The prevailing raindrop shape obtained by polarimetric radar measurements

Polarimetric radar measurements are used to retrieve properties of raindrop distributions. While there has been extensive research conducted on microphysical retrievals such as hydrometeor classification or hail detection, there has not been much research into polarimetric radar based deduction of raindrop shape even though the shape of raindrops plays a critical role in rainfall estimation from polarimetric radars. Equilibrium shape of raindrops as the result of a balance of surface tension, aerodynamic forces, and hydrostatic and internal pressures has been assumed in earlier studies, although it was observed that the average shape departs significantly from that of the equilibrium. There has been considerable discussion about the deviation of the drop axis ratio from its equilibrium value (Goddard et al. 1982; Beard and Chuang 1987; Chandrasekar et al. 1988; Bringi et al. 1998; Andsager et al. 1999; Gorgucci et al. 2000; Keenan et al. 2001; Brandes et al. 2002; Thurai and Bringi 2005). Studies have produced different models emphasizing that a nonlinear relationship should be better than a linear one. Using the self-consistency of the polarimetric radar measurements, Gorgucci et al. (2000) proposed a shape-size model in terms of the linear slope (β) approximating the implied shape-size function as