Ground-Based, High-Resolution Measurements of the Spatial and Temporal Distribution of Rainfall

Abstract

Preliminary data from ground-based measurements of rainfall using an optical disdrometer and high-resolution rain gage network are described. The recurrence of the rain period is shown to be non-Poisson with evidence of clustering, whereas a lognormal distribution is shown to be an approximate fit to the distribution of amount of rainfall in a rain period. About 40% of rain periods possess a total rainfall smaller than that resolvable by conventional recording rain gages; three-quarters of these were resolvable by the high-resolution rain gages used. Rapid fluctuations of rainfall intensity (?1 mm h?1 s?1) are evident in individual rainfall intensity records and the distribution of duration of rainfall above a specified threshold intensity is shown to be approximately lognormal; these observations are consistent with a lognormal distribution of precipitation region sizes. An empirical fit to the average fractional duration of rainfall is given, although the curve is generally a poor fit to fractional duration data for individual rain periods; periods of intense rainfall tend to be more singular than expected from the curve, and the maximum intensity reached in a rain period is shown to be independent of the period's duration. A method for estimating spatial sizes and shapes of precipitation regions using a high-resolution rain gage array is demonstrated.