A nonlinear atmosphere-like dynamical system with sparse horizontal resolution including orographic and thermal forcing in a long wave and its nonlinear interaction with both a baroclinic wave and a zonal flow is constructed and has been integrated over 10.000 years. It reproduces variability in a broad range of timescales from intraseasonal to decadal and even centenary ones. Empirical orthogonal function analysis, including Fourier spectra of the principal components computations, as well as wavelet transform analysis, are applied to the results of 10.000 years' model runs with and without a seasonal cycle in an axis-symmetric thermal forcing. The dominant mechanisms generating the long-term climate variability are internally driven by shorttime scale instabilities and nonlinearities connected to large-scale atmospheric processes related to orography. Mountains play an important role in triggering baroclinic instability processes. Interactions between the zonal flow, and both baroclinic and planetary waves generate a frequency spectrum with a large portion of the variance concentrated in the decadal and centenary timescale. We hypothesize that variations of the atmospheric climate might be consistent with those exhibited by our nonlinear dynamical system. Copyright 1998 by the American Geophysical Union.