model projections suggest severe long-term consequences for global climate if all the fossil fuel carbon is ultimately released into the atmosphere.
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Eliseev, A. V., M. Zhang, R. D. Gizatullin, A. V. Altukhova, Yu P. Perevedentsev e A. I. Skorokhod. "Impact of sulphur dioxide on the terrestrial carbon cycle". Известия Российской академии наук. Физика атмосферы и океана 55, n. 1 (16 aprile 2019): 41–53. http://dx.doi.org/10.31857/s0002-351555141-53.
Testo completoAbstract (sommario):
In this paper, the earlier results, which were obtained with the climate model developed at the A.M. Obu khov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM) and related to the impact of the atmospheric sulphur dioxide on terrestrial carbon cycle, are elucidated. Because of the unavailability of the global data for near surface SO2 concentration, it was reconstructed by using statistical model which was fitted employing the output of the atmospheric chemistry-transport model RAMS-CMAQ. The obtained results are in general agreement with those reported earlier. In particular, the most significant SO2 impact on terrestrial carbon cycle is simulated for south-east North America and for Europe. However, such impact for south-east Asia is markedly weaker in comparison to that reported earlier, which is related to excessive moisture content in the atmosphere of this region.
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Monib, Abdul Wahid, Parwiz Niazi, Shah Mahmood Barai, Barbara Sawicka, Abdul Qadeer Baseer, Amin Nikpay, Safa Mahmoud Saleem Fahmawi, Deepti Singh, Mirwais Alikhail e Berthin Thea. "Nitrogen Cycling Dynamics: Investigating Volatilization and its Interplay with N2 Fixation". Journal for Research in Applied Sciences and Biotechnology 3, n. 1 (1 febbraio 2024): 17–31. http://dx.doi.org/10.55544/jrasb.3.1.4.
Testo completoAbstract (sommario):
The nitrogen cycle is the biogeochemical cycle by which nitrogen is converted into multiple chemical forms as it circulates among atmospheric, terrestrial, and marine ecosystems, the conversion of nitrogen can be carried out through both biological and physical processes. Important processes in the nitrogen cycle include fixation, ammonification, nitrification, and denitrification. The majority of Earth's atmosphere (78%) is atmospheric nitrogen, making it the largest source of nitrogen. However, atmospheric nitrogen has limited availability for biological use, leading to a scarcity of usable nitrogen in many types of ecosystems. The nitrogen cycle is of particular interest to ecologists because nitrogen availability can affect the rate of key ecosystem processes, including primary production and decomposition. Human activities such as fossil fuel combustion, use of artificial nitrogen fertilizers, and release of nitrogen in wastewater have dramatically altered the global nitrogen cycle. Human modification of the global nitrogen cycle can negatively affect the natural environment system and also human health. Volatilization and its Relationship to N2 fascination in Nitrogen Cycle in agriculture field is discuss in this paper.
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Yang, Wenchang, Richard Seager, Mark A. Cane e Bradfield Lyon. "The Annual Cycle of East African Precipitation". Journal of Climate 28, n. 6 (13 marzo 2015): 2385–404. http://dx.doi.org/10.1175/jcli-d-14-00484.1.
Testo completoAbstract (sommario):
Abstract East African precipitation is characterized by a dry annual mean climatology compared to other deep tropical land areas and a bimodal annual cycle with the major rainy season during March–May (MAM; often called the “long rains”) and the second during October–December (OND; often called the “short rains”). To explore these distinctive features, ERA-Interim data are used to analyze the associated annual cycles of atmospheric convective stability, circulation, and moisture budget. The atmosphere over East Africa is found to be convectively stable in general year-round but with an annual cycle dominated by the surface moist static energy (MSE), which is in phase with the precipitation annual cycle. Throughout the year, the atmospheric circulation is dominated by a pattern of convergence near the surface, divergence in the lower troposphere, and convergence again at upper levels. Consistently, the convergence of the vertically integrated moisture flux is mostly negative across the year, but becomes weakly positive in the two rainy seasons. It is suggested that the semiarid/arid climate in East Africa and its bimodal precipitation annual cycle can be explained by the ventilation mechanism, in which the atmospheric convective stability over East Africa is controlled by the import of low MSE air from the relatively cool Indian Ocean off the coast. During the rainy seasons, however, the off-coast sea surface temperature (SST) increases (and is warmest during the long rains season) and consequently the air imported into East Africa becomes less stable. This analysis may be used to aid in understanding overestimates of the East African short rains commonly found in coupled models.
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Brovkin, V., A. Ganopolski, D. Archer e G. Munhoven. "Glacial CO<sub>2</sub> cycle as a succession of key physical and biogeochemical processes". Climate of the Past 8, n. 1 (9 febbraio 2012): 251–64. http://dx.doi.org/10.5194/cp-8-251-2012.
Testo completoAbstract (sommario):
Abstract. During glacial-interglacial cycles, atmospheric CO2 concentration varied by about 100 ppmv in amplitude. While testing mechanisms that have led to the low glacial CO2 level could be done in equilibrium model experiments, an ultimate goal is to explain CO2 changes in transient simulations through the complete glacial-interglacial cycle. The computationally efficient Earth System model of intermediate complexity CLIMBER-2 is used to simulate global biogeochemistry over the last glacial cycle (126 kyr). The physical core of the model (atmosphere, ocean, land and ice sheets) is driven by orbital changes and reconstructed radiative forcing from greenhouses gases, ice, and aeolian dust. The carbon cycle model is able to reproduce the main features of the CO2 changes: a 50 ppmv CO2 drop during glacial inception, a minimum concentration at the last glacial maximum 80 ppmv lower than the Holocene value, and an abrupt 60 ppmv CO2 rise during the deglaciation. The model deep ocean δ13C also resembles reconstructions from deep-sea cores. The main drivers of atmospheric CO2 evolve in time: changes in sea surface temperatures and in the volume of bottom water of southern origin control atmospheric CO2 during the glacial inception and deglaciation; changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycle, respectively. These feedback mechanisms could also significantly impact the ultimate climate response to the anthropogenic perturbation.
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Liptak, Jessica, Gretchen Keppel-Aleks e Keith Lindsay. "Drivers of multi-century trends in the atmospheric CO<sub>2</sub> mean annual cycle in a prognostic ESM". Biogeosciences 14, n. 6 (20 marzo 2017): 1383–401. http://dx.doi.org/10.5194/bg-14-1383-2017.
