Diurnal variations in rainfall over Arizona during the North American monsoon

A majority of research on precipitation in the North American summer monsoon has focused on several characteristics of precipitation that include intensity, frequency, and amount. In general, the spatial and temporal variations in the character of monsoon precipitation have been analyzed using daily averages. These analyses have assisted in quantifying the variability in precipitation throughout the region, but they have not addressed diurnal variations in rainfall on time scales of less than one day. This research focused on diurnal precipitation for the state of Arizona during the North American Monsoon season of July through August. It characterized spatial and temporal variations in hourly precipitation event timing, and determined the intraseasonal and interannual relationship to elevation and climate teleconnections.;Data were collected from 39 first-order, second order, and co-operative National Weather Service weather stations throughout Arizona for the period from 1948 through 2005. Application of a series of statistical tests (independent samples T-tests, harmonic analysis, linear regression, and Pearson Product-Moment correlation) and spatial analyses determined that the timing of diurnal rainfall on an intraseasonal basis has been consistent over time. These findings identified elevation as being a major factor in determining the first harmonic time of maximum precipitation frequency. High (low) elevation have consistent afternoon (evening) rainfall occurrence in each of four monsoon quarters (biweekly periods) and the season. Standardized hours of maximum precipitation frequency showed no distinct trend toward earlier or later time of event rainfall event occurrence for the period of study. A limited role is identified for various teleconnections indices and their phases (El Nino/La Nina, Pacific Decadal Oscillation, Pacific/North American teleconnection, and the Madden-Julian Oscillation) with regard to rainfall event timing. Analysis of climate teleconnections with hourly precipitation data indicated that the antecedent January through June index averages were minimally related to precipitation event timing.