Observations of charged particle precipitation into the auroral zone

Abstract

An array of sensitive electrostatic analyzers was borne on the earth satellite Injun 5 in a nearly polar low-altitude orbit. The energy spectrums and angular distributions of proton and electron intensities over the energy range 5 • E • 50,000 ev were measured separately and simultaneously with good temporal and energy resolutions over the auroral zones and polar cap regions and within the outer radiation zone. Fully color-coded energy-time (E-t) spectrograms are utilized to present and effectively digest a massive body of individual intensity measurements. Several of the principal observational results were: (1) In the late evening sector the electron precipitation patterns are usually characterized by two or more bands of low-energy electron precipitation during periods of relative magnetic quiescence, Kp --• 0 to 2. (2) With increasing magnetic activity, Kp --• 3 to 4+, these 'bands' of precipitated electron intensities become more intense, and often less well defined, relative to those observed during quiescent periods. (3) During these periods of relative magnetic disturbance, a persistent inverted 'V' substructure in the E-t spectrograms is evident. This substructure displays a well-defined increase of the electron energy for peak differential intensities with time to a maximum energy usually •kiloelectron volts followed by a subsequent decrease of this energy. (4) Occasionally a relatively structureless, broad precipitation pattern is observed at late local evening during magnetically disturbed periods. (5) In the late local evening sector the dominant band of proton precipitation is often located just inside, i.b., equatorward of, the termination of low-energy electron precipitation. (6) Energy influxes into the earth's upper atmosphere during late evening have been observed to be as low as •1 erg (cm • sec) -• during magnetic quiescence and as high as --•250 ergs (cm 2 sec) -• for disturbed periods. (7) The over-all features of electron precipitation in the late-morning sector are generally more diffuse and less intense relative to those observed during local evening. (8) The late-morning precipitation patterns are often characterized by a subtructure, not spanning the width of the entire precipitation region, that displays decreasing average electron energies with increasing invariant latitudes. (9) The electron pre'Cipitation in the late morning sector is often bounded at its high-latitude edge by a remarkably intense, narrow band of low-energy electron intensities. Typical widths of this intense., unique structure are •20 to 30 kin. The electron spectrums and densities are similar to those observed in the distant magnetosheath. These observations are discussed in terms of previous results gained with similar instrumentation at great distances within the earth's magnetosphere near the magnetic equator and the implications concerning the source regions and mechanisms for the auroral plasmas. During the past several years instrumentation capable of obtaining measurements of lowenergy charged particles pr...

Characteristics of Magnetosheath Plasma Observed at Low Altitudes in the Dayside Magnetospheric Cusps

“…The results presented in this paper and those of Frank (1970), Frank andAckerson (1971), Heikkila and Winningham (1971), Russell et al (1971), andWinningham (1970) data (Frank and Ackerson, 1970) which would support this. On the other hand the ISIS 1 data indicates a region which is on the average -2 to 3° wide at low altitudes.…”

The Kilometric Radio Emission Spectrum: Relationship to Auroral Acceleration Processes

“…The earth is, therefore, a very intense radio emitter, comparable in many respects to Jupiter, which has long been recognized as an intense planetary radio source. Because of the association with discrete auroral arcs, Gurnett 119741 suggested that the radiation was associated with the inverted-V electron precipitation bands detected by low-altitude satellites [Frank and Ackerson, 1971]. This relationship has now been confirmed by direct in situ measurements in the auroral regions [Bensen and Calvert, 1979;Green et al, 19791.…”

Numerical simulations on ion acoustic double layers

“…In fact, there are several observations to support this idea [Frank and Ackerson, 1971;GVc.ns, 1974;Arnoldy.et al, 1974;see, also, a review by toeng, 1976;haerendel, et al, 1976;and Wescott ,et al, 1976]. Among others, a double layer, or an electrostatic shock, is believed to bt the most feasible and likely candidate for causing parallel electric fields [wozer,et al, 1977].…”