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<br />empirically by matching the initial calculated not-seeded curve with the not-seeded <br />historical curve in the section from A to B. This same correction factor is applied <br />to the calculated seeded curve from A to C. In the region from B to C a separate <br />adjustment factor is calculated for each temperature category of the calculated not- <br />seeded curve. The point D, called the critical temperature, is where the historical <br />curve starts to falloff due to a dearth of ice forming nuclei at warmer temperatures. <br />The seeding is considered effective in a positive sense to the right of D and <br />the historical curve is subtracted from the adjusted seeded curve beyond D, to find <br />the seeding effect. The differences in each temperature category is multiplied by <br />the frequency of occurrence and summed to get the net seeding effect with the assump- <br />tion that only those categories with plus differences are being treated. The poten- <br />tial, or percentage increase in precipitation which optimally effective cloud seeding <br />could produce, is given by the ratio of the net-seeding effect (4.67 inches in the <br />illustration) to the total historical precipitation (55.11 inches) as determined by <br />summing the products of the mean precipitation and number of cases in each of the <br />cloud top temperature categories. A value of 8.47% was calculated in the illustration. <br />This represents the percentage increase in precipitation potentially available from <br />cloud seeding during the snow accumulation season. The seeding would be practiced <br />on all cases where cloud top temperatures were warmer than -25C, or 18.1% of the <br />time. It must be remembered that the hourly precipitation data in the sample covers <br />only 14 out of 24 hours and only cases where adequate sounding data were available. <br />The percentage increase factor thus derived can~ however, be applied to all precipi- <br />tation in the snow accumulation season to estimate the net seeding potential. <br />The determination of the P-T curves for an upslope or a downslope location, in <br />the absence of historical data, is achieved by applying the same'overall adjustment <br />factors as found for the crest station to the values ~alculated for an upwind, or a <br />downwind location. The seeding effect is then the difference between the seeded and <br />not-seeded adjusted, calculated values. In case precipitation records are available <br />only at an upwind, or a downwind'station, then this is used to derive the adjustments <br />to apply to the other locations. <br />The proced4re thus far corrects for model errors in Item 1 of the list on <br />page 1-6. The errors of Item 3 are adjusted for by simply shifting the calculat- <br />ed precipitation profile an appropriate distance upwind. Details of the proce- <br />dure and curves for the various massifs ~ppear in Appendix A. <br /> <br />1-9 <br />