Plasma in the Earth's polar magnetosphere

Abstract

First observations of the plasmas in the dayside polar magnetosphere were obtained with the earth-satellite IMP 5 during July -August 1969. Several of the more important observational results are: the polar neutral 'points' which appear at the high-latitude magnetopause in mathematical models for the shape of the geomagnetic cavity formed by the interaction of the solar wind with the geomagnetic field are observationally 'bands' with width Q 1 R across the dayside high-latitude magnetopauge (one 'band' in the Northern hemisphere and presumably a second in the Southern hemisphere) I these two 'bands', or regions of the magnetopause through which the magnetosheath plasma has direct access to the magnetosphere.. and the corresponding extension of these bands from magnetopause to auroral altitudes have been designated herein as the 'polar cusps', at all other positions of the dayside magnetopausep the magnetopause appears to be an effective barrier against the direct entry of magnetosheath plasmap during periods of relative magnetic quiescence the intersection of the dayside polar cusp with the auroral zone is positioned at invariant latitude A = 7 9 " (-+ 1") and its latitudinal width is 10 to 30 km projected onto the auroral zone during periods of relative magnetic disturbance the position of the polar cusp moves equatorward by several degrees in invariant latitude without a large increase in its latitudinal width, i.e., by factors < 2 .i the high-latitude termination of energetic trapped electron (E > 45 keV) intensities in the high-latitude dayside outer radiation zone occurs coincident with the polar cusp, albeit these intensities are small and of irregular profile with radial distance in this region, no measurable intensities of energetic electrons (E > 40 keV) magnetosheath protons and electronsp and ring-current protons were observed at latitudes above the polar cuspl i.e., in the polar cap region, the proton and electron differential energy spectrums as viewed in the solar direction in the distant polar cusp (within several earth radii of the magnetopause) are identical to those observed within the magnetosheath to within observational accuracy,.the bulk velocity of protons in the distant polar cusp as deduced from the angular distributions appears to be lower than that of the magnetosheath plasma near the magnetopause by factors -2 or 3 , in the mid-altitude polar cusp at -4 to 5 R geocentric radial distances, the proton specgrum differs from that at the magnetosheath in that protons with energies 6 500 eV are severely less than those observed in the magnetosheath, the proton spectrums in the mid-altitude polar e similar to those in the distant plasma ith the exception that the proton number densities in the polar cusp are typically larger by factors Q 2 0 to 200, the angular distributions of proton intensities in the mid-altitude polar cusp are strongly peaked along the l o c a l magnetic field ( i a e a R down into the auroral zone); the dimensions of the atmospheric loss cone at these altitudes ...

High-latitude day side electric field and particle measurements

“…Recent observations using particle detectors on satellites (Heikkila and Winningham 1971, Frank 1971, Frank and Ackerson 1971, Russell, et al, 1971 have confirmed the existence of the neutral points and detected the leakage of particles at various altitudes above the earth from 1000 kms to many earth radii showing that the spectrum of the particles is very similar to that of magnetosheath particles. Hoffman (1972) completed a detailed survey of a "soft zone" of particle precipitation at low altitudes which coincides on the dayside with this neutral point or "polar cusp" region.…”

“…Frank (1971)hypothesised that the polar cusp is spatially connected to the distant plasma sheet in the magnetotail with the cusp field lines being convected around the flank of the magnetopause. Winningham (1971) has put the longitudinal width of the cusp as from o800 to 1600 (MLT magnetic local time).…”

“…Winningham (1971) has put the longitudinal width of the cusp as from o800 to 1600 (MLT magnetic local time). The width in latitude according to Heikkila and Winningham (1971) is 2 to 5 degrees and to Frank (1971) is 0.2 to 4 degrees. The cusp moves toward the equator during times of magnetic activity as the front side of the magnetosphere is compressed.…”

Impact of HIWIND balloon measurements on thermospheric density models

“…In the meanwhile, the Canadian Alouette and ISIS satellites were supplying copious information about the ionosphere and about the deposition of energy from the magnetosphere into the thermosphere at high northern latitudes [Chan and Colin, 1969;Craven, 1970;Frank, 1971;Heikkila and Winningham, 1971;Shepherd and Thirkettle, 1973]. Not all of this information was understandable at first, but gradually, it led to a coherent picture of the energy flowing from the magnetosphere into the ionosphere and thermosphere at high latitudes.…”

“…In contrast, the balloon measurements are consistent with a semiempirical thermospheric density model (M1975), which was developed from 1972 to 1975 . This model was based on the measurements of energetic particle precipitation through the dayside cusps of the magnetosphere as well as the associated density enhancements in the ionosphere and neutral atmosphere, measured by the satellites Alouette [Chan and Colin, 1969], ISIS [Craven, 1970;Frank, 1971;Heikkila and Winningham, 1971;Shepherd and Thirkettle, 1973], LOGACS [Bruce, 1972;DeVries, 1972;Pearson, 1973], and SPADES [Moe et al, 1977]. Figure 3 from this density model shows a Mercator projection of the global neutral density distribution at 12 h UT in late May at an altitude of 400 km at a time of low geomagnetic activity and moderate ultraviolet activity (F = 115).…”