Simultaneous Observations of Noctilucent Clouds and Polar Mesospheric Radar Echoes: Evidence of Noncorrelation

Noctilucent clouds (NLC) and strong polar mesosphere summer echoes (PMSE) appear at similar heights, similar latitudes and at about the same time of year. To determine whether these two phenomena are related in detail, a visual and photographic search for NLC over the EISCAT radar site at Tromsö, Norway, was made on several nights in August 1988 when the VHP radar was observing in the zenith at mesospheric heights. Both phenomena were observed several times during the campaign, but only once did they occur simultaneously. These observations indicate that noctilucent clouds and PMSE are not closely correlated, at least during the late summer. Auroral particle precipitation appeared to enhance the detectability of PMSE during this period