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Outflows at the Edges of an Active Region in a Coronal Hole: A Signature of Active Region Expansion?  

Deborah Baker   Submitted: 2009-12-07 03:14

Outflows of plasma at the edges of active regions surrounded by quiet Sun are now a common observation with the Hinode satellite. While there is observational evidence to suggest that the outflows are originating in the magnetic field surrounding the active regions, there is no conclusive evidence that reveals how they are driven. Motivated by observations of outflows at the periphery of a mature active region embedded in a coronal hole, we have used a three-dimensional simulation to emulate the active region?s development in order to investigate the origin and driver of these outflows. We find outflows are accelerated from a site in the coronal hole magnetic field immediately surrounding the active region and are channelled along the coronal hole field as they rise through the atmosphere. The plasma is accelerated simply as a result of the active region expanding horizontally as it develops. Many of the characteristics of the outflows generated in the simulation are consistent with those of observed outflows: velocities up to 45 km s-1, properties akin to the coronal hole, proximity to the active region?s draining loops, expansion with height, and projection over monopolar photospheric magnetic concentrations. Although the horizontal expansion occurs as a consequence of the active region?s development in the simulation, expansion is also a general feature of established active regions. Hence, it is entirely possible and plausible that the expansion acceleration mechanism displayed in the simulation is occurring in active regions on the Sun and, in addition to reconnection, is driving the outflows observed at their edges.

Authors: M.J. Murray, D. Baker, L. van Driel-Gesztelyi, J. Sun
Projects: Hinode/EIS

Publication Status: Accepted by Solar Physics
Last Modified: 2009-12-07 10:35
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Signatures of Interchange Reconnection: STEREO, ACE and Hinode Observations Combined  

Deborah Baker   Submitted: 2009-09-30 07:55

Combining STEREO, ACE and Hinode observations has presented an opportunity to follow a filament eruption and coronal mass ejection (CME) on the 17th of October 2007 from an active region (AR) inside a coronal hole (CH) into the heliosphere. This particular combination of `open' and closed magnetic topologies provides an ideal scenario for interchange reconnection to take place. With Hinode and STEREO data we were able to identify the emergence time and type of structure seen in the in-situ data four days later. On the 21st, ACE observed in-situ the passage of an ICME with `open' magnetic topology. The magnetic field configuration of the source, a mature AR located inside an equatorial CH, has important implications for the solar and interplanetary signatures of the eruption. We interpret the formation of an `anemone' structure of the erupting AR and the passage in-situ of the ICME being disconnected at one leg, as manifested by uni-directional suprathermal electron flux in the ICME, to be a direct result of interchange reconnection between closed loops of the CME originating from the AR and `open' field lines of the surrounding CH.

Authors: D. Baker, A. P. Rouillard, L. van Driel-Gesztelyi, P. Demoulin, L. K. Harra, B. Lavraud, J. A. Davies, A. Opitz, J. G. Luhmann, J. A. Sauvaud, A. B. Galvin
Projects: STEREO

Publication Status: Annales Geophysicae (Accepted)
Last Modified: 2009-09-30 08:09
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Magnetic Reconnection along Quasi-Separatrix Layers as a Driver of Ubiquitous Active Region Outflows  

Deborah Baker   Submitted: 2009-09-25 07:01

Hinode's EUV Imaging Spectrometer (EIS) has discovered ubiquitous outflows of a few to 50 km s-1ec from active regions (ARs). These outflows are most prominent at the AR boundary and appear over monopolar magnetic areas. They are linked to strong non-thermal line broadening and are stronger in hotter EUV lines. The outflows persist for at least several days. Using Hinode EIS and X-Ray Telescope observations of AR 10942 coupled with magnetic modeling, we demonstrate that the outflows originate from specific locations of the magnetic topology where field lines display strong gradients of magnetic connectivity, namely quasi-separatrix layers (QSLs), or in the limit of infinitely thin QSLs, separatrices. We found the strongest AR outflows to be in the vicinity of QSL sections located over areas of strong magnetic field. We argue that magnetic reconnection at QSLs separating closed field lines of the AR and either large-scale externally connected or `open' field lines is a viable mechanism for driving AR outflows which are likely sources of the slow solar wind.

Authors: D. Baker, L. van Driel-Gesztelyi, C. H. Mandrini, P. Demoulin, M. J. Murray
Projects: Hinode/EIS

Publication Status: ApJ (accepted)
Last Modified: 2009-09-25 08:08
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Evidence for interchange reconnection between a coronal hole and an adjacent emerging flux region  

Deborah Baker   Submitted: 2007-04-27 10:26

Coronal holes are regions of dominantly monopolar magnetic field on the Sun where the field is considered to be 'open' towards interplanetary space. Magnetic bipoles emerging in proximity to a coronal hole boundary naturally interact with this surrounding open magnetic field. In the case of oppositely aligned polarities between the active region and the coronal hole, we expect interchange reconnection to take place, driven by the coronal expansion of the emerging bipole as well as occasional eruptive events. Using SOHO/EIT and SOHO/MDI data, we present observational evidence of such interchange reconnection by studying AR 10869 which emerged close to a coronal hole. We find closed loops forming between the active region and the coronal hole leading to the retreat of the hole. At the same time, on the far side of the active region, we see dimming of the corona which we interpret as a signature of field line `opening' there, as a consequence of a topological displacement of the `open' field lines of the coronal hole.

Authors: Baker, D., van Driel-Gesztelyi, L., Attrill, G.D.R.
Projects: SoHO-EIT,SoHO-MDI

Publication Status: Astronomische Nachrichten (in press)
Last Modified: 2007-04-27 10:26
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Abstracts by Author
Outflows at the Edges of an Active Region in a Coronal Hole: A Signature of Active Region Expansion?
Signatures of Interchange Reconnection: STEREO, ACE and Hinode Observations Combined
Magnetic Reconnection along Quasi-Separatrix Layers as a Driver of Ubiquitous Active Region Outflows
Evidence for interchange reconnection between a coronal hole and an adjacent emerging flux region

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