The impact of the summer monsoon on the convective boundary layer height in different regions of the Tibetan Plateau

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 in different regions of TP during monsoon advance and retreat are limited. Here, we investigated the convective boundary layer height (CBLH) during the pre-monsoon, monsoon, and post-monsoon periods using radio sounding data. As the monsoon advanced, the spatial distribution of CBLH shifted from high in the south and low in the north to low in the south and high in the north. During this transition, although there was a decrease in downward shortwave radiation in regions significantly influenced by the monsoon (southern and central TP), the net radiation increased or remained constant in most regions. In the southern and central TP, both sensible heat flux and CBLH decreased, accompanied by a substantial drop in the contribution ratio (CR) of sensible heat flux to convective boundary layer (CBL) development. The CRs decreased to 25.13% and 31.30% at two stations significantly affected by the monsoon, respectively. In contrast, in regions less affected by the monsoon (northern TP), sensible heat flux didn't exhibit a significant decrease, and CBLH increased. The CR of sensible heat flux to CBL development at one station less affected by the monsoon was high, reaching 58.92%. As the monsoon retreated, the maximum CBLH appeared in the western TP. Downward shortwave radiation and net radiation at all stations decreased during this period. Sensible heat flux either increased or remained stable in regions significantly influenced by the monsoon, alongside elevated CBLH. Conversely, sensible heat flux and CBLH decreased in regions less affected by the monsoon. Furthermore, the monsoon-impacted regions exhibited the highest stability of the mid-lower atmosphere during the monsoon period, hindering CBL development. The advance and retreat of the monsoon impact the allocation of sensible and latent heat flux, along with the stability of the mid-lower atmosphere, ultimately influencing the CBLH in different regions of the TP.