Outflows at the Edges of Active Regions: Contribution to Solar Wind Formation?

Harra, L. K.; Sakao, Taro; Mandrini, C. H.; Hara, Hirohisa; Imada, Shinsuke; Young, Peter R.; Driel-Gesztelyi, L. van; Baker, D.

doi:10.1086/587485

Cited by 207 publications

(233 citation statements)

References 22 publications

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“…2, and their travelling speeds, given by the slopes of the dashed line, are indicated. This type of intensityenhancement propagation seen in soft X-rays suggests a relation to plasma outflow, since steady Doppler blue-shifts of the Fe xii line were discovered at the roots of these strands (Harra et al 2008). From Fig.…”

Section: Properties Of the Recurrent Intermittent Outflowsmentioning

confidence: 74%

“…These authors claimed that continuous outflow does exist, a notion based on the appearance of the very frequent outward propagation of intensity enhancements in the X-ray movie. The outflow observed by XRT has been reconfirmed by EIS observation of strong steady blueshifts (20-50 km s −1 ) of Fe xii at the root sections of open field lines (Harra et al 2008). Doschek et al (2008) also used EIS observations to investigate strong blueshifts at the periphery of an AR, which might contribute significantly to the solar wind.…”

Section: Introductionmentioning

confidence: 80%

“…During solar minimum, the fast solar wind is recognized to originate in the (polar) coronal holes (CHs), in particular from the magnetic funnels according to both observations (Xia et al 2003;Tu et al 2005a,b;Marsch et al 2006;Tian et al 2010) and theoretical models Hackenberg et al 2000;Esser et al 2005;He et al 2008). The slow solar wind has several possible source regions, such as the boundaries of polar CHs (Wang et al 1990), the helmet streamers , the funnel-like structures in the quiet regions (He et al 2007;Tian et al 2008aTian et al , 2009, and the edges of active regions (ARs) (e.g., Sakao et al 2007;Harra et al 2008). For a comprehensive review of previous studies of plasma characteristics and magnetic features in the solar wind source regions, we refer to Marsch (2006).…”

Section: Introductionmentioning

confidence: 99%

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Intermittent outflows at the edge of an active region – a possible source of the solar wind?

He¹,

Marsch²,

Tu³

et al. 2010

A&A

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Context. It has already been established that the solar wind may originate at the edges of active regions (ARs), but the key questions of how frequently these outflows occur, and at which height the nascent solar wind originates have not yet been addressed. Aims. We study the occurrence rate of these intermittent outflows, the related plasma activities beneath in the low solar atmosphere, and the interplanetary counterparts of the nascent solar wind outflow. Methods. We use the observations from XRT/Hinode and TRACE to study the outflow patterns. The occurrence frequency of the intermittent outflow is estimated by counting the occurrences of propagating intensity enhancements in height-time diagrams. We adopt observations of SOT/Hinode and EIS/Hinode to investigate the phenomena in the chromosphere associated with the coronal outflows. The ACE plasma and field in-situ measurements near Earth are used to study the interplanetary manifestations. Results. We find that in one elongated coronal emission structure, referred to as strand, the plasma flows outward intermittently, about every 20 min. The flow speed sometimes exceeds 200 km s −1 , which is indicative of rapid acceleration, and thus exceeds the coronal sound speed at low altitudes. The inferred flow speed of the soft-X-ray-emitting plasma component seems a little higher than that of the Fe ix/x-emitting plasma component. Chromospheric jets are found to occur at the root of the strand. Upflows in the chromosphere are also confirmed by blue-shifts of the He ii line. The heliospheric plasma counterpart close to the Earth is found to be an intermediate-speed solar wind stream. The AR edge may also deliver some plasmas to a fraction of the fast solar wind stream, most of which emanate from the neighboring CH. Conclusions. The possible origin of the nascent solar wind in the chromosphere, the observed excessive outflow speed of over 200 km s −1 in the lower corona, and the corresponding intermediate-speed solar wind stream in interplanetary space are all linked in our case study. These phenomena from the low solar atmosphere to the heliosphere near Earth in combination shed new light on the solar wind formation process. These observational results will constrain future modeling of the solar winds originating close to an AR.

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Section: Properties Of the Recurrent Intermittent Outflowsmentioning

confidence: 74%

Section: Introductionmentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Intermittent outflows at the edge of an active region – a possible source of the solar wind?

