The 30 MHz imaging radar observations of auroral irregularities during the JOULE campaign

Abstract

The observations were made at the same time that ionospheric electric fields and plasma number densities were measured in situ by instruments on sounding rockets. Neutral wind profiles were also measured during the campaign from triangulation of chemiluminescent trails from rocket releases. Aperture synthesis radar imaging techniques permit the sorting of the coherent backscatter into small azimuth and range bins and the determination of the scattering altitude. Individual Doppler spectra could thereby be unambiguously associated with in situ electric field measurements in the same small volume. We find that the Doppler shifts of the auroral echoes correspond to the ion acoustic speed times the cosine of the flow angle, where the former is predicted according to an empirical wave heating law. Type I echoes are only observed for very small flow angles regardless of the convection speed.

A first comparison of irregularity and ion drift velocity measurements in the E-region

“…The present study provides an alternative view on the phase velocity at large flow angles to that proposed in Bahcivan et al (2005) as we consider the ion drift rather than the ion acoustic speed to be important for Doppler observations at large flow angles. It is not clear why exactly the C s cos θ idea fails in the "overspeed" case nor whether these two ideas could be reconciled.…”

“…(1), can occur. Based on 30-MHz imaging radar observations in conjunction with in situ electric field measurements, Bahcivan et al (2005) proposed that the phase velocity outside the flow angle cone is better described by the cosine component of the ion acoustic speed, C s cos θ , than by the more often cited plasma drift component, V d cos θ . The ion acoustic speed was taken from the empirical formula derived by Nielsen and Schlegel (1985) with the electric field magnitude as an input parameter.…”

Imaging observations of nighttime mid-latitude F-region field-aligned irregularities by an MU radar ultra-multi-channel system

“…The radar imaging technique is now widely used for studying fine structures of ionospheric irregularities from equatorial to high latitudes (Hysell, 1996;Hysell and Burcham, 2000;Hysell and Chau, 2002;Hysell et al, , 2004Bahcivan et al, 2005;Saito et al, 2006Saito et al, , 2007. With this technique, structures smaller than the radar beam width can be resolved.…”

The electron drift velocity, ion acoustic speed and irregularity drifts in high-latitude E-region

“…Thus, the STARE Doppler velocities are only slightly larger than the "l-o-s ion-acoustic speed", C s cos , and the ratio gradually grows as a function of the l-o-s electron velocity. Thus, for the reference set =60 • the idea presented by Bahcivan et al (2005) appears to give a reasonable fit.…”

“…In the adjustment based on the second ratio, where V N,F irr ∝A N,F C s cos n , we used the idea presented by Bahcivan et al (2005) that the 30-MHz Doppler velocity variations with the flow angle can be ". .…”