Comparison between wavenumber truncation and horizontal diffusion methods in spectral models

Commonly used horizontal diffusion and wavenumber truncation dealiasing met hods in spectral models are verified using the National Center for Atmosphe ric Research Community Climate Model version 3. For the same horizontal gri d resolution, time step, physical processes, boundary conditions, and initi al conditions, the simulated climate, using the horizontal diffusion alone model, is better than that using the wavenumber truncation method. In compa rison with the observed climate data, the global root-mean-square of simula ted January monthly mean 500-hPa geopotential using the horizontal diffusio n alone model is 25% less than that using the wavenumber truncation model. However, for the same spectral resolution, the wavenumber truncation model (high horizontal grid resolution) leads to more accurate solutions than the horizontal diffusion model (low horizontal grid resolution).