Testo completoAbstract (sommario):
Abstract. The amplitude of the mean annual cycle of atmospheric CO2 is a diagnostic of seasonal surface–atmosphere carbon exchange. Atmospheric observations show that this quantity has increased over most of the Northern Hemisphere (NH) extratropics during the last 3 decades, likely from a combination of enhanced atmospheric CO2, climate change, and anthropogenic land use change. Accurate climate prediction requires accounting for long-term interactions between the environment and carbon cycling; thus, analysis of the evolution of the mean annual cycle in a fully prognostic Earth system model may provide insight into the multi-decadal influence of environmental change on the carbon cycle. We analyzed the evolution of the mean annual cycle in atmospheric CO2 simulated by the Community Earth System Model (CESM) from 1950 to 2300 under three scenarios designed to separate the effects of climate change, atmospheric CO2 fertilization, and land use change. The NH CO2 seasonal amplitude increase in the CESM mainly reflected enhanced primary productivity during the growing season due to climate change and the combined effects of CO2 fertilization and nitrogen deposition over the mid- and high latitudes. However, the simulations revealed shifts in key climate drivers of the atmospheric CO2 seasonality that were not apparent before 2100. CO2 fertilization and nitrogen deposition in boreal and temperate ecosystems were the largest contributors to mean annual cycle amplification over the midlatitudes for the duration of the simulation (1950–2300). Climate change from boreal ecosystems was the main driver of Arctic CO2 annual cycle amplification between 1950 and 2100, but CO2 fertilization had a stronger effect on the Arctic CO2 annual cycle amplitude during 2100–2300. Prior to 2100, the NH CO2 annual cycle amplitude increased in conjunction with an increase in the NH land carbon sink. However, these trends decoupled after 2100, underscoring that an increasing atmospheric CO2 annual cycle amplitude does not necessarily imply a strengthened terrestrial carbon sink.
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Isaia, Ion. "Regional Particularities of the Metonic Meteorological Cycle on Earth". Present Environment and Sustainable Development 10, n. 2 (1 ottobre 2016): 119–32. http://dx.doi.org/10.1515/pesd-2016-0030.
Testo completoAbstract (sommario):
Abstract This paper intends to demonstrate that, on Terra's surface, there are cycles of air's temperature and of other meteorological elements having a duration of 19 years (the Metonic cycle). These 19-year cycles are recorded on every continent, especially in temperate climate areas where the (planetary) Rossby waves exhibit very clearly. As in the case of other cycles of meteorological elements, the atmospheric tides play a very important role in their occurrence. In the case of this cycle, the atmospheric tides are also generated mainly by Moon’s and Sun’s attraction.
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Antico, Andrés, Olivier Marchal, Lawrence A. Mysak e Françoise Vimeux. "Milankovitch Forcing and Meridional Moisture Flux in the Atmosphere: Insight from a Zonally Averaged Ocean–Atmosphere Model". Journal of Climate 23, n. 18 (15 settembre 2010): 4841–55. http://dx.doi.org/10.1175/2010jcli3273.1.
Testo completoAbstract (sommario):
Abstract A 1-Myr-long time-dependent solution of a zonally averaged ocean–atmosphere model subject to Milankovitch forcing is examined to gain insight into long-term changes in the planetary-scale meridional moisture flux in the atmosphere. The model components are a one-dimensional (latitudinal) atmospheric energy balance model with an active hydrological cycle and an ocean circulation model representing four basins (Atlantic, Indian, Pacific, and Southern Oceans). This study finds that the inclusion of an active hydrological cycle does not significantly modify the responses of annual-mean air and ocean temperatures to Milankovitch forcing found in previous integrations with a fixed hydrological cycle. Likewise, the meridional overturning circulation of the North Atlantic Ocean is not significantly affected by hydrological changes. Rather, it mainly responds to precessionally driven variations of ocean temperature in subsurface layers (between 70- and 500-m depth) of this basin. On the other hand, annual and zonal means of evaporation rate and meridional flux of moisture in the atmosphere respond notably to obliquity-driven changes in the meridional gradient of annual-mean insolation. Thus, when obliquity is decreased (increased), the meridional moisture flux in the atmosphere is intensified (weakened). This hydrological response is consistent with deuterium excess records from polar ice cores, which are characterized by dominant obliquity cycles.
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Taylor, Patrick C. "Variability of Regional TOA Flux Diurnal Cycle Composites at the Monthly Time Scale". Journal of the Atmospheric Sciences 71, n. 9 (28 agosto 2014): 3484–98. http://dx.doi.org/10.1175/jas-d-13-0336.1.
Testo completoAbstract (sommario):
Abstract Diurnal variability is a fundamental component of Earth’s climate system. Clouds, temperature, and precipitation exhibit robust responses to the daily cycle of solar insolation. Recent work indicates significant variability in the top-of-the-atmosphere (TOA) flux diurnal cycle in the tropics associated with monthly changes in the cloud diurnal cycle evolution. It has been proposed that the observed month-to-month variations in the TOA flux diurnal cycle are caused by anomalies in the atmospheric dynamic and thermodynamic state. This hypothesis is tested using a regression analysis to quantify the relationship between diurnal cycle shape and the atmospheric dynamic and thermodynamic state. TOA radiative fluxes are obtained from Clouds and the Earth’s Radiant Energy System (CERES) Edition 3 data and the atmospheric dynamic and thermodynamic state is taken from the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Re-Analysis. Four regions representing traditional diurnal cycle regimes are used in this analysis: North Africa (land nonconvective), central South America (land convective), Peru marine stratocumulus (ocean nonconvective), and Indian Ocean (ocean convective). The results show a statistically significant diurnal cycle shape change and cloud response related to monthly atmospheric state anomalies. Using the single-variable regression relationships to predict monthly diurnal cycle variability shows improvements of 1%–18% over assuming a climatological diurnal cycle shape; the most significant gains are found in North Africa. The proposed hypothesis, therefore, contributes to diurnal cycle variability explaining at least 10%–20% of the total monthly-mean diurnal cycle variability.
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Berner, R. A. "PALEOCLIMATE:The Sulfur Cycle and Atmospheric Oxygen". Science 282, n. 5393 (20 novembre 1998): 1426–27. http://dx.doi.org/10.1126/science.282.5393.1426.
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Taylor, John A. "Atmospheric mixing and the CO2seasonal cycle". Geophysical Research Letters 25, n. 22 (15 novembre 1998): 4173–76. http://dx.doi.org/10.1029/1998gl900018.
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Sunquist, Eric T., e Wallace S. Broecker. "The Carbon Cycle and Atmospheric CO2". Eos, Transactions American Geophysical Union 67, n. 15 (1986): 191. http://dx.doi.org/10.1029/eo067i015p00191.
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Boer, G. J., e S. Lambert. "The energy cycle in atmospheric models". Climate Dynamics 30, n. 4 (26 ottobre 2007): 371–90. http://dx.doi.org/10.1007/s00382-007-0303-4.
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Kloster, S., J. Feichter, E. Maier-Reimer, K. D. Six, P. Stier e P. Wetzel. "DMS cycle in the marine ocean-atmosphere system – a global model study". Biogeosciences 3, n. 1 (11 gennaio 2006): 29–51. http://dx.doi.org/10.5194/bg-3-29-2006.
