Evaluation of Planetary Boundary-Layer Schemes in the WRF Model for Modeling Low-Level Winds in the Marine Atmospheric Boundary Layer: Cases Studies of Various Boundary-Layer Types

Despite the accelerating development of offshore wind energy, forecasting winds and turbulence over the ocean remains challenging. Offshore the U.S. East Coast, extremely stable stratification can occur during the warm season when westerly winds blow from land that is significantly hotter than the ocean surface. Conversely, during the cold season, extremely unstable stratification can arise due to the reversed land-sea thermal contrast. Additionally, internal boundary layers can form due to discontinuities in surface roughness and temperature. Under these conditions, the performance of planetary boundary-layer (PBL) schemes in the WRF model for predicting low-level winds has not been adequately evaluated. In this study, real cases of three marine atmospheric boundary layer types (unstable, stable, and internal boundary layers) are simulated using the WRF model with five different PBL schemes: MYJ, YSU, ACM2, MYNN-EDMF, and 3DTKE. The model uses a one-way nested grid with horizontal resolutions of 7500 m, 1500 m, and 300 m, crossing the gray zone. Vertically, the model uses three sets of high-resolution vertical levels, with the lowest model level heights set at z₁ = 6, 12, and 24 m, respectively. The study compares results for surface momentum and heat fluxes, atmospheric stability, PBL height, and vertical profiles of wind speed and direction, potential temperature, and turbulence characteristics across the different model settings. Sensitivities to model resolution are found to depend not only on the boundary layer types but also on the stratification categories within each boundary layer type. The performance of these different model settings is evaluated by comparing low-level wind speed and direction with LIDAR measurements from the Air-Sea Interaction Tower (ASIT) at WHOI’s Martha’s Vineyard Coastal Observatory (MVCO).