Study on the Land-Atmosphere Interaction in the Coordination Effect of Westerly Wind and Monsoon

^{By using sounding data from Mount. Everest, Nyingchi, Nam Co, Nagqu and Shiquan River sites and ERA5 reanalysis data in 2104 and 2019. The characteristics of the temporal and spatial changes of the atmospheric boundary layer structure and its relationship with sensible heat, latent heat flux, and vertical velocity field, in order to deeply understand the different characteristics of the plateau atmospheric boundary layer structure under the coordinated action of westerly and monsoon and its change mechanism. The main findings of this study are as follows:}

^{(1)     The height of the convective boundary layer at each station under the westerly south branch wind field is higher than that under the summer monsoon wind field. The hight of convective boundary layers of Mount Everest, Nyingchi, Nam Co, Nagqu and Shiquan River under the westerly south branch wind field are 4500m, 3000m, 2400m, 2760m and 3500m. In the plateau monsoon field, the hight convective boundary layers are 3000 m, 2100 m, 2200 m, 1650 m and 2000 m.}

^{(2)     The specific humidity of the lower atmospheric boundary layer at each station under the westerly south branch wind field is smaller than that of the lower atmospheric boundary layer under the plateau monsoon wind field. The specific humidity of the near-surface layer in Linzhi area is obviously larger than that of the other four areas, and its maximum specific humidity is 12.88 g.kg-1. The lower layers of Mount Everest are often affected by the northerly valley wind at 14 o'clock and the glacier wind with southerly wind at 20 o'clock.}

^{(3)     The boundary layer has strong atmospheric turbulence and strong convection, which makes the boundary layer high. However, the latent heat flux at each station under the plateau summer monsoon wind field is large, and the moisture content in the air is large, which inhibits the development of the boundary layer.}

^{(4)     Convection in the boundary layer at each site is active during the day, with ascending and sinking movements alternately occurring. There was a strong sinking motion at Nyingchi Station at 14:00 on May 16th and October 25th, 2019, and at the same time, there was inverse humidity at the lower level. The vertical velocity in the atmospheric boundary layer of Nyingchi area is basically sinking. This may be one of the reasons that the height of the convective boundary layer in the Nyingchi area is lower than that of other stations, and it is also one of the reasons why inverse humidity often occurs in Nyingchi.}

^{Key words: the Tibetan plateau, South branch of westerly, Plateau monsoon, Atmospheric boundary layer}