The Small-Scale Structure of Coronal Loops

1994 ◽  
Vol 144 ◽  
pp. 189-193
Author(s):  
M. A. Berger
Keyword(s):  
Equilibrium State ◽  
Coronal Loop ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Primary Source ◽  
Small Scale ◽  
Topological Complexity ◽  
Coronal Loops ◽  
Before And After ◽  
Dissipation Model

AbstractHow do we model coronal loops which contain a rich internal structure? Coronal loops usually lie close to the equilibrium state, but equilibrium fields are generally nonlinear, three-dimensional, and contain intense current layers. Nevertheless, it is important to study highly structured loops. Small reconnection events (microflares and nanoflares) which simplify the structure may be the primary source of heat in the closed corona. The magnetic energy released during a reconnection event can be estimated if one knows the equilibrium energy before and after the event. Furthermore, structured or tangled fields dissipate wave energy more efficiently than smooth fields. Here we present a method for studying tangled fields. Lower bounds can be placed on the energy of the equilibrium field, given a measure of the topological complexity known as the crossing number. These bounds provide an estimate of the energy generated in a coronal loop due to random photospheric motions. This calculation is used to estimate the heating rate in Parker’s topological dissipation model.

Strong MHD helical turbulence and the nonlinear dynamo effect

1976 ◽  
Vol 77 (2) ◽  
pp. 321-354 ◽  
Author(s):  
A. Pouquet ◽  
U. Frisch ◽  
J. Léorat
Keyword(s):  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Power Laws ◽  
Inertial Range ◽  
Small Scale ◽  
Mhd Turbulence ◽  
Inverse Cascade ◽  
Small Scales ◽  
Dynamo Effect

To understand the turbulent generation of large-scale magnetic fields and to advance beyond purely kinematic approaches to the dynamo effect like that introduced by Steenbeck, Krause & Radler (1966)’ a new nonlinear theory is developed for three-dimensional, homogeneous, isotropic, incompressible MHD turbulence with helicity, i.e. not statistically invariant under plane reflexions. For this, techniques introduced for ordinary turbulence in recent years by Kraichnan (1971 a)’ Orszag (1970, 1976) and others are generalized to MHD; in particular we make use of the eddy-damped quasi-normal Markovian approximation. The resulting closed equations for the evolution of the kinetic and magnetic energy and helicity spectra are studied both theoretically and numerically in situations with high Reynolds number and unit magnetic Prandtl number.Interactions between widely separated scales are much more important than for non-magnetic turbulence. Large-scale magnetic energy brings to equipartition small-scale kinetic and magnetic excitation (energy or helicity) by the ‘Alfvén effect’; the small-scale ‘residual’ helicity, which is the difference between a purely kinetic and a purely magnetic helical term, induces growth of large-scale magnetic energy and helicity by the ‘helicity effect’. In the absence of helicity an inertial range occurs with a cascade of energy to small scales; to lowest order it is a −3/2 power law with equipartition of kinetic and magnetic energy spectra as in Kraichnan (1965) but there are −2 corrections (and possibly higher ones) leading to a slight excess of magnetic energy. When kinetic energy is continuously injected, an initial seed of magnetic field will grow to approximate equipartition, at least in the small scales. If in addition kinetic helicity is injected, an inverse cascade of magnetic helicity is obtained leading to the appearance of magnetic energy and helicity in ever-increasing scales (in fact, limited by the size of the system). This inverse cascade, predicted by Frischet al.(1975), results from a competition between the helicity and Alféh effects and yields an inertial range with approximately — 1 and — 2 power laws for magnetic energy and helicity. When kinetic helicity is injected at the scale linjand the rate$\tilde{\epsilon}^V$(per unit mass), the time of build-up of magnetic energy with scaleL[Gt ] linjis$t \approx L(|\tilde{\epsilon}^V|l^2_{\rm inj})^{-1/3}.$

scholarly journals Solar Magnetic Loops Observed with TRACE and EIT

2004 ◽  
Vol 219 ◽  
pp. 503-516
Author(s):  
Markus J. Aschwanden ◽  
Alan M. Title
Keyword(s):  
Transition Region ◽  
Energy Budget ◽  
Coronal Loop ◽  
Extreme Ultraviolet ◽  
Magnetic Energy ◽  
Coronal Loops ◽  
Uniform Heating ◽  
Magnetic Topology ◽  
Oscillations And Waves

