Abstract
Narrow layers of enhanced radar echoes from the winter mesosphere have been observed by the ESRAD 52 MHz radar (68°N,21°E) during recent solar proton events. These layers have been named PMWE, Polar Mesosphere Winter Echoes. Comparison of the characteristics of the radar echoes to the expected characteristics of neutral turbulence in the winter mesosphere leads to the conclusion that PMWE are unlikely to be caused by neutral turbulence alone. Their strength, and their persistence in conditions when moderately high concentrations of negative ions can be expected, are however consistent with the expected influence of small charged aerosol particles on radar scatter. During a solar proton event in January 2002 measurements were made by both the ESRAD radar and a lidar situated at the same site. The lidar observed a region of enhanced backscatter in the same height interval as the radar observed PMWE. The lidar observations can be interpreted either as a sharp temperature minimum or as a layer of aerosol particles. The latter interpretation offers consistency with the radar observations.
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