Downstream Effects of Northern Hemisphere Extratropical Transition in a Future Climate

When a Tropical Cyclone (TC) encounters a more baroclinic environment, the structure of the TC can change to an asymmetric cold core cyclone in a process known as Extratropical Transition (ET). Transport of warm air from the tropics and latent heat release from precipitation associated with ET can modify the jet and downstream environment through the propagation of Rossby wave packets, which have been linked to atmospheric blocking and extreme weather. For ET to occur, a TC must survive far enough poleward to interact with the jet. Interaction with a faster and higher latitude jet provides a more amplified downstream effect (Finnochio and Doyle 2019). In a future climate, the jet has been projected to weaken and shift poleward. A poleward extension of TC tracks due to warmer sea surface temperatures has also been projected. As such, a consensus on how ET is expected to change in a future environment has not been reached. However, the change in downstream effects of ET is the least studied and understood. Studies point to a possible stronger downstream effect through an increase in precipitation and broadening and strengthening of the wind field associated with ET(Jung and Lackmann 2019,21,23; Michaelis and Lackmann 2021). This study makes use of high-resolution CMIP6 climate datasets to assess projected future changes in ET and its associated downstream impacts in the Northern Hemisphere. Using TempestExtremes, a cyclone tracking framework, first verified on ERA5 data, ET can be tracked in a future climate and downstream impacts assessed.