AN EMPIRICAL-MODEL OF BAROTROPIC ATMOSPHERIC DYNAMICS AND ITS RESPONSE TO TROPICAL FORCING

A linear empirical model of barotropic atmospheric dynamics is constru cted in which the streamfunction tendency field is optimally predicted using the concurrent streamfunction state as a predictor. The predict ion equations are those resulting from performing a linear regression between tendency and state vectors. Based on the formal analogy betwee n this model and the linear nondivergent barotropic vorticity equation , this empirical model is applied to problems normally addressed with a conventional model based on physical principles. It is found to qual itatively represent the horizontal dispersion of energy and to skillfu lly predict how a general circulation model will respond to steady tro pical heat sources. Analysis of model solutions indicates that the emp irical model's dynamics include processes that are not represented by conventional nondivergent linear models. Most significantly, the influ ence of internally generated midlatitude divergence anomalies and of a nomalous vorticity fluxes by high-frequency transients associated with low-frequency anomalies are automatically incorporated into the empir ical model. The results suggest the utility of empirical models of atm ospheric dynamics in situations where estimates of the response to ext ernal forcing are needed or as a standard of comparison in efforts to make models based on physical principles more complete.