Other
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.a11b0091h&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #A11B-0091
Other
3334 Middle Atmosphere Dynamics (0341, 0342), 3362 Stratosphere/Troposphere Interactions, 3384 Waves And Tides
Scientific paper
In a previous statistical analysis of the relationship between tropospheric and stratospheric wave 1 fields during Northern Hemisphere winter a significant correlation was found when the troposphere leads the stratosphere by a few days, which indicates upward propagation of planetary waves. It was also found that when the polar vortex is anomalously strong in the lower stratosphere, there is a second significant peak when the stratosphere leads the troposphere by a few days. It has been suggested that this peak is due to downward reflection of planetary waves, but this can not be verified by the statistical analysis. In this study we look closer at the data, using various dynamical based diagnostics to determine whether downward reflection is indeed the mechanism behind the statistical signal. Using the statistical analysis on individual winters allows us to choose those years during which the second peak signal is strongest. Looking at the wave geometry of the basic state of these years suggests that during strong vortex conditions, there is a very clear high latitude waveguide in the lower stratosphere, which guides any reflected wave activity back down to the troposphere, modifying the geopotential height wave field there. Looking at the time series used for the statistical analysis, we also find that the correlation comes from time scales corresponding to the wave life cycles. The daily evolution of wave 1 shows a clear life cycle of upward propagation, followed by downward reflection that occurs several times during the 90 day winter period, which is the source of the statistical correlation. These results suggest that downward reflection of waves, which is a direct mechanism by which the stratosphere can influence the troposphere, might contribute significantly to the coupling between the troposphere and stratosphere during years when the polar vortex is strong. The possible relation of this mechanism to other wave-mean flow processes that have been suggested to contribute to the NAM stratosphere-troposphere coupling will be discussed.
Harnik Nili
Perlwitz Ja.
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