Seasonal and latitudinal variation of noctilucent cloud altitudes

摘要

We present a summary of similar to 1500 hours of lidar measurements of noctilucent cloud (NLC) altitudes at Ku hlungsborn (54 degrees N), ALOMAR (69 degrees N), and Spitsbergen (78 degrees N). Mean centroid altitudes (z(c)) are 82.75 km, 83.33 km, and 83.68 km, respectively. Standard deviations sigma representing geophysical variability are similar to 0.7-1.6 km. Errors of mean heights Delta z(c) are much smaller (60-340 m). Several processes which are not yet fully understood influence z(c). Therefore, sigma is a better measure of uncertainties in z(c) compared to Delta z(c). The increase of NLC heights with latitude is very small (43 +/- 65 m/deg) and statistically not significant. At ALOMAR zc varies with season by up to similar to 1-1.5 km. NLC heights accumulate around climatological temperatures of 145 K at 69 degrees N and 78 degrees N (higher at 54 degrees 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 degrees N.