Predictability of Rossby wave packets: Climatology and dynamical characteristics
Final Report Abstract
Undulations of the midlatitude jet stream play a crucial role in organizing the weather in the extratropics. These undulations organize in zonally confined structures, so-called Rossby wave packets (RWPs). We currently lack understanding of the predictability of these largescale precursors to midlatitude weather events. This project worked towards closing this gap. An improved understanding is hoped to contribute to increasing the lead time, with which skillful forecasts of disruptive weather events can be delivered in the future. We first developed a metrics tailored to measure forecast skill of RWPs in a large data set of forecasts started from historical data (“re-forecasts”). Using this metric, we analyzed general characteristics of RWP predictability in terms of average characteristics of particularly good and bad forecasts. We find a strong dependence of predictability on the stage of the life cycle and on season, with summer being less predictable than winter. Lower predictability is further found for RWPs occurring over the ocean than for those over Eurasia. First investigations of the dynamical processes that are associated with high and low predictability have not directly led to additional insight but provide an improved starting point for future research.
