Effects Of Soil Moisture And Altitude On The Summer Boundary Layer Height In China And Its Regional Differences

Planetary boundary layer height(PBLH)is one of the key variables to describe the Planetary boundary layer(PBL)structure.It plays a decisive role in the vertical turbulent mixing,convective motion of the atmospheric boundary layer and land-atmosphere coupling.However,few studies have been made to systematically explain the spatial differences and the influencing factors of PBLH over the complex surface land state in a huge area.Based on the5-year(2012-2016)record of high-resolution summertime radiosonde measurements,combined with three commonly used reanalysis data,using Liu-Liang method,we focus on the spatial difference of PBLH.Then the spatial characteristics of PBLH and the effects of soli moisture(SM)and altitude on it are discussed in terms of regional and thermal states.The related physical mechanisms are discussed from the perspective of thermal and dynamic The main conclusions are as follows:(1)The reanalysis data,including ERA5,FNL and CERA-SAT could not describe the daily cycle of PBLH and PBLH under different thermal states at any time.During the diurnal cycle,PBLH in China reaches the peak at 1400BJT(daytime),showing a spatial pattern of " Northwest High Southeast low ".The boundary layer is further classified into convective(CBL),neutral(NBL)and stable boundary layer(SBL)according to the thermodynamic conditions.The CBL usually prevails at daytime,but the SBL can also form.Abnormally wet atmosphere and more cloud,which means inhibited PBL,possibly leading to the daytime SBL.ERA5 performs better in the whole country.(2)CBL and NBL height seems to be more strongly correlated with meteorological quantities over dry areas and soil moisture(SM)over wet area.A negative correlation exists between SM and daytime PBLH for CBL and NBL,exhibiting a spatial pattern of “Northeast Strong Southwest Weak”,related to the negative correlation between SM and sensible heat flux(SHF),albeit a positive correlation for SBL.Besides,the cloudy,humid and stable atmosphere result in CBL and NBL shoaling.PBLH less correlates with the sensible heat flux over wet area than dry area(CBL: 0.25,NBL: 0.33 in dry area;CBL: 0.16,NBL: 0.18 in wet area).(3)In the whole country,there is a positive correlation between altitude and daytime CBL height,which has a strong regional difference.Daytime CBL height is more sensitive to altitude changes in dry areas.The daytime CBL height in high altitude terrain is significantly higher,and a positive correlation exits between altitude and the sum of sensible latent heat flux(SHF+ LHF)and 100 m wind speed,with the correlation coefficients of 0.59 and 0.49 respectively.High altitude terrain has larger SHF and wind speed.The combination of SHF and wind speed leads to the enhancement of turbulent mixing in the boundary layer,favoring CBL development.Low SM in dry area leads to less LHF and higher SHF,and vice versa.SHF heats up the atmosphere and raises the boundary layer,while LHF inhibits the development of the boundary layer.There are two ways for the land surface to affect the boundary layer height: the thermal way: the terrain affects the total energy received by the land surface,while the SM affects the energy distribution,thus affecting the boundary layer height;the dynamic way: the increase of altitude leads to the increase of wind speed,thus enhancing the turbulent mixing and thickening the boundary layer,and vice versa.(4)The Climate Extension of Weather Research and Forecast(CWRF)can simulate the daily mean characteristics of PBLH well in China,while the ensemble mean of multi-schemes can significantly reduce the model deviation.The daily mean of summer PBLH in China is sensitive to the physical process scheme(PBL>surface and radiation>cloud).Based on the large regional differences of simulation results,different scheme configurations are recommended for different areas.This paper focuses on the spatial differences of the effects of soil moisture and altitude on the PBLH in China during summer,which provides the basis for studying the influence factors of the PBLH in different regions,and the selection of model parameterization scheme and reanalysis data.