Interaction between emerging flux and large scale loop systems observed with Hinode XRT

Abstract

Hinode XRT reveals ubiquitous large-scale connections between solar active regions and relatively distant reaches of the corona, both quiet and active. How do these large scale connections form? Data from the first several months of the mission suggest that large-scale connections tend to exist prior to active region emergence, rather than being due to long-term diffusion of a single active region. We describe the life-history of two large-scale loop systems. We find that they cyclically decay and reform due to repeated flux emergence in approximately the same location through successive solar rotations. We present a detailed look at the effect of flux emergence on the existing loop systems and the nature of the magnetic reconnection that takes place.

Hinode takes full-disk synoptics every six hours in order to view large-scale phenomena.

Long loops are ubiquitous in both quiet and active regions of Hinode observations. Here, an active region takes up > 30% of the visible disk.

Due to extremely broad temperature coverage and high spatial resolution, Hinode XRT is an exceptional instrument for studying large-scale solar magnetic connections and their interaction with smaller elements.

The first and second panels at left show a pair of active regions with strong initial interconnection. Over the next five solar rotations, the region interconnectivity remains long after the regions themselves have dispersed. The large-scale structures are partly re-created due to repeated flux emergence in the same general location.

Long-lasting ConnectionsMDI Magnetogram

After 3 rotations After 4 rotations After 5 rotations

Initial Active Regions After 2 rotations

Active Region Interactions

A loop system that persists through one rotation (as well as substantial flaring from the active region in the west). New flux emerges into the middle of the resulting large loop scale structure after two solar rotations, which alters the remaining large-scale structure, though it remains relatively intact after 3 rotations.

The loop system remains visible even in XRT's thin Be filter in panel (b), indicating a relatively high temperature component.

After 2 rotations After 3 rotations

Initial Active Regions After 1 rotation

Loraine L. Lundquist and the US & Japan XRT TeamsHarvard/Smithsonian Center for Astrophysics

Flux emerging into pre-existing loop connections, Part 1

Here we show a time series of emergence into the larger loop structure shown in the middle page on the left. The initial flux emergence interacts in a complex manner with the overlying arcade, but by the time the emergence matures, the overlying loops conform roughly to the same loop-structure of the newly formed active region. Thus the large spatial extent of the region is due not to loops extended from the emergence process, but from interaction with pre-existing connections.

A second time-series of emergence into an arcade. In this case, the flux emerges just into the footpoint of the arcade. The result is reconnection that results in shrinking the loops. Unlike the previous example this case results in an overall shortening of overlying loops rather than a broadening of the emerging region’s spatial extent.

Flux emerging into pre-existing loop connections, Part 2

Time

MDI magnetogram contours (green = positive, blue = negative) are overlayed on the XRT data from the previous page. White dotted lines show the original arcade and the reconnection that occurs as a result of flux emergence. The same process occurs on two scales: first with the larger flux emergence of the whole region, and second with a tiny bipole of flux that emerges to the north of the primary active region.

Reconnection Topology

Tim

e

Summary

• Large scale loop systems last long after their counterpart active regions and are often visible even at relatively high temperatures.

• Repeated emergence may fuel these persistent structures.

• A likely cause for the large spatial extent of many active regions is reconnection with these pre-existing structures, rather than inherent size structure.