Contrasting Air Mass Advection Explains Significant Differences in Boundary Layer Depth Seasonal Cycles Under Onshore Versus Offshore Flows Geophysical Research Letters

Abstract The complexities in the atmospheric boundary layer depth (BLD) features over coastal regions pose challenges for meteorological forecasts, air quality, greenhouse gas mixing and transport, and wind energy production. Here, for the first time, we investigated afternoon BLD variability over 18 coastal sites in the contiguous United States located along the Gulf of Mexico, Atlantic Ocean, and Pacific Ocean using 25 years of rawinsonde launches. Due to influence of shallow marine layer air via onshore flow, substantially large BLD contrasts (∆BLD, BLD under offshore minus onshore) were found. ∆BLDs over the sites varied both seasonally and spatially among the coastal regions and within a region. For the sites along the Gulf of Mexico and Atlantic Ocean, ∆BLDs were found to be higher in spring and summer (500–1,500 m) than in winter and fall (100–450 m). Results underscore the importance of advection on BLD footprints and provide observational constraints for model evaluation.