What causes the mid-winter cooling?
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- Institutt for fysikk 
This thesis investigated the influence and conditions of vertical propagation ofplanetary waves on the mid-winter cooling in the southern hemispheric polar meso-sphere. MERRA zonal wind data was used to extract planetary waves with zonalwavenumber 1, 2 and 3 at 72°S in 2008 and 2009. The wave periods of 4, 5, 10and 16 days were separated using Morlet wavelet analysis.A correlation between the wave amplitude and carbon monoxide as a tracer forvertical motion could be found from autumn until late winter (from March until lateAugust/mid September). Between the wave amplitude and the mean zonal windanticorrelation was shown from early winter until late winter (April until late Au-gust/mid September). Both correlations were found to stop when the mesosphericcirculation restores in September. In addition agreement between calculations forthe upper bound of the Charney-Drazin criterion for vertical propagation and thewave activity was found until late August/mid September.