Seminars

Lecturer: Grigory Nikulin
Date: 2003-10-30 10:00
Place: Aniara

Influence of early winter wave activity on midwinter circulation in the stratosphere and troposphere

Using NCEP/NCAR reanalysis data we show that the November-December
averaged stratospheric eddy heat flux is strongly anticorrelated with
the January-February averaged eddy heat flux in the midlatitude
stratosphere and troposphere. This finding further emphasizes
differences between early and midwinter stratospheric wave activity
behavior, which have recently been found in long-term variations. Our
analysis suggests that this anticorrelation results from changes in
wave activity generation in the troposphere. Stronger (weaker) wave
activity in early winter leads to weaker (stronger) wave activity
generation in the troposphere during midwinter. We show also that
enhanced equatorward wave refraction during midwinter that is due to
the stronger polar night jet, is associated with weak wave activity in
the early winter. It is suggested that the effect of enhanced
midwinter wave activity generation in the troposphere in the years
with weak early winter wave activity overcompensates the effect of
increased equatorward wave refraction in midwinter, leading to a net
increase of the midwinter wave activity flux into the stratosphere.

Trends are opposite in early- (positive) and midwinter (negative) wave
activity for the 1979-2002 period. However, the early winter trends
are at the edge of statistical significance and very sensitive to the
choice of period in contrast to the midwinter trends.
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Created 2003-10-22 16:21:26 by
Last changed 2004-11-02 14:43:50 by Rick McGregor