THE ACOUSTIC-ELECTRIC COALESCENCE AND THE INTENSIFICATION OF PRECIPITATION RADAR ECHOES IN CLOUDS

Droplet motion and electrical effects produced by lightning within clo uds may cause a rapid and effective drop coalescence process. The prob lem of spectrum evolution in warm convective clouds is investigated us ing a one dimensional axial-symmetric time-dependent model. It is anal yzed with the influence of acoustic waves on rain gushes as well as th e effects of the rearrangement of charge deposited along the lightning channel on the coalescence of droplets. The numerical results for dif ferent cloud conditions (liquid water content, mean droplet radius, en ergy density of lightning channel, values of droplet charge intensity and distribution of charged droplets) show that acoustic-electric coal escence for less than 1 s can increase the mean volume radius of the i nitial spectra by 10 to 20% and the radar reflectivity by about 2 dBZ. That increase of droplet size could be important for further gravitat ional growth, which suggests the idea that lightning has the potential to initiate rain gushes and gives an additional explanation for inten sification of radar echoes. (C) 1998 Elsevier Science B.V. All rights reserved.