X1 Flare Causes Rare ‘Magnetic Crochet’ and Faint CME

The X1 flare thrown off by sunspot AR2017 has caused a surge in the ionization of earth’s atmosphere: A magnetic crochet.

A magnetic crochet is a ripple in Earth’s magnetic field caused by electrical currents flowing in air 60 km to 100 km above our heads. Unlike geomagnetic disturbances that arrive with CMEs days after a flare, a magnetic crochet occurs while the flare is in progress.

It arises from the increased ionisation in the D and E layers of the ionosphere caused by the massive increase in X-ray radiation generated by the solar flare. This ionisation changes the properties (especially the conductivity) of these ionospheric layers allowing electric currents to flow more easily. It is the magnetic effect of these currents which produce the jump in the earth’s magnetic field. As the flare declines, the ionospheric layers quickly return to their previous state, the electric currents in the layers return to normal, and the change in the magnetic field ends.

Magnetic crochets are quite rare because they are only observed during large flares which rise to a peak very quickly. Also, they are mostly observed in locations close to the sub-solar point (i.e. the point on earth when the sun is overhead). (source)

The CME will deliver a glancing blow to our magnetic field on April 1st or 2nd. The chances of further flares remain unchanged at 20% for X-class and 55% for M-class over the next 24 hours. The sunspot number is 132.