Interannual variability in mesospheric wintertime descent: Implications for thermosphere- stratosphere coupling

Details Interannual variability in mesospheric wintertime descent: Implications for thermosphere- stratosphere coupling Interannual variability in mesospheric wintertime descent: Implications for thermosphere- stratosphere coupling

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsa24a..03k&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SA24A-03

Computer Science

Sound

0310 Airglow And Aurora, 0340 Middle Atmosphere: Composition And Chemistry, 0341 Middle Atmosphere: Constituent Transport And Chemistry (3334), 0342 Middle Atmosphere: Energy Deposition (3334), 0358 Thermosphere: Energy Deposition (3369)

Scientific paper

Satellite observations of odd nitrogen (NOx) in the middle and upper atmosphere have long shown that NOx produced by electron impact on molecular nitrogen in the thermosphere can, under some circumstances, be transported downward to the middle atmosphere. This transport is most favorable in winter when the combination of polar night and downward circulation combine to bring NOx from above 90 km into the stratosphere below 50 km before photodissociation of NO can occur. It has also been shown that the entrainment of thermospheric NOx in the stratosphere varies with geomagnetic activity, at least in the Southern Hemisphere (SH). Most recently however, observations of NOx in the NH indicate a striking year-to- year variability in the flux of NOx into the stratosphere that appears unrelated to any obvious variations in geomagnetic activity. Instead it has been suggested that meteorological variability in the middle atmosphere serves to modulate the downward transport of NOx. Here we explore this hypothesis using data from the Sounding of the Atmosphere with Broadband Emission Radiometry (SABER) experiment on the NASA/TIMED satellite. SABER temperatures show that in 2004 and 2006, an unusually warm stratopause existed at unusually high altitudes (75 km). These two years have been linked with large NOx fluxes into the stratosphere. By contrast in 2003 and 2005, years in which there was little NOx flux into the stratosphere, the winter stratopause occurred at the more conventional 50-55 km altitude region. Since the polar winter stratopause is a dynamically created feature from wave-driven diabatic descent, we use the NOGAPS-ALPHA model to simulate the different dynamics between the so-called normal and anomalous years. Preliminary results suggest that differences in planetary wave activity in the lowermost stratosphere are important in governing the propagation of gravity waves to the mesosphere. Thus the differing winter temperatures may reflect the relative variations between planetary and gravity wave activity in the winter mesosphere. Ultimately these variations may be important for coupling the upper atmosphere with the middle atmosphere.

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