How does a solar flare cause a magnetic crochet?

[Dotini]

When I linked to this morning's spaceweather.com, I read the following, which appears to be a notable disturbance of Earth's magnetic field simultaneous to a strong flare on the sun. Normally it's said to take hours or days for the effects of a flare to be felt on Earth, but in this case there was no such delay. How does it work so quickly?

SOLAR FLARE CAUSES RARE 'MAGNETIC CROCHET': On March 29th at 17:52 UT, the magnetic canopy of sunspot AR1890 erupted, producing a brief but intense X1-class solar flare. NASA's Solar Dynamics Observatory recorded the extreme ultraviolet flash:
http://sdowww.lmsal.com/sdomedia/h2...1730-20140329T1809_AIA_131-193-171_N10W32.mov

Radiation from the flare caused a surge in the ionization of Earth's upper atmosphere--and this led to a rare magnetic crochet, measuring 17 nT at the magnetometer in Boulder, Colorado.

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. They tend to occur during fast impulsive flares like this one.
http://www.ips.gov.au/Educational/3/1/1

 

[willem2]

The crochet is caused by ionization in the atmosphere by x-rays emitted by the solar flare. These move at the speed of light. See the last link you posted.