Magnetic Reconnection Along Quasi-Separatrix Layers as a Driver of Ubiquitous Active Region Outflows

We propose a unified interpretation for persistent coronal outflows and metric radio noise storms, two phenomena typically observed in association with quiescent solar active regions. Our interpretation is based on multi-wavelength observations of two such regions as they crossed the meridian in May and July 2007. For both regions, we observe a persistent pattern of blue-shifted coronal emission in high-temperature lines with Hinode/EIS, and a radio noise storm with the Nançay Radioheliograph. The observations are supplemented by potential and linear force-free extrapolations of the photospheric magnetic field over large computational boxes, and by a detailed analysis of the coronal magnetic field topology. We find true separatrices in the coronal field and null points high in the corona, which are preferential locations for magnetic reconnection and electron acceleration. We suggest that the continuous growth of active regions maintains a steady reconnection across the separatrices at the null point. This interchange reconnection occurs between closed, high-density loops in the core of the active region and neighbouring open, low-density flux tubes. Thus, the reconnection creates strong pressure imbalances which are the main drivers of plasma upflows. Furthermore, the acceleration of low-energy electrons in the interchange reconnection region sustains the radio noise storm in the closed loop areas, as well as weak type III emission along the open field lines. For both active regions studied, we find a remarkable agreement between the observed places of persistent coronal outflows and radio noise storms with their locations as predicted by our interpretation.

show abstract

“…Similar results on other ARs have been found (see, e.g. Del Zanna & Bradshaw 2009;Doschek et al 2008;Hara et al 2008;Baker et al 2009). …”

Section: Introductionsupporting

confidence: 88%

A single picture for solar coronal outflows and radio noise storms

Zanna¹,

Aulanier

Klein

et al. 2011

A&A

View full text Add to dashboard Cite

show abstract

“…Figure 7 shows that the observed blueshifted fan-like feature is rooted in a single polarity of the AR. The same has been previously reported for two ARs, which were studied by Doschek et al (2008) and Baker et al (2009). We used the very basic approach of producing light curves to study the general evolution of the magnetic field in the AR.…”

Section: Magnetic Field Evolutionmentioning

confidence: 96%

Active region upflows

Vanninathan

Madjarska

Galsgaard

et al. 2015

A&A

View full text Add to dashboard Cite

Context. We study upflows at the edges of active regions, called AR outflows, using multi-instrument observations. Aims. This study intends to provide the first direct observational evidence of whether chromospheric jets play an important role in furnishing mass that could sustain coronal upflows. The evolution of the photospheric magnetic field, associated with the footpoints of the upflow region and the plasma properties of active region upflows is investigated with the aim of providing information for benchmarking data-driven modelling of this solar feature. Methods. We spatially and temporally combine multi-instrument observations obtained with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode, the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager instruments on board the Solar Dynamics Observatory and the Interferometric BI-dimensional Spectro-polarimeter installed at the National Solar Observatory, Sac Peak, to study the plasma parameters of the upflows and the impact of the chromosphere on active region upflows. Results. Our analysis shows that the studied active region upflow presents similarly to those studied previously, i.e. it displays blueshifted emission of 5-20 km s −1 in Fe xii and Fe xiii and its average electron density is 1.8 × 10 9 cm −3 at 1 MK. The time variation of the density is obtained showing no significant change (in a 3σ error). The plasma density along a single loop is calculated revealing a drop of 50% over a distance of ∼20 000 km along the loop. We find a second velocity component in the blue wing of the Fe xii and Fe xiii lines at 105 km s −1 reported only once before. For the first time we study the time evolution of this component at high cadence and find that it is persistent during the whole observing period of 3.5 h with variations of only ±15 km s −1 . We also, for the first time, study the evolution of the photospheric magnetic field at high cadence and find that magnetic flux diffusion is responsible for the formation of the upflow region. High cadence Hα observations are used to study the chromosphere at the footpoints of the upflow region. We find no significant jet-like (spicule/rapid blue excursion) activity to account for several hours/days of plasma upflow. The jet-like activity in this region is not continuous and blueward asymmetries are a bare minimum. Using an image enhancement technique for imaging and spectral data, we show that the coronal structures seen in the AIA 193 Å channel are comparable to the EIS Fe xii images, while images in the AIA 171 Å channel reveal additional loops that are a result of contribution from cooler emission to this channel. Conclusions. Our results suggest that at chromospheric heights there are no signatures that support the possible contribution of spicules to active region upflows. We suggest that magnetic flux diffusion is responsible for the formation of the coronal upflows. The existence of two velocity components possibly indicates the presence of two different flows, which are produce...

show abstract

“…Using a LFF field model, they were able to associate sharp changes in the Doppler velocity (inferred from SOHO/SUMER Dopplergrams) to the border between topologically different field configurations (open and closed). Furthermore, there seems to be a connection between the strength of the flows and the underlying magnetic field: the strongest flows seem to be associated to that portion of QSLs which are situated above strong magnetic fields (Baker et al 2009). …”

Section: Relation To Dynamic Phenomenamentioning

confidence: 99%

“…Because the trigger for magnetic reconnection has often been suspected around an existing coronal null point or within a QSL, studies have been undertaken to relate flare-associated features to the magnetic topology of the corona (Luoni et al 2007;Baker et al 2009;van Driel-Gesztelyi et al 2012;Sun et al 2012a). Aulanier et al (2000) inferred the location of a coronal null point and separatrix surfaces from a potential field reconstruction and highlighted that, a current-free model cannot be expected to reproduce the observations in detail-especially in the presence of strong shear.…”

Section: Relation To Dynamic Phenomenamentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

176

125

View full text Add to dashboard Cite

This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.

show abstract

Magnetic Reconnection Along Quasi-Separatrix Layers as a Driver of Ubiquitous Active Region Outflows

Cited by 117 publications

References 31 publications

A single picture for solar coronal outflows and radio noise storms

A single picture for solar coronal outflows and radio noise storms

Active region upflows

The magnetic field in the solar atmosphere

Contact Info

Product

Resources

About