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 Effects of MHD slow shocks propagating along magnetic flux tubes in a dipole magnetic field

2002 ◽  
Vol 9 (2) ◽  
pp. 163-172 ◽  
Author(s):  
N. V. Erkaev ◽  
V. A. Shaidurov ◽  
V. S. Semenov ◽  
H. K. Biernat
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Plasma Pressure ◽  
Mhd Waves ◽  
Magnetic Flux Tube ◽  
Flux Tubes ◽  
Dipole Magnetic Field ◽  
Pressure Pulses ◽  
Magnetic Flux Tubes

Abstract. Variations of the plasma pressure in a magnetic flux tube can produce MHD waves evolving into shocks. In the case of a low plasma beta, plasma pressure pulses in the magnetic flux tube generate MHD slow shocks propagating along the tube. For converging magnetic field lines, such as in a dipole magnetic field, the cross section of the magnetic flux tube decreases enormously with increasing magnetic field strength. In such a case, the propagation of MHD waves along magnetic flux tubes is rather different from that in the case of uniform magnetic fields. In this paper, the propagation of MHD slow shocks is studied numerically using the ideal MHD equations in an approximation suitable for a thin magnetic flux tube with a low plasma beta. The results obtained in the numerical study show that the jumps in the plasma parameters at the MHD slow shock increase greatly while the shock is propagating in the narrowing magnetic flux tube. The results are applied to the case of the interaction between Jupiter and its satellite Io, the latter being considered as a source of plasma pressure pulses.

scholarly journals Resonant absorption in expanding coronal magnetic flux tubes with uniform density

2019 ◽  
Vol 631 ◽  
pp. A105 ◽  
Author(s):  
T. A. Howson ◽  
I. De Moortel ◽  
P. Antolin ◽  
T. Van Doorsselaere ◽  
A. N. Wright
Keyword(s):  
Magnetic Flux ◽  
Flux Tube ◽  
Density Profile ◽  
Resonant Absorption ◽  
Magnetic Flux Tube ◽  
Length Scales ◽  
Flux Tubes ◽  
Kink Mode ◽  
Wave Heating ◽  
Field Lines

Aims. We investigate the transfer of energy between a fundamental standing kink mode and azimuthal Alfvén waves within an expanding coronal magnetic flux tube. We consider the process of resonant absorption in a loop with a non-uniform Alfvén frequency profile but in the absence of a radial density gradient. Methods. Using the three dimensional magnetohydrodynamic (MHD) code, Lare3d, we modelled a transversely oscillating magnetic flux tube that expands radially with height. An initially straight loop structure with a magnetic field enhancement was allowed to relax numerically towards a force-free state before a standing kink mode was introduced. The subsequent dynamics, rate of wave damping and formation of small length scales are considered. Results. We demonstrate that the transverse gradient in Alfvén frequency required for the existence of resonant field lines can be associated with the expansion of a high field-strength flux tube from concentrated flux patches in the lower solar atmosphere. This allows for the conversion of energy between wave modes even in the absence of the transverse density profile typically assumed in wave heating models. As with standing modes in straight flux tubes, small scales are dominated by the vorticity at the loop apex and by currents close to the loop foot points. The azimuthal Alfvén wave exhibits the structure of the expanded flux tube and is therefore associated with smaller length scales close to the foot points of the flux tube than at the loop apex. Conclusions. Resonant absorption can proceed throughout the coronal volume, even in the absence of visible, dense, loop structures. The flux tube and MHD waves considered are difficult to observe and our model highlights how estimating hidden wave power within the Sun’s atmosphere can be problematic. We highlight that, for standing modes, the global properties of field lines are important for resonant absorption and coronal conditions at a single altitude will not fully determine the nature of MHD resonances. In addition, we provide a new model in partial response to the criticism that wave heating models cannot self-consistently generate or sustain the density profile upon which they typically rely.

scholarly journals Damping rates of p-modes by an ensemble of randomly distributed thin magnetic flux tubes

2010 ◽  
Vol 6 (S273) ◽  
pp. 351-355
Author(s):  
Andrew Gascoyne ◽  
Rekha Jain
Keyword(s):  
Boundary Condition ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Magnetic Flux Tube ◽  
Plasma Properties ◽  
Flux Tubes ◽  
Damping Rate ◽  
Magnetic Flux Tubes ◽  
Mode Energy ◽  
Upper Boundary

AbstractThe magnetohydrodynamic (MHD) sausage tube waves are excited in the magnetic flux tubes by p-mode forcing. These tube waves thus carry energy away from the p-mode cavity which results in the deficit of incident p-mode energy. We calculate the loss of incident p-mode energy as a damping rate of f- and p-modes. We calculate the damping rates of f- and p-modes by a model Sun consisting of an ensemble of many thin magnetic flux tubes with varying plasma properties and distributions. Each magnetic flux tube is modelled as axisymmetric, vertically oriented and untwisted. We find that the magnitude and the form of the damping rates are sensitive to the plasma-β of the tubes and the upper boundary condition used.

