Analysis and Case Study on the Generation of Radar Echo Bright Band

In this study, the vertical profiles of radar refractive factors (Z) observed with an X-band Doppler Radar in Jurong, China in different periods on July 13, 2012 during a stratiform cloud precipitation were simulated by using SimRAD (a software we developed based on Radar meteorological equation and has been used in a few studies), and the contributions from different impacts resulting in the bright band were analyzed quantitatively. In the simulation, the parameters input into SimRAD were updated until the output Z profile was nearly consistent with the observed. The input parameters were then deemed to reflect real conditions of the cloud and precipitation. The results show that a wider (narrower) and brighter (darker) bright band is associated with a larger (smaller) amount, wider (narrower) vertical distribution, and larger (smaller) mean diameter of melting particles in the melting layer. Numerical experiments on the sensitivity of the bright band generation to each impact show that a drastic increasing of the complex refractive index due to melting was the largest impact, making the radar reflectivity factors increase by ~15 dBZ. Fragmentation of large particles was the second most important influence, making the value decrease by 10 dBZ. The impacts such as collision–coalescence between melting particles, volumetric shrinking due to melting, and the falling speed of raindrops made the radar reflectivity factors change by about 3–7 dBZ. And shape transformation from spheres to oblate ellipsoids resulted in only a slight increase in the radar reflectivity factors (about 0.2 dBZ), which might be due to the fact that there are few large particles in stratiform cloud.