A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures
We report a superposed epoch analysis of the hemispheric open magnetic flux, maximum nightside auroral intensity, geomagnetic activity, and solar wind and interplanetary magnetic field conditions around the time of substorm onset for three distinct categories of substorms defined by their energetic particle injection signatures. Substorms identified from global auroral imagery are classified into one of three categories based on their energetic particle injection signatures as seen at geosynchronous orbit by the Los Alamos National Laboratory spacecraft. Category 1 events are associated with a "classic" substorm injection, category 2 events show varied activity (i.e., energetic enhancements not following the evolution expected for classic substorms), and category 3 events show no apparent injection activity. The superposed epoch analysis reveals that the three distinct particle injection categories exhibit distinct differences in the level and continuity of magnetospheric driving by the solar wind, such that category 1 events can be described as classic substorm events, category 2 as continuously driven events, and category 3 as weak events. The results of this study suggest that the level and continuity of the dayside solar wind driving of the magnetosphere during substorms have a direct impact on the injection of energetic particles to geosynchronous orbit at substorm onset. These results could have considerable value in empirical predictions of the space weather environment.
Authors: Boakes, P.D., Milan, S.E., Abel, Gary A., Freeman, Mervyn P., Chisham, Gareth, Hubert, B.