BAROTROPIC INSTABILITY AND A LOW-FREQUENC Y PATTERN OF VARIABILITY OFCIRCULATION GENERATED BY A 2-LAYER BAROCLINIC MODEL OF THE ATMOSPHERE

Extremely low-frequency variability of atmospheric circulation (with p eriods longer than 50 days) is studied by using a two-layer baroclinic model as an example. It is shown that, with a random forcing in the f orm of a white noise, a barotropic model linearized about the upper-le vel state describes 70% of this variability (the correlation coefficie nt of the first orthogonal functions is meant). With the zero addition al Rayleigh friction, the barotropic model linearized about upper leve ls may be applied to describing large-scale components of low-frequenc y variability.