QUASI-PERIODIC FLUCTUATIONS AND CHROMOSPHERIC EVAPORATION IN A SOLAR FLARE RIBBON OBSERVED BY<i>IRIS</i>

Brosius, J. W.; Daw, A. N.

doi:10.1088/0004-637x/810/1/45

Cited by 64 publications

(81 citation statements)

References 55 publications

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“…Perhaps the most significant challenge presented by these data is the persistent redshifts observed in Si IV and C II. Persistent redshifts have been observed with IRIS for a number of events and are not an idiosyncrasy of the data that we have analyzed (see Brannon et al 2015;Brosius & Daw 2015;Sadykov et al 2015;Polito et al 2016).…”

Section: Summary and Discussionmentioning

confidence: 68%

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Warren

Reep

Crump

et al. 2016

ApJ

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We exploit the high spatial resolution and high cadence of the Interface Region Imaging Spectrograph (IRIS) to investigate the response of the transition region and chromosphere to energy deposition during a small flare. Simultaneous observations from the Reuven Ramaty High Energy Solar Spectroscopic Imager provide constraints on the energetic electrons precipitating into the flare footpoints, while observations of the X-Ray Telescope, Atmospheric Imaging Assembly, and Extreme Ultraviolet Imaging Spectrometer (EIS) allow us to measure the temperatures and emission measures from the resulting flare loops. We find clear evidence for heating over an extended period on the spatial scale of a single IRIS pixel. During the impulsive phase of this event, the intensities in each pixel for the Si IV 1402.770 Å, C II 1334.535 Å, Mg II 2796.354 Å, and O I 1355.598 Å emission lines are characterized by numerous small-scale bursts typically lasting 60 s or less. Redshifts are observed in Si IV, C II, and Mg II during the impulsive phase. Mg II shows redshifts during the bursts and stationary emission at other times. The Si IV and C II profiles, in contrast, are observed to be redshifted at all times during the impulsive phase. These persistent redshifts are a challenge for one-dimensional hydrodynamic models, which predict only short-duration downflows in response to impulsive heating. We conjecture that energy is being released on many small-scale filaments with a power-law distribution of heating rates.

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Section: Summary and Discussionmentioning

confidence: 68%

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Warren

Reep

Crump

et al. 2016

ApJ

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“…Since the slit covers only a very limited and fixed field of view, it is difficult to obtain data across entire flare kernels, however. Thus, flare studies based on sit-and-stare observations are still rare (e.g., Brosius 2001Brosius , 2013aBerkebile-Stoiser et al 2009;Veronig et al 2010;Brosius & Daw 2015).…”

Section: Introductionmentioning

confidence: 99%

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Gömöry

Veronig

et al. 2016

A&A

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Aims. We study the response of the solar atmosphere during a GOES M1.6 flare using spectroscopic and imaging observations. In particular, we examine the evolution of the mass flows and electron density together with the energy input derived from hard X-ray (HXR) in the context of chromospheric evaporation.Methods. We analyzed high-cadence sit-and-stare observations acquired with the Hinode/EIS spectrometer in the Fe xiii 202.044 Å (log T = 6.2) and Fe xvi 262.980 Å (log T = 6.4) spectral lines to derive temporal variations of the line intensity, Doppler shifts, and electron density during the flare. We combined these data with HXR measurements acquired with RHESSI to derive the energy input to the lower atmosphere by flare-accelerated electrons.Results. During the flare impulsive phase, we observe no significant flows in the cooler Fe xiii line but strong upflows, up to 80-150 km s −1 , in the hotter Fe xvi line. The largest Doppler shifts observed in the Fe xvi line were co-temporal with the sharp intensity peak. The electron density obtained from a Fe xiii line pair ratio exhibited fast increase (within two minutes) from the pre-flare level of 5.01 × 10 9 cm −3 to 3.16 × 10 10 cm −3 during the flare peak. The nonthermal energy flux density deposited from the coronal acceleration site to the lower atmospheric layers during the flare peak was found to be 1.34 × 10 10 erg s −1 cm −2 for a low-energy cut-off that was estimated to be 16 keV. During the decline flare phase, we found a secondary intensity and density peak of lower amplitude that was preceded by upflows of ∼15 km s −1 that were detected in both lines. The flare was also accompanied by a filament eruption that was partly captured by the EIS observations. We derived Doppler velocities of 250-300 km s −1 for the upflowing filament material. Conclusions. The spectroscopic results for the flare peak are consistent with the scenario of explosive chromospheric evaporation, although a comparatively low value of the nonthermal energy flux density was determined for this phase of the flare. This outcome is discussed in the context of recent hydrodynamic simulations. It provides observational evidence that the response of the atmospheric plasma strongly depends on the properties of the electron beams responsible for the heating, in particular the steepness of the energy distribution. The secondary peak of line intensity and electron density detected during the decline phase is interpreted as a signature of flare loops being filled by expanding hot material that is due to chromospheric evaporation.

