DYNAMICS OF FINE-SCALE VARIABLES VERSUS AVERAGED OBSERVABLES IN A T21L3 QUASI-GEOSTROPHIC MODEL

The dynamics of space- and time-averaged observables of a 3-level quas i-geostrophic model is investigated and compared with that of the fine -scale variables, with emphasis on the role of the initial error field on predictability. The invariance of the largest Lyapunov exponent ag ainst averaging of up to 10 days is established. Some improvements of predictability of the averaged variables turn out to be possible, at l east for certain classes of initial perturbations. Finally, a map of e rror distribution in space and a classification of weather regimes are derived on the basis of the average properties of the Lyapunov vector s.