HR: 1340h
AN: A43B-0049    [Abstracts]
TI: Oceanic Forcing Of The Interdecadal Trend In Sahel Rainfall
AU: * Lu, J
EM: Jian.Lu@noaa.gov
AF: University Corporation for Atmospheric Research and Geophysical Fluid Dynamics Laboratory, NOAA, Forrestal Campus, Princeton Unviersity, US Route 1, Princeton, NJ 08542 United States
AU: Delworth, T L
EM: Tom.Delworth@noaa.gov
AF: Geophysical Fluid Dynamics Laboratory, NOAA, Forrestal Campus, Princeton Unviersity, US Route 1, Princeton, NJ 08542 United States
AB: Sahel rainfall underwent a pronounced interdecadal drying trend since the 1960s. An ensemble of runs with AM2, an AGCM recently developed at GFDL, driven by the observed record of SST and sea ice from 1950 to 2003, can successfully capture the interdecadal trend as well as some of the interannual variability of Sahelian rainfall. An idealized experiment with only the trend component of the SST forcing reproduces the pattern of the rainfall trend and the associated circulation structure. Decomposing the SST trend into tropical Atlantic and Indian oceans seems able to differentiate the contributions from respective oceans. The oceanic forcing over the tropical Atlantic is characteristic of an inter-hemispheric dipole with warm SST anomalies to the south and cold to the north, which, in the model, generates anomalous wetness centered at 7 deg N, thus moving the center of the tropical Atlantic ITCZ slightly towards the equator. On the other hand, a warming Indian ocean SST drives a subsidence over most of the sub-Sahara, leading to an overall weakening of the tropical Atlantic-African ITCZ. The tropical circulation and mechanisms associated with these oceanic forcing are also discussed.
DE: 3322 Land/atmosphere interactions
DE: 3339 Ocean/atmosphere interactions (0312, 4504)
DE: 3374 Tropical meteorology
DE: 4215 Climate and interannual variability (3309)
DE: 3309 Climatology (1620)
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting