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This analysis suggests rather strongly that there exists a diurnal variationin the effect of seeding on precipitation over the extended area. Thecase for a similar diurnal variation in the effect of seeding on station pressureis not so clear cut, but there is a suggestion of its presence.The occurrence of any diurnal effect of seeding not related directly tothe daylight-nighttime breakdown is indeed puzzling. A partition of all 108stations into daylight (0600-1800) and nighttime (1800-0600) showed no differencein precipitation ratio. Somewhat similar diurnal effects of seeding onprecipitation have been in New Mexico (Keyes 1971).CONCLUSIONS AND RECOMMENDATIONSThe data gathered during four years of seeding convective bands with pyrotechnicsat a ground based point source in Santa Barbara County has providedrather conclusive statistical evidence that this seeding has altered the precipitationpatterns over a very large area. These changes within the seeded bandsare generally in the form of increases in precipitation on the order of 50%, to100%, in the primary seeding zone extending from the seeding site to about 30miles downwind, and increases of more than 100% over a large area 70 or moremiles downwind from the seeding source. A non-parametric rank test and a binomialtest produce a high level of confidence in the indicated results.It was also found that the seeding effect was highly temperature dependentwith a large number of stations showing decreases in precipitation ouring thecolder storms.One of the more conclusive findings from a statistical viewpoint is theapparent increase in the time duration of a seeded band at a given point.Whether this increased duration is caused by a widening of the band due todynamic growth or a slowing of band movement has not been completely determined,but the former appears to be the case.The possibility of interaction between successive bands and also between aband and its surrounding environment was also studied. There appears to be someevidence that when a band is seeded there will also be an increase in the precipitationin a band preceding it by two to four hours. Conversely, it appearsthat a seeded band may possibly suppress the rainfall in a band that follows itby two to four hours.A preliminary study of surfacq prossure valu,,s at the time of band passagethrough the extended area shows somo very interesting possibilities. It-41-