Presentation #313.18 in the session “Solar Physics Division (SPD): Instrumentation and Active Regions”.
This poster gives an overview of Moore, R. L., Tiwari, S. K., Panesar, N. K., & Sterling, A. C. 2020, ApJ Letters, 902:L35. We propose that the magnetic-flux-rope omega loop that emerges to become any bipolar magnetic region (BMR) is made by a convection cell of the omega-loop’s size from initially horizontal magnetic field ingested through the cell’s bottom. This idea is based on (1) observed characteristics of BMRs of all spans (~1000 to ~200,000 km), (2) a well-known simulation of the production of a BMR by a supergranule-sized convection cell from horizontal field placed at cell bottom, and (3) a well-known convection-zone simulation. From the observations and simulations, we (1) infer that the strength of the field ingested by the biggest convection cells (giant cells) to make the biggest BMR omega loops is ~103 G, (2) plausibly explain why the span and flux of the biggest observed BMRs are ~200,000 km and ~1022 Mx, (3) suggest how giant cells might also make “failed BMR” omega loops that populate the upper convection zone with horizontal field, from which smaller convection cells make BMR omega loops of their size, (4) suggest why sunspots observed in a sunspot cycle’s declining phase tend to violate the hemispheric helicity rule, and (5) support a previously proposed amended Babcock scenario (Moore, R. L., Cirtain, J. W., & Sterling, A. C. 2016, arXiv:1606.05371) for the sunspot cycle’s dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR omega loop avoids having ~105 G field in the initial flux rope at the bottom of the convection zone, it is an appealing alternative to the present magnetic-buoyancy-based standard scenario and warrants testing by high-enough-resolution giant-cell magnetoconvection simulations.