Analysis of the land surface heterogeneity and its impact on atmospheric variables and the aerodynamic and thermodynamic roughness lengths

Abstract

The land surface heterogeneity has a very significant impact on atmospheric variables (air temperature T-a, wind speed u, and humidity q), the aerodynamic roughness length z(0m), thermodynamic roughness length z(0h), and the excess resistance to heat transfer kB(-1). First, in this study the land surface heterogeneity has been documented through the comparison of surface reflectance r(0), surface temperature T-0, net radiation flux R-n, and sensible heat flux H partitioning over the different land cover types in the experimental areas of the Global Energy and Water Cycle Experiment (GEWEX) Asian Monsoon Experiment on the Tibetan Plateau (GAME/Tibet), the Coordinated Enhanced Observing Period (CEOP) Asia-Australia Monsoon Project on the Tibetan Plateau (CAMP/Tibet), the Heihe Basin Field Experiment (HEIFE), the Arid Environment Comprehensive Monitoring Plan, 95 (AECMP' 95), and the Dun Huang Experiment (DHEX). The results show that the surface heterogeneity was very significant in the areas of the HEIFE, the AECMP' 95, and the DHEX and that it was less significant in the areas of CAMP/Tibet and GAME/Tibet. Second, the vertical profiles of T-a, u, and q in the near-surface layer and above the blending height z(b) have been analyzed using the atmospheric boundary layer (ABL) tower data, radiosonde data, and tethered balloon data observed during the HEIFE, the DHEX, and the CAMP/Tibet. The results show that the land surface heterogeneity leads in the near-surface layer to different vertical profiles of u, T-a, and q overlying the surfaces of the Gobi and the oasis in the areas of the HEIFE and DHEX. The values of u, T-a, and q become well mixed above a height of about 300 m at the HEIFE and 150 m at the DHEX. z(0m), z(0h), and kB(-1) over the different land surfaces have also been determined in this study. The results show that the land surface heterogeneity leads to different aerodynamic and thermodynamic parameters over the areas of the HEIFE, the AECMP' 95, and the GAME/Tibe