Some Microphysical Processes Affecting Aircraft Icing.

This report summarizes work done as part of the aircraft icing probabilities program. It contains a look at icing in layer-type clouds, a comparison of Particle Measuring System (PMS)2-D data from two flights. and a look at additional data obtained from researchers in the Federal Republic of Germany. The parameters measured in a warm and cold layer-type cloud near Peoria, IL are analyzed and compared. Liquid water content (LWC), cloud depth, particle diameter and particle concentration are compared. Variations of these parameters are compared. In mature clouds, where droplet sizes are approximately equal, the LWC is directly related to the number concentration. The icing rate, LWC and droplet size all increase as a function of height above cloud base. Synoptic patterns and PMS 2-D data obtained on two flights are compared. The first flight, made near Greensboro, NC was in an area of heavy precipitation. The large particles present produced very little icing. The other flight, near Flint, MI was in an area which was experiencing only spotty precipitation. The aircraft, however, experienced moderate icing. Data gathered on aircraft observations in the Federal Republic of Germany are examined. The data show that in strong icing situations, there are many particles with diameters of 10 to 20 microns. The results match those obtained by our research flights. Keywords: Cloud physics; Aviation meteorology; Particle distribution.