Paper#: 103
Poster #:
Session Name: Workshop 6B: Inonspheric Process
Room: 200ABC
Day: Thursday
Time: 4:55-5:15 p.m.
Abstract Title: Do Interplanetary Shocks Really Trigger Substorm Expansion Onset?
PresentSurname: Liou, K.
All Authors: K. Liou, P.T. Newell, C.-I. Meng, C.-C. Wu, R.P. Lepping
Abstract : One of the outstanding issues in magnetospheric physics is the trigger mechanism(s) of the substorm expansion phase onset. Previous studies have shown connections between substorms and storm sudden commencements/sudden impulses (SSC/SI) caused by discontinuities in the solar wind and suggested a magnetospheric compression trigger mechanism [e.g., Kawasaki et al., 1971; Kokubun et al., 1977]. However, the reported triggering probabilities are small, ranging from 4% to 49% under various conditions. In a series of studies of substorm timing conducted recently, we found that some of the most widely used substorm onset signatures such as high-latitude magnetic bays, low-latitude Pi2 pulsations, and energetic particle injections at geosynchronous orbits occur more frequently than auroral breakups. Hence, it is reasonable to cast doubt on the compression trigger mechanism because the actual probability for compression triggering of substorm should be lower when using a more reliable substorm onset identifier such as auroral breakups. In the present study we re-investigate the relationship between interplanetary shocks and substorm onsets by using auroral breakups determined with the Polar UVI image data. We will present detailed results and discuss implications of the findings.