Flux Retraction and Recycling

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Session 86 -- Solar Active Regions
Display presentation, Wednesday, 11, 1995, 9:20am - 6:30pm

[86.08] Flux Retraction and Recycling

Sydney D'Silva (NOAO)

Observations show that magnetically active regions on the sun cluster together as activity complexes. They are maintained at an almost constant flux level by recurring flux emergences accompanied by local disappearance of flux, and the in situ flux disappearance shows evidence of flux retraction. Parker (1987) suggested thermal shadows to act as dynamical barriers, suppressing magnetic buoyancy in the lower convection zone (CZ), and intermittently letting flux emerge through a thermal relaxation oscillation, which could explain the recurrent flux injection into these activity complexes. We suggest negative buoyancy to account for flux retraction. Flux tubes can cool and become heavier than their surroundings. The negatively buoyant flux tube can fall through the CZ, hit the top of the stable radiative zone where it has to encounter a rapidly rising Brunt-V\"{a}is\"{a}l\"{a} frequency $N$ and bounce back to the surface in an oscillatory fashion. The oscillation can be damped by dissipative processes like viscosity, the tube can be fragmented by instabilities, or the rising flux tube can grab flux from the overshoot region when it re-emerges; overall, the negative buoyancy induced oscillation could retract flux, recycle it, and explain the recurrent flux injection, and in situ flux disappearance observed in activity complexes.

Wednesday program listing