Dependence of Rain-Rate Distribution on Rain-Gauge Integration Time

details of those rainfalls which exceed a threshold which is a function of rain-gauge integration time T as shown in Table I. For example, the thresholds are 76 and 20 mm/h for T = 5 and 60 min, respectively. A method for obtaining 5-min rain-rate distributions from these longterm (^ 20 years) data is described in a companion paper.2 A straightforward extension of this method allows us to obtain rainrate distributions appropriate to other integration times, such as 10, 15, 30, and 60 min. Figure 1 shows 20-year distributions with various integration time in the New York metropolitan area. The distributions for the New York metropolitan area represent an average of those obtained from LaGuardia Airport, Central Park, and Newark Airport. The thresholds noted in Table I, however, indicate that the rain-rate distributions processed from these data are accurate only in the range above the thresholds. The 5-min rain-rate distribution above 76 mm/h is generally sufficient for engineering terrestrial radio paths at frequencies above 10 GHz in the eastern or midwestern U. S. A. For engineering long terrestrial paths in the western U. S. A. or for millimeter-wave satellite radio links, distributions for rain rates less than 76 mm/h are needed. Fortunately, the long-term hourly precipitation data published by The National Climatic Center3-4 contain all rainfalls. As a result, the low-rain-rate portion of the 5-min rain-rate distribution 135 in the U. S. A., published by the National Climatic Center, 1 records An important problem in designing terrestrial and earth-satellite radio systems at frequencies above 10 GHz is the radio outage caused by rain attenuation.