We select some highlights and new results that have been obtained from detailed “microscopic” observations of coronal loop structures with the Transition Region and Coronal Explorer (TRACE) and Extreme Ultraviolet Imager (EIT) instruments, including: (1) the inhomogeneous substructure of EUV loops, (2) the dynamic and non-hydrostatic nature, (3) the non-uniform heating, (4) the magnetic topology at the loop foot-points, (5) the magnetic energy budget for heating, and (6) oscillations and waves in coronal loops.

scholarly journals Multi-scale dynamics of magnetic flux tubes and inverse magnetic energy transfer

2020 ◽  
Vol 86 (4) ◽  
Author(s):  
Muni Zhou ◽  
Nuno F. Loureiro ◽  
Dmitri A. Uzdensky
Keyword(s):  
Magnetic Flux ◽  
Time Evolution ◽  
Magnetic Energy ◽  
Numerical Study ◽  
Three Dimensional ◽  
Early Time ◽  
Small Scale ◽  
Flux Tubes ◽  
Seed Field ◽  
Magnetic Flux Tubes

We report on an analytical and numerical study of the dynamics of a three-dimensional array of identical magnetic flux tubes in the reduced-magnetohydrodynamic description of the plasma. We propose that the long-time evolution of this system is dictated by flux-tube mergers, and that such mergers are dynamically constrained by the conservation of the pertinent (ideal) invariants, viz. the magnetic potential and axial fluxes of each tube. We also propose that in the direction perpendicular to the merging plane, flux tubes evolve in a critically balanced fashion. These notions allow us to construct an analytical model for how quantities such as the magnetic energy and the energy-containing scale evolve as functions of time. Of particular importance is the conclusion that, like its two-dimensional counterpart, this system exhibits an inverse transfer of magnetic energy that terminates only at the system scale. We perform direct numerical simulations that confirm these predictions and reveal other interesting aspects of the evolution of the system. We find, for example, that the early time evolution is characterized by a sharp decay of the initial magnetic energy, which we attribute to the ubiquitous formation of current sheets. We also show that a quantitatively similar inverse transfer of magnetic energy is observed when the initial condition is a random, small-scale magnetic seed field.

scholarly journals Ultra-long and quite thin coronal loop without significant expansion

2020 ◽  
Vol 639 ◽  
pp. A114
Author(s):  
Dong Li ◽  
Ding Yuan ◽  
Marcel Goossens ◽  
Tom Van Doorsselaere ◽  
Wei Su ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Line ◽  
Cross Section ◽  
Magnetic Field Line ◽  
Coronal Loop ◽  
Scale Height ◽  
Local Magnetic Field ◽  
Small Scale ◽  
Coronal Loops ◽  
Loop Model

Context. Coronal loops are the basic building blocks of the solar corona. They are related to the mass supply and heating of solar plasmas in the corona. However, their fundamental magnetic structures are still not well understood. Most coronal loops do not expand significantly, but the diverging magnetic field would have an expansion factor of about 5−10 over one pressure scale height. Aims. We investigate a unique coronal loop with a roughly constant cross section. The loop is ultra long and quite thin. A coronal loop model with magnetic helicity is presented to explain the small expansion of the loop width. Methods. This coronal loop was predominantly detectable in the 171 Å channel of the Atmospheric Imaging Assembly (AIA). Then, the local magnetic field line was extrapolated within a model of the potential field source-surface. Finally, the differential emission measure analysis made from six AIA bandpasses was applied to obtain the thermal properties of this loop. Results. This coronal loop has a projected length of roughly 130 Mm, a width of about 1.5 ± 0.5 Mm, and a lifetime of about 90 min. It follows an open magnetic field line. The cross section expanded very little (i.e., 1.5−2.0) along the loop length during its whole lifetime. This loop has a nearly constant temperature at about 0.7 ± 0.2 MK, but its density exhibits the typical structure of a stratified atmosphere. Conclusions. We use the theory of a thin twisted flux tube to construct a model for this nonexpanding loop and find that with sufficient twist, a coronal loop can indeed attain equilibrium. However, we cannot rule out other possibilities such as footpoint heating by small-scale reconnection or an elevated scale height by a steady flow along the loop.

