Near-Earth magnetic signature of magnetospheric substorms and an improved substorm current model

Based on a comprehensive catalogue with more than 4000 magnetospheric substorm entries from the years 2000-2005, the spatial distribution of the substorm-related magnetic signatures at mid and low latitudes around local midnight was investigated. Superposed epoch analysis of a larger number of recent observatory data from mid and low latitudes revealed a field strength increase that is consistent with the results of earlier studies. For the first time, the magnetic signature of the substorm current wedge formation is studied also in near-Earth satellite data from CHAMP. The average maximal deflection measured on board the satellite is smaller by a factor of 2 than that determined from ground observations. The recurrence frequency of substorms as well as the amplitude of their magnetic signature depends strongly on the prevailing magnetic activity. The observed average substorm-related magnetic field signatures cannot be described adequately by a simple current wedge model. A satisfactory agreement between model results and observations at satellite height and on ground can be achieved only if the current reconfiguration scenario combines four elements: (1) the gradual decrease of the tail lobe field, (2) the re-routing of a part of the cross-tail current through the ionosphere, (3) eastward ionospheric currents at low and mid latitudes driven by Region-2 field-aligned currents, and (4) a partial ring current connected to these Region-2 FACs.