Undercatch of tipping-bucket gauges in high rain rate events

摘要

We have investigated differences in rainfall accumulations forseven high rain rate events from three gauges: a Geonor T-200Bvibrating-wire weighing gauge and two MetOne tipping-bucket gauges. TheGeonor gauge and one tipping-bucket gauge are located in a pit so that theircollection orifices are at ground level. Thus their measured rainfallaccumulations are minimally affected by wind speed. The other tipping-bucketgauge is located 105 m from the pit and is surrounded by an Alter-typeslatted wind screen. Its collection orifice is positioned 1 m above groundlevel.The results from the seven events show that the tipping-bucket gaugesnoticeably underestimated storm event rainfall totals relative to theweighing-bucket gauge when 1-min rain rates exceeded about 50 mm/h(2 in/h). In addition, we conclude that observable wind induced undercatchby the aboveground tipping bucket gauge begins when the wind speed at a heightof 2 m exceeds around 5 m/s. In this paper we show and discuss time series of rain rates, differences inrain rates, and wind speeds for two of the seven events in an attempt toaccount for the lower storm totals from the two tipping bucket gaugesrelative to the weighing-bucket gauge.