Empirical and theoretical assessment of the wind induced error of rain measurement

The computational fluid dynamics and the simulation of precipitation trajectories was applied to assess the wind induced error of precipitation measurements using the Hellmann gauge. The results agree well with the empirical correction formula for the same gauge type derived from field data obtained from inter comparison measurements of paired Hellmann elevated and pit gauges in Les Avants (982m asl), Switzerland. This means that correction procedures can be derived for any type of gauge using the theoretical approach instead of the empirical one. The computational and empirical results fit a model which uses the intensity of rain as an independent variable and produces a set of one parameter curves (wind speed) with increasing threshold value of intensity for increasing wind speed. Below the threshold values the wind-induced error increases quickly with decreasing intensity of precipitation; above it the increase is slow.