Simultaneous observation of noctilucent clouds, mesospheric summer echoes, and temperature at a midlatitude station (54°N)

Abstract

Between 2003 and 2005, 12.9 h (8 events) of noctilucent clouds (NLC) and 250 h of mesospheric summer echoes (MSE) were observed above Kühlungsborn (54°N, 12°E) by lidar and radar, respectively. The ice‐layer seasons typically last for 50 (NLC) and 70 days (MSE). The observations are compared with simultaneous lidar temperature soundings. Altogether, 79 soundings were performed in the periods 10 May to 8 August of each year. These profiles revealed a minimum mesopause temperature of 145 K at 87 km shortly after summer solstice. The mean temperatures are below the frost point temperature for a period of ∼15 days after summer solstice and in the altitude range ∼85–89 km. Simultaneous observations of temperature, MSE/NLC, and winds by radar and lidar show that ice particles occur primarily during southward winds and during the cold phases of gravity waves and tides, providing temperatures up to ∼20 K lower than the mean. Water vapor saturation profiles are calculated from the temperatures and modeled water vapor concentrations, showing that the ice layers occur at the bottom of the supersaturated region. Only about one fifth of all supersaturation events below 85 km in fact yield NLC above our site. Even saturation ratios of 10–100 lasting for at least 4 h do not necessarily lead to the formation of NLC. We conclude that NLC at midlatitudes are strongly coupled to the advection of preexisting ice particles from northern latitudes. If the ice particles have sublimated prior to the observation, they do not form again even in the cold phases of waves.