scholarly journals Toroidal models of magnetic field with twisted structure

2019 ◽  
Vol 5 (2) ◽  
pp. 69-75 ◽  
Author(s):  
Анастасия Петухова ◽  
Anastasia Petukhova ◽  
Станислав Петухов ◽  
Stanislav Petukhov
Keyword(s):  
Magnetic Field ◽  
Flux Rope ◽  
Forbush Decrease ◽  
Magnetic Clouds ◽  
Integral Model ◽  
Model Parameters ◽  
Magnetic Field Region ◽  
Transport Effects ◽  
Mass Ejection ◽  
The Magnetic Field

We present and discuss properties of the following magnetic field models in a magnetic cloud: Miller and Turner solution, modified Miller–Turner solution, Romashets–Vandas toroidal and integral models, and Krittinatham–Ruffolo model. Helicity of the magnetic field in all the models is the main feature of magnetic clouds. The first three models describe the magnetic field inside an ideal torus. In the integral model, parameters of a generating torus ambiguously determine the volume and form of the magnetic field region. In the Krittinatham–Ruffolo model, the cross-section radius of the torus is variable, thereby it corresponds more closely to the real form of magnetic clouds in the inner heliosphere. These models can be used to interpret in-situ observations of the magnetic flux rope, to study a Forbush decrease in magnetic clouds and transport effects of solar energetic particles injected into a coronal mass ejection.

scholarly journals Toroidal models of magnetic field with twisted structure

2019 ◽  
Vol 5 (2) ◽  
pp. 74-81
Author(s):  
Анастасия Петухова ◽  
Anastasia Petukhova ◽  
Станислав Петухов ◽  
Stanislav Petukhov
Keyword(s):  
Magnetic Field ◽  
Flux Rope ◽  
Forbush Decrease ◽  
Magnetic Clouds ◽  
Integral Model ◽  
Model Parameters ◽  
Magnetic Field Region ◽  
Transport Effects ◽  
Mass Ejection ◽  
The Magnetic Field

We present and discuss properties of the following magnetic field models in a magnetic cloud: Miller and Turner solution, modified Miller–Turner solution, Romashets–Vandas toroidal and integral models, and Krittinatham–Ruffolo model. Helicity of the magnetic field in all the models is the main feature of magnetic clouds. The first three models describe the magnetic field inside an ideal torus. In the integral model, parameters of a generating torus ambiguously determine the volume and form of the magnetic field region. In the Krittinatham–Ruffolo model, the cross-section radius of the torus is variable, thereby it corresponds more closely to the real form of magnetic clouds in the inner heliosphere. These models can be used to interpret in-situ observations of the magnetic flux rope, to study a Forbush decrease in magnetic clouds and transport effects of solar energetic particles injected into a coronal mass ejection.

The self-similar, non-linear evolution of rotating magnetic flux ropes

1995 ◽  
Vol 13 (8) ◽  
pp. 815-827 ◽  
Author(s):  
C. J. Farrugia ◽  
V. A Osherovich ◽  
L. F. Burlaga
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Small Amplitude ◽  
Symmetry Axis ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Linear Evolution ◽  
Multiplicative Factor ◽  
Self Similar ◽  
The Magnetic Field

Abstract. We study, in the ideal MHD approximation, the non-linear evolution of cylindrical magnetic flux tubes differentially rotating about their symmetry axis. Our force balance consists of inertial terms, which include the centrifugal force, the gradient of the axial magnetic pressure, the magnetic pinch force and the gradient of the gas pressure. We employ the "separable" class of self-similar magnetic fields, defined recently. Taking the gas to be a polytrope, we reduce the problem to a single, ordinary differential equation for the evolution function. In general, two regimes of evolution are possible; expansion and oscillation. We investigate the specific effect rotation has on these two modes of evolution. We focus on critical values of the flux rope parameters and show that rotation can suppress the oscillatory mode. We estimate the critical value of the angular velocity Ωcrit, above which the magnetic flux rope always expands, regardless of the value of the initial energy. Studying small-amplitude oscillations of the rope, we find that torsional oscillations are superimposed on the rotation and that they have a frequency equal to that of the radial oscillations. By setting the axial component of the magnetic field to zero, we study small-amplitude oscillations of a rigidly rotating pinch. We find that the frequency of oscillation ω is inversely proportional to the angular velocity of rotation Ω; the product ωΩbeing proportional to the inverse square of the Alfvén time. The period of large-amplitude oscillations of a rotating flux rope of low beta increases exponentially with the energy of the equivalent 1D oscillator. With respect to large-amplitude oscillations of a non-rotating flux rope, the only change brought about by rotation is to introduce a multiplicative factor greater than unity, which further increases the period. This multiplicative factor depends on the ratio of the azimuthal speed to the Alfvén speed. Finally, considering interplanetary magnetic clouds as cylindrical flux ropes, we inquire whether they rotate. We find that at 1 AU only a minority do. We discuss data on two magnetic clouds where we interpret the presence in each of vortical plasma motion about the symmetry axis as a sign of rotation. Our estimates for the angular velocities suggest that the parameters of the two magnetic clouds are below critical values. The two clouds differ in many respects (such as age, bulk flow speed, size, handedness of the magnetic field, etc.), and we find that their rotational parameters reflect some of these differences, particularly the difference in age. In both clouds, a rough estimate of the radial electric field in the rigidly rotating core, calculated in a non-rotating frame, yields values of the order mV m–1.

