Jones, S.C.

Riemer, Michael

The interaction of a tropical cyclone undergoing extratropical transition (ET) and the midlatitude synoptic-scale flow is investigated using full physics numerical experiments with idealised initial conditions. The emphasis of this work is on the impact in the midlatitudes downstream of ET. In the benchmark experiment the midlatitude flow is represented by a balanced straight jet stream. The tropical cyclone is found to initiate downstream baroclinic development in the midlatitudes. The evolution of the upper-level flow is characterised by the excitation and subsequent dispersion of a Rossby wave train along the jet. Piecewise inversion of potential vorticity verifes that characteristic features of the interaction are sensitive to the structure of the ET system. A further set of experiments consider the interaction of the ET system and distinct scenarios of baroclinic wave development. Baroclinic waves constitute a more realistic albeit more complex representation of the midlatitude flow. The midlatitude evolution downstream of ET shows high sensitivity with respect to the initial position and intensity of the tropical cyclone. Several mechanisms that are important for the impact of ET on the downstream region are identifed. The results of this work demonstrate the importance of a realistic representation of the ET system in numerical weather prediction models for the predictability of the midlatitude flow pattern.