München 2004 – wissenschaftliches Programm

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UP: Umweltphysik

UP 2: Atmosph
äre und Klima I

UP 2.7: Fachvortrag

Montag, 22. März 2004, 15:45–16:00, HS 118

Linear theory of tropical thermodynamics and the link between SST and West African rainfall in a regional climate model — •Heiko Paeth — Meteorologisches Institut, Universit"at Bonn, Auf dem H"ugel 20, 53121 Bonn

Here, we present sensitivity experiments from a regional climate model with respect to expected SST changes under global warming. This dynamical downscaling approach provides information about the nonlinear response of the atmosphere to oceanic heating. It has been suggested that this response is at least partly accounted for by the linear theory of tropical thermodynamics, involving a Kelvin and Rossby wave response to a tropical heat source. We compute the major modes of the linear Matsuno-Gill model for geopotential height and horizontal wind components and project the simulated response patterns onto these linear modes, in order to evaluate to which extent the simple linear theory may explain the SST-induced climate anomalies over Africa.

Increasing greenhouse-gas (GHG) concentrations are associated with a substantial warming of the oceanic surfaces in the low latitudes by about 2K, as revealed by a global climate model. Forcing the regional climate model by these warmer SSTs leads to substantial climate anomalies over tropical Africa: Rainfall is increasing over the Guinea Coast region (GCR) and tropical East Africa, but decreasing over the Congo Basin and the Sahel Zone (SHZ). These changes in the atmospheric dynamics strongly project onto the leading modes of the linear Matsuno-Gill model at various zonal wave numbers. The corresponding atmospheric heating pattern is highly reminiscent of the simulated nonlinear model reponse.