engleski

Improving mixing length-scale for stable boundary layers

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.

diffusion; katabatic flow; Prandtl model; parametrization; stably-stratified turbulence

EMEP4HR (Grant Number: 175183/S30), Research Council of Norway