The magnetic helicities of two emerging flux regions

The behavior of magnetic fields and helicities have been studied in two fast emerging flux regions NOAA 10488 and NOAA 10720 which eventually form δ spots. It is found that the helicity inferred from the horizontal motion of both active regions (ARs) amount to -2.5 × 1043 Mx2 in a few days. And the ratio of the coronal helicity accumulation to the square of the mean magnetic flux both reach -0.03. However, there are four X-class flares occurred in AR 10720 within about 200 hours while none in AR 10488 within about 150 hours. Our results support that both high helicity injection and strong magnetic flux are needed in major flares.