The Observed and Computed Microstructure of Hail-Producing Clouds in Northeastern Colorado

Abstract

The modification of thunderstorms to suppress hail requires a knowledge of where, when and how much to seed. We show that growth by accretion by precipitating particles (hail, rain and graupel) in a summer convective storm depends on the path that the particles take with respect to the cloud air circulation in which the cloud droplets are embedded, as well as on the ambient atmospheric parameters of temperature, moisture, stability and larger scale circulations. For this purpose we used a two-dimensional simulation of the circulation in which the most important features of one-dimensional time-dependent microphysics simulation can be incorporated into the calculations at each time step. The effect of changes in the altitude of ice particle initiation is calculated using simulations of the clouds and their environment on two days during this period when the total amount of hail differed by more than an order of magnitude. The simulated hail size and amount varied in the same sense as the observed. The simulation is applied to the case used by Browning and Foote (1976) to develop a conceptual model of a severe hailstorm. The results show that in order to obtain the tilt of the updraft shown by Browning and Foote, the presence of a squall line or gust front would be required?a situation that they say is possible from their observed meteorological data.