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Space Weather Alert - 23rd August 2013

What Has Happened?


SOHO/LASCO C2 image of the CME on 20th August. Image NASA

A combination of events on the Sun is expected to lead to an increase in geomagnetic activity over the weekend.

Two Coronal Mass Ejections (CME) left the Sun on Tuesday and Wednesday, both caused by erupting solar filaments. Alone, neither of these CMEs might be expected to greatly increase geomagnetic activity. However, their anticipated arrivals close together on Friday and Saturday evenings, whilst the Earth is simultaneously buffeted by high speed solar wind from a coronal hole, could lead to a geomagnetic storm.

Assuming clear dark skies, there is an increased chance of seeing the aurora in the hours following the arrival of the CMEs, particularly at high latitudes in the North of Scotland. Depending on the strength of the storm, there is some chance that aurorae might be visible further south.



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

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.

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

Filament Eruption
An eruption of solar plasma (i.e. ions and electrons) associated with the upward movement of solar magnetic field lines into the corona. Filaments are usually dark against the bright solar disk but can appear bright (as 'erupting prominences') on the limbs of the Sun against the darkness of space. Filaments are often associated with CMEs.
Energy released by the explosive reorganisation of magnetic fields within the Sun's atmosphere.

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.

A region of intense magnetic field in the Sun's visible outer atmosphere often associated with flares and CMEs.