An observational study on vertical raindrop size distributions during stratiform rain in a semiarid plateau climate zone

Vertical raindrop size distributions of two stratiform rain events were measured with a Micro Rain Radar during summer 2009 at a semiarid continental site located in Xilinhot, China (43 degrees 38'N, 116 degrees 42'E). The sequential intensity filtering technique (SIFT) was used to minimize the effect of the spurious variability on disdrometric data to obtain the reflectivity-rain rate (Z-R) relationship (Z = aR(b)). Compared with the least squares regression (LSR) method, SIFT led to a -5% to 4% change in the coefficient (a) and an 8%-15% increase in the exponent (b) of the Z-R relationship at 300 m. Rainfall estimation using the Z-R relationship with SIFT had lower standard deviation than that with LSR. The vertical variability of the mean rain rate, total raindrop numbers, and parameters (a and b) of the Z-R relationship was small below a melting layer, suggesting that using the radar reflectivity of weather radar to estimate stratiform rainfall is relatively accurate, at least in the Xilinhot area.