How Turbulent is the Magnetically Closed Corona?

Klimchuk, J. A.; Antiochos, S. K.

doi:10.3389/fspas.2021.662861

Cited by 9 publications

(4 citation statements)

References 28 publications

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“…The other hypothesis is that true hydrodynamic-like turbulence kicks in at low temperatures, and that this turbulence accounts for the energy transport rather than the thermal conduction (Cally 1990). There is no doubt that, under many circumstances, turbulence can transport heat much more effectively than thermal conduction-for example, in the solar convection zone-but it is far from clear whether such turbulence can ever be generated in the low-beta corona and TR (e.g., Klimchuk & Antiochos 2021). It appears, therefore, that the physical origin of the form of the DEM of the lower TR is still not fully understood.…”

Section: Orcid Idsmentioning

confidence: 99%

The Transition Region of Solar Flare Loops

Gontikakis

Antiochos

Young

2023

ApJ

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The transition region between the Sun’s corona and chromosphere is important to the mass and energy transfer from the lower atmosphere to the corona; consequently, this region has been studied intensely with ultraviolet and extreme ultraviolet (EUV) observations. A major result of these studies is that the amount of plasma at low temperatures, <105 K, is far too large to be compatible with the standard theory of thermal conductivity. However, it is not clear whether the disagreement lies with a problem in the observations or a problem in the theory. We address this issue by analyzing high–spatial and temporal resolution EUV observations from an X1.6-class flare, taken with the Interface Region Imaging Spectrograph and the Solar Dynamic Observatory/Atmospheric Imaging Assembly (AIA). These data allow us to isolate the emission of flare loops from that of surrounding structures. We compare the emission measures (EMs) derived from the C ii 1334.525 Å and Si iv 1402.770 Å transition region spectral lines, the Fe xxi 1354.066 Å flare line, and the AIA 171 Å coronal images. We find that the EM ratios are incompatible with a standard conduction-dominated transition region model. Furthermore, the large increases in the EM magnitudes due to flare heating make it highly unlikely that the disagreement between data and theory is due to observational uncertainties in the source of the emission. We conclude that the standard Spitzer–Härm thermal conductivity must be invalid for, at least, flare loops. We discuss the possibility that turbulent suppression of thermal conduction can account for our results.

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Section: Orcid Idsmentioning

confidence: 99%

The Transition Region of Solar Flare Loops

Gontikakis

Antiochos

Young

2023

ApJ

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“…However, if the instability induces true MHD turbulence, the energy dissipation rates may be largely independent of the dissipation coefficients (e.g., [48]). Consequently, whether the corona is truly turbulent is an important open question, which has significant consequences for the energetics of the system [73].…”

Section: Discussionmentioning

confidence: 99%

Heating and Cooling in Transversely Oscillating Coronal Loops Powered by Broadband, Multi-Directional Wave Drivers

Howson

Moortel

2023

Physics

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Recent studies have identified the potential for coronal wave heating to balance radiative losses in a transversely oscillating low-density loop undergoing resonant absorption, phase mixing and the Kelvin–Helmholtz instability. This result relied on a continuous, resonant oscillatory driver acting on one of the loop footpoints and similar setups with non-resonant driving produce insufficient heating. Here, we consider broadband and multi-directional drivers with power in both resonant and non-resonant frequencies. Using three-dimensional magnetohydrodynamic simulations, we impose transverse, continuous velocity drivers at the footpoints of a coronal loop, which is dense in comparison to the background plasma. We include the effects of optically thin radiation and a uniform background heating term that maintains the temperature of the external plasma but is insufficient to balance energy losses within the loop. For both broadband and multi-directional drivers, we find that the energy dissipation rates are sufficient to balance the average energy losses throughout the simulation volume. Resonant components of the wave driver efficiently inject energy into the system and these frequencies dominate the energetics. Although the mean radiative losses are balanced, the loop core cools in all cases as the wave heating rates are locally insufficient, despite the relatively low density considered here.

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“…There is no doubt that under many circumstances turbulence can transport heat much more effectively than thermal conduction, for example, in the solar convection zone, but it is far from clear whether such turbulence can ever be generated in the low-beta corona and transition region (e.g. Klimchuk & Antiochos 2021). It appears, therefore, that the physical origin of the form of the DEM of the lower TR is still not fully understood.…”

Section: Discussionmentioning

confidence: 99%

The Transition Region of Solar Flare Loops

Gontikakis¹,

Antiochos²,

Young³

2023

Preprint

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The transition region between the Sun's corona and chromosphere is important to the mass and energy transfer from the lower atmosphere to the corona; consequently, this region has been studied intensely with ultraviolet (UV) and extreme ultraviolet observations. A major result of these studies is that the amount of plasma at temperatures < 10 5 K, is far too large to be compatible with the standard theory of thermal conductivity. However, it is not clear whether the disagreement lies with a problem in the observations or in the theory. We address this issue by analysing high-spatial and temporal resolution EUV observations from an X1.6-class flare taken with the Interface Region Imaging Spectrograph (IRIS) and the Solar Dynamic Observatory/Atmospheric Imaging Assembly (SDO/AIA). These data allow us to isolate the emission of flare loops from that of surrounding structures. We compare the Emission Measures (EMs) derived from the C II 1334.525Å, Si IV 1402.770Å transition region spectral lines, the Fe XXI 1354.066Å flare line and the AIA 171Å coronal images. We find that the EM ratios are incompatible with a standard conduction-dominated transition region model. Furthermore, the large increases in the EM magnitudes due to flare heating make it highly unlikely that the disagreement between data and theory is due to observational uncertainties in the source of the emission. We conclude that the standard Spitzer Harm thermal conductivity must be invalid for, at least, flare loops. We discuss the possibility that turbulent suppression of thermal conduction can account for our results.

show abstract

How Turbulent is the Magnetically Closed Corona?

Cited by 9 publications

References 28 publications

The Transition Region of Solar Flare Loops

The Transition Region of Solar Flare Loops

Heating and Cooling in Transversely Oscillating Coronal Loops Powered by Broadband, Multi-Directional Wave Drivers

The Transition Region of Solar Flare Loops

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