Particle and wave observations of low‐altitude ionospheric ion acceleration events

Abstract

We report energetic ion and electron, wave, and ambient plasma observations from two sounding rockets which were launched from Churchill, Canada, into the expansive phases of two auroral substorms and which passed through source regions of transversely accelerated ionospheric ions (TAI). The two events were observed at low altitudes (400-600 kin) and resulted in ion energization of hundreds of electron volts. In the acceleration region, the ionospheric ion velocity distribution function in the direction perpendicular to the local magnetic field (lB) displayed a distinct, non-Maxwellian, high-energy tail, suggesting ion cyclotron heating. The plasma density was lower than theoretical quiescent values, by as much as 2 decades in the stronger event. Strong thermal ion drift was observed in the perpendicular (lB) direction, but was absent in the parallel (liB) direction. Large-amplitude, low-frequency fluctuations in plasma density were present, and a number of wave modes were observed, including upper hybrid and Langmuir waves, and whistler, ion acoustic, and ion cyclotron waves. No consistent correlation existed between the energetic particle precipitation and the TAI. However, strong field-aligned electron enhancements were observed at times coincident with the TAI acceleration region. The characteristics of the TAI ion energy spectra were consistent with a simple model of ion cyclotron acceleration and energy loss due to ion-neutral collisions. These observations are discussed in terms of current theories on electrostatic ion cyclotron acceleration and lower hybrid acceleration. concluded from their S3-3 data that, at least for O + conics, a substantial fraction of the ion energy originated from transverse acceleration. Gorney et al. [1981] found that conic source regions, estimated by mapping the pitch angles of the peak measured fluxes in conics down to their magnetic mirror points, tended to be below 3000 km. These authors also found that perpendicular conics (conics with peak fluxes within a few degrees of 90 ø and also referred to as transversely accelerated 341 ions, TAI) were observed primarily in the 1500-to 2000-km altitude region.In this paper, we report particle, wave, and ambient plasma observations from two sounding rockets which passed through such conic source regions. The events were observed at low altitudes (400-600 km) and resulted in ion energization of hundreds of electron volts. EXPERIMENTSBlack Brant rockets AAF-IVB-33 and AAF-IVB-36 were launched from Churchill Research Range, Manitoba, Canada (58.74øN, 93.82øW) into the expansive phases of two auroral substorms, IVB-33 on February 5, 1976, at 0522:55 UT (2322:55 LT) to an apogee of 735 km and IVB-36 on January 26, 1981, at 0720:06 UT (0120:06 LT) to an apogee of 585 km. Both payloads were instrumented with electrostatic analyzers to measure electron and ion spectra in the 0.1-to 20-keV/q range, solid state detectors to measure energetic particles (E > 20 keV/q), low-energy ion sensors to measure ambient ion velocity distributions (0.1-5 ...

On the altitude dependence of transversely heated O<sup>+</sup> distributions in the cusp/cleft

“…The simplest explanation for their generation is a local, perpendicular energy transfer to cold ions. Such distributions have been mainly observed by sounding rockets, low and mid-altitude satellites (Sharp et al, 1977;Yau et al, 1983;Kintner et al, 1996;André et al, 1988;Whalen et al, 1991). A second type, called elevated or bi-modal conics, has been first identified by Klumpar et al (1984).…”

The suprathermal ion mass spectrometer(SMS) onboard the Agebono (EXOS-D) satellite

“…Ion energization varies from a few eV in the polar wind (BANKS and HOLZER, 1969) to hundreds of eV in transverse ion acceleration (Tai, Conics) events (SHARP et al, 1977;WHALEN et al, 1978;KLUMPAR, 1979;YAU et al, 1983) and may extend into the keV range (SHELLEY et al, 1976) at higher altitudes where magnetic field aligned electric fields are believed to play a significant role in ion energization.…”

Akebono Observations of the Polar Wind and Suprathermal Auroral Ions: An Overview.

“…Peterson et al (1993) have presented simultaneous Akebono and DE-1 observations at two different altitudes on (nearly) the same field line in the dayside cusp, which are indicative of the simultaneous occurrence of ion acceleration at two widely separated altitudes on a field line. Yau et al (1983) observed transversely energized ions up to 500 eV on sounding rockets down to 400 km altitude during active aurora. During extended periods of auroral activity, SMS occasionally observes upflowing molecular ions (NO' and N2') in the high-altitude aurora] zone both in the dayside and the nightside .…”