High‐latitude Pc 1 bursts arising in the dayside boundary layer region

Abstract

Dayside Pc 1 geomagnetic pulsation bursts have been studied using a three‐station array of induction magnetometers located at high latitudes (geomagnetic latitude (MLAT) of −70° to −81°). The data set reveals that when these emissions are continually recorded at Davis (MLAT = −74.5°; L = 14), the low‐latitude cleft, observed by the DMSP F7 satellite, is located at the Davis latitude. Associated magnetic variations in the form of solitary pulses often lead the Pc 1 bursts by 1 to 2 min. These pulses are typically associated with riometer absorption events and consequently the precipitation of fluxes of keV electrons. The Pc 1 bursts are interpreted as resulting from ion cyclotron waves which have propagated to the ionosphere from the equatorial boundary layer region. The associated boundary layer ions, identified by the low‐altitude DMSP F7 satellite, range between 1 and 5 keV in energy. These particles are considered to be the most likely free energy source for the ion cyclotron waves. It is considered that such resonant ions enter the magnetosphere via the cleft and cusp because this enables a prenoon time of occurrence of most of the observations to be explained. Measured time delays of 40 to 120 s between the associated riometer absorption and Pc 1 bursts are consistent with an ion cyclotron wave generation region located in the equatorial magnetosphere.