On the dynamics, thermodynamics and fine structure of virtual erupting filaments

Abstract

It is not fully understood why some solar filaments erupt while others do not. Those that do typically undergo a slow rise followed by an acceleration phase, though this transition requires further investigation. Erupting prominences have been observed to heat up during the acceleration phase, but the origin of this heating remains unclear. Moreover, some coronal mass ejections possess additional fine structure in white-light observations beyond the classical three-part morphology. We aim to elaborate on the dynamics of erupting prominences, investigate the heating during the acceleration phase, and correlate our findings with observations. We employ the open-source MPI-AMRVAC code to solve the 2.5D MHD equations on a coronal domain extending to 300 Mm, using adaptive mesh refinement to attain high resolution. Controlled combinations of footpoint shearing and converging motions applied to an initial magnetic arcade produce erupting flux ropes with self-consistent prominence and coronal rain formation due to thermal instability. We find both non-erupting and erupting cases related to the system energization. Comparison with observations from the AIA Filament Eruption Catalog shows that the slow-rise and impulsive phases are modulated by magnetic reconnection. The transition to acceleration corresponds to an increase in the inflow Alfvén Mach number. Thermal conduction and compressional heating can lead to prominence evaporation. We obtain nested circular fine structure in EUV images of the ejected flux ropes, partly resulting from plasmoid interactions. We conclude that internal heating processes and magnetic reconnection play key roles in the early evolution of CMEs.

Figures (14)

• Figure 1: Temperature evolution of the six simulations. From left to right, the columns are the simulations for $\sigma \in \{0, 0.75, 1, 1.25, 1.5,2 \}$. The first row are snapshots of the simulations at the time when footpoint driving motion is disabled $t=t_1$; the second row when coronal rain ($\sigma=0$) and the solar prominence ($\sigma=0$ and $0.75$) develop and plasmoids ($\sigma \in \{1, 1.25, 1.5,2\}$), and finally, the third row at the end of the respective simulations. The thin black lines show magnetic field lines. Note that the end stage is at different timestamps for the different $\sigma$ cases: $253 \ \mathrm{min} \ (\sigma \in \{ 0, 0.75, 1\}), \, 257 \ \mathrm{min} \ (\sigma=1.25), \, 234 \ \mathrm{min} \ (\sigma=1.5)$ and $232 \ \mathrm{min} \ (\sigma=2)$. An animation of this figure is available in the journal's online webpage.
• Figure 2: Height evolution $y$ of the flux rope centres in solar radius (top panel) and vertical velocity $v_y$ in km/s for the six different shearing cases. Note that $\Delta \, t=t - t_\mathrm{fr}$ indicates the time difference with respect to the moment when the flux rope has already been formed. The black vertical line indicates the instant when footpoint driving motion has been disabled at $t=t_1$ or $\Delta \, t = t_1 - t_\mathrm{fr}$. The last point of all height- and velocity curves indicates the moment when the flux rope centre has crossed the altitude $y=200 \ \mathrm{Mm}$. Bottom panel displays the height evolution of an observed erupting prominence, data from DiLorenzo2025.
• Figure 3: Height $y$ in megameters (top panel) and vertical velocity $v_y$ in kilometers per second (bottom panel) of the central arcades' apexes in function of time $t$ in minutes for $\sigma=1$. The change in colours ranging from black to orange indicate lower lying arcades to higher located arcades, respectively. The thick black line is the evolution of the flux rope centre. The vertical red line marks the time when footpoint driving is disabled at $t=t_1$.
• Figure 4: Demonstration of how magnetic reconnection leads to the expansion of the flux rope and consequently how it affects the location of the flux rope centre. Top row shows the temperature evolution in MK for the case $\sigma=1$. Thin black lines are magnetic arcades, the thick black line is the separatrix and the blue magnetic field is a tracked magnetic arcade that eventually reconnects into a closed magnetic field line. The top white cross shows the flux rope centre, defined as the only point within the flux rope with a vanishing magnetic curvature, and the lower white cross locates the X-point as another, isolated point with zero magnetic curvature. Bottom row is a cartoon that extracts the ongoing process from our simulation and represents it in a simplified manner.
• Figure 5: Evolution of the flux rope centre and vertical dimension for the erupting cases $\sigma \in \{ 1, 1.25, 1.5, 2\}$ due to magnetic reconnection. Top panel shows the height evolution of the flux rope centre $y_\mathrm{frc}$, middle panel shows the vertical length of the flux rope $\Delta y_\mathrm{fr}$ and third panel the inflow Alfvén Mach number $M_\mathrm{A}$. The time difference $\Delta t = t - t_\mathrm{fr}$ is with respect to the onset of flux rope formation $t_\mathrm{fr}$. We remark that all curves in the current figure terminate before the formation of their first plasmoids.