Models of coronal heating, turbulence and fast reconnection

Velli, Marco; Pucci, Fulvia; Rappazzo, A. F.; Tenerani, Anna

doi:10.1098/rsta.2014.0262

Cited by 26 publications

(25 citation statements)

References 24 publications

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“…There is, however, increasing consensus that 'the' coronal heating mechanism is unlikely to exist, but rather coronal heating is due to different mechanisms in different places and/or at different times. Furthermore, the traditional dichotomy between waves and reconnection is not appropriate, since there are interactions between these processes (waves may drive reconnection and vice versa); also turbulence, which may combine aspects of both wave and reconnection scenarios, is likely to play an important role [9]. Recent work proposing coronal heating through Alfvénic turbulence [10] has attracted much attention.…”

Section: The Coronal Heating Problemmentioning

confidence: 99%

Recent advances in coronal heating

Moortel

Browning

2015

Phil. Trans. R. Soc. A.

116

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The solar corona, the tenuous outer atmosphere of the Sun, is orders of magnitude hotter than the solar surface. This 'coronal heating problem' requires the identification of a heat source to balance losses due to thermal conduction, radiation and (in some locations) convection. The review papers in this Theo Murphy meeting issue present an overview of recent observational findings, large- and small-scale numerical modelling of physical processes occurring in the solar atmosphere and other aspects which may affect our understanding of the proposed heating mechanisms. At the same time, they also set out the directions and challenges which must be tackled by future research. In this brief introduction, we summarize some of the issues and themes which reoccur throughout this issue

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Section: The Coronal Heating Problemmentioning

confidence: 99%

Recent advances in coronal heating

Moortel

Browning

2015

Phil. Trans. R. Soc. A.

116

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“…The physical mechanisms responsible for the solar-corona heating are still in debate, but they all require magnetic fields as a key ingredient (see, e.g. Aschwanden 2005; Klimchuk 2015; Velli et al 2015). The solar magnetic field (a product of the solar dynamo that operates within the convection zone) threads the solar photosphere, expands throughout the solar atmosphere and eventually connects with and energizes the solar wind.…”

Section: Introductionmentioning

confidence: 99%

Magnetic Braking of Sun-like and Low-mass Stars: Dependence on Coronal Temperature

Pantolmos

2017

ApJ

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Sun-like and low-mass stars possess high temperature coronae and lose mass in the form of stellar winds, driven by thermal pressure and complex magnetohydrodynamic processes. These magnetized outflows probably do not significantly affect the star's structural evolution on the Main Sequence, but they brake the stellar rotation by removing angular momentum, a mechanism known as magnetic braking. Previous studies have shown how the braking torque depends on magnetic field strength and geometry, stellar mass and radius, mass-loss rate, and the rotation rate of the star, assuming a fixed coronal temperature. For this study we explore how different coronal temperatures can influence the stellar torque. We employ 2.5D, axisymmetric, magnetohydrodynamic simulations, computed with the PLUTO code, to obtain steady-state wind solutions from rotating stars with dipolar magnetic fields. Our parameter study includes 30 simulations with variations in coronal temperature and surfacemagnetic-field strength. We consider a Parker-like (i.e. thermal-pressure-driven) wind, and therefore coronal temperature is the key parameter determining the velocity and acceleration profile of the flow. Since the mass loss rates for these types of stars are not well constrained, we determine how torque scales for a vast range of stellar mass loss rates. Hotter winds lead to a faster acceleration, and we show that (for a given magnetic field strength and mass-loss rate) a hotter outflow leads to a weaker torque on the star. We derive new predictive torque formulae for each temperature, which quantifies this effect over a range of possible wind acceleration profiles.

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“…The analysis also shows that while the larger temporal scales present multifractality, the multiscaling is lost at the smaller temporal scales. While a proper comparison would be between the observational data and synthetic time series for 171 Å emission, this initial result is important in that in this case the detailed impulsive heating mechanism is not prescribed a priori but is determined self-consistently by the development of the turbulent nonlinear dynamics as put forward in the Parker model for coronal heating (Einaudi et al 1996;Dmitruk & Gómez 1997, Velli et al 2015Parker & Rappazzo 2016).…”

Section: Summary and Discussionmentioning

confidence: 99%

Multifractal Solar Euv Intensity Fluctuations and Their Implications for Coronal Heating Models

Cadavid

Lawrence

Christian

et al. 2016

ApJ

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We investigate the scaling properties of the long-range temporal evolution and intermittency of Atmospheric Imaging Assembly/Solar Dynamics Observatoryintensity observations in four solar environments: anactive region core, a weak emission region, and two core loops. We use two approaches: the probability distribution function (PDF) of time series incrementsand multifractal detrended fluctuation analysis (MF-DFA). Noise taints the results, so we focus on the 171 Å waveband, which has the highest signal-to-noise ratio. The lags between pairs of wavebands distinguish between coronal versus transition region (TR) emission. In all physical regions studied, scaling in the range of 15-45 minutes is multifractal, and the time series are anti-persistent on average. The degree of anti-correlation in the TR time series is greater than that for coronal emission. The multifractality stems from long-term correlations in the data rather than the wide distribution of intensities. Observations in the 335 Å waveband can be described in terms of a multifractal with added noise. The multiscaling of the extreme-ultraviolet data agrees qualitatively with the radiance from a phenomenological model of impulsive bursts plus noise, and also from ohmic dissipation in a reduced magnetohydrodynamic model for coronal loop heating. The parameter space must be further explored to seek quantitative agreement. Thus, the observational "signatures" obtained by the combined tests of the PDF of increments and the MF-DFA offer strong constraints thatcan systematically discriminate among models for coronal heating.

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Models of coronal heating, turbulence and fast reconnection

Cited by 26 publications

References 24 publications

Recent advances in coronal heating

Recent advances in coronal heating

Magnetic Braking of Sun-like and Low-mass Stars: Dependence on Coronal Temperature

Multifractal Solar Euv Intensity Fluctuations and Their Implications for Coronal Heating Models

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