文档介绍：MARCH 2005 GRAY ET AL. 651
A Possible Influence of Equatorial Winds on the September 2002 Southern
Hemisphere Sudden Warming Event
LESLEY GRAY AND WARWICK NORTON
Meteorology Department, Reading University, Reading, United Kingdom
CHARLOTTE PASCOE
Rutherford Appleton Laboratory, Chilton, United Kingdom
ANDREW CHARLTON
Meteorology Department, Reading University, Reading, United Kingdom
(Manuscript received 23 May 2003, in final form 13 January 2004)
ABSTRACT
The stratospheric sudden warming in the Southern Hemisphere (SH) in September 2002 was unexpected
for two reasons. First, ary wave activity in the Southern Hemisphere is very weak, and midwinter
warmings have never been observed, at least not since observations of the upper stratosphere became
regularly available. Second, the warming occurred in a west phase of the quasi-biennial oscillation (QBO)
in the lower stratosphere. This is unexpected because warmings are usually considered to be more likely in
the east phase of the QBO, when a zero wind line is present in the winter subtropics and hence confines
ary wave propagation to higher latitudes closer to the polar vortex. At first, this evidence suggests that
the sudden warming must therefore be simply a result of anomalously strong ary wave forcing from
the troposphere. However, recent model studies have suggested that the midwinter polar vortex may also
be sensitive to the equatorial winds in the upper stratosphere, the region dominated by the semiannual
oscillation. In this paper, the time series of equatorial zonal winds from two different data sources, the 40-yr
ECMWF Re-Analysis (ERA) and the Met Office assimilated dataset, are reviewed. Both suggest that the
equatorial winds in the upper stratosphere above 10 hPa were anomalously easterly in 2002. Idealized model
experiments are described in which the modeled equatorial winds were relaxed toward these observations
for various years to examine whether the ano