Application of Transfer Function to Correct Precipitation Measurements on the Swiss National Meteorological Network

Accurate measurement of liquid and solid precipitation is the foundation for reliable services in water management, hydrology modelling, nowcasting or for extreme events anticipation. It is well known and established that the measurement of this atmospheric parameter is perturbed by a number of external influences, the most important being the wind induced error on rain gauges measurement, especially for solid precipitation. A number of studies and intercomparison have already documented this effect, and provided mitigation solutions. The latest intercomparison, the WMO/CIMO SPICE (Solid Precipitation Intercomparison Experiment), and its final report (WMO IOM Report- No. 131), analyses the performances of several traditional gauges (tipping bucket and weighing gauges), as well as non-catchment type instruments (disdrometer, PWD, etc.), in measuring solid precipitation. In this report, a method to correct the precipitation measured by weighing gauges (Kochendorfer, 2017 and 2018), using transfer functions with wind speed and temperature as input, is developed and presented as an alternative or a complement to traditional mechanical correction using metal shields. MeteoSwiss, the Federal Office of Meteorology and Climatology for Switzerland, has tested this new transfer function at three sites located at different height and with different terrain complexity during two winter seasons. Parallel measurements using weighing gauges with and without Single Alter shields were conducted on each site, and transfer functions finally applied. Results from this test and the following steps implemented on the Swiss national precipitation measurement network regarding correction of precipitation measurement are presented in this contribution.