Using Local Wave Activity to Quantify the Impacts of Tropical Cyclones undergoing Extratropical Transition on the Jet Stream Waviness

Tropical cyclones (TC) undergoing extratropical transition (ET) are known to amplify the jet stream, acting as a wave source for Rossby waves. An amplifying Rossby wave packet during ET can cause extreme weather thousands of miles downstream of the TC (Keller et al. 2019). The manifestation of the downstream high impact weather includes among many; blocking anticyclones (Riboldi et al. 2019), atmospheric conditions conducive to strong cyclogenesis (Hoskins and Berrisford 1988), and heavy precipitation (Martius et al. 2008). The jet is mainly amplified by the circulation of the TC itself, latent heating released during the transition, and advection of upstream waviness. It is important to quantify the contributions from each term, because TCs undergoing ET are expected to become more frequent (Liu et al. 2017), carrying increased moisture and associated latent heat release (Jung and Lackmann 2021).

To quantify the impacts of the TC on the jet, previous studies have used either a Potential Vorticity framework or a Kinetic Energy framework. Such frameworks have proved useful in confirming that TCs amplify the jet. However, the budget needs to be applied to specific areas, making the interpretation more complex. Our modified Local Wave Activity (LWA) budget (Nakamura and Huang 2018) quantifies the waviness of the jet in a PV framework. All the relevant physical process are separate terms in the budget, making it easy to understand which term is driving the changes in jet waviness. Moreover, the LWA budget allows to calculate a jet carrying capacity of maximum waviness, meaning a maximum waviness before the jet breaks. Rossby wave breaking is relevant because the downstream impacts of ET terminate.

We track all TCs undergoing ET from 2000 to present in three reanalyses and apply the LWA budget. We analyze the contributions from latent heating using the precipitation product of IMERG (Huffman et al. 2019) and the contributions from radiation with CERES (Rutan et al. 2015). By allowing the LWA budget to run forward in time, we find that if we remove latent heating from the budget, the downstream ridge does not form in several cases. Meanwhile, if we increase latent heating, the downstream waviness increases non-linearly. In certain events, a doubling of latent heating is associated with a quintupling of the downstream waviness. We are currently building a climatology of ET events in each basin, analyzing how the separate terms contribute to downstream amplification, and how each basin differs in jet capacity.