Spatial Variability of the Rain Drop Size Distributions during Stratiform Rain Events

A case study to understand the spatial variability of the integral parameters of the rain drop size distributions (DSDs) is conducted. The data used are DSD measurements from four Precipitation Occurrence Sensor Systems(POSSs) located around Montreal area and radar reflectivity observations from the operational McGill S-band scanning radar. We have selected four stratiform events that show bright band above 1.5 km height. The DSD parameters analyzed include the 3rd to 6th moments of the DSDs, rainfall intensities from DSDs (RD) and transformed rainfall intensities (RZ) from Z, the ratio (XR) of the RD and RZ, and normalized characteristic diameter(Dm') and characteristic number density(No'). In addition to the DSD parameters, the spatial variations of the coefficients of the R-Z relationships were investigated as well. The preliminary results of the analysis show, 1) the spatial correlation functions for each parameter exponentially decrease with separation distance, 2) the correlation values of each parameter were Dm'> XR > RZ > RD >No' , and 3) the spatial variation of the coefficient of R-Z relationships was noticeably larger than statistical error.

Key words : Spatial variability, Drop size distributions, Precipitation Occurrence Sensor System