The small-scale structure of VHF mesospheric summer echo layers observed at mid-latitudes

摘要

The VHF radar system at Aberystwyth (52.4°N, 4.1°E) has been used to make high-time-resolution, multi-beam observationsof mesospheric summer echo layers. These show that the altitude and the sense ofvertical movement of the layers can vary over time-scales of minutes andhorizontal scales of kilometres. In general, the altitude profiles ofsignal-to-noise ratio provide evidence of a bifurcated structure with sharpchanges in the horizontal wind vector and vertical velocity, and enhancedspectral width occurring at the bifurcation level. The implications of thesmall-scale structure for studies of the aspect sensitivity of radar returns arediscussed, and the changes in wind-field at the bifurcation level are comparedwith 'wind corners' observed in rocket studies of the mesosphere at polarlatitudes.