scholarly journals New Force-Free Models of Magnetic Clouds

2005 ◽  
Vol 13 ◽  
pp. 133-133
Author(s):  
M. Vandas ◽  
E. P. Romashets ◽  
S. Watari
Keyword(s):  
Magnetic Field ◽  
Magnetic Cloud ◽  
Free Field ◽  
Flux Rope ◽  
Field Vector ◽  
Magnetic Clouds ◽  
Field Magnitude ◽  
Flux Ropes ◽  
Magnetic Field Magnitude ◽  
The Magnetic Field

AbstractMagnetic clouds are thought to be large flux ropes propagating through the heliosphere. Their twisted magnetic fields are mostly modeled by a constant-alpha force-free field in a circular cylindrical flux rope (the Lundquist solution). However, the interplanetary flux ropes are three dimensional objects. In reality they possibly have a curved shape and an oblate cross section. Recently we have found two force-free models of flux ropes which takes into account the mentioned features. These are (i) a constant-alpha force-free configuration in an elliptic flux rope (Vandas & Romashets 2003, A&A, 398, 801), and (ii) a non-constant-alpha force-free field in a toroid with arbitrary aspect ratio (Romashets & Vandas 2003, AIP Conf Ser. 679, 180). Two magnetic cloud observations were analyzed. The magnetic cloud of October 18-19, 1995 has been fitted by Lepping et al. (1997, JGR, 102, 14049) with use of the Lundquist solution. The cloud has a very flat magnetic field magnitude profile. We fitted it by the elliptic solution (i). The magnetic cloud of November 17-18, 1975 has been fitted by Marubashi (1997) with use of a toroidally adjusted Lundquist solution. The cloud has a large magnetic field vector rotation and a large magnetic field magnitude increase over the background level. We fitted it by the toroidal solution (ii). The both fits match the rotation of the magnetic field vector in a comparable quality to the former fits, but the description of the magnetic field magnitude profiles is remarkable better. It is possible to incorporate temporal effects (expansion) of magnetic clouds into the new solutions through a time-dependent alpha parameter as in Shimazu & Vandas (2002, EP&S, 54, 783).

scholarly journals Shearing motions and torus instability in the 2010 April 3 filament eruption

2013 ◽  
Vol 8 (S300) ◽  
pp. 475-476
Author(s):  
F. P. Zuccarello ◽  
P. Romano ◽  
F. Zuccarello ◽  
S. Poedts
Keyword(s):  
Magnetic Field ◽  
Active Region ◽  
Flux Rope ◽  
Active Region Noaa ◽  
Axial Field ◽  
Drift Motion ◽  
Filament Eruption ◽  
Onset Condition ◽  
Mass Ejection ◽  
The Magnetic Field

AbstractThe magnetic field evolution of active region NOAA 11059 is studied in order to determine the possible causes and mechanisms that led to the initiation of the 2010 April 3 coronal mass ejection (CME).We find (1) that the magnetic configuration of the active region is unstable to the torus instability and (2) that persistent shearing motions characterized the negative polarity, resulting in a southward, almost parallel to the meridians, drift motion of the negative magnetic field concentrations.We conclude that these shearing motions increased the axial field of the filament eventually bringing the flux rope axis to a height where the onset condition for the torus instability was satisfied.

scholarly journals The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds

2009 ◽  
Vol 27 (10) ◽  
pp. 4057-4067 ◽  
Author(s):  
M. J. Owens ◽  
N. U. Crooker ◽  
T. S. Horbury
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Pitch Angle ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Magnetic Field Direction ◽  
Magnetic Flux Rope ◽  
Suprathermal Electron ◽  
Angle Scattering ◽  
The Magnetic Field

