Mesospheric structure of the 2009 major stratospheric sudden warming as seen in the 0-100km analysis fields from the NOGAPS-ALPHA data assimilation system

The 60^oN zonal-mean zonal winds associated with the major stratospheric sudden warming (SSW) of January 2009 switched from westerlies to easterlies in the mesosphere 8-10 days before the mid-stratospheric wind reversal. Here we use NOGAPS-ALPHA (Navy Operational Global Atmospheric Prediction System- Advanced Level Physics High Altitude), a high-altitude data assimilation system, to examine the zonal wind reversal, wave amplitudes, and wave EP-fluxes from the surface to ~95 km from early December 2008 through February 2009, with special emphasis on mesospheric structures. The meteorological fields from NOGAPS-ALPHA incorporate conventional operational meteorological observations in the troposphere and lower stratosphere plus research temperature soundings from both the Aura MLS (Microwave Limb Sounder) and TIMED SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instruments over the region from ~100-0.002 hPa (~16-85 km altitude). Results show that the early forming mesospheric easterlies join the stratospheric tropical easterlies before the descent of stratospheric easterlies at 60^oN. The EP-fluxes show strong wave-2 propagation into the mesosphere at mid-latitudes with continued mesospheric propagation into the tropics. Wave-2 propagation into the mesosphere is shown to occur across the developing easterlies while the depth of the easterlies is still narrow. After the warming, NOGAPS-ALPHA is able to capture the high-altitude reformation of the polar stratosphere. These results highlight the changing mesospheric structures possible during a SSW as well as the complex interaction between stratosphere and mesosphere.