AN EXAMINATION OF THE WIND-DRIVEN EFFECT ON THE DRIFT OF PRECIPITATION PARTICLES USING THE CHUNG-LI VHF RADAR

One of the essential assumptions made in estimating the terminal veloc ity and the drop-size distribution of hydrometeor from the precipitati on Doppler spectrum observed by VHF/UHF radar (or wind profiler) is th at all of the precipitation particles are moving together at the same velocity as the ambient wind. However, this may not be the case. In th is paper, taking advantage of the capability of simultaneously measuri ng the motions of precipitation particles and the clear-air turbulence with a VHF radar, we develop a method to examine the wind-driven effe ct on the drift of precipitation particles using the Chung-Li VHF rada r. By appropriately setting the radar parameters and steering the rada r beams, experimental results show that the drift velocity of the prec ipitation particles in response to the drag force exerted by the backg round atmosphere is not the same as the ambient wind velocity, approxi mately 83% of the latter in this case. This feature indicates that the precipitation particles are not moving with the background wind, caus ing inaccurate estimations of the terminal velocity and the drop-size distribution of hydrometeor if this effect is not taken into account.