An examination of the wind-driven effect on the drift of precipitation particles using the Chung-Li VHF radar

Abstract

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