Analysis of local land-atmosphere coupling in rainy season over a typical underlying surface in Tibetan Plateau based on field measurements and ERA5

Abstract

This study investigates the local land-atmosphere coupling (LoCo) in the rainy season by applying a mixing diagram method to the field measurements and ERA5 data over a typical underlying surface in Tibetan Plateau (TP). Comparison of frequencies of meteorological variables in June, July, August, and September (JJAS) in 2011 in the two datasets suggests that the ranges of meteorological variables are similar although the ERA5 shows a cold and wet bias. The mixing diagram analysis on 12 July, and 7–8 August 2011 calculated based on the two datasets reveals that the ERA5 could provide similar curves of the mixing diagram in the sunny days, although it tends to overestimate surface sensible and latent heat fluxes (Hsfc, LEsfc), and entrainment sensible heat fluxes (Hent), underestimate entrainment latent heat fluxes (LEent) in sunny days. The mixing diagram analysis under four different weather conditions based on ERA5 shows that LoCo behaves differently under different weather conditions and that as cloud amount increases, less heat and more water vapor are transported into the PBL from the land surface. Study of the monthly mean mixing diagram in JJAS from 2011 to 2014 based on the two datasets indicates the curves of the monthly-mean Cp*θ and Lv*q and PBL energy budgets exhibit a monthly variation, which relates to Southern Asian monsoon (ASM). Discussion of the relationship between mean Hsfc and max PBLH in the daytime reveals that the role of Hsfc in PBL growth at the daily scale is weakest in July due to the impact of ASM.