Climate

Njord: A Probabilistic Graph Neural Network for Ensemble Ocean Forecasting

Daniel Holmberg, Joel Oskarsson, Erik Larsson, Fredrik Lindsten, Teemu Roos

Featured May 22, 2026

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Simply

Njord uses graph-based AI to predict ocean conditions, creating multiple possible future scenarios to help scientists understand uncertainty and better prepare for extreme weather events at sea.

In depth

The paper introduces Njord, a probabilistic ocean forecasting model that utilizes a hierarchical Graph Neural Network (GNN) architecture. By employing a novel K-means clustering mesh that adapts to irregular ocean geometries, the model efficiently generates ensemble forecasts, providing calibrated uncertainty estimates that deterministic models lack.

Key Takeaways

1
Njord is the first generative ensemble model for global ocean physics, providing calibrated uncertainty estimates alongside accurate forecasts.
2
The authors introduce a clustering-based graph layout that conforms to irregular sea surface geometry, improving spatial representation over traditional icosahedral meshes.
3
The model incorporates sea ice physical constraints using a density channel and soft clamping, ensuring physically realistic predictions during autoregressive rollouts.

Conceptual Flow

HIGH LEVEL

Methodology

The model uses a smart map of the ocean to learn how water moves and changes over time.

Ocean Data

Atmospheric Forcing

Process via Graph Neural Network

Probabilistic Ocean Forecast

Results

The new model provides more accurate predictions and tells us how confident it is in its forecast.

Deterministic Baseline

Njord Ensemble

Compare Accuracy and Uncertainty

Lower Error and Confidence Intervals