Charles A. Perry
Published: 1980
Total Pages: 32
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Precipitation variability plays a major role in nearly every aspect of the hydrologic cycle. Precipitation is not a random event, but it occurs after a sequence of prerequisites has been fulfilled. Recent investigations have shown that activity of the sun can affect atmospheric vorticity, an important factor in precipitation formation. Solar activity is known to be periodic; therefore, through a complex series of physical processes, precipitation variance is solar forced to a certain degree. A preliminary analysis of precipitation periodicity was made for eight regions scattered across the central United States. Each region contained 5 to 10 stations with long-term precipitation records that were averaged to obtain yearly regional-precipitation values. Graphic analysis shows 11-year and 22-year cycles that are nearly in phase with the solar cycles. An example of the effect of cyclic precipitation is presented for the Powder River basin in Wyoming and Montana. A cycle of 22 years exhibits fluctuations of approximately 22 to 27% for precipitation and 38 to 50% for runoff. A more detailed study that investigates solar-forced precipitation cycles and their relationship to hydrologic processes is needed.