scholarly journals Coronal Loop Mapping to Infer the Best Magnetic Field Models for Active Region Prominences

2013 ◽  
Vol 8 (S300) ◽  
pp. 416-417
Author(s):  
G. Allen Gary ◽  
Qiang Hu ◽  
Jong Kwan Lee
Keyword(s):  
Magnetic Field ◽  
Coronal Loop ◽  
Field Model ◽  
Three Dimensional ◽  
Coronal Loops ◽  
Magnetic Field Model ◽  
Free Parameters ◽  
Field Lines ◽  
Fitness Parameter ◽  
The Magnetic Field

AbstractThis article comments on the results of a new, rapid, and flexible manual method to map on-disk individual coronal loops of a two-dimensional EUV image into the three-dimensional coronal loops. The method by Gary, Hu, and Lee (2013) employs cubic Bézier splines to map coronal loops using only four free parameters per loop. A set of 2D splines for coronal loops is transformed to the best 3D pseudo-magnetic field lines for a particular coronal model. The results restrict the magnetic field models derived from extrapolations of magnetograms to those admissible and inadmissible via a fitness parameter. This method uses the minimization of the misalignment angles between the magnetic field model and the best set of 3D field lines that match a set of closed coronal loops. We comment on the implication of the fitness parameter in connection with the magnetic free energy and comment on extensions of our earlier work by considering the issues of employing open coronal loops or employing partial coronal loop.

Self-biased Dual-phase Energy Harvesting System

2013 ◽  
Vol 1556 ◽  
Author(s):  
Yuan Zhou ◽  
Amar Bhalla ◽  
Shashank Priya
Keyword(s):  
Magnetic Field ◽  
Magnetic Energy ◽  
Synthesis Method ◽  
Three Dimensional ◽  
Deposition Process ◽  
Small Scale ◽  
Dual Phase ◽  
Mems Devices ◽  
Power Sources ◽  
Dc Magnetic Field

ABSTRACTIn this study, we report the design and fabrication of a dual-phase energy harvester which can synchronously harvest both mechanical and magnetic energy in the absence of DC magnetic field. The harvester consists of a magnetostrictive cantilever beam and a magnetostrictive/ piezoelectric (M/P) self-biased laminate composite structure. This structure allows us to utilize piezoelectric and self-biased magnetoelectric effect simultaneously. By combining these mechanisms together, a sum effect for harvesting both magnetic and vibration energy was realized under DC magnetic field free condition. The bilayer structure provides a simplified geometry that can be easily incorporated into MEMS devices. We demonstrate a hybrid synthesis method for fabrication of complex three-dimensional thin films using a cost-effective and mask-less aerosol jet deposition process. The combination of the hybrid aerosol jet process with dual phase harvester design provides the opportunity to fabricate small scale power sources required for structural health monitoring applications.

scholarly journals Coronal energy release by MHD avalanches: continuous driving

2018 ◽  
Vol 615 ◽  
pp. A84 ◽  
Author(s):  
J. Reid ◽  
A. W. Hood ◽  
C. E. Parnell ◽  
P. K. Browning ◽  
P. J. Cargill
Keyword(s):  
Magnetic Field ◽  
Steady State ◽  
Coronal Loop ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Mhd Simulations ◽  
First Time ◽  
Viable Mechanism ◽  
The Magnetic Field ◽  
Heating Profile

