WRRCTR No. 78 Some Characteristics of Hawaiian High-Intensity Rainfall

Abstract

A computer monitored network of rapid response Raymond-Wilson rainfall intensity gauges has been established at the Cloud Physics Observatory (CPO), on the windward coast of the island of Hawaii, to record the passage of both warm and cold showers. These showers are characterized by high intensity rainfall (50 to 300 mm/hr) and an associated increase in atmospheric pressure, a change in wind velocity, and a reversal of the electric potential gradient. The showers often occur at night, during the maximum of the diurnal pressure oscillation, and frequently in groups of two to four with an interval of 10 3 to 10 4 seconds between separate showers. A relationship between the height of the base of the trade wind inversion and the total amount of rainfall was observed, indicating that almost no rainfall occurs if the inversion base is less than 2 km. A drop-size instrument (DSI) was developed and used to measure the raindrop-size spectrum. From this measurement and the rainfall intensity, an estimation of the liquid water content (LWC) of precipitating clouds was derived. The LWC (2.0 to 8.0 g/m3) was found to be larger than that generally assumed for trade wind showers.