A Comparative Study On Turbulent Fluxes Exchange Over Nanjing Urban And Suburban In Summer

Urban is one of the largest areas of human activity. Human activity participation gradually changed surface albedo, roughness and thermal condition in city, caused the ground-gas material and energy exchange process and the change of surface turbulence flux characteristics, and also further influence urban climate and environment. The observation study on the urban and suburban underlying surface material and energy exchange, ground-gas interactions and turbulent transfer characteristics help to reveal the impact mechanism of urbanization on the boundary layer and urban climate.The study utilizes the data from the three-dimensional experiments at the urban and suburban sites during summer in Nanjing in2010, quantitative analysis the radiation balance, flux changes and turbulence characteristics in different underlying surfaces between urban and suburb, and the flux differences under different weather conditions. The result shows:(1) Frequency compensation has little effect on urban and suburban of CO2flux, so high-frequency compensation correction on urban and suburban is very small. The urban ultrasound virtual temperature correction is larger than suburban; it shows the necessary to do ultrasound virtual temperature correction in suburban. The daytime WPL corrections of CO2flux in both urban and suburban is much larger, and the corrections in urban is larger; the nighttime WPL corrections of CO2flux in both urban and suburban is much smaller. The result observed by ultrasonic anemometer fit spectrum analysis inertia branch area linear transfer energy theory.(2) Sensible heat flux in urban is larger than suburban. Because of the cloud blocking effect, sensible heat flux in sunny day is larger than in cloudy, the weather conditions impact of urban sensible heat flux is larger than suburban. Urban sensible heat flux is always greater than zero, but the suburban sensible heat flux is lower than zero. Latent heat flux in urban is smaller than suburban. From cloudy to sunny, suburban latent heat flux decrease slightly; but the urban latent heat flux in sunny is much larger than in cloudy. Net radiation over urban and suburban in sunny is larger than in cloudy.(3) Urban CO2flux in sunny is obviously smaller than in cloudy, the main reason is photosynthesis of the vegetation in sunny is stronger than in cloudy so that more CO2was consumed. CO2flux of suburban during the daytime as a negative value is carbon sinks, and CO2flux of suburban during the nighttime as a positive value is carbon source. Comparison of flux in urban and suburb shows urban CO2emissions in two weather conditions is always negative, as the carbon source which had been developed. But in general the suburban net contribution of CO2flux is positive, as the carbon sinks.