南京地区大口径闪烁仪与涡动相关仪感热通量观测对比

湍流是地表与大气间物质与能量交换的主要形式,因而准确观测湍流通量历来是城市边界层研究的重要问题。本研究基于架设在南京信息工程大学内的大口径闪烁仪(large aperture scintillometer,LAS)和涡动相关仪(eddy covariance,EC)的同步观测,对比了LAS测得的感热通量和EC测得的感热通量的差异,结合归一化植被指数(NDVI)和归一化建筑指数(NDBI),分析了下垫面不均匀性对于两种仪器测得感热通量的影响。结果表明:城市地区LAS与EC具有较好的相关性(R2=0.76),拟合线斜率为0.95;白天,LAS的感热通量大于EC的感热通量,二者差值为18.8~39.4 W·m^-2;夜间,二者均在零值附近波动,差值为4.8~28.7 W·m^-2;月尺度上两种仪器的差值8月最大,其次为7月、4月,6月最小;差异产生的主要原因是风向造成的通量源区不同;通量源区内的NDVI值越大,感热通量与净辐射之比越小,二者呈显著负相关(k=-0.34,P<0.05);NDBI值越大,感热通量与净辐射之比越大,二者呈显著正相关(k=1.15,P<0.05)。

Comparative analysis of sensible heat flux observed by large aperture scintillometer and eddy-covariance system in Nanjing

Turbulence is one of the key processes for energy exchange between land surface and atmosphere. Accurate observation on turbulent fluxes has been an important issue in the researches on urban boundary layer. Based on simultaneous observation of a large aperture scintillometer(LAS) and an eddy covariance system(EC) installed in the campus of Nanjing University of Information Science and Technology,we compared sensible heat flux measured by those two systems. The effects of underlying surface heterogeneity on the sensible heat flux were analyzed combined with the normalized vegetation index(NDVI) and the normalized building index(NDBI).The results showed that LAS and EC had a good correlation(R2= 0.76),with a regression slope of 0.95. During the daytime,sensible heat flux obtained from LAS was larger than that by EC,and their difference varied between 18. 8 and 39. 4 W·m^-2. At night,both of them fluctuated around zero,and the difference varied between 4.8 and 28.7 W·m^-2. On the monthly scale,the difference between LAS and EC was the largest in August,followed by July and April,and the least in June. The difference attributed to the different footprints caused by the changes of wind direction. NDVI in the footprint was negatively correlated with sensible heat flux to net radiation(k =-0.34,P<0.05). NDBI in the footprint was significantly positively correlated with ratio of sensible heat flux to net radiation(k = 1.15,P<0.05).