Previous work has confirmed the concept of a magnetohydrodynamic (MHD) avalanche in pre-stressed threads within a coronal loop. We undertook a series of full, three-dimensional MHD simulations in order to create three threads by twisting the magnetic field through boundary motions until an instability ensues. We find that, following the original instability, one unstable thread can disrupt its neighbours with continued driving. A “bursty” heating profile results, with a series of ongoing energy releases, but no evident steady state. For the first time using full MHD, we show that avalanches are a viable mechanism for the storing and release of magnetic energy in the solar corona, as a result of photospheric motions.

High-Resolution Three-Dimensional MHD Simulations of Plasmoid Formation in Solar Flares

2020 ◽  
Author(s):  
Joel Dahlin ◽  
Spiro Antiochos ◽  
C. Richard DeVore
Keyword(s):  
Current Sheet ◽  
Adaptive Mesh Refinement ◽  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Dimensional Structure ◽  
Small Scale ◽  
Ample Evidence ◽  
Current Sheets

<p>In highly conducting plasmas, reconnecting current sheets are often unstable to the generation of plasmoids, small-scale magnetic structures that play an important role in facilitating the rapid release of magnetic energy and channeling that energy into accelerated particles. There is ample evidence for plasmoids throughout the heliosphere, from in situ observations of flux ropes in the solar wind and planetary magnetospheres to remote-sensing imaging of plasma ‘blobs’ associated with explosive solar activity such as eruptive flares and coronal jets. Accurate models for plasmoid formation and dynamics must capture the large-scale self-organization responsible for forming the reconnecting current sheet. However, due to the computational difficulty inherent in the vast separation between the global and current sheet scales, previous numerical studies have typically explored configurations with either reduced dimensionality or pre-formed current sheets. We present new three-dimensional MHD studies of an eruptive flare in which the formation of the current sheet and subsequent reconnection and plasmoid formation are captured within a single simulation. We employ Adaptive Mesh Refinement (AMR) to selectively resolve fine-scale current sheet dynamics. Reconnection in the flare current sheet generates many plasmoids that exhibit highly complex, three-dimensional structure. We show how plasmoid formation and dynamics evolve through the course of the flare, especially in response to the weakening of the reconnection “guide field” linked to the global reduction of magnetic shear. We discuss implications of our results for particle acceleration and transport in eruptive flares as well as for observations by Parker Solar Probe and the forthcoming Solar Orbiter.</p>

Nilai-Nilai Pendidikan Akhlak dalam Al-Qur’an

2018 ◽  
Vol 10 (2) ◽  
pp. 269-295
Author(s):  
Sri Waluyo
Keyword(s):  
Moral Education ◽  
Primary Source ◽  
Secondary Data ◽  
Primary Data ◽  
The Core ◽  
Primary Data Source ◽  
Before And After ◽  
Data Source

This paper discusses the content of Q.S. al-Baqarah ([2]: 67-73). The data used in the preparation of this paper is the data that is primary and secondary. The primary source is data obtained from the core source. In conducting a study of a verse, it is clear that the primary data source is derived from the Qur'an,precisely on Q.S. al-Baqarah ([2]: 67-73). Secondary data is dataobtained from other sources that are still related to the problemand provide interpretation of the primary source. The method usedin analyzing this paper is the tahlili method. This method describesthe meaning contained by the Qur'an, verse by verse, and letterafter letter according to the order in the Mushaf. The descriptionincludes the various aspects which the interpreted verses contain,such as the meaning of the vocabulary, the connotation of thesentence, the background of the verse down, its relation to otherverses, both before and after. And do not miss the opinion that hasbeen given regarding the interpretation of these verses, whetherdelivered by the Prophet, companions, the tabi'in, as well as othercommentators. This study shows that in Q.S. (2): 67-73) there arevalues of moral education which include: 1) morals in asking, (2)morals to parents, (3) patience of educators, (4) educator honesty,and (5) obedience of learners.

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