风廓线雷达对降水相态变化的观测分析

The macro and micro structures of the weather process in which surface rain turns into snow are analyzed in this paper by using the data obtained from wind profile radar on 3 November 2012 in Yanqing of Beijing. The results show that the products of intensity and velocity field of wind profile radar are good for diagnosing and distinguishing the evolution of precipitation phase change from rainfall into snowfall. Features of reflectivity, signal to noise ratio (SNR), spectral width and other factors are discontinuous before raining, bright band appears in the 800—1000 m height when surface rainfall is seen, but with bright band disappearing, rainfall turns into snow. In the surface rainfall stage, the figure of the echo intensity spectra has a clear hierarchical structure, showing solid particles above 1300 m height and liquid below 700 m height, respectively. So, close relations are found between stratification height and temperature. General-ly, there is a melting layer with temperature of 274 — 275 K, and with the most significant change of echo intensity spectra. In addition, statistics of radial velocity and SNR of the stratus precipitation in the recent 3 years show that, radial velocity ranges within 3 — 6m* s_1 and SNR is in 15 — 25 dB when raining; but in the process of snowing they are 0 — 1. 5 m • s_1 and 3 —15 dB respectively.