Abstract
Abstract. Norway and Finland STARE radar measurements in the eastward auroral electrojet are combined with EISCAT CP-1 measurements of the electron density and electric field vector in the common scattering volume to investigate the variation of the auroral radar volume cross section (VCS) with the flow angle of observations (radar look direction with respect to the E×B electron drift). The data set available consists of ~6000 points for flow angles of 40–85° and electron drifts between 500 and 2000 m s−1. The EISCAT electron density N(h)-profile data are used to estimate the effective electron density, aspect angle and thickness of the backscattering layer. It is shown that the flow angle variation of the VCS is rather weak, only ~5 dB within the range of the considered flow angles. The VCS values themselves respond almost linearly to the square of both the electron drift velocity magnitude and the effective electron density. By adopting the inferred shape of the VCS variation with the flow angle and the VCS dependence upon wavelength, the relative amplitude of electrostatic electron density fluctuations over all scales is estimated. Inferred values of 2–4 percent react nearly linearly to the electron drift velocity in the range of 500–1000 m s−1 but the rate of increase slows down at electron drifts >1000 m s−1 and density fluctuations of ~5.5 percent due to, perhaps, progressively growing nonlinear wave losses.
Highlights
The auroral ionosphere is filled with plasma density irregularities whose scales range from tens of kilometers to some centimeters
It is accepted that the auroral electrojet (AEJ) irregularities are excited through the Farley-Buneman (FB) and the gradient-drift (GD) plasma instabilities occurring, first of all, owing to the E × B drift of the electrons with respect to almost stationary ions
If we suggest that the volume cross section is controlled only by the electron drift velocity, i.e. σv ∝ VE2×B, the velocity increment by a factor of 21/2 should increase VCS by 3 dB
Summary
The auroral ionosphere is filled with plasma density irregularities whose scales range from tens of kilometers to some centimeters. Applying the Oksman et al.’s (1986) approach to the Scandinavian Twin Auroral Radar Experiment (STARE) radar measurements in the westward electrojet, Nielsen et al (1988) confirmed the original findings by Uspensky et al (1983a, b) and Starkov et al (1983) that the EDFA increases linearly with VE×B magnitude but experiences “saturation effect” at drifts above ∼600–800 m s−1. The EDFA derivation procedure relies on k dependence for the VCS; this was inferred from earlier VHF radar measurements at various frequencies (Leadabrand et al, 1967; Chesnut et al, 1968; Moorcroft, 1987) These authors measured the absolute values of the received power and corrected it in accordance with the antenna beamwidth and radar parameters. The EISCAT N (h)-profiles are used to estimate the effective aspect angle of STARE measurements, the effective electron density and the thickness of the irregularity layer
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