Abstract
Abstract. The polarization characteristics of 930-MHz meteor head echoes have been studied for the first time, using data obtained in a series of radar measurements carried out with the tristatic EISCAT UHF high power, large aperture (HPLA) radar system in October 2009. An analysis of 44 tri-static head echo events shows that the polarization of the echo signal recorded by the Kiruna receiver often fluctuates strongly on time scales of tens of microseconds, illustrating that the scattering process is essentially stochastic. On longer timescales (> milliseconds), more than 90 % of the recorded events show an average polarization signature that is independent of meteor direction of arrival and echo strength and equal to that of an incoherent-scatter return from underdense plasma filling the tristatic observation volume. This shows that the head echo plasma targets scatter isotropically, which in turn implies that they are much smaller than the 33-cm wavelength and close to spherically symmetric, in very good agreement with results from a previous EISCAT UHF study of the head echo RCS/meteor angle-of-incidence relationship. Significant polarization is present in only three events with unique target trajectories. These all show a larger effective target cross section transverse to the trajectory than parallel to it. We propose that the observed polarization may be a signature of a transverse charge separation plasma resonance in the region immediately behind the meteor head, similar to the resonance effects previously discussed in connection with meteor trail echoes by Herlofson, Billam and Browne, Jones and Jones and others.
Highlights
Meteor head echoes at UHF frequencies have been systematically observed by high power, large aperture (HPLA) radar systems for more than 20 years
The polarization characteristics of 930-MHz meteor head echoes have been studied for the first time, using data obtained in a series of radar measurements carried out with the tristatic EISCAT UHF high power, large aperture (HPLA) radar system in October 2009
When the UHF radar is used in its “standard”, i.e. incoherentscatter (IS), mode, the polarization of the incoherent-scatter signals received at the Kiruna and Sodankylasites can take on any value from right-hand circular (RHC) via elliptical and linear to left-hand circular (LHC), depending on the location of the common scattering volume
Summary
Meteor head echoes at UHF frequencies have been systematically observed by high power, large aperture (HPLA) radar systems for more than 20 years. Even after this time, our understanding of the detailed characteristics of the plasma targets that create the head echoes is still inconclusive and there is not much substantive data on their actual size and shape. This is so primarily because the targets are much smaller than the spatial resolution of the radar systems and remain unresolved. In a measurement series carried out in October 2009, we made use of this feature, together with the capability of the tristatic system to uniquely determine the vector velocities of head echo targets, to study the polarization of 930-MHz meteor head echoes for the first time
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