Stratospheric initial conditions provide seasonal predictability of the North Atlantic and Arctic Oscillations

• Published in: Environmental Research Letters
• Main Authors: Yu Nie, Adam A Scaife, Hong-Li Ren, Ruth E Comer, Martin B Andrews, Philip Davis, Nicola Martin
• Format: Article in Journal/Newspaper
• Language: English
• Published: IOP Publishing 2019
• Subjects: seasonal prediction; stratosphere; NAO/AO; GloSea5; Environmental technology. Sanitary engineering; TD1-1066; Environmental sciences; GE1-350; Science; Q; Physics; QC1-999; Arctic; North Atlantic; North Atlantic oscillation
• Online Access: https://doi.org/10.1088/1748-9326/ab0385; https://doaj.org/article/7f22d3d719d943cfb83638fae9f3163c

The North Atlantic Oscillation (NAO), the regional manifestation of the Arctic Oscillation (AO), dominates winter climate variability in Europe and North America. Skilful seasonal forecasting of the winter NAO/AO has been demonstrated recently by dynamical prediction systems. However, the role of initial conditions in this predictability remains unknown. Using a latest generation seasonal forecasting system and reanalysis data, we show that the initial upper stratospheric zonal wind anomaly contributes to winter NAO/AO predictability through downward propagation of initial conditions. An initial polar westerly/easterly anomaly in the upper stratosphere propagates down to the troposphere in early winter, favoring a poleward/equatorward shift of the tropospheric mid-latitude jet. This tropospheric anomaly persists well into the late winter and induces the positive/negative phase of NAO/AO in the troposphere. Our results imply that good representation of stratospheric initial condition and stratosphere-troposphere coupling in models is important for winter climate prediction.