Dynamics of raindrop size distribution from the data of high-frequency Doppler sodar measurements

A new method has been suggested for reconstruction of raindrop size distribution and rain intensity from the normalized spectra of acoustic signals measured with a cw bistatic Doppler sodar. A data processing algorithm has been constructed and successively used for real sodar data processing, based on the analytical formulas derived in the Rayleigh approximation and with the use of the exact Mie formulas. The raindrop size spectra were reconstructed from the individual power spectra of signals recorded every 20 s and from the signal power spectra averaged of 2-, 3-, %-, and 25-min periods. This has allowed us to track the dynamics of the raindrop size distribution. The presence of the second maximum of the number density of large raindrops was established, whose position shifted with time from 0.3 to 1 mm. Our study has shown that the large raindrops were grouped in ensembles and the second maximum of the raindrop size distribution was observed only periodically. The obtained results demonstrate that high- frequency cw bistatic sodars are very promising for measurements of rain.