The observed extratropical flow response to recurving western North Pacific tropical cyclones
To study the characteristic downstream extratropical response to recurving WNP TCs, a compositing analysis is performed using the 2.5° NCEP–NCAR reanalysis for 100 selected recurving WNP TC episodes between 1979 and 2009. The composite analyses are used to assess the dependence of the extratropical flow response to recurving WNP TCs on a variety of factors, including time of year, latitude of TC recurvature, and the strength of the interaction between the TC and the North Pacific jet stream. Further, both composite analyses and case studies are employed to investigate how the aforementioned factors influence the evolution of model forecast error downstream of recurving TCs. Results reveal that recurving WNP TCs are favored to initiate or amplify Rossby wave trains in fall and spring when the Pacific jet stream is relatively strong and shifted equatorward relative to its overall climatological position. Preliminary findings also suggest that the strength of the initial interaction between the recurving TC and the North Pacific jet stream (as measured, e.g., by the magnitude of negative potential vorticity advection associated with the divergent TC outflow) is positively correlated with the amplitude of the resulting Rossby wave response over North America.