Abstract
Polar mesosphere winter echoes (PMWE) were observed at 70 km over Tromsø, Norway, on 8 January 2014 using the tristatic configuration of the European incoherent scatter VHF radar. For the interval 11:00–13:00 UT where the strongest patch of PMWE of about 6-min duration was detected, the spectra of the received signal were analysed for the Tromsø site and altitude profiles of spectral parameters were derived. For the remote sites Kiruna and Sodankylä, the Doppler velocities and their vertical shear were determined by using the measured autocorrelation functions. Ducted gravity waves with periods of 5–10 min were found in the vertical wind velocity between 66 and 81 km altitudes. The duct might be formed around 70 and 77 km altitude where horizontal wind maxima were observed with the Kiruna receiver. However, we did not find any close relation between wind shear at 70 km altitude and PMWE at the same height: the wind shear was present for 2 h, but PMWE for only 6 min. Enhanced spectral width in the vertical Tromsø beam was observed for the PMWE patch. We discussed these experimental findings in relation to the winter echo generation mechanism. Our conclusion is that the presence of patchy negatively charged small-sized dust might explain the observations although a gravity wave breaking mechanism cannot be completely rejected.
Highlights
Polar mesosphere winter echoes (PMWE) are enhanced backscatter from 50 to 80 km altitudes observed by VHF radars in the winter and equinox seasons in polar regions
Rapp (2013) based on 32-h PMWE observations with the European incoherent scatter (EISCAT) VHF radar. They found that the autocorrelation function (ACF) inside PMWE have exponent median value of 1.6, whereas outside the echoes this value is about 1
Small patches of PMWE were observed during solar proton event on 8 January 2014 using the tristatic configuration of the EISCAT VHF radar
Summary
Polar mesosphere winter echoes (PMWE) are enhanced backscatter from 50 to 80 km altitudes observed by VHF radars in the winter and equinox seasons in polar regions. PMWE have been observed with atmospheric radars in the Arctic at about 50 MHz as well as with the European incoherent scatter (EISCAT) VHF radar at 224 MHz (e.g. Czechowsky et al 1979; Ecklund and Balsley 1981; Belova et al 2005; Kirkwood et al 2006a; Zeller et al 2006; Strelnikova and Rapp 2013). They have been observed over Antarctica (Morris et al 2011; Kirkwood et al 2015; Nishiyama et al 2015). Lübken et al (2006) suggested that at least some PMWE can be explained by layered neutral turbulence
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