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From 1997 to 2003, noctilucent clouds (NLC) were observed by lidar\udabove the ALOMAR observatory in Northern Norway (69° N) during\uda total of 1880 measurement hours. This data set contains NLC\udsignatures for 640h, covering all local times, even during the\udhighest solar background conditions. After data limitation\udimposing a threshold value of 4x10-10m-1sr-1 for the\udvolume backscatter coefficient of the NLC particles, a measure for\udthe cloud brightness, local time dependencies of the NLC\udoccurrence frequency, altitude, and brightness were determined. On\udaverage, over the 7 years NLC occurred during the whole day and\udpreferably in the early morning hours, with a maximum occurrence\udfrequency of ~40% between 4 and 7 LT. Splitting the data\udinto weak and strong clouds yields almost identical amplitudes of\uddiurnal and semidiurnal variations for the occurrence of weak\udclouds, whereas the strong clouds are dominated by the diurnal\udvariation. NLC occurrence, altitude, as well as brightness, show a\udremarkable persistence concerning diurnal and semidiurnal\udvariations from 1997 to 2003, suggesting that NLC above ALOMAR are\udsignificantly controlled by atmospheric tides. The observed mean\udanti-phase behavior between cloud altitude and brightness is\udattributed to a phase shift between the semidiurnal components by\ud~6h. Investigation of data for each individual year\udregarding the prevailing oscillation periods of the NLC parameters\udshowed different phase relationships, leading to a complex\udvariability in the cloud parameters

Mean diurnal variations of noctilucent clouds during 7 years of lidar observations at ALOMAR