On the possibility of auroral remote sensing with the Viking ultraviolet imager

Steele, D. P.; McEwen, D. J.; Murphree, J. S.

doi:10.1029/91ja02608

Cited by 7 publications

(2 citation statements)

References 35 publications

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“…The goal of remotely sensing the mean energy and flux of the precipitating particles, which motivated the choice of a dual-camera system, has not been fully met, however. In a previous work [Steele et al, 1992, referred to hereinafter as paper 1] we showed that the total energy deposition can be estimated from the imager signal, with roughly 50% uncertainty. However, we also showed that the mean precipitating electron energy cannot be inferred from Viking two-camera image signal ratios, because the experimentally measured effective sensitivities of both cameras (i.e., the camera signals per unit precipitating electron energy flux over the viewed region of the atmosphere) vary similarly with the mean electron energy.…”

Section: Introductionmentioning

confidence: 96%

A comparison of Viking UVI auroral observations and model calculations of camera responses

Steele¹,

McEwen²,

Murphree³

1995

J. Geophys. Res.

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We have performed model calculations of far ultraviolet (FUV) auroral emissions, their radiative transfer, and the responses of the two cameras of the Viking UVI to these emissions for comparison with a small sample of Viking images with complementary simultaneous DMSP F7 particle data. We selected the images on the basis of good viewing of the DMSP F7 footprint and stable electron precipitation around the image time. We used current models to calculate the FUV auroral emissions resulting from the measured electron spectra, atmospheric absorption of LBH emissions, and the O I 130.4‐nm and 135.6‐nm auroral radiances seen by the Viking UVI. In five of six LBH camera events and one of two 1304 camera events, the model calculations agreed with the observations within experimental error, validating the cross sections and model atmospheres used in the model calculations and the UVI sensitivity at FUV wavelengths. We attribute the remaining discrepancies chiefly to errors in radiative transfer calculations caused by the failure of the approximation of horizontally uniform emission, in two events where the precipitating auroral electron flux had sharp gradients. The events treated here, occurring under quiet to moderately disturbed geomagnetic conditions, were modeled successfully without adjusting MSIS 86 species concentrations.

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Section: Introductionmentioning

confidence: 96%

A comparison of Viking UVI auroral observations and model calculations of camera responses

Steele¹,

McEwen²,

Murphree³

1995

J. Geophys. Res.

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“…Instead of quenching mechanisms, the FUV technique relied on absorption of 02 at lower altitudes to supply an energy dependence. The potential of using FUV emissions from the Viking satellite as remote measures of characteristic energy was examined by Steele et al [1992]. They found only a weak dependence on energy, but they were only able to examine energies below 1.4 keV.…”

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Determination of ionospheric conductivities from FUV auroral emissions

Torr¹,

Richards²,

Torr

et al. 1994

J. Geophys. Res.

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The purpose of this paper is to examine the viability of using LBH emission ratios to infer auroral conductances and to quantify the strengths and weaknesses of this technique. We show that column-integrated Hall and Pealersen conductances may be determined from a single remote measurement of a pair of auroral LBH emissions, one in the region of strong 02 absorption (1464 ]i) and one lying outside of this region (1838 ]i). The dependence of the determined conductivities on incident average energy, total energy flux, and changes in solar and magnetic activity levels is examined. We show that, for energies above 5 keV, auroral conductances may be scaled by the square root of the incident energy flux with errors less than about 20%. For lower energies, however, the scaling may deviate significantly from a power of 0.5. We provide appropriate scaling factors as a function of average energy. We also note that the choice of either a Gaussian or Maxwellian distribution can significantly affect low-energy (<1 keV) conductance calculations. Finally, we quantify the conditions under which the mean energy of a Gaussian energy distribution may differ significantly from the characteristic energy. Introduction Knowledge of ionospheric conductivities is central to an understanding of the coupled nature of the ionosphere, thermosphere, and magnetosphere. This is reflected in models of ionospheric electrodynamics and convection requiring conductance distributions [e.g., Richmond and Kamide, 1988; Rasmussen and Schunk, 1987; Senior and Blanc, 1984; Spiro and Wolf, 1984; Roble et al., 1982]. Considerable effort has been directed toward modeling ionospheric conductances from EUV solar illumination, nocturnal sources, and auroral precipitation (see, for example, Moen and Brekke [1993], Brekke and Hall [1988], Rasmussen et al. [1988], and the reviews by Brekke and Moen [1993] and Reiff [1984]). Conductivities have been inferred from ground-based radar observations by a number of investigators, including Robinson et al. [1987, 1985]; Robinson and Vondrak [1984]; and Vickrey et al. [1981, 1982]. Satellite data are commonly used to determine conductances [e.g., Watermann et al., 1993; Fuller-Rowell and Evans, 1987; Vondrak and Robinson, 1985; Wallis and Budzinski, 1981], with many studies featuring satellite overflights of ground-based facilities. 1Center for Space Plasma and Aeronomic Research, Optical

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