ACCURACY OF TRETYAKOV PRECIPITATION GAUGE - RESULT OF WMO INTERCOMPARISON

The Tretyakov non-recording precipitation gauge has been used historic ally as the official precipitation measurement instrument in the Russi an (formerly the USSR) climatic and hydrological station network and i n a number of other European countries. From 1986 to 1993, the accurac y and performance of this gauge were evaluated during the WMO Solid Pr ecipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence i ntercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercompari son data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared u sing mean wind speed at the height of the gauge orifice during the obs ervation period. The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. T hese data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were inv estigated. Wind speed was found to be the most important factor determ ining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature o n a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have b een conducted at those Intercomparison stations and a good agreement ( difference less than 10%) has been obtained. The use of such adjustmen t procedures should significantly improve the accuracy and homogeneity of gauge-measured precipitation data over large regions of the former USSR and central Europe.