AN INTERPRETATION OF ATMOSPHERIC LOW-ORDER MODELS

Low-order models (LOMs) arising in various popular fluid dynamic and a tmospheric problems are shown to be equivalent to coupled three-mode n onlinear systems known in mechanics as Volterra gyrostats. The Volterr a equations of the gyrostat differ from the Euler equations of the gyr oscope by the presence of linear terms, which, unlike ordinary viscous terms, do not affect the energy or the phase volume conservation. In atmospheric LOMs such linear terms, exerting considerable influence on the dynamics, are caused by various factors peculiar to geophysical f luid dynamics (e.g., stratification, rotation, and topography). The si mplest Volterra gyrostat in the forced regime is equivalent to the cel ebrated Lorenz model. Systems of coupled gyrostats also inherently pos sess fundamental properties of the hydrodynamic equations. Therefore, gyrostats are proposed as elementary modules for developing LOMs of no nlinear fluid dynamic and atmospheric phenomena.