Long-term climate variability in a simple, nonlinear atmospheric model

A nonlinear, baroclinic, hemispheric, low-order model of the atmosphere with nonzonal orographic and zonal thermal forcings has been constructed. The model is used to investigate the long-term climate variability by running it over 1100 years, The model runs show a chaotic behavior in a realistic parameter range. With and without a seasonal cycle in the thermal forcing, the model generates decadal climate variations which are of the same order as interannual variations, The maximum variability is found in a broad range of periods between 3 and 44 years, Empirical orthogonal function analysis reveals that these fluctuations are predominantly caused by the interaction between the orographically excited standing wave and the mean zonal flow. The computed power spectra of the principal component time series stress the importance of the high-frequency transients in long-term climate variability.