The Development And Evaluation Of The Peking University Land-atmosphere Interaction Model

Land surface and planetary boundary layer are the key components of the earthclimate system. Land surface physical and biochemical processes, turbulent transportprocesses in planetary boundary layer together play a great role in the global energyand water cycle and have a significant impact on the climate change. Land surface ishighly heterogenic, and land surface processes interact with planetary boundary layerclosely. In order to study these highly non-linear, interacted processes, the landsurface-planetary boundary layer interaction model is needed.Using the NWC-ALIEX (Northwest China Atmosphere–Land InteractionExperiment) data, we developed the Peking University Land-Atmosphere InteractionModel by three steps. Firstly, we developed the Peking University Land Model(PKULM), and evaluated it with data observed over desert and cropland that arelocated in Badanjilin and Pingliang respectively. Then, five sensitivity tests wereperformed to validate the model future. Secondly, we developed the PekingUniversity Boundary Layer Model (PKUBLM) and evaluated it with GPS radiosondedata observed over Dunhuang Gobi. Thirdly, by coupling the PKULM and thePKUBLM, we developed the Peking University Land-Atmosphere Interaction model,and then simulated the planetary boundary structure and atmospheric circulation in anidealized desert-oasis system. We draw the following conclusions:(1) The PKULM was developed. PKULM use two-stream approximation tosimulate the radiation transfer within canopy, use similarity theory to modelthe turbulent transport process in near surface layer, use multi-layer thermal diffusion model to calculate soil temperature, use the h-based soil waterdiffusion model to simulate the soil moisture distribution and it’s interactionwith water table. By improving the stomatal conductance calculationalgorithm, the model could be used at arid and semi-arid region.(2) Using the observation data over desert and cropland, the performance of thePKULM was evaluated by calculating the heat and water vapor fluxesbetween land and atmosphere. The simulated fluxes are close to the observeddata and the results from NOAH land surface model. Five sensitivity testswere performed further. The PKULM responded correctly to the changes ofsoil albedo, emissivity, roughness length, CO2concentration and leaf areaindex. These results showed that the PKULM performed well in typical aridand semi-arid region.(3) The PKUBLM was developed. PKUBLM is a three-dimensionalincompressible hydrostatic fluid dynamic model with Yamada1.5orderturbulent closure scheme. PKUBLM use standard Arakawa-C staged grid,terrain-following coordinate and forward integration method. In the test ofsimulating the planetary boundary layer structure over Dunhuang Gobi, thePKUBLM reasonably reproduced the observed profiles of the potentialtemperature and wind speed. This result showed that the model is reasonableand correct.(4) The Peking University Land-Atmosphere Interaction Model was developed.The PKULM and PKUBLM were coupled through the10m wind speed,10m and2m air temperature, and2m wind speed scale. An idealized desert-oasis has been set up and used to validate the performance of the couplingmodel. In the test, different vertical profiles of the planetary boundary layerand the atmospheric circulation which driven by the heterogeneous surfaceheating were produced. The results showed that the model could be used tostudy the impacts of land surface processes on the boundary layer structureand atmosphere circulation patterns.