Testo completoAbstract (sommario):
Abstract. A global coupled ocean-atmosphere modeling system is established to study the production of dimethylsulfide (DMS) in the ocean, the DMS flux to the atmosphere, and the resulting sulfur concentrations in the atmosphere. The DMS production and consumption processes in the ocean are simulated in the marine biogeochemistry model HAMOCC5, embedded in a ocean general circulation model (MPI-OM). The atmospheric model ECHAM5 is extended by the microphysical aerosol model HAM, treating the sulfur chemistry in the atmosphere and the evolution of the microphysically interacting internally- and externally mixed aerosol populations. We simulate a global annual mean DMS sea surface concentration of 1.8 nmol l−1, a DMS emission of 28 Tg(S) yr−1, a DMS burden in the atmosphere of 0.077 Tg(S), and a DMS lifetime of 1.0 days. To quantify the role of DMS in the atmospheric sulfur cycle we simulate the relative contribution of DMS-derived SO2 and SO42− to the total atmospheric sulfur concentrations. DMS contributes 25% to the global annually averaged SO2 column burden. For SO42− the contribution is 27%. The coupled model setup allows the evaluation of the simulated DMS quantities with measurements taken in the ocean and in the atmosphere. The simulated global distribution of DMS sea surface concentrations compares reasonably well with measurements. The comparison to SO42− surface concentration measurements in regions with a high DMS contribution to SO42− shows an overestimation by the model. This overestimation is most pronounced in the biologically active season with high DMS emissions and most likely caused by a too high simulated SO42− yield from DMS oxidation.
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Kloster, S., J. Feichter, E. Maier-Reimer, K. D. Six, P. Stier e P. Wetzel. "DMS cycle in the marine ocean-atmosphere system – a global model study". Biogeosciences Discussions 2, n. 4 (22 agosto 2005): 1067–126. http://dx.doi.org/10.5194/bgd-2-1067-2005.
Testo completoAbstract (sommario):
Abstract. A global coupled ocean-atmosphere modeling system is established to study the production of Dimethylsulfide (DMS) in the ocean, the DMS flux to the atmosphere, and the resulting sulfur concentrations in the atmosphere. The DMS production and consumption processes in the ocean are simulated in the marine biogeochemistry model HAMOCC5, embedded in a ocean general circulation model (MPI-OM). The atmospheric model ECHAM5 is extended by the microphysical aerosol model HAM, treating the sulfur chemistry in the atmosphere and the evolution of the microphysically interacting internally- and externally mixed aerosol populations. We simulate a global annual mean DMS sea surface concentration of 1.8 nmol/l, a DMS emission of 28 Tg(S)/yr, a DMS burden in the atmosphere of 0.077 Tg(S), and a DMS lifetime of 1.0 days. To quantify the role of DMS in the atmospheric sulfur cycle we simulate the relative contribution of DMS-derived SO2 and SO4-2 to the total atmospheric sulfur concentrations. DMS contributes 25% to the global annually averaged SO2 column burden. For SO4-2 the contribution is 27%. The coupled model setup allows the evaluation of the simulated DMS quantities with measurements taken in the ocean and in the atmosphere. The simulated global distribution of DMS sea surface concentrations compares reasonably well with measurements. The comparison to SO4-2 surface concentration measurements in regions with a high DMS contribution to SO4-2 shows an overestimation by the model. This overestimation is most pronounced in the biologically active season with high DMS emissions and most likely caused by a too high simulated SO4-2 yield from DMS oxidation.
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Brovkin, V., A. Ganopolski, D. Archer e G. Munhoven. "Glacial CO<sub>2</sub> cycle as a succession of key physical and biogeochemical processes". Climate of the Past Discussions 7, n. 3 (30 maggio 2011): 1767–95. http://dx.doi.org/10.5194/cpd-7-1767-2011.
Testo completoAbstract (sommario):
Abstract. During glacial-interglacial cycles, atmospheric CO2 concentration varied by about 100 ppmv in amplitude. While testing mechanisms that had led to the low glacial CO2 level could be done in equilibrium model experiments, an ultimate goal is to explain CO2 changes in transient simulations through the complete glacial-interglacial cycle. A computationally efficient Earth System model of intermediate complexity CLIMBER-2 is used to simulate global biogeochemistry over the last glacial cycle (126 kyr). The physical core of the model (atmosphere, ocean, land and ice sheets) is driven by orbital changes and reconstructed radiative forcing from greenhouses gases, ice, and aeolian dust. The carbon cycle model is able to reproduce the main features of the CO2 changes: a 50 ppmv CO2 drop during glacial inception, a minimum concentration at the last glacial maximum by 80 ppmv lower than the Holocene value, and an abrupt 60 ppmv CO2 rise during the deglaciation. The model deep ocean δ13C also resembles reconstructions from deep-sea cores. The main drivers of atmospheric CO2 evolve with time: changes in sea surface temperatures and in the volume of bottom water of southern origin controls atmospheric CO2 during the glacial inception and deglaciation, while changes in carbonate chemistry and marine biology are dominant during the first and second parts of the glacial cycle, respectively. These feedback mechanisms could also significantly impact the ultimate climate response to the anthropogenic perturbation.
25
Solomon, Abraham, Gang Chen e Jian Lu. "Finite-Amplitude Lagrangian-Mean Wave Activity Diagnostics Applied to the Baroclinic Eddy Life Cycle". Journal of the Atmospheric Sciences 69, n. 10 (4 giugno 2012): 3013–27. http://dx.doi.org/10.1175/jas-d-11-0294.1.
Testo completoAbstract (sommario):
Abstract Lagrangian-mean wave activity diagnostics are applied to the nonlinear baroclinic eddy life cycle in a simple general circulation model of the atmosphere. The growth of these instabilities through baroclinic conversion of potential temperature gradients and their subsequent barotropic decay can exhibit two distinct life cycles. One life cycle results in equatorward propagation of the growing eddy, anticyclonic wave breaking, and a poleward shift of the mean jet. The second life cycle is distinguished by limited equatorward propagation and cyclonic wave breaking on the poleward flank of the jet. Using a conservative finite-amplitude, Lagrangian-mean wave activity (negative pseudomomentum) to quantify wave growth and propagation reveals more details about the life cycles than could be discerned from eddy kinetic energy (EKE) or other Eulerian metrics. It is shown that the distribution of pseudomomentum relative to the latitude of the axis of the jet can be used to provide a clear distinction between the two life cycles at an early stage in their development and, hence, a prediction for the subsequent shift of the jet. This suggests that the distribution of pseudomomentum may provide some predictability for the atmospheric annular modes.
26
Tziperman, Eli, e Hezi Gildor. "The Stabilization of the Thermohaline Circulation by the Temperature–Precipitation Feedback". Journal of Physical Oceanography 32, n. 9 (1 settembre 2002): 2707–14. http://dx.doi.org/10.1175/1520-0485-32.9.2707.
Testo completoAbstract (sommario):
Abstract The meridional freshwater flux in the atmosphere, and hence the strength of the hydrological cycle, undergoes variations on glacial–interglacial as well as on some shorter timescales. A significant portion of these changes to the hydrological cycle are due to the temperature–precipitation feedback according to which there is more precipitation over the higher latitudes during warm periods when the moisture holding capacity of the atmosphere is higher. It is proposed here that this feedback may play an important role in determining the stability of the thermohaline circulation (THC). The THC stability to different parameterizations of the meridional atmospheric freshwater flux is therefore investigated using a simple box model of the ocean, atmosphere, and sea ice. It is demonstrated that parameterizations that are consistent with the temperature–precipitation feedback, and hence with the observed variations of the hydrological cycle during glacial–interglacial cycles, stabilize the THC for a wide range of forcing parameters.
