Analysis of tropical-extratropical interactions with influence functions of a barotropic model

Abstract

Influence functions (IFs) of a linear barotropic vorticity equation model are computed in order to determine the regions in which anomalous divergence at upper levels, related to tropical heating anomalies, has the largest impact on certain prominent low-frequency anomalies. The present computation differs from that of Branstator in two aspects: (a) the model includes the effects of the basic-flow divergence and the advection by anomalous divergent wind and (b) the influence functions directly assess the influence of upper-level divergence anomalies rather than sources of vorticity. The IFs are applied to the study of low-frequency tropical-extratropical interactions at the interannual (ENSO) and intraseasonal (30-60-day oscillation) timescales. The origin of well-known teleconnection patterns is explored through the identification of common influence regions in the Tropics and subtropics for their main action centers. -from Authors