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“…They interpreted it as a signature of quasi-periodic slipping, generated by a mode of three-dimensional reconnection (Aulanier et al 2006). A similar pattern was observed by Brannon et al (2015) and Brosius & Daw (2015) in the ribbons of the 2014 April 18 flare (SOL2014-04-18T13:03). Brosius & Daw (2015) and subsequently Brosius et al (2016) noted that individual pixels on the IRIS slit exhibited quasi-period brightenings and Doppler shifts at ∼ 3 minute intervals in a number of spectral lines observed by IRIS as well as Hinode EIS.…”

Section: Introductionmentioning

confidence: 55%

“…This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection (Brosius & Daw 2015;Brosius et al 2016) and slipping occurring during three-dimensional magnetic reconnection (Li & Zhang 2015;Li et al 2016). While able to account for periodicities in both intensity and Doppler velocity these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure, or for the relative phasing of the oscillations.…”

Section: Introductionmentioning

confidence: 97%

“…Recent UV spectral and imaging observations of flare ribbons at extremely high spatial resolution, made by IRIS (De Pontieu et al 2014), have revealed distinctive quasi-periodic, sawtooth patterns in certain flare ribbons (Li & Zhang 2015;Brannon et al 2015;Brosius & Daw 2015;Brosius et al 2016). These may offer a new clue to some facet of magnetic reconnection.…”

Section: Introductionmentioning

confidence: 99%

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Modeling a Propagating Sawtooth Flare Ribbon Structure as a Tearing Mode in the Presence of Velocity Shear

Parker

Longcope

2017

ApJ

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On April 18, 2014 (SOL2014-04-18T13:03) an M-class flare was observed by IRIS. The associated flare ribbon contained a quasi-periodic sawtooth pattern that was observed to propagate along the ribbon, perpendicular to the IRIS spectral slit, with a phase velocity of ∼ 15 km s −1 (Brannon et al. 2015). This motion resulted in periodicities in both intensity and Doppler velocity along the slit. These periodicities were reported by Brannon et al. (2015) to be approximately ±0.5 arcseconds in position and ±20 km s −1 in velocity and were measured to be ∼ 180• out of phase with one another. This quasi-periodic behavior has been attributed by others to bursty or patchy reconnection (Brosius & Daw 2015;Brosius et al. 2016) and slipping occurring during three-dimensional magnetic reconnection (Li & Zhang 2015;Li et al. 2016). While able to account for periodicities in both intensity and Doppler velocity these suggestions do not explicitly account for the phase velocity of the entire sawtooth structure, or for the relative phasing of the oscillations. Here we propose that the observations can be explained by a tearing mode instability occurring at a current sheet across which there is also a velocity shear.Using a linear model of this instability we reproduce the relative phase of the oscillations, as well as the phase velocity of the sawtooth structure. We suggest a geometry and local plasma parameters for the April 18 flare which would support our hypothesis. Under this proposal the combined spectral and spatial IRIS observations of this flare may provide the most compelling evidence to date of a tearing mode occurring in the solar magnetic field.

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QUASI-PERIODIC FLUCTUATIONS AND CHROMOSPHERIC EVAPORATION IN A SOLAR FLARE RIBBON OBSERVED BYIRIS

Cited by 64 publications

References 55 publications

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Transition Region and Chromospheric Signatures of Impulsive Heating Events. I. Observations

Chromospheric evaporation flows and density changes deduced from Hinode/EIS during an M1.6 flare

Modeling a Propagating Sawtooth Flare Ribbon Structure as a Tearing Mode in the Presence of Velocity Shear

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