Nonsingular Zero-Order Bulk Models of Sheared Convective Boundary Layers
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hdl:2117/180940
Tipus de documentArticle
Data publicació2019-12-01
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Abstract
Two zero-order bulk models (ZOMs) are developed for the velocity, buoyancy, and moisture of a
cloud-free barotropic convective boundary layer (CBL) that grows into a linearly stratified atmosphere. The
models differ in the entrainment closure assumption: in the first one, termed the ‘‘energetics-based model,’’
the negative and positive areas of the buoyancy flux are assumed to match between the model and the actual
CBL; in the second one, termed the ‘‘geometric-based model,’’ the modeled CBL depth is assumed to match
different definitions of the actual CBL depth. Parameterizations for these properties derived from direct
numerical simulation (DNS) are employed as entrainment closure equations. These parameterizations, and
hence the resulting models, are free from the potential singularity at finite wind strength that has been a major
limitation in previous bulk models. The proposed ZOMs are verified using the DNS data. Model results show
that the CBL depths obtained from the energetics-based model and previous ZOMs correspond to the height
that marks the transition from the lower to the upper entrainment-zone sublayer; this reference height is few
hundred meters above the height of the minimum buoyancy flux. It is also argued that ZOMs, despite their
simplicity compared to higher-order models, can accurately represent CBL bulk properties when the relevant
features of the actual entrainment zone are considered in the entrainment closures. The vertical structure of
the actual entrainment zone, if required, can be constructed a posteriori using the available relationships
between the predicted zero-order CBL depth and various definitions of the actual CBL depth.
CitacióHaghshenas, A.; Hartmann, M.; Mellado, J. P. Nonsingular Zero-Order Bulk Models of Sheared Convective Boundary Layers. "Journal of the atmospheric sciences", 1 Desembre 2019, vol. 76, núm. 12, p. 3697-3715.
ISSN0022-4928
Versió de l'editorhttps://journals.ametsoc.org/doi/10.1175/JAS-D-19-0022.1
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HaghshenasMellado2019b.pdf | 2,350Mb | Visualitza/Obre |