STUDIES OF POLAR MESOSPHERE SUMMER ECHOES BY VHF RADAR AND ROCKET PROBES

At radar frequencies in the range 50 MHz to 250 MHz, at times even to over 1 GHz, strong enhancements of scattering cross section occur between similar or equal to 80km and similar or equal to 95km altitude in summer at high latitudes. These echoes, termed ''Polar Mesosphere Summer Echoes'' (PMSE), have attracted considerable experimental effort. Observations of this phenomenon are reviewed in the context of atmospheric dynamics and of scattering processes. Recent rocket and radar measurements indicate that a partial reflection from a multitude of ion layers and constructive interference causes at least some of the PMSE. It is discussed which further observations are necessary and some possible practical consequences of PMSE we pointed out.