16 research outputs found
Plasma Jets and Eruptions in Solar Coronal Holes: a 3D flux emergence experiment
A three-dimensional numerical experiment of the launching of a hot and fast
coronal jet followed by several violent eruptions is analyzed in detail. These
events are initiated through the emergence of a magnetic flux rope from the
solar interior into a coronal hole. We explore the evolution of the emerging
magnetically-dominated plasma dome surmounted by a current sheet and the
ensuing pattern of reconnection. A hot and fast coronal jet with inverted-Y
shape is produced that shows properties comparable to those frequently observed
with EUV and X-Ray detectors. We analyze its 3D shape, its inhomogeneous
internal structure, and its rise and decay phases, lasting for some 15-20 min
each. Particular attention is devoted to the field-line connectivities and the
reconnection pattern. We also study the cool and high-density volume that
appears encircling the emerged dome. The decay of the jet is followed by a
violent phase with a total of five eruptions. The first of them seems to follow
the general pattern of tether-cutting reconnection in a sheared arcade,
although modified by the field topology created by the preceding reconnection
evolution. The two following eruptions take place near and above the strong
field-concentrations at the surface. They show a twisted, \Omega-loop like rope
expanding in height, with twist being turned into writhe, thus hinting at a
kink instability (perhaps combined with a torus-instability) as the cause of
the eruption. The succession of a main jet ejection and a number of violent
eruptions that resemble mini-CME's and their physical properties suggest that
this experiment may provide a model for the blowout jets recently proposed in
the literature.Comment: Accepted for publication in The Astrophysical Journal (vol 770, June
2013
Are tornado-like magnetic structures able to support solar prominence plasma?
Recent high-resolution and high-cadence observations have surprisingly
suggested that prominence barbs exhibit apparent rotating motions suggestive of
a tornado-like structure. Additional evidence has been provided by Doppler
measurements. The observations reveal opposite velocities for both hot and cool
plasma on the two sides of a prominence barb. This motion is persistent for
several hours and has been interpreted in terms of rotational motion of
prominence feet. Several authors suggest that such barb motions are rotating
helical structures around a vertical axis similar to tornadoes on Earth. One of
the difficulties of such a proposal is how to support cool prominence plasma in
almost-vertical structures against gravity. In this work we model analytically
a tornado-like structure and try to determine possible mechanisms to support
the prominence plasma. We have found that the Lorentz force can indeed support
the barb plasma provided the magnetic structure is sufficiently twisted and/or
significant poloidal flows are present.Comment: Accepted for publication in ApJ
Interaction of solar jets with filaments: Triggering of large-amplitude filament oscillations
Large-amplitude oscillations (LAOs) are often detected in filaments. Using
multiwavelength observations, their origin can be traced back to the
interaction with eruptions and jets. We present two different case studies as
observational evidence in support of 2.5D MHD numerical experiments that show
that the LAOs in the filament channels can be initiated by solar jets. In the
two studied events, we can identify a quadrupolar configuration with an X-point
at the top of the parasitic region suggestive of a classical null-point. A
reconnection flow emanates from this structure leading to a jet that propagates
along the filament channel. In both cases we can identify the quiescent and
eruptive phases of the jet. The triggered LAOs have periods of around 70-80
minutes and are damped after a few oscillations. The minimum magnetic field
intensity inferred with seismology for the filament turns out to be around 30
Gauss. We conclude that the two case studies are consistent with the recent
numerical model of Luna and Moreno-Insertis (2021), in which the LAOs are
initiated by jets. The relationship between the onset of the jet and filament
oscillations is straight-forward for the first case and less for the second
case. In the second event, although there is some evidence, we cannot rule out
other possibilities such as activity unrelated to the null-point or changes in
the magnetic structure of the filament. Both jets are associated with very weak
flares which did not launch any EUV wave. Therefore the role of EUV waves for
triggering the filament oscillations can be eliminated for these two case.Comment: 12 pages, 13 figures, Accepted for publication in Astronomy &
Astrophysic
temperature distribution
Temperature map in vertical cross section across Xray jet in the solar coron
Interaction of solar jets with filaments: Triggering of large-amplitude filament oscillations
Interaction of solar jets with filaments: Triggering of large-amplitude filament oscillations
International audienceLarge-amplitude oscillations (LAOs) are often detected in filaments. Using multiwavelength observations, their origin can be traced back to the interaction with eruptions and jets. We present two different case studies as observational evidence in support of 2.5D MHD numerical experiments that show that the LAOs in the filament channels can be initiated by solar jets. In the two studied events, we can identify a quadrupolar configuration with an X-point at the top of the parasitic region suggestive of a classical null-point. A reconnection flow emanates from this structure leading to a jet that propagates along the filament channel. In both cases we can identify the quiescent and eruptive phases of the jet. The triggered LAOs have periods of around 70-80 minutes and are damped after a few oscillations. The minimum magnetic field intensity inferred with seismology for the filament turns out to be around 30 Gauss. We conclude that the two case studies are consistent with the recent numerical model of Luna and Moreno-Insertis (2021), in which the LAOs are initiated by jets. The relationship between the onset of the jet and filament oscillations is straight-forward for the first case and less for the second case. In the second event, although there is some evidence, we cannot rule out other possibilities such as activity unrelated to the null-point or changes in the magnetic structure of the filament. Both jets are associated with very weak flares which did not launch any EUV wave. Therefore the role of EUV waves for triggering the filament oscillations can be eliminated for these two case
Judaism and the Love of Reason
Context. Magnetic flux emergence from the solar interior has been shown to be a key mechanism for unleashing a wide variety of phenomena. However, there are still open questions concerning the rise of the magnetized plasma through the atmosphere, mainly in the chromosphere, where the plasma departs from local thermodynamic equilibrium (LTE) and is partially ionized.
Aims. We aim to investigate the impact of the nonequilibrium (NEQ) ionization and recombination and molecule formation of hydrogen, as well as ambipolar diffusion, on the dynamics and thermodynamics of the flux emergence process.
Methods. Using the radiation-magnetohydrodynamic Bifrost code, we performed 2.5D numerical experiments of magnetic flux emergence from the convection zone up to the corona. The experiments include the NEQ ionization and recombination of atomic hydrogen, the NEQ formation and dissociation of H2 molecules, and the ambipolar diffusion term of the generalized Ohm’s law.
Results. Our experiments show that the LTE assumption substantially underestimates the ionization fraction in most of the emerged region, leading to an artificial increase in the ambipolar diffusion and, therefore, in the heating and temperatures as compared to those found when taking the NEQ effects on the hydrogen ion population into account. We see that LTE also overestimates the number density of H2 molecules within the emerged region, thus mistakenly magnifying the exothermic contribution of the H2 molecule formation to the thermal energy during the flux emergence process. We find that the ambipolar diffusion does not significantly affect the amount of total unsigned emerged magnetic flux, but it is important in the shocks that cross the emerged region, heating the plasma on characteristic times ranging from 0.1 to 100 s. We also briefly discuss the importance of including elements heavier than hydrogen in the equation of state so as not to overestimate the role of ambipolar diffusion in the atmosphere