Calculation Of Urban Surface Zero-plane Displacement And Roughness Length

Heterogeneous Surface land-an accurate estimate of the energy between air, water and material fluxes exchange, is the current difficulties of frontier land surface processes and scientific research, but also "reduce the climate system model to simulate and predict uncertainty" key scientific One of the issues. In view of the surface roughness of the ground-the intrinsic link interface flux important role in the exchange of research, as well as surface roughness and non-uniform surface morphology between this thesis city inhomogeneous surface roughness of the underlying surface as a starting point, based Institute of Atmospheric Physics 325 m tower (B325 tower) observations, on the basis of strict quality control data, through data analysis, theoretical research and statistical calculations to obtain the surface roughness of Beijing urban development and land surface features to improve the non-uniformity of the underlying surface land-atmosphere interaction description and, ultimately, to achieve enhanced ability to simulate and predict weather and climate patterns.The results showed that(1) the flux of data quality evaluation results:a year of sensible heat flux data,56.5 per cent of good quality data,99.8% of good quality data,0.1 percent for the need to eliminate the data. Xmax maximum flux distribution footprint concentrated, uniform, does not depend on wind direction, amplitude range of 36 m to 596 m, of which 30-200 m range there is a dense area; greater impact on the stability of atmospheric stratification by Xmax, The more stable stratification, the more extensive Xmax distribution.(2) With the increase of the overall number of Richardson, turbulent momentum transfer coefficients and heat transfer coefficients will decrease. In addition, the grass, the wind speed on the one hand by a simple dynamic effect turbulence momentum and heat transfer coefficients, on the other hand will change the state of the grass surface (ie, surface roughness) and thus also affect the turbulent momentum and heat transfer coefficients. In addition, the analysis found that the surface roughness measurement error of measurement error and friction velocity exponentially,5% of the friction velocity measurement error will cause 44.1 percent of roughness measurement error.(3) B325 tower city near surface layer momentum flux has obvious seasonal, summer and autumn showed smaller, larger winter and spring. Centralized distribution momentum flux of between 0-0.3 kg/m s2; minimum and maximum sensible heat flux, respectively--100 W/m2 and 400 W/m2, also showed some seasonal variations, which In spring the biggest summer autumn, winter minimum. A strong wind momentum flux dependence, clearly showed two characteristic intervals to change a flat area, a region of rapid change, where a large area surface roughness of its momentum flux is significantly larger; sensible heat flux the amount of wind direction in each section is basically nearly uniform distribution. When the atmosphere unstable or neutral state, the sensible heat flux increased significantly, but the difference was not under layers knot conditions; when the atmosphere is stable, sensible heat flux, although often become negative, but only slightly less than zero.(4) With the development of urbanization, the relative wind speed decreasing trend year by year, Beijing urbanization little effect on the characteristics of the atmospheric boundary layer height above 200m and 120m below the height of the greater impact, and more close to the ground, reducing the relative wind speed is more obvious, which reflects the urban architecture of the friction surface layer of air flow. Winds from the slope of the line profile fitting, both near the ground floor or a higher level, increasing the rate of vertical wind speed has increased year by year trend. And affect the underlying surface roughness extended to senior year, reflecting the increasing urbanization of the development of urban canopy gradually enhance the friction of the wind speed. Martano law by the estimated surface roughness showed significant spatial differences, obviously depends on the wind direction, in which the surface roughness of the maximum and minimum values were 1.9 m and 0.67 m.