Statistics and Dynamics of Persistent Anomalies

Abstract

Persistent anomalies with recurrent spatial patterns play an important role in the atmosphere's low-frequency variability. We establish a connection between statistical and dynamical methods of description and prediction of persistent anomalies. This is done by computing and analyzing the empirical orthogonal functions (EOFs) in a simple deterministic model, on the one hand, and in Southern Hemisphere geopotential heights, on the other. The dynamical model is governed by the fully nonlinear, equivalent-barotropic vorticity equation on the sphere, with simplified forcing, dissipation and topography. Model solutions exhibit persistent anomalies identifiable with blocked, zonal and wave-train anomalies in Northern Hemisphere atmospheric data. Flow structures similar to the patterns above occur as high-variance EOFs of this nonlinear model. The Southern Hemisphere data we analyze consist in gridded daily maps of 500 mb heights from June 1972 to July 1983. Two types of persistent anomalies appear in t... Abstract Persistent anomalies with recurrent spatial patterns play an important role in the atmosphere's low-frequency variability. We establish a connection between statistical and dynamical methods of description and prediction of persistent anomalies. This is done by computing and analyzing the empirical orthogonal functions (EOFs) in a simple deterministic model, on the one hand, and in Southern Hemisphere geopotential heights, on the other. The dynamical model is governed by the fully nonlinear, equivalent-barotropic vorticity equation on the sphere, with simplified forcing, dissipation and topography. Model solutions exhibit persistent anomalies identifiable with blocked, zonal and wave-train anomalies in Northern Hemisphere atmospheric data. Flow structures similar to the patterns above occur as high-variance EOFs of this nonlinear model. The Southern Hemisphere data we analyze consist in gridded daily maps of 500 mb heights from June 1972 to July 1983. Two types of persistent anomalies appear in t...