WRRCTR No. 67 Rainfall Intensity Instruments and Measurements

Two instruments have been used to measure the rate of rainfall from tropical clouds over the windward coast of the Island of Hawaii. The Workman intensity gauge employs strain gauges to sense the deflection in a movable trough and hence the flow of water down the trough. The Raymond-Wilson gauge, a new instrument developed during this program, measures the electrical resistance of flowing water to determine the rainfall rate. These instruments were deployed in a small scale array of eight gauges to measure space and time variations in high intensity rainfall as showers move across the network. Comparative measurements were made with a standard weighing rain gauge, a tipping bucket rain gauge and the Jardi rate of rainfall gauge. Both the Workman gauge and the Raymond-Wilson gauge are clearly superior to the other instruments, because of their rapid response time and their capacity to measure high intensity showers continuously and automatically. The Raymond-Wilson gauge contains no moving parts and is operationally more suitable than the Workman gauge for deployment in a network of gauges. A sensor which measures the rate of change of atmospheric pressure has also been developed and is being used in the research program. An example of rainfall intensity measured during a 43-day period in October and November, 1972, is presented, along with a preliminary estimate of the in-cloud liquid water content of shallow Hawaiian clouds.OWRR Project No. B-024-HI, Grant Agreement No. 14-31-0001-3575 The programs and activities described herein were supported in part by funds provided by the United States Department of the Interior as authorized under the Water Resources Research Act of 1964, Public Law 88-379, and were performed with the cooperation of the Cloud Physics Observatory, Department of Meteorology, University of Hawaii