Snowfall rate estimation using C-band polarimetric radars

Radar quantitative precipitation estimation plays an important role in weather forecasting, nowcasting and hydrological models. This study evaluates the Sekhon and Srivastava (1970) snow water equivalent (SWE) algorithm currently implemented by the Canadian Radar Network of Environment and Climate Change Canada, suggests an improved algorithm and also evaluates the ability of polarimetric radars in estimating SWE. The radar data were collected from the dual polarimetric King City radar (CWKR) near Toronto, Ontario, and the Doppler Holyrood radar (CWTP) in Newfoundland. SWE data were collected at Oakville, Ontario, at Pearson International Airport (CYYZ), Toronto, Ontario, and at Mount Pearl, Newfoundland. The ground observations show that the polarimetric variables could be used to infer a few of the microphysical processes during snowfall. It is suggested that the co-polar correlation co-efficient ((hv)) could be sensitive to the size ranges of different snow habits. Also, higher differential reflectivity (Z(dr)) values were measured with large aggregates. The results show a severe underestimation of SWE rates by the Sekhon and Srivastava algorithm. One hour accumulations from each site were used to develop SWE(Z(eH)) and SWE(Z(eH), Z(DR)) algorithms (Z(eH) and Z(DR) are the reflectivity factor and differential reflectivity, respectively). Similarly, algorithms were developed using SWE at 10 min intervals from CYYZ and Mount Pearl but these algorithms appeared to overestimate SWE. The hourly SWE accumulations from the three sites were combined to produce an additional SWE(Z(eH)) algorithm which showed better statistical results. A modest difference was found between the conventional and polarimetric algorithms for estimating snowfall amounts (SWE).