A numerical study of daily transitions in the convective boundary layer |
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Authors: | Zbigniew Sorbjan |
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Institution: | (1) Department of Physics, Marquette University, Wehr Phys. Blg., 540 North 15th Street, Milwaukee, WI 53201-1881, USA |
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Abstract: | We examine daily (morning–afternoon) transitions in the atmospheric boundary layer based on large-eddy simulations. Under
consideration are the effects of the stratification at the top of the mixed layer and of the wind shear. The results describe
the transitory behaviour of temperature and wind velocity, their second moments, the boundary-layer height Z
m
(defined by the maximum of the potential temperature gradient) and its standard deviation σ
m
, the mixed-layer height z
i
(defined by the minimum of the potential temperature flux), entrainment velocity W
e, and the entrainment flux H
i
. The entrainment flux and the entrainment velocity are found to lag slightly in time with respect to the surface temperature
flux. The simulations imply that the atmospheric values of velocity variances, measured at various instants during the daytime,
and normalized in terms of the actual convective scale w*, are not expected to collapse to a single curve, but to produce a significant scatter of observational points. The measured
values of the temperature variance, normalized in terms of the actual convective scale Θ*, are expected to form a single curve in the mixed layer, and to exhibit a considerable scatter in the interfacial layer. |
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Keywords: | Convective boundary layer Daily transitions Interfacial layer Large-eddy simulations Mixed layer |
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