Storm time occurrence of relativistic electron microbursts in relation to the plasmapause

Abstract

Microbursts, or short‐duration bursts of precipitating relativistic electrons observed at low altitudes, are associated with whistler mode chorus and have been proposed as one of the primary mechanisms for storm time depletion of the outer radiation belt. Whistler chorus occurs outside the plasmapause and is generated by wave‐particle interactions involving soft electrons (1–100 keV). We use low‐altitude identifications of the plasmapause from the DMSP satellites and microburst observations from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite to identify the relationship between the plasmapause and microburst locations. Microbursts move radially inward during geomagnetic storms in concert with plasmapause movement, with the microbursts consistently located outside the plasmapause. Near storm peak, as Dst reaches minimum values, microbursts occur at a given L value within hours of erosion of the plasmasphere. This time delay between erosion of the plasmasphere and the appearance of microbursts is positively correlated with L value. We find the occurrence of relativistic microbursts to be associated with a combination of daily averaged 1.5–6 MeV electron fluxes exceeding about 1 particle s−1 sr−1 cm−2 (observed at SAMPEX altitudes) and the presence of soft electrons from the plasma sheet. These observations are consistent with the suggestion that microbursts are associated with chorus and contribute significantly to storm time radiation belt depletion.