A study of the predictability of a 28-variable atmospheric model

A 28-variable model of the atmosphere is constructed by expanding the equations of a two-level geostrophic model in truncated double-Fourier series. The model includes the nonlinear interactions among disturbances of three different wave lengths. Nonperiodic time-dependent solutions are determined by numerical integration.By comparing separate solutions with slightly different initial conditions, the growth rate of small initial errors is studied. The time required for errors comparable to observational errors in the atmosphere to grow to intolerable errors is strongly dependent upon the current circulation pattern, and varies from a few days to a few weeks.Some statistical predictability of certain quantities seems to be present even after errors in the complete circulation pattern are no longer small.The feasibility of performing similar studies with much larger atmospheric models is considered.