Ambipolar Diffusion in the Lower Solar Atmosphere: MHD Simulations of a Sunspot

TL;DR

This study uses MHD simulations to explore how ambipolar diffusion influences wave propagation in the partially ionized lower solar atmosphere, emphasizing its significance in the dynamics of sunspot regions.

Contribution

It introduces a detailed simulation approach incorporating ambipolar diffusion to better understand wave behavior in the lower solar atmosphere, highlighting its importance in modeling and interpretation.

Findings

Ambipolar diffusion significantly affects wave characteristics in the weakly ionized regions.

Including ambipolar diffusion alters the energy spectral densities of propagating waves.

The results suggest the necessity of considering ambipolar diffusion in solar atmospheric models.

Abstract

Magnetohydrodynamic (MHD) simulations of the solar atmosphere are often performed under the assumption that the plasma is fully ionized. However, in the lower solar atmosphere a reduced temperature often results in only the partial ionization of the plasma. The interaction between the decoupled neutral and ionized components of such a partially ionized plasma produces ambipolar diffusion. To investigate the role of ambipolar diffusion in propagating wave characteristics in the photosphere and chromosphere, we employ the Mancha3D numerical code to model magnetoacoustic waves propagating through the atmosphere immediately above the umbra of a sunspot. We solve the non-ideal MHD equations for data-driven perturbations to the magnetostatic equilibrium and the effect of ambipolar diffusion is investigated by varying the simulation to include additional terms in the MHD equations that account for this process. Analyzing the energy spectral densities for simulations with/without ambipolar diffusion, we find evidence to suggest that ambipolar diffusion plays a pivotal role in wave characteristics in the weakly ionized low density regions, hence maximizing the local ambipolar diffusion coefficient. As a result, we propose that ambipolar diffusion is an important mechanism that requires careful consideration into whether it should be included in simulations, and whether it should be utilized in the analysis and interpretation of particular observations of the lower solar atmosphere.