Proton Aurora Dynamics in Response to IMF and Solar Wind Variations

Chang, S.-W., S. B. Mende, and R. P. Lepping

The dayside proton auroras observed by IMAGE FUV/SI12 on May 23, 2000
show many dynamics. Proton auroral intensity in the cusp is well
correlated with IMF and solar wind parameters observed by the Wind
spacecraft. When IMF is northward, cusp proton aurora occurs at high
latitude poleward of the auroral oval. The high-latitude aurora
brightened as solar wind ion temperature increased while solar wind
density and bulk speed remained the same. This suggests that energetic
protons (~10 keV) can facilitate the production of the high-latitude
proton auroras. After IMF turned southward, the aurora disappeared and
aurora dynamics only occurred in the dayside auroral oval at low
latitude. Auroral intensity in the oval varied with the solar wind
density and temperature. As IMF Bz later reverted to northward, cusp
proton aurora reappeared at high latitude. The magnetic local time of
the cusp proton aurora changes with the IMF By polarity as expected in
the magnetic merging model. These results suggest an upstream source of
the high-latitude cusp proton aurora. One possible explanation is that
bow shock energetic ions are transported into the cusp via the magnetic
merging process to induce the observed optical emissions in the
high-latitude ionosphere.

_______________
To be presented at the Magnetospheric Imaging Workshop, 
Yosemite National Park, California, U.S.A., Feb. 5-8, 2002.