EXPERIMENTAL AND NUMERICAL-STUDIES OF SMALL-SCALE RAINFALL MEASUREMENTS AND VARIABILITY

A high-resolution rainfall observatory was established at the Iowa Ins titute of Hydraulic Research to support studies of small scale rainfal l variability. It includes a vertically pointing X-band radar, a two-d imensional video disdrometer, an optical rain gauge, a standard tippin g bucket raingauge, and high temporal resolution sensors for measureme nts of wind velocity and direction, temperature, humidity, and pressur e. All the instruments are collocated. The observatory is being upgrad ed to include a Doppler processor for the radar, a mobile platform to enable participation in community-organized hydrometeorological experi ments, and a network of about 15 high-resolution raingauges to be inst alled at a nearby airport. The airport network design includes innovat ive concepts of dual sensors constituting a single observational point , connected to the same data logger The observational points are separ ated with distances ranging from 10-1000 metres. We present comparison s of data collected by the various sensors and discuss implications fo r radar-rainfall estimation. The capabilities of the experimental setu p at IIHR will facilitate numerical studies of rainfall measurements. in particular, we present results of computational fluid dynamics calc ulations of the measurement error of the video disdrometer based on th e high resolution observations of drop size distribution and wind velo city. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.