Impulsive particle precipitation and concurrent magnetic field changes observed in conjugate areas near L = 4

Abstract

Using sensitive riometers (30 MHz) and magnetometers at Siple Station, Antarctica, and at four locations in the conjugate area in the northeastern United States and Southern Quebec, we have studied the temporal and spatial extent of the impulsive losses of electrons from the radiation belts and the concurrent accompanying magnetic field variations produced by the changes in ionospheric current systems. The impulsive variations have a short (∼2–4 s) onset time and a ∼5–10 s decay time. The observed decay times in the riometer and magnetometer signals are consistent with the recombination times in the ionosphere at ∼90–100 km. Often the magnetic field fluctuations are observed to occur primarily in the east‐west direction and are out of phase between the southern and northern hemispheres. These observations suggest that predominantly north‐south ionospheric currents are modified and/or produced by such impulsive precipitation. Time delays in the occurrence of the events between the northern and southern hemispheres, as well as time and spatial differences observed between the northern hemisphere stations, suggest that irregularly shaped, gradient B drifting patches of precipitating electrons could be the source of these impulsive events.