Structure and dynamics of the summertime Pacific–Japan teleconnection pattern

TLDR

Convective activity over the tropical western Pacific influences extratropical circulation over East Asia in summer via the Pacific–Japan teleconnection, but its structure and dynamics remain poorly understood. The study aims to elucidate the structure and dynamics of the PJ pattern. It does so by performing a composite analysis of 32 monthly events of enhanced convection east of the Philippines. The composite reveals a zonally elongated, poleward‑tilted vorticity anomaly that differs from the traditional baroclinic–barotropic model, with low‑level Rossby wave teleconnection via a south‑westerly jet, energy exchanges in jet exits, and moist processes that generate available potential energy and enhance moisture supply, suggesting the PJ pattern is a self‑sustaining dynamical mode of the Asian summer monsoon. © 2006 Royal Meteorological Society.

Abstract

Convective activity over the tropical western Pacific is known to influence the extratropical circulation over East Asia in the boreal summer in the form of teleconnection, called the 'Pacific–Japan (PJ) pattern', but its structure and dynamics have not yet been studied in depth. In this study, a composite analysis is performed for 32 monthly events of enhanced convection observed to the east of the Philippines. The composited monthly mean vorticity anomalies associated with the PJ pattern are elongated zonally with a distinct poleward tilt with height. This structure differs fundamentally from a combination of the first baroclinic mode in the tropics and the barotropic structure in midlatitudes, as has widely been accepted as a conceptual model of the PJ pattern. A wave-activity flux points polewards only in the lower troposphere, indicating that Rossby wave teleconnection occurs primarily through a low-level south-westerly jet. Those tilted anomalies over the western Pacific can effectively gain kinetic energy in the exits of the mean jet streams in the upper and lower troposphere and available potential energy (APE) in the presence of the vertically sheared jets. The enhanced convection can generate APE effectively, and the associated low-level anomalous circulation acts to increase moisture supply into the convective region while enhancing evaporation from the pre-warmed ocean surface. It is thus hypothesized that the PJ pattern may be regarded as a dynamical mode that can be effectively excited in the zonally asymmetric baroclinic mean flow associated with the Asian summer monsoon with an efficient self-sustaining mechanism through moist processes. Copyright © 2006 Royal Meteorological Society