Reduced Loss in Precipitation Measurements Using a New Wind Shield for Raingages

Abstract

A problem of great concern in precipitation measurements is the wind loss. This paper presents a new wind shield that reduces this loss. Tests of the new shield were made in a wind tunnel and in the field. The wind shield consisted of a flange with its upper surface mounted level with the rim of a cylindrical collector. The diameter of the flange was about three times the diameter of the collector. The deformation of the wind field was much smaller above the orifice of the gage equipped with the new wind shield compared to an unshielded gage. Field comparisons showed that the catches of the gage, a gage equipped with a Swedish standard shield and an unshielded gage, were 98%, 95.4%, and 93.9%, respectively, of a reference pit gage catch. The gage with the new wind shield was found significantly different from the unshielded gage and from the gage with the standard wind shield (level of significance α<1% in both cases). The last two gages were also significantly different (α<2.5%) from each other. The remaining 2% difference between the catch of the new gage and of the reference gage could be explained in terms of differences in evaporation losses.