On Making Magnetic-flux-rope Ω Loops for Solar Bipolar Magnetic Regions of All Sizes by Convection Cells

Abstract

We propose that the flux-rope Ω loop that emerges to become any bipolar magnetic region (BMR) is made by a convection cell of the Ω-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 Ω 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" Ω loops that populate the upper convection zone with horizontal field, from which smaller convection cells make BMR Ω 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 for the sunspot cycle's dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR Ω 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.