Interannual Variability in Mesospheric Wintertime Descent: Implications for Thermosphere-Stratosphere Coupling

Observations from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) experiment on the NASA/Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED) satellite show an unusual vertical displacement of the winter stratopause in 2006 with zonal mean temperatures at 0.01 hPa (80 km) exceeding 250 K. By contrast, at the conventional stratopause location near 50 km, temperatures were unusually cold. Simulations with the NOGAPS-ALPHA model suggest that these are coupled to an unusually warm and disturbed lower stratosphere that filtered out many of the gravity waves that normally break at and above 50 km. The model also shows that downward transport in the 2006 Arctic vortex at mesospheric altitudes was enhanced relative to 2005. These results might explain observations of enhanced upper atmospheric NO descending to the upper stratosphere in 2006. They highlight the importance of gravity waves and their filtering by winds in the stratosphere in modulating the coupling of the upper atmosphere with the stratosphere. The implications of this are that solar-terrestrial coupling studies must consider meteorological variability forced from the lower atmosphere in addition to the more familiar solar/geomagnetic variations.