On Solving the Coronal Heating Problem

By J. Klimchuk. 2005

734 citations recorded by the source corpus.

The question of what heats the solar corona remains one of the most important problems in astrophysics. Finding a definitive solution involves a number of challenging steps, beginning with an identification of the energy source and ending with a prediction of observable quantities that can be compared directly with actual observations. Critical intermediate steps include realistic modeling of both the energy release process (the conversion of magnetic stress energy or wave energy into heat) and the response of the plasma to the heating. A variety of difficult issues must be addressed: highly disparate spatial scales, physical connections between the corona and lower atmosphere, complex microphysics, and variability and dynamics. Nearly all of the coronal heating mechanisms that have been proposed produce heating that is impulsive from the perspective of elemental magnetic flux strands. It is this perspective that must be adopted to understand how the plasma responds and radiates. In our opinion, the most promising explanation offered so far is Parker's idea of nanoflares occurring in magnetic fields that become tangled by turbulent convection. Exciting new developments include the identification of the “secondary instability” as the likely mechanism of energy release and the demonstration that impulsive heating in sub-resolution strands can explain certain observed properties of coronal loops that are otherwise very difficult to understand. Whatever the detailed mechanism of energy release, it is clear that some form of magnetic reconnection must be occurring at significant altitudes in the corona (above the magnetic carpet), so that the tangling does not increase indefinitely. This article outlines the key elements of a comprehensive strategy for solving the coronal heating problem and warns of obstacles that must be overcome along the way.

Subfields: Astronomy and Astrophysics, Mechanical Engineering, Renewable Energy, Sustainability and the Environment

View Paper: https://www.semanticscholar.org/paper/a1cdb3e7bd25d70881a3883d2346967322732c4c

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Citations in the corpus

The EUV Imaging Spectrometer for Hinode (2007, methodology): “In addition, the spatially resolved loop temperature and density measurements that EIS will obtain will allow comparison with the output of increasingly sophisticated MHD models (Klimchuk, 2006).”
A NEW APPROACH TO ANALYZING SOLAR CORONAL SPECTRA AND UPDATED COLLISIONAL IONIZATION EQUILIBRIUM CALCULATIONS. II. UPDATED IONIZATION RATE COEFFICIENTS (2008, background): “For example, the so-called coronal heating problem remains unsolved (Gudiksen & Norlund 2005; Klimchuk 2006) and we are still unable to explain the onset processes that cause solar flares and coronal mass ejections (Forbes 2000; Priest & Forbes 2002).”
Self-consistent Coronal Heating and Solar Wind Acceleration from Anisotropic Magnetohydrodynamic Turbulence (2007, background): “For example, it seems increasingly clear that closed loops in the low corona are heated by smallscale, intermittent magnetic reconnection that is driven by the continual stressing of their magnetic footpoints (see recent reviews by Longcope 2004; Gudiksen 2005; Aschwanden 2006; Klimchuk 2006).”
Flows and Nonthermal Velocities in Solar Active Regions Observed with the EUV Imaging Spectrometer on Hinode: A Tracer of Active Region Sources of Heliospheric Magnetic Fields? (2008, methodology): “EIS can therefore help address fundamental unsolved problems in active region physics, such as heating in active region loops (e.g., Klimchuk 2006; Warren & Winebarger 2007), and the associations of active regions with the solar wind and heliospheric magnetic flux (e.g., Liewer et al. 2004;…”
Coronal Loops: Observations and Modeling of Confined Plasma (2010, background): “, 2001; Reale, 2005), in particular on coronal heating (Zirker, 1993; Cargill, 1995; Klimchuk, 2006), that have in general a larger or different scope but include information about coronal loops.”
Physics of Solar Prominences: II—Magnetic Structure and Dynamics (2010, background): “Condensations also form when the energy input is impulsive in nature and randomly distributed in time, as in nanoflare models of coronal heating (Klimchuk, 2006), so long as the average interval between energy bursts is shorter than the radiative loss time in the ambient corona (Karpen & Antiochos,…”
MULTISPECTRAL EMISSION OF THE SUN DURING THE FIRST WHOLE SUN MONTH: MAGNETOHYDRODYNAMIC SIMULATIONS (2008, methodology): “This mismatch has been discussed by Klimchuk (2006) and was also found by Mok et al. (2008), who concluded that dynamic solutions may be necessary to reproduce the observations.”
Highly Efficient Modeling of Dynamic Coronal Loops (2005, background): “For another, it moves up and down a significant distance in response to changes in the spatially integrated heating rate within the strand (Klimchuk 2006).”
Coronal Heating by MHD Waves (2020, background): “As the local density in closed loops is related to the magnitude of the heating (see e.g. Klimchuk 2006; Reale 2014), the phase mixing heating profile is not consistent with the heating profile to sustain the density profile.”
The multi-thermal emission in solar active regions (2013, background): “It is thought that individual magnetic flux tubes are isothermal, and thatresolved loops are composed of a superposition of such elementary structures (Klimchuk 2006).”
Magnetic Reconnection in Astrophysical and (2009, background): “This supports the idea that the solar corona is heated by small reconnection events, or nanoflares (Parker 1990, Klimchuk 2006; but see Aschwanden 2008).”
The Solar Orbiter mission (2020, background): “…mechanisms proposed attribute key roles to the Sun’s convective motions in the photosphere and its magnetic field, which can release energy via magnetic reconnection and/or guide waves that might dissipate energy in the corona (for reviews, see Klimchuk 2006; Reale 2010; Cranmer & Winebarger 2019).”
OBSERVING THE ROOTS OF SOLAR CORONAL HEATING—IN THE CHROMOSPHERE (2009, background): “Such models predict high-speed upflows at very high temperatures of several million degrees, with either lower velocities or no detectable upflows at lower temperatures (<1,000,000 K; Patsourakos & Klimchuk 2006).”
EXTENSION OF THE MURAM RADIATIVE MHD CODE FOR CORONAL SIMULATIONS (2016, background): “The nature of coronal heating has been a subject of heavy debate (see, e.g. Klimchuk 2006; van Ballegooijen et al. 2014), most of the discussion is focused on the time scales involved in the coronal energy transport and release.”
Solar Orbiter (2012, background): “eSOLA: Solar_Orbiter_Mueller+al.tex; 15 August 2019; 6:17; p. 9 Muller et al. connection are implicated theoretically and observationally in coronal heating and acceleration (for reviews, see, e.g., Klimchuk, 2006 and Reale, 2010). However, existing observations have not been able to adequately cons”
The magnetic field in the solar atmosphere (2014, background): “y Parnell and De Moortel, 2012). A discussion about the corresponding coronal heating processes is outside the scope of our review and interested readers might consult also the in-depth discussion by Klimchuk (2006) and dedicated chapters in Cranmer (2009) and Reale (2010). The time scale on which m”
The Polarimetric and Helioseismic Imager on Solar Orbiter (2019, background): “Nanoflares associated with magnetic reconnection and Ohmic dissipation at current sheets are prime candidate drivers of coronal heating (Parker 1988; Priest & Forbes 2002; Klimchuk 2006; Reale 2014), but it is not settled where the reconnection takes place.”