A nonlinear atmosphere-like dynamical system with sparse horizontal resolution includingorographic and thermal forcing in a long wave and its nonlinear interaction with both a baroclinicwave and a zonal flow is constructed and has been integrated over 10.000 years. It reproducesvariability in a broad range of timescales from intraseasonal to decadal and even centenary ones.Empirical orthogonal function analysis, including Fourier spectra of the principal componentscomputations, 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 dominantmechanisms generating the long-term climate variability are internally driven by shorttime scaleinstabilities and nonlinearities connected to large-scale atmospheric processes related toorography. Mountains play an important role in triggering baroclinic instability processes.Interactions between the zonal flow, and both baroclinic and planetary waves generate afrequency spectrum with a large portion of the variance concentrated in the decadal andcentenary timescale. We hypothesize that variations of the atmospheric climate might beconsistent with those exhibited by our nonlinear dynamical system.