The modification of inertial stability on the poleward edge of the ITCZ in association with a breaking Rossby wave over the subtropical North Pacific

Global analyses from the ECMWF are used to diagnose changes in the inertial stability on the north side of the intertropical convergence zone (ITCZ) that occurred in association with a Rossby wave breaking event over the subtropical North Pacific in early June 1992. An equatorward-migrating Rossby wave packet near the 350-K surface over the North Pacific, whose evolution is traced backward in time to a cluster of potential vorticity (PV) anomalies over central Asia, and whose equatorward flux of wave activity over the western Pacific basin is linked to baroclinic growth near the east coast of Asia, reversed PV gradients across the tropopause at 25°N as it entered relatively weak subtropical wind fields. The equatorward penetration of relatively high PV, in association with the wave packet’s apparent interaction with a critical layer, initiated the northeastward advection of PV from the deep tropics around the poleward edge of the ITCZ. The local reduction of inertial stability triggered by this process was accompanied by an enhancement of outflow atop the ITCZ convection and the subsequent formation of a "tropical plume".