Lidar temperature measurements during a rare mid-latitude noctilucent cloud event

Abstract

We present lidar soundings of the only noctilucent cloud event recorded above GERES station in the Bavarian Forest (48.8 N, 13.7 E) during the 2016 season. A single thin NLC layer was observed for several hours at a low mean altitude of 81.1 km. Due to darkness and the high power of the CORAL lidar, Rayleigh temperatures could be obtained between 30 and 86 km altitude, reaching well above the NLC layer. By density interpolation, we estimate temperatures also within the NLC layer. Interestingly, we find high temperatures directly above the NLC layer which is embedded in a cold region extending well below the layer. Using meteor radar data, we argue that the NLC did not nucleate at the site of observation but was meridionally transported from higher latitudes during a 2-day planetary wave event. The NLC was unusally bright given the latitude and during observation, the layer was subject to variations with periods ranging from 11 min to 60 min. We bring small scale variations in NLC centroid altitude and brightness in relation with gravity wave structures inferred from temperature measurements. The lidar measurements reveals that the NLC layer resides in the cold phases of gravity waves passing through the mesosphere, lower thermosphere region.