AN UPDATED REVIEW OF POLAR MESOSPHERE SUMMER ECHOES - OBSERVATION, THEORY, AND THEIR RELATIONSHIP TO NOCTILUCENT CLOUDS AND SUBVISIBLE AEROSOLS

Peculiar atmospheric radar echoes from the high-latitude summer mesosp here have spurred much research in recent years. The radar data (taken on frequency bands ranging from 2 to 1290 MHz) have been supplemented by measurements from an increasing arsenal of in situ (rocket borne) and remote sensing (satellites and lidars) instruments. Theories to ex plain these polar mesosphere summer echoes (PMSEs) have also prolifera ted. Although each theory is distinct and fundamentally different, the y all share the feature of being dependent on the existence of electri cally charged aerosols. It is therefore natural to assume that PMSEs a re intimately linked to the other fascinating phenomenon of the cold s ummer mesopause, noctilucent clouds (NLCs), which are simply ice aeros ols that are large enough to be seen by the naked eye. In this paper w e critically examine both the data collected and the theories proposed , with a special focus on the relationship between PMSEs and NLCs.