Estimation of The 90m Wind from Low-Level Observations

摘要

Hourly averages of temperature and wind were collected from a 90m tower at Tyson's corner, Virginia. From these observations, an empirical method was developed for the estimation of the wind at 90m from wind and temperature at 30m and below. The method accounted for about 80% of the variance of the 90m - 30m wind ratio. Monin and Obukhov similarity theory was modified by the inclusion of the effects of Coriolis and pressure gradient forces in order to arrive at a theoretical equivalent to the empirical estimation process. Agreement between observations and theory was quite good. Due to the varying roughness characteristics of the terrain around the tower a dependence of roughness length on wind direction could be demonstrated; further, roughness decreases significantly when the ground was snow-covered. The roughness length during the summer varied from 50 cm for SW winds to 10 cm for NW winds; during the winter the value for NW winds decreased to 1 cm over open-ground and .01 cm over snow-covered ground. The theoretical and practical relationships were valid for unstable, neutral, and slightly stable stratification. In very stable air, no successful method was found for the estimation of the 90m wind. An attempt to use the geostrophic wind as a predictor was not successful. (Author)