12th Conference on Middle Atmosphere

Wednesday, 6 November 2002
The 6.5-day Wave in the Mesosphere and Lower Thermosphere: Evidence for Baroclinic Instability
Ruth S. Lieberman, Northwest Research Associates, Boulder, CO; and D. Riggin
A westward propagating zonal wavenumber one wave with a period near 6.5 days was a prominent feature in the HRDI mesospheric and lower thermospheric winds and temperatures during the 1994 equinoxes. The meridional structure of the wave is consistent with the 5-day wave structure predicted by normal mode theory. However, the vertical structure of the 6.5-day wave is indicative of a propagating wave with origins below the mesosphere.

The vertical structure, horizontal structure, and Eliassen-Palm flux divergence of the wave are examined using HRDI winds and stratospheric assimilated data from the United Kingdom Met Office. The amplitude of the wave as seen by HRDI increases sharply above 80 km, where the wave exhibits a highly organized baroclinic circulation. The eddy fluxes and the background state suggest that the wave is amplified by instability of the mesospheric easterly jet.

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