19 research outputs found
Numerical simulation of the internal plasma dynamics of post-flare loops
We integrate the MHD ideal equations of a slender flux tube to simulate the
internal plasma dynamics of coronal post-flare loops. We study the onset and
evolution of the internal plasma instability to compare with observations and
to gain insight into physical processes and characteristic parameters
associated with flaring events. The numerical approach uses a finite-volume
Harten-Yee TVD scheme to integrate the 1D1/2 MHD equations specially designed
to capture supersonic flow discontinuities. We could reproduce the
observational sliding down and upwardly propagating of brightening features
along magnetic threads of an event occurred on October 1st, 2001. We show that
high--speed downflow perturbations, usually interpreted as slow magnetoacoustic
waves, could be better interpreted as slow magnetoacoustic shock waves. This
result was obtained considering adiabaticity in the energy balance equation.
However, a time--dependent forcing from the basis is needed to reproduce the
reiteration of the event which resembles observational patterns -commonly known
as quasi--periodic pulsations (QPPs)- which are related with large scale
characteristic longitudes of coherence. This result reinforces the
interpretation that the QPPs are a response to the pulsational flaring
activity.Comment: Accepted MNRAS, 10 pages, 14 figures, 1 tabl
Stability and mode analysis of solar coronal loops using thermodynamic irreversible energy principles
We study the modes and stability of non - isothermal coronal loop models with
different intensity values of the equilibrium magnetic field. We use an energy
principle obtained via non - equilibrium thermodynamic arguments. The principle
is expressed in terms of Hermitian operators and allow to consider together the
coupled system of equations: the balance of energy equation and the equation of
motion. We determine modes characterized as long - wavelength disturbances that
are present in inhomogeneous media. This character of the system introduces
additional difficulties for the stability analysis because the inhomogeneous
nature of the medium determines the structure of the disturbance, which is no
longer sinusoidal. Moreover, another complication is that we obtain a
continuous spectrum of stable modes in addition to the discrete one. We obtain
a unique unstable mode with a characteristic time that is comparable with the
characteristic life-time observed for loops. The feasibility of wave-based and
flow-based models is examined.Comment: 29 pages 10 figure
The Physical Processes of CME/ICME Evolution
As observed in Thomson-scattered white light, coronal mass ejections (CMEs) are manifest as large-scale expulsions of plasma magnetically driven from the corona in the most energetic eruptions from the Sun. It remains a tantalizing mystery as to how these erupting magnetic fields evolve to form the complex structures we observe in the solar wind at Earth. Here, we strive to provide a fresh perspective on the post-eruption and interplanetary evolution of CMEs, focusing on the physical processes that define the many complex interactions of the ejected plasma with its surroundings as it departs the corona and propagates through the heliosphere. We summarize the ways CMEs and their interplanetary CMEs (ICMEs) are rotated, reconfigured, deformed, deflected, decelerated and disguised during their journey through the solar wind. This study then leads to consideration of how structures originating in coronal eruptions can be connected to their far removed interplanetary counterparts. Given that ICMEs are the drivers of most geomagnetic storms (and the sole driver of extreme storms), this work provides a guide to the processes that must be considered in making space weather forecasts from remote observations of the corona.Peer reviewe
Origin and ion charge state evolution of solar wind transients during 4 - 7 August 2011
This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 647214). The computational work for this article was carried out on the joint STFC and SFC (SRIF) funded clusters at the University of St Andrews (Scotland, UK). The work is partially supported by RFBR grants 17-02-00787, 14-02-00945 and the P7 Program of the Russian Academy of Sciences.We present a study of the complex event consisting of several solar wind transients detected by the Advanced Composition Explorer (ACE) on 4 - 7 August 2011, which caused a geomagnetic storm with Dst=-110 nT. The supposed coronal sources, three flares and coronal mass ejections (CMEs), occurred on 2 - 4 August 2011 in active region (AR) 11261. To investigate the solar origin and formation of these transients, we study the kinematic and thermodynamic properties of the expanding coronal structures using the Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA) EUV images and differential emission measure (DEM) diagnostics. The Helioseismic and Magnetic Imager (HMI) magnetic field maps were used as the input data for the 3D magnetohydrodynamic (MHD) model to describe the flux rope ejection (Pagano, Mackay, and Poedts, 2013b). We characterize the early phase of the flux rope ejection in the corona, where the usual three-component CME structure formed. The fluxrope was ejected with a speed of about 200 km s-1 to the height of 0.25 R⊙. The kinematics of the modeled CME front agrees well with the Solar Terrestrial Relations Observatory (STEREO) EUV measurements. Using the results of the plasma diagnostics and MHD modeling, we calculate the ion charge ratios of carbon and oxygen as well as the mean charge state of iron ions of the 2 August 2011 CME, taking into account the processes of heating, cooling, expansion, ionization, and recombination of the moving plasma in the corona up to the frozen-in region. We estimate a probable heating rate of the CME plasma in the low corona by matching the calculated ion composition parameters of the CME with those measured in situ for the solar wind transients. We also consider the similarities and discrepancies between the results of the MHD simulation and the observations.PostprintPeer reviewe
Characterization of intensity and spatial variations along coronal loops
We describe dynamical features and evolutionary
characteristics of brightening coronal loops. We describe
intensity variations, both in space and time, along a coarse grain
loop structure, confirming high speed velocity scenarios. We apply
the method to TRACE space-born images that show a compound of
several magnetic threads. MICA ground-based images display a
unique non-resolved loop structure. We confirm that a coherent
behavior of the intensity along neighboring magnetic tubes occurs,
i.e. we obtain a similar pattern from both telescopes: each has
two branches, suggesting the sliding down of plasma in both
directions from a given position on the loop structure. The
apparent sliding down occurs in approximately 12 min. After
the first appearance, TRACE registers two reiterations of the
phenomenon suggesting a wave-based explanation. The feasibility of
wave-based and flow-based models is analyzed. In either case, in
order to explain the coherent coronal behavior the scenario of
apparently non-interacting coronal threads requires theoretical
explanations that consider uniform chromospheric conditions
covering the footpoints of all the related magnetic tubes. We
suggest a characteristic longitude of coherence.