Abstract
An improved non-stationary two-layer model is presented for the simulation of wind speed maxima in the nocturnal boundary layer. The model is based on the idea of Blackadar (1957), who proposed as forcing mechanism an inertial oscillation of the ageostrophic component of the wind vector in the levels above the top of the nocturnal radiation inversion. First, the time-dependent variation of the nocturnal boundary-layer height is studied by means of prognostic equations; there is a good agreement between observed and calculated height data for three days of the Wangara experiment. Furthermore, a diurnal variation of the drag coefficient is considered in the lower layer by decreasing the coefficient by a factor of 10–20 due to stabilization of this layer during the night. The marked temporal decrease (increase) of the drag coefficient in the first hours after sunset (sunrise) is described by a function\(C_{D(t)} = C_{DN} - A\sqrt[4]{{\sin ({\pi \mathord{\left/ {\vphantom {\pi {2T}}} \right. \kern-\nulldelimiterspace} {2T}})t}}\). The incorporation of these two effects into the model gives results which are in good agreement with observed wind data for Wangara days 13/14, 30/31, and 33/34.
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Beyrich, F., Klose, B. Some aspects of modelling low-level jets. Boundary-Layer Meteorol 43, 1–14 (1988). https://doi.org/10.1007/BF00153966
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DOI: https://doi.org/10.1007/BF00153966