Sigmoids - not so Freudian

This dramatic "sigmoid", an "S"-shaped bundle of plasma, appeared on the surface of the sun in 2007 and later erupted. Now a new model has reproduced the event (Image: NASA/STFC/ISAS/JAXA)

The formation and eruption of large "S"-shaped structures on the surface of the sun have been modelled in the best detail yet. Further refinements of the model might help sun-watchers predict severe space storms days in advance.

'Sigmoids' are S-shaped structures that appear intermittently on the sun's surface. Many produce eruptions of hot ionised gas, or plasma, such as coronal mass ejections and flares. If the eruptions are powerful enough, they can zap satellites, endanger astronauts, and knock out power grids (see Space storm alert: 90 seconds from catastrophe).

Until now, models of the structures have not been able to reproduce the full lifetime of a sigmoid from its beginnings within the sun to its eventual eruption sometimes days later. But now researchers say they have come up with a simple model that could do just that.

"For the first time, we have built a three-dimensional model that shows in a very nice and self-consistent way the evolution and final eruption of a sigmoid," says Vasilis Archontis of St Andrews University in Scotland.