Interplanetary magnetic clouds, helicity conservation, and current-core flux-ropes

1996 ◽  
Vol 101 (A7) ◽  
pp. 15667-15684 ◽  
Author(s):  
Ashok Kumar ◽  
D. M. Rust
Keyword(s):  
Magnetic Clouds ◽  
Helicity Conservation ◽  
Flux Ropes

The flux of flux ropes embedded within magnetic clouds near 5 AU

2021 ◽  
Author(s):  
Yan Zhao ◽  
Hengqiang Feng ◽  
Qiang Liu ◽  
Ake Zhao ◽  
Guoqing Zhao ◽  
...  
Keyword(s):  
Magnetic Clouds ◽  
Flux Ropes

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 Magnetic Helicity Conservation

2005 ◽  
Vol 13 ◽  
pp. 85-88 ◽  
Author(s):  
Mitchell A. Berger
Keyword(s):  
Interplanetary Space ◽  
Energy State ◽  
Minimum Energy ◽  
Free Field ◽  
Space Physics ◽  
Magnetic Clouds ◽  
Magnetic Helicity ◽  
Dynamo Theory ◽  
Mhd Turbulence ◽  
Helicity Conservation

AbstractMagnetic Helicity measures basic structural properties of magnetic fields such as twist, shear, linking, writhe, and handedness. It is conserved in ideal MHD and approximately conserved during reconnection. The minimum energy state of a field with a given magnetic helicity is a linear force free field. Helicity plays an important role in MHD turbulence and dynamo theory, and provides a valuable observational tool in solar and space physics. Helicity conservation can be tracked from the solar dynamo to active regions to coronal mass ejections to magnetic clouds in interplanetary space.

scholarly journals Magnetic helicity content in solar wind flux ropes

2008 ◽  
Vol 4 (S257) ◽  
pp. 379-389 ◽  
Author(s):  
Sergio Dasso
Keyword(s):  
Solar Wind ◽  
Interplanetary Medium ◽  
Dynamical Evolution ◽  
Magnetic Clouds ◽  
Magnetic Helicity ◽  
Flux Tubes ◽  
Global Configuration ◽  
Flux Ropes ◽  
Field Lines

AbstractMagnetic helicity (H) is an ideal magnetohydrodynamical (MHD) invariant that quantifies the twist and linkage of magnetic field lines. In magnetofluids with low resistivity, H decays much less than the energy, and it is almost conserved during times shorter than the global diffusion timescale. The extended solar corona (i.e., the heliosphere) is one of the physical scenarios where H is expected to be conserved. The amount of H injected through the photospheric level can be reorganized in the corona, and finally ejected in flux ropes to the interplanetary medium. Thus, coronal mass ejections can appear as magnetic clouds (MCs), which are huge twisted flux tubes that transport large amounts of H through the solar wind. The content of H depends on the global configuration of the structure, then, one of the main difficulties to estimate it from single spacecraft in situ observations (one point - multiple times) is that a single spacecraft can only observe a linear (one dimensional) cut of the MC global structure. Another serious difficulty is the intrinsic mixing between its spatial shape and its time evolution that occurs during the observation period. However, using some simple assumptions supported by observations, the global shape of some MCs can be unveiled, and the associated H and magnetic fluxes (F) can be estimated. Different methods to quantify H and F from the analysis of in situ observations in MCs are presented in this review. Some of these methods consider a MC in expansion and going through possible magnetic reconnections with its environment. We conclude that H seems to be a ‘robust’ MHD quantity in MCs, in the sense that variations of H for a given MC deduced using different methods, are typically lower than changes of H when a different cloud is considered. Quantification of H and F lets us constrain models of coronal formation and ejection of flux ropes to the interplanetary medium, as well as of the dynamical evolution of MCs in the solar wind.

scholarly journals Interplanetary flux ropes of any twist distribution

2019 ◽  
Vol 627 ◽  
pp. A90
Author(s):  
M. Vandas ◽  
E. P. Romashets
Keyword(s):  
Magnetic Field ◽  
Unit Length ◽  
Flux Rope ◽  
Field Configuration ◽  
Magnetic Clouds ◽  
Magnetic Field Configuration ◽  
Flux Ropes ◽  
Envelope Model ◽  
The Common ◽  
Free Fields

