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Last modified
7/28/2009 2:40:36 PM
Creation date
4/24/2008 2:53:26 PM
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Weather Modification
Title
The Rain Stimulation Campaign in Panama Summer 1983
Date
6/1/1984
Weather Modification - Doc Type
Report
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<br />detailed correspondence between model-derived ex- <br />pectations and observational verifications is bound to <br />involve an expensive effort to reduce sampling and <br />instrumental errors. Last summer's seeding has fur- <br />nished input for a large array of model outputs (fig. 5) <br />which are the source of hints rather than conclusions. <br /> <br />Specific raininess. This is an evaluation method that <br />was born of necessity. It was suggested, as early as <br />1951, that seeding would have little effect on the. <br />frequency of rainy days but would increase the amount <br />of rainfall per rainy day. <br /> <br />The data from the Panama Canal rain gage network for <br />the 11 summers (1972-1982) shows a weak but definite <br />relationship between the number of summer "rainy" <br />days (when rain exceeded 0.10 in) and the median <br />rainfall of these days. In 1983 there were 53 "rainy" <br />days, with a mean rainfall of 11.7 mm (0.46 in) and a <br />median of 7.9 mm (0.31 in). A regression of median <br />daily rainfall on number of rainy days per season <br />suggests that reduction in median daily rainfall is, to <br />some degree, characteristic of an abnormally dry year. <br />The point for the summer of 1983 (fig. 6) lies about <br />0.018 in of rainfall above the regression line. One might <br />extrapolate this indication to a suggested increase of <br />about 6 percent in summer rainfall, or about 4 inches in <br />the level of Gatun Lake. <br /> <br />Visual estimates of response. Experienced observers <br />often report visual estimates of response to seeding on <br />the basis of a departure of the subsequent growth of the <br />cloud from what their experience had led them to <br />expect. The report may be of unexpectedly rapid or <br />vigorous growth, or of unexpededly sudden dissi- <br />pation. Such departures from expectation are ordinarily <br />based on comparison of the seeded cloud with nearby <br />un seeded clouds observed in the same general area at <br />about the same time. During the Panama operation, the <br />pilots were directed to make visual estimates of res- <br />ponses on each occasion of seeding. Subsequently, <br />these reports were correlated with radar indications of <br />precipitation in the area where the response was <br />reported. In this way, each seeding event during the <br />Panama operation was given a response rating of good, <br />fair, or no response noted. "Good" responses were <br />recognized on nine days, and "fair" on an additional <br />nineteen days. Among the "good" days there were <br />several days when seeding was followed by a higher <br /> <br />10 <br /> <br />degree of organization among the radar echoes and <br />also the pilots reported speeded convective develop- <br />ment. Unfortunately there is no objective standard by <br />which to judge the significance of these observations; <br />they are encouraging but not at all abnormal. As <br />expected, there was a strong correlation between <br />positive visually estimated responses, vigorous cloud <br />development, and heavy rain. Similarly, reports of no <br />response tended to correlate with occasions of zero or <br />light rain. <br /> <br />~ <br />'I <br />, <br />, <br /> <br /> <br />CA~'Eyf;;-::tf:;;"'f{ 6':.r5 <br /> <br />F:ANANA 5cA?f+1R.G7~<Af15 <br /> <br />t ~,\u~~\t--. <br /> <br />Figure 5. - Computer printouts of calculations estimating the <br />development of clouds and cloud clusters in the environment <br />of Panama. <br /> <br />~ <br />
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