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Geomagnetic storm update - 15th December 2025

What Has Happened?

Kp index (a measure of geomagnetic activity) showing the storm intervals up to in early December 2025. Source: BGS (c) UKRI 2025.

 

The coronal mass ejection (CME) associated with an M-class solar flare from the 6th of December arrived much later than expected, in the evening hours on the 10th of December, and caused less severe impact than originally predicted.

A combination of several further CMEs that left the Sun on the 8th and 9th of December seems to have given the Earth a glancing blow on the 11th of December, resulting in additional periods of elevated geomagnetic activity. A coronal hole high-speed stream that followed kept the conditions at ACTIVE and STORM levels throughout the 12th and 13th of December.

 

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Glossary

BGS
The British Geological Survey is a geoscience research centre that is part of UK Research and Innovation (UKRI) and affiliated to the Natural Environment Research Council (NERC).

CME or Coronal Mass Ejection
The eruption of a portion of the outer atmosphere of the Sun into space, caused by rapid changes in its magnetic field. Often occurs along with a solar flare.

Solar Flare
Energy released by the explosive reorganisation of magnetic fields within the Sun's atmosphere.

Coronal Hole
A region in the Sun’s outer atmosphere (corona) where hot material can flow unrestrained by its magnetic fields out into space.

High Speed Stream
A fast moving stream of solar wind, responsible for magnetic storms.