A case study of orographic rainfall processes incorporating multiscaling characterization techniques

Abstract

Abstract. The Southern Alps field experiment was designed to identify the dominant rainfall processes in intense orographic events in the South Island of New Zealand and included the deployment of a rain gauge network and meteorological radar. Multiscaling statistics, used to characterize the rainfall from a single extreme event, revealed both orographic and temporal changes in the rainfall nature, with significantly more incessant rainfall observed in the higher-altitude regions. Central to this work was physical interpretation of the statistical parameters, which contributes toward forming links between multiscaling analysis and meteorological processes necessary for practical applications of multiscaling statistics. A further step was taken by combining the statistical results with other meteorological data to infer details of the physical processes, hence providing an example of the utility of multiscaling characterization of rainfall for improving our understanding of physical rainfall processes. Evidence is presented of lateral broadening of precipitating elements as the alpine divide is approached and is used, in conjunction with the wind profile, to explain the quasiincessant rainfall observed near the divide.

Investigating the multifractality of point precipitation in the Madeira archipelago

“…In particular, for orographic precipitation see also e.g. Harris et al (1996), Purdy et al (2001), Nykanen and Harris (2003) and Deidda et al (2006). Two main reasons were identified by Deidda et al (2006) as contributing to different outcomes in rainfall analyses: a physical factor lies in the different orographic range covered by the data (a limited range may not represent a significant obstacle for perturbations); a second explanation may be the differences in the length of the observation periods (relatively brief observation period may not allow filtering the single events high space-time variability from the possible spatial heterogeneity).…”

“…Analyses of storm event samples yield upper limits for the scaling range that are typically of the order of a few hours (even less than one hour), scales comparable to the mean storm duration (see e.g. Olsson et al, 1992;Onof et al, 1996;Harris et al, 1996;Purdy et al, 2001;Venugopal et al, 2006). Also the precipitation statistics are, in this case, for particular events.…”

“…algebraic tails of the probability distributions); these are associated with processes' "violent" character (see e.g. Hubert et al, 1993;Olsson, 1995;de Lima, 1998;Purdy et al, 2001;de Lima et al, 2002;Douglas and Barros, 2003;García-Marín et al, 2007).…”

Modulation of homogeneous space-time rainfall cascades to account for orographic influences

“…In order to reproduce observed spatial heterogeneity they multiplied a homogeneous spatial random cascade by a deterministic factor depending on the spatial location without linking it to local features. Analyzing a transect along the Southern Alps of New Zealand, Harris et al (1996) and Purdy et al (2001) found a dependence of scaling parameters on orography and rain features. More recently Deidda et al (2006) investigated the presence of rainfall spatial heterogeneity induced by orography on rainfall fields retrieved over Brazil by radars (TRMM-LBA, Tropical Rainfall Measurement Mission -Large Scale Biosphere Atmosphere Experiment).…”

“…The opportunity of introducing a heterogeneous component when modelling synthetic rainfall fields over land was investigated by Harris et al (1996), Jothityangkoon et al (2000), Purdy et al (2001), Pathirana and Herath (2002). Specifically Jothityangkoon et al (2000) and Pathirana and Herath (2002) analysed a 400 km×400 km area in southwestern Australia and a 128 km×128 km region centered in the Japanese archipelago, respectively.…”