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Space Weather Alert - 26th September 2019

What Has Happened?

EUV image from SDO satellite showing centrally located coronal hole (black area). Image from SDO (NASA).


A high speed solar wind stream from a large, recurrent, trans-equatorial coronal hole is anticipated to arrive at the weekend (27th-28th September). On the previous rotation this coronal hole caused peaks of STORM G2 geomagnetic conditions (see NOAA space weather scales for more details about these storm levels).

Geomagnetic activity is again likely to reach a maximum of STORM G2 from Friday through to Sunday as we are closer to the autumn equinox and the coronal hole remains broadly similar in scope to the previous rotation. We cannot rule out a small chance of an isolated period of STORM G3. Some peak activity is likely to occur with the initial arrival of the high speed stream with the elevated solar wind likely to remain geoeffective for around 48 hours before starting to subside.

Assuming clear, dark skies there is an increased chance of seeing the aurora on Friday and Saturday evening into the night. Those in Scotland, northern England and Northern Ireland may have the best chance, if the weather is favourable and if geomagnetic activity levels are as anticipated.


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The British Geological Survey is one of the Natural Environment Research Council's Research Centres.

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.

The variation, minute by minute, of the strength and direction of the Earth’s magnetic field. Measured in units of nano-Tesla (for the strength of the field) or in degrees (direction of the field).

Solar Wind
The ever-present expansion of the Sun’s hot outer atmosphere into the solar system, which carries space weather within it.