He¹,

Marsch²,

Tu³

et al. 2010

A&A

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show abstract

“…Velocities, obtained from blueshifts, range from ≈ 3 km s −1 to ≈ 50 km s −1 and increase with temperature (Del Zanna, 2008). Non-thermal line broadening and the appearance of blue-wing asymmetries are observed to correlate with velocity (Del Zanna, 2008;Harra et al, 2008;Bryans, Young, and Doschek, 2011). This could suggest the presence of multiple upflow sites for plasma at different speeds.…”

Section: Introductionmentioning

confidence: 91%

Tracking Solar Active Region Outflow Plasma from Its Source to the Near-Earth Environment

Culhane¹,

Brooks

Driel-Gesztelyi

et al. 2014

Sol Phys

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Seeking to establish whether active-region upflow material contributes to the slow solar wind, we examine in detail the plasma upflows from Active Region (AR) 10978, which crossed the Sun's disc in the interval 8 to 16 December 2007 during Carrington rotation (CR) 2064. In previous work, using data from the Hinode/EUV Imaging Spectrometer, upflow velocity evolution was extensively studied as the region crossed the disc, while a linear forcefree-field magnetic extrapolation was used to confirm aspects of the velocity evolution and to establish the presence of quasi-separatrix layers at the upflow source areas. The plasma properties, temperature, density, and first ionisation potential bias [FIP-bias] were measured with the spectrometer during the disc passage of the active region. Global potential-field source-surface (PFSS) models showed that AR 10978 was completely covered by the closed field of a helmet streamer that is part of the streamer belt. Therefore it is not clear how any of the upflowing AR-associated plasma could reach the source surface at 2.5 R and contribute to the slow solar wind. However, a detailed examination of solar-wind in-situ data obtained by the Advanced Composition Explorer (ACE) spacecraft at the L 1 point shows that increases in O 7+ /O 6+ , C 6+ /C 5+ , and Fe/O -a FIP-bias proxy -are present before the heliospheric current-sheet crossing. These increases, along with an accompanying reduction in proton velocity and an increase in density are characteristic of both AR and slow-solarwind plasma. Finally, we describe a two-step reconnection process by which some of the upflowing plasma from the AR might reach the heliosphere.

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“…Doschek et al 2007Doschek et al , 2008Sakao et al 2007;Del Zanna 2008;Harra et al 2008;Hara et al 2008;De Pontieu & McIntosh 2010;Tian et al 2011a,b;Martínez-Sykora et al 2011). A single Gaussian fit to the spectral lines suggest that the flow speed is about ∼10 km s −1 , much less than the observed apparent speed of propagating disturbances.…”

Section: Introductionmentioning

confidence: 96%

Measuring the apparent phase speed of propagating EUV disturbances

Yuan

Nakariakov

2012

A&A

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Context. Propagating disturbances of the EUV emission intensity are commonly observed over a variety of coronal structures. Parameters of these disturbances, particularly the observed apparent (image-plane projected) propagation speed, are important tools for MHD coronal seismology. Aims. We design and test tools to reliably measure the apparent phase speed of propagating disturbances in imaging data sets. Methods. We designed cross-fitting technique (CFT), 2D coupled fitting (DCF) and best similarity match (BSM) to measure the apparent phase speed of propagating EUV disturbances in the running differences of time-distance plots (R) and background-removed and normalised time-distance plots (D).Results. The methods were applied to the analysis of quasi-periodic EUV disturbances propagating at a coronal fan-structure of active region NOAA11330 on 27 Oct. 2011, observed with the Atmospheric Imaging Assembly (AIA) on SDO in the 171 Å bandpass. The noise propagation in the AIA image processing was estimated, resulting in the preliminary estimation of the uncertainties in the AIA image flux. This information was used in measuring the apparent phase speed of the propagating disturbances with the CFT, DCF and BSM methods, which gave consistent results. The average projected speed is measured at 47.6 ± 0.6 km s −1 and 49.0 ± 0.7 km s −1 for R and D, with the corresponding periods at 179.7 ± 0.2 s and 179.7 ± 0.3 s, respectively. We analysed the effects of the lag time and the detrending time in the running difference processing and the background-removed plot, on the measurement of the speed, and found that they are fairly weak. Conclusions. The CFT, DCF and BSM methods are found to be reliable techniques for measuring the apparent (projected) phase speed. The samples of larger effective spatial length are more suitable for these methods. Time-distance plots with background removal and normalisation allow for more robust measurements, with little effect of the choice of the detrending time. Cross-fitting technique provides reliable measurements on good samples (e.g. samples with large effective detection length and recurring features). 2D coupled-fitting is found to be sensitive to the initial guess for parameters of the 2D fitting function. Thus DCF is only optimised in measuring one of the parameters (the phase speed in our application), while the period is poorly measured. Best similarity measure is robust for all types of samples and very tolerant to image pre-processing and regularisation (smoothing).

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Outflows at the Edges of Active Regions: Contribution to Solar Wind Formation?

Cited by 207 publications

References 22 publications

Intermittent outflows at the edge of an active region – a possible source of the solar wind?

Intermittent outflows at the edge of an active region – a possible source of the solar wind?

Tracking Solar Active Region Outflow Plasma from Its Source to the Near-Earth Environment

Measuring the apparent phase speed of propagating EUV disturbances

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