FAST Observations Of Solar Illumination And Solar Cycle Dependence Of The Altitude Of Auroral Acceleration And Ion Outflow

Details FAST Observations Of Solar Illumination And Solar Cycle Dependence Of The Altitude Of Auroral Acceleration And Ion Outflow FAST Observations Of Solar Illumination And Solar Cycle Dependence Of The Altitude Of Auroral Acceleration And Ion Outflow

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm44a..06c&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM44A-06

Physics

Plasma Physics

[2431] Ionosphere / Ionosphere/Magnetosphere Interactions, [2451] Ionosphere / Particle Acceleration, [2704] Magnetospheric Physics / Auroral Phenomena, [7845] Space Plasma Physics / Particle Acceleration

Scientific paper

The auroral ionosphere is an important source of plasma for the magnetosphere and numerous studies have examined aspects of the effect of solar illumination and solar cycle on ion outflow. The importance of the altitude profile of ionospheric density to the occurrence, magnitude and altitude of parallel electric field that accelerates ion beams in the auroral zone has also been extensively investigated, both experimentally and theoretically. The thirteen years of data from the FAST satellite provide a unique opportunity to examine the effect of solar cycle on this process. We report on the distribution of ion beams in magnetic local time, invariant latitude and altitude, and their dependence on whether the ionospheric footpoint of the satellite is illuminated or dark, on solar cycle, as indicated by F10.7, and on magnetic activity. Consistent with previous studies, the occurrence of upflowing ion beams peaks in the pre-midnight local time sector and the occurrence increases dramatically with altitude over the altitude range of FAST (~200 km to ~4000 km). Solar illumination at the footpoint both reduces the occurrence of ion beams by more than a factor of 10 and increases the altitude where the acceleration occurs so that beams are almost never seen below ~4000 km altitude. The effect of solar maximum conditions (indicated by F10.7) is almost as large. The inferred potential drops, even during dark conditions, are usually less than 1 keV; during sunlit and/or high F10.7, the potentials are usually less than 500 eV. The effects are similar to the solar illumination suppression of upflowing electrons observed in the downward current region. We will discuss comparisons between the electron and ion beam observations and the constraints the new observations place on the altitude of the parallel potential drop and on relative importance of ionospheric conductivity and plasma density on the acceleration processes.

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