Solar Wind Control of Proton Precipitation into the Cusp

H. U. Frey and S. A. Fuselier


The SI-12 instrument on the IMAGE spacecraft observes the Doppler-shifted
Lyman-alpha emission from charge-exchanging, energetic protons. It is most
sensitive to precipitating protons of 2-8 keV energy and thus an excellent
monitor for proton precipitation from magnetopause reconnection in the cusp.
Depending on the orientation of the IMF B_z component two different
morphologies of the proton aurora at the cusp footprints are observed, a spot
poleward of the auroral oval for northward IMF, and an MLT-extended region on
top of the auroral oval for southward IMF. The location of the cusp footprint
in local time is controlled by the IMF B_y component and the brightness is
determined by the solar wind dynamic pressure. Long duration auroral
observations during steady solar wind conditions allow for a determination of
the temporal behavior of reconnection if total area and brightness of the cusp
aurora are analyzed simultaneously. All these properties demonstrate the
importance of the solar wind conditions for the reconnection process and the
reconnection site.

_______________
Presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 9 - 13, 2003.