[论文解读] The role of ambipolar heating in the energy balance of solar prominences

Llorenç Melis, R. Soler|arXiv (Cornell University)|Mar 17, 2026

Solar and Space Plasma Dynamics被引用 0

一句话总结

本论文在自洽的一维 prominences 平衡沿 Kippenhahn–Schlüter 场线测试了伴隙扩散作为加热机制，显示它能在现实参数下帮助抵消损失并形成立体条状结构。

ABSTRACT

Solar prominence threads are typically located around magnetic dips, where cold and dense plasma is suspended against gravity in the hot corona thanks to the upward magnetic force. Because prominences are partially ionized, ambipolar diffusion can deposit part of the energy of their non-force-free magnetic field into the plasma. This ambipolar heating may therefore play a role in the energy balance of prominences. In this proof-of-concept work, we explore the effect of ambipolar diffusion in one-dimensional models that satisfy both mechanical equilibrium and energy balance. The magnetic configuration is based on the classic Kippenhahn-Schlüter model, incorporating a sheared magnetic field. The temperature profile along the magnetic field is computed numerically by balancing radiative losses, thermal conduction, and ambipolar heating. The resulting models consistently consist of a cold, dense, partially ionized thread with prominence core conditions, a very thin prominence-corona transition region, and an extended, hot, fully ionized region with coronal conditions. In addition to providing heating that partly compensates for radiative losses, ambipolar diffusion also gives rise to stationary flows associated with the gravitational drainage of neutrals in the partially ionized region. We investigate how the length of the cold threads depends on the central temperature, central pressure, magnetic field strength, and shear angle, and show that thread lengths compatible with observations are obtained for realistic values of these parameters. Therefore, we demonstrate that ambipolar diffusion plays a relevant role in this simple configuration, indicating that this effect should be incorporated into more elaborate multi-dimensional models and simulations.

研究动机与目标

• Motivate the study of energy balance in prominences beyond radiative cooling and standard heating
• Incorporate ambipolar diffusion as a heating term in a partially ionized plasma
• Develop a self-consistent 1D equilibrium that satisfies both mechanical balance and energy balance
• Demonstrate how ambipolar heating affects thread formation and stationary flows
• Identify parameter ranges yielding physically realistic prominence thread lengths

提出的方法

• Adopt a modified Kippenhahn–Schlüter magnetic configuration with a uniform horizontal field and a shear angle to model a dip supporting prominence plasma
• Use single-fluid MHD for partially ionized plasma with ambipolar diffusion as the non-ideal term in the induction equation
• Compute ionization fractions for H and He (via LTE/Saha-like relations) to determine mean atomic weight and thermodynamic properties
• Balance radiative losses, thermal conduction, and ambipolar heating to determine the temperature profile along a magnetic field line
• Derive ambipolar heating as Q_A = (η_A / μ0) (B0^2 cos^2 φ + B_z^2) (dB_z/dx)^2 and incorporate into the energy balance equation along s
• Solve the energy balance equation numerically along a field line using an iterative self-consistent approach until convergence (ε < 1e-7)
• Impose boundary conditions with central temperature T0, symmetry at x=0, and the positivity constraint L_rad > Q_A at the center

Figure 1: Ionization fractions of hydrogen and helium for $p=5\times 10^{-3}$ Pa as functions of the temperature, $T$ .

实验结果

研究问题

• RQ1 Does ambipolar diffusion provide a meaningful heating source that can partially balance radiative losses in prominences?
• RQ2 How does ambipolar heating influence the temperature, density, and velocity structure along a prominence thread?
• RQ3 What parameter ranges (central temperature, central pressure, field strength, shear angle) yield self-consistent equilibria that resemble observed thread lengths?
• RQ4 Are stationary flows induced by ambipolar diffusion generally present, and what is their nature along the field line?

主要发现

• Ambipolar heating contributes to the energy balance and can partially offset radiative losses in the modeled prominence plasma
• The equilibrium develops stationary flows related to gravitational drainage of neutrals in the partially ionized region, driven by ambipolar diffusion
• A cold, dense thread forms with a length a ≈ 2.56 Mm in the reference model, consistent with observed thread scales
• Thread length increases or decreases with central temperature, central pressure, magnetic field strength, and shear angle within realistic parameter ranges
• The study demonstrates that ambipolar diffusion plays a relevant role in the energy balance and should be included in more complex multi-dimensional models

Figure 2: Visualization in 3D of the magnetic dip obtained for the reference model with $T_{0}=$ 8,000 K, $p_{0}=5\times 10^{-3}$ Pa, $B_{0}=10$ G, and $\phi=88^{\circ}$ . The color gradient denotes the variation of the density along the magnetic field line. Note that the axes are not to scale.