The acoustic–electric coalescence and the intensification of precipitation radar echoes in clouds

Droplet motion and electrical effects produced by lightning within clouds may cause a rapid and effective drop coalescence process. The problem of spectrum evolution in warm convective clouds is investigated using a one dimensional axial-symmetric time-dependent model. It is analyzed with the influence of acoustic waves on rain gushes as well as the effects of the rearrangement of charge deposited along the lightning channel on the coalescence of droplets. The numerical results for different cloud conditions (liquid water content, mean droplet radius, energy density of lightning channel, values of droplet charge intensity and distribution of charged droplets) show that acoustic–electric coalescence for less than 1 s can increase the mean volume radius of the initial spectra by 10 to 20% and the radar reflectivity by about 2 dBZ. That increase of droplet size could be important for further gravitational growth, which suggests the idea that lightning has the potential to initiate rain gushes and gives an additional explanation for intensification of radar echoes.