Analysis of a Prototypical Substorm with Conjugate Ground Magnetic Data
Monday, 14 December 2015
Poster Hall (Moscone South)
The substorm at about 5 UT on February 26, 2008 (Angelopoulos et al., Science, 2008) has been taken as prototypical of reconnection in the Near-Earth Neutral Line model. Further examination by Pu et al. (JGR, 2010) showed that the event was preceded an hour earlier by one with very similar signatures. Traditional use of AE-related indices suggests that the first event was smaller in terms of electric currents than the second. More detailed examination of ground magnetic data shows that it was in fact comparable: in addition, the second event was considerably further to the west. We present results from Automated Meridian Modeling showing that a simple electrojet model with only three parameters (electrojet borders and current) matches data well with approximately 0.2 MA cross-meridian current in both subevents. There was also good conjugacy between hemispheres for both, as indicated by Antarctic magnetometers and inversion based on them. SuperMag data gives dense enough magnetometer coverage that the layout of the substorm current wedge, with auroral zone westward electrojet and subauroral perturbations mainly due to field-aligned current, can be determined. The quantitative data from the ground provides a context in which flows, magnetic fields, and other parameters at the THEMIS constellation and other conjugate spacecraft may be interpreted.