Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling
07 January 2020

Climate Variability and Change of the SAM and SH Surface Zonal Winds in E3SM

Science

To reproduce the Southern Annular Mode (SAM) characteristics and position and strength of the surface zonal wind stress, the ability of two ensembles of Energy Exascale Earth System Model (E3SM) simulations, E3SM-HIST and AMIP, is assessed. The variability and change of the SAM in the two CO2 experiments (E3SM-1pctCO2 and 4xCO2) are also analyzed to show the model sensitivity in response to different types of increasing CO2 forcings. All E3SM simulations capture the dominant characteristics of the SAM in the SH reasonably well.

Impact

The relationship between the SAM and kinematic properties of the surface TAUX shows the variability of the SAM index was closely related to the kinematic properties of the surface TAUX. The overall results of Southern Hemisphere (SH) climate variability in the simulations are a promising indication for the E3SM coupled climate system. In addition, the E3SM- HIST and AMIP simulations covering the historical record provide useful information to better understand the atmospheric variability and ocean circulation in the SH through the model performance and diagnostic evaluation for the SAM and surface TAUX based on indirect/direct comparison with observations.

Summary

The variability and trend in the SAM and position and strength of the surface zonal wind stress (TAUX), using two ensembles of simulations covering the historical record from the Energy Exascale Earth System Model (E3SM-HIST and AMIP) for 1979–2014 are investigated. In addition, the performance of two CO2 forcing simulations from the E3SM (E3SM-1pctCO2 and 4xCO2) is assessed to examine the sensitivity of the variability and changes in the SAM and SH surface TAUX to climate forcing. In general, all E3SM simulations tend to capture the dominant feature of the SAM pattern reasonably well. The annual SAM index in the E3SM-HIST simulation shows a significant increasing trend. These features are similar to the trends in the strength (along with the poleward shift in the position) of the annual surface TAUX. For the climatological surface TAUX position and strength, the two CO2 forcing simulations show slightly poleward movement and stronger intensity, while the E3SM-HIST is equatorward and weaker than observations. Especially, the E3SM- HIST and AMIP simulations covering the historical record provide useful information to better understand the atmospheric variability and ocean circulation in the SH through the model performance and diagnostic evaluation for the SAM and surface TAUX.

Contact
Doo Young Lee
Los Alamos National Laboratory
Publications
Lee, D, MR Petersen, and W Lin.  2019.  "The Southern Annular Mode and Southern Ocean Surface Westerly Winds in E3SM."  Earth and Space Science 6: 1-20.  https://doi.org/10.1029/2019ea000663.