Characteristics and Influencing Factors of Convective Boundary Layer Height on the Tibetan Plateau During Different Periods of the Summer Monsoon

The study of the atmospheric boundary layer (ABL) on the Tibetan Plateau (TP) is important to understand surface heat and moisture balances, as well as weather and climate change on the TP and surrounding areas. However, studies focusing on the ABL during different monsoon periods across the TP are limited. Here, we investigated the convective boundary layer height (CBLH) during the pre-monsoon, monsoon, and post-monsoon periods using radio sounding data at six research stations on and near the TP. During the pre-monsoon period, the CBLH of TP stations gradually decreased from south to north, peaking at 3444 m. During the monsoon period, there was a gradual decrease in CBLH from north to south, with a peak of 3393 m. Notably, stations heavily influenced by the monsoon (Shiquanhe, BJ, and QOMS stations) experienced declining CBLH as the monsoon advanced, while others saw an increase. During the post-monsoon period, the CBLH at Shiquanhe station, located on the western TP, was consistently highest, reaching a maximum of 3679 m. CBLH increased at Shiquanhe, BJ, and QOMS stations as the monsoon retreated but decreased at the remaining stations. Surface flux observations revealed that stations heavily impacted by the monsoon exhibited a minimal contribution ratio (CR) of sensible heat flux to convective boundary layer (CBL) development during the monsoon period. Furthermore, these monsoon-impacted stations exhibited the highest stability of the mid-lower atmosphere during the monsoon period, hindering CBL development.