Surface currents on models of force-free solar magnetic flux tubes

1994 ◽  
Vol 51 (1) ◽  
pp. 163-176 ◽  
Author(s):  
D. B. Melrose ◽  
Jennifer Nicholls ◽  
N. G. Broderick
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Flux Tube ◽  
Surface Currents ◽  
Current Profile ◽  
Flux Tubes ◽  
Piecewise Constant ◽  
Cylindrically Symmetric ◽  
Magnetic Flux Tubes ◽  
A Current

A model of a cylindrically symmetric, force-free magnetic field consisting of a sequence of concentric layers with piecewise-constant α is used to construct models of the surface currents on isolated, force-free magnetic flux tubes. Two boundary conditions are considered: a current-neutralized flux tube (Bφ = 0, Bz φ 0, Bz ≠ O at r > r0), and an isolated current-carrying flux tube (Bφ ≠ 0, Bz = 0 at r > r0). A single-a model that is current-neutralized is a reverse-field pinch, and is unacceptable as a model for a solar flux tube. Examples of two-α models for a current-neutralized flux tube are presented. The models of the surface currents satisfying either boundary condition are shown to simplify considerably when the surface layer is thin. A model consisting of several layers, with piecewise-constant α, may be used to find an approximate solution for a force-free flux tube with an arbitrarily specified current profile.

scholarly journals Amateur/Professional Cooperation in 2 Solar Studies

1988 ◽  
Vol 98 ◽  
pp. 168-168
Author(s):  
T. Roudier ◽  
R. Muller ◽  
J.C. Hulot ◽  
F. Vaissière
Keyword(s):  
Magnetic Flux ◽  
Flux Tube ◽  
General Trend ◽  
Magnetic Flux Tube ◽  
Theoretical Studies ◽  
Flux Tubes ◽  
Angular Measurements ◽  
Magnetic Flux Tubes ◽  
First Time ◽  
Initial Results

AbstractThe modification of properties of granules around magnetic flux tubes has been studied for the first time from photographs (at λ = 4803Å and 5770Å) taken with the 50-cm refractor at Pic du Midi. Statistically, these granules are more numerous, smaller, and more elongated than other granules. During their first two minutes of life they show very pronounced radial orientation to the magnetic flux tube.Angular measurements on the same granules have a precision of ± 10°, which is sufficient as theoretical studies show that they rotate by 360° in the course of their life. Initial results appeared to show that only explosive granules had intrinsic rotation, but further examination showed that it is a general trend. It seems that the granules do rotate significantly, but that there is a more important “push-pull” effect, in agreement with A. Title’s theory drawn from SOUP images.

scholarly journals Flux quanta, magnetic field lines, merging – some sub-microscale relations of interest in space plasma physics

2011 ◽  
Vol 29 (6) ◽  
pp. 1121-1127 ◽  
Author(s):  
R. A. Treumann ◽  
R. Nakamura ◽  
W. Baumjohann
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Quantum Mechanical ◽  
Space Plasma Physics ◽  
Flux Tubes ◽  
Magnetic Diffusion ◽  
Macro Scale ◽  
Magnetic Flux Tubes ◽  
Field Lines ◽  
The Given

Abstract. We clarify the notion of magnetic field lines in plasma by referring to sub-microscale (quantum mechanical) particle dynamics. It is demonstrated that magnetic field lines in a field of strength B carry single magnetic flux quanta Φ0=h/e. The radius of a field line in the given magnetic field B is calculated. It is shown that such field lines can merge and annihilate only over the length ℓ∥ of their strictly anti-parallel sections, for which case we estimate the power generated. The length ℓ∥ becomes a function of the inclination angle θ of the two merging magnetic flux tubes (field lines). Merging is possible only in the interval 12πθ≤π. This provides a sub-microscopic basis for "component reconnection" in classical macro-scale reconnection. We also find that the magnetic diffusion coefficient in plasma appears in quanta D0m=eΦ0/me=h/me. This lets us conclude that the bulk perpendicular plasma resistivity is limited and cannot be less than η0⊥=μ0eΦ0/me=μ0h/me~10−9 Ohm m. This resistance is an invariant.

scholarly journals The Emergence of Magnetic Flux in Active Regions

2001 ◽  
Vol 203 ◽  
pp. 225-228
Author(s):  
W. P. Abbett ◽  
G. H. Fisher ◽  
Y. Fan
Keyword(s):  
Magnetic Flux ◽  
Flux Tube ◽  
Active Regions ◽  
Large Degree ◽  
Solar Interior ◽  
Magnetic Flux Tube ◽  
Initial Field ◽  
Flux Tubes ◽  
Mhd Simulations ◽  
Magnetic Flux Tubes

