A numerical study of the nocturnal atmospheric boundary layer

Abstract

The evolution of the structure of the atmospheric boundary layer during the cooling phase of the diurnal cycle is studied with the help of a one-dimensional numerical model. The model uses a turbulent energy equation for the determination of the eddy exchange coefficients, which also involve the local value of the Monin-Obukhov length. The surface temperature is prescribed as a function of time and the geostrophic wind is held constant. Results are presented in nondimensional form and cover a wide range of possible values for the external parameters. After several hours of cooling the inversion layer is found to reach a maximum depth, which depends strongly upon the magnitude of the geostrophic wind and, to a lesser extent, on the cooling rate of the ground surface. * Present affiliation: Dynamic Prediction Research Division, Environment ofCanada, West Isle Office Tower, 5th Floor, 2121Trans-Canada Highway, Dorval, Quebec, Canada.

On the length‐scale of the wind profile

“…The investigation of the length-scale of the wind profile was initiated by Prandtl (1925), who introduced the concept of the mixing length when analyzing mean velocity profiles in laboratory flows. Prandtl's work has motivated the use of mixing-length theory for the entire boundary layer (Blackadar, 1962;Lettau, 1962;Delage, 1974;Gryning et al, 2007). This has been used to derive wind profile parameterizations that fit wind speed observations performed beyond the surface layer both over land and water surfaces (Gryning et al, 2007;Peña et al, 2008Peña et al, , 2010a better than traditional surface-layer theory.…”

Analytical description of a nocturnal low‐level jet

“…Thorpe and Guymer (1977), Beyrich and Klose (1988), and Singh et al (1993) further modified the one-dimensional Blackadar theory of the nocturnal low-level jet by considering a variety of stress parametrizations, though with various structural or dynamical features treated as vertically discontinuous, slab-like or layered. Wippermann (1973), Delage (1974), Brook (1985), and Davies (2000) extended the Blackadar conceptual model by incorporating vertically continuous (apart from numerical discretization) turbulent stress parametrizations in their one-dimensional planetary boundary layer models. Recent advances in computer technology are making large-eddy simulation (LES) of the Blackadar jet scenario increasingly feasible, with some simulations extending over the daytime dry convective regime, the evening transition period, and the nocturnal period during which the jet develops.…”

Modelling of the Evolving Stable Boundary Layer

“…This fact can be taken into consideration by adopting the inverse linear approximation of Delage (1974), between the limits of the mixing length near the underlying surface (= κz) and in the neutral boundary layer (= λ o ) : 1/l = 1/(κz)+1/(λ o ), which is equivalent to l = z/(1 + κz/λ o ). Blackadar (1962) suggested that λ o = 0.009u * / f , where f is the Coriolis parameter.…”