Magnetohydrodynamic Waves in Two-Dimensional Prominences Embedded in Coronal Arcades

Abstract

Solar prominence models used so far in the analysis of MHD waves in such structures are quite elementary. In this work, we calculate numerically magnetohydrostatic models in two-dimensional configurations under the presence of gravity. Our interest is in models that connect the magnetic field to the photosphere and include an overlying arcade. The method used here is based on a relaxation process and requires solving the time-dependent nonlinear ideal MHD equations. Once a prominence model is obtained, we investigate the properties of MHD waves superimposed on the structure. We concentrate on motions purely two-dimensional neglecting propagation in the ignorable direction. We demonstrate how by using different numerical tools we can determine the period of oscillation of stable waves. We find that vertical oscillations, linked to fast MHD waves, are always stable and have periods in the 4-10 min range. Longitudinal oscillations, related to slow magnetoacoustic-gravity waves, have longer periods in the range of 28-40 min. These longitudinal oscillations are strongly influenced by the gravity force and become unstable for short magnetic arcades.

Morphology and Dynamics of Solar Prominences From 3d MHD Simulations

“…The basic initial configuration is an isothermal stratified atmosphere as in Terradas et al (2013). The same parameters have been used in the present work.…”

“…In Terradas et al (2013) a two-dimensional (2D) prominence model embedded in a coronal quadrupolar arcade was constructed to mimic a normal polarity prominence. In that work, dense material representing the prominence was injected in an initially stable magnetic structure, increasing the gravitational energy.…”

The effects of magnetic-field geometry on longitudinal oscillations of solar prominences: Cross-sectional area variation for thin tubes

“…In our approximation, v A ≫ c s and then c T ∼ c s . In addition, in Equations (13) and (14) of Terradas et al (2013) (5)- (7) and the equations of the cited authors.…”

The Dynamics of Funnel Prominences

“…Note that these requirements determine B z0 and B p0 uniquely. The potential field given above is inspired by a similar quadrupolar field configuration adopted in Terradas et al (2013) to study linear MHD wave motions in prominences. This initial condition represents an ideal MHD, stratified equilibrium, but we actually simulate the MHD equations extended with nonideal effects including optically thin radiative losses Q, anisotropic (field-aligned) thermal conduction, and a parameterized heating function H. These terms appear in the evolution equation for the total energy as follows:…”

“…Those magnetohydrostatic conditions are the starting point for detailed prominence seismology (Blokland & Keppens 2011b), which can extend current insights based on simple geometric models (Ballester 2014). The step to multidimensional studies of linear waves in prominences has meanwhile been made using source-term injected plasma in a 2D potential arcade system (Terradas et al 2013), and we here adopt the quadrupolar arcade from that study, to demonstrate the in situ formation of prominences due to evaporation-condensation. The pre-prominence arcade already has field lines that show a dipped structure, but does not meet the requirements for fluxrope-cavity structures that are so often observed.…”