Size distributions of NLC particles as determined from 3-color observations of NLC by ground-based lidar

Abstract

From June to August 1998 the ALOMAR Rayleigh/Mie/ Raman lidar, located at 69°N and 16°E in Northern Norway, repeatedly observed noctilucent clouds (NLCs) overhead the lidar. Due to a recent upgrade in detector technology, the lidar was able to obtain 151 hours of NLC observations, simultaneously at 355, 532, and 1064 nm. For the 11 strongest NLC events, we have calculated size distributions for the NLC particles from the backscatter ratios measured at the 3 wavelengths and using the assumptions of spherical ice particles with a monomodal lognormal size distribution. For all events evaluated at the layer maxima, we obtain well-defined median radii r(med), width parameters σ, and particle number densities N(NLC) for the NLC particle distributions. Mean values for 10 out of the 11 events are r(med) = 51 nm, σ = 1.42, and N(NLC) = 82 cm-3.