Relativistic electron and energetic ion precipitation spikes near the plasmapause

Abstract

An investigation has been made of electron and associated ion precipitation spikes near the plasmapause that are narrow in L shell and in which relativistic electrons are favored. The electron energy spectra during the spikes sometimes had equivalent e fold energies in excess of 500 keV. In approximately 31% of these spike events observed from the low‐altitude polar orbiting satellites P72‐1, P78‐1, and S81‐1, nearly simultaneous precipitation was measured in energetic ions above ∼30 keV at about the same L value. Several of the precipitation spikes occurred primarily in the drift loss cone, but in some cases, significant precipitation (∼10−2 ergs/cm² s) was also observed in the bounce loss cone. The electron spikes occurred preferentially in the evening sector, and all of the associated narrow ion spikes were in that local time interval. Narrow relativistic electron spikes were observed on less than 1% of the crossings of the plasmapause. From the set of S81‐1 events a search was made for those also observed on the NOAA 6 spacecraft. On rare occasions, nearly simultaneous (<2000 s) narrow spikes with hard electron spectra were found at approximately the same L value from both spacecraft and at longitudes differing by 8°–47°. These findings suggest a patchy profile, sometimes with an arc structure which may extend over longitude intervals as great as 25° and time intervals as long as 2000 s. From consideration of the AE index for 17 events, 12 were found to occur close to the times of substorms. The spike precipitation is interpreted in terms of cyclotron resonance wave‐particle interactions involving radiation belt particles, the narrow widths being associated with fine structure in the cold plasma density profiles near the plasmapause and the energy selectivity associated with an upper frequency cutoff in the waves.

Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations

“…The preferential occurrence of REP on the duskside has been observed by both satellites [Vampola, 1971;Green et al, 2004;Carson et al, 2013;Comess et al, 2013] and balloons [Foat et al, 1998;Lorentzen et al, 2000;Millan et al, 2002]. Coincident precipitation of electrons and ions has been reported by various satellite studies [Imhof et al, 1986;Bortnik et al, 2006;Sandanger et al, 2009;Carson et al, 2013]. Storm Probes (RBSP, now called "the Van Allen Probes") mission, provides the first balloon measurements of REP while comprehensive in situ measurements of both plasma waves and energetic particles are available .…”

Actively produced high-energy electron bursts within the magnetosphere: the APEX project

“…Some relativistic electron precipitation bursts, many of which were observed in the drift loss cone, were previously found to occur in the vicinity of the plasmapause position estimated from the K P index (Imhof et al, 1986). These bursts were predominantly in the L shell range of ∼ 4 to ∼ 7 and, therefore, probably near the trapping boundary.…”

Strong localized variations of the low-altitude energetic electron fluxes in the evening sector near the plasmapause

“…According to Thorne and Kennel (1971) the presence of the proton precipitation is expected during the relativistic electron precipitation. But, as shown by Imhof et al (1986), localized precipitation of electrons from the inner part of the radiation belt correlates with the proton precipitation spikes only in 31% of the observed events.…”

“…Sometimes the precipitation was registered nearly simultaneously on board dierent satellites spaced tens of degrees in longitude apart. Duration of the relativistic electron precipitation bursts varies from <1 s to 10± 30 s (Imhof et al, 1986(Imhof et al, , 1991(Imhof et al, , 1992Nakamura et al, 1995) Thorne and Kennel (1971) suggested a mechanism for the relativistic electron precipitation in the evening and night sectors near the plasmapause. The precipitation from the radiation belt was thought to be related to the electromagnetic ion cyclotron waves.…”

“…Vampola, 1971;Thorne and Andreoli, 1980;Imhof et al, 1986;Nakamura et al, 1995). In particular, Imhof et al (1986) considered the electron precipitation spikes that were registered in the narrow L-shell range near the plasmapause. Sometimes the precipitation was registered nearly simultaneously on board dierent satellites spaced tens of degrees in longitude apart.…”