Study of a precipitating cloud system using Chung-Li VHF radar

In this paper, Chung-Li VHF radar returns from hydrometeors and reflectivity fluctuations associated with “showery” precipitating cloud systems are studied in detail. The space antenna drift method is applied to three rain gauges in the vicinity of the radar to obtain the drift velocity of the rain cells during the passage of the precipitation cloud systems. The drift velocity of the rain cells is found to be 13.4 m/s and moving in the southwest to northeast direction, and these results are in good agreement with the simultaneous observations of the horizontal wind velocity observed with the radar. VHF radar can see the frontal structure so clearly because of its sensitivity to thermal stratification in the atmosphere. A composite analysis of the turbulence and precipitation echo intensity and vertical air velocity indicates that the vertical air velocity plays a vital role for the occurrence of showery precipitation. The mean raindrop diameters are estimated from the air motion adjusted Doppler velocities resolved by the radar. Observational results show that the mean raindrop sizes of 0.5–3.5 mm are primarily responsible for the showery precipitation. The ambient air motions and turbulent broadening effects are discussed before and during the passage of the precipitation event. The analysis suggests that the beam-broadening effect needs to be considered if the information of the drop size distribution is to be estimated from the observed Doppler spectral width.