In this paper we present a new description about statistical probability density distributions (pdfs) of Polar Mesopheric Clouds (PMC) and noctilucent clouds (NLC) occurrence frequencies. The analysis bases on observations of maximum backscatter ratios measured by the ALOMAR RMR-lidar for aNLC seasons from 1997 to 2013. From these lidar data record we estimate an additional observational quantity of ice water density. For these two data sets we derive new classes of pdfs that describe the statistics of PMC/NLC events different from previously statistical methods using the approach of an exponential distribution commonly named g-distribution. The new theory is very successful in describing the probability statistic of ALOMAR lidar data. It turns out that the former g-function statistic is embedded in our new theory as a special case. In general the new theory allows to derive basic parameters of climatological ice particle distributions, namely mean ice radii and variances, and, secondly, the theory can be generally applied to many kinds of different observational data sets, e.g. measurements of albedo, ice water content, and ice water densities by satellite instruments, or backscatter signals by lidars, respectively.