Spatial distribution of energetic particles in the distant magnetotail

Abstract

The spatial distribution of energetic particles in the distant magnetotail is examined by using identical sets of two complementary energetic particle experiments aboard the IMP 7 and 8 spacecraft. The combined IMP 7 and 8 data set provides nearly 10 years of satellite observation. The quantitative distributions of energetic electrons in two energy ranges (30 keV ≤Ee ≤100 keV, 220 keV ≤Ee ≤2.5 MeV) and energetic protons (50 keV ≤Ep ≤220 keV, 290 keV ≤Ep ≤500 keV) are presented in terms of occurrence frequency and the average particle flux intensity over an 80 RE × 70 RE plane perpendicular to the sun‐earth line. The θ‐shaped particle distribution over the solar magnetospheric YZ plane in the antisolar direction is clearly demonstrated at all energies and for both species. The ‘O’ part of the θ corresponds to the magnetosheath region, and the cross bar is the average plasma sheet configuration. A distinct, species dependent, dawn‐dusk asymmetry in particle distribution is observed in the plasma sheet and to a lesser extent also in the magnetosheath. Energetic electrons are observed most often in the morningside of the plasma sheet and protons in the evening side. The degree of asymmetry differs for electrons and protons and is energy dependent. Geomagnetic activity affects the particle distribution substantially. At high geomagnetic activity, the occurrence frequency increases by about a factor of 2 and the average flux intensity is enhanced by approximately one order of magnitude.

Spectral characteristics of protons in the Earth's plasmasheet: statistical results from Cluster CIS and RAPID

“…Similar results were also been reported by e.g., Meng et al (1981) and Sarafopoulos et al (2001), but at different radial distances.…”

“…One should then observe higher fluxes of the energetic part of the spectra near the dusk side. This argument was also mentioned byÅsnes et al (2008) (though reversed dawn-dusk asymmetry since they discussed electrons), and also by Meng et al (1981) and Sarafopoulos et al (2001). However, we note that the geomagnetic conditions, reflected by the Dst index, is more disturbed during the dusk traversals (average Dst is −35 nT, versus −8 nT for the dawn side), so this apparent effect does not seem to be solely a local time dependence, but also an effect of different average geomagnetic activity for the two sides.…”

“…Dawn-dusk asymmetries in flux levels were also found in IMP7 and IMP8 data (Meng et al, 1981 -although they studied radial distances around 30-40 R E ). Sarafopoulos et al (2001) used a series of ≈8 h averages based on Interball energetic (27 to 857 keV) ion measurements from radial distances between 15-28 R E .…”

Restless quiescence: thermonuclear flashes between transient X-ray outbursts

“…They occur especially in the Earth's magnetotail in the anti-Sun direction, but also in the magnetosheath which extends to ±∼30 • from the anti-Sun direction, and around the bow shock (to ±∼45 • from anti-Sun); see, e.g., Sarris et al (1976), Baker & Stone (1978), Meng et al (1981). They arise during geomagnetic activity.…”

Formation of the high-energy ion population in the earth's magnetotail: spacecraft observations and theoretical models

“…For example, statistics collected by IMP-8 spacecraft clearly showed that the maximum of fluxes is observed at the dusk flank of the magnetosphere (Meng et al, 1981), where ions drift due to the quasi-stationary gradient drift.…”