MATHEMATICAL MODEL FOR RAIN DROP DISTRIBUTION AND RAINFALL KINETIC ENERGY.

AN analytical function is proposed for representing the rain drop size distribution. The function can be easily differentiated to yield the drop size density distribution function and allow two different ways of fitting to measured data either by using the observed inflection point or any other two points on the measured distribution curve. A modified weighted regression procedure is developed for best fitting the proposed function to experimental data. Using rain drop distributions measured in Rhodesia and in Washington, DC, it was possible to calibrate the model for each place. Applying the calibrated model together with a continuous function of the terminal velocity versus the drop size, it was possible to predict systematically the kinetic energy per unit mass, and per unit time as a function of rainfall intensity.