Polar Winter Middle Atmosphere Gravity Wave Generation and Mesosphere Cooling

Throughout the winter season the polar middle atmosphere is intermittently disturbed by planetary wave activity that can produce synoptic-scale regions of high baroclinicity in the upper stratosphere. These regional baroclinic zones are accompanied by 50K warmings in the upper stratosphere (~42 km) and 50k coolings in the mesosphere (~75 km). These disturbances have been observed in lidar and rocket soundings, soundings from the TIMED/SABER instrument and UK Meteorological Office (MetO) assimilated data. They are also accurately captured in the WACCM and ECMWF models. Using these models we show that these disturbances may be middle atmospheric sources of gravity waves. The vertical structure resulting from these disturbances extends into the mesosphere where significant cooling can occur. These synoptic-scale disturbances of the polar middle atmosphere occur more frequently than major stratospheric warmings and always precede major warmings when they occur. Here we investigate a case study of from the Northern Hemisphere winter of 2009-2010 using a ECMWF high spatial resolution T799 model run to examine the gravity wave generating properties and dynamical circulation impacts of these middle atmospheric weather events.