A Climatological Analysis of the Extratropical Flow Response to Recurving Western North Pacific Tropical Cyclones

Abstract

lthough prior studies have established that the extratropical flow pattern often amplifies downstream of recurving tropical cyclones (TCs), the extratropical flow response to recurving TCs has not to the authors' knowledge been systematically examined from a climatological perspective. In this study, a climatology of the extratropical flow response to recurving western North Pacific TCs is constructed from 292 cases of TC recurvature during 1979?2009. The extratropical flow response to TC recurvature is evaluated based on a time-lagged composite time series of an index of the North Pacific meridional flow surrounding TC recurvature. Similar time series are constructed for recurving TCs stratified by characteristics of the large-scale flow pattern, the TC, and the phasing between the TC and the extratropical flow to assess factors influencing the extratropical flow response to TC recurvature. Results reveal that following TC recurvature, significantly amplified flow develops over the North Pacific and persists for ~4 days. The tendency for significantly amplified North Pacific flow to develop following TC recurvature is sensitive to the strength of the TC?extratropical flow interaction (the phasing between the TC and the extratropical flow), which is based on the negative potential vorticity advection by the divergent outflow of the TC. In contrast, the tendency for significantly amplified North Pacific flow to develop following TC recurvature is relatively insensitive to the intensity or size of the recurving TC, or whether it subsequently reintensifies after becoming extratropical.