Time Durations of Rain Rates Exceeding Specified Thresholds

摘要

Rainfall may hamper military operations in ways as diverse as the visual detection of enemy movements to the attenuation of sophisticated, electro-optical, weapon-guidance systems. Thus, it would obviously be advantageous to have the ability to predict probable rain-rate intensities from forecast information or, for planning purposes, from climatological data. The rain investigation detailed in this report was conducted with the objective of developing a method for estimating durations and occurrences of rates of specified intensities. The data base consisted of 185 events taken from 31 days of rain-rate measurements. The rate variability of each event was mathematically defined and we found that the individual variabilities did not depend upon the amount of rain or the length of time rainfall occurred. Analysis revealed that variability could be expressed as a percentage of time that rain rates were equal to or exceeded specified threshold levels that were relative to their mean values and could be described by an equation set. Although the diversity of the data negated all attempts to estimate the frequency that specific rate intensities occurred, it was shown that averaged rain-rate date (< or = 10 min) changed predictably with relative measures. Thus, the authors deduced a method by which rain-rate variability, in terms of the percentage of time the rates are > or = intensity levels relative to their means, may be estimated from knowledge or deduction of two parameters, the mean and maximum rates. (Author)