The sensitivity of the numerical simulation to orography specification in the lowresolution spectral model-Part II: Impact of the smoothed orography and ripples on simulations

In order to investigate the impact of the smoothed orography and the spurious orographic ripples on simulations in the low-resolution spectral model, three different numerical tests, that is, the unsmoothed orography scheme, the smoothed orography scheme and non-ripples scheme are performed. In this paper, the model used by us is the same as Part I except for orographic specification. The results from simulations indicate that, as far as the climatic simulation is concerned, some aspects of the simulated stationary disturbances, zonal and meridional wind, temperature and precipitation in the low-resolution spectral model with properly smoothed mountains are significantly improved, especially in winter hemisphere. The deep ripples in the model with the unsmoothed orography produce spurious high pressure regions at the surface with subsidence, and suppress rainfall, causing an unrealistic splitting of the precipitation area in northern winter and summer. Removal of the deep ripples by using the special procedure for smoothing topography allows a strong upward motion in the ripple area with heavy rainfall, eliminating the unrelistic split in the precipitation area.