Simultaneous observations at different altitudes of ionospheric backscatter in the eastward electrojet

Abstract

Abstract. A common feature of evening near-range ionospheric backscatter in the CUTLASS Iceland radar ®eld of view is two parallel, approximately L-shellaligned regions of westward¯ow which are attributed to irregularities in the auroral eastward electrojet region of the ionosphere. These backscatter channels are separated by approximately 100±200 km in range. The orientation of the CUTLASS Iceland radar beams and the zonally aligned nature of the¯ow allows an approximate determination of¯ow angle to be made without the necessity of bistatic measurements. The twō ow channels have di erent azimuthal variations in¯ow velocity and spectral width. The nearer of the two regions has two distinct spectral signatures. The eastern beams detect spectra with velocities which saturate at or near the ion-acoustic speed, and have low spectral widths (less than 100 m s À1 ), while the western beams detect lower velocities and higher spectral widths (above 200 m s À1 ). The more distant of the two channels has only one spectral signature with velocities above the ionacoustic speed and high spectral widths. The spectral characteristics of the backscatter are consistent with Eregion scatter in the nearer channel and upper-E-region or F-region scatter in the further channel. Temporal variations in the characteristics of both channels support current theories of E-region turbulent heating and previous observations of velocity-dependent backscatter cross-section. In future, observations of this nature will provide a powerful tool for the investigation of simultaneous E-and F-region irregularity generation under similar (nearly co-located or magnetically conjugate) electric ®eld conditions.

CUTLASS HF radar observations of high-velocity E-region echoes

“…3b,c) show two bands of echoes, or two channels, similar to observations of Milan and Lester (1998). Both channels are marked by white dashed lines in panel (b).…”

“…An HF radar simply cannot detect irregularities outside the area of exact orthogonality or acceptable non-orthogonality. If one applies the model to various azimuths, a tendency for the L-shell alignment of both channel 1 and channel 2 echoes (Milan and Lester, 1998) can be demonstrated. Indeed, for observations perpendicular to the L-shells, the distances of near zero aspect angles are smaller and thus, the echo power should have a maximum at shorter distances.…”

“…In agreement with this conclusion on the current flows, the Stokkseyri radar shows negative velocities at short-to-moderate distances in beams 0-5 (low latitudes) and positive velocities at higher latitudes in beams 7-13. (Milan and Lester, 1998).…”

“…Villain et al (1987Villain et al ( , 1990 were the first to study E-region decametre irregularities in a systematic fashion. Some distinct properties of such irregularities have been refined in subsequent studies (Hanuise et al, 1991;Uspensky et al, 1994a;Eglitis et al, 1995;Milan et al, 1997;Milan and Lester, 1998;Jayachadran et al, 2000;Koustov et al, 2001). Milan and Lester (1999) put forward the idea that at HF there might be several classes of E-region echoes and that not all of them are necessarily related to the F-B and G-D instabilities, though the conventional type 1 and type 2 echoes probably constitute the bulk of HF data.…”

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

“…This usually has to be inferred, with wide margins of uncertainty. In an attempt to overcome this, effort has been made to compare echo characteristics with F-region backscatter (Milan and Lester 1998;Makarevitch et al 2004), incoherent scatter radar measurements (Makarevitch et al 2006), or low-altitude spacecraft measurements . In addition, there has been comparison of echo characteristics at widely differing frequencies, for instance in the HF and VHF bands (e.g.…”