Over the past decade, “thin flux tube” models have proven successful in explaining many properties of active regions in terms of magnetic flux tube dynamics in the solar interior. On the other hand, recent 2-D MHD simulations of the emergence of magnetic flux have shown that many of the assumptions adopted in the thin flux tube approximation are invalid. For example, unless the flux tubes exhibit a large degree of initial field line twist — and observations of emerging active regions suggest they do not — they will fragment (break apart) before they are able to emerge through the surface. We attempt to resolve this paradox using a number of 3-D MHD simulations (in the anelastic approximation) that describe the rise and fragmentation of twisted magnetic flux tubes. We find that the degree of fragmentation of an evolving Ω-loop depends strongly on the 3-D geometry of the loop, and that the Coriolis force plays a dynamically important role in the evolution and emergence of magnetic flux.

scholarly journals Waves in Magnetic Flux Tubes

1990 ◽  
Vol 142 ◽  
pp. 159-174
Author(s):  
B Roberts
Keyword(s):  
Wave Propagation ◽  
Magnetic Flux ◽  
Solar Atmosphere ◽  
Flux Tube ◽  
Seismic Waves ◽  
Wave Guide ◽  
Magnetic Flux Tube ◽  
Flux Tubes ◽  
Ocean Layer ◽  
Magnetic Flux Tubes

The basic aspects of wave propagation in a magnetic flux tube are reviewed, with particular emphasis on the types of flux tube that occur in the solar atmosphere. Two fundamental speeds arise naturally in a description of wave propagation in a flux tube: the slow magnetoacoustic (cusp) speed cT, which is both subsonic and sub-Alfvénic, and a mean Alfvén speed ck. Both surface and body modes are supported by a tube. It is stressed that a flux tube may act as a wave guide, similar to the guidance of light by a fibre optic, or sound in an ocean layer, or seismic waves in the Earth's crust.

scholarly journals The structure and origin of magnetic clouds in the solar wind

1998 ◽  
Vol 16 (1) ◽  
pp. 1-24 ◽  
Author(s):  
V. Bothmer ◽  
R. Schwenn
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Magnetic Flux ◽  
Flux Tube ◽  
White Light ◽  
Large Scale ◽  
Magnetic Clouds ◽  
Flux Tubes ◽  
Magnetic Flux Tubes

Abstract. Plasma and magnetic field data from the Helios 1/2 spacecraft have been used to investigate the structure of magnetic clouds (MCs) in the inner heliosphere. 46 MCs were identified in the Helios data for the period 1974–1981 between 0.3 and 1 AU. 85% of the MCs were associated with fast-forward interplanetary shock waves, supporting the close association between MCs and SMEs (solar mass ejections). Seven MCs were identified as direct consequences of Helios-directed SMEs, and the passage of MCs agreed with that of interplanetary plasma clouds (IPCs) identified as white-light brightness enhancements in the Helios photometer data. The total (plasma and magnetic field) pressure in MCs was higher and the plasma-β lower than in the surrounding solar wind. Minimum variance analysis (MVA) showed that MCs can best be described as large-scale quasi-cylindrical magnetic flux tubes. The axes of the flux tubes usually had a small inclination to the ecliptic plane, with their azimuthal direction close to the east-west direction. The large-scale flux tube model for MCs was validated by the analysis of multi-spacecraft observations. MCs were observed over a range of up to ~60° in solar longitude in the ecliptic having the same magnetic configuration. The Helios observations further showed that over-expansion is a common feature of MCs. From a combined study of Helios, Voyager and IMP data we found that the radial diameter of MCs increases between 0.3 and 4.2 AU proportional to the distance, R, from the Sun as R0.8 (R in AU). The density decrease inside MCs was found to be proportional to R–2.4, thus being stronger compared to the average solar wind. Four different magnetic configurations, as expected from the flux-tube concept, for MCs have been observed in situ by the Helios probes. MCs with left- and right-handed magnetic helicity occurred with about equal frequencies during 1974–1981, but surprisingly, the majority (74%) of the MCs had a south to north (SN) rotation of the magnetic field vector relative to the ecliptic. In contrast, an investigation of solar wind data obtained near Earth's orbit during 1984–1991 showed a preference for NS-clouds. A direct correlation was found between MCs and large quiescent filament disappearances (disparition brusques, DBs). The magnetic configurations of the filaments, as inferred from the orientation of the prominence axis, the polarity of the overlying field lines and the hemispheric helicity pattern observed for filaments, agreed well with the in situ observed magnetic structure of the associated MCs. The results support the model of MCs as large-scale expanding quasi-cylindrical magnetic flux tubes in the solar wind, most likely caused by SMEs associated with eruptions of large quiescent filaments. We suggest that the hemispheric dependence of the magnetic helicity structure observed for solar filaments can explain the preferred orientation of MCs in interplanetary space as well as their solar cycle behavior. However, the white-light features of SMEs and the measured volumes of their interplanetary counterparts suggest that MCs may not simply be just Hα-prominences, but that SMEs likely convect large-scale coronal loops overlying the prominence axis out of the solar atmosphere.

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.

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