Katabatic flow with Coriolis effect and gradually varying eddy diffusivity

Belušić

2008

ABSTRACT:We intend to improve the 'z-less' mixing length-scale for parametrization of turbulence in the stable atmospheric boundary layers (SABL). Since the SABL structures are far from being fully understood today, their parametrizations or explicit treatment are still usually very sketchy in most mesoscale and climate models. Typically an over-diffusion through the SABL occurs in most numerical models. With the 'z-less' mixing length-scale proposed here the over-diffusion is absent. In particular, the mesoscale model used gave results similar to those from an improved (calibrated) Prandtl model, i.e. katabatic flow occupying the lower and more active part of the SABL developed in both models. The corresponding low-level jet that is embedded in the strong near-surface inversion appears similar in both models. Certain details vary, simply because of the very different nature of the models deployed. The results, that should be also valid for other types of SABL flows, could be used in different types of numerical modelling, parametrizations of the SABL, further development of analytical models and data interpretation.

Section: Improved Prandtl Modelmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 95%

Section: Improved Prandtl Modelmentioning

confidence: 99%

Section: Model Comparisonsmentioning

confidence: 99%

Section: Sensitivity Testsmentioning

confidence: 99%

See 3 more Smart Citations

Improving mixing length‐scale for stable boundary layers

Belušić

2008

The low‐level katabatic jet height versus Monin–Obukhov height

Kraljević

Jeričević

2007

ABSTRACT:In this short note we discuss a long-standing problem in modelling the atmospheric boundary layer (ABL) over complex terrain: namely, an excessive use of the Monin-Obukhov length scale L MO . This issue becomes increasingly relevant with the ever-increasing resolution of numerical weather-prediction and climate models, which typically use L MO in one way or another for parametrizing the surface layer, or at least for formulating the lower boundary conditions. Hence, inevitably, the models under-represent a significant part of the mesoscale flow variability.We focus here on the stable ABL over land: in particular, sloped cooled flows. However, a qualitatively similar reasoning applies to the corresponding unstable ABL. We show that for sufficiently stratified flows over moderately sloped surfaces, Monin-Obukhov scaling is inadequate for describing the basic ABL dynamics, which is often governed by katabatic and drainage flows.

Generalizing ‘z‐less’ mixing length for stable boundary layers

2010

A couple of important shortcomings of the current turbulence parametrizations for the SABL, as modelled in numerical weather prediction, air-chemistry and climate models, will be remedied by using this new generalized 'z-less' mixing length. This approach also recommends that it should be better if various mixing length scales were derived from simplified main principles, instead of only being guessed from plausible reasoning or dimensional analysis. In particular, it has often been assumed that K and profiles could be chosen for modelling purposes more or less independently from each other. It is shown, based on a simple renormalization for , that this is not the case if one wishes to use a more consistent parametrization scheme.