Multipulse and double‐pulse velocities of Scandinavian Twin Auroral Radar Experiment (STARE) echoes

Abstract

[1] The Scandinavian Twin Auroral Radar Experiment (STARE) coherent radars are a powerful instrument for studying auroral zone plasma convection. In recent years the STARE radars have been collecting both double-pulse (DP) and multipulse (MP) data to measure the Doppler velocity of auroral echoes. We assess here DP-MP measurements for eight events covering 28 hours of operation. More often, there is a reasonable agreement between the DP and MP velocities. Exceptions are afternoon-evening observations for which the Finland radar DP velocity is nearly half the MP velocity obtained through fitting of the autocorrelation function of a received signal (ACF-FIT), although the DP and MP1 (first lag) velocities are in reasonable agreement. We demonstrate that for periods with strong differences between the DP and MP ACF-FIT velocities the spectra are strongly asymmetric, and the phase angle-lag number dependence is nonlinear with a slower rate of angle increase at small-number lags (<3) and a faster rate of angle increase at larger-number lags. Contrary to the DP velocity, the MP ACF-FIT velocity (obtained in some cases without one or two first-lag data) is fairly close to the spectral power peak and power-weighted (over spectrum) velocity. In an attempt to understand the DP-MP velocity differences, we consider the role of the asymmetry of observed spectra and show that it can explain the discrepancies but only partially. As another potentially important effect, we consider the possibility of weak, but not negligible, cross-range correlation between the signals coming from the target and aliasing volumes that are closely spaced for the current STARE mode of operation.

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

“…Larger velocities in the measurements cited have no simple explanation, since the ACF velocities used in this study have to be larger than the Nielsen et al double-pulse velocities (Nielsen et al, 2002;Nielsen, 2004;Uspensky et al, 2005). Nielsen and Schlegel (1985) did not actually find a pronounced flow angle dependence when their data covered the interval =30−60 • (see their Fig.…”

“…(Note that the term V N,F irr can be called synonymously the irregularity drift (phase or Doppler) velocity). Of importance to this study is the fact that due to an asymmetry of STARE Doppler spectra (and others factors, Uspensky et al, 2005), the phase angle dependence of the echo autocorrelation function versus the lag number (Hanuise et al, 1993) is often nonlinear (Nielsen, 2004). In the eastward electrojet this feature renders the ACF-to-double-pulse (DP) velocity-velocity ratio to factor ∼1.1 and ∼1.7 for the Norway and Finland radar, respectively.…”

“…In the eastward electrojet this feature renders the ACF-to-double-pulse (DP) velocity-velocity ratio to factor ∼1.1 and ∼1.7 for the Norway and Finland radar, respectively. The STARE ACF velocities have better accuracy than DP velocities and consequently we use them to define the peaks of the power spectra as well as the power-weighted velocities (Uspensky et al, 2005). The standard merging of two velocities V N irr and V F irr measured by Norway and Finland STARE radar, Fig.…”

“…In this study we extend the STARE-EISCAT flow angle velocity measurements in the eastward electrojet with increased statistical significance using STARE multi-pulse (MP) mode and the ACF velocities (Uspensky et al, 2005). Our attention is concentrated on larger flow angles between =45 and 85 • .…”

The STARE/SABRE story

“…Nielsen (2004) discussed the observed mean velocities measured with the double-pulse technique for increasing time lag between the pulses. Uspensky et al (2005) proceeded to utilize multipulse power spectra observations with a view to further improve the drift velocity estimates one can derive from STARE data.…”