A Global Climatology of Tropical Cyclone Diabatic Rossby Wave Sources and Their Extratropical Flow Response
Abstract/Description
High-impact weather events can occur downstream from recurving western North Pacific (WNP) tropical cyclones (TCs) that undergo extratropical transition and interact strongly with the midlatitude flow. These events are the result of jet streak intensification and downstream wave amplification triggered by a prolonged period of strong negative potential vorticity (PV) advection by the divergent component of the wind in the TC outflow region, here called Rossby wave (RW) forcing. A 46-yr global climatology of all TC-related RW forcing episodes during 1979–2024 is obtained to test the hypothesis that RWforcing events can occur outside of the recurvingWNP TC context. Using global TC data from the International Best Track Archive for Climate Stewardship (IBTrACS) database, it is first demonstrated that strong RW forcing events associated with recurving TCs are mostly confined to the WNP basin. Downstream response is assessed by determining composite time series of the downstream meridional index, 250-hPa wind speed, and a proxy for midlatitude cyclones. Removing the requirement for TC recurvature resulted in a ;72% increase in cases but with no significant change in downstream response, suggesting that TC recurvature is not a prerequisite for excitation or amplification of Rossby waves. A similar but smaller downstream response occurred in other TC basins. Spatial composites for recurving TCs revealed that the downstream response reflected the direct impact of TCs migrating into the compositing domain rather than remote downstream Rossby wave amplification triggered by the RW forcing. Spatial composites for nonrecurving TCs having little eastward progression revealed an amplifying standing wave pattern downstream from the longitude of the RWforcing.
