Skillful Subseasonal-to-Seasonal Forecasting of Extreme Events with a Multi-Sphere Coupled Probabilistic Model

TL;DR

This paper introduces TianXing-S2S, a novel multi-sphere probabilistic model that enhances subseasonal-to-seasonal forecasts of extreme weather events by integrating complex interactions and uncertainty modeling.

Contribution

The paper presents TianXing-S2S, a new multi-sphere coupled probabilistic model that improves S2S forecasting accuracy and stability for extreme events using a diffusion process and optimal transport coupling.

Findings

Outperforms ECMWF and FuXi-S2S in 45-day ensemble forecasts.

Achieves skillful prediction of heat waves and heavy precipitation.

Demonstrates stable forecasts up to 180 days.

Abstract

Accurate subseasonal-to-seasonal (S2S) prediction of extreme events is critical for resource planning and disaster mitigation under accelerating climate change. However, such predictions remain challenging due to complex multi-sphere interactions and intrinsic atmospheric uncertainty. Here we present TianXing-S2S, a multi-sphere coupled probabilistic model for global S2S daily ensemble forecast. TianXing-S2S first encodes diverse multi-sphere predictors into a compact latent space, then employs a diffusion model to generate daily ensemble forecasts. A novel coupling module based on optimal transport (OT) is incorporated in the denoiser to optimize the interactions between atmospheric and multi-sphere boundary conditions. Across key atmospheric variables, TianXing-S2S outperforms both the European Centre for Medium-Range Weather Forecasts (ECMWF) S2S system and FuXi-S2S in 45-day daily-mean ensemble forecasts at 1.5 resolution. Our model achieves skillful subseasonal prediction of extreme events including heat waves and anomalous precipitation, identifying soil moisture as a critical precursor signal. Furthermore, we demonstrate that TianXing-S2S can generate stable rollout forecasts up to 180 days, establishing a robust framework for S2S research in a warming world.