Auroral Precipitation as a Driver of Neutral Upwelling in the Cusp

Details Auroral Precipitation as a Driver of Neutral Upwelling in the Cusp Auroral Precipitation as a Driver of Neutral Upwelling in the Cusp

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsm21c..06s&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SM21C-06

Physics

[2407] Ionosphere / Auroral Ionosphere, [2475] Ionosphere / Polar Cap Ionosphere, [2706] Magnetospheric Physics / Cusp, [2776] Magnetospheric Physics / Polar Cap Phenomena

Scientific paper

Recent observations have confirmed neutral particle upwelling at high latitudes which are localized to the polar cusp region. The small-scale density structures associated this upwelling are consistently correlated with strong small-scale field-aligned currents and are often associated with soft electron precipitation similar to that which drives night-side aurora ("auroral precipitation"). We investigate this issue with a numerical model originally developed to study dynamics associated with precipitation in general. It incorporates detailed electron, ion and neutral dynamics to study various processes (e.g., heating, ion outflow, auroral luminosity) in a general sense. No mechanism is explicitly included to accelerate particles upward. Field and particle data from FAST and accelerometer data from CHAMP from a single favorable conjunction alignment event are input to the model. Results are given which support auroral precipitation as a driver to the density enhancement for this event, the mechanism of which is summarized as follows. Auroral precipitation transfers energy to the ambient electron "gas", which subsequently undergoes a thermal (upward) expansion, establishing a vertical ambipolar field. The expanding electron gas pulls the ions upwards through the parallel electric field arising from the need for charge neutrality. The momentum carried by upflowing ions, though, is significant and appears to be capable of dragging neutral gas upward. This mechanism requires a "cooking time" of 10 to 30 minutes before the density enhancement achieves steady state. Model results are compared with measured data from CHAMP for the event.

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