Aerosol versus greenhouse gas impacts on Southern Hemisphere general circulation changes
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This study re-examines the possible impacts of anthropogenic aerosols (AERs), which are primarily concentrated in the Northern Hemisphere extratropics, on atmospheric general circulation changes in the Southern Hemisphere (SH). The long-term trends of the SH Hadley Cell edge and Southern Annular Mode (SAM) are evaluated for the historical and single forcing experiments of 12 models archived for the Fifth Coupled Model Inter-comparison Project (CMIP5). The AER-induced temperature changes are typically opposite in sign to that of the greenhouse gas (GHG)-induced changes. However, the zonal-mean circulation changes driven by the AERs are not simply opposite to those due to the GHGs. Depending on the analysis period, they can be either opposite or the same as the GHG-induced ones. It is also found that the inter-model spread of AER-driven circulation changes is primarily dependent on the uncertainty of tropospheric temperature changes, particularly static stability changes in the subtropics, whereas that of GHG-induced changes in the austral summer is influenced by the uncertainty of both the tropospheric and polar lower-stratospheric temperature changes. This accentuates that the AER-induced SH circulation changes are not simply mirroring the GHG-induced ones.
This work was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1C1B1006827) and Korea Ministry of Environment as ‘Climate Change Correspondence Program’. We acknowledge the World Climate Research Programme’s Working Group on Coupled Modelling, which is responsible for CMIP, and we thank the climate modeling groups (listed in Table 1 of this paper) for producing and making available their model output. For CMIP, the U.S. Department of Energy’s Program for Climate Model Diagnosis and Intercomparison provides coordinating support and led the development of software infrastructure in partnership with the Global Organization for Earth System Science Portals. The HadSLP and Marshall-SAM index were obtained from the Met Office Hadley Centre (http://www.metoffice.gov.uk/hadobs/hadslp2/) and https://legacy.bas.ac.uk/met/gjma/sam.html, respectively. We thank Dr. Laura Wilcox for sharing HadGEM2-ES simulations. We thank two reviewers for their constructive comments.
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