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This cartoon nicely anticipates the 1993 observations of H. Wang, who found that an X-class flare can be accompanied by an increase of the observers' shear in the photospheric field. The theoretical work does not actually predict the observations, since the model has the same shear before and after the event, but it is clearly a step in the right direction. We now have clear evidence for photospheric field changes occurring systematically in all flares above a sensitivity-limited magnitude. These changes probably reflect the coronal restructuring well enough so that, once we have good vector field measurements (Hinode? SDO? ATST?) we can really figure things out.
Dec. 28, 2006