Velocities of auroral coherent echoes at 12 and 144 MHz

Abstract

Abstract. Two Doppler coherent radar systems are currently working at Hankasalmi, Finland, the STARE and CUTLASS radars operating at ∼ 144 MHz and ∼ 12 MHz, respectively. The STARE beam 3 is nearly co-located with the CUTLASS beam 5, providing an opportunity for echo velocity comparison along the same direction but at significantly different radar frequencies. In this study we consider an event when STARE radar echoes are detected at the same ranges as CUT-LASS radar echoes. The observations are complemented by EISCAT measurements of the ionospheric electric field and electron density behaviour at one range of 900 km. Two separate situations are studied; for the first one, CUTLASS observed F-region echoes (including the range of the EIS-CAT measurements), while for the second one CUTLASS observed E-region echoes. In both cases STARE E-region measurements were available. We show that F-region CUT-LASS velocities agree well with the convection component along the CUTLASS radar beam, while STARE velocities are typically smaller by a factor of 2-3. For the second case, STARE velocities are found to be either smaller or larger than CUTLASS velocities, depending on the range. Plasma physics of E-and F-region irregularities is discussed in attempt to explain the inferred relationship between various velocities. Special attention is paid to ionospheric refraction that is important for the detection of 12-MHz echoes.

Rankin Inlet PolarDARN radar observations of duskward moving Sun-aligned optical forms

“…Indeed, the electron density inside the polar cap arc can reach values of ∼2×10 5 cm −3 (Robinson et al, 1987), which is sufficient to strongly bend radio waves even at short ranges and large geometric aspect angles (e.g. Koustov et al, 2002). Additional argument for the above opinion comes from the elevation angle measurements presented on the bottom panel.…”

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

“…In addition, there has been comparison of echo characteristics at widely differing frequencies, for instance in the HF and VHF bands (e.g. Koustov et al 2001Koustov et al , 2002Makarevitch et al 2001). However, in general, such approaches suffer from poor radar geometries and/or conflicting spatial and temporal resolutions.…”

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

“…They also found that Doppler velocities of FB irregularities in the E-region are limited to a value near the ion acoustic velocity. Recently, Koustov et al (2002) noted that in the EISCAT flux tube the STARE radars cannot always see a purely orthogonal backscatter, i.e. they suggested that a deficiency of the velocity measurements can be contaminated partly due to this fact.…”

“…The west-east asymmetry in STARE echo intensities is well known (see, e.g. by Koustov et al, 2002, their Fig. 4; Uspensky et al, 2003, their Fig.…”

“…Based on the EISCAT N(h) profiles, they defined the effective values of the backscatter altitude, h eff , the aspect angle, eff , and the mean electron density of the backscatter volume, N eff , as a power weighted average of the relative value of the radar volume cross section along altitude. Basic parameters in the estimates are the altitude of zero aspect angle at ∼97 and 99 km (Koustov et al, 2002), a growth of the aspect angle with height by ∼0.07 and ∼0.08 • /km (Uspensky et al, 2003) for the Finland and Norway radars, respectively, as well as the mean power attenuation with the aspect angle of 10 dB/ • . An event from our statistics (12 February 1999, see corresponding N(h) profiles in the LHS panel of Fig.…”