HR: 0830h
AN: A31E-0093    [PDF]
TI: Composite Evolution of the Northern Hemisphere Stratospheric Sudden Warming
AU: * Limpasuvan, V
EM: var@coastal.edu
AF: Department of Chemistry and Physics, Coastal Carolina University, Conway, SC 29526 United States
AU: Thompson, D W
EM: davet@atmos.colostate.edu
AF: Department of Atmospheric Sciences, Colorado State University, Fort Collins, CO 80523 United States
AU: Hartmann, D L
EM: dennis@atmos.washington.edu
AF: Department of Atmospheric Sciences, University of Washington, Seattle, WA 98195 United States
AB: This study examines the evolution of the atmospheric flow and wave fluxes during the composite life cycle of a stratospheric sudden warming (SSW) in the Northern Hemisphere. Previous studies of SSWs have focused on the evolution of the flow and wave fluxes at stratospheric levels. Motivated by recent evidence of strong coupling between the circulations of the stratosphere and troposphere during the Northern Hemisphere winter, we provide here a comprehensive analysis of the evolution of the flow and wave fluxes during a SSW at levels throughout the depth of the stratosphere and troposphere. During the onset of a SSW, the polar stratosphere is disturbed by poleward heat and momentum flux anomalies associated mainly with waves of zonal wavenumber one and two. When the waves break in the lower stratosphere, they act to weaken the strength of the circumpolar flow there, and drive an anomalous mean meridional circulation that gives rise to anomalously high polar stratospheric temperatures. As the SSW progresses, the induced stratospheric circulation anomalies descend to the lower stratosphere, where they coincide with the growth of anomalous equatorward momentum fluxes by waves in the upper troposphere centered near 50N, and by anomalous equatorward heat fluxes by waves in the lower troposphere centered near 60N. The anomalies in tropospheric wave activity are mainly associated with waves of zonal wavenumber four and higher, and are concentrated over the Atlantic half of the hemisphere. The anomalous upper tropospheric momentum fluxes drive anomalies in the tropospheric mean meridional circulation that transport easterly zonal wind anomalies from the upper troposphere to the surface where they compose negative polarity of the Northern Hemisphere Annular Mode (NAM).
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0340 Middle atmosphere--composition and chemistry
DE: 0399 General or miscellaneous
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting