Modulation of turbulence and mesoscale structure in nested large‐eddy simulations with a gray‐zone parent domain

High‐resolution atmospheric simulations are increasingly essential for applications such as urban air mobility, wind energy, and urban meteorology, where boundary layer turbulence plays a critical role. Large‐eddy simulation (LES) explicitly resolves turbulent motions, while mesoscale models provide the larger‐scale forcing that governs boundary layer evolution. In mesoscale‐to‐LES coupling, however, resolutions of the parent domain approaching the gray‐zone regime – where grid spacing becomes comparable to dominant turbulent scales – can influence the turbulence characteristics that develop in the nested LES domain. Understanding this sensitivity is important for improving multiscale coupling strategies. Using idealized convective boundary layer simulations within the WRF‐LES framework, this study examines the influence of gray‐zone parent domain resolution and the role of the cell perturbation (CP) method under different convective regimes. Simulations are benchmarked against stand‐alone LES to isolate the effects of mesoscale structures originating from the parent domain on turbulence representation in the nested LES. Results show that coarser resolutions of the parent domain enhance the penetration of mesoscale structures into the nested LES domain, which can suppress the development of resolved turbulence. The CP method facilitates earlier turbulence development by introducing buoyancy‐driven perturbations that accelerate eddy growth and shorten spin‐up time. In addition, CP exhibits a filtering effect on mesoscale structures imported from the parent domain, with its influence becoming more pronounced under weakly convective conditions and increasing grid refinement ratios. To systematically quantify these behaviors, the nesting ratio between the parent and child domains is used as the primary control parameter, enabling a sensitivity‐based assessment of gray‐zone‐induced mesoscale influence and CP‐mediated turbulence adjustment.