CLIMATE VARIABILITY IN A NONLINEAR ATMOSPHERE-LIKE DYNAMICAL SYSTEM

A nonlinear atmosphere-like dynamical system with sparse horizontal re solution including orographic and thermal forcing in a long wave and i ts nonlinear interaction with both a baroclinic wave and a zonal flow is constructed and has been integrated over 10.000 years. It reproduce s variability in a broad range of timescales from intraseasonal to dec adal 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-sym metric thermal forcing. The dominant mechanisms generating the long-te rm climate variability are internally driven by shorttime scale instab ilities and nonlinearities connected to large-scale atmospheric proces ses related to orography. Mountains play an important role in triggeri ng baroclinic instability processes. Interactions between the zonal fl ow; and both baroclinic and planetary waves generate a frequency spect rum with a large portion of the Variance concentrated in the decadal a nd centenary timescale. We hypothesize that variations of the atmosphe ric climate might be consistent with those exhibited by our nonlinear dynamical system.