We carried out a superposed epoch analysis, using a database of substorm chorus events observed at Halley, Antarctica, within an hour of magnetic midnight, to define a set of 123 substorm expansion phase onsets. The method is applied to the 3-component ground magnetic field variations and Pi2 pulsation power. The results may be considered in some sense the "typical" substorm signature at the station when located close to the substorm current wedge.
Authors: Smith, A.J., Freeman, M.P. ORCID record for M.P. Freeman, Hunter, S.