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Accueil du site Doctorat Chine 2013 Study On Land-Atmosphere Interaction In Surface Layer Over Semi-arid Loess Platean Of China

** Titre : **Study On Land-Atmosphere Interaction In Surface Layer Over Semi-arid Loess Platean Of China

** Auteur : ** Bao J

** Grade : ** Doctoral Dissertation 2013

** Université : ** China University

**Résumé partiel **

The land-atmosphere interaction in semi-arid Loess Plateau of China plays a key role in the formation of the northwest arid climate and the East Asia monsoon circulation, also has very important effect on global climate and the change of the atmospheric circulation.In this paper, by using the continuous observation data of the boundary layer meteorological tower, eddy covariance system, soil parameters monitoring system, and surface radiation monitoring system at the Semi-arid Climate and Environment Observatory of Lanzhou University (SACOL) from March2007to February2011, the character of micrometeorology, turbulent parameters, turbulent flux, and energy exchange were analyzed to understand the Land-atmosphere interaction in the region better, and to provide the theory basis to improve Land surface parameterization scheme process. The results show that :(1) At SACOL, the prevailing wind direction is southeast, and the second prevailing wind direction is southwest all year round ; summer and autumn are wet seasons ; wind, barometric pressure, temperature, and humidity all have obvious diurnal and seasonal variation ; the vertical profiles of wind, temperature, and humidity all have kinks ; the aerodynamic roughness length (z0m) calculated by the flux method, is larger than which calculated by the profile method, the respective mean calculation is0.040m,0.033m ; z0m is the largest in autumn, and is the smallest in winter ; there is difference in z0m between different wind directions because the influence of topography, NW>SW>NE>SE ; wind direction and atmospheric stability have important effect on footprint, and the flux measurements of SACOL were representative of two types of topography : flat terrain and mountain terrain.(2) Stability were normal distribution, near neutral stability is in the majority ; the turbulence intensity related to wind velocity and stability are as the general law Iu>Iv>Iw ; the relationship between wind velocity normalized standard deviation and stability is conform to power1/3, normalized standard deviation of u,v,w component under near neutral stability is3.35,3.30,1.35, respectively ; turbulent kinetic energy (e) has obvious diurnal variation, is largest in spring, and is smallest in winter, e is increasing year by year, u,v components are close to each other, larger than w component ; dimensionless turbulent kinetic energy is related to stability ; bulk momentum transfer coefficient (CD) has obvious diurnal variation, but bulk sensible heat (CH) has a large fluctuation ; mean value of CD in spring, summer, autumn, winter is8.45×10-3,8.20×10-3,8.30×10-3,7.85×10-3, and mean value of CH in spring, summer, autumn, winter is6.18×10-3,9.22×10-3,7.14×10-3,5.01×10-3, CD>CH ; dynamic factor plays a greater role than heat factor in bulk transport processes. (3) Momentum flux, heat flux and CO2flux (Fc) have obvious diurnal, seasonal and annual variation ; the Bowen ratio (B) is greater than1at daytime, hence the sensible heat flux is dominant, and B is lesser than1at night, hence the latent heat flux is dominant ; the sensible heat flux is dominant at all winter ; the turbulent flux calculated by gradient method and eddy covariance method have the same diurnal variation, the value calculated by gradient method is still in the trusted range although it is overall larger than which calculated by eddy covariance method ; Fc is absorption in total at SACOL. Fc is positive at night, and negative at daytime ; the annual season change range of Fc reduced year by year.(4) The diurnal variation of radiation components is obvious except the upward long wave radiation, the solar radiation, upward shortwave and net radiation have similar phase variation, but upward and downward long wave radiation lag ; the monthly and seasonal average of radiation components is positive has obvious seasonal and annual variation, the interannual variability is small, the mean value are as a law Lo>Li>Si>Rn>So:370.5Wm-2,281.5Wm-2,190.0Wm-2,63.4Wm-2,37.7Wm-2 ;

**Mots clés : ** Semi-arid Loess Plateau, Land-atmosphere interaction, Micrometeorology, Turbulent parameters, Turbulent flux, Radiation, Ground heat flux, Energy balance, Dust

Page publiée le 21 avril 2013, mise à jour le 10 janvier 2018