Low altitude acceleration of ionospheric ions

Whalen, B. A.; Bernstein, W.; Daly, P. W.

doi:10.1029/gl005i001p00055

Cited by 172 publications

(66 citation statements)

References 3 publications

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“…Examples of relatively low altitude upward ion velocities (V i ) up to 2 km/s in magnitude have been reported by Whalen et al (1978) from rocket observations at altitudes of 400 to 600 km. More recently, Wahlund and Opgenoorth (1989) and Wahlund et al (1992) have also presented EIS-CAT incoherent-scatter radar measurements of thermal ion upflows (TIU) above the F-layer peak, with V i values increasing rapidly with altitude and achieving speeds of the order of 1 km/s.…”

Section: Introductionmentioning

confidence: 99%

Origin of type-2 thermal-ion upflows in the auroral ionosphere

Kagan

St.-Maurice

2005

Ann. Geophys.

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Abstract. The origin of thermal ion outflows exceeding 1 km/s in the high-latitude F-region has been a subject of considerable debate. For cases with strong convection electric fields, the "evaporation" of the ions due to frictional heating below 400-500 km has been shown to provide some satisfactory answers. By contrast, in the more frequent subclass of outflow events observed over auroral arcs, called type-2, there is no observational evidence for ion frictional heating. Instead, an electron temperature increase of up to 6000 • K is observed over the outflow region. In this case, field-aligned electric fields have long been suspected to be involved, but this explanation did not seem to agree with expectations from the ion momentum balance. In the present work we provide a consistent scenario for the type-2 ion upflows based on our case study of an event that occurred on 20 February 1990. We introduce, for the first time, the electron energy balance in the analysis. We couple this equation with the ion momentum balance to study the salient features of the observations and conclude that type-2 ion outflows and the accompanying electron heating events are indeed consistent with the existence of a field-aligned electric field. However, for our explanation to work, we have to require that an allowance be made for electron scattering by high frequency turbulence. This turbulence could be generated at first by the very fast response of the electrons themselves to a newly imposed electric field that would be partly aligned with the geomagnetic field. The high frequencies of the waves would make it impossible for the ions to react to the waves. We have found the electron collision frequency associated with scattering from the waves to be rather modest, i.e. comparable to the ambient electron-ion collision frequency. The field-aligned electric field inferred from the observations is likewise of the same order of magnitude as the normal ambipolar field, at least for the case that we have studied in detail. We propose that the field-aligned electric field is maintained by the north-south motion of an east-west arc. The magnetic perturbation associated with the arc itself converts a small fraction of the perpendicular electric field into a field parallel to the total Correspondence to: L. M. Kagan (lkagan@uwo.ca) magnetic field, while the north-south motion ensures that the conversion never stops.

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Section: Introductionmentioning

confidence: 99%

Origin of type-2 thermal-ion upflows in the auroral ionosphere

Kagan

St.-Maurice

2005

Ann. Geophys.

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“…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.…”

Section: Introductionmentioning

confidence: 99%

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

Whalen

Burrows

Yau

et al. 1990

J. geomagn. geoelec

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The Suprathermal Ion Mass Spectrometer (SMS) was developed to study the thermal (0-25 eV) and suprathermal (25 eV-several keV) ion distributions in the low altitude magnetosphere. The instrument has a mass (1-70 amu/e) and plasma density (10-3 to 105 cm-3) dynamic range sufficient to measure, on a regular basis, the major and the minor ion distribution functions at apogee (=104 km) as well as at perigee (=300 km). The instrument is a radio frequency type mass spectrometer and has a programmable selected.We present here measurements of the thermal ion mass composition near apogee which show that the composition varies from one dominated by H+ and O+ to one in which the density of "minor" ions (O++, He+, N+) is comparable to or greater than that of H+ and O+. We also present high time resolution mass/energy/angle observations in the topside ionospheric plasma in or near the cusp region where rapid heating of the bulk of the plasma and the formation of conic distributions is clearly evident. These unique observations will be compared with other plasma diagnostics on the spacecraft to increase our understanding of ionospheric ion production, convection and loss processes as well as low altitude ion energization phenomena.

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“…Experimental evidence for perpendicular ion acceleration (ion conics) has been accumulated from at least four magnetospheric satellites and two sounding rockets (Shelley et al, 1976;Sharp et al, 1977;Klumpar, 1979;Horwitz, 1980;Whalen et al, 1978, Yau et al, 1982. In contrast there exists scant evidence for the mechanism that produces perpendicular ion acceleration.…”

Section: Introductionmentioning

confidence: 99%