A Model of Intense Downdrafts Driven by the Melting and Evaporation of Precipitation

Abstract A ono-dimensioral time-dependent model of a downdraft driven by the melting and evaporation of precipitation and precipitation loading is formulated. Equations for particle melting, particle evaporation, particle concentration, precipitation content, thermodynamic energy, and vertical air velocity are formulated and solved numerically. In the environment, the lapse rate of temperature and the relative humidity are prescribed. At the top of the downdraft column, the temperature, relative humidity, vertical air velocity, and the phase and size distribution of the precipitation particles are prescribed. Two types of particle size distribution are considered: a distribution consisting of a single exponential function of the negative of the particle diameter, and a distribution consisting of two exponential functions of different slopes joining continuously at a melted diameter of 3 mm. The effects of lapse rate of environmental temperature, precipitation content, its phase and size distribution on th...