Annular modes forced from the stratosphere and interactions with the oceans

Abstract

Long time-scale variations of the climate system can be induced by forcings loaded onto the stratosphere, such as increase of carbon dioxide, solar activity, and volcanic eruption, which is possibly modulated by the interaction with the oceans. Spatial structure of the atmospheric response resembles the Northern Annular Mode (NAM) in an experiment of a coupled atmosphere-ocean general circulation model with a westerly momentum forcing in the winter midlatitude stratosphere. The atmospheric response further induces distinctive patterns of the sea surface temperature (SST) change in the Atlantic and the Pacific, which are reminiscent of the observed decadal to interdecadal variability dominant in each basin. Investigation of oceanic feedback with the atmospheric model forced by the SST change suggests that the oceanic response has positive feedback effects on the NAM-like atmospheric structure, implying enforcement or maintenance of the response to the stratospheric forcing. The positive feedback effect in the Atlantic is significant in winter, while that in the Pacific is significant in spring. © 2007, Meteorological Society of Japan.