Magnetic impulse events and associated Pc 1 bursts at dayside high latitudes

Abstract

Ground measurements of bursts of Pc 1 pulsations (minutes duration) are a common dayside phenomenon at high latitudes. For the past several years, dayside ground measurements of similar‐duration bursts of Pc 5 period pulsations, magnetic impulse events (MIE), have attracted a great deal of interest concerning their role in dayside reconnection. From an analysis of several years of induction antenna data from southern and northern hemisphere sites in the Antarctic, Greenland, and Canada, it is found that about 70% of all isolated MIE events are associated with Pc 1 bursts, and about half of all events are conjugate between hemispheres. There appears to be no definitive phase relationship between the onset of the Pc 1 bursts and the MIE, suggesting that both might be produced by the same event on the dayside but have different source locations. Correlative data from ground and spacecraft measurements suggest this to be the case and also show that the Pc 1 are waves inside the magnetosphere propagating into the ionosphere. Finally, a timing study between ground sites separated by 2 hours local time shows that the isolated MIEs are measured first near the subsolar point and at later times down both flanks of the magnetosphere. This suggests that the source mechanism for these events has an E–W component of motion which when projected to the equatorial plane is of the order of the antisunward flow velocity in the magnetosheath. As this source moves down the magnetospheric flanks it creates well within the magnetosphere conditions (pressure pulses?) ripe for the ion cyclotron generation of the Pc 1 bursts associated with the MIE.