Monthly variation of local land–atmosphere coupling over the Tibetan Plateau in the rainy season and its relationship with the South Asian summer monsoon

Abstract

AbstractThe local land–atmosphere coupling (LoCo) over the Tibetan Plateau (TP) in the rainy season and the possible influence of the South Asian monsoon (SAM) on LoCo characteristics are investigated by applying two LoCo diagnostic metrics to 12‐year observational data at six stations over the TP and the ERA5 from June to September (JJAS) from 1980 to 2018. The validation of ERA5 in estimating monthly mean diurnal evolutions of T2m, q2m, and surface fluxes (Hsfc and LEsfc) at the six stations reveals that these variables in the ERA5 are relatively reliable for the LoCo analysis. The mixing diagram analysis based on the observational data and ERA5 suggests that the monthly variations in the planetary boundary layer (PBL) energy budget are strong and vary from station to station, revealing the complexity of the influence of the SAM on the PBL energy budget over TP. The relationship between Hsfc and PBL height (PBLH) and lifted condensation level (LCL) deficit at the six stations based on the ERA5 reveal a strong influence of soil moisture on PBL growth and convective cloud formation, although the topography may also exert its influence. Analyses of the correlations of the PBL energy budget, PBLH, and LCL deficit over the TP with the SAM in JJAS indicate that the LoCo characteristics over the TP show large spatial variability between the southeastern and central‐western parts of the TP. Such spatial variability can be attributed to the spatial differences in monthly mean soil moisture and rainfall closely related to the evolution of SAM's influence and the complex topography of the TP. The topography of the TP can also affect the LoCo characteristics in JJAS, but the mechanisms in the areas dominated by SAM and by the westerly winds are different.