Shock-Induced Proton Aurora: Five Case Studies

The shock-induced proton aurora, observed in Doppler-shifted Lyman alpha with the IMAGE FUV Spectrographic Imager, is characterized by the same general features and behavior that have been reported in recent studies of the aurora that is produced primarily by precipitating electrons. Typical features include (1) a sudden, short-lived dayside brightening, covering over several hours of local time and often extending over a wide latitude range, coincident with the storm sudden commencement/sudden impulse; (2) subsequent instantaneous brightening of the entire oval or a rapid propagation of enhanced luminosity from the dayside to the nightside; (3) a thickening and poleward expansion of the oval; and (4) shrinking of the polar cap. Comparison of the proton emission pattern with the distribution of OI emissions observed at 135.6 nm with the FUV/SI13 channel allows differences between the proton and electron components of the shock-induced aurora to be distinguished. In one of the cases presented, the dayside cusp and a localized emission feature at the polar cap boundary are observed to move in local time in concert with one another in response to a strong variation in IMF By.