150 The Downstream Response to Explosive Extratropical Cyclone Intensification over the North Pacific

Monday, 11 January 2016
Kevin M. Lupo, Plymouth State University, Plymouth, NH; and J. Cordeira and E. G. Hoffman

Recent literature has shown that recurving tropical cyclones undergoing extratropical transition (ET) induce a response in the downstream midlatitude flow. Additional research has explored the difference in the response of the downstream flow to ET events and extratropical cyclones events. This study expands upon the existing research by exploring the downstream response to explosive cyclone intensification over the North Pacific. Using a sample of 292 cases of explosive cyclone intensification within the domain (30N - 70N, 140E - 220E) during a nine-year period from 2006-2014, composite analyses of the downstream midlatitude flow were performed. Events and composites are stratified by criteria based on both deepening rate and minimum pressure, location within the domain (west vs east), and season. Time-lagged composite analyses of standardized meridional wind and geopotential height anomalies revealed amplitude differences in the downstream response based on cyclone deepening rate and minimum pressure for each respective location. Cyclones that deepen faster to a lower minimum pressure are associated with larger meridional wind anomalies. Differences in the downstream response to cyclones over the western Pacific and eastern Pacific were observed. Downstream Rossby wave propagation for explosively deepening cyclones in the western Pacific was generally more progressive, and acted to weaken a climatological ridge over the eastern Pacific, whereas explosively deepening cyclones in the eastern Pacific amplified the climatological ridge with little downstream propagation. The signal of a coherent, statistically significant composite downstream response diminished 72 hours following the cyclone's explosive intensification for both locations and all strengths. Weakening of the meridional gradient of the downstream upper-tropospheric potential vorticity waveguide observed in the composite analysis likely inhibited of the downstream response after 72 hours. Composite analysis of the dynamic evolution of the downstream response, initiated by the negative upper-tropospheric potential vorticity advection by the irrotational wind, suggested weak diabatic contributions to explosive intensification, as compared to studies of ET. This overall weaker diabatic contribution to amplification of the large-scale flow likely resulted in a shorter-lived downstream response.
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