State-resolved multimodal contributions to stratospheric polar vortex predictability

TL;DR

This paper introduces a state-resolved, quantitative framework using eigen microstate theory and Granger-causality to analyze stratospheric polar vortex predictability, revealing the roles of persistence, structural variability, and cross-level coupling.

Contribution

It provides a novel, physically interpretable multimodal framework for understanding and improving stratospheric polar vortex predictability.

Findings

Short-term predictability is dominated by persistence of the leading stratospheric state.

Extended predictability involves higher-order structures and tropospheric variability.

Predictability contributions vary with lead time and intensify during sudden stratospheric warming events.

Abstract

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.