ON THE SIMPLIFIED EXPRESSION OF REALISTIC RAINDROP SHAPES

The Pruppacher-and-Pitter (PP) raindrop model has been well accepted a s a realistically distorted raindrop model. To employ this model for t he investigation of radio wave attenuation by rain requires tedious nu merical calculations. In this Letter a simple mathematical formula is used to simplify and improve the expression of the nonaxisymmetric dis torted raindrop shapes, enabling the scattered field by rain to be der ived analytically. The coefficients in the formula are determined for different raindrop sizes by translating the polar coordinates vertical ly and fitting the shapes of the Prupacker-and-Pitter-form raindrops t o the shapes discussed in this Letter. Using the least-squares method, a general expression for the coefficients in terms of the raindrop si zes is obtained. A comparison of the raindrop shapes obtained from the Pruppacher and Pitter expression and the expression in this Letter de monstrates the validity of the simplified formula for realistically di storted raindrops. (C) 1994 John Wiley & Sons, Inc.