Proton aurora dynamics in response to the IMF and solar wind variations

On May 23, 2002, proton auroras observed by IMAGE FUV on the dayside were very dynamic. Auroral pattern at the cusp footpoint is well correlated with IMF and solar wind parameters. A proton aurora brightened at high latitude poleward from the dayside oval after solar wind ion temperature increased while solar wind density and bulk speed were steady. It then vanished after IMF turned southward. Under this IMF condition, auroral activity occurred only in the dayside oval. As IMF B_z reverted to northward, cusp proton aurora reappeared at high latitude. The location of the cusp proton aurora changes with the IMF B_y polarity, consistent with previous reports. These results suggest an upstream source for the observed high-latitude cusp proton aurora. One possible explanation is that bow shock energetic ions are transported into the cusp via the high-latitude magnetic merging process to induce optical emissions in the ionosphere.