Integrating a Three‐Dimensional TKE‐Based Subgrid Diffusion Scheme Into GFDL FV3

Abstract

We present the implementation of an inline three‐dimensional (3D) turbulent kinetic energy (TKE)‐based subgrid diffusion scheme in the Geophysical Fluid Dynamics Laboratory (GFDL) Finite‐Volume Cubed‐Sphere (FV3) dynamical core. This scheme addresses the need for a unified and physically grounded treatment of turbulence as FV3 is increasingly used across the gray zone and large‐eddy simulation scales. Building on the 3D TKE framework introduced in Zhu et al. (2025, https://doi.org/10.1038/s41612‐025‐01117‐6 ), we embed the full TKE budget calculations, including the 3D shear production, and TKE‐informed horizontal and vertical diffusion directly into the FV3 core. Key features include computation of 3D TKE shear production based on FV3 D‐grid winds, updating of TKE and diffusion coefficients within FV3 time‐stepping loop, and extension of TKE‐based horizontal diffusion to all dynamical quantities. This integration avoids reliance on external physics packages and improves consistency between resolved and subgrid processes. The inline 3D TKE scheme offers a robust alternative to numerical damping in FV3 and enables a physically based representation of 3D subgrid‐scale diffusion that is well suited for applications at grid spacings of ∼100 m and finer.