Abstract. Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons must traverse longer magnetic field lines to reach the same heliocentric distance. This increased time of flight allows greater pitch-angle scattering to occur, meaning suprathermal electron pitch-angle distributions should be systematically broader at the edges of the flux rope than at the axis. We model this effect with an analytical magnetic flux rope model and a numerical scheme for suprathermal electron pitch-angle scattering and find that the signature of a magnetic flux rope should be observable with the typical pitch-angle resolution of suprathermal electron data provided ACE's SWEPAM instrument. Evidence of this signature in the observations, however, is weak, possibly because reconnection of magnetic fields within the flux rope acts to intermix flux tubes.

scholarly journals Long-duration magnetic clouds: a comparison of analyses using torus- and cylinder-shaped flux rope models

2007 ◽  
Vol 25 (11) ◽  
pp. 2453-2477 ◽  
Author(s):  
K. Marubashi ◽  
R. P. Lepping
Keyword(s):  
Magnetic Field ◽  
Model Fitting ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Heat Flows ◽  
Spacecraft Trajectory ◽  
Long Duration ◽  
The Difference ◽  
Magnetic Field Variations ◽  
The Magnetic Field

Abstract. We identified 17 magnetic clouds (MCs) with durations longer than 30 h, surveying the solar wind data obtained by the WIND and ACE spacecraft during 10 years from 1995 through 2004. Then, the magnetic field structures of these 17 MCs were analyzed by the technique of the least-squares fitting to force-free flux rope models. The analysis was made with both the cylinder and torus models when possible, and the results from the two models are compared. The torus model was used in order to approximate the curved portion of the MCs near the flanks of the MC loops. As a result, we classified the 17 MCs into 4 groups. They are (1) 5 MC events exhibiting magnetic field rotations through angles substantially larger than 180° which can be interpreted only by the torus model; (2) 3 other MC events that can be interpreted only by the torus model as well, though the rotation angles of magnetic fields are less than 180°; (3) 3 MC events for which similar geometries are obtained from both the torus and cylinder models; and (4) 6 MC events for which the resultant geometries obtained from both models are substantially different from each other, even though the observed magnetic field variations can be interpreted by either of the torus model or the cylinder model. It is concluded that the MC events in the first and second groups correspond to those cases where the spacecraft traversed the MCs near the flanks of the MC loops, the difference between the two being attributed to the difference in distance between the torus axis and the spacecraft trajectory. The MC events in the third group are interpreted as the cases where the spacecraft traversed near the apexes of the MC loops. For the MC events in the fourth group, the real geometry cannot be determined from the model fitting technique alone. Though an attempt was made to determine which model is more plausible for each of the MCs in this group by comparing the characteristics of associated bidirectional electron heat flows, the results were not very definitive. It was also found that the radii of the flux ropes obtained from the torus fitting tend to be generally smaller than those obtained from the cylinder fitting. This result raises a possible problem in estimating the magnetic flux and helicity carried away from the Sun by the MCs.

Connecting a Star’s Convection Zone with its Corona

1995 ◽  
Vol 12 (2) ◽  
pp. 180-185 ◽  
Author(s):  
D. J. Galloway ◽  
C. A. Jones
Keyword(s):  
Magnetic Field ◽  
Convection Zone ◽  
Flux Rope ◽  
Field System ◽  
Stellar Convection ◽  
Coronal Activity ◽  
Flux Concentration ◽  
Global Understanding ◽  
The Magnetic Field

AbstractThis paper discusses problems which have as their uniting theme the need to understand the coupling between a stellar convection zone and a magnetically dominated corona above it. Interest is concentrated on how the convection drives the atmosphere above, loading it with the currents that give rise to flares and other forms of coronal activity. The role of boundary conditions appears to be crucial, suggesting that a global understanding of the magnetic field system is necessary to explain what is observed in the corona. Calculations are presented which suggest that currents flowing up a flux rope return not in the immediate vicinity of the rope but rather in an alternative flux concentration located some distance away.

scholarly journals Photospheric magnetic field of an eroded-by-solar-wind coronal mass ejection

2016 ◽  
Vol 12 (S327) ◽  
pp. 67-70
Author(s):  
J. Palacios ◽  
C. Cid ◽  
E. Saiz ◽  
A. Guerrero
Keyword(s):  
Magnetic Field ◽  
Solar Wind ◽  
Coronal Mass Ejection ◽  
Coronal Hole ◽  
Interplanetary Medium ◽  
Flux Rope ◽  
Magnetic Characteristics ◽  
Interplanetary Coronal Mass Ejection ◽  
Fast Wind ◽  
Mass Ejection