27
Huang, Theresa Y. W., e Guy P. Brasseur. "Response of the Middle Atmosphere to Solar Variability — Model Simulations". International Astronomical Union Colloquium 143 (1994): 315–29. http://dx.doi.org/10.1017/s0252921100024817.
Testo completoAbstract (sommario):
Solar flux variations could affect the middle atmosphere through modulating the photolysis of chemical series and solar heating rates. Indirect feedback effects from chemical, radiative, and dynamical interactions could provide additional sources for perturbations in the middle atmosphere. In this paper, recent developments in modeling the effect of solar variability on the middle atmosphere is described. For the 27-day solar rotational cycle, the temperature and ozone response in the stratosphere predicted by one- and two-dimensional models compares well with data analyses. For the 11-year solar cycle, model simulations suggest a non-negligible ozone/temperature response compared to changes produced by anthropogenic perturbations in the stratosphere. There is no sufficient long-term atmospheric dataset to establish a statistically significant correlation with the 11-year solar cycle. But in general, agreement between the observational analysis (for periods of one to two solar cycles) and model simulations of the long-term solar variability effect is unsatisfactory.
28
He, Shuzhong, Zhongming Chen e Xuan Zhang. "Photochemical reactions of methyl and ethyl nitrate: a dual role for alkyl nitrates in the nitrogen cycle". Environmental Chemistry 8, n. 6 (2011): 529. http://dx.doi.org/10.1071/en10004.
Testo completoAbstract (sommario):
Environmental contextAlkyl nitrates are considered to be important intermediates in the atmospheric hydrocarbons–nitrogen oxides–ozone cycle, which significantly determines air quality and nitrogen exchange between the atmosphere and the Earth’s surfaces. The present laboratory study investigates reaction products of alkyl nitrates to elucidate their photochemical reaction mechanisms in the atmosphere. The results provide a better understanding of the role played by alkyl nitrates in the atmospheric environment. AbstractAlkyl nitrates (ANs) are important nitrogen-containing organic compounds and are usually considered to be temporary reservoirs of reactive nitrogen NOx (NO2 and NO) in the atmosphere, although their atmospheric fates are incompletely understood. Here a laboratory study of the gas-phase photolysis and OH-initiated reactions of methyl nitrate (CH3ONO2) and ethyl nitrate (C2H5ONO2), as models of atmospheric ANs, is reported with a focus on elucidating the detailed photochemical reaction mechanisms of ANs in the atmosphere. A series of intermediate and end products were well characterised for the first time from the photochemical reactions of methyl and ethyl nitrate conducted under simulated atmospheric conditions. Notably, for both the photolysis and OH-initiated reactions of CH3ONO2 and C2H5ONO2, unexpectedly high yields of HNO3 (photochemically non-reactive nitrogen) were found and also unexpectedly high yields of peroxyacyl nitrates (RC(O)OONO2, where R = H, CH3, CH3CH2,…) (reactive nitrogen) have been found as CH3C(O)OONO2 in the C2H5ONO2 reaction or proposed as HC(O)OONO2 in the CH3ONO2 reaction. Although the yields of HNO3 from the ANs under ambient conditions are likely variable and different from those obtained in the laboratory experiments reported here, the results imply that the ANs could potentially serve as a sink for reactive nitrogen in the atmosphere. The potential for this dual role of organic nitrates in the nitrogen cycle should be considered in the study of air quality and nitrogen exchange between the atmosphere and surface. Finally, an attempt was made to estimate the production of HNO3 and peroxyacyl nitrates derived from NOx by ANs as intermediates in the atmosphere.
29
Murphy, JO. "Annual Reconstruction of the Solar Cycle from Atmospheric 14C Variations". Australian Journal of Physics 43, n. 3 (1990): 357. http://dx.doi.org/10.1071/ph900357.
Testo completoAbstract (sommario):
Initially, the rise and fall components of the ll-year solar sunspot cycle are approximated by separate least-squares polynomials for four cycle classifications, which are determined by the magnitude of the average of the annual sunspot numbers per cycle. Following, a method is formulated to generate detailed reconstruction of the annual variation of a solar cycle based on this cycle average, and the results obtained for cycles -4 through to 21 are compared with the annual Zurich values. This procedure is then employed to establish annual sunspot numbers using published average cycle values obtained from atmospheric carbon 14 variations, which have been derived from the chemical analysis of tree ring sections. The reconstructed sequences are correlated with the observed cycle values and with tree ring width index chronologies which exhibit a significant II-year periodicity. It is anticipated that the long carbon 14 records and parallel dendrochronological data could be employed to obtain a more detailed portrayal of previous periods of strong solar activity than that given by current estimates based on historical records.
30
Wu, Xingren, W. F. Budd e Ian Simmonds. "Sensitivity of the Antarctic sea ice distribution to its advection in a general circulation model". Antarctic Science 9, n. 4 (dicembre 1997): 445–55. http://dx.doi.org/10.1017/s0954102097000588.
Testo completoAbstract (sommario):
A dynamic-thermodynamic sea ice model is used and coupled with an atmospheric general circulation model to simulate the seasonal cycle of the global sea ice distribution. We have run the coupled system and obtain a creditable seasonal simulation of the Antarctic sea ice. To understand the role of ice advection on the seasonal cycle of Antarctic sea ice in the coupled system, results from the thermodynamiconly (T) sea ice model have been compared with those from the dynamic thermodynamic (DT) sea ice model. The seasonal cycle of sea ice differs between the two models. When ice motion is eliminated sea ice becomes more compact and thinner, and sea ice is more extensive in summer. A number of previous studies have examined the effect of ice dynamics on sea ice simulations with prescribed atmospheric conditions. Here experiments have been performed with a fully coupled atmosphere sea ice system and also using prescribed daily atmospheric forcing and monthly mean atmospheric forcing, to examine the differences of the sensitivity of the ice advection between the coupled and forcing models. Similar differences have been observed between DT and T in the forcing models but the magnitude is smaller than in the fully coupled model, and with monthly mean atmospheric forcing the difference is least. These differences highlight the importance of the inclusion of ice advection when undertaking studies using a fully interactive atmosphere sea ice model, or using prescribed daily/monthly atmospheric conditions to force a sea ice model for the Antarctic.
31
Hack, James J., Julie M. Caron, Stephen G. Yeager, Keith W. Oleson, Marika M. Holland, John E. Truesdale e Philip J. Rasch. "Simulation of the Global Hydrological Cycle in the CCSM Community Atmosphere Model Version 3 (CAM3): Mean Features". Journal of Climate 19, n. 11 (1 giugno 2006): 2199–221. http://dx.doi.org/10.1175/jcli3755.1.
