The Heating of the Solar Corona

Viall, N. M.; Moortel, I. De; Downs, Cooper; Klimchuk, J. A.; Parenti, S.; Reale, F.

doi:10.1002/9781119815600.ch2

Cited by 13 publications

(13 citation statements)

References 438 publications

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“…Wave dissipation and magnetic field reconnection are present in the solar atmosphere and are the main candidate processes for the solar corona's plasma heating. See for instance Reale (2014) and Viall et al (2021) for a review on the argument.…”

Section: Introductionmentioning

confidence: 99%

“…His theory is based on the shuffling and inter-mixing of the photospheric footpoints of magnetic flux tubes, which would produce reconnection and subsequent formation of tiny current sheets in which the energy is dissipated. This idea has been generalized in recent years, particularly for active region heating where processes other than reconnection (wave propagation) may also be at the origin of the nanoflares energy (Van Doorsselaere et al 2020;Viall et al 2021). For instance, small-scale energy dissipation can occur through a turbulent cascade created by the interaction of nonlinear waves (e.g., Buchlin & Velli 2007) or through shock heating from nonlinear mode conversion (Moriyasu et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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Temperature of quiet Sun small scale brightenings observed by EUI on board Solar Orbiter: Evidence for a cooler component

Parenti

Auchère

et al. 2023

A&A

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Context. On May 30, 2020, small and short-lived extreme-UV (EUV) brightenings in the quiet Sun were observed over a four-minute sequence by the EUV channel of the Extreme Ultraviolet Imager – High Resolution Imager (EUIHRIEUV) on board the Solar Orbiter. The brightenings’ physical origin and possible impact on coronal or transition region (TR) heating are still to be determined. Aims. Our aim is to derive the statistical thermal evolution of these events in order to establish their coronal or TR origin. Methods. Our thermal analysis took advantage of the multithermal sensitivity of the Atmospheric Imaging Assembly (AIA) imager on board the Solar Dynamics Observatory. We first identified the HRIEUV events in the six coronal bands of AIA. We then performed a statistical time lag analysis that quantified the delays between the light curves from different bands, as these time lags can give significant insight into the temperature evolution of the events. The analysis was performed taking into account the possible contribution of the background and foreground emissions to the results. Results. For all nine couples of AIA bands analyzed, the brightening events are characterized by time lags inferior to the AIA cadence of 12 s. Our interpretation for these short time lags is the possible copresence of events that reach or do not reach coronal temperatures (≈1 MK). We believe that the cool population dominates the events analyzed in this work.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Temperature of quiet Sun small scale brightenings observed by EUI on board Solar Orbiter: Evidence for a cooler component

Parenti

Auchère

et al. 2023

A&A

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“…This paper reexamines the concept that the corona is observed to be in a state of continual dynamic readjustment. This idea has historically been inferred from decades of space observations at X-ray, EUV, and UV wavelengths, using evidence that is, when scrutinized, largely indirect (e.g., Viall et al 2021). Is the observable variability of coronal plasma related directly to irreversible heating, such as commonly assumed by, for example, nanoflares, reconnection, or wave turbulence?…”

Section: Introductionmentioning

confidence: 99%

Steadiness of Coronal Heating

Judge

2023

ApJ

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The EUI instrument on the Solar Orbiter spacecraft has obtained the most stable, high-resolution images of the solar corona from its orbit with a perihelion near 0.4 au. A sequence of 360 images obtained at 17.1 nm, between 2022 October 25 19:00 and 19:30 UT, is scrutinized. One image pixel corresponds to 148 km at the solar surface. The widely held belief that the outer atmosphere of the Sun is in a continuous state of magnetic turmoil is pitted against the EUI data. The observed plasma variations appear to fall into two classes. By far the dominant behavior is a very low amplitude variation in brightness (1%) in the coronal loops, with larger variations in some footpoint regions. No hints of observable changes in magnetic topology are associated with such small variations. The larger-amplitude, more rapid, rarer, and less well organized changes are associated with flux emergence. It is suggested therefore that while magnetic reconnection drives the latter, most of the active corona is heated with no evidence of a role for large-scale (observable) reconnection. Since most coronal emission-line widths are subsonic, the bulk of coronal heating, if driven by reconnection, can only be of tangentially discontinuous magnetic fields, with angles below about 0.5c S /c A ∼ 0.3β, with β the plasma beta parameter (∼0.01) and c S and c A the sound and Alfvén speeds, respectively. If heated by multiple small flare-like events, then these must be ≲1021 erg, i.e., picoflares. But processes other than reconnection have yet to be ruled out, such as viscous dissipation, which may contribute to the steady heating of coronal loops over active regions.

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“…The solar corona contains low-density plasma that is maintained at temperatures in excess of 1 million K, despite energy losses due to thermal conduction (to the chromosphere), optically thin radiation and solar wind (which carries energy and mass into Space). The exact processes which maintain these surprisingly high temperatures remain unclear and are the focus of one of the greatest unsolved questions in solar physics; the coronal heating problem (see reviews by [10][11][12][13][14][15][16][17]).…”

Section: Contextmentioning

confidence: 99%

How Transverse Waves Drive Turbulence in the Solar Corona

Howson

2022

Symmetry

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Oscillatory power is pervasive throughout the solar corona, and magnetohydrodynamic (MHD) waves may carry a significant energy flux throughout the Sun’s atmosphere. As a result, over much of the past century, these waves have attracted great interest in the context of the coronal heating problem. They are a potential source of the energy required to maintain the high-temperature plasma and may accelerate the fast solar wind. Despite many observations of coronal waves, large uncertainties inhibit reliable estimates of their exact energy flux, and as such, it remains unclear whether they can contribute significantly to the coronal energy budget. A related issue concerns whether the wave energy can be dissipated over sufficiently short time scales to balance the atmospheric losses. For typical coronal parameters, energy dissipation rates are very low and, thus, any heating model must efficiently generate very small-length scales. As such, MHD turbulence is a promising plasma phenomenon for dissipating large quantities of energy quickly and over a large volume. In recent years, with advances in computational and observational power, much research has highlighted how MHD waves can drive complex turbulent behaviour in the solar corona. In this review, we present recent results that illuminate the energetics of these oscillatory processes and discuss how transverse waves may cause instability and turbulence in the Sun’s atmosphere.

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The Heating of the Solar Corona

Cited by 13 publications

References 438 publications

Temperature of quiet Sun small scale brightenings observed by EUI on board Solar Orbiter: Evidence for a cooler component

Temperature of quiet Sun small scale brightenings observed by EUI on board Solar Orbiter: Evidence for a cooler component

Steadiness of Coronal Heating

How Transverse Waves Drive Turbulence in the Solar Corona

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