Diurnal variations of midlatitude NLC parameters observed by daylight-capable lidar and their relation to ambient parameters

Noctilucent Clouds (NLCs) are an important phenomenon of the summer mesopause region. While relatively common in high latitudes, NLCs are sparse (≤10% occurrence rate) below 60°latitude. We present the first study of diurnal variations of midlatitude NLCs based on lidar observations with full diurnal coverage at Kühlungsborn since 2010 independent from solar elevation. Overall, ∼100h of NLCs with a backscatter coefficient of βmax,532nm>0.5·10−10m−1sr−1are observed within ∼1800h. Occurrence rates decrease regularly from 12% at 5local solar time (LST) to ∼2% at 19LST. The mean NLC brightness varies between ∼1 and ∼3·10−10m−1sr−1with maxima at 4 and 18LST. The simultaneously observed temperatures show a systematic (tidal) variation, but we do not find a direct relation to NLC rates. Comparing NLCs and ambient winds, we find strong indications for the meridional wind (advection) being the main driver for NLC occurrence above our site. Key Points NLC occurrence highest in early morning, lowest in early evening NLC occurrence independent from temperature tide NLC occurrence depends on meridional wind tide (advection)