Radar observations of cleft dynamics

A continuous radar monitoring, during a six hour period which included an onset and recovery of global substorm activity, of an ionospheric density enhancement associated with the cleft is reported. Observations of the cleft showed a rapid equatorward excursion to 70 deg Lambda before occurrence of a major substorm intensification, continued location at low magnetic latitude during substorm expansion, and a poleward retreat to about 73.5 deg Lambda during substorm recovery in response to a northward turning of the IMF. Furthermore, the latitudinal width of the cleft density enhancement varied from less than 1 deg during the presubstorm equatorward motion to about 4 deg after substorm recovery.