scholarly journals Examining Flux Tube Interactions as a Cause of Sub-alfvénic Outflow

2021 ◽  
Vol 923 (2) ◽  
pp. 248
Author(s):  
John Unverferth ◽  
Dana Longcope
Keyword(s):  
Magnetic Flux ◽  
Drag Force ◽  
Flux Tube ◽  
Plasma Sheet ◽  
Solar Flares ◽  
Proper Choice ◽  
Magnetic Tension ◽  
Reconnection Site

Abstract In accepted models, magnetic tension drives reconnected magnetic flux away from the reconnection site at the local Alfvén speed. Numerous observational signatures of these outflows have been identified in solar flares, notable among them being supra-arcade downflows (SADs), almost none move at the Alfvén speed as predicted by models. Well-studied examples of SADs or SAD loops found in the flare of 2017 September 10 (SOL2017-09-10T15:35:00) move at a quarter or less of the expected Alfvén speed. Among those reasons posited to explain such discrepancies is the possibility that reconnected flux experiences a drag force during its outflow. Drag has not been included in previous reconnection models. Here, we develop the first such model in order to test the possibility that drag can explain sub-alfveńic reconnection outflows. Our model uses thin flux tube dynamics, previously shown to match features of flare observations other than outflow speed, including for the 2017 September 10 flare. We supplement the dynamics with a drag force representing the tube’s interaction with surrounding plasma through the formation of a wake. The wake’s width appears as a parameter in the force. We perform simulations, varying the drag parameter and synthesizing EUV observations, to test whether a drag force can produce a reasonable fit to observed features of the September 10 flare. We find that that slower retraction increases the brightness of emission and lowers the temperature of the synthetic plasma sheet. With proper choice of parameters the drag enables the simulation to agree reasonably with the observations.

scholarly journals Flux Tube Shredding and its Infrared Signature

1994 ◽  
Vol 154 ◽  
pp. 459-463
Author(s):  
M. Bünte ◽  
O. Steiner ◽  
S.K. Solanki ◽  
V.J. Pizzo
Keyword(s):  
Magnetic Flux ◽  
Flux Tube ◽  
Flux Tubes ◽  
Infrared Signature ◽  
Magnetic Tension ◽  
Magnetic Flux Tubes ◽  
Interchange Instability

The interchange instability of solar magnetic flux tubes and possible stabilization mechanisms are reviewed. Special attention is paid to the influence of magnetic tension forces and the internal atmosphere, both of which were neglected in earlier studies of this instability. It is found that whirl flows with velocities of only 2.2 km s–1 are strong enough to stabilize the flux tubes. However, their absence or the excitation of other instabilities might lead to a shredding of the tubes. The observability of such a scenario in the infrared is briefly discussed.

scholarly journals Modulational Instability of Fast Sausage Mode as One of the Possible Mechanisms for Quasiperiodic Pulsations during Solar Flares

2021 ◽  
Vol 923 (2) ◽  
pp. 131
Author(s):  
Naga Varun Yelagandula
Keyword(s):  
Magnetic Flux ◽  
Flux Tube ◽  
Solar Flares ◽  
Coronal Loop ◽  
Numerical Solutions ◽  
Modulational Instability ◽  
Magnetic Flux Tube ◽  
Electromagnetic Spectrum ◽  
Plane Wave Solution ◽  
Density Perturbations

Abstract Quasiperiodic pulsations (QPPs) are frequently observed in the entire range of the electromagnetic spectrum during solar flares, and there can be many possible mechanisms leading to this phenomenon. In the present work, we demonstrate the possibility of the generation of QPPs by a nonlinear fast sausage mode in a coronal loop. The coronal loop itself is represented by an infinitely long homogenous magnetic flux tube, which in many cases is a good approximation, and the nonlinearity of the fast sausage mode is modeled by the nonlinear Schrödinger equation (NSE) with a cubic nonlinearity. We have shown that the frequency-renormalized plane wave solution, which happens to be an exact solution of the NSE, transforms into a series of quasiperiodic oscillations (QPOs) due to the so-called modulational instability or the Benjamin–Feir instability. Our numerical solutions show that such QPOs evolve at almost every point above a certain height along the magnetic flux tube, which represents the coronal loop. As the fast sausage mode perturbs the plasma density strongly, the density perturbations caused by the QPOs of the nonlinear fast sausage mode correspondingly modulate the radiation throughout the electromagnetic spectrum, resulting in the emergence of the corresponding QPPs. This mechanism should therefore be able to describe some of the observed QPPs.

