Mesospheric tides and waves in the NOGAPS-ALPHA high-altitude data assimilation system

NOGAPS-ALPHA is a high-altitude global numerical weather prediction and data assimilation system that combines a spectral forecast model with NAVDAS, the NRL Atmospheric Variational Data Assimilation System. NAVDAS is a 3DVAR system that assimilates conventional meteorological observations in the troposphere and lower stratosphere plus temperature soundings from both the Aura MLS (Microwave Limb Sounder) and SABER (Sounding of the Atmosphere using Broadband Emission Radiometry) instruments over the region from ~100-0.006 hPa (~16-80 km altitude). The resulting meteorological analyses extend from the surface to the upper mesosphere. The assimilation system has been run for both January-February 2006 and June-September 2007 periods. Space-time spectral analysis of the 4-times daily NOGAPS-ALPHA wind and temperature fields clearly show the vertically propagating diurnal tides in the tropics, the vertically trapped diurnal tide in the extra-tropics, and the strong semi-diurnal tidal structures. The assimilation results also show the global structure and temporal evolution of the 2-day and 5-day waves that have significant amplitude in the mesosphere. Evidence for inertial waves related to planetary wave forcing in the winter stratosphere is seen in the tropics near the stratopause. In addition to the high-altitude results, Kelvin and mixed-Rossby gravity waves are seen in the lower stratosphere. Results highlight the ability of global data assimilation to capture realistic tides and waves in the mesosphere.