Effects of stability functions in a dynamic model convective boundary layer simulation

Mary‐Jane M Bopape,Maria Valdivieso,Georgios A Efstathiou,Omduth Coceal,Robert S Plant

doi:10.1002/asl.1008

Abstract

AbstractDynamic subgrid models are increasingly being used in simulations of the atmospheric boundary layer. We have implemented several variant forms of dynamic models in the UK Met Office Large Eddy Model (MetLEM), including a state‐of‐the‐art Lagrangian‐Averaged‐Scale‐Dependent (LASD) model. The implementation includes optional use of stability functions in the specification of the eddy viscosity and diffusivity, as well as optional use within the dynamic calculation of the Smagorinsky parameter. This paper reports on the behaviour of the LASD model with different choices for the inclusion and treatment of stability functions in convective boundary layer simulations at different resolutions. Results are compared against a high‐resolution Large‐Eddy simulation (LES) and against simulations employing the Smagorinsky–Lilly subgrid model. We conclude that the use of stability functions improves the behaviour of the LASD model in the grey zone regime. Moreover, a careful treatment of the stability functions in the calculation of the dynamic parameters, while attractive theoretically, is found to be unnecessary in practical terms.

Highlights

While a variety of sub-grid parameterizations for largeeddy models (LEMs) exist, the simple Smagorinsky scheme and its variants are still probably the mostAbbreviations: LASD, Lagrangian-averaged scale-dependent dynamic model; NO-STABF, LASD model without stability functions; PARSTABF, LASD model with stability functions partially implemented; SMAG, Smagorinsky model; STABF, LASD model with stability functions fully implemented.widely-used approach (Yang, 2015)
Introducing stability functions in the calculation of the viscosity and diffusivity has a substantial impact on the behaviour of the LASD model at near grey-zone resolutions
Additional advantages are that profiles of viscosity and TKE in the LASD model are more similar in shape to those of the high-resolution simulations

Summary

Introduction

While a variety of sub-grid parameterizations for largeeddy models (LEMs) exist, the simple Smagorinsky scheme and its variants are still probably the mostwidely-used approach (Yang, 2015). This paper reports on the behaviour of the LASD model with different choices for the inclusion and treatment of stability functions in convective boundary layer simulations at different resolutions. This study is focused on the use of the scaledependent dynamic model in convective boundary-layer simulations at different resolutions from the near-LES through to the so-called grey zone regimes.

Results

Conclusion