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<br />1478
<br />
<br />JOURNAL OF APPLIED METEOROLOGY
<br />
<br />VOLUME 20
<br />
<br />The theoretical isohyetal patterns were then re-
<br />lated to observed isohyetal maps and the character-
<br />istics of their structure. The observations suggested
<br />a tendency for the precipitation gradient to be
<br />steepest, increasing rapidly toward the storm precip-
<br />itation maximum, in short-duration convective storms
<br />of small areal extent. More uniform precipitation
<br />gradients tend to be found in steady-type rains and
<br />large, long-lasting storms. Expressed in terms of the
<br />percentage of storm area containing 50% of the pre-
<br />cipitation volume, the precipitation gradient' was
<br />found to vary from 15 to 30%. It also was found that
<br />convective raincell patterns tend to be elliptical in
<br />shape.
<br />Finally, the relative importance of network sam-
<br />pling variance and natural storm precipitation vari-
<br />ability was examined in connection with the evalu-
<br />ation of precipitation augmentation experiments.
<br />The sample sizes required to evaluate such experi-
<br />ments due to network sampling variance alone can
<br />be appreciable; however, for reasonable gage densi-
<br />ties, it only contributes ~ 10% to the total sample
<br />size requirement. 'Methods of obtaining reductions
<br />in sample precipitation variability through the use
<br />of covariates will have to be found before the use of
<br />higher gage network densities is warranted.
<br />
<br />Acknowledgments. The authors wish to thank
<br />John Middleton and Robert Pritchard for their as-
<br />sistance in obtaining the radar precipitation char-
<br />acteristics of Montana convective storms and their
<br />statistical properties. The authors are also indebted
<br />to Dr. K, Ruben Gabriel whose critical comments
<br />and constructive suggestions led to significant im-
<br />provements in the clarity and quality of this paper.
<br />
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