Distance-Scaled Water Concentrations versus Mass-Median Drop Size, Temperature, and Altitude in Supercooled Clouds

Abstract

Abstract About 28 000 nautical miles (n mi) of select in-flight measurements of liquid water content (LWC), droplet sizes, temperature, and other variables in supercooled clouds from a variety of research projects over portions of North America, Europe, and the northern oceans have been compiled into a computerized database for obtaining new statistics on the ranges, frequency of occurrence, and interrelationships of the variables. The LWCs are averaged over uniform cloud intervals of variable length. LWC probabilities are then generated as a function of averaging distance, temperature, droplet mass-median diameter (MMD), altitude, and freezing-level height. These variously scaled LWCs (different averaging intervals from 1 s to 200 n mi) are easily accommodated by distance-based graphing (LWC versus averaging distance). These graphs provide realistic LWCs for modeling, and they can serve as a common reference for comparing LWC measurements over any averaging scale. Maximum recorded LWCs are about 1.6 g m−3 in stratiform clouds and about 5 g m−3 in convective clouds, both over short (<0.5 km) distances. A sharp MMD mode near 15 μm appears to be a stable condition in which the LWCs can be the largest and extend the farthest. The larger the MMD above the mode, the shorter its spatial extent will be, the rarer its occurrence, and the lower the maximum LWC that can be present.