On Making Magnetic-Flux-Rope $\Omega$ Loops for Solar Bipolar Magnetic Regions of All Sizes by Convection Cells

Abstract

We propose that the 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 ($\sim$ 1000 km to $\sim$ 200,000 km), (2) a well-known simulation of the production of a BMR by a supergranule-size 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 $\sim$ 10${}^3$ G, (2) plausibly explain why the span and flux of the biggest observed BMRs are $\sim$ 200,000 km and $\sim$ 10${}^{22}$ 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 for the sunspot cycle's dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR $\Omega$ loop avoids having $\sim$ 10${}^5$ 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.

15 pages, 3 figures, accepted for publication in ApJ Letters

References in corpus (8)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Chromospheric Anemone Jets as Evidence of Ubiquitous Reconnection
• Structure and Evolution of Giant Cells in Global Models of Solar Convection
• On the Formation of Active Regions
• Transient horizontal magnetic fields in solar plage regions
• Coronal-Jet-Producing Minifilament Eruptions as a Possible Source of Parker Solar Probe (PSP) Switchbacks
• Fine-scale explosive energy release at sites of prospective magnetic flux cancellation in the core of the solar active region observed by Hi-C 2.1, IRIS and SDO
• Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar Magnetic Network Lane

Cited by in corpus (2)

• Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation, and Solar Magnetic Explosions
• What Causes Faint Solar Coronal Jets from Emerging Flux Regions in Coronal Holes?