The characteristics of VHF echoes from the summer mesopause region at mid-latitudes

Radar observations were carried out during the period May-August 1990 to search for echoes analogous to the polar mesosphere summer echoes commonly observed at high latitudes. Signal strength measurements in the vertical and at 12 deg from the vertical are used to examine the aspect sensitivity of echoes, and Doppler measurements at 6 deg from the vertical and in the vertical to estimate wind velocities. The observations show the presence of two types of moderately strong echoes from heights above 80 km. On most days a spectrally broad echo is observed with characteristics consistent with isotropic turbulence scatter. On certain days between mid-June and mid-July, stronger spectrally narrow echoes are observed with characteristics similar to polar mesosphere summer echoes.