| The atmospheric boundary layer is one of the most important parts of the entire atmosphere and is extremely complex,interacting with weather,climate formation and development.At the same time,energy,momentum and various substances in the atmosphere are exchanged by boundary layer in the near stratum.In the environment of our life,the boundary layer structure not only has prominent daily changes,but also has the spatial variation caused by uneven surface distribution.Northwest arid desert in our country,at the edge of the summer monsoon influence,due to the complexity of terrain and the dry area has a strong heating effect during the daytime.Making the atmospheric boundary layer has obvious characteristics of the formation and development process in the region.At present,the development of the boundary layer in the typical weather background of the northwest region and the response of the region's unique land-surface process to the east Asian summer monsoon has yet to be further studied.This paper,by using 1980-2016 ERA-Interim reanalysis data,Sounding data of dunhuang field observation in summer 2006,Precipitation data of 661 sites in China and the average monthly ground observation data of 96 sites in northwest China from 1982 to 2010.Using the empirical orthogonal function(EOF)decomposition,the least square method,linear trend analysis,spatial analysis and potential temperature profile method to study the characteristics of the atmospheric boundary layer and its response to the land surface process during summer in the northwest arid region,discussing the relationship between the height of the boundary layer and the temperature of the near ground with the sensible surface heat flux.Analyzed the response characteristics of sensible surface heat flux to east summer mosoon and the mechanism of this phenomenon.The following main conclusions are obtained:(1)the difference between the sunny and cloudy boundary layer in the northwest arid region is mainly due to the difference of thermal factor and dynamic factor.First of all,strong solar radiation and strong heat flux conversion rate make sunny days more prosperous than cloudy.Second,Near ground level wind speed in sunny day is greater than cloudy day.The dynamic action in the form of turbulent flow also provides a certain dynamic background for the development of the boundary layer in sunny days.(2)The convective boundary layer has a strong dependence on net radiation,surface temperature and sensible heat flux at the initial stage of development,and the boundary layer height will increase rapidly once the boundary layer is broken.Net radiation,the earth's surface temperature and the daily variation processes of sensible heat flux and boundary layer thickness are basically agree with corresponding relation,but the development of the boundary layer on the time and all three shows a certain lag,this may be related to the energy conversion and transmission.(3)LV1 with sensible heat flux intensity in the arid and semi-arid areas in the northwest of summer is the east-west reverse type.PC1 reflects the change trend of heat flux change intensity around 1998,after 1998 west(east),sensible heat flux began to increase(decrease).LV2 shows the consistency of the sensible heat flux intensity in the east and west,but the negative value is significant in the east,and the PC2 has been negative since the early 1990 s,and is negative after entering the 21 st century.(4)The temperature of 2m in the arid and semi-arid regions of northwest China has been increasing significantly since 1980(0.57 ? /10 a),there was a sudden change in ground temperature around 1998.The change of the near ground temperature in summer is related to the sensible heat fluxes,especially in the northwest arid region where the heat flux is greater,sensible heat flux is large(small)can lead to the development of atmospheric heat convection is strong(weak),vertical diffusion rate of heating is strong(weak),further affect the near surface temperature increase(decrease).In the eastern part of northwest region is summer monsoon transition region,land surface characteristics significantly,land surface process is complex.(5)In summer,because of the unique land surface process and boundary layer spatial distribution,the lower troposphere in the northwest arid and semi-arid region as an upward movement,the upper troposphere is sinking movement,this is due to the sense of summer sensible surface heat fluxes and the region of vertical diffusion rate of heating is very strong in the lower troposphere,vertical diffusion heat radiation cooling can not balance,can only rely on cooling adiabatic rise to balance,more than 600 hpa radiation cooling plays a main role,so the main balance by adiabatic cooling down.(6)The spring sensible heat fluxes increase in the northwest region has the inhibitory effect on the outbreak of summer monsoon and northward push,and the southward retreat of the summer monsoon has a catalytic effect,sensible heat fluxes decrease shows the opposite relationship.The possible mechanism of this phenomenon is: the anomalous thermal anomaly in the northwest can cause local circulation anomaly,further impact on a wide range of atmospheric circulation.The northwest region sensible heat fluxes is very strong(weak)year.western Pacific subtropical high position just by east(west),However,the different influence of the western Pacific subtropical high position results in the change of water vapor transmission.From water vapor flux analysis,China is mainly affected by the water vapor in the sea of Japan and the huaihai basin when the sensible heat flux is unusually strong,There is no adequate water vapor in the summer monsoon.China is mainly affected by the water vapor in the sea of Japan and the huaihai basin when the sensible heat fluxes is unusually strong;the east and central of China is affected by the water vapor from the sea of Japan and the huaihe river,the south is affected by the water vapor from the south China sea when the sensible heat fluxes is unusually weak. |
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