Quadratic Growth Hypothesis, Classification of Cumulus Based On Rate of Growth, Concept of Reaction Time and Cumulus Motion Speed

Abstract

This paper is a new attempt to evaluate hail storm severity and hail suppression effects. In this paper a new concept of Quadratic Growth Hypothesis (QGH) has been proposed and examined in the prediction of hailstorm. Another new concept of Reaction Time (RT) has been presented which is useful for effective seeding in hail mitigation campaigns. Given complex nature of cumulus growth, rate of growth of cumulus (r) have been broadly categorized as Slow (r ? 0.2 dBZ/min), Moderate (0.2 < r < 0.8 dBZ/min) and Fast (r? 0.8 dBZ/min). Often cumulus shows reverse growth too. It is found that QGH based predictions are 100% correct for Slow growing cumulus and 62.5% accurate for Moderate. However, QGH predictions are incorrect when the cumulus growth reverses or when it is Fast. Empirically a “QGH-Rectangle” has been identified wherein QGH is precisely valid. Prediction skill scores [= (Correct prediction/Total Predictions made)] of 0.79, 0.79 and 0.75 are obtained from scan intervals of 10, 12 and 19 minutes data, respectively. Amongst the three data sets, 10 minutes scan interval is operationally safer for RT computation during hail mitigation campaigns. In most of the cases RT may range from 17.3 to 29.6 minutes. Maximum RT of 43 minutes is also noted for slow growing cumulus. Linear Extrapolation (LE) has been used to predict the cumulus motion speed which has been observed from 5 m/s to as high as 19.3 m/s. It is noted that larger scan interval of DWR data would exhibit more consistent and reliable speed prediction by LE method.