Context. Recent investigations indicate that the magnetic field configuration in interplanetary flux ropes is in contrast with the common magnetic field models that are used to fit them, namely constant-alpha force-free fields, whose twist increases without limits toward the flux-rope boundary. Therefore, magnetic field configurations with a constant twist are now being employed in fits. Aims. Real flux ropes have varying twist. Therefore, analytical magnetic field configurations with prescribed twist distributions are searched for in cylindrical geometry. Methods. Equations for the field solenoidality and for the force-free condition are solved for case when a twist profile is prescribed. Results. A model of a force-free magnetic field configuration with an arbitrarily given twist distribution in a cylinder and its relative helicity per unit length are presented. It is applied to a core-envelope model recently suggested in studies of twist in magnetic clouds.

scholarly journals Magnetic Helicity in Sigmoids, Coronal Mass Ejections and Magnetic Clouds

2005 ◽  
Vol 13 ◽  
pp. 105-108
Author(s):  
D. M. Rust
Keyword(s):  
Solar Cycle ◽  
Coronal Mass Ejections ◽  
Magnetic Clouds ◽  
Magnetic Helicity ◽  
The Sun ◽  
X Ray ◽  
The North ◽  
Negative Helicity ◽  
Flux Ropes ◽  
Lines Of Evidence

AbstractSigmoids, coronal mass ejections (CMEs) and magnetic clouds (MCs) all show signatures of twisted and writhing magnetic fields. CMEs are often associated with MCs, whose fields are regularly mapped with sensitive magnetometers. These measurements reveal that MC fields are helical, and each MC carries magnetic helicity away from the sun. It is more difficult to determine the magnetic helicity of the corresponding features on the sun. This presentation surveys recent work on helicity in solar features, focusing especially on the interpretation of sigmoids, which are S-shaped, bright features seen in images from the Yohkoh soft X-ray telescope. Several lines of evidence indicate that sigmoids are twisted and writhing flux ropes that erupt as components of CMEs. CMEs may be initiated by MHD-instable flux ropes. The fact that the ejected flux ropes carry off a large amount of positive helicity from the south and negative helicity from the north each solar cycle implies an equal, compensating flow of helicity through the sun’s equatorial plane.

scholarly journals THE INTERNAL STRUCTURE OF CORONAL MASS EJECTIONS: ARE ALL REGULAR MAGNETIC CLOUDS FLUX ROPES?

2009 ◽  
Vol 695 (2) ◽  
pp. L171-L175 ◽  
Author(s):  
C. Jacobs ◽  
I. I. Roussev ◽  
N. Lugaz ◽  
S. Poedts
Keyword(s):  
Internal Structure ◽  
Coronal Mass Ejections ◽  
Magnetic Clouds ◽  
Flux Ropes

Study of flux-rope characteristics at sub-astronomical-unit distances using the Helios 1 and 2 spacecraft

2020 ◽  
Vol 495 (2) ◽  
pp. 1566-1576
Author(s):  
Anil Raghav ◽  
Sandesh Gaikwad ◽  
Yuming Wang ◽  
Zubair I Shaikh ◽  
Wageesh Mishra ◽  
...  
Keyword(s):  
Magnetic Flux ◽  
Magnetic Energy ◽  
Ambient Medium ◽  
Flux Rope ◽  
Magnetic Clouds ◽  
Astronomical Unit ◽  
Magnetic Flux Ropes ◽  
Flux Ropes ◽  
External Conditions ◽  
Internal Properties

ABSTRACT Magnetic flux ropes observed as magnetic clouds near 1 au have been extensively studied in the literature and their distinct features are derived using numerous models. These studies summarize the general characteristics of flux ropes at 1 au without providing an understanding of the continuous evolution of the flux ropes from near the Sun to 1 au. In the present study, we investigate 26 flux ropes observed by the Helios 1 and 2 spacecraft (from 0.3 to 1 au) using the velocity-modified Gold–Hoyle model. The correlation and regression analyses suggest that the expansion speed, poloidal speed, total magnetic helicity and twist per au of the flux rope are independent of heliospheric distance. The study implies that the aforementioned features are more strongly influenced by their internal properties compared with external conditions in the ambient medium. Moreover, the poloidal magnetic flux and magnetic energy of the studied flux ropes exhibit power-law dependence on heliospheric distance. A better understanding of the underlying physics and corroboration of these results is expected from the Parker Solar Probe measurements in the near future.

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