Multifractal characterization of rain fields with a strong orographic influence

Data from networks of high time resolution (15 second) rain gauges forming a transect from the base to the divide of a mountain range are used to study the multifractal characteristics of precipitation at different locations along the transect. In particular, scaling power spectra, multiscaling moments and power law exceedence probability tails are analyzed from rain gauge time series of similar to 35-70 hours in length. The parameters discussed are specifically the spectral scaling exponent, beta, the intermittency parameter, C-1 (a fundamental parameter of the moment scaling function, K(q)) and q(cr), the power law probability tail exponent. Results show a systematic trend in the exponents, indicating a decrease in intermittency, the frequency of extreme values and smoothness of the time series with increasing altitude along the transect. K(q) and q(cr) are briefly discussed and derived as natural properties of multifractal cascades. It is concluded that the parameters of multifractal cascade models of rainfall are related to the physical processes which are qualitatively discussed in the context of the observed changes in the statistics.