Abstract
Abstract. In the mid-latitude E-region there is now evidence suggesting that neutral winds play a significant role in driving the local plasma instabilities and electrodynamics inside sporadicE layers. Neutral winds can be inferred from coherent radar backscatter measurements of the range-/azimuth-time-intensity (RTI/ATI) striations of quasi-periodic (QP) echoes, or from radar interferometer/imaging observations. In addition, neutral winds in the E-region can be estimated from angle-of-arrival ionosonde measurements of sporadic-E layers. In the present paper we analyse concurrent ionosonde and HF coherent backscatter observations obtained when a Canadian Advanced Digital Ionosonde (CADI) was operated under a portion of the field-of-view of the Valensole high frequency (HF) radar. The Valensole radar, a mid-latitude radar located in the south of France with a large azimuthal scanning capability of 82° (24° E to 58° W), was used to deduce zonal bulk motions of QP echoing regions using ATI analysis. The CADI was used to measure angle-of-arrival information in two orthogonal horizontal directions and thus derive the motion of sporadic-E patches drifting with the neutral wind. This paper compares the neutral wind drifts of the unstable sporadic-E patches as determined by the two instruments. The CADI measurements show a predominantly westward aligned motion, but the measured zonal drifts are underestimated relative to those observed with the Valensole radar.
Highlights
Coherent radar backscatter studies of the unstable midlatitude E-region have shown that sporadic-E layers (Es) and neutral winds play a fundamental role in formulating the plasma physics unique to this region (e.g. Riggin et al (1986); Hussey et al (1998); Hysell et al (2002), among others)
Given the anticipated importance of the westward neutral winds in mid-latitude sporadic-E layer instabilities, the present paper aims to provide a further test of the neutral wind role on unstable Es by comparing the bulk motions deduced from azimuth-time-intensity striations of the Valensole high frequency (HF) radar quasi-periodic echoes, and those from a Canadian Advanced Digital Ionosonde (CADI)
HF measurements are in agreement with several studies showing that unstable Es patches in the pre-midnight sector drift mostly westward across the radar field-of-view, presumably with the neutral wind
Summary
Coherent radar backscatter studies of the unstable midlatitude E-region have shown that sporadic-E layers (Es). The great majority of these structures drift with westward speeds between about 20 to 100 m/s, whereas values as high as 150 m/s are not uncommon These predominately westward motions of sporadic-E patches have been measured in several radar and rocket studies Tanaka and Venkateswaran (1982); Yamamoto et al (1992); Bourdillon et al (1995); Larsen et al (1998); Haldoupis et al (2001); Hysell et al (2002) among several others) In their discussion, Haldoupis et al (2003) suggested that the westward motions in sporadic-E backscatter is an inherent property of the phenomenon which might be of importance in creating the Es layering (in accordance with the wind shear theory), and in the destabilising process, as well. The CADI drift measurements are compared, in an effort to be validated, with those deduced by ATI plots of the Valensole radar
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