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 TCNPJ 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 TCNPJ 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 TCNPJ interaction, whereas the latter is considered an indirect TCNPJ interaction. For both direct and indirect TCNPJ 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.
![](images/flag.png)
![](images/blue_ribbon.png)