Magnetospheric forcing of the high-latitude thermosphere, as observed by CHAMP

Details Magnetospheric forcing of the high-latitude thermosphere, as observed by CHAMP Magnetospheric forcing of the high-latitude thermosphere, as observed by CHAMP

Dec 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufmsa23b..01l&link_type=abstract

American Geophysical Union, Fall Meeting 2007, abstract #SA23B-01

Physics

0358 Thermosphere: Energy Deposition (3369), 2427 Ionosphere/Atmosphere Interactions (0335), 2736 Magnetosphere/Ionosphere Interactions (2431), 3369 Thermospheric Dynamics (0358)

Scientific paper

It is known since quite a while that the magnetospheric input to the high-latitude thermosphere can surmount the solar energy deposition during disturbed time. There have been several model approaches to estimate the heating rate from ionospheric currents. Only during recent years CHAMP observations provide direct observations of the air density distribution at auroral latitudes. Opposed to earlier expectations these observations suggest particularly strong heating around the cusp region. This is present both during quiet and disturbed periods. A secondary enhancement in air density is observed in the pre-midnight substorm region. Interestingly, regions of low density are observed in the early morning sector, where the strongest electrojets occur. During geomagnetic storms major thermospheric heating occurs at auroral regions, in particular on the dayside. Density bulges formed at high latitudes propagate equatorward subsequently. Simultaneously with the density CHAMP is able to measure the cross-track wind. By combining many passes over the pole an average wind pattern has been deduced. Special features of that is the strong asymmetry between the dawn and dusk sides. While we observe strong zonal winds from day to night on the dawn side, an anti-cyclonic vortex develops on the dusk side. The "eye" of this cyclone forms at a latitude around 70° MLat and 18 MLT. The combined action of Coriolis and centrifugal force are the reason for the asymmetry. Only by considering the heating rates and the wind systems at the same time the observed thermospheric air distribution can be interpreted properly.

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