Climatology of Atmospheric Boundary Layer Height Over Nearshore and Open Ocean Regions of the Western North Pacific

Atmospheric boundary layer height (ABLH) plays an important role in air–sea interactions and regional climate over the western North Pacific (WNP). Using ERA5 reanalysis data from 1979 to 2025, this paper investigates the interannual variability, monthly variations, and seasonal spatial patterns of ABLH. To explore potential drivers of ABLH variability, correlation analyses are conducted between ABLH and three key predictors: wind shear, surface sensible heat flux (HFX) and Brunt–Väisälä frequency ( N 2 ). In addition, records from nearshore (NS) and open ocean (OS) stations are analyzed to examine spatial differences in ABLH behavior. The results reveal clear regional differences. Open ocean ABLH increases consistently during both daytime and nighttime, with mean changes of 17.07 and 14.91 m per decade, respectively. Nearshore changes are weaker, particularly at night. Open ocean ABLH is generally highest in winter and lowest in summer, whereas NS ABLH exhibits a mixed land–sea seasonal pattern, with relatively high values commonly occurring around September and October. The controlling factors also vary by region and season. Open ocean ABLH is strongly associated with wind shear and N 2 , with mechanical forcing becoming particularly important in winter. In contrast, NS daytime ABLH is primarily associated with HFX, while the influence of wind shear becomes more pronounced at night. The findings contribute to a comprehensive understanding of the marine ABL and provide valuable insights for its modeling, OS wind energy assessment, and pollutant dispersion studies.