Development and Application of a Physical Approach to Estimating Wind Gusts

Abstract

A new wind gust estimate method (denoted WGE method) is proposed. Contrary to most techniques used in operational weather forecasting, the determination of gusts in this approach is fully based on physical considerations. The main motivation for developing such an approach is to improve the knowledge of the physical processes that control the determination of gusts. The proposed approach assumes that surface gusts result from the deflection of air parcels flowing higher in the boundary layer, which are brought down by turbulent eddies. The WGE method takes into account the mean wind and the turbulent structure of the atmosphere. Moreover, this method includes the computation of a bounding interval around the gust estimate, which provides a range of likely gust magnitudes. The WGE method has been tested on two explosive cyclogenesis events that were satisfyingly simulated with the Modèle Atmosphérique Régional mesoscale model nested in the ECMWF analysis. Daily maximum gusts are predicted with good accuracy, while the hourly temporal evolution of estimated gusts depends strongly on the accuracy of the meteorological fields generated by the model. Typical error range for the gust estimates range is about 5 m s?1. The bounding interval is useful for determining the uncertainty around estimated gusts. Statistical evaluation of the WGE method shows that the main features of the climatology of gusts during the period from January to March 1990 are reproduced, even though estimated gusts have a negative bias (from 3% to 10%) compared to observations. An interesting aspect of the WGE method is the reliability of the bounding interval, with 73% of the predicted daily gusts lying in this interval. Compared to other approaches, the WGE method is as good as other methods used in weather forecasting although extensive testing remains to be done.