Large-Scale Instabilities of the Lower Thermosphere During an Active Period

Details Large-Scale Instabilities of the Lower Thermosphere During an Active Period Large-Scale Instabilities of the Lower Thermosphere During an Active Period

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm32a..06w&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #SM32A-06

Physics

[3369] Atmospheric Processes / Thermospheric Dynamics

Scientific paper

The occurrence during disturbed conditions of high-latitude structures that are more complex than the forcing itself suggests that these structures have a dynamical origin. Is it possible that large-scale instabilities are the source of much or most of this structure and complexity? These large scale instabilities, of the same kind that produce complexity in the lower atmosphere, are present in the thermosphere but have been ignored to date. We have simulated the high-latitude thermosphere during an active period with a general circulation model and have examined the stability of the thermospheric polar jets spun up by ion drag. We find that the jets are unstable as a result of strong vertical shears on the bottom side (baroclinic instability) and strong lateral shears on the flanks (barotropic instability). The model output was examined for evidence of structures indicative of instability and we found disturbances in the region of strong vertical shear indicative of baroclinic instability and structures at higher altitudes indicative of barotropic instability. These novel findings suggest that it may be possible to understand high-latitude structures such as neutral density cells in the framework of instabilities. These structures are presently not included in the empirical models used for density prediction in the upper atmosphere.

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