Bursts of transverse ion acceleration at rocket altitudes

Abstract

High time resolution ion mass spectrometer distribution function measurements and wave data from a sounding rocket flight over an aurora have revealed the fine structure of the transverse ion acceleration mechanism in the upper ionosphere. The transversely accelerated ion (TAI) events can occur in a volume with a cross‐field dimension as small as several tens of meters and thus appear as 50–100 ms ion bursts due to the rocket payload motion. Bulk heating to a characteristic energy of several eV and tail heating in the direction perpendicular to B of a few percent of ambient ions to a characteristic energy the order of 10 eV occur for both hydrogen and oxygen ions. The TAI at 90° pitch angle occur in localized regions of intense lower hybrid waves and in regions of density depletion. On close examination of the correlation between the wave bursts and the TAI it is believed that the waves produce the ion acceleration. The TAI occur during periods of field‐aligned auroral electron bursts. Finally, near 1000 km altitude they occur about once every second. If the event presented here is considered average, the flux of TAI oxygen ions above 7 eV could account for the ion conic fluxes measured by the ISIS spacecraft.

A statistical study of diurnal, seasonal and solar cycle variations of F-region and topside auroral upflows observed by EISCAT between 1984 and 1996

“…At high altitudes, transverse acceleration of ions resulting from heating by, for example, ion cyclotron or lower hybrid waves generates out¯ows with con®ned pitch angle distributions, so-called ion conics (Ungstrup et al, 1979;Lockwood, 1982). Rocket and satellite observations indicate that ion conics are typically generated above about 1000 km altitude, often above auroral arcs (Arnoldy et al, 1992). Also, within regions of electron precipitation, ®eld-aligned currents can induce lowfrequency plasma turbulence, which can lead to increased resistivity and hence enhancements in both the electron temperature and the ®eld-parallel electric ®eld.…”

High-altitude and high-latitude O<sup>+</sup> and H<sup>+</sup> outflows: the effect of finite electromagnetic turbulence wavelength

“…Transversely accelerated ions at altitudes ranging from a few hundred kilometers to several Earth radii at auroral and polar cusp latitudes have been observed (Klumpar et al, 1984;Winningham and Burch, 1984;Arnoldy et al, 1992;Lundin et al, 1995;Eklund et al, 1997;Moore et al, 1999;Huddleston et al, 2000;Arvelius et al, 2005). The ion acceleration through wave-particle interaction with plasma turbulence at high latitudes of the Earth's magnetosphere has generally been accepted to explain the origin of the above observations.…”

Sub‐kilometer thermal plasma structure near 1750 km altitude in the polar cusp/cleft

“…A striking demonstration of the small spatial scales on which the ion acceleration process can operate was provided by the TOPAZ 3 sounding rocket [Arnoldy et al, 1992;Kintner et al, 1992]. These data, taken in the nightside auroral zone below 1000 km, show bursts of ion energization with a characteristic energy increase of several eV, perpendicular to the geomagnetic field B0, and within localized regions of the order of 50 m across.…”