CESM1(WACCM) Stratospheric Aerosol Geoengineering Large Ensemble Project
Simone TilmesJadwiga H. RichterBen KravitzDouglas G. MacMartinMichael MillsIsla R. SimpsonAnne A. GlanvilleJohn FasulloAdam S. PhillipsJean‐François LamarqueJoseph TribbiaJim EdwardsSheri MickelsonSiddhartha Sankar Ghosh
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This paper describes the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) project, which promotes the use of a unique model dataset, performed with the Community Earth System Model, with the Whole Atmosphere Community Climate Model as its atmospheric component [CESM1(WACCM)], to investigate global and regional impacts of geoengineering. The performed simulations were designed to achieve multiple simultaneous climate goals, by strategically placing sulfur injections at four different locations in the stratosphere, unlike many earlier studies that targeted globally averaged surface temperature by placing injections in regions at or around the equator. This advanced approach reduces some of the previously found adverse effects of stratospheric aerosol geoengineering, including uneven cooling between the poles and the equator and shifts in tropical precipitation. The 20-member ensemble increases the ability to distinguish between forced changes and changes due to climate variability in global and regional climate variables in the coupled atmosphere, land, sea ice, and ocean system. We invite the broader community to perform in-depth analyses of climate-related impacts and to identify processes that lead to changes in the climate system as the result of a strategic application of stratospheric aerosol geoengineering.Keywords:
Geoengineering
Earth system science
The Arctic stratosphere winter season of 2021–2022 was characterized by a stable, cold stratospheric polar vortex with a volume of polar stratospheric clouds (PSC) close to the maximum values since 1980, before the beginning of minor sudden stratospheric warming (SSW) events in the late February and early March and major SSW on 20 March. Analysis of dynamical processes of the Arctic stratosphere using reanalysis data indicates that the main reasons for the strengthening of the stratospheric polar vortex in January–February are the minimum propagation of planetary wave activity from the troposphere to the stratosphere over the past 40 years and its reflection in the upper stratosphere–lower mesosphere in the second half of January. The first minor SSW was limited to the upper polar stratosphere, whereas the second one propagated to the middle and lower stratosphere and led to the disappearance of the PSC, which prevented significant ozone depletion. Both minor and major SSW events led to a weakening of the residual meridional circulation in the upper Arctic stratosphere and its intensification in the middle and lower stratosphere, which contributed to additional warming of the subpolar region and weakening of the polar vortex.
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Ozone Depletion
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Abstract. ESMs (Earth System Models) are important tools that help scientists understand the complexities of the Earth's climate. Advances in computing power have permitted the development of increasingly complex ESMs and the introduction of better, more accurate parameterizations of processes that are too complex to be described in detail. One of the least well-controlled parameterizations involves human activities and their direct impact at local and regional scales. In order to improve the direct representation of human activities and climate, we have developed a simple, scalable approach that we have named the POPEM module (POpulation Parameterization for Earth Models). This module computes monthly fossil fuel emissions at grid point scale using the modeled population projections. This paper shows how integrating POPEM parameterization into the CESM (Community Earth System Model) enhances the realism of global climate modeling, improving this beyond simpler approaches. The results show that it is indeed advantageous to model CO2 emissions and pollutants directly at model grid points rather than using the forcing approach. A major bonus of this approach is the increased capacity to understand the potential effects of localized pollutant emissions on long-term global climate statistics, thus assisting adaptation and mitigation policies.
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The stratosphere is an aeronautical resource whose use is of benefit to the government in delivering aviation services. It also provides a freely cooling environment making it suitable for hosting non-terrestrial data centers. However, the development of a framework enabling the utilization of the stratosphere requires further research attention. The research presents a multientity architecture that describes the role of a stratosphere-bound airport that supports the deployment and use of future stratosphere-based data centers. The solution being presented is intended to increase the operational duration of future deployed stratosphere-based data centers. The focus here is on enhancing the operational duration of the stratosphere-based data center. This is important for its role in future networks. Analysis shows that the proposed solution improved the operational duration by at least 33% and by up to 76% on average.
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Geoengineering
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Stratospheric wave propagation during the unusually cold NH early winter 99–00 is studied and compared to the recent cold winters of 94–95, 95–96 (the previous coldest NH winter) and 96–97. EP fluxes reveal less wave activity entered the stratosphere in 95–96 and 99–00, substantial temperature decreases during long periods of little wave activity in 94–95 and 99–00, and little wave propagation into the upper stratosphere in Nov 99–Jan 00 and Nov 95–mid‐Jan 96. 2‐D and 3‐D EP fluxes for 95–96 and 99–00 show both that wave activity was inhibited from propagating upward and poleward through the middle stratosphere until mid–Jan, and there was large horizontal propagation of wave activity in the middle and lower stratosphere during Nov and Dec. Thus, both less wave activity entering the stratosphere, and a background structure that prevented wave activity from propagating into the upper stratosphere, were important factors in producing unusually cold early winters in 95–96 and 99–00.
