On the Correlation between Coronal and Lower Transition Region Structures at Arcsecond Scales

Vourlidas, A.; Klimchuk, J. A.; Korendyke, C. M.; Tarbell, T. D.; Handy, B. N.

doi:10.1086/323835

Cited by 42 publications

(43 citation statements)

References 37 publications

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“…Support for the classical picture of the transition region comes from observations of Fe IX 17.1 nm "moss" at the footpoints of hot coronal loops Fletcher & De Pontieu 1999;Martens et al 2000;Vourlidas et al 2001). These studies show that the locations of such bright, spongytextured areas are well correlated with the presence of coronal emission at temperatures T  2 MK, from which it is inferred that the moss represents the conductively heated, upper transition region of the overlying hot coronal loops.…”

Section: Introductionmentioning

confidence: 91%

The Ubiquitous Presence of Looplike Fine Structure Inside Solar Active Regions

Wang

2016

ApJL

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Although most of the solar surface outside active regions (ARs) is pervaded by small-scale fields of mixed polarity, this magnetic "carpet" or "junkyard" is thought to be largely absent inside AR plages and strong network. However, using extreme-ultraviolet images and line-of-sight magnetograms from the Solar Dynamics Observatory, we find that unipolar flux concentrations, both inside and outside ARs, often have small, loop-shaped Fe IX 17.1 and Fe XII 19.3 nm features embedded within them, even though no minority-polarity flux is visible in the corresponding magnetograms. Such looplike structures, characterized by horizontal sizes of ∼3-5 Mm and varying on timescales of minutes or less, are seen inside bright 17.1 nm moss, as well as in fainter moss-like regions associated with weaker network outside ARs. We also note a tendency for bright coronal loops to show compact, looplike features at their footpoints. Based on these observations, we suggest that present-day magnetograms may be substantially underrepresenting the amount of minority-polarity flux inside plages and strong network, and that reconnection between small bipoles and the overlying large-scale field could be a major source of coronal heating both in ARs and in the quiet Sun.

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Section: Introductionmentioning

confidence: 91%

The Ubiquitous Presence of Looplike Fine Structure Inside Solar Active Regions

Wang

2016

ApJL

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“…Moreover, the emission recorded in this channel covers the temperature range 1.0-3.0 × 10 4 K (Handy et al 1999a), i.e., not only the formation temperature of the Ly α line, which is ∼2.0 × 10 4 K (e.g. Vourlidas et al 2001). Therefore, we considered the TRACE 1216 Å data only as an approximation of chromospheric emission and drew no conclusions about absolute intensity changes.…”

Section: Data and Data Reductionmentioning

confidence: 99%

Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop

Gömöry

Balthasar

Puschmann

2013

A&A

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Aims. We investigate the temporal evolution of magnetic flux emergence in the quiet-Sun atmosphere close to disk center. Methods. We combined high-resolution SoHO/MDI magnetograms with TRACE observations taken in the 1216 Å channel to analyze the temporal evolution of an emerging small-scale magnetic loop and its traces in the chromosphere. Results. We find signatures of flux emergence very close to the edge of a supergranular network boundary located at disk center. The new emerging flux appeared first in the MDI magnetograms in form of an asymmetric bipolar element, i.e., the patch with negative polarity is roughly twice as weak as the corresponding patch with opposite polarity. The average values of magnetic flux and magnetic flux densities reached 1.6 × 10 18 Mx, −8.5 × 10 17 Mx, and 55 Mx cm −2 , -30 Mx cm −2 , respectively. The spatial distance between the opposite polarity patches of the emerged feature increased from about 2. 5 to 5. 0 during the lifetime of the loop, which was 36 min. A more precise lifetime-estimate of the feature was not possible because of a gap in the temporal sequence of the MDI magnetograms. The chromospheric response to the emerged magnetic dipole occurred ∼9 min later than in the photospheric magnetograms. It consisted of a quasi-periodic sequence of time-localized brightenings visible in the 1216 Å TRACE channel for ∼14 min that were co-spatial with the axis connecting the two patches of opposite magnetic polarity. Conclusions. We identify the observed event as a small-scale magnetic loop emerging at photospheric layers that subsequently rose to the chromosphere. We discuss the possibility that the fluctuations detected in the chromospheric emission probably reflect magneticfield oscillations which propagate to the chromosphere in the form of waves.

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“…Observations of the moss are particularly useful for constraining physical models since the observed intensity is proportional to the loop pressure and independent of the loop length (Martens et al 2000;Vourlidas et al 2001). That is, I const1 is the computed intensity for the constant cross-section model computed from the intensity-pressure relationships, I const2 is the constant cross-section model computed from the least-squares fitting, and I funnel is the best-fit model for the funnel geometry.…”

Section: Modeling the Mossmentioning

confidence: 99%

EVIDENCE FOR STEADY HEATING: OBSERVATIONS OF AN ACTIVE REGION CORE WITHHINODEANDTRACE

Warren

Winebarger

Brooks

2010

ApJ

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The timescale for energy release is an important parameter for constraining the coronal heating mechanism. Observations of "warm" coronal loops (∼1 MK) have indicated that the heating is impulsive and that coronal plasma is far from equilibrium. In contrast, observations at higher temperatures (∼3 MK) have generally been consistent with steady heating models. Previous observations, however, have not been able to exclude the possibility that the high temperature loops are actually composed of many small-scale threads that are in various stages of heating and cooling and only appear to be in equilibrium. With new observations from the EUV Imaging Spectrometer and X-ray Telescope (XRT) on Hinode we have the ability to investigate the properties of high temperature coronal plasma in extraordinary detail. We examine the emission in the core of an active region and find three independent lines of evidence for steady heating. We find that the emission observed in XRT is generally steady for hours, with a fluctuation level of approximately 15% in an individual pixel. Short-lived impulsive heating events are observed, but they appear to be unrelated to the steady emission that dominates the active region. Furthermore, we find no evidence for warm emission that is spatially correlated with the hot emission, as would be expected if the high temperature loops are the result of impulsive heating. Finally, we also find that intensities in the "moss," the footpoints of high temperature loops, are consistent with steady heating models provided that we account for the local expansion of the loop from the base of the transition region to the corona. In combination, these results provide strong evidence that the heating in the core of an active region is effectively steady, that is, the time between heating events is short relative to the relevant radiative and conductive cooling times.

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On the Correlation between Coronal and Lower Transition Region Structures at Arcsecond Scales

Cited by 42 publications

References 37 publications

The Ubiquitous Presence of Looplike Fine Structure Inside Solar Active Regions

The Ubiquitous Presence of Looplike Fine Structure Inside Solar Active Regions

Evidence of quiet-Sun chromospheric activity related to an emerging small-scale magnetic loop

EVIDENCE FOR STEADY HEATING: OBSERVATIONS OF AN ACTIVE REGION CORE WITHHINODEANDTRACE

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