Deciphering Pre-solar-storm Features Of September-2017 Storm From Global And Local Dynamics

We investigate whether global toroid patterns and local magnetic field topology of solar active region AR12673 together can hindcast occurrence of the biggest X-flare of solar cycle(SC) 24. Magnetic toroid patterns (narrow latitude-belts warped in longitude, in which active regions are tightly stringed) derived from surface distribution of active regions, prior/during AR12673 emergence, reveal that the portions of South-toroid containing AR12673 was not tipped-away from its North-toroid counterpart at that longitude, unlike the 2003 Halloween storms scenario. During minimum-phase there were too few emergences to determine multi-mode warped toroid patterns in longitude. A new emergence within AR12673 produced a complex/non-potential structure, which led to rapid build-up of helicity and winding that triggered the biggest X-flare of SC-24. Such a minimum-phase storm can be forecast with only hours' lead-time. However, global patterns and local dynamics for a peak-phase storm, such as that from AR11263, behaved like 2003 Halloween storms, producing the second biggest X-flare of SC-24. AR11263 was present at the longitude where the North and South toroids tipped-away from each other. While global toroid patterns indicate that pre-storm features can be forecast with a lead-time of a few months,its application on observational data can be complicated by complex interactions with turbulent flows. Complex/non-potential field structure development hours before the storm are necessary for short term prediction. We infer that minimum-phase storms cannot be forecast accurately more than a few hours ahead, while flare-prone active regions in peak-phase may be anticipated much earlier, possibly months ahead from global toroid patterns.