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 states. Here, we develop a wave-phase-resolved solver 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. Built on PALM’s framework, the solver can be seamlessly integrated with the multi-scale nesting module and coupled with wave models, enabling high-fidelity simulations to improve understanding and parameterization of wind-wave coupling under realistic conditions.