Effect of Asymmetry on a Trap Model for Solar Hard Xray Bursts

1979 ◽  
Vol 3 (6) ◽  
pp. 369-371 ◽  
Author(s):  
D. B. Melrose ◽  
S. M. White
Keyword(s):  
Magnetic Flux ◽  
Flux Tube ◽  
Magnetic Trap ◽  
Energetic Particles ◽  
Magnetic Flux Tube ◽  
X Rays ◽  
Radio Observations ◽  
X Ray ◽  
Additional Information ◽  
Basic Model

The basic model for the precipitation of trapped energetic particles from a magnetic flux tube is Kennel and Petschek’s (1966) model. Their model is symmetric, implying equal precipitation rates at the two feet of the flux tube. We have developed a model for precipitation in an asymmetric flux tube (Melrose and White 1979). Here we explore some of the consequences for the precipitation model of Melrose and Brown (1976) for solar hard X-ray bursts. In Melrose and Brown’s model roughly half the X-rays arise from precipitating electrons. With present instruments it is not possible to resolve the two feet of the flux tube. However, if the feet can be resolved, either directly by future X-ray telescopes, or indirectly through secondary optical, UV or radio observations, then, as we shall show, the additional information obtained could be used to derive information on processes in the magnetic trap.

scholarly journals Ion velocity distributions within the LLBL and their possible implication to multiple reconnections

2004 ◽  
Vol 22 (1) ◽  
pp. 213-236 ◽  
Author(s):  
O. L. Vaisberg ◽  
L. A. Avanov ◽  
T. E. Moore ◽  
V. N. Smirnov
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Magnetic Flux Tube ◽  
Flux Tubes ◽  
Different Types ◽  
Subsolar Point ◽  
Magnetic Flux Tubes ◽  
Ion Velocity ◽  
Field Lines

Abstract. We analyze two LLBL crossings made by the Interball-Tail satellite under a southward or variable magnetosheath magnetic field: one crossing on the flank of the magnetosphere, and another one closer to the subsolar point. Three different types of ion velocity distributions within the LLBL are observed: (a) D-shaped distributions, (b) ion velocity distributions consisting of two counter-streaming components of magnetosheath-type, and (c) distributions with three components, one of which has nearly zero parallel velocity and two counter-streaming components. Only the (a) type fits to the single magnetic flux tube formed by reconnection between the magnetospheric and magnetosheath magnetic fields. We argue that two counter-streaming magnetosheath-like ion components observed by Interball within the LLBL cannot be explained by the reflection of the ions from the magnetic mirror deeper within the magnetosphere. Types (b) and (c) ion velocity distributions would form within spiral magnetic flux tubes consisting of a mixture of alternating segments originating from the magnetosheath and from magnetospheric plasma. The shapes of ion velocity distributions and their evolution with decreasing number density in the LLBL indicate that a significant part of the LLBL is located on magnetic field lines of long spiral flux tube islands at the magnetopause, as has been proposed and found to occur in magnetopause simulations. We consider these observations as evidence for multiple reconnection Χ-lines between magnetosheath and magnetospheric flux tubes. Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; solar wind-magnetosphere interactions)

scholarly journals Linking Thin Flux Tube MHD Models to Apparent Stellar Surface Activity

2004 ◽  
Vol 219 ◽  
pp. 546-551
Author(s):  
T. Granzer ◽  
K. G. Strassmeier
Keyword(s):  
Magnetic Flux ◽  
Surface Activity ◽  
Flux Tube ◽  
Convection Zone ◽  
Active Regions ◽  
Similar Model ◽  
Flux Tubes ◽  
Stellar Convection ◽  
Magnetic Flux Tubes ◽  
Spot Formation

We model thin magnetic flux tubes as they rise from the bottom of a stellar convection zone to the photosphere. On emergence they form active regions, i.e. star spots. This model was very successfully applied to the solar case, where the simulations where in agreement with the butterfly diagram, Joy's law, and Hale's law. We propose the use of a similar model to describe stellar activity in the more extreme form found on active stars. A comparison between Doppler-images of well-observed pre-MS stars and a theoretically derived probability of star-spot formation as a function of latitude is presented.

Generation of nonlinear magnetic flux tube wave energies in Procyon A

2019 ◽  
Author(s):  
D E Fawzy ◽  
A T Saygac ◽  
K Stȩpień
Keyword(s):  
Magnetic Flux ◽  
Acoustic Wave ◽  
Flux Tube ◽  
Convection Zone ◽  
Frequency Factor ◽  
Turbulent Energy ◽  
Current Approach ◽  
Magnetic Flux Tube ◽  
Tube Wave ◽  
Wave Modes

Abstract The aim of the current study is the computation of the magnetic flux tube wave energies and fluxes generated in the convection zone of Procyon A. This is a subgiant of spectral type F5 IV-V showing chromospheric and coronal activities. The mechanisms responsible for the generation of different wave modes include the interaction of the thin and vertically oriented magnetic flux tube embedded in magnetic-free regions with turbulence in the convection zone of Procyon A. We are considering longitudinal, transverse and acoustic wave modes. Turbulence in the convection zone is modeled by the extended Kolmogorov turbulent energy spectrum and the modified Gaussian frequency factor. Different magnetic flux tube models with different degrees of magnetic activities were considered. The current approach takes the nonlinear effects into consideration. The results show that there is enough wave energy in the three different forms to heat the outer layers of the star. The obtained acoustic wave energies are larger than those of the longitudinal tube wave energies compared to the solar case. This can be explained by the relatively low magnetic field strength. On the other side, our computations show the importance of the transverse wave energies compared to the energies carried by the longitudinal waves. The former waves carry energy several (between 2 and 14) times higher than the latter. The obtained wave energies are essential for constructing time-dependent model chromospheres and for the predictions of atmospheric oscillations to be compared e.g. with the data collected by the CoRoT and Kepler missions.

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