High‐latitude ionospheric transient events in a global context

This paper presents a comprehensive global study of bow shock motion, magnetosheath dynamic pressure variations, dayside magnetospheric magnetic field perturbations, and cosmic noise absorption events attending a sequence of transient events observed in high‐latitude global ground magnetograms on February 14, 1986. ISEE 2 spacecraft observations indicated that most of the transient ground magnetometer events were associated with abrupt inward and outward motions of the dawn bow shock during a prolonged period of strongly northward and orthospiral interplanetary magnetic field orientation. Geosynchronous GOES 5 and 6 magnetometer observations provide evidence for corresponding compressions and expansions, which propagated duskward through the prenoon magnetosphere. The magnetopause moved inward past the CCE spacecraft during some of the compressions. The compressions scattered magnetospheric particles and thereby produced quasi‐periodic oscillations in the cosmic noise absorption recorded by high‐latitude ground riometers. We infer that (unobserved) strong transient variations in the solar wind dynamic pressure produced the various phenomena and that the ground magnetometer signatures are best explained in terms of the pressure pulse model of Southwood and Kivelson [1990], in which a single sharp change in the solar wind dynamic pressure generates a pair of field‐aligned currents.