Summer mesospheric warmings and the quasi 2 day wave



High-altitude meteorological analyses are used to study the interannual variability of mesospheric weather in the Southern extratropics over five recent January's (2005, 2006, 2008, 2009, and 2010). Two features are apparent. First, there is significant variability in the quasi 2 day wave (Q2DW) with the largest amplitudes in January 2006 and also the last half of January 2005. Second, these periods coincide with high-latitude temperature enhancements of 8–12 K. Previous studies have linked summer mesospheric warmings to interhemispheric coupling (IHC); however, the observed temperature and zonal wind anomalies do not agree with the predictions of IHC. Rather it appears that the westward momentum forcing from these Q2DW enhancements counteracts the gravity wave drag forcing which normally produces the cold summer mesopause. Since these temperature increases have been linked to Polar Mesospheric Cloud (PMC) disappearance, the present study supports the suggestion that the Q2DW may be an important factor governing PMC variability.