Flux observation research on urban and suburban atmospheric boundary layers in Nanjing

In the summer of 2005 and the spring of 2006, flux measurements were twice taken in Nanjing Municipal Party School and Pukou area. Heat flux, latent heat flux, carbon dioxide flux as well as friction velocity were obtained applying the eddy-covariance (EC) technique. In order to eliminate the impact of complex terrain, a planar-fit (PF) method for tilt correction was adopted. A thorough analysis of the PF method indicated that PF coefficients are closely related to wind direction. Thus, wind directions must be taken into consideration when processing data. To be specific, winds from all directions were divided into several sectors and PF method was applied to each of them in order to generate a fitted plane for each sector. This method was named sector planar fit (SPF) as distinguished from the general planar fit (GPF) which doesnt consider wind sectors. The differences of corrected fluxes by the two methods (GPF/SPF) for the two seasons and two locations were mainly considered. It was clearly revealed that both urban and suburban flux results share a consistent trend in spring and summer; geographically, in urban areas, the corrected fluxes using SPF and GPF show obvious differences, differences are much smaller in suburban areas. Moreover, the vertical velocity w was corrected using the two methods and it was found that w also exhibits significant differences. Finally, according to the probability distribution of corrected vertical wind velocity by the two methods, it was concluded that the distribution of corrected vertical velocities by SPF is closer to normal than GPF.