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Sub-Peaks of CO Concentration in the Stratosphere over Polar Regions during Winter to Spring Seasons
Analysis of CO from spaceborne ACE-FTS(Atmospheric Chemistry Experiment, Fourier Transform Spectrometer) and Aura-MLS(Aura satellite, Microwave Limb Sounder) satellite observations highlights the existence of a sub–peak in CO profiles from late winter to early spring in the polar regions of both the northern and southern hemispheres at the 10 hPa level(i.e., in the middle of the stratosphere). Further analysis of Aura-MLS satellite data demonstrates that air from the mesosphere, which is rich in CO, descends into the stratosphere gradually in early winter. Moreover, while the CO concentration in the upper stratosphere decreases rapidly during late winter, CO concentration in the middle stratosphere changes very slowly. This results in the dramatic emergence of a suspended spherical structure in the stratosphere, defined by high CO concentrations; the satellite observation shows such a sub-peak in the CO concentration profiles. Analysis of the MERRA(the Modern Era Retrospective-analysis for Research and Applications) assimilated data and OH concentrations from Aura-MLS satellite observations suggests that weakening of vertical transport from the mesosphere to stratosphere, enhancement of horizontal exchange, and recovery of the OH concentration may play important roles in reducing CO concentration in the upper stratosphere. However, CO in the middle stratosphere can survive for a relatively long time owing to both the isolation imposed by the transport barrier and the lower OH concentration in the polar regions, thus allowing the sub-peak to persist from late winter to spring.
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Sudden stratospheric warming
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Abstract By analyzing data from satellite measurements, a reanalysis, and a chemistry‐climate model, we found clear zonally uniform tidal signals in the tropical stratosphere, particularly during the Northern Hemisphere summer. Antisymmetric components with respect to the equator are dominant and are characterized by a vertical wavelength of ~15 km and a diurnal frequency. The temperature and vertical wind diurnal amplitudes in the stratosphere are 0.2–1 K and 1–7 mm s –1 , respectively. The latter is generally larger than the climatological ascent motion in the stratosphere. The observed latitudinal and vertical structures can be explained by the second, propagating, antisymmetric Hough mode. These tidal oscillations should be carefully considered in analyses of zonal mean fields at a particular universal time.
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Universal Time
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Abstract Using Microwave Limb Sounder (MLS) satellite observations, ERA‐Interim reanalysis data, and a chemistry transport model simulation, we analyze and investigate the causes of the asymmetric hemispheric trends of N 2 O, CH 4 , and HCl in the stratosphere during the period 2004–2012. We find significant hemispheric asymmetries in the trends of these trace gases in the midlatitude middle and lower stratosphere. With regard to N 2 O and CH 4 , the enhanced downwelling branch of the residual circulation in the Northern Hemisphere (NH) middle and upper stratosphere transports more N 2 O/CH 4 ‐poor air from the upper stratosphere to the lower stratosphere. The enhanced poleward meridional branch of the residual circulation in the Southern Hemisphere (SH) stratosphere brings more N 2 O/CH 4 ‐rich air from lower to middle latitudes. These processes therefore contribute to the negative trends of N 2 O and CH 4 in the NH lower stratosphere and the positive trends in the SH middle stratosphere. A corresponding positive trend is found for HCl in the NH, where the deep branch of the residual circulation located in the middle and upper stratosphere strengthens, bringing more HCl‐rich air downward to the lower stratosphere, while the shallow branch of the residual circulation in the lower stratosphere weakens and leads to enhanced conversion of chlorine‐containing source gases of different lifetimes to HCl. A reversed picture emerges in the SH, where the deep branch of the residual circulation in the middle and upper stratosphere weakens, while the shallow branch in the lower stratosphere strengthens, resulting in less HCl there. In addition, the southward shift of the upwelling branch of the residual circulation in recent decades can partly explain trace gas trends above 20 hPa, while the eddy mixing has a small effect on the trends. Understanding these contributions from different processes to the hemispheric asymmetries in trends of these trace gases can help us to evaluate more accurately future changes in stratospheric composition.
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Abstract. ESMs (Earth system models) are important tools that help scientists understand the complexities of the Earth's climate. Advances in computing power have permitted the development of increasingly complex ESMs and the introduction of better, more accurate parameterizations of processes that are too complex to be described in detail. One of the least well-controlled parameterizations involves human activities and their direct impact at local and regional scales. In order to improve the direct representation of human activities and climate, we have developed a simple, scalable approach that we have named the POPEM module (POpulation Parameterization for Earth Models). This module computes monthly fossil fuel emissions at grid-point scale using the modeled population projections. This paper shows how integrating POPEM parameterization into the CESM (Community Earth System Model) enhances the realism of global climate modeling, improving this beyond simpler approaches. The results show that it is indeed advantageous to model CO2 emissions and pollutants directly at model grid points rather than using the same mean value globally. A major bonus of this approach is the increased capacity to understand the potential effects of localized pollutant emissions on long-term global climate statistics, thus assisting adaptation and mitigation policies.
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The bulk of O sub 3 destruction in the Antarctic stratosphere takes place in the lower stratosphere between 15 and 25 km. Both O sub 3 and the halogen reservoir species have their origins in the higher altitude region (20 to 30 km) in the equatorial and mid-latitude stratosphere. Using the Caltech-JPL two-dimensional residual circulation model, researchers investigate the growth of stratospheric halogen due to the increase of CFCl sub 3 and CF sub 2 Cl sub 2.
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