The Ionospheric Cusp, A Region of Thermospheric Up-welling

Details The Ionospheric Cusp, A Region of Thermospheric Up-welling The Ionospheric Cusp, A Region of Thermospheric Up-welling

Dec 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufmsa21b0066l&link_type=abstract

American Geophysical Union, Fall Meeting 2003, abstract #SA21B-0066

Physics

0350 Pressure, Density, And Temperature, 0358 Thermosphere: Energy Deposition, 2407 Auroral Ionosphere (2704), 2409 Current Systems (2708)

Scientific paper

The satellite CHAMP with its sensitive accelerometer on board provides the opportunity to investigate the thermospheric dynamics in great detail. On its near-polar, low-Earth (about 400 km) orbit it is well suited to map the air density along the track. In this study we concentrate on density structures in the auroral region. Special attention is paid to features in the cusp. During 25 Sep. 2000, the day we take as an example, air density enhancements of almost a factor of two are observed whenever the satellite passes the cusp region. For the interpretation of these events we consider also the concurrent ionospheric Hall and field-aligned currents (FACs) which are estimated from the magnetic field measurements. As expected, sizable currents are found in the regions of dense air. The reverse is however not always true. On the nightside there are partly even stronger currents, but no thermospheric response is observed. Small-scale FAC filaments (1-km size) seem to play an important role in the heating. Whenever these very intense FACs with amplitudes of several hundreds of A/km**2 show up, density enhancements occur. So far these FAC filaments have not received a lot of attention in the context of Joule heating. Our new observations suggest that the cusp, where small-scale FACs occur rather frequently, seems to be a prominent region for refilling the upper atmosphere.

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