A statistical study of polar mesosphere summer echoes observed by EISCAT
A comprehensive survey of data on ‘Polar Mesosphere Summer Echoes’, observed by the EISCAT VHF radar during 1988–1993, confirms that (1) these echoes are a summer phenomenon, with a season lasting from June to August; (2) PMSE occur most frequently around noon and midnight, and thus follow a semidiurnal pattern; (3) PMSE occur at a mean height of 85±2 km; (4) there is often a good correlation between the vertical Doppler velocity and the rate of change of echo height, which suggests that the echoing structures move bodily, perhaps in response to gravity waves. Previous results on the lack of correlation between the occurrence of PMSE and noctilucent clouds are reinforced.