Observations of > 100-keV protons in the Earth's magnetosheath

Abstract

Bursts of energetic protons, 100–1300 keV, were observed on Ogo 5 in the magnetosheath and upstream wave region beyond the earth's bow shock during periods of generally enhanced solar and magnetic activity in 1968. From these data, we present the first comprehensive study of energetic protons in the magnetosheath. These magnetosheath protons are found to be directional with the peak flux directed downstream. Typical downstream‐to‐upstream flux ratios are from 10/1 to 20/1 in most regions but often as great as 100/1 near the afternoon magnetopause. The fluxes correlate roughly with magnetic activity. The downstream flux can be expressed as j(> 100 keV) = 500 × 100.412Kp/cm² sr s to about an order of magnitude. Peak unidirectional fluxes near the magnetopause are often similar in spectra and intensity to the peak intensities of trapped fluxes in the nearby magnetosphere. Enhanced proton fluxes occur in the sheath in correlation with depressions in the sheath magnetic field and in correlation with enhanced turbulence. Often at such times, magnetopause boundary layer effects are observed. Energetic proton bursts, in agreement with earlier observations (Lin et al., 1974), are also observed in the upstream wave region beyond the shock, predominately on the morning side of the earth. They correlate well with the wave observations; however, on occasion, they are offset as much as 10 min in time. Directional observations indicate downstream‐to‐upstream directed flux ratios of 10/1 as being typical of the upstream wave region. The directional anisotropies in both the sheath and the upstream wave regions are largely explained by combinations of the Compton‐Getting effect, proton flux spatial gradients, and the free streaming of protons along field lines from an upstream source region. Possible sources of the energetic magnetosheath protons are magnetospheric escape or the energization of low‐energy protons in the magnetosheath, shock, and/or upstream wave region. No strong preference is presently ascribed to any one source.

Properties and origin of energetic particles at the duskside of the Earth's magnetosheath throughout a great storm

“…It was reported (West and Buck, 1976) that magnetosheath¯uxes occurred with depressed and turbulent magnetic ®eld. Instead, in this work intense bursts are observed even with almost unperturbed magnetic ®eld magnitudes (see the bursts of Figs.…”

“…Hones et al (1972) reported the existence of 10 to 30 keV protons in the magnetosheath plasma and suggested the magnetosphere as the source of this population. The ®rst comprehensive survey of ³100 keV ions in the magnetosheath is that reported by West and Buck (1976). They found that the energetic ion uxes correlated with both geomagnetic activity and enhanced turbulence in the magnetosheath magnetic ®eld.…”

Scattering of terrestrial kilometric radiation at very high altitudes

“…If ion waves in the magnatosheath can also be (1-2) kin in wavelength, then a very large, permnnent scattering region extends nround the Earth which is easily within the radiation patterns of TKR from both north and south terrestrial poles. The source of plasma wave turbulence in the magnetoshenth is not well established, but may he associated with energetic particles in the magnetosheath, such as the such as the energetic ions observed by West and Buck (1976).…”

Energetic Magnetosheath Ions Connected to the Earth's Bow Shock: Possible Source of CEPs

“…Two dominant sources are the magnetosphere [e.g., Hones et al, 1972;West and Buck, 1976;Sibeck et al, 1987;Fuselier et al, 1991] and the solar wind energized at the bow shock [e.g., West and Buck, 1976;Asbridge et al, 1978;Crooker et al, 1981;Fuselier et al, 1991]. To understand the origins of energetic magnetosheath ions would greatly facilitate the determination of the mass, momentum, and energy transfer processes within the geospace.…”