Downward flowing ions and evidence for injection of ionospheric ions into the plasma sheet

Abstract

Energetic (keV) protons and 0+ ions with field aligned pitch angle distributions and peak fluxes up to ∼ 7 × 107 (cm² s sr keV)−1 have been observed streaming downward in the high altitude (∼ 1 RE) auroral ionosphere. In two examples described in detail, the correlations observed between the downward flowing and coincident trapped ion populations suggest a common origin. Downward flowing ion events are a much less frequent phenomenon than upward flowing ion events in the auroral region. The significant difference implies that the energetic upward flowing ions from the auroral ionosphere are commonly injected into the trapped population of the plasma sheet, and furthermore that parallel electric fields involving potential drops of ≳500 V are directed preferentially upward in the altitude range from 2000 km to ∼ 3 RE. Spatially localized regions of enhanced hot (∼keV) plasma density were frequently observed in the low L portion of the plasma sheet. The statistical location of these ‘plasma clouds’ correlates well with the substorm injection boundary near dusk inferred by McIlwain (1974) and with the upward flowing ion events observed at ∼ 1 RE altitude (Ghielmetti et al., 1978a, b). The downward flowing ion events occurred preferentially within such ‘plasma clouds.’ The results described in this paper suggest that upward flowing ions from the auroral acceleration regions are responsible for both the downward flowing ions and for at least some of the plasma clouds. A significant fraction of the equatorial substorm injected plasma clouds may thus result from this ionospheric source region.

Low-Energy Ion Pitch-Angle Distributions in the Outer Magnetosphere: Ion Zipper Distributions.

“…Such a source would provide predominantly field-aligned ions. Also the composition would be essentially that measured by the GEOS experiments in the outer magnetosphere (Ghielmettiet al, 1978;Ghielmetti et al, 1979;Geiss et al, 1978;Young, 1979). Such a source would also be in agreement with the results of Kaye et al (1981).…”

“…This has lead to the observation that low energy ions are often found to have field-aligned components in the regions of the outer magnetosphere near the equator (Mauk and McIlwain, 1975;L cIlwain. 1975;Borg et al, 1978;Geiss et al, 1978;Young 1979;Horwitz, 1980;Comfort and Vorwjtz 1980;Uorwitz et al, 1980) and at high latitudes near the earth (Mizera and Fennell, 1977;Sharp et al, 1977;Whalen et al, 1978;Ghielmetti et al, 1979;and Klumpar, 1979).…”

Observation of Field Aligned Ion and Electron Beams from SCATHA (P78-2).

“…Ion cyclotron waves are observed to be associated with ion beams (Kintner et al, 1979;Gorney, private communication, 1981) providing a possible mechanism for this scattering. Ghielmetti et al (1979) have concluded on the basis of a study of downflowing ions that strong pitch angle scattering does occur within a bounce period. There are five days on which S3-3 data is available at the same time as ion beams were observed from SCATHA.…”

An Alternative Interpretation of Ion Ring Distribution Observed by the S3-3 Satellite.

“…Downflowing ion beams are quite rare compared to upflowing beams (Ghielmetti et al, 1979), but downflowing ions in the low-altitude cusp region are quite ccmmon, and can have beam-like distributions (Shelley et al, 1976 a and b;Reiff et al, 1977;Burch et al, 1982). The magnetic defocussing of these downstreaming distributions can lead to the formation of rings of ions in perpendicular velocity as well as positive gradients in parallel velocity.…”

“…Ing ion beams generated by electrical potential drops along auroral field lines are obvious candidates for the parallel (beam) instability, while ion conics have been treated in the limit of the flute mode instability, Sharp et al, 1977;Ghielmetti et al, 1978Ghielmetti et al, , 1979Gorney et al, 1981).…”