A comparison of the influence of recurving and nonrecurving tropical cyclones on the intensification of the North Pacific jet stream

Autumnal changes in the structure of the large-scale flow over the North Pacific are often influenced by the life cycles of western North Pacific (WNP) tropical cyclones (TCs). These changes in the structure of the large-scale flow can be manifested as variability in the strength of the North Pacific jet stream (NPJ), amplification and dispersion of Rossby wave trains, and the development of persistent upper-tropospheric geopotential height anomalies over the eastern North Pacific and western North America. The purpose of this presentation is to investigate and compare the influence of recurving and nonrecurving WNP TCs on the intensification of the NPJ.

The intensification of the NPJ associated with recurving or nonrecurving WNP TCs is investigated within a potential vorticity (PV) framework. The interaction between a TC and the NPJ is diagnosed using the upper-tropospheric PV advection by the irrotational component of the horizontal wind. Composite analyses suggest that recurving TC–NPJ interactions occur in conjunction with negative upper-tropospheric PV advection by the irrotational wind, where the irrotational wind corresponds to the diabatic outflow of the TC. Alternatively, nonrecurving TC–NPJ interactions occur in conjunction with negative upper-tropospheric PV advection by the irrotational wind, where the irrotational wind is attributed to latent heating occurring within an elongated region of stratiform precipitation located between the distant TC and the NPJ. The former is considered a direct TC–NPJ interaction, whereas the latter is considered an indirect TC–NPJ interaction. For both direct and indirect TC–NPJ interactions, the negative upper-tropospheric PV advection by the irrotational wind leads to increases in the magnitude of the poleward-directed PV gradient in the entrance region of the NPJ and thus to the intensification of the NPJ.