Abstract 123

Abstract ID: 123

Predictability of Long-lived of Rossby Wave Packets during Southern Hemisphere Summer

Lead Author: Iago Perez Fernández
Universidad de la República, Uruguay

Keywords: Rossby Wave Packets, S2S, Predictability, MJO

Abstract: Rossby wave packets, or RWPs, are atmospheric perturbations considered as precursors of extreme weather events such as extreme rainfall, heatwaves and extratropical cyclone development. Under certain conditions, these packets can last from several days to 2-3 weeks in the atmosphere before disappearing. Due to their link to extreme weather events, sub-seasonal forecast models should be able to correctly predict their development in order to enhance extreme weather events detection from 10 to 30 days in advance. The goal of this study is to assess the skill of the IAP-CAS and NCEP sub-seasonal models at forecasting the development of long-lived RWPs, (RWPs that last more than 8 days or LLRWPs) during southern hemisphere summer. Results show that LLRWPs forecasted by both models rapidly loose energy after the 6th lead day of simulation, limiting LLRWPs prediction to the synoptic time scale. In addition, we observe higher skill at forecasting LLRWPs when the wave packets start their propagation in the eastern Pacific. Additionally, high skill forecasts are obtained when a strong cyclonic circulation is predicted in the western Pacific basin, which favors RWPs propagation into the Pacific basin. On the other hand, low skill simulations display a blocking situation to the south of Australia. Lastly, an inactive MJO seems to favor the development of high skill forecasts in both models, whereas low skill forecasts are observed during phases 3 to 5 of the MJO in the NCEP model, and only in phase 3 for IAP-CAS model.

Marcelo Barreiro (Universidad de la República)