Comparison of Atmospheric Stability at Wind Observation Tower Height and Hub/Rotor Height Using 200 m Meteorological Observation Tower Data

ABSTRACT In computational fluid dynamics (CFD) models, it is generally assumed that the atmospheric stability is constant throughout the entire domain. Furthermore, CFD models perform simulations for each wind direction separately. However, atmospheric stability, both onshore and offshore, varies daily and also exhibits diurnal variation. In this study, using 9 years of data from a 200‐m high meteorological mast, we investigated the differences in atmospheric stability calculated at altitudes below the hub height and at hub/rotor heights for 16 wind directions. The following findings were obtained. The investigation of 16 wind directions revealed significant differences in the Richardson number obtained from meteorological variables at 10‐ and 50‐m heights, which correspond to typical wind observation tower heights in Japan, and those obtained at 100‐ and 150‐m heights, which correspond to the current hub and rotor heights. The frequency of stable conditions followed the order: current hub and rotor heights > future hub and rotor heights (calculated using meteorological variables at 150‐ and 200‐m heights) > wind observation tower heights. The comparison of the occurrence frequency of atmospheric stability between the current hub height/rotor height (100 to 150 m) and the future hub height/rotor height (150 to 200 m) revealed differences in the frequency of stable conditions. Investigation using the temperature lapse rate showed that the stable layer is weaker at the future hub/rotor height compared with the current hub/rotor height.