Main Influencing Factors And Regional Differences Of Boundary Layer Height In Summer In Chin

The underlying surface of China is complex and the driving factors of the boundary layer are numerous.Because of the lack of observational datas,previous studies on the basic processes of the boundary-layer are limited,and the research on the main driving factors and regional differences of the boundary-layer height in China is still insufficient.This paper uses the K-prototypes algorithm to cluster the boundary-layer height and its twelve possible influencing factors,based on the high-resolution radiosonde measurements from CRN from2012 to 2016.On this basis,we explore the possible mechanism of the development of the boundary-layer.The results show that the main driving factors of the boundary-layer height in China vary significantly at different times and regions,and the mechanisms are not consistent.The main conclusions are as follows:(1)According to the characteristics of the boundary-layer height and its impact factors,the 100 stations in China can be divided into four regions: northeast of China,southeast of China,northwest of China and southwest of China at 08:00,14:00 and 20:00,and the main driving factors of boundary-layer height in these four regions are different.(2)As for the development mechanism of the boundary-layer,the development of the stable boundary-layer in the morning and evening is mainly affected by the turbulent dynamics of the wind speed in all regions,while at noon it is closely related to intermittent turbulence.The development of the neutral and convective boundary-layer is also mainly driven by wind speed in the morning,while at noon it is mainly driven by the turbulent thermal caused by higher surface temperature and larger net surface radiation flux.What’s more,the cloud amount and specific humidity in the northeast,the latent heat flux in the southeast,the sensible heat flux and specific humidity in the northwest,and the sensible heat flux and soil moisture in the southwest can also affect the development of the neutral and convective boundary layer through direct or indirect effects on thermal turbulence.At night,because of the time difference,wind speed tend to be the main influence factor of the neutral and convective boundary-layer in the east of Chine,while in the west of China,the main influence factors may still be the thermal factors.Finally,it is worth noting that the surface pressure can affect the development of the nocturnal boundary layer in the northeast of China by influencing the ascending and descending movements of the air flow.(3)There are certain regional differences in the influence of cloud forcing on the boundary-layer height at noon.In the south of Chine,the increase of the cloud will significantly reduce the surface temperature,while in the west of China,the increase of the cloud will significantly increase the atmospheric humidity.The changes of these factors will inhibit the development of the boundary-layer by regulating the sensible heat and the latent heat.The study revealed the main driving factors of the boundary-layer height in various regions of China at different times and the possible mechanisms of the factors driving the development of the boundary-layer,providing a reference for future research on the development process of the boundary-layer.