Implementation of a sigma coordinate system in PALM-Sigma v1.0 (based on PALM v21.10) for LES study of the marine atmospheric boundary layer

Abstract. In large-eddy simulation studies of the marine atmospheric boundary layer, wind–wave interactions are often oversimplified using wall-stress models parameterized by roughness length, overlooking the complex coupling dynamics, especially under wind–wave non-equilibrium. Here, we develop a new LES solver based on the PALM model architecture that employs a surface-following sigma-coordinate system to explicitly resolve evolving wave geometry. Simulations under low-wind conditions with different wave regimes reproduce characteristic features of wave-driven winds reported in previous studies. Notably, the results show that wave-induced form stress significantly modulates vertical momentum flux, with effects extending well beyond the wave boundary layer. Leveraging PALM’s parallelized framework, the solver can be integrated with existing multi-scale nesting and coupled with wave models. This high-fidelity modeling tool advances the understanding and parameterization of wind–wave coupling under realistic met-ocean conditions.