Direct Numerical Simulations of a smoke cloud-top mixing layer as a model for stratocumuli
Visualitza/Obre
Cita com:
hdl:2117/190397
Tipus de documentArticle
Data publicació2013-08-05
Condicions d'accésAccés obert
Llevat que s'hi indiqui el contrari, els
continguts d'aquesta obra estan subjectes a la llicència de Creative Commons
:
Reconeixement-NoComercial-SenseObraDerivada 3.0 Espanya
Abstract
A radiatively driven cloud-top mixing layer is investigated using direct numerical simulations. This configuration mimics the mixing process across the inversion that bounds the stratocumulus-topped boundary
layer. The main focus of this paper is on small-scale turbulence. The finest resolution (7.4 cm) is about two
orders of magnitude finer than that in cloud large-eddy simulations (LES). A one-dimensional horizontally
averaged model is employed for the radiation. The results show that the definition of the inversion point with
the mean buoyancy of hbi(zi) 5 0 leads to convective turbulent scalings in the cloud bulk consistent with the
Deardorff theory. Three mechanisms contribute to the entrainment by cooling the inversion layer: a molecular flux, a turbulent flux, and the direct radiative cooling by the smoke inside the inversion layer. In the
simulations the molecular flux is negligible, but the direct cooling reaches values comparable to the turbulent
flux as the inversion layer thickens. The results suggest that the direct cooling might be overestimated in lessresolved models like LES, resulting in an excessive entrainment. The scaled turbulent flux is independent of
the stratification for the range of Richardson numbers studied here. As suggested by earlier studies, the
turbulent entrainment only occurs at the small scales and eddies larger than approximately four optical
lengths (60 m in a typical stratocumulus cloud) perform little or no entrainment. Based on those results,
a parameterization is proposed that accounts for a large part (50%–100%) of the entrainment velocities
measured in the Second Dynamics and Chemistry of the Marine Stratocumulus (DYCOMS II) campaign.
Citacióde Lozar, A.; Mellado, J. P. Direct Numerical Simulations of a smoke cloud-top mixing layer as a model for stratocumuli. "Journal of the atmospheric sciences", 5 Agost 2013, vol. 70, p. 2356-2375.
ISSN0022-4928
Versió de l'editorhttps://journals.ametsoc.org/doi/full/10.1175/JAS-D-12-0333.1
Col·leccions
Fitxers | Descripció | Mida | Format | Visualitza |
---|---|---|---|---|
DeLozarMellado2013.pdf | 1,661Mb | Visualitza/Obre |