Solar Flare Forecasts Based on Subsurface Helicity

One possible mechanism for solar flares is the twisting of magnetic field lines that eventually results in explosive reconnection. The source of the twisting is likely to be below the photosphere, where the plasma beta is greater than one and the kinetic energy of the plasma flow is greater than the magnetic energy. With the ring-diagram method of local helioseismology, we can determine the flows down to a depth of 16 Mm, and measure the strength of the twisting motions in terms of vorticity and helicity. We have found that the level of solar flare activity in an active region is correlated with the level of helicity below the surface and the surface magnetic field strength (Komm and Hill JGR 114). We have now analyzed the time evolution of the subsurface helicity and have found that there is a significant increase in the helicity one to two days before the occurrence of X- and M-class flares. A preliminary analysis shows that the helicity provides a flare prediction with a success rate of about 0.9, and a Heidke skill score of about 0.6.