Pancake pitch angle distributions in warm ions observed with ISEE 1

Abstract

Observations of pancake (peak flux near 90° pitch angle) distributions of low‐energy (≲100 eV) ions are reported. Pancake distributions occur often in H+ and He+ simultaneously while O+ fluxes are either undetectable or field‐aligned. These H+ and He+ pancake distributions typically display characteristic energies of the order of 10 eV and are frequently mixed with higher density, colder (κT≲3 eV), isotropic, quasi‐Maxwellian components. They appear often within the outer regions of the plasmasphere, and seem to occur most frequently on the dayside and near the magnetic equator.

Characteristics of thermal and suprathermal ions associated with the dayside plasma trough as measured by the Dynamics Explorer Retarding Ion Mass Spectrometer

“…0148-0227/83/003A-1148505.00 velocities for the ionospheric plasma as it enters the collisionless regions above 2000 to 3000 km. In the outer plasmasphere, observations of anisotropic warm (a few electron volts to tens of electron volts) ions have been made [Bezrukikh and Gringauz, 1976;Horwitz and Chappell, 1979;Horwitz et al, 1981aHorwitz et al, , 1982Chappell, 1982;Chappell et al, 1982;Gurgiolo and Burch, 1982]. Unfortunately, very limited data are available concerning these boundary conditions.…”

Equatorially confined warm trapped ions at around 100 eV near the plasmapause

“…The equatorially‐trapped warm ions are observed during nearly all geomagnetic conditions, and are mainly found at 3∼5 R E at all local times (4∼5 R E in the dusk side and <4 R E in the dawn side) except 4∼8 MLT where they can be distributed at <3 R E where DE‐1 satellite did not traverse [ Olsen et al , 1987]. The pancake‐distributed tens of eV ions are also found by low‐inclination satellites such as geosynchronous satellites [ Horwitz et al , 1981], in which the pitch angle distribution is consistent with the confinement to the equator [ Olsen et al , 1994].…”

Entry and acceleration of He+ in the low latitude boundary layer

“…In the boundary layer, these He + distributions would be accelerated to boundary layer flow speeds, eventually attaining energies of a few keV. Observations of cold He + distributions in the dayside magnetosphere [Horwitz et at., 1981] and He + at keV energies in the dayside boundary layer [Peterson et at., 1982] are generally consistent with this proposed circulation model. While He + observations relevant to the proposed circulation model have been reported, the details of the entry of low energy magnetospheric plasma into the boundary layer and its subsequent acceleration have not been studied extensively.…”

“…The evolution of cold He + in the boundary layer depends on the concentration of cold He + in the magnetosphere. Cold plasmaspheric He + is observed to convect toward the dayside boundary layer in "blobs", thus the density of the cold He + population varies considerably in the outer magnetosphere [Horwitz et at., 1981 ]. The features in Figure 2 are best seen when the low energy magnetospheric He + distribution has a relatively high density, that is when a cold "blob" is present.…”