Performance of Japanese precipitation gauges in winter

Abstract

Comparative observation of precipitation gauges has been carried out in Joetsu, Niigata Prefecture Japan over six winters to know their catch efficiency in winter.The“True”precipitation is estimated from the value measured by a Double Fence Intercomparison Reference (DFIR)gauge in accordance with the WMO recommendation. The tested gauges are RT-1(Tipping bucket type with heated funnel), RT-3 (Warm water type with water jacket) and RT-4 (Overflow type with heated reservoir), which are often used in Japan.The catch ratio, defined by Measured/True, was in the order RT-4>RT-1>RT-3, decreasing with increase of wind speed.The difference between the instruments is possibly due to the shape of the gauges.The tested gauges performed better for rain than for snow.The relationship between the catch ratio and the wind speed at the orifice has been established for gauge models and precipitation types (Snow or Rain)by regression analysis.The approximate catch ratio for snow was 0.8 for RT-4, 0.7 for RT-1 and 0.6 for RT-3 at a wind speed of 2 ms^-1, and that for rain at a wind speed of 6 ms^-1 was 0.9, 0.8, 0.7 respectively.In most winter precipitation, the measured value should be subjected to a correction.In areas of heavy snowfall such as Joetsu, a heating device to melt snow is necessary for the precipitation gauges to work properly.