1. 1 Center for Ocean-Land-Atmosphere Studies, George Mason University, Fairfax, VA 22030 2 Department of Atmospheric, Oceanic and Earth Sciences, George Mason University, Fairfax, VA 22030 Projected changes of the tropical Atlantic vertical wind shear and its relationship with ENSO in the SP-CCSM4 Xiaojie Zhu 1, Li Xu 1, and Cristiana Stan 1,2 Model and Experiments Acknowledgements We thank all the scientists and software engineers who contributed to the development of the CCSM4 and the super-parameterization. This work has been supported by the Regional and Global Climate Modeling Program funded by U.S. Department of Energy, Office of Science under award number SC0006722. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Projected change of vertical wind shear in RCP8.5 ENSO-shear relationship Control run SP-CCSM4 CCSM4 Abstract The vertical wind shear over the tropical Atlantic and its relationship with ENSO are analyzed in the Super Parameterized Community Climate System Model version 4 (SP-CCSM4) and in the conventional CCSM4. The climatology of vertical wind shear over the tropical Atlantic and the ENSO-shear relationship are well simulated in the control runs of SP-CCSM4 and CCSM4. However, due to different representations of cloud processes, in a warmer climate such as the RCP8.5 scenario, the suppression of convection over the western Africa in SP-CCSM4 is stronger than in CCSM4. As a result, SP-CCSM4 projects increased westerlies at 200hPa that further contributes to an increased vertical wind shear over the equatorial Atlantic. Furthermore, in the RCP8.5 scenario, projection of the ENSO-shear relationship by the SP- CCSM4, with and without long-term linear trend, retains similar features as in observation. Conversely, the ENSO-shear relationship, with long-term trend, over the equatorial Atlantic projected by the CCSM4 is opposite to that in SP-CCSM4 and observation. Likewise, the two models simulate a different response of the tropical Atlantic SST to ENSO. These differences are also present in the response of tropical Atlantic precipitation and convection to ENSO in warmer climate. CAM CLM POP CICE CPL fv19 gx1_v6 CCSM4 Historical run, RCP8.5 2006 – 2100 CAM CLM POP CICE CPL fv09 gx1_v6 3 km SP-CCSM4 Control run, RCP8.5 2005 – 2100 Climatology in Control runs Walker Circulation and Convection Projected JASO ENSO pattern and its impact on cloud The JASO climatological mean vertical wind shear in (a) ERA-Interim reanalysis, and control run in (c) SP-CCSM4 and in (e) CCSM4. The JASO climatology zonal wind at 200hPa in (b) ERA-Interim reanalysis, control run in (d) SP-CCSM4 and in (f) CCSM4. Unit: m/s. Shading represents vertical wind shear lower than 10m/s. The regression of JASO mean vertical wind shear on JASO mean Niño3.4 index Climatology in the Control run Change in the RCP8.5 Scenario RCP8.5 Scenario Without trend With trend SP-CCSM4 CCSM4