A Study of Assimilation of Surface Observational Data in Complex Terrain Part II: Representative Error of the Elevation Difference Between Model Surface and Observation Site
复杂地形下地面观测资料同化II. 模式地形与观测站地形高度差异代表性误差

Since the topography distribution of China is very complex,there exists elevation difference between surface observation station measurement and numerical model surface.The surface observation data are currently only used as backup or process analysis,but not used in numerical models sufficiently.Reasonable assimilation schemes of surface observation data will put these data into numerical models sufficiently.In Part I,results have shown that the difference in elevation between observation site and numerical model surface can impact the results of surface observation data assimilation.In this paper,surface observation data are assimilated into meso-scale model MM5 directly, based on the similarity theory,using MM5_3DVAR(MM5 three-dimensional variational) system.A new representative error,i.e.Terrain Error of Representativeness(TER),is introduced to solve the influence of elevation difference between observation site and model surface.TER is added into surface observation error of surface observation data assimilation in MM5_3DVAR system.Some experiments are performed with surface observation data and radiosonde data.Results show that the influence of elevation difference between observation site and model surface can be solved when TER is added.Better results can be obtained when surface observation data are assimilated into a numerical model with TER,which is related to the elevation difference between model surface and observation site.Using this method,surface observation data bring less contribution to the analysis field,while some useful information is put into the analysis field through data assimilation,and the lower analysis field is closer to the actual field.The surface data are used more sufficiently.