The Origins of Hot Plasma in the Solar Corona

Pontieu, Bart De; McIntosh, Scott W.; Carlsson, Mats; Hansteen, V. H.; Tarbell, T. D.; Boerner, P.; Martínez-Sykora, Juan; Schrijver, Carolus J.; Title, A. M.

doi:10.1126/science.1197738

Cited by 358 publications

(322 citation statements)

References 26 publications

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“…It is therefore plausible that the few brightenings in the AIA 304, 171, and 211 Å bands that we and De Pontieu et al (2011) observe near the footpoint of active region loops are signatures of upflowing chromospheric material heated to transition-region temperatures, up to 0.5 MK, although the EIS observations presented here cannot rule out heating to even higher temperatures.…”

Section: Discussionmentioning

confidence: 52%

“…The contribution of cool (log T [K] < 5.7) plasma to the 171 Å channel is also clearly significant. Our results suggest that the interpretation given by De Pontieu et al (2011) of the AIA 171 Å and 211 Å observations near active region loop footpoints should be treated with extreme caution. Indeed we have shown that for both a loop footpoint and a loop leg region, the contribution of "cool" (log T [K] < 5.7) plasma is large.…”

Section: Discussionmentioning

confidence: 67%

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SDO AIA and Hinode EIS observations of “warm” loops

Zanna

O’Dwyer

Mason

2011

A&A

131

106

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We present simultaneous observations of active region "warm" (1 MK) loops using the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and Hinode EUV Imaging Spectrometer (EIS). Sample EIS spectra for a loop footpoint and a lop leg region are presented, and are used to describe the spectral lines which contribute to the six AIA EUV channels, both directly and predicted with DEM modeling. We find good overall agreement between observed and predicted count rates for the 131 Å, 193 Å, and 335 Å bands, but highlight a number of problems, partly to be ascribed to inter-calibration issues, partly due to the fact that a large number of lines remain unidentified for the 94 Å, 171 Å, and 211 Å bands. We also found that the 335 Å band is severely affected by cross-talk with the 131 Å band and by second order contributions. We extend our previous work where we highlighted the multi-thermal nature of the SDO AIA bands to show that emission from lines formed at typical transition region temperatures (log T [K] = 5.0-5.8) can be significant for all the EUV channels, and even dominant in some cases. We also assess the possibility of deriving accurate emission measures from the AIA observations. We have found that the inversion of the AIA data to obtain a description of the thermal characteristics of warm loops is unreliable. We highlight the need for further work on the relevant atomic data before the AIA data can be reliably used for plasma diagnostic purposes.

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Section: Discussionmentioning

confidence: 52%

Section: Discussionmentioning

confidence: 67%

SDO AIA and Hinode EIS observations of “warm” loops

Zanna

O’Dwyer

Mason

2011

A&A

131

106

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“…That in SUMER spectra no EEs are observed in coronal lines -besides the fact that no really good coronal lines for disk observations exist in the SUMER wavelength range -does not contradict the scenario suggested by De Pontieu et al (2011), who found that the heated volume is outside the leading edge of the jet. If heating takes place while the jet propagates and expands, then spectrometers, in particular slow spectrometers, will have difficulties to observe this heating process.…”

Section: Discussionmentioning

confidence: 64%

“…These candidates could be type II spicules or rapid blueshifted events (RBEs; De Pontieu et al , 2011McIntosh et al 2009; Rouppe van der Voort 2009) because they have very similar characteristics in terms of velocity, lifetime, size, and repeatability. A direct proof of helicity in RBEs through imaging instruments has to our knowledge not been reported yet and may be difficult to achieve.…”

