Contrasting Effect of Soil Moisture on the Daytime Boundary Layer Under Different Thermodynamic Conditions in Summer Over China

The investigation is still lacking concerning the effect of soil moisture (SM) on the evolution of planetary boundary layer (PBL) under different land conditions in a huge domain as large as China. We perform an explicit correlation analysis between daytime PBL height (PBLH) and SM for convective, neutral and stable boundary layer regimes (i.e., CBL, NBL, and SBL), respectively. A negative correlation exists between SM and daytime PBLH for CBL and NBL, exhibiting a spatial pattern of “east strong west weak”, albeit a positive correlation for SBL. The standard deviation of PBLH for CBL and NBL exhibits a spatial pattern of “northwest high southeast low”. Cloudy, humid, and stable atmosphere result in CBL shoaling. PBLH more correlates with the sensible heat flux (CBL: r = 0.25; NBL: r = 0.33) over dry areas, but over Northwest China the PBL depends more on meteorology likely owing to the extremely dry soil. Plain Language Summary The effect of soil moisture (SM) on the evolution of planetary boundary layer (PBL) throughout China remains elusive. This study explores the correlation between PBL height (PBLH) and SM under different PBL regimes, using the 5‐year record of high‐resolution summertime soundings across China. The convective boundary layer (CBL) and neutral boundary layer (NBL) heights during daytime are found to negatively correlate with SM. In contrast, the stable boundary layer (SBL) height anticorrelates with SM, likely due to more fluid and moisture intermittent turbulence caused by enhanced SM in SBL. The spatial pattern of the standard deviation of CBL and NBL height exhibits a pronounced “northwest high southeast low” pattern. Our study also reveals more significant impact of sensible heat flux on CBL and NBL regimes over dry areas, compared to over wet areas, indicating that land surface processes are more coupled to the PBL evolution over dry areas. Besides, less cloud, dry and unstable atmosphere favor the development of CBL in wet areas, and PBLH is more dependent on meteorological quantities, but less on SM in dry areas, likely owing to extremely dry soil and bare land over Northwest China. Key Points Soil moisture positively correlated with heights of the connective boundary layer (CBL) and neutral boundary layer (NBL) but negatively correlated with stable boundary layer (SBL) height The planetary boundary layer (PBL) depends less on SM but more on meteorology over Northwest China unexpectedly, likely owing to the extremely dry soil Th