The Effects of Altitude and Electrical Force on the Terminal Velocity of Hydrometeors

Abstract

A formula has been developed for computing the terminal velocity V from a reference velocity V0 by use of an adjustment factor f=V/V0 for a change in altitude or electric force. The drag coefficients for bodies of regular geometry were analyzed, and found to be sufficiently similar that a single adjustment formula could be used for all hydrometeor shapes. Comparisons with drag data showed that a formula for f, that is only a function of size, air density, viscosity, charge and electric field, predicts V/V0 to within 2% in most cases. This method also provides a reasonable means of computing V/V0 for complex geometries such as rimed ice crystals, aggregates and graupel, and for drops undergoing electrical stress.