Gray Zone Partitioning Functions and Parameterization of Turbulence Fluxes in the Convective Atmospheric Boundary Layer. Issue 22 (18th November 2020)

• Record Type: Journal Article
• Authors: Senel, Cem Berk; Temel, Orkun; Muñoz‐Esparza, Domingo; Parente, Alessandro; van Beeck, Jeroen
• Is Part Of: Journal of geophysical research. Volume 125:Issue 22(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-11-18
• Subjects: gray zone -- terra incognita -- turbulence -- atmospheric boundary layer; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1029/2020JD033581
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract: Here, we present the first attempt to fully represent three‐dimensional turbulence fluxes in the "Terra Incognita" or the gray zone in other words. In order to derive partitioning functions, representing the partitioning between subgrid and total fluxes, we make use of high‐resolution large‐eddy simulations (LES), which are performed with the Weather Research and Forecasting (WRF) model. LES computations are performed for various levels of convective instability, ranging from pure buoyant to strongly sheared convection. Then, the resulting reference‐LES fields are successively coarse grained from its original microscale grid spacing ( Δ = 50 m) up to typical mesoscale grid spacings ( Δ = 3 km). The given process is applied by means of an advanced filter, that is, the Butterworth filter. It enables a clear scale‐specific filtering that results in a more controlled energy transition from lower to higher wavenumbers, unlike the drawbacks of current filters in use. Finally, we parameterize the subgrid scale (SGS) partitioning functions of 10 SGS turbulence quantities: momentum fluxes ( τ i j, six terms), heat fluxes ( q j, three terms), and turbulence kinetic energy ( k ). Turbulence partitioning relations are parameterized in a scale‐aware, stability‐dependent, and height‐dependent form, using the sigmoidal Gompertz function. Thus, the new gray zone model provides a framework that bridges the mesoscale and microscale limits and that is suitable for the development of next generation three‐dimensional, multiscale turbulence parameterization methods or planetary boundary layer schemes. Plain Language Summary: Traditionally, numerical weather prediction (NWP) models are mostly run with grid spacing to cover the mesoscale range, that is, from O (100 km) to ∼ O (1 km), meteorological phenomenon, where the effect of turbulence is mostly one dimensional. With the increased computational resources, NWP models can now be run at subkilometer grid spacings, where the contribution of atmospheric turbulence is fully three dimensional, the so‐called microscale range. However, up to date, subgrid schemes to parameterize the contribution of turbulent fluxes on the atmospheric transport, the so‐called planetary boundary layer schemes, were developed to take only the vertical turbulent fluxes into account. Here, we present a novel approach to represent the three‐dimensional turbulent fluxes from microscale to mesoscale range. This parameterization is of greatly significance for handling one of the most challenging issues in NWP models, as it stands as the first available turbulence parameterization methodology designed for the transition between mesoscales and microscales. Key Points: A full three‐dimensional representation of gray zone turbulence is presented for the first time Proposed gray zone partitioning functions are retrieved in a scale‐aware and stability‐dependent form The new parameterization builds a promising framework for mesoscale‐microscale bridging