Determination of ionospheric conductivities from FUV auroral emissions

Abstract

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

A statistical comparison of SuperDARN spectral width boundaries and DMSP particle precipitation boundaries in the morning sector ionosphere

“…This boundary is approximately co-located with the OCB in all MLT regions except the 02:00-08:00 MLT region. The intensity of LBHL emissions is approximately proportional to the energy flux of precipitating electrons (Germany et al, 1997;Carbary et al, 2004) and varies very little with the average energy of the electrons (Germany et al, 1994). Hence, the correlation between spectral width and LBHL auroral emission boundaries would imply that, statistically, regions of high spectral width correspond to regions of low electron energy flux and that regions of low spectral width correspond to regions of high electron energy flux.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…Their results supported cusp FAC production by a rotational discontinuity of the magnetic field at the dayside magnetopause due to reconnection (Lee et al 1985), rather than by the penetration of the IMF B y component into the magnetosphere. Bristow and Lummerzheim (2001) improved on this technique by combining Super-DARN convection maps with ionospheric conductances independently determined from a model of photoionization combined with auroral particle precipitation inferred from Polar UVI images (Lummerzheim et al 1991;Germany et al 1994). Combining these two-dimensional datasets allowed them to instantaneously image the two-dimensional FAC pattern and monitor the evolution of the pattern.…”

Height‐integrated Joule and auroral particle heating in the night side high latitude thermosphere

“…Emissions at two wavelengths in the Lyman-Birge-Hopfield (LBH) N 2 bands can be combined with auroral modeling to estimate Q P and the average energy, e, of auroral precipitation [Germany et al, 1994]. S P can be calculated from Q P and e using empirical relations [Robinson et al, 1987].…”