Turbulent Flux Observation And Heat Island Intensity Study On Complex Underlying Surfaces In Urban And Suburban Areas

Both urban and topographic underlying surfaces belong to complex underlying surfaces.The classical M-O similarity theory is not applicable to complex underlying surfaces.Therefore,it is very important to carry out micrometeorological observation on complex underlying surfaces.Turbulent flux and temperature are important elements in micrometeorological observation,and their characteristics and processes deserve attention.In view of the above problems,this paper carries out the following work.Based on the data from Nanjing and Suzhou urban observation stations at two heights among the rough sublayers above the canopy,and the data from SORPES observation station at three heights above the canopy at Xianlin campus of Nanjing University,the representative problems of the relationship between the turbulent fluxes and the surface energy balance over the complex underlying surface were analyzed and studied.The results show that the near-ground momentum flux,sensible heat flux and latent heat flux of the underlying surface of the city increase with height,the observed surface albedo of the underlying surface of the city increases with height,and the observed surface net radiation decreases with height,which causes the balance of urban surface energy to change with height;In the SORPES observation in Xianlin Campus of Nanjing University,which is located in hilly area,the observed values of momentum flux,sensible heat flux and latent heat flux in ground observation field are obviously different from those at two heights of the tower,while the observed values at two heights of the tower are very close.These results mean that only when the flux observation is carried out over the complex underlying surface can the observation results have sufficient local representativeness,and the turbulent flux observation results at the lower altitude in the urban area will have lower estimates,while the turbulent flux observation results near the surface in the hilly complex underlying surface environment will have large deviations.Based on the data of air temperature and long wave radiation flux from three stations in Nanjing,the diurnal variation characteristics of air temperature and surface radiant temperature and the variation characteristics of air temperature with height are analyzed.The representative and limitations of heat island intensity under different heat island types in Nanjing are discussed.The results show that the urban and rural heat island intensity calculated by the surface radiant brightness temperature is a weak negative value in the daytime due to the shading effect at noon,and a significant positive value in the night due to the influence of human heat and urban heat storage.The surface radiant brightness temperature in the SORPES observation field of Xianlin campus of Nanjing University is not representative of Xianlin area,but can only represent the undersurface of short grass in the observation field.The intensity of the urban and rural heat island in the rough sublayer above the canopy varies with the temperature observation height,and even the reversal of the hot and cold island may occur in the daytime.The diurnal variation of the suburban heat island intensity is very small,and it always remains a heat island.Comparing the temperature of SORPES observation tower in Xianlin Campus of Nanjing University with the temperature of rural stations,it shows a cold island due to transpiration and evaporation of vegetation in the daytime,and a heat island due to partial urbanization effect in the night.The diurnal variation of heat island intensity at the higher observation height is consistent with that at the higher observation height.These results mean that the representative temperature of each observation point should be selected when calculating the heat island intensity.The temperature near the ground is greatly affected by the heterogeneous underlying surface,and the heat island intensity calculated by the temperature of the average temperature of multiple layers in the roughness sublayer or the top layer of the tower is more locally representative.The average diurnal variation characteristics of turbulent kinetic energy,vertical flux exchange coefficient and turbulent transfer efficiency at different heights were analyzed by using the eddy correlation data of SORPES at three levels in Xianlin Campus of Nanjing University.The results show that the statistical characteristics of the two layers on the Xianlin tower are similar,and there are significant differences between the statistical characteristics of the two layers and those observed on the ground.Different from the natural flat underlying surface,the high exchange efficiency does not necessarily correspond to the high turbulence order when the turbulence behavior characteristics are different greatly.