Catastrophic cooling and cessation of heating in the solar corona

Peter, Hardi; Bingert, Sven; Kamio, S.

doi:10.1051/0004-6361/201117889

Cited by 27 publications

(14 citation statements)

References 26 publications

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“…Recently, based upon the observed properties of the hot, and warm loops in active regions, Klimchuk et al (2010) have argued that the high concentration of heating low in the corona, and the steady or quasi-steady heating models (leading to thermal nonequilibrium) can be ruled out. However, Peter et al (2012) claim that a steady supply of energy is required even in the events of condensation in the corona, to keep the coronal pressure. They also suggested that thermal non-equilibrium can be a valuable tool in investigating the plasma dynamics and heat input in the regions where condensation forms.…”

Section: Summary and Discussionmentioning

confidence: 99%

OBSERVATIONS AND MODELING OF THE EMERGING EXTREME-ULTRAVIOLET LOOPS IN THE QUIET SUN AS SEEN WITH THESOLAR DYNAMICS OBSERVATORY

Chitta

Kariyappa

Ballegooijen

et al. 2013

ApJ

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We used data from the Helioseismic and Magnetic Imager (HMI), and Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO) to study coronal loops at small scales, emerging in the quiet Sun. With HMI line-of-sight magnetograms, we derive the integrated and unsigned photospheric magnetic flux at the loop footpoints in the photosphere. These loops are bright in the EUV channels of AIA. Using the six AIA EUV filters, we construct the differential emission measure (DEM) in the temperature range 5.7 − 6.5 in log T (K) for several hours of observations. The observed DEMs have a peak distribution around log T ≈ 6.3, falling rapidly at higher temperatures. For log T < 6.3, DEMs are comparable to their peak values within an order of magnitude. The emission weighted temperature is calculated, and its time variations are compared with those of magnetic flux. We present two possibilities for explaining the observed DEMs and temperatures variations. (a) Assuming the observed loops are comprised of hundred thin strands with certain radius and length, we tested three time-dependent heating models and compared the resulting DEMs and temperatures with the observed quantities. This modeling used Enthalpy-based Thermal Evolution of Loops (EBTEL), a zero-dimensional (0D) hydrodynamic code. The comparisons suggest that a medium frequency heating model with a population of different heating amplitudes can roughly reproduce the observations. (b) We also consider a loop model with steady heating and non-uniform cross-section of the loop along its length, and find that this model can also reproduce the observed DEMs, provided the loop expansion factor γ ∼ 5 -10. More observational constraints are required to better understand the nature of coronal heating in the short emerging loops on the quiet Sun.

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Section: Summary and Discussionmentioning

confidence: 99%

OBSERVATIONS AND MODELING OF THE EMERGING EXTREME-ULTRAVIOLET LOOPS IN THE QUIET SUN AS SEEN WITH THESOLAR DYNAMICS OBSERVATORY

Chitta

Kariyappa

Ballegooijen

et al. 2013

ApJ

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“…It is known that such heating is not able to keep loop atmosphere in steady equilibrium because they are thermally unstable (Antiochos and Klimchuk, 1991 ; Antiochos et al , 1999 ; Müller et al , 2004 ; Karpen and Antiochos, 2008 ; Mok et al , 2008 ). Catastrophic cooling occurs along the loops some time after the heating is switched on and might explain deviations from hydrostatic equilibrium, and some features of the light curves measured in the EUV band (Peter et al , 2012 ). However, the timescales required by this scenario seem too long compared to the measured loop lifetimes (Klimchuk et al , 2010 ).…”

Section: Loop Physics and Modelingmentioning

confidence: 99%

Coronal Loops: Observations and Modeling of Confined Plasma

Reale

2014

Living Rev. Solar Phys.

299

265

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Coronal loops are the building blocks of the X-ray bright solar corona. They owe their brightness to the dense confined plasma, and this review focuses on loops mostly as structures confining plasma. After a brief historical overview, the review is divided into two separate but not independent parts: the first illustrates the observational framework, the second reviews the theoretical knowledge. Quiescent loops and their confined plasma are considered and, therefore, topics such as loop oscillations and flaring loops (except for non-solar ones, which provide information on stellar loops) are not specifically addressed here. The observational section discusses the classification, populations, and the morphology of coronal loops, its relationship with the magnetic field, and the loop stranded structure. The section continues with the thermal properties and diagnostics of the loop plasma, according to the classification into hot, warm, and cool loops. Then, temporal analyses of loops and the observations of plasma dynamics, hot and cool flows, and waves are illustrated. In the modeling section, some basics of loop physics are provided, supplying fundamental scaling laws and timescales, a useful tool for consultation. The concept of loop modeling is introduced and models are divided into those treating loops as monolithic and static, and those resolving loops into thin and dynamic strands. More specific discussions address modeling the loop fine structure and the plasma flowing along the loops. Special attention is devoted to the question of loop heating, with separate discussion of wave (AC) and impulsive (DC) heating. Large-scale models including atmosphere boxes and the magnetic field are also discussed. Finally, a brief discussion about stellar coronal loops is followed by highlights and open questions.

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“…In Fig. 1 we display the synthesized emission in the AIA 171 Å channel from the computational domain showing plasma at just below 10 6 K. This image was synthesized using the AIA temperature response functions (Boerner et al, 2011;Peter et al, 2012).…”

Section: Synthesized and Real Euv Imagesmentioning

confidence: 99%

Constant cross section of loops in the solar corona

Peter

Bingert

2012

A&A

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Context. The corona of the Sun is dominated by emission from loop-like structures. When observed in X-ray or extreme ultraviolet emission, these million K hot coronal loops show a more or less constant cross section. Aims. In this study we show how the interplay of heating, radiative cooling, and heat conduction in an expanding magnetic structure can explain the observed constant cross section. Methods. We employ a three-dimensional magnetohydrodynamics (3D MHD) model of the corona. The heating of the coronal plasma is the result of braiding of the magnetic field lines through footpoint motions and subsequent dissipation of the induced currents. From the model we synthesize the coronal emission, which is directly comparable to observations from, e.g., the Atmospheric Imaging Assembly on the Solar Dynamics Observatory (AIA/SDO). Results. We find that the synthesized observation of a coronal loop seen in the 3D data cube does match actually observed loops in count rate and that the cross section is roughly constant, as observed. The magnetic field in the loop is expanding and the plasma density is concentrated in this expanding loop; however, the temperature is not constant perpendicular to the plasma loop. The higher temperature in the upper outer parts of the loop is so high that this part of the loop is outside the contribution function of the respective emission line(s). In effect, the upper part of the plasma loop is not bright and thus the loop actually seen in coronal emission appears to have a constant width. Conclusions. From this we can conclude that the underlying field-line-braiding heating mechanism provides the proper spatial and temporal distribution of the energy input into the corona -at least on the observable scales.

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Catastrophic cooling and cessation of heating in the solar corona

Cited by 27 publications

References 26 publications

OBSERVATIONS AND MODELING OF THE EMERGING EXTREME-ULTRAVIOLET LOOPS IN THE QUIET SUN AS SEEN WITH THESOLAR DYNAMICS OBSERVATORY

OBSERVATIONS AND MODELING OF THE EMERGING EXTREME-ULTRAVIOLET LOOPS IN THE QUIET SUN AS SEEN WITH THESOLAR DYNAMICS OBSERVATORY

Coronal Loops: Observations and Modeling of Confined Plasma

Constant cross section of loops in the solar corona

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