Testo completoAbstract (sommario):
Abstract The seasonal and annual climatological behavior of selected components of the hydrological cycle are presented from coupled and uncoupled configurations of the atmospheric component of the Community Climate System Model (CCSM) Community Atmosphere Model version 3 (CAM3). The formulations of processes that play a role in the hydrological cycle are significantly more complex when compared with earlier versions of the atmospheric model. Major features of the simulated hydrological cycle are compared against available observational data, and the strengths and weaknesses are discussed in the context of specified sea surface temperature and fully coupled model simulations. The magnitude of the CAM3 hydrological cycle is weaker than in earlier versions of the model, and is more consistent with observational estimates. Major features of the exchange of water with the surface, and the vertically integrated storage of water in the atmosphere, are generally well captured on seasonal and longer time scales. The water cycle response to ENSO events is also very realistic. The simulation, however, continues to exhibit a number of long-standing biases, such as a tendency to produce double ITCZ-like structures in the deep Tropics, and to overestimate precipitation rates poleward of the extratropical storm tracks. The lower-tropospheric dry bias, associated with the parameterized treatment of convection, also remains a simulation deficiency. Several of these biases are exacerbated when the atmosphere is coupled to fully interactive surface models, although the larger-scale behavior of the hydrological cycle remains nearly identical to simulations with prescribed distributions of sea surface temperature and sea ice.
32
P Kalaiselvi, RM Devi, E Parameswari, SP Sebastian, V Dayamani e T Ilakiya. "The ocean carbon pool: a vital component of the global carbon cycle". Journal of Agriculture and Ecology 17 (10 novembre 2023): 80–84. http://dx.doi.org/10.58628/jae-2317-314.
Testo completoAbstract (sommario):
The global carbon cycle is an integral part of the Earth System. Of the land, atmosphere, and ocean components of the global carbon cycle that exchange carbon on the timescales of decades to centuries, the ocean contains more than 90% of carbon. The ocean carbon pool represents a critical component of the Earth's carbon cycle, playing a pivotal role in regulating atmospheric carbon dioxide (CO2) levels and influencing climate dynamics. The exponential increase of total anthropogenic CO2 emissions in the industrial era implies the ocean's uptake has increased exponentially, reaching 2.5 ± 0.6 Pg C yr-1 for 2009-2018. Without the ocean and land sinks, atmospheric CO2 levels would be close to 600 ppm. The ocean carbon pool comprises dissolved inorganic carbon (DIC), organic carbon, and particulate organic matter, collectively responsible for the sequestration and release of carbon into the atmosphere. Phytoplankton, the microscopic marine plants, play a fundamental role in the oceanic carbon cycle by photosynthesizing and fixing atmospheric CO2 into organic matter. This organic matter can be transferred to the deep ocean through the biological pump, further contributing to the storage of carbon in the form of sinking particles. The bulk of the global ocean margin represents a carbon sink of ~0.1-0.2 Pg C. Oceanic processes, such as ocean circulation and upwelling, help redistribute carbon from surface waters to the deep ocean. The solubility pump, which is driven by changes in temperature and salinity, also affects the solubility of CO2 in seawater. These natural processes work to mitigate the increase in atmospheric CO2 concentrations and help regulate global temperatures.
33
Norin, Lars. "Observations of anomalous propagation over waters near Sweden". Atmospheric Measurement Techniques 16, n. 7 (4 aprile 2023): 1789–801. http://dx.doi.org/10.5194/amt-16-1789-2023.
Testo completoAbstract (sommario):
Abstract. Radio waves propagating in the atmosphere are affected by the prevailing atmospheric state. The state of the atmosphere can cause radio waves to refract more or less towards the ground. When the refractive index of the atmosphere differs from standard atmospheric conditions, the propagation is considered to be anomalous. Radars which are affected by anomalous propagation can observe ground clutter far beyond the radar horizon. In this work, 4.5 years' worth of data from five operational Swedish C-band dual-polarization weather radars are presented. Analyses of the data reveal a strong seasonal cycle and a weaker diurnal cycle in ground clutter from coastal regions across nearby waters. A comparison was drawn between the impacts of anomalous propagation on ground clutter measured with horizontal polarization and vertical polarization, respectively; however, no clear difference was found.
34
Archibald, David C. "Climate Outlook to 2030". Energy & Environment 18, n. 5 (settembre 2007): 615–20. http://dx.doi.org/10.1260/0958-305x.18.5.615.
Testo completoAbstract (sommario):
Our forecast for global average temperature to 2030 has been updated for the progression of Solar Cycle 23 and the contribution that will be made by increased carbon dioxide in the atmosphere. The increased length of Solar Cycle 23 supports the view that Solar Cycle 24 will be weak, with the consequence of increased certainty that that there will be a global average temperature decline in the range of 1° to 2°C for the forecast period. The projected increase of 40 ppm in atmospheric carbon dioxide to 2030 is calculated to contribute a global atmospheric temperature increase of 0.04°C. The anthropogenic contribution to climate change over the forecast period will be insignificant relative to natural cyclic variation.
35
Dirmeyer, Paul A., Randal D. Koster e Zhichang Guo. "Do Global Models Properly Represent the Feedback between Land and Atmosphere?" Journal of Hydrometeorology 7, n. 6 (1 dicembre 2006): 1177–98. http://dx.doi.org/10.1175/jhm532.1.
Testo completoAbstract (sommario):
Abstract The Global Energy and Water Cycle Experiment/Climate Variability and Predictability (GEWEX/CLIVAR) Global Land–Atmosphere Coupling Experiment (GLACE) has provided an estimate of the global distribution of land–atmosphere coupling strength during boreal summer based on the results from a dozen weather and climate models. However, there is a great deal of variation among models, attributable to a range of sensitivities in the simulation of both the terrestrial and atmospheric branches of the hydrologic cycle. It remains an open question whether any of the models, or the multimodel estimate, reflects the actual pattern and strength of land–atmosphere coupling in the earth’s hydrologic cycle. The authors attempt to diagnose this by examining the local covariability of key atmospheric and land surface variables both in models and in those few locations where comparable, relatively complete, long-term measurements exist. Most models do not encompass well the observed relationships between surface and atmospheric state variables and fluxes, suggesting that these models do not represent land–atmosphere coupling correctly. Specifically, there is evidence that systematic biases in near-surface temperature and humidity among all models may contribute to incorrect surface flux sensitivities. However, the multimodel mean generally validates better than most or all of the individual models. Regional precipitation behavior (lagged autocorrelation and predisposition toward maintenance of extremes) between models and observations is also compared. Again a great deal of variation is found among the participating models, but remarkably accurate behavior of the multimodel mean.
36
Li, Tao, Laura F. Robinson, Tianyu Chen, Xingchen T. Wang, Andrea Burke, James W. B. Rae, Albertine Pegrum-Haram et al. "Rapid shifts in circulation and biogeochemistry of the Southern Ocean during deglacial carbon cycle events". Science Advances 6, n. 42 (ottobre 2020): eabb3807. http://dx.doi.org/10.1126/sciadv.abb3807.
