Modeling the Thermodynamic Evolution of Coronal Mass Ejections Using Their Kinematics

Abstract

Earlier studies on Coronal Mass Ejections (CMEs), using remote sensing and in situ observations, have attempted to determine some of the internal properties of CMEs, which were limited to a certain position or a certain time. For understanding the evolution of the internal thermodynamic state of CMEs during their heliospheric propagation, we improve the selfsimilar flux rope internal state (FRIS) model, which is constrained by measured propagation and expansion speed profiles of a CME. We implement the model to a CME erupted on 2008 December 12 and probe the internal state of the CME. It is found that the polytropic index of the CME plasma decreased continuously from 1.8 to 1.35 as the CME moved away from the Sun, implying that the CME released heat before it reached adiabatic state and then absorbed heat. We further estimate the entropy changing and heating rate of the CME. We also find that the thermal force inside the CME is the internal driver of CME expansion while Lorentz force prevented the CME from expanding. It is noted that centrifugal force due to poloidal motion decreased with the fastest rate and Lorentz force decreased slightly faster than thermal pressure force as CME moved away from the Sun. We also discuss the limitations of the model and approximations made in the study.

Probing the Thermodynamic State of a Coronal Mass Ejection (CME) Up to 1 AU

“…Further, it is evident from Table 1 that if the absolute value of the proton number density is obtained by other means independent of the model, one can derive the unknown factor M/k 7 . In this factor, M is the mass of the CME and k 7 is an important proportionality constant between the axial length (l) of the flux rope and the distance of the center of the flux rope from the solar surface, i.e., l = k 7 L, as derived in Mishra and Wang (2018). The model derived the proton number density of the CME at 1 AU is 3.09 × 10 −13 × M/k 7 cm −3 while the in situ observed proton density of the magnetic cloud is 2 cm −3 .…”

“…The flux rope internal state (FRIS) model was first developed by Wang et al (2009) and later by Mishra and Wang (2018). To better define the basis of the present study, we briefly describe the FRIS model here.…”

“…The internal thermodynamic parameters of the CME can be estimated up to 1 AU if the measured propagation and expansion speed profiles of the CME to be used as inputs in the FRIS model (Mishra and Wang, 2018) could be measured up to 1 AU. However, we could not unambiguously identify CME flux rope using GCS forward fitting model (Thernisien et al, 2009) beyond D = 42 R ⊙ , as explained in section 3.1.…”

“…The pioneering attempt to investigate the internal state of an individual CME during its propagation in the outer corona (i.e., 2-70 R ⊙ ) was done by Wang et al (2009) by developing a Flux Rope Internal State (FRIS) model. The model was further improved by Mishra and Wang (2018) and they applied it to the coronagraphic observations of a slow CME to understand the internal forces and thermodynamic properties (polytropic index, heating rate, entropy change, etc.). The use of coronagraphic observations in combination with the FRIS model allowed to track the thermodynamic evolution of a specific CME with distance from the Sun.…”

“…Right: A representative picture for the cross-section of the CME flux rope. The radius of the flux rope is R, the distance from the flux rope axis to the solar surface is L, the distance of the CME leading edge from the Sun's center is h, and the minimum and the maximum position angles (PA) are shown with dotted blue lines (adapted from Mishra and Wang, 2018). CME near the Earth.…”