Are repetitive particle injections during high-speed solar wind streams classic substorms?

Abstract

The relation between substorm occurrences, energetic particle injections, and High-Intensity Long-Duration Continuous AE Activity (HILDCAA) events has been an issue. To understand their relationship, we use global auroral images from the Wideband Imaging Camera (WIC) on the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft to investigate auroral activity near the times of repetitive particle injections that occur every ∼0.5 to 4 h during HILDCAA events. For the examined HILDCAA intervals during January-July 2003, we identified a total of 481 injection events. Good WIC imaging was available for 121 of these and showed substorm onset brightenings for a significant fraction of the 121 injections. Specifically, excluding 16 injections with ambiguous timings owing to the lack of a near-midnight spacecraft, we find that 93 of 105 injections (∼88%) occurred within ±5 min of a substorm auroral onset. If we include cases with up to 10-min timing difference, the percentage becomes 97%. These results indicate that a significant fraction of HILDCAA-time repetitive particle injections are substorm-associated and thus suggest that substorms are a major component of HILDCAA geomagnetic activity and a possible contributor to the sustained small negative Dst during these periods. Copyright 2008 by the American Geophysical Union.