Testo completoAbstract (sommario):
The Southern Ocean plays a crucial role in regulating atmospheric CO2 on centennial to millennial time scales. However, observations of sufficient resolution to explore this have been lacking. Here, we report high-resolution, multiproxy records based on precisely dated deep-sea corals from the Southern Ocean. Paired deep (∆14C and δ11B) and surface (δ15N) proxy data point to enhanced upwelling coupled with reduced efficiency of the biological pump at 14.6 and 11.7 thousand years (ka) ago, which would have facilitated rapid carbon release to the atmosphere. Transient periods of unusually well-ventilated waters in the deep Southern Ocean occurred at 16.3 and 12.8 ka ago. Contemporaneous atmospheric carbon records indicate that these Southern Ocean ventilation events are also important in releasing respired carbon from the deep ocean to the atmosphere. Our results thus highlight two distinct modes of Southern Ocean circulation and biogeochemistry associated with centennial-scale atmospheric CO2 jumps during the last deglaciation.
37
Angot, Hélène, Olivier Magand, Detlev Helmig, Philippe Ricaud, Boris Quennehen, Hubert Gallée, Massimo Del Guasta et al. "New insights into the atmospheric mercury cycling in central Antarctica and implications on a continental scale". Atmospheric Chemistry and Physics 16, n. 13 (8 luglio 2016): 8249–64. http://dx.doi.org/10.5194/acp-16-8249-2016.
Testo completoAbstract (sommario):
Abstract. Under the framework of the GMOS project (Global Mercury Observation System) atmospheric mercury monitoring has been implemented at Concordia Station on the high-altitude Antarctic plateau (75°06′ S, 123°20′ E, 3220 m above sea level). We report here the first year-round measurements of gaseous elemental mercury (Hg(0)) in the atmosphere and in snowpack interstitial air on the East Antarctic ice sheet. This unique data set shows evidence of an intense oxidation of atmospheric Hg(0) in summer (24-hour daylight) due to the high oxidative capacity of the Antarctic plateau atmosphere in this period of the year. Summertime Hg(0) concentrations exhibited a pronounced daily cycle in ambient air with maximal concentrations around midday. Photochemical reactions and chemical exchange at the air–snow interface were prominent, highlighting the role of the snowpack on the atmospheric mercury cycle. Our observations reveal a 20 to 30 % decrease of atmospheric Hg(0) concentrations from May to mid-August (winter, 24 h darkness). This phenomenon has not been reported elsewhere and possibly results from the dry deposition of Hg(0) onto the snowpack. We also reveal the occurrence of multi-day to weeklong atmospheric Hg(0) depletion events in summer, not associated with depletions of ozone, and likely due to a stagnation of air masses above the plateau triggering an accumulation of oxidants within the shallow boundary layer. Our observations suggest that the inland atmospheric reservoir is depleted in Hg(0) in summer. Due to katabatic winds flowing out from the Antarctic plateau down the steep vertical drops along the coast and according to observations at coastal Antarctic stations, the striking reactivity observed on the plateau most likely influences the cycle of atmospheric mercury on a continental scale.
38
Archer, D. "A model of the methane cycle, permafrost, and hydrology of the Siberian continental margin". Biogeosciences 12, n. 10 (21 maggio 2015): 2953–74. http://dx.doi.org/10.5194/bg-12-2953-2015.
Testo completoAbstract (sommario):
Abstract. A two-dimensional model of a sediment column, with Darcy fluid flow, biological and thermal methane production, and permafrost and methane hydrate formation, is subjected to glacial–interglacial cycles in sea level, alternately exposing the continental shelf to the cold atmosphere during glacial times and immersing it in the ocean in interglacial times. The glacial cycles are followed by a "long-tail" 100 kyr warming due to fossil fuel combustion. The salinity of the sediment column in the interior of the shelf can be decreased by hydrological forcing to depths well below sea level when the sediment is exposed to the atmosphere. There is no analogous advective seawater-injecting mechanism upon resubmergence, only slower diffusive mechanisms. This hydrological ratchet is consistent with the existence of freshwater beneath the sea floor on continental shelves around the world, left over from the last glacial period. The salt content of the sediment column affects the relative proportions of the solid and fluid H2O-containing phases, but in the permafrost zone the salinity in the pore fluid brine is a function of temperature only, controlled by equilibrium with ice. Ice can tolerate a higher salinity in the pore fluid than methane hydrate can at low pressure and temperature, excluding methane hydrate from thermodynamic stability in the permafrost zone. The implication is that any methane hydrate existing today will be insulated from anthropogenic climate change by hundreds of meters of sediment, resulting in a response time of thousands of years. The strongest impact of the glacial–interglacial cycles on the atmospheric methane flux is due to bubbles dissolving in the ocean when sea level is high. When sea level is low and the sediment surface is exposed to the atmosphere, the atmospheric flux is sensitive to whether permafrost inhibits bubble migration in the model. If it does, the atmospheric flux is highest during the glaciating, sea level regression (soil-freezing) part of the cycle rather than during deglacial transgression (warming and thawing). The atmospheric flux response to a warming climate is small, relative to the rest of the methane sources to the atmosphere in the global budget, because of the ongoing flooding of the continental shelf. The increased methane flux due to ocean warming could be completely counteracted by a sea level rise of tens of meters on millennial timescales due to the loss of ice sheets, decreasing the efficiency of bubble transit through the water column. The model results give no indication of a mechanism by which methane emissions from the Siberian continental shelf could have a significant impact on the near-term evolution of Earth's climate, but on millennial timescales the release of carbon from hydrate and permafrost could contribute significantly to the fossil fuel carbon burden in the atmosphere–ocean–terrestrial carbon cycle.
39
Nakayama, T. "Visualization of the missing role of hydrothermal interactions in a Japanese megalopolis for a win–win solution". Water Science and Technology 66, n. 2 (1 luglio 2012): 409–14. http://dx.doi.org/10.2166/wst.2012.205.
Testo completoAbstract (sommario):
The urban heat island effect has become a serious environmental problem with the expansion of cities and industrial areas. Prohibition of the use of groundwater has caused a further serious problem such as floating of subways, stations and buildings through an imbalance of the hydrologic cycle in a Japanese megalopolis. Most of the previous research has evaluated separately hydrologic and thermal cycles in atmospheric, land and water areas because of the complexity in this feedback mechanism. In this study, the author used the process-based National Integrated Catchment-based Eco-hydrology (NICE) model, which includes surface–unsaturated–saturated water processes coupled with the urban canopy and regional atmospheric models, to simulate the effect of urban geometry and anthropogenic exhaustion on the hydrothermal changes in the atmospheric/land areas of the Japanese megalopolis. The simulation was conducted with multi-scale in horizontal regional–urban-point levels and in vertical atmosphere–surface–unsaturated–saturated layers, and projected the effect of water resources use to ameliorate the heat island and its impact on the hydrologic change in the catchment. Finally, the author presented the procedure to visualize the missing role of hydrothermal interactions in atmospheric, land and water areas, which would be effective to recover a sound hydrologic cycle and to create thermally pleasing environments in an eco-conscious megalopolis.
40
Ogata, Tomomichi, e Shang-Ping Xie. "Semiannual Cycle in Zonal Wind over the Equatorial Indian Ocean". Journal of Climate 24, n. 24 (15 dicembre 2011): 6471–85. http://dx.doi.org/10.1175/2011jcli4243.1.
