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Tropical Pacific impacts of convective momentum transport in the SNU coupled GCM |
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| Authors: | Daehyun Kim Jong-Seong Kug In-Sik Kang Fei-Fei Jin Andrew T Wittenberg |
| Institution: | 1. School of Earth and Environmental Sciences, Seoul National University, Seoul, South Korea 2. Climate Environmental System Research Center, Seoul National University, Seoul, South Korea 3. Department of Meteorology, SOEST, University of Hawaii, Honolulu, USA 4. Geophysical Fluid Dynamics Laboratory, NOAA, Princeton, USA |
| Abstract: | Impacts of convective momentum transport (CMT) on tropical Pacific climate are examined, using an atmospheric (AGCM) and coupled GCM (CGCM) from Seoul National University. The CMT scheme affects the surface mainly via a convection-compensating atmospheric subsidence which conveys momentum downward through most of the troposphere. AGCM simulations—with SSTs prescribed from climatological and El Nino Southern Oscillation (ENSO) conditions—show substantial changes in circulation when CMT is added, such as an eastward shift of the climatological trade winds and west Pacific convection. The CMT also alters the ENSO wind anomalies by shifting them eastward and widening them meridionally, despite only subtle changes in the precipitation anomaly patterns. During ENSO, CMT affects the low-level winds mainly via the anomalous convection acting on the climatological westerly wind shear over the central Pacific—so that an eastward shift of convection transfers more westerly momentum toward the surface than would occur without CMT. By altering the low-level circulation, the CMT further alters the precipitation, which in turn feeds back on the CMT. In the CGCM, CMT affects the simulated climatology by shifting the mean convection and trade winds eastward and warming the equatorial SST; the ENSO period and amplitude also increase. In contrast to the AGCM simulations, CMT substantially alters the El Nino precipitation anomaly patterns in the CGCM. Also discussed are possible impacts of the CMT-induced changes in climatology on the simulated ENSO. |
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