| With the increasing resolution of numerical forecasting model, the slopes of model terrain become steep. It is a big problem in the development of the refined numerical forecasting model that the errors of the PGF calculation (Pressure Gradient Force)and the2D-ADV calculation (2-dimensional mass advection) increase because of the terrain following coordinate in the model. The thesis focuses on how to improve the traditional coordinate so as to enhance the performances of solving complex topography.The errors of the PGF calculation and the2D-ADV calculation can be reduced by smoothing the coordinate plans in high levels. The approach is to divide the absolute plan height into relative height term and the terrain-related term。The later can beadjusted by controlling the coefficient before it which is named as the decaying coefficient b‘. The coordinate transformation term changes with the coefficient.Several kinds of typical height-based terrain-following coordinates, such as Gal-Chen&Somerville coordinate (hereafter Gal.C.S‘coordinate), smooth level vertical coordinate (hereafter SLEVE coordinate) and a new coordinate called as cosine coordinate(hereafter COS‘coordinate),were theoretically analyzed and inter-compared each other inthe induced errors by calculations of the PGF and the2D-ADV.The results of calculation of the PGF showed that the induced errors of the calculation of the PGF were significantly decreased with coordinate height by using SLEVE1,SLEVE2and COS‘coordinates in comparison to Gal.C.S coordinate. SLEVE2and COS‘coordinates were relatively better in reduction of the errors of the PGF calculation. The COS‘coordinate produces scarcely errors for its plat plans in high levels. However, its decaying speed grows slow at first then get fast in low levels，so the errors of the SLEVE2coordinate are relatively small there. The similar remarks could be made for the tests of2D-ADV calculation. The errors of the2D-ADV calculation by using the COS‘coordinate were the smallest as those of the reference test in which there were no terrain. The COS‘coordinate was most advantageous to other coordinates in tests. Besides，the lower the critical height is，the smaller the errors are in high levels. The critical height isbounded by the maximum terrain height. The decaying coefficient b‘and its Jocabian derivative played a deterministic role in reduction of the errors according to the ide al tests.Real topography and the coupling between physical processes and the model fr ame work are very complex in model simulation. Will the new Coordinate maintain theirgood characters in the real model? The Reformulation of the atmospheric motion equations based on the general form of vertical coordinate demonstrates that both the equations and the physical quantity related to the vertical coordinate contains the decaying coefficient b‘or its Jocabian derivative.Typical weather case simulation and daily continuous simulation were carried outwith the reformed model with the selected coordinates except the SLEVE2coordinate.The24hours simulation of the precipitation case in April4th2011showed that, compared with Gal.C.S coordinate, the small-scaled disturbances on isoclines of the vertical cross-sections of the wind and temperature fields along34.5°N were smoothed which at the same time reduced the fictitious vertical velocity caused by the topographic effect on the higher plans.24hours and48hours daily continuous simulation on September2011shows that, the monthly total rainfall of the SLEVE1coordinate is reduced to the degree that are closer to the fact compared with the left two coordinates; the SLEVE1coordinate maintains the minimum numeral value between the forecastingheight and wind field and the fact on500hPa，250hPa and100hPa while on the100hPa,it is the COS‘coordinate maintaining the value. The rms error and the correlation of various variables on different height，such as1000hPa,850hPa,500hPa,250hPa and100hPa,show the same characters, either. |
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