An objective exposure correction method for average wind speeds measured at a sheltered location

Abstract

AbstractThe representativity of station wind measurements can be increased by elimination of sheltering effects caused by small‐scale obstacles. It is shown how correction factors for this purpose can be obtained for each wind azimuth sector from analog wind records of the station itself, by extracting maximum gust speeds during periods with strong wind. The transformation is achieved using a gust factor model (Wieringa 1973) which relates the ratio of maximum and average wind speed to measuring height, surrounding roughness and gust wavelength. The concept of ‘effective height’ is criticized. It is indicated how the actual duration of the recorded maximum gusts can be obtained from station instrumentation response specifications, and it is shown that this duration exceeds 10 seconds for the usual combination of cup anemometer and galvanometric recorder. A trial climatological application shows how omission of exposure correction may lead to exaggeration of mesoscale horizontal wind gradients.