Other
Scientific paper
May 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agusm.a51a..09m&link_type=abstract
American Geophysical Union, Spring Meeting 2002, abstract #A51A-09
Other
3334 Middle Atmosphere Dynamics (0341, 0342), 3349 Polar Meteorology, 3362 Stratosphere/Troposphere Interactions, 3367 Theoretical Modeling
Scientific paper
Observed atmospheric polar vortex reversals which correspond with the stratospheric sudden warming have been investigated by using the NCEP data. The strength of stratospheric polar vortex averaged over winter season in high latitudes has much fluctuations year by year. In the frequency distribution of the strength of the winter mean polar vortex ( zonal mean zonal wind ) during the past 50 years, we can see not the Gaussian which has one peak at mean value, but the double peaks which correspond with the strong westerly zonal mean wind and the weak one, respectively. _@Index of deceleration of stratospheric polar vortex in winter high latitudes was defined at each year, and fluctuation of the index was compared with other winter mean indexes in sub-tropical and mid-latitudinal regions, year by year. It was found that the polar vortex deceleration index has not only strong positive correlation with sub-tropical tropospheric jet but also negative correlation with mid-latitudinal stratospheric westerly wind. This fact implies that the polar vortex reversals happen with horizontal propagation of planetary waves from lower latitudes to higher latitudes, as well as the vertical propagation. Furthermore, this fact is consistent with the result of laboratory experiments of mine which is focused into horizontal propagation of planetary waves. In my shallow water rotating tank experiment, the weak initial westerly polar vortex is easily reversed, and the reversal of strong initial polar vortex is hard to happen. This property of the reversal suggests a positive feedback mechanism between the polar vortex and the reversal. Through weak initial westerly polar vortex, once the deceleration of polar vortex would happen, the secondary deceleration would happen much more easily, even if the polar vortex would be restored through the way of thermal process. As a result, the weak winter mean polar vortex may have a tendency to be maintained. Vice versa, in strong initial polar vortex. This mechanism can explain the above double peaks in the frequency distribution.
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