Browsing Institute of Atmospheric Physics Reports by Title
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Variability of Precipitation in an Arid Region: A Survey of Characteristics for ArizonaA number of statistical and meteorological aspects of the temporal and spatial variability of precipitation in Arizona have been examined in terms of their bearing on the water resources of the arid southwestern United States. Most of the work summerized has been of the nature of initial exploratory investigations made in order to lay the foundation for the much more extensive studies that will shortly be begun as part of the University of Arizona-U.S. Weather Bureau Cooperative Punchcard Climatological program. A selected sample of long-record Weather Bureau precipitation stations in Arizona were analyzed for their historic variability properties, a number of statistical and calculational techniques were tested, and a general plan has been developed for the next phases of the Institute's variability program. It is believed that these findings will be of interest not only to investigators in arid regions themselves but also to investigators chiefly concerned with more humid areas; for, in many respects, the statistical characteristics of arid-lands precipitation pose the most stringent of all requirements on statistical methodology. In that sense, the quantitative results of the present report may serve as useful indicators of upper bounds on the effects of non-normality, skewness, and heteroscedasticity of precipitation frequency distributions for North America in general.
Wind Gradients and Variance of Doppler SpectraAn X-band pulsed-Doppler radar having its beam fixed at an elevation angle of 3 deg, was used to measure radial velocity spectra in a light shower. Observations were made at intervals of 152 m between radar ranges of 7 and 18 km. It was found that the mean Doppler velocity, variance of the Doppler spectrum and radar reflectivity varied markedly over distances of the order of 100 m. The observed variance was below about 1 m2 sec-2 in 80 percent of the observations, but in about 4 percent of the cases, it exceeded 3m2 sec-2. An analysis of ~V/~r, the radial gradient of the mean Doppler velocity yielded a nearly Gaussian curve having a mean of 0.2 x 10-3 sec-1 and a standard deviation of 5.9 x 10-3 sec-1. The largest value observed was 3 X 10- 2 sec-1. The effects of the radial gradient of the radial wind apparently can explain about 25 percent of the observed variance of the Doppler spectrum.