Land Surface Process Numerical Simulation Research In Rainstorm And Heterogeneous Conditions In Arid Regions

Land surface is an important interface between earth and atmosphere, which has significant influence on weather and climate. As the one and only reflection of land surface process in climate model, land surface model is an indispensable and important part of it. Arid region is special and widely distributed, it has various specific underlying surfaces. In arid regions, different underlying surfaces have entirely different physical and chemical characteristics, and its characteristics are also influenced severely by weather and season change. Hence, the research of land surface process in arid regions are very essential. For the sake of grasping different underlying surfaces’ characteristics and examining different land surface models’ simulation performance in arid areas, this article first deeply analyzed oasis-desert land surface characteristics; Second, comparatively evaluated simulation performance of land surface models Noah, SHAW and CLM4.0’s before and after a rainstorm in arid regions; Last, tentatively explored influence of different heights of atmospheric forcing on land surface model in heterogeneous underlying surface which has wind secondary boundary layer. The achievements are as follows:(1)First, this article analyzed land surface data observed at "Gulang Heterogeneous Underlying Surface Layer Experiment" and "Microclimate and Evaporation Experiment in Inner Mongolia", and mainly analyzed the influence of vegetation and rainstorm on land surface process. The main conclusions are:(a) Vegetation has obvious influence on turbulence flux. In desert, sensible heat flux is 7 times larger than its latent heat flux, but in oasis, latent heat flux is 4 times larger than its sensible heat flux. Also, the growing of vegetation may cause oasis cropland energy closure level reducing and land surface albedo decreasing. Oasis soil temperature daily variation amplitude is less than desert, together with albedo decreasing, causing oasis net radiation larger than desert; (b)After rainstorm, arid gobi region soil water content increased, soil temperature daily variation amplitude and daily maximum value both decreased, as a result, turbulence flux is redistributed, land surface albedo decreased, upward long wave radiation decreased, causing net radiation obviously increased. Rainstorm dramatically changed the arid gobi bare soil underlying surface’s land surface process, the influence last a significant time.(2)In consideration of obvious influence of rainstorm on arid gobi bare soil land surface process, the second section using data observed at "Microclimate and Evaporation Experiment in Inner Mongolia", compared land surface model CLM, Noah and SHAWs performance before and after the rare rainstorm which occurred during the simulated period. The results show that all of the three models can simulate the trend of turbulence flux, radiation flux, soil moisture and soil temperature before and after the rare rainstorm. Except the simulation of soil temperature and soil water content, the performance of Noah land surface model is the best, especially the simulation of latent heat flux of Noah LSM, with the 0.99 correlation coefficient and 7.89 W/m2 root mean square error. The performance of three models in sensible heat flux, upward long wave radiation and net radiation are better after the rainstorm, and the models performance in soil temperature is better before the rainstorm, this shows that all of the three models are more appropriate to simulate sensible heat flux, upward long wave radiation and net radiation in moister land after rainstorm and more appropriate to simulate soil temperature without rainfall.(3)The performance of land surface model not only depends on the parameterization scheme of model itself, but also depends on the selection of atmospheric forcing. Therefore, the third section using 2m and 16m wind speed, air temperature, air humidity and radiation data observed at "Gulang Heterogeneous Underlying Surface Layer Experiment" sparse forest cropland site which has wind secondary boundary layer, to form two different atmospheric forcing, and forced land surface model TBLSHAW_MULCH differently, to explore the influence of different atmospheric forcing which changed with height seriously on land surface model. Then expanded 16m forcing wind speed artificially to explore the sensitivity of land surface model to forcing wind speed. The results shows that except the simulation of short wave radiation and net radiation, the difference between 2m and 16m atmospheric forcing simulation results are remarkably obvious, especially the simulation of turbulence flux and soil temperature. From the view of simulation performance, except the simulation of soil water content and soil temperature,2m atmospheric forcing simulation performance is better; With the forcing wind speed expanding, the simulated sensible heat flux negative value at night became more obvious, latent heat flux peak value enlarged, soil temperature and soil moisture both declined. Simulated soil temperature and soil moisture are more sensitive to forcing wind speed.