Coastal circulations like the sea breeze are key drivers of variability within the marine atmospheric boundary layer (MABL) near the coast. In this study, we analyze 36 idealized, mesoscale simulations designed to better understand how coastal soil moisture influences the MABL through the sea-breeze circulation. We find that decreasing coastal soil moisture increases the strength, extent, and depth of the sea-breeze circulation over the ocean. The onshore-directed segment of the sea breeze in the simulations with the driest soil moisture extends over 200 km seaward from the coast and has near-surface wind speeds exceeding 8 m s −1 . The stronger onshore flow in the drier soil conditions increases humidity within the MABL by enhancing surface latent heat fluxes near the coast. Statistical analysis of all 36 simulations with different soil moisture, SST, and cloud settings reveals that the sea-breeze characteristics over the ocean have the strongest relationship to the depth of the mixed layer over land and the weakest relationship to the lower-tropospheric static stability over the ocean. Afternoon clouds and convection limit the diurnal growth of the mixed layer over land by reducing surface heat fluxes and stabilizing the lower troposphere. As a result, the simulations with clouds have weaker, shallower, and more coastally confined sea breezes over the ocean than corresponding cloud-free simulations. These findings suggest that accurate representations of coastal soil moisture and cloud processes in numerical weather prediction models are crucial for forecasting basic characteristics of the MABL more than 200 km offshore. Significance Statement The coastal land surface can influence the nearby marine environment through sea breezes that develop at the coast. We conduct simulations with a weather model to better understand how changing soil moisture near the coast influences sea breezes in the marine environment. We find that as near-coastal soils become drier, sea breezes become stronger and extend higher above the sea surface and farther offshore. As a result, the marine environment becomes more humid. Land surface properties and inland clouds have a greater influence on the sea-breeze characteristics than the ocean temperature, suggesting that an accurate representation of coastal land surface characteristics and clouds in weather prediction models is important for forecasting weather in coastal marine environments.
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Finocchio et al. (2025) studied this question.