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Green, L.M.; Fuentes, M. C. López; Mandrini, C. H.; Démoulin, P.; Driel-Gesztelyi, L. van; Culhane, J. L.

doi:10.1023/a:1019658520033

Cited by 159 publications

(151 citation statements)

References 33 publications

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“…During the second AR limb transit, AR 8100 was fairly active: the shearing motions have been highlighted by Green et al (2002), and according to the LASCO CME catalog (http://cdaw.gsfc.nasa.gov/CME list/), on November 8 a CME spanning 76 degrees occurred at PA = 271 deg at 08:59 UT, and two CMEs occurred on the previous day at PAs 270 deg and 278 deg, respectively. This shows that the magnetic configuration of the region experienced disruptions, although no event is recorded on November 9.…”

Section: Second Limb Transitmentioning

confidence: 99%

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Evolution of active region outflows throughout an active region lifetime

Zangrilli

Poletto

2016

A&A

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Context. We have shown previously that SOHO/UVCS data allow us to detect active region (AR) outflows at coronal altitudes higher than those reached by other instrumentation. These outflows are thought to be a component of the slow solar wind. Aims. Our purpose is to study the evolution of the outflows in the intermediate corona from AR 8100, from the time the AR first forms until it dissolves, after several transits at the solar limb. Methods. Data acquired by SOHO/UVCS at the time of the AR limb transits, at medium latitudes and at altitudes ranging from 1.5 to 2.3 R , were used to infer the physical properties of the outflows through the AR evolution. To this end, we applied the Doppler dimming technique to UVCS spectra. These spectra include the H i Lyα line and the O vi doublet lines at 1031.9 and 1037.6 Å. Results. Plasma speeds and electron densities of the outflows were inferred over several rotations of the Sun. AR outflows are present in the newly born AR and persist throughout the entire AR life. Moreover, we found two types of outflows at different latitudes, both possibly originating in the same negative polarity area of the AR. We also analyzed the behavior of the Si xii 520 Å line along the UVCS slit in an attempt to reveal changes in the Si abundance when different regions are traversed. Although we found some evidence for a Si enrichment in the AR outflows, alternative interpretations are also plausible.Conclusions. Our results demonstrate that outflows from ARs are detectable in the intermediate corona throughout the whole AR lifetime. This confirms that outflows contribute to the slow wind.

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Section: Second Limb Transitmentioning

confidence: 99%

“…2c. Green et al (2002) made linear force-free extrapolations of the coronal field to match low-lying Yohokh SXT loops for five rotations of AR 8100. In their Fig.…”

Section: Third and Fourth Limb Transitsmentioning

confidence: 99%

Evolution of active region outflows throughout an active region lifetime

Zangrilli

Poletto

2016

A&A

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“…The age of an AR can be determined quite easily to the time scale of a solar rotation by locating it on synoptic magnetograms in successive Carrington rotations. Most (10/11) of the GLE ARs are less than one solar rotation old, even though some of them survived a few more rotations after the GLEs, such as AR 08100 (see Green et al 2002). Six of the GLE ARs were seen to emerge on the visible disk, but it was at least a week before a GLE occurred.…”

Section: Basic Properties Of the Ars Associated With Glesmentioning

confidence: 99%

What Are Special About Ground-Level Events?

et al. 2012

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Ground level events (GLEs) occupy the high-energy end of gradual solar energetic particle (SEP) events. They are associated with coronal mass ejections (CMEs) and solar flares, but we still do not clearly understand the special conditions that produce these rare events. During Solar Cycle 23, a total of 16 GLEs were registered, using ground-based neutron monitor data. We first ask if these GLEs are clearly distinguishable from other SEP events observed from space. Setting aside possible difficulties in identifying all GLEs consistently, we then try to find observables which may unmistakably isolate these GLEs by studying the basic properties of the associated eruptions and the active regions (ARs) that produced them. It is found that neither the magnitudes of the CMEs and flares nor the complexities of the ARs give sufficient conditions for GLEs. It is possible to find CMEs, flares or ARs that are not associated with GLEs but that have more extreme properties than those associated with GLEs. We also try to evaluate the importance of magnetic field connection of the AR with Earth on the detection of GLEs and their onset times. Using the potential field source surface (PFSS) model, a half of the GLEs are found to be well-connected. However, the GLE onset time with respect to the onset of the associated flare and CME does not strongly depend on how well-connected the AR is. The GLE onset behavior may be largely determined by when and where the CME-driven shock develops. We could not relate the shocks responsible for the onsets of past GLEs with features in solar images, but the combined data from the Solar TErrestrial RElations Observatory (STEREO) and the Solar Dynamics Observatory (SDO) have the potential to change this for GLEs that may occur in the rising phase of Solar Cycle 24.

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“…It was shown that differential rotation cannot supply enough helicity to the corona and CMEs (Demoulin et al 2002;Green et al 2002;Mandrini et al 2004). Many authors have studied the helicity of active regions.…”

Section: Introductionmentioning

confidence: 99%

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

Yang

Zhang²,

Büchner

2009

A&A

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Context. It has been known for years that there is a general dominance of negative (positive) helicity of active regions (ARs) in the northern (southern) solar hemisphere. For a better understanding of the role of helicity in the evolution of active regions, it is necessary to know more about the accumulation of helicity during the emergence of active regions. In particular, different conclusions were drawn in the past about the relationship between the accumulated helicity and the writhe of active regions. Aims. We investigate the accumulation of helicity in newly emerging simple bipolar solar active regions. We also investigate the relation between the accumulated helicity and writhe. Methods. We obtain helicity accumulation by applying Fast Fourier Transforms (FFT) and local correlation tracking (LCT) to MDI data. We deduce the writhe of the active regions according to the evolution of the tilt angle between the connecting line of the weighting centers of opposite polarities in the ARs. Results. It is found that the accumulated helicity is proportional to the exponent of magnetic flux (|H| ∝ Φ 1.85 ) in the 58 selected newly emerged simple ARs. 74% of ARs have a negative (positive) helicity when the above defined tilt angle rotates clockwise (counterclockwise). This means that the accumulated helicity and writhe have the same sign for most of the investigated ARs according to the tilt angle evolution of ARs. We also found that 56% (57.6%) of these ARs in the northern (southern) photosphere provide negative (positive) helicity to the corona in the course of the emergence of magnetic flux.

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Cited by 159 publications

References 33 publications

Evolution of active region outflows throughout an active region lifetime

Evolution of active region outflows throughout an active region lifetime

What Are Special About Ground-Level Events?

Magnetic helicity accumulation and tilt angle evolution of newly emerging active regions

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