GRAUPEL TRAJECTORIES AND CHARGING - A NEW NUMERICAL APPROACH FOR CLOUD ELECTRIFICATION STUDIES

In this work the growth, motion and charging of graupel particles are simulated by computer. The cloud fields are calculated by a three-dime nsional cloud model. Another program calculates the time evolution, in side these cloud fields, of graupel properties (size, position, charge and others). The electricity enters both in the charging of the parti cles through their interactions with other particles and in the motion itself, since in the equation of motion the electrical force is inclu ded. Embryos with 500 mu m initial diameter are released at 656 locati ons uniformly distributed in the updraught centre at four altitudes. T he trajectories of all the particles are followed all the way to the 0 degrees C altitude. The graupel is charged by the ice-crystal-graupel non-inductive mechanism. This kind of approach appears to be a powerf ul tool to study the electric charging of the graupel in greater detai l, since a very high spatial resolution (about 1 m) is easily achieved . Some preliminary analysis of the charges on the precipitation partic les is carried our and the results are related to in situ observations . For the sake of comparison, trajectories without the electrical inte raction are also computed, and it is shown that in some cases the fina l radius with and without the electrical force can differ by a factor of two to three in either direction depending on the initial position.