HR: 0800h
AN: A31A-0015    [Abstracts]
TI: Precipitation and large scale circulation change with global warming in the coupled GCMs : effect of the SST forcing
AU: * Le Treut, H
EM: letreut@lmd.ens.fr
AF: Laboratoire de Météorologie Dynamique, 4 place Jussieu, PARIS, 75252, France
AU: Gastineau, G
EM: gglmd@lmd.jussieu.fr
AF: Laboratoire de Météorologie Dynamique, 4 place Jussieu, PARIS, 75252, France
AU: Li, Z
EM: li@lmd.jussieu.fr
AF: Laboratoire de Météorologie Dynamique, 4 place Jussieu, PARIS, 75252, France
AB: The features of the Sea Surface Temperature (SST) changes which may explain the response of the IPSL-CM4 atmosphere-ocean coupled models (AOGCM) in terms global circulation and precipitation patterns are diagnosed when the carbon dioxide concentration is doubled. Simulation using the atmospheric component of the IPSL-CM4 AOGCM, called LMDZ4, forced by prescribed SST are run. The AOGCM shows a global weakening of the Hadley/Walker circulation, accompanied with a comparatively smaller increase of the precipitation for southern hemisphere winter. For northern hemisphere winter an increase of the Hadley circulation is diagnosed. To explain the nature of these changes, we run specific atmospheric simulations in response respectively to the global mean SST changes, the zonal mean SST anomalies and the longitudinal anomalies of the SST fields. When forced by the uniform changes of the SST, the AGCM LMDZ4 fails to represent the horizontal pattern of the Hadley circulation changes. It is able to reproduce roughly the modifications in the intensity of the hydrological cycle, but fail to capture the main regional changes. Prescribing the zonal anomalies of SST changes is enough to represent fairly well the horizontal changes in the Hadley circulation simulated by the coupled model, even if the main thermodynamical state of the tropical atmosphere does not change. The longitudinal SST anomalies are shown to have a much lesser impact on the precipitation and on the large scale tropical circulation. The results show that the geographical (meridional and longitudinal) pattern of the SST warming are crucial to assess the Hadley circulation and the precipitation changes in the AGCM.
DE: 1610 Atmosphere (0315, 0325)
DE: 1626 Global climate models (3337, 4928)
DE: 3319 General circulation (1223)
DE: 3337 Global climate models (1626, 4928)
DE: 3374 Tropical meteorology
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting