CHARACTERISTICS OF THE COOCCURRENCE OF WIND AND RAIN AND THE DRIVING-RAIN INDEX

The relationship between the amount of wind-driven rain or driving-rai n and the driving-rain index (product of annual rainfall and mean wind speed) is studied. An analytical approach is proposed to obtain the r elationship between these two quantities. It is observed that they are related by two factors, (a) the driving-rain coefficient and (b) the co-occurrence factor. The driving-rain coefficient is shown in the pap er to be a function of drop size distribution which depends on the rai nfall intensity and the type of rain. The co-occurrence factor describ es the amount of correlation between wind and rain. The characteristic s of wind and rain at four meteorological stations across Sydney, Aust ralia are studied, The driving-rain characteristics for these sites ar e observed to be different. The amount of driving-rain for a given sit e is also found to be very different for the different compass directi ons. They can differ by a factor of 10 and more. It is believed that f or the purpose of weather resistance design of building facade, the di rectional driving-rain index should be used. Using the proposed method , the co-occurrence factor for the dominant driving-rain direction in Sydney is found to be 1.12 and the driving rain coefficient is calcula ted to be 0.204. With these two factors the amount of driving rain can be calculated from the driving-rain index.