Stochastic dynamics of the PNA

Abstract

The dynamics of the PNA are investigated with the aid of a linear-stochastic model. The dynamical operator of the stochastic model is derived from NCEP/NCAR Reanalysis data, and the leading optimal perturbation is found to evolve into the PNA. The leading optimal is also found to closely resemble the adjoint mode of one of the empirical normal modes of the operator. Excitation of this mode produces streamfunction tendencies that match those seen in the growth of the PNA. Comparison to the results of a vorticity budget analysis suggests that the excitation of this mode represents an interaction between the stationary waves and the growing anomaly.

We also consider results from several configurations of a linear-barotropic stochastic model. No configuration considered is found to be consistent with the observations. One-point correlation maps and the results of the vorticity budget analysis suggest that the deficiencies of the barotropic models are due largely to their neglect of the effects of divergence.