Testo completoAbstract (sommario):
Abstract The semiannual cycle in zonal wind over the equatorial Indian Ocean is investigated by use of ocean–atmospheric reanalyses, and linear ocean–atmospheric models. In observations, the semiannual cycle in zonal wind is dominant on the equator and confined in the planetary boundary layer (PBL). Results from a momentum budget analysis show that momentum advection generated by the cross-equatorial monsoon circulation is important for the semiannual zonal-wind cycle in the equatorial Indian Ocean. In experiments with a linearized primitive model of the atmosphere, semiannual momentum forcing due to the meridional advection over the central equatorial Indian Ocean is important to simulate the observed maxima of the semiannual cycle in equatorial zonal wind. Off Somalia, diabatic heating and surface friction over land weaken the semiannual response to large momentum forcing there. Results from a linear ocean model suggest that the semiannual zonal wind stress over the central equatorial Indian Ocean generates large semiannual variability in zonal current through a basin-mode resonance.
41
Moon, Woosok, e Steven B. Feldstein. "Two Types of Baroclinic Life Cycles during the Southern Hemisphere Summer". Journal of the Atmospheric Sciences 66, n. 5 (1 maggio 2009): 1401–17. http://dx.doi.org/10.1175/2008jas2826.1.
Testo completoAbstract (sommario):
Abstract Baroclinic eddy life cycles of the Southern Hemisphere (SH) summer are investigated with NCEP–NCAR reanalysis data. A composite analysis is performed for the years 1980 through 2004. Individual life cycles are identified by local maxima in synoptic-scale eddy energy. Two types of baroclinic life cycles are examined, each defined by the strength of the barotropic energy conversion 2 days prior to the maximum baroclinic growth. For one life cycle, the barotropic conversion is anomalously weak before the maximum baroclinic growth; for the other, the barotropic conversion is anomalously strong. These two life cycles are referred to as the weak barotropic (WB) and strong barotropic (SB) life cycles. The analyses for the WB life cycle find that a poleward anomalous wave activity flux is observed within the SH tropics and subtropics just before the initial growth of the synoptic-scale eddies. In contrast, the SB life cycle exhibits an equatorward anomalous wave activity flux prior to the initial wave development. For the WB life cycle, these changes in the wave activity flux are shown to induce a mean meridional circulation that weakens and broadens the midlatitude zonal mean jet and reduces the baroclinicity in the midlatitude lower troposphere. Opposite characteristics are observed for the SB life cycle. Since the eddy growth rate is found to be greater in the WB life cycle, these results suggest that the influences of the barotropic governor mechanism (a reduction in horizontal shear coinciding with more rapidly growing baroclinic eddies) and the midlatitude baroclinicity oppose each other at the beginning of the life cycle, with the former being dominant. Both the WB and SB life cycles coincide with anomalous tropical convection. For the WB life cycle, there is a strengthening of the convection over the Maritime Continent, and for the SB life cycle there is a weakening in the convection over the same region. These results suggest that the two types of baroclinic life cycles are ultimately triggered by convection in the tropics.
42
Lowe, D. C., e W. Allan. "A Simple Procedure for Evaluating Global Cosmogenic 14C Production in the Atmosphere Using Neutron Monitor Data". Radiocarbon 44, n. 1 (2002): 149–57. http://dx.doi.org/10.1017/s0033822200064754.
Testo completoAbstract (sommario):
Radiocarbon (14C) produced by cosmogenic processes in the atmosphere reacts rapidly with atomic oxygen to form 14CO. The primary sink for this species is oxidation by the OH radical, the single most important oxidation mechanism for pollutants in the atmosphere. Hence, knowledge of the spatial and temporal distribution of 14CO allows important inferences to be made about atmospheric transport processes and the distribution of OH. Because the chemical lifetime of 14CO against OH attack is relatively short, 1–3 months, its distribution in the atmosphere should show modulations due to changes in 14C production caused by variations in the solar cycle. In this work we present a simple methodology to provide a time series of global 14C production to help interpret time series of atmospheric 14CO measurements covering the whole of solar cycle 23. We use data from neutron monitors, a readily available proxy for global 14C production, and show that an existing 6-year time series of 14CO data from Baring Head, New Zealand, tracks changes in global 14C production at the onset of solar cycle 23.
43
Kunii, Masaru, Kosuke Ito e Akiyoshi Wada. "Preliminary Test of a Data Assimilation System with a Regional High-Resolution Atmosphere–Ocean Coupled Model Based on an Ensemble Kalman Filter". Monthly Weather Review 145, n. 2 (febbraio 2017): 565–81. http://dx.doi.org/10.1175/mwr-d-16-0068.1.
Testo completoAbstract (sommario):
An ensemble Kalman filter (EnKF) that uses a regional mesoscale atmosphere–ocean coupled model was preliminarily examined to provide realistic sea surface temperature (SST) estimates and to represent the uncertainties of SST in ensemble data assimilation strategies. The system was evaluated through data assimilation cycle experiments over a one-month period from July to August 2014, during which time a tropical cyclone (TC) as well as severe rainfall events occurred. The results showed that the data assimilation cycle with the coupled model reproduced SST distributions realistically even without assimilating SST and sea surface salinity observations, and atmospheric variables provided to ocean models can, therefore, control oceanic variables physically to some extent. The forecast error covariance calculated in the EnKF with the coupled model showed dependency on oceanic vertical mixing for near-surface atmospheric variables due to the difference of variability between the atmosphere and the ocean as well as the influence of SST variations on the atmospheric boundary layer. The EnKF with the coupled model reproduced the intensity change of Typhoon Halong (2014) during the mature phase more realistically than with an uncoupled atmosphere model, although there remained a degradation of the SST estimate, particularly around the Kuroshio region. This suggests that an atmosphere–ocean coupled data assimilation system should be developed that is able to physically control both atmospheric and oceanic variables.
44
Kanamori, Hironari, Tomo’omi Kumagai, Hatsuki Fujinami, Tetsuya Hiyama e Tetsuzo Yasunari. "Effects of Long- and Short-Term Atmospheric Water Cycles on the Water Balance over the Maritime Continent". Journal of Hydrometeorology 19, n. 9 (1 settembre 2018): 1413–27. http://dx.doi.org/10.1175/jhm-d-18-0052.1.
Testo completoAbstract (sommario):
Abstract This study investigated atmospheric water cycles over several time scales to understand the maintenance processes that control heavy precipitation over the islands of the Maritime Continent. Large island regions can be divided into land, coastal, and ocean areas based on the characteristics of both the hydrologic cycle and the diurnal variation in precipitation. Within the Maritime Continent, the major islands of Borneo and New Guinea exhibit different hydrologic cycles. Large-scale circulation variations, such as the seasonal cycle and the Madden–Julian oscillation, have a lesser effect on the hydrologic cycle over Borneo than over New Guinea because the effects depend on their shapes and locations. The impact of diurnal variations on both regional-scale circulation and water exchange between land and coastal regions is pronounced over both islands. The recycling ratio of precipitation, which can be related to stronger diurnal variation in the atmospheric water cycle that results from enhanced evapotranspiration over tropical rain forests, is higher over Borneo than over New Guinea.
