Climatology of noctilucent cloud radii and occurrence frequency using SCIAMACHY

We present a climatology of noctilucent cloud (NLC) occurrence rate (northern and southern hemisphere) and particle size (northern hemisphere) based on SCIAMACHY measurements between 2002 and 2007. An interannual analysis of occurrence rates shows no trend in the northern hemisphere despite the decreasing solar activity during that period. The mean NLC particle radius for a Gaussian particle size distribution with σ=22nm is 68.0±11.4nm. There is an increase of the particle size with latitude, with a gradient as large as 2nm/deg for latitudes larger than 75∘. SCIAMACHY observes an increase of mean NLC particle size during the last 5 years at latitudes higher than 70∘, which might be linked to the decrease in solar activity. The interannual variability of the seasonally averaged particle size is ±2nm in a given latitude band. Results concerning the sensitivity of the retrieval to the particle shape and particle size distribution assumed width are also presented.