WIND FLUCTUATIONS NEAR THE GROUND DURING RAIN

Measurements of wind speed were made above short grass during periods of rainfall using hot-film anemometers. A filtering algorithm was used to identify spikes in the anemometer signal time series, induced by raindrop impacts on the hot-film sensors. A relatively small number of such spikes, comprising about 0.1-0.2% of the data points, were identified in signals recorded during rainfall with rates ranging from less than 0.1 to 7.2 mm h(-1). After these spikes were removed from the time series by filtering, the resulting values of the first four moments of wind speed were very similar to those found above grass during fair weather. Values of sigma(w)/u* and sigma(u)/u* determined during rain using a 3-D sonic anemometer(l.3 and 2.6, respectively) were also in good agreement with corresponding values found during conditions of fair weather and near-neutral atmospheric stability.