EMS Annual Meeting Abstracts
Vol. 18, EMS2021-362, 2021
EMS Annual Meeting 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Numerical Analysis of a Hybrid Stochastic Turbulence Model for Stable Stratification

Vyacheslav Boyko1 and Nikki Vercauteren2
Vyacheslav Boyko and Nikki Vercauteren
  • 1Department of Mathematics and Computer Sciences, Freie Universitaet Berlin, Berlin, Germany (vyacheslav.boyko@fu-berlin.de)
  • 2Department of Geosciences, University of Oslo, Oslo, Norway (nikki.vercauteren@geo.uio.no)

We present results on the modeling of intermittent turbulence in the nocturnal boundary
layer using a data-driven approach. In high stratification and weak wind conditions, the
bulk shear can be too weak to sustain continuous turbulence and the sporadic submesoscale
motions trigger the turbulence production.
The main idea is to extend a TKE-based, 1.5 order turbulence closure model by in-
troducing a stochastic differential equation (SDE) for the nondimensional correction of the
mixing length. Such a nonstationary SDE model is built upon the traditional surface-layer
scaling functions, which model the effect of the static stability on the surface-layer profiles
using scaling with the Richardson (Ri) number . The nonstationary parameters of the SDE
equation are determined from data with a model-based clustering approach. Furthermore, it
is found that parameters scale with the local gradient Ri number, resulting in a closed-form
nonstationary stability correction depending only on this local gradient Ri number. Benefi-
cial is the interpretation of the noise term of the SDE. This term is interpreted as an effect
of the submesoscale motions on turbulent mixing. Furthermore, the SDE model provides
a conceptual view on intermittent turbulence, whereby in the noise-free limit, the steady-
state solution converges to the traditional functional scaling. Per construction, the SDE
is readily incorporated in a turbulence closure by modifying the definition of the stability
correction. Details will be provided.
We will present a numerical analysis of such a hybrid model for quasi-steady-state so-
lutions with different model settings. Furthermore, we investigate the regime transitions
between weakly and strongly stable flows under intermittent mixing based on the temper-
ature inversion characteristics.

How to cite: Boyko, V. and Vercauteren, N.: Numerical Analysis of a Hybrid Stochastic Turbulence Model for Stable Stratification, EMS Annual Meeting 2021, online, 6–10 Sep 2021, EMS2021-362, https://doi.org/10.5194/ems2021-362, 2021.

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