南京市区及郊区近地层通量观测比较

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

2005年夏季、2006年春季在南京市区及南京郊区进行了两次近地层通量观测实验,运用涡动相关(eddy-covariance,EC)技术得到感热通量、潜热通量、二氧化碳通量和摩擦速度.为了消除地形对这些测量值的影响,运用平面拟合方法(PF)对其进行倾斜校正.进一步研究发现,平面拟合因子与风向角度密切相关,因而在采用平面拟合方法处理数据时,必须考虑风向的影响,分别做出不同风向扇区的拟合平面,我们命名这种改进后的新方法为分角度平面拟合法(sector planar fit,SPF);相应的,称不区分风向扇区的平面内拟合法为总体平面拟合(general planar fit,GPF).着重比较了不同季节、不同地点两种方法修正后的通量结果的差异.春夏两季,市区各通量分布总体趋势一致;地域上,市区SPF法、GPF法修正后通量值之间有明显的差异,郊区二者差异较小.接着,运用SPF法、GPF法修正垂直速度,两方法修正后垂直速度差异显著;最终,得出两种方法修正后垂直速度的概率分布,SPF方法得到的垂直速度更接近于正态分布.

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 velocityby the two methods, it was concluded that the distribution of corrected vertical velocities by SPF is closer to normal than GPF.