AbstractWe have investigated the case of a coronal mass ejection that was eroded by the fast wind of a coronal hole in the interplanetary medium. When a solar ejection takes place close to a coronal hole, the flux rope magnetic topology of the coronal mass ejection (CME) may become misshapen at 1 AU as a result of the interaction. Detailed analysis of this event reveals erosion of the interplanetary coronal mass ejection (ICME) magnetic field. In this communication, we study the photospheric magnetic roots of the coronal hole and the coronal mass ejection area with HMI/SDO magnetograms to define their magnetic characteristics.

scholarly journals Non-damping oscillations at flaring loops

2018 ◽  
Vol 617 ◽  
pp. A86 ◽  
Author(s):  
D. Li ◽  
D. Yuan ◽  
Y. N. Su ◽  
Q. M. Zhang ◽  
W. Su ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Line Width ◽  
Line Emission ◽  
Flux Rope ◽  
Doppler Velocity ◽  
Narrow Slit ◽  
Plasma Properties ◽  
Spectral Window ◽  
Peak Intensity ◽  
The Magnetic Field

Context. Quasi-periodic oscillations are usually detected as spatial displacements of coronal loops in imaging observations or as periodic shifts of line properties (i.e., Doppler velocity, line width and intensity) in spectroscopic observations. They are often applied for remote diagnostics of magnetic fields and plasma properties on the Sun. Aims. We combine the imaging and spectroscopic measurements of available space missions, and investigate the properties of non-damping oscillations at flaring loops. Methods. We used the Interface Region Imaging Spectrograph (IRIS) to measure the spectrum over a narrow slit. The double-component Gaussian fitting method was used to extract the line profile of Fe XXI 1354.08 Å at the “O I” spectral window. The quasi-periodicity of loop oscillations were identified in the Fourier and wavelet spectra. Results. A periodicity at about 40 s is detected in the line properties of Fe XXI 1354.08 Å, hard X-ray emissions in GOES 1−8 Å derivative, and Fermi 26−50 keV. The Doppler velocity and line width oscillate in phase, while a phase shift of about π/2 is detected between the Doppler velocity and peak intensity. The amplitudes of Doppler velocity and line width oscillation are about 2.2 km s−1 and 1.9 km s−1, respectively, while peak intensity oscillates with amplitude at about 3.6% of the background emission. Meanwhile, a quasi-period of about 155 s is identified in the Doppler velocity and peak intensity of the Fe XXI 1354.08 Å line emission, and AIA 131 Å intensity. Conclusions. The oscillations at about 40 s are not damped significantly during the observation; this might be linked to the global kink modes of flaring loops. The periodicity at about 155 s is most likely a signature of recurring downflows after chromospheric evaporation along flaring loops. The magnetic field strengths of the flaring loops are estimated to be about 120−170 G using the magnetohydrodynamic seismology diagnostics, which are consistent with the magnetic field modeling results using the flux rope insertion method.

scholarly journals Magnetic field disturbances in the sheath region of a super-sonic interplanetary magnetic cloud

2008 ◽  
Vol 26 (10) ◽  
pp. 3153-3158 ◽  
Author(s):  
E. Romashets ◽  
M. Vandas ◽  
S. Poedts
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Storms ◽  
Magnetic Cloud ◽  
The Body ◽  
Magnetic Clouds ◽  
Shock Surface ◽  
Sheath Region ◽  
Magnetic Field Magnitude ◽  
The Magnetic Field ◽  
Magnetic Disturbances

Abstract. It is well-known that interplanetary magnetic clouds can cause strong geomagnetic storms due to the high magnetic field magnitude in their interior, especially if there is a large negative Bz component present. In addition, the magnetic disturbances around such objects can play an important role in their "geo-effectiveness". On the other hand, the magnetic and flow fields in the CME sheath region in front of the body and in the rear of the cloud are important for understanding both the dynamics and the evolution of the interplanetary cloud. The "eventual" aim of this work is to calculate the magnetic field in this CME sheath region in order to evaluate the possible geo-efficiency of the cloud in terms of the maximum |Bz|-component in this region. In this paper we assess the potential of this approach by introducing a model with a simplified geometry. We describe the magnetic field between the CME shock surface and the cloud's boundary by means of a vector potential. We also apply our model and present the magnetic field distribution in the CME sheath region in front of the body and in the rear of the cloud formed after the event of 20 November 2003.

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