A comparative study of the characteristics of the clear sky land surface processes over the different underlying surfaces in the northern part of China during July-September 2008

By selecting the 9 land cover types including bare soil, cropland, forest, and grassland, the characteristics of the clear-sky land surface processes over the different underlying surfaces in the northern part of China are investigated compared using the data measured during July to September 2008, provided by the project of the Experimental Coobservation and Integral Research in Semi arid and Arid Regions over North China. The results show that the pronounced differences in the land surface radiation and energy processes are found within and between the various land cover types. The differences can primarily be attributed to those in the optical, thermal, and hydrologic property of land covers as well as the amount of available water in the land-atmosphere system. For radiation components, upward long wave radiation increases in the order of forest, cropland, grassland, and bare soil. The reflectivity of the different underlying surfaces reduces in the order of bare soil, grassland, cropland and forest. Land surface net radiation is small in poorly vegetated underlying surfaces such as bare soil and grass land, and is high in cropland and forest. For energy components, 80% of the land surface available energy on bare soil is consumed by heating the atmosphere, and the remaining 20% is used for evaporation and heating the soil. For the grassland and forest, higher available energy goes to the atmosphere heating than that lost to evaporation with alpine meadow being an exception. Large part of energy is lost owing to evaporation on cropland, and 20% is used in heating the atmosphere. In addition, for all underlying surfaces, the closure rate decreases with the increasing latent heat flux.