Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Interannual Variations of Polar Climate: Relationships to Annual Modes
Murry Salby1
1Program in Atmospheric and Oceanic Sciences, University of Colorado, UCB 311, Boulder, CO, 80309, USA, mls@icarus.colorado.edu
The atmospheric circulation varies from one year to the next, involving time scales of a couple of years, as well as secular changes that operate coherently over decades. These interannual changes are
pronounced over the polar caps. They are represented in the so-called annular modes, which derive from the leading EOF of sea level pressure: the Northern Annular Mode (NAM) and Southern Annular MOde (SAM). Related to the Arctic Oscillation, and its counterpart over the Antarctic, the NAM and SAM describe variability that operates coherently from stratospheric levels down into the troposphere.
I will present an overview of annular modes, along with their involvement in intraseasonal changes
and long-term trends. Such behavior will be shown to bear a close relationship to changes of the residual mean circulation of the stratosphere. Comprised of downwelling over the winter pole and upwelling that compensates it at subpolar latitudes, the residual circulation is coupled to the troposphere through mass
continuity.
It is forced by momentum that is transmitted upward from the troposphere by planetary waves. Changes operating coherently with the residual circulation have the same basic structure as the NAM and SAM. They reflect changes
over the Arctic, as well as coherent changes in the storm tracks. Such changes account for nearly all of the interannual variance of Arctic temperature, even during unusually cold winters. A similar conclusion holds for wintertime ozone, which, like temperature, is regulated by the residual circulation.
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