Substorm-injected protons and electrons and the injection boundary model

Abstract

Observations of substorm‐associated enhancements of proton and electron fluxes were made by Explorer 45 below L = 5.3 in the dusk magnetosphere on February 13, 1972. The particles were observed after a substorm that started at 1116 ± 0010 UT in the wake of an ssc at 0939 and that initiated a small magnetic storm with maximum Dst = 47 γ. The protons in the range between 1 and 40 keV exhibit strong dispersion effects in both energy and pitch angle. The electrons also show dispersion effects above 40 keV, while those below that energy are not observed until the satellite crosses the plasmapause. The observations are interpreted in terms of McIlwain's model electric field E3 and an injection boundary close to or coinciding with the plasmapause. Good quantitative agreement is obtained between the observed and the predicted proton energies and pitch angle dispersions and electron energy dispersions. In view of strong temporal fluctuations in the electron flux, no comparison in pitch angle dispersion of electrons is possible. The conclusion drawn is that in this event protons and electrons were injected at the onset of the substorm more or less instantaneously into the magnetosphere along or above the injection boundary and particles with energies below 10 keV were not convected in from the magnetospheric tail.

Plasmapause Disturbances Synchronized with Magnetospheric Disturbances.

“…The plasma injection into the inner magnetosphere due to the electric field convection at the time of substorms has been studied (e.g., Mcllwain, 1974;Konradi et al, 1975;Ejiri et al, 1980). However, the present phenomena can not be interpreted by this popularly known process because SPDD's at the plasmapause appear almost simultaneously with enhancements of the magnetospheric disturbances related to the on-sets of substonns, without the significant time delay supposed to be needed to transport the plasma from the region of the origin of aurora] particles.…”

Pitch angle dispersion of ion injections

“…In particular, the demonstration that energy dispersion of electron and ion injections implies the same injection time is a signal success of particle drift theory [Konradi et al, 1975]. This success is due to the fact that the gradient and curvature drift velocities scale with energy, so that for sufficiently high energies the drift velocity is strictly proportional to energy.…”

“…Dispersionless injections typically occur within a few hours of midnight [Baker et al, 1979;Lopez et al, 1990], although they are not uncommon as far west as 1500 magnetic local time (MLT) and as far east as 0400 MLT [Friedel et al, 1996]. The region of dispersionless injections appears to have a boundary [e.g., Lopez et al, 1990] corresponding to the edge of the injection source region [Mcllwain, 1974;Mauk and Mcllwain, 1974;Konradi et al, 1975].…”

“…One feature often associated with magnetospheric substorms is the injection of >10 keV ions and electrons onto trapped and quasi-trapped drift orbits [Konradi, 1967;Pfitzer and Winckler, 1969 0148-0227/00/1998JA000332509.00 persion is attributed to the direct scaling between energy and gradient curvature drift velocity [Roederer, 1967] and has been used extensively to determine the injection time, the source local time of the injected ions, and the local time extent of the injection [Mcllwain, 1974;Konradi et al, 1975;Reeves et al, 1990Reeves et al, , 1991Friedel et al, 1996;Birn et al, 1997b]. The absence of energy dispersion therefore indicates that the injection is observed locally.…”

Plasmas in the Earth's Magnetotail

“…Kavanagh et al, 1968). During substorm activity, earthward convection of magnetotail plasmas is observed and the electron boundary of the plasma sheet similarly moves toward Earth (Konradi et al, 1975;Moore et al, 1981). The earthward edge of this body of new magnetotail plasma that is injected into the inner magnetosphere is referred to as an injection boundary or front.…”