How the Jet Stream Determines Predictability Downstream of Recurving Tropical Cyclones

Recurving tropical cyclones (TCs) can amplify the midlatitude flow pattern and trigger extreme weather events far downstream. The flow amplification following TC recurvature originates from Rossby wave-like disturbances that propagate along midlatitude jet streams and can be associated with reduced downstream predictability. Many previous studies attribute the reduced predictability to uncertainties in the diabatic perturbations to the jet stream associated with the recurving TC. Much less work has focused on the role of the jet stream, which acts as the conduit for Rossby wave packets generated by the recurving TC, in modulating the downstream response and its predictability. This talk describes a set of idealized simulations with the Coupled Ocean Atmosphere Mesoscale Prediction System (COAMPS) model in which a TC recurves into a series of different zonal jet streams. The jet streams differ in their baroclinicity and their ability to serve as a Rossby waveguide. Based on these simulations, we construct a surrogate of the nonlinear COAMPS model relating various measures of downstream flow amplification to three parameters controlling the latitude, width, and maximum velocity of the zonal jet. Owing to the low computational cost of running the surrogate model, we can construct response surfaces that reveal parameter ranges for which there is elevated sensitivity to the different aspects of the jet stream. The possibility of using such a surrogate model to predict flow amplification and the possibility of extreme weather downstream of recurving TCs based on observable characteristics of midlatitude jet streams is discussed.