State-resolved multimodal contributions to stratospheric polar vortex predictability

The dynamical basis of stratospheric polar vortex predictability remains unclear, particularly the relative roles of persistence, structural variability, and cross-level coupling. Here we provide a state-resolved and quantitative framework using eigen microstate theory applied to ERA5 geopotential height fields, enabling attribution of predictability to dynamically coherent circulation states via a mesoscopic Granger-causality approach. We show that short-term predictability is dominated by persistence of the leading stratospheric state, whereas extended predictability arises from higher-order stratospheric structures and tropospheric variability. These contributions exhibit strong lead-time dependence and become more distributed during sudden stratospheric warming events. Our results unify SPV predictability within a multimodal, state-resolved framework and provide a physically interpretable pathway for improving subseasonal-to-seasonal forecasts.