Heating of the Solar Chromosphere and Corona by Alfvén Wave Turbulence (original) (raw)
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The Astrophysical Journal, 2005
We show that the coronal heating and the fast solar wind acceleration in the coronal holes are natural consequence of the footpoint fluctuations of the magnetic fields at the photosphere, by performing onedimensional magnetohydrodynamical simulation with radiative cooling and thermal conduction. We initially set up a static open flux tube with temperature 10 4 K rooted at the photosphere. We impose transverse photospheric motions corresponding to the granulations with velocity dv ⊥ = 0.7km/s and period between 20 seconds and 30 minutes, which generate outgoing Alfvén waves. We self-consistently treat these waves and the plasma heating. After attenuation in the chromosphere by ≃ 85% of the initial energy flux, the outgoing Alfvén waves enter the corona and contribute to the heating and acceleration of the plasma mainly by the nonlinear generation of the compressive waves and shocks. Our result clearly shows that the initial cool and static atmosphere is naturally heated up to 10 6 K and accelerated to ≃ 800km/s. The mpeg movie for is available at \protect\vrule width0pt\protect\href{http://www-tap.scphys.kyoto-u.ac.jp\\string\~stakeru/research/suzuki\_2005
2005
We show that the coronal heating and the fast solar wind acceleration in the coronal holes are natural consequence of the footpoint fluctuations of the magnetic fields at the photosphere, by performing onedimensional magnetohydrodynamical simulation with radiative cooling and thermal conduction. We initially set up a static open flux tube with temperature 10 4 K rooted at the photosphere. We impose transverse photospheric motions corresponding to the granulations with velocity dv ⊥ = 0.7km/s and period between 20 seconds and 30 minutes, which generate outgoing Alfvén waves. We self-consistently treat these waves and the plasma heating. After attenuation in the chromosphere by ≃ 85% of the initial energy flux, the outgoing Alfvén waves enter the corona and contribute to the heating and acceleration of the plasma mainly by the nonlinear generation of the compressive waves and shocks. Our result clearly shows that the initial cool and static atmosphere is naturally heated up to 10 6 K and accelerated to ≃ 800km/s.
Threaded-field-line Model for the Low Solar Corona Powered by the Alfvén Wave Turbulence
The Astrophysical Journal
We present an updated global model of the solar corona, including the transition region. We simulate the realistic three-dimensional (3D) magnetic field using the data from the photospheric magnetic field measurements and assume the magnetohydrodynamic (MHD) Alfvén wave turbulence and its nonlinear dissipation to be the only source for heating the coronal plasma and driving the solar wind. In closed-field regions, the dissipation efficiency in a balanced turbulence is enhanced. In the coronal holes, we account for a reflection of the outward-propagating waves, which is accompanied by the generation of weaker counterpropagating waves. The nonlinear cascade rate degrades in strongly imbalanced turbulence, thus resulting in colder coronal holes. The distinctive feature of the presented model is the description of the low corona as almost-steady-state low-beta plasma motion and heat flux transfer along the magnetic field lines. We trace the magnetic field lines through each grid point o...
Magnetohydrodynamic Waves and Coronal Heating: Unifying Empirical and MHD Turbulence Models
The Astrophysical Journal, 2013
We present a new global model of the solar corona, including the low corona, the transition region and the top of chromosphere. The realistic 3D magnetic field is simulated using the data from the photospheric magnetic field measurements. The distinctive feature of the new model is incorporating the MHD Alfven wave turbulence. We assume this turbulence and its non-linear dissipation to be the only momentum and energy source for heating the coronal plasma and driving the solar wind. The difference between the turbulence dissipation efficiency in coronal holes and that in closed field regions is because the non-linear cascade rate degrades in strongly anisotropic (imbalanced) turbulence in coronal holes (no inward propagating wave), thus resulting in colder coronal holes with the bi-modal solar wind originating from them. The detailed presentation of the theoretical model is illustrated with the synthetic images for multi-wavelength EUV emission compared with the observations from SDO AIA and Stereo EUVI instruments for the Carrington rotation 2107.
Alfven waves in the solar corona and solar wind
Advances in Space Research - ADV SPACE RES, 1994
In situ solar wind measurements of magnetohydrodynamic (MHD) turbulence first showed, 20 years ago, that Alfven waves propagating away from the sun are a dominant component, at least in high speed streams at solar minimum, with sufficient energy to explain the heating of the distant solar wind. Here we discuss some aspects of the propagation of these waves upward from the solar coronal base, where they are presumably generated, with particular emphasis on the effects of the large scale gradients on the transmission, the development of turbulence and wave dissipation.
A Study of Alfvén Wave Propagation and Heating the Chromosphere
The Astrophysical Journal, 2013
Alfvén wave propagation, reflection, and heating of the chromosphere are studied for a one-dimensional solar atmosphere by self-consistently solving plasma, neutral fluid, and Maxwell's equations with incorporation of the Hall effect and strong electron-neutral, electron-ion, and ion-neutral collisions. We have developed a numerical model based on an implicit backward difference formula of second-order accuracy both in time and space to solve stiff governing equations resulting from strong inter-species collisions. A non-reflecting boundary condition is applied to the top boundary so that the wave reflection within the simulation domain can be unambiguously determined. It is shown that due to the density gradient the Alfvén waves are partially reflected throughout the chromosphere and more strongly at higher altitudes with the strongest reflection at the transition region. The waves are damped in the lower chromosphere dominantly through Joule dissipation, producing heating strong enough to balance the radiative loss for the quiet chromosphere without invoking anomalous processes or turbulences. The heating rates are larger for weaker background magnetic fields below ∼500 km with higher-frequency waves subject to heavier damping. There is an upper cutoff frequency, depending on the background magnetic field, above which the waves are completely damped. At the frequencies below which the waves are not strongly damped, the interaction of reflected waves with the upward propagating waves produces power at their double frequencies, which leads to more damping. The wave energy flux transmitted to the corona is one order of magnitude smaller than that of the driving source.
