Abstract:
Using the micro rain radar (MRR) observations in Xingtai, Hebei Province, the vertical structure and evolution of precipitation associated with clouds along a cold front are explored. The accuracy of MRR observations has been examined by comparing with observations of the weather radar, raindrop disdrometer, and rain gauge. Combining the MRR with the disdrometer and the laser ceilometer, factors in different relative humidity ranges and average vertical distribution of the raindrop size as well as the evolution of precipitation characters with the altitude and time have been investigated. The results show that the observed cumulative rainfall and its trend are similar among different data. The difference between the rainfall intensity observed by the MRR 200 m and that observed by the disdrometer is the minimum with an average value of about 0.05 mm h
−1 and the correlation coefficient is 0.93. Compared with the disdrometer, the MRR overestimated the small drop concentration and underestimated the large drop concentration. However, the medium drop concentration is consistent between observations of the MRR and the disdrometer. Precipitation is greatly affected by evaporation under low-humidity condition and affected by different microphysical processes inside and outside the clouds. The vertical variations are different. During the initial stage of precipitation, the average reflectivity (Z) and rainfall intensity (R) obviously decreased below the cloud base and the average concentration of small and medium drops decreased rapidly under the influence of evaporation. At other time, the average Z and R slightly increased and the concentration of small drops changed little. The concentration of big and medium drops increased, which indicates that coalescence processes have happened between raindrops and cloud droplets withinthe cloud. The average effective diameter increased obviously and the average total concentration of raindrops decreased with decreasing height in lower levels outside the cloud. Besides, the decreasing of small drops and increasing of big drops indicate that the coalescence processes in low levels outside the cloud are stronger.