FIRST HF RADAR MEASUREMENTS OF SUMMER MESOPAUSE ECHOES AT SURA

HF sounding of the mesosphere was first carried out at SURA in summer 1994 at frequencies in the range 8-9 MHz using one of the sub-arrays o f the SURA heating facility. The observations had a range resolution o f 3 km. Almost all measurements indicated the presence of strong radar returns from altitudes between 83 and 90 km with features very simila r to VHF measurements of mesopause summer echoes at midlatitudes and p olar mesopause summer echoes. In contrast to VHF observations, HF meso pause echoes are almost always present.