Seasonal and latitudinal variation of noctilucent cloud altitudes

[1] We present a summary of $1500 hours of lidar measurements of noctilucent cloud (NLC) altitudes at Kühlungsborn (54°N), ALOMAR (69°N), and Spitsbergen (78°N). Mean centroid altitudes (z c ) are 82.75 km, 83.33 km, and 83.68 km, respectively. Standard deviations s representing geophysical variability are $0.7 -1.6 km. Errors of mean heights Dz c are much smaller (60 -340 m). Several processes which are not yet fully understood influence z c . Therefore, s is a better measure of uncertainties in z c compared to Dz c . The increase of NLC heights with latitude is very small (43 ± 65 m/deg) and statistically not significant. At ALOMAR z c varies with season by up to $1 -1.5 km. NLC heights accumulate around climatological temperatures of 145 K at 69°N and 78°N (higher at 54°N). The LIMA model nicely reproduces observations and indicates that non-variation of NLC heights at polar latitudes is caused by temperature uniformity: the 145 K isotherm varies in height by less than 250 m from the pole to 60°N