The effect of rainfall on measurements of mean wind speed with cup anemometers in the surface layer at sea

A mathematical model is developed to estimate rain-induced errors in cup anemometer readings. Based upon a two-cup hemispheric model, the indicated wind speed is calculated for a given true wind speed, fall velocities of the drops, and a general drop-size distribution.The results of these computations show that the effect of rainfall is small as expected. The influence on derived profiles of mean wind speed is rather a displacement of the profile to lower velocities than a change in the slope of the profile.The magnitude of these errors is a few percent or less even for heavy rainfall.Now Deutscher Wetterdienst, Offenbach, F.R.G.