Surface Energy Balance And Land-atmosphere Exchange Characteristics At SORPES Station,Xianlin Campus Of Nanjing University

In this paper,the characteristics of the surface energy balance,the energy closure,the land-atmosphere exchange and surface layer construction under the complex underlying surface at Xianlin station in Nanjing area,compared with Lishui station,whose underlying surface is grass,were analyzed by using the eddy-correlation observation and conventional meteorological data.In the aspect of surface energy balance,the turbulent fluxes and radiation fluxes of two stations under different conditions were analyzed.For the energy closure,several statistical methods were used.And the energy closure of Xianlin station and Lishui station was evaluated comprehensively,and the diurnal and seasonal variations of energy closure were given.For the characteristics of land-atmosphere exchange,the flux data on the Xianlin station tower was used to analyze the temporal variations of the turbulent flux(momentum flux,sensible heat flux,latent heat flux).At the same time,the spatial and temporal distribution characteristics of carbon dioxide(CO2)flux were explored.As for surface layer,the suitability of the flux-gradient relationship was assessed under this complex surface.What's more,the relationship was localized at Xianlin station.On the basis of HOST(Hockey-Stick Transition)hypothesis,the characteristics of turbulence for nocturnal boundary layer was explored.The research shows that:(1)The observation results of the Xianlin SORPES station represent the surface energy characteristics of the subtropical monsoon climate in Nanjing,that is,summer is hot and rainy,with the smallest Bowen ratio(the ratio of sensible heat flux to latent heat flux),and winter is cold and dry,with the biggest Bowen ratio.(2)There is energy imbalance in the observation of Xianlin station.The energy balance ratio EBR is 0.72 during the day and 0.32 at night.During morning and evening transition period,the EBR jumps due to the phase difference.Compared to the even and flat underlying surface of Lishui,the energy closure of the complex underlying surface of Xianlin station is similar.(3)All the turbulent fluxes,except the latent heat flux,show a small difference of 25m and 50m,and the difference from 3m is larger,indicating that 25m and 50m are in the inertial sublayer and 3m is in the roughness sublayer.That is to say,the surface layer construction under the complex underlying surface is similar to the urban underlying surface,and there is roughness sublayer.(4)Under the complex underlying surface,the surface layer frictional velocity increases with height,the sensible heat flux decreases with height,and the latent heat flux differs little between upper and lower layers,and the absolute value of carbon dioxide flux decreases with height;At the same time,the different underlying winds on the complex underlying surface will lead to different flux characteristics,with different source regions and corresponding changes in the corresponding land-atmosphere exchange characteristics.(5)The flux data of 3m can only reflect the local conditions,and 25m and 50m can better reflect the regional situation.Under the complicated underlying surface,the surface layer structure is complex and requires multiple observations to fully reflect the characteristics of the surface layer.(6)The momentum flux gradient relationship of the complex underlying surface basically meets the local similarity relationship,which is consistent with the results in the urban roughness sublayer,and is far below the classical results under the homogeneous underlying surface under stable conditions.(7)The zero-plane displacement at different heights is inconsistent.The 3 m layer near the ground is mainly affected by the observation field.And at this time the zero plane displacement is estimated to be high by using the canopy dynamics parameters directly.(8)There is a HOST feature between the surface turbulence intensity and wind speed at night in Xianlin station,which further confirms the universality of the HOST assumption;at the same time,the critical wind speed increases with height and is related to the nature of the underlying surface.The critical wind speed under the complex underlying surface is lower than that of the homogeneous underlying surface.