POLAR MESOSPHERE SUMMER RADAR ECHOES - OBSERVATIONS AND CURRENT THEORIES

The remarkably strong radar echoes from the summer polar mesosphere ha ve been an enigma to atmospheric and radar scientists since their disc overy more than a decade ago. Since then, more sophisticated radar exp eriments and in situ rocket measurements have shed some light on the u nderlying physics and chemistry, and theories have been formulated to explain the generation of the intense radar backscatter and the remark able physical conditions associated with it. First, we review the key observations and examine the proposed theories. We then evaluate the p rogress that has been made in understanding this phenomenon and explor e its connection to global change, to the newly recognized material re ferred to as a dusty plasma, and to the highest clouds in the Earth's atmosphere. Finally, we end with suggestions for future research.