Chromospheric Heating in the Late Phase of Two‐Ribbon Flares

Czaykowska, A.; Alexander, David; Pontieu, Bart De

doi:10.1086/320553

Cited by 57 publications

(36 citation statements)

References 35 publications

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“…Karpen & Devore (1987) carried out numerical simulations exploring the effects of nonlocal and saturated heat flux in addition to classical Spitzer heat flux. Observational evidence for such "gentle" evaporation was found by Zarro & Lemen (1988) in observations from the Solar Maximum Mission, and the flows observed by Milligan et al (2006a) and Czaykowska et al (1999Czaykowska et al ( , 2001 were also found to be consistent with conductive evaporation, due to both their relatively low speeds and absence of significant HXR radiation.…”

Section: Introductionmentioning

confidence: 69%

Observations of conduction driven evaporation in the early rise phase of solar flares

Battaglia¹,

Fletcher

Benz³

2009

A&A

107

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Context. The classical flare picture features a beam of electrons, which were accelerated in a site in the corona, hitting the chromosphere. The electrons are stopped in the dense chromospheric plasma, emitting bremsstrahlung in hard X-rays. The ambient material is heated by the deposited energy and expands into the magnetic flare loops, a process termed chromospheric evaporation. In this view hard X-ray emission from the chromosphere is succeeded by soft-X-ray emission from the hot plasma in the flare loop, the soft X-ray emission being a direct consequence of the impact of the non-thermal particle beam. However, observations of events exist in which a pronounced increase in soft X-ray emission is observed minutes before the onset of the hard X-ray emission. Such pre-flare emission clearly contradicts the classical flare picture. Aims. For the first time, the pre-flare phase of such solar flares is studied in detail. The aim is to understand the early rise phase of these events. We want to explain the time evolution of the observed emission by means of alternative energy transport mechanisms such as heat conduction. Methods. RHESSI events displaying pronounced pre-flare emission were analyzed in imaging and spectroscopy. The time evolution of images and full sun spectra was investigated and compared to the theoretical expectations from conduction driven chromospheric evaporation. Results. The pre-flare phase is characterized by purely thermal emission from a coronal source with increasing emission measure and density. After this earliest phase, a small non-thermal tail to higher energies appears in the spectra, becoming more and more pronounced. However, images still only display one X-ray source, implying that this non-thermal emission is coronal. The increase of emission measure and density indicates that material is added to the coronal region. The most plausible origin is evaporated material from the chromosphere. Energy provided by a heat flux is capable of driving chromospheric evaporation. We show that the often used classical Spitzer treatment of the conductive flux is not applicable. The conductive flux is saturated. During the preflare-phase, the temperature of the coronal source remains constant or increases. Continuous heating in the corona is necessary to explain this observation. Conclusions. The observations of the pre-flare phase of four solar flares are consistent with chromospheric evaporation driven by a saturated heat flux. Additionally, continuous heating in the corona is necessary to sustain the observed temperature.

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Section: Introductionmentioning

confidence: 69%

Observations of conduction driven evaporation in the early rise phase of solar flares

Battaglia¹,

Fletcher

Benz³

2009

A&A

107

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“…This is rarely seen in spatially unresolved observations (Mariska et al 1993). At the spatial resolution of several thousand kilometers some completely blueshifted high temperature profiles are observed (e.g., Czaykowska et al 2001;Doschek et al 2013). At the approximately 200 km spatial resolution of IRIS, completely blueshifted Fe XXI emission is observed routinely (Tian et al 2014Graham & Cauzzi 2015;Young et al 2015;Polito et al 2016).…”

Section: Introductionmentioning

confidence: 93%

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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“…The upper two panels show the radio spectrogram for SOL1980-03-29T09:18, with the lower one filtered to show temporal gradients; the bottom two panels show the radio flux integrated over 100-400 MHz and the HXR flux. from thermal conduction from the overlying hot loops (see the analysis of Czaykowska et al 2001). The flare ribbons in Hα can be some tens of arcseconds wide, particularly in the gradual phase, and show internal structure (also visible in some cases in UV).…”

Section: Morphology Of Flare Footpoints and Ribbonsmentioning

confidence: 99%

“…These can be used to determine the expected momentum balance between the evaporated and condensing material (Canfield et al 1987). Gentle Evaporation: Plasma flows attributed to gentle evaporation driven by thermal conduction from the overlying hot corona have frequently been observed during the gradual/decay phase of flares, after the non-thermal beam heating has ceased and upflows are sustained by the thermal conduction fronts set up by the steep temperature gradients (e.g., Schmieder et al 1987;Zarro & Lemen 1988;Czaykowska et al 1999Czaykowska et al , 2001). However, gentle evaporation due to a weak non-thermal electron flux has only recently been observed by SOHO/CDS in conjunction with RHESSI in SOL2002-07-15T11:55 (C9.1) (Milligan et al 2006b).…”

Section: Chromospheric Evaporationmentioning

confidence: 99%

An Observational Overview of Solar Flares

et al. 2011

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We present an overview of solar flares and associated phenomena, drawing upon a wide range of observational data primarily from the RHESSI era. Following an introductory discussion and overview of the status of observational capabilities, the article is split into topical sections which deal with different areas of flare phenomena (footpoints and ribbons, coronal sources, relationship to coronal mass ejections) and their interconnections. We also discuss flare soft X-ray spectroscopy and the energetics of the process. The emphasis is to describe the observations from multiple points of view, while bearing in mind the models that link them to each other and to theory. The present theoretical and observational understanding of solar flares is far from complete, so we conclude with a brief discussion of models, and a list of missing but important observations.

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Chromospheric Heating in the Late Phase of Two‐Ribbon Flares

Cited by 57 publications

References 35 publications

Observations of conduction driven evaporation in the early rise phase of solar flares

Observations of conduction driven evaporation in the early rise phase of solar flares

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

An Observational Overview of Solar Flares

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