45
Torres, Mark A., Nils Moosdorf, Jens Hartmann, Jess F. Adkins e A. Joshua West. "Glacial weathering, sulfide oxidation, and global carbon cycle feedbacks". Proceedings of the National Academy of Sciences 114, n. 33 (31 luglio 2017): 8716–21. http://dx.doi.org/10.1073/pnas.1702953114.
Testo completoAbstract (sommario):
Connections between glaciation, chemical weathering, and the global carbon cycle could steer the evolution of global climate over geologic time, but even the directionality of feedbacks in this system remain to be resolved. Here, we assemble a compilation of hydrochemical data from glacierized catchments, use this data to evaluate the dominant chemical reactions associated with glacial weathering, and explore the implications for long-term geochemical cycles. Weathering yields from catchments in our compilation are higher than the global average, which results, in part, from higher runoff in glaciated catchments. Our analysis supports the theory that glacial weathering is characterized predominantly by weathering of trace sulfide and carbonate minerals. To evaluate the effects of glacial weathering on atmospheric pCO2, we use a solute mixing model to predict the ratio of alkalinity to dissolved inorganic carbon (DIC) generated by weathering reactions. Compared with nonglacial weathering, glacial weathering is more likely to yield alkalinity/DIC ratios less than 1, suggesting that enhanced sulfide oxidation as a result of glaciation may act as a source of CO2 to the atmosphere. Back-of-the-envelope calculations indicate that oxidative fluxes could change ocean–atmosphere CO2 equilibrium by 25 ppm or more over 10 ky. Over longer timescales, CO2 release could act as a negative feedback, limiting progress of glaciation, dependent on lithology and the concentration of atmospheric O2. Future work on glaciation–weathering–carbon cycle feedbacks should consider weathering of trace sulfide minerals in addition to silicate minerals.
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Stein, Karl, Axel Timmermann, Eun Young Kwon e Tobias Friedrich. "Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks". Proceedings of the National Academy of Sciences 117, n. 9 (18 febbraio 2020): 4498–504. http://dx.doi.org/10.1073/pnas.1908670117.
Testo completoAbstract (sommario):
The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here, we use a transient run of an intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of 10. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared with the current climate. Sensitivity tests with a steady-state carbon cycle model indicate that the two mechanisms combined can reduce atmospheric carbon by 40 ppm, with ocean stratification acting early within a glacial cycle to amplify the carbon cycle response.
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Asaadi, Ali, e Vivek K. Arora. "Implementation of nitrogen cycle in the CLASSIC land model". Biogeosciences 18, n. 2 (29 gennaio 2021): 669–706. http://dx.doi.org/10.5194/bg-18-669-2021.
Testo completoAbstract (sommario):
Abstract. A terrestrial nitrogen (N) cycle model is coupled to the carbon (C) cycle in the framework of the Canadian Land Surface Scheme Including Biogeochemical Cycles (CLASSIC). CLASSIC currently models physical and biogeochemical processes and simulates fluxes of water, energy, and CO2 at the land–atmosphere boundary. CLASSIC is similar to most models and its gross primary productivity increases in response to increasing atmospheric CO2 concentration. In the current model version, a downregulation parameterization emulates the effect of nutrient constraints and scales down potential photosynthesis rates, using a globally constant scalar, as a function of increasing CO2. In the new model when nitrogen (N) and carbon (C) cycles are coupled, cycling of N through the coupled soil–vegetation system facilitates the simulation of leaf N amount and maximum carboxylation capacity (Vcmax) prognostically. An increase in atmospheric CO2 decreases leaf N amount and therefore Vcmax, allowing the simulation of photosynthesis downregulation as a function of N supply. All primary N cycle processes that represent the coupled soil–vegetation system are modelled explicitly. These include biological N fixation; treatment of externally specified N deposition and fertilization application; uptake of N by plants; transfer of N to litter via litterfall; mineralization; immobilization; nitrification; denitrification; ammonia volatilization; leaching; and the gaseous fluxes of NO, N2O, and N2. The interactions between terrestrial C and N cycles are evaluated by perturbing the coupled soil–vegetation system in CLASSIC with one forcing at a time over the 1850–2017 historical period. These forcings include the increase in atmospheric CO2, change in climate, increase in N deposition, and increasing crop area and fertilizer input, over the historical period. An increase in atmospheric CO2 increases the C:N ratio of vegetation; climate warming over the historical period increases N mineralization and leads to a decrease in the vegetation C:N ratio; N deposition also decreases the vegetation C:N ratio. Finally, fertilizer input increases leaching, NH3 volatilization, and gaseous losses of N2, N2O, and NO. These model responses are consistent with conceptual understanding of the coupled C and N cycles. The simulated terrestrial carbon sink over the 1959–2017 period, from the simulation with all forcings, is 2.0 Pg C yr−1 and compares reasonably well with the quasi observation-based estimate from the 2019 Global Carbon Project (2.1 Pg C yr−1). The contribution of increasing CO2, climate change, and N deposition to carbon uptake by land over the historical period (1850–2017) is calculated to be 84 %, 2 %, and 14 %, respectively.
48
Michaelides, Silas. "Lorenz Atmospheric Energy Cycle in Climatic Projections". Climate 9, n. 12 (10 dicembre 2021): 180. http://dx.doi.org/10.3390/cli9120180.
Testo completoAbstract (sommario):
The aim of this study is to investigate whether different Representative Concentration Pathways (RCPs), as they are determined in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC), lead to different regimes in the energetics components of the Lorenz energy cycle. The four energy forms on which this investigation is based are the zonal and eddy components of the available potential and kinetic energies. The corresponding transformations between these forms of energy are also studied. RCPs are time-dependent, consistent scenarios of concentrations of radiatively active gases and particles. In the present study, four RCPs are explored, namely, rcp26, rcp45, rcp60, rcp85; these represent projections (for the future period 2006–2100) that result in radiative forcing of approximately 2.6, 4.5, 6.0 and 8.5 Wm−2 at year 2100, respectively, relative to pre-industrial conditions. The results are presented in terms of time projections of the energetics components from 2020 to 2100 and show that the different RCPs yield diverse energetics regimes, consequently impacting the Lorenz energy cycle. In this respect, projections under different RCPs of the Lorenz energy cycle are presented.
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Hocke, Klemens, Francisco Navas-Guzmán, Lorena Moreira, Leonie Bernet e Christian Mätzler. "Diurnal Cycle in Atmospheric Water over Switzerland". Remote Sensing 9, n. 9 (31 agosto 2017): 909. http://dx.doi.org/10.3390/rs9090909.
Testo completo
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Aqramunnisah, D. A. Suriamihardja, A. H. Assegaf e B. A. Samad. "Phase Changes in the Atmospheric Hydrology Cycle". IOP Conference Series: Earth and Environmental Science 279 (5 settembre 2019): 012048. http://dx.doi.org/10.1088/1755-1315/279/1/012048.
Testo completo