Transient Magnetic Field Signatures Under the Equatorial Electrojet

Transient increases in the H components of dayside ground magnetograms have long been associated with southward IMF turnings (DP2 convection patterns) and abrupt enhancements in the solar wind dynamic pressure (sudden impulses and storm commencements). The amplitudes of these perturbations peak under the equatorial electrojet, indicating that both the pressure changes and the southward IMF turnings apply duskward electric fields to the dayside equatorial ionosphere.  Southward IMF turnings increase the likelihood of reconnection on the dayside magnetopause, drive sunward flows in the magnetosphere towards the dayside reconnection line on the magnetopause, and apply the required duskward electric fields to the ionosphere.   However, compressions of the magnetosphere drive antisunward flows and are associated with dawnward (not duskward) electric fields in the dayside magnetosphere.  The contradiction can be resolved if it is supposed that the same sudden compressions of the magnetosphere also enhance reconnection on the dayside magnetopause.  Thus one would expect the strongest north/south perturbations in equatorial ground magnetograms to be associated with BOTH southward IMF turnings and increases in the solar wind dynamic pressure.  We present results from a statistical survey of OMNI solar wind,  GOES magnetospheric, and equatorial ground magnetometer observations.