Estimating the contribution of Alfvén waves to the process of heating the quiet solar corona
We solve numerically the ideal magnetohydrodynamic equations with an external gravitational field in 2D in order to study the effects of impulsively generated linear and non-linear Alfvén waves into isolated solar arcades and coronal funnels. We analyse the region containing the interface between the photosphere and the corona. The main interest is to study the possibility that Alfvén waves triggers the energy flux transfer towards the quiet solar corona and heat it, including the case that two consecutive waves can occur. We find that in the case of arcades, short or large, the transferred fluxes by Alfvén waves are sufficient to heat the quiet corona only during a small lapse of time and in a certain region. In the case of funnels the threshold is achieved only when the wave is faster than 10 km s −1 , which is extremely high. We conclude from our analysis, that Alfvén waves, even in the optimistic scenario of having two consecutive Alfvén wave pulses, cannot transport enough energy as to heat the quiet corona.
The Astrophysical Journal, 2012
The heating and acceleration of the solar wind is an active area of research. Alfvén waves, because of their ability to accelerate and heat the plasma, are a likely candidate in both processes. Many models have explored wave dissipation mechanisms which act either in closed or open magnetic field regions. In this work, we emphasize the boundary between these regions, drawing on observations which indicate unique heating is present there. We utilize a new solar corona component of the Space Weather Modeling Framework, in which Alfvén wave energy transport is self-consistently coupled to the magnetohydrodynamic equations. In this solar wind model, the wave pressure gradient accelerates and wave dissipation heats the plasma. Kolmogorov-like wave dissipation as expressed by Hollweg along open magnetic field lines was presented in van der Holst et al. Here, we introduce an additional dissipation mechanism: surface Alfvén wave (SAW) damping, which occurs in regions with transverse (with respect to the magnetic field) gradients in the local Alfvén speed. For solar minimum conditions, we find that SAW dissipation is weak in the polar regions (where Hollweg dissipation is strong), and strong in subpolar latitudes and the boundaries of open and closed magnetic fields (where Hollweg dissipation is weak). We show that SAW damping reproduces regions of enhanced temperature at the boundaries of open and closed magnetic fields seen in tomographic reconstructions in the low corona. Also, we argue that Ulysses data in the heliosphere show enhanced temperatures at the boundaries of fast and slow solar wind, which is reproduced by SAW dissipation. Therefore, the model's temperature distribution shows best agreement with these observations when both dissipation mechanisms are considered. Lastly, we use observational constraints of shock formation in the low corona to assess the Alfvén speed profile in the model. We find that, compared to a polytropic solar wind model, the wave-driven model with physical dissipation mechanisms presented in this work is more aligned with an empirical Alfvén speed profile. Therefore, a wave-driven model which includes the effects of SAW damping is a better background to simulate coronal-mass-ejection-driven shocks.
The Astrophysical Journal, 1998
We present the Ðrst model of resonant heating of coronal loops that incorporates the dependence of the loop density on the heating rate. By adopting the quasi-static equilibrium scaling law o P Q5@7, where o is the density and Q is the volumetric heating rate, we are able to approximate the well-known phenomena of chromospheric evaporation and chromospheric condensation, which regulate the coronal density. We combine this scaling law with a quasi-nonlinear MHD model for the resonant absorption of Alfve n waves in order to study the spatial and temporal dependence of the heating. We Ðnd that the heating is concentrated in multiple resonance layers, rather than in the single layer of previous models, and that these layers drift throughout the loop to heat the entire volume. These newfound properties are in much better agreement with coronal observations.
Alfvénic waves with sufficient energy to power the quiet solar corona and fast solar wind
Nature, 2011
Energy is required to heat the outer solar atmosphere to millions of degrees (refs 1, 2) and to accelerate the solar wind to hundreds of kilometres per second (refs 2-6). Alfvén waves (travelling oscillations of ions and magnetic field) have been invoked as a possible mechanism to transport magneto-convective energy upwards along the Sun's magnetic field lines into the corona. Previous observations 7 of Alfvénic waves in the corona revealed amplitudes far too small (0.5 km s 21 ) to supply the energy flux (100-200 W m 22 ) required to drive the fast solar wind 8 or balance the radiative losses of the quiet corona 9 . Here we report observations of the transition region (between the chromosphere and the corona) and of the corona that reveal how Alfvénic motions permeate the dynamic and finely structured outer solar atmosphere. The ubiquitous outward-propagating Alfvénic motions observed have amplitudes of the order of 20 km s 21 and periods of the order of 100-500 s throughout the quiescent atmosphere (compatible with recent investigations 7,10 ), and are energetic enough to accelerate the fast solar wind and heat the quiet corona.