Liquid Water in Squall Lines and Hurricanes

I n convective clouds jet aircraft encounter icing at air temperatures lower th211 -60' C. It may be reesoned that this results from (1) the melting of frozen droplets duc to dynamic or frictional heating in the quasi-potential flow around the air foil; (2) the impact of precipitation consisting of ice spheres with liquid water cores; (3) the possibility that raindrops are carried upward by vertical currents so rapidly that the water temperature remains higher than the spontaneous nucleation temperature (-40" C.) while the air temperature is much lorn-er; or (4) the possibility that the spontaneous nucleation temperature is pressure dependent or otherwise variable. This paper investigates the third of these possibilities and finds that the difference in temperature of liquid water and air at 13 km. can be no more than a few degrees except in the case of very large drops carried through deep layers of cloud by intense steady-state updrafts of the kind associated with hail-producing thunderstorms.