Two-fluid numerical simulations of solar spicules

TL;DR

This study uses advanced two-fluid numerical simulations to model the formation and evolution of solar spicules, revealing their shock-driven dynamics and neutral-dominated core, consistent with classical spicule observations.

Contribution

First two-fluid simulations of solar spicules that incorporate ion-neutral interactions and self-consistent magnetic field evolution.

Findings

Spicules are formed by shock steepening of pressure signals.

Spicules exhibit a 3-4 minute lifetime with upward velocities of 20-25 km/s.

Neutral component dominates the core structure of the simulated spicule.

Abstract

We aim to study the formation and evolution of solar spicules by means of numerical simulations of the solar atmosphere. With the use of newly developed JOANNA code, we numerically solve two-fluid (for ions + electrons and neutrals) equations in 2D Cartesian geometry. We follow the evolution of a spicule triggered by the time-dependent signal in ion and neutral components of gas pressure launched in the upper chromosphere. We use the potential magnetic field, which evolves self-consistently, but mainly plays a passive role in the dynamics. Our numerical results reveal that the signal is steepened into a shock that propagates upward into the corona. The chromospheric cold and dense plasma lags behind this shock and rises into the corona with a mean speed of 20-25 km s$^{-1}$. The formed spicule exhibits the upflow/downfall of plasma during its total lifetime of around 3-4 minutes, and it follows the typical characteristics of a classical spicule, which is modeled by magnetohydrodynamics. The simulated spicule consists of a dense and cold core that is dominated by neutrals. The general dynamics of ion and neutral spicules are very similar to each other. Minor differences in those dynamics result in different widths of both spicules with increasing rarefaction of the ion spicule in time.