A Universal Approach for the Non‐Iterative Parametrization of Near‐Surface Turbulent Fluxes in Climate and Weather Prediction Models

V M Gryanik,D Sidorenko,C Lüpkes,A Grachev

doi:10.1029/2021ms002590

Abstract

AbstractWeather prediction and climate simulations need reliable parameterizations of turbulent fluxes in the stable surface layer. Especially in these conditions, the uncertainties of such parametrizations are still large. Most of them rely on the Monin‐Obukhov similarity theory (MOST), for which universal stability functions (SFs) represent important ingredients. The SFs are nonlinear, if so, a numerical iteration of the MOST equations is required. Moreover, presently available SFs are significantly different at large stability. To simplify the calculations, a non‐iterative parametrization of fluxes is derived and corresponding bulk transfer coefficients for momentum and heat for a package of five pairs of state‐of‐the‐art SFs are proposed. For the first time, a parametrization of the related transfer coefficients is derived in a universal framework for all package members. The new parametrizations provide a basis for a cheap systematic study of the impact of surface layer turbulent fluxes in weather prediction and climate models.

Highlights

Parametrizations of surface layer turbulent fluxes used in numerical weather prediction (NWP) and climate models describe the impact of the unresolved turbulent mixing of momentum, heat, and humidity on resolved physical processes
The parametrizations cover the entire range of Rib, m and t as observed during the most famous and most comprehensive campaigns for atmospheric surface layer conditions over sea-ice and land
The new non-iterative surface flux parametrizations are presented in a package, which is well suited for practical use in models, especially for those relying already on aggregated schemes of transfer coefficients

Summary

Introduction

Parametrizations of surface layer turbulent fluxes used in numerical weather prediction (NWP) and climate models describe the impact of the unresolved turbulent mixing of momentum, heat, and humidity on resolved physical processes. In numerical atmospheric models as, for example, in the WRF model (Jiménez et al, 2012), the regional climate model HIRHAM5 (Christensen et al, 2007) and in coupled atmosphere-ocean models like ECHAM6-FESOM (Sidorenko et al, 2015), the turbulent transports of momentum, heat, and humidity in the surface layer are usually described by Monin-Obukhov similarity theory (MOST, Monin & Obukhov, 1954). It connects the surface boundary conditions with the lowest model level above the surface. These functions, correspondingly the stability correction functions (SCFs, m and h-functions, sometimes called integral SFs) are nonlinear, GRYANIK ET AL

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