The impact of tropical cyclones on midlatitude Rossby wave packets: a climatological perspective

Tropical cyclones (TCs) that undergo extratropical transition (ET) have the ability to modify the synoptic-scale midlatitude flow. Recent case studies and numerical experiments identified physical key-processes and conditions that favor a downstream development after ET. While previous studies focused predominantly on specific cases, this study investigates the role of TCs in tropical-extratropical interactions from a climatological point of view.

We identified Rossby Wave packets of synoptic-scale wavelength downstream of recurving TCs in the south Indian Ocean and western North Pacific for the period 1980-2010. This identification is based on a Hilbert-Transform of the upper-level meridional wind and a zonal wavenumber filter. In both basins, composite maps show a statistically significant increase of Rossby wave packet amplitude and occurrence frequency downstream of the TCs compared to the climatological mean.

For the western North Pacific TCs, a statistically robust signal of an increase in amplitude and occurrence frequency extends from the western North Pacific to North America. We identified for these cases synoptic conditions that favor a downstream development. The results indicate that a precursor Rossby wave that emerges from the Asian continent provides favorable conditions for a downstream development. Composite maps of eddy-kinetic energy (EKE) budgets suggests that the strength of EKE production in the region between the TC's outflow and an approaching midlatitude trough is crucial for the further amplification of the midlatitude flow.