Abstract: Eddy covariance (EC) and large aperture scintillometer (LAS) are two commonly used methods for surface flux observation. Investigating the distribution of source area is helpful to improve the spatial representativeness and enhance the understanding of scaling issues such as up-scaling of surface flux data. Based on the observation data from EC and LAS in Minqin, an oasis-desert ecotone, the distribution and variation of source areas were analyzed. In different directions of the source area, the influence of the ratio of weighted-footprint area between EC and LAS (CEC&LAS) on the difference of observed values was compared. The results indicate that: (1) the northwest wind prevails in the non-growing season, while the east wind prevails in the growing season. The spatial distribution of source areas consistent with the prevailing wind direction, and the source areas in the non-growing season are larger than those in the growing season. (2) Source areas of EC and LAS in stable atmospheric conditions are generally larger than those in unstable conditions. With the increase of source contribution (from 50% to 90%), the overlapping area and CEC&LAS also increase. In growing and non-growing season, source areas of EC and LAS distributed in an irregular shape. (3) Compared with the value in east and west, the CEC&LAS in north and south of growing season is higher. Meanwhile, the determination index (R2) in north and south is also greater than it is in east and west. It reveals that in some degree, CEC&LAS can explain the difference of the observation results between these two methods. This study has contributed to the improvement of the spatial representativeness of surface flux and provide a reference of methodology for the up-scaling of surface flux.

Key words: Eddy covariance, Large aperture scintillometer, Flux source area, Atmospheric stability, Ratio of weighted-footprint area between EC and LAS