Abstract
In this paper we further develop a model for the heating of coronal loops by
Alfvèn wave turbulence (AWT). The Alfvèn waves are assumed to be launched
from a collection of kilogauss flux tubes in the photosphere at the two ends
of the loop. Using a three-dimensional magneto-hydrodynamic (MHD) model
for an active-region loop, we investigate how the waves from neighboring
flux tubes interact in the chromosphere and corona. For a particular
combination of model parameters we find that AWT can produce enough heat
to maintain a peak temperature of about 2.5 MK, somewhat lower than the
temperatures of 3 – 4 MK observed in the cores of active regions. The heating
rates vary strongly in space and time, but the simulated heating events have
durations less than 1 minute and are unlikely to reproduce the observed broad
Differential Emission Measure distributions of active regions. The simulated
spectral line non-thermal widths are predicted to be about 27 km s−1,
which is high compared to the observed values. Therefore, the present AWT
model does not satisfy the observational constraints. An alternative “magnetic
braiding” model is considered in which the coronal field lines are subject to slow
random footpoint motions, but we find that such long period motions produce
much less heating than the shorter period waves launched within the flux tubes.
We discuss several possibilities for resolving the problem of producing
sufficiently hot loops in active regions.
Alfvèn wave turbulence (AWT). The Alfvèn waves are assumed to be launched
from a collection of kilogauss flux tubes in the photosphere at the two ends
of the loop. Using a three-dimensional magneto-hydrodynamic (MHD) model
for an active-region loop, we investigate how the waves from neighboring
flux tubes interact in the chromosphere and corona. For a particular
combination of model parameters we find that AWT can produce enough heat
to maintain a peak temperature of about 2.5 MK, somewhat lower than the
temperatures of 3 – 4 MK observed in the cores of active regions. The heating
rates vary strongly in space and time, but the simulated heating events have
durations less than 1 minute and are unlikely to reproduce the observed broad
Differential Emission Measure distributions of active regions. The simulated
spectral line non-thermal widths are predicted to be about 27 km s−1,
which is high compared to the observed values. Therefore, the present AWT
model does not satisfy the observational constraints. An alternative “magnetic
braiding” model is considered in which the coronal field lines are subject to slow
random footpoint motions, but we find that such long period motions produce
much less heating than the shorter period waves launched within the flux tubes.
We discuss several possibilities for resolving the problem of producing
sufficiently hot loops in active regions.
| Original language | English |
|---|---|
| Article number | 46 |
| Journal | Astrophysical Journal |
| Volume | 849 |
| Issue number | 1 |
| Early online date | 17 Oct 2017 |
| DOIs | |
| Publication status | Published - 30 Oct 2017 |
Keywords
- Magnetohydrodynamics (MHD)
- Sun: corona
- Sun: magnetic fields
- Turbulence
- Waves
