Noctilucent clouds: One‐ and two‐color lidar observations

Abstract

From early July until mid‐August 1995 we observed six noctilucent clouds (NLC) above the ALOMAR observatory in Northern Norway (69°N, 16°E) with ground based lidar. The NLC layers had maximum backscatter ratios between 17 and 190 at 532 nm, their mean altitude was 83.0 km. The latest of these events (August 12/13, 1995) was observed by two lidars, both, the Rayleigh‐ and the ozone lidar, located in the ALOMAR observatory, on wavelengths of 532 nm and 308 nm, respectively. During the period of common‐volume observations from 23:55 UT until 01:30 UT, maximum averaged backscatter ratios of 56 and 28 were measured at 532 and 308 nm, respectively. If we assume spherical particles and a lognormal particle size distribution of width s, standard Mie theory yields median radii rm of the NLC particles between 16 nm and 44 nm with number densities between 2780 cm−3 and 160 cm−3 for assumed values of s between 1.6 and 1.2, respectively.