Section: Discussionmentioning

confidence: 99%

Spectroscopic evidence for helicity in explosive events

Curdt

Tian

2011

A&A

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Aims. We report spectroscopic observations in support of a novel view of transition region explosive events, observations that lend empirical evidence that at least in some cases explosive events may be nothing else but spinning narrow spicule-like structures. Methods. Our spectra of textbook explosive events with simultaneous Doppler flow of a red and a blue component are extreme cases of high spectroscopic velocities that lack apparent motion, to be expected if interpreted as a pair of collimated, linearly moving jets. The awareness of this conflict led us to the alternative interpretation of redshift and blueshift as a spinning motion of a small plasma volume. In contrast to the bidirectional jet scenario, a small volume of spinning plasma would be fully compatible with the observation of flows without detectable apparent motion. We suspect that these small volumes could be spicule-like structures and try to find evidence for this. We show observations of helical motion in macrospicules and argue that these features -if scaled down to a radius comparable to the slit size of a spectrometer -should have a spectroscopic signature similar to that observed in explosive events, which is admittedly not easily detectable by imagers. Despite of this difficulty, evidence of helicity in spicules has been reported in the literature. This led us to the new insight that the same narrow spinning structures may be the drivers in both cases, structures that imagers observe as spicules and that in spectrometers cross the slit and are seen as explosive events. Results. We arrive at a concept that supports the idea that explosive events and spicules are different manifestations of the same helicity-driven scenario. In contrast to the conventional view of explosive events as linear bidirectional jets that are triggered by a reconnection event in the transition region, this new interpretation is compatible with the observational results. Consequently, in this case a photospheric or subphotospheric trigger has to be assumed. Conclusions. We suggest that explosive events/spicules are to be compared to the unwinding of a loaded torsional spring.

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“…The large spatial superposition of spicules, particularly at the limb, makes it challenging to track every individual spicule (e.g., see "Selection Effects and Errors" in Pereira et al 2012). Spicules also recur frequently from the same footpoint region (Beckers 1968;Suematsu et al 1995;De Pontieu et al 2011;Pereira et al 2012;Sekse et al 2013b;Yurchyshyn et al 2013), meaning that when a particular spicule disappears it can be quickly replaced by another of similar intensity in the same place. Judge et al (2012;hereafter JCR12) study disk spicules at a wavelength of Hα + 0.11 nm, and find spicules that appear and disappear suddenly over several Mm.…”

Section: Appearance and Disappearancementioning

confidence: 99%

THE APPEARANCE OF SPICULES IN HIGH RESOLUTION OBSERVATIONS OF Ca ii H AND Hα

Pereira

Voort

Carlsson

2016

ApJ

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Solar spicules are chromospheric fibrils that appear everywhere on the Sun, yet their origin is not understood. Using high resolution observations of spicules obtained with the Swedish 1 m Solar Telescope, we aim to understand how spicules appear in filtergrams and Dopplergrams, how they compare in Ca II H and Hα filtergrams, and what can make them appear and disappear. We find that spicules display a rich and detailed spatial structure, and show a distribution of transverse velocities that, when aligned with the line of sight, can make them appear at different Hα wing positions. They become more abundant at positions closer to the line core, reflecting a distribution of Doppler shifts and widths. In Hα width maps they stand out as bright features both on disk and off limb, reflecting their large Doppler motions and possibly higher temperatures than in the typical Hα formation region. Spicule lifetimes measured from narrowband images at only a few positions will be an underestimate because Doppler shifts can make them disappear prematurely from such images; for such cases, width maps are a more robust tool. In Hα and Ca II H filtergrams, off-limb spicules essentially have the same properties, appearance, and evolution. We find that the sudden appearance of spicules can be explained by Doppler shifts from their transverse motions, and does not require other convoluted explanations.

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The Origins of Hot Plasma in the Solar Corona

Cited by 358 publications

References 26 publications

SDO AIA and Hinode EIS observations of “warm” loops

SDO AIA and Hinode EIS observations of “warm” loops

Spectroscopic evidence for helicity in explosive events

THE APPEARANCE OF SPICULES IN HIGH RESOLUTION OBSERVATIONS OF Ca ii H AND Hα

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