scholarly journals Coronal global EIT waves as tools for multiple diagnostics

2007 ◽  
Vol 3 (S247) ◽  
pp. 243-250
Author(s):  
I. Ballai ◽  
M. Douglas
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Solar Disk ◽  
Coronal Loop ◽  
Large Scale ◽  
Theoretical Models ◽  
Coronal Loops ◽  
Quiet Sun ◽  
Propagating Waves ◽  
Global Magnetic Field

AbstractObservations in EUV lines of the solar corona revealed large scale propagating waves generated by eruptive events able to travel across the solar disk for large distances. In the low corona, CMEs are known to generate, e.g. EIT waves which can be used to sample the coronal local and global magnetic field. This contribution presents theoretical models for finding values of magnetic field in the quiet Sun and coronal loops based on the interaction of global waves and local coronal loops as well as results on the generation and propagation of EIT waves. The physical connection between local and global solar coronal events (e.g. flares, EIT waves and coronal loop oscillations) will also be explored.

scholarly journals Propagation of an MHD Shock in the Vicinity of a Magnetic Neutral Sheet

1980 ◽  
Vol 91 ◽  
pp. 323-326
Author(s):  
D. J. Mullan ◽  
R. S. Steinolfson
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Solar Corona ◽  
Large Scale ◽  
Field Structure ◽  
Neutral Sheet ◽  
Solar Cosmic Rays ◽  
Magnetic Field Structure ◽  
Large Scale Magnetic Field ◽  
Highly Correlated

The acceleration of solar cosmic rays in association with certain solar flares is known to be highly correlated with the propagation of an MHD shock through the solar corona (Svestka, 1976). The spatial structure of the sources of solar cosmic rays will be determined by those regions of the corona which are accessible to the flare-induced shock. The regions to which the flare shock is permitted to propagate are determined by the large scale magnetic field structure in the corona. McIntosh (1972, 1979) has demonstrated that quiescent filaments form a single continuous feature (a “baseball stitch”) around the surface of the sun. It is known that helmet streamers overlie quiescent filaments (Pneuman, 1975), and these helmet streamers contain large magnetic neutral sheets which are oriented essentially radially. Hence the magnetic field structure in the low solar corona is characterized by a large-scale radial neutral sheet which weaves around the entire sun following the “baseball stitch”. There is therefore a high probability that as a shock propagates away from a flare, it will eventually encounter this large neutral sheet.

scholarly journals On the origin of variable structures in the winds of hot luminous stars

2013 ◽  
Vol 440 (1) ◽  
pp. 2-9 ◽  
Author(s):  
Yannick J. L. Michaux ◽  
Anthony F. J. Moffat ◽  
André-Nicolas Chené ◽  
Nicole St-Louis
Keyword(s):  
Magnetic Field ◽  
Empirical Evidence ◽  
Temporal Variability ◽  
Large Scale ◽  
Small Scale ◽  
Ionization Zone ◽  
Corotating Interaction Regions ◽  
Wind Variability ◽  
Global Magnetic Field ◽  
Interaction Regions

Abstract Examination of the temporal variability properties of several strong optical recombination lines in a large sample of Galactic Wolf–Rayet (WR) stars reveals possible trends, especially in the more homogeneous WC than the diverse WN subtypes, of increasing wind variability with cooler subtypes. This could imply that a serious contender for the driver of the variations is stochastic, magnetic subsurface convection associated with the 170 kK partial-ionization zone of iron, which should occupy a deeper and larger zone of greater mass in cooler WR subtypes. This empirical evidence suggests that the heretofore proposed ubiquitous driver of wind variability, radiative instabilities, may not be the only mechanism playing a role in the stochastic multiple small-scaled structures seen in the winds of hot luminous stars. In addition to small-scale stochastic behaviour, subsurface convection guided by a global magnetic field with localized emerging loops may also be at the origin of the large-scale corotating interaction regions as seen frequently in O stars and occasionally in the winds of their descendant WR stars.

scholarly journals Prominence Disappearance Related to CMEs

1998 ◽  
Vol 167 ◽  
pp. 380-383
Author(s):  
E. Hiei
Keyword(s):  
Magnetic Field ◽  
Solar Disk ◽  
Large Scale ◽  
Coronal Magnetic Field ◽  
X Ray ◽  
Dynamic Phenomena

AbstractDB (disparition brusque) events are associated with dynamic phenomena such as a CME, a flare, brightening of a soft X-ray arcade, and soft X-ray dimming, and probably a change of the coronal magnetic field on a large scale. The DB event observed on January 16, 1993 identified with a CME occurred on the solar disk.

scholarly journals CMEs ‘en rafale’ observations and simulations

2008 ◽  
Vol 4 (S257) ◽  
pp. 251-255
Author(s):  
Cristiana Dumitrache
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Solar Disk ◽  
Large Scale ◽  
Stable Equilibrium ◽  
Time Dependent ◽  
Kink Mode ◽  
Mhd Equilibrium ◽  
Ideal Mhd ◽  
Slow Evolution

AbstractA CME is triggered by the disappearance of a stable equilibrium as a result of the slow evolution of the photospheric magnetic field. This disappearance may be due to a loss of ideal-MHD equilibrium or stability as in the kink mode, or to a loss of resistive-MHD equilibrium as a result of magnetic reconnection. We have obtained CMEs in sequence by a time dependent magnetohydrodynamic computation performed on three solar radii. These successive CMEs resulted from a prominence eruption. Velocities of these CMEs decrease in time, from a CME to another. We present observational evidences for large-scale magnetic reconnections that caused the destabilization of a sigmoid filament. These reconnections covered half of the solar disk and produced CMEs in squall (sequential CMEs).

scholarly journals Coronal waves in coronal loops during non-flare stage

2008 ◽  
Vol 4 (S257) ◽  
pp. 245-249
Author(s):  
Dmitry Prosovetsky
Keyword(s):  
Magnetic Field ◽  
Wave Propagation ◽  
Solar Disk ◽  
Solar Limb ◽  
Active Area ◽  
Perpendicular Direction ◽  
Coronal Loops ◽  
New Type ◽  
The Waves ◽  
Outer Area

AbstractUsing SOHO/EIT Fe XII λ195 Å observations the new type of oscillations in coronal loops was detected. The oscillation corresponds to wave propagated to outer area of atmosphere of active area. As opposed to most kind of oscillations associated with coronal loops the waves are observed at non-flare stage of active areas evolution. Velocities of the wave propagation were 8-20 km s−1 and had quasi-perpendicular direction with magnetic field. Such waves were detected in active areas located on solar disk and loops structures outside solar limb. Investigation of EIT data shows the waves are not result of changes of topology of a magnetic field and loops configuration. The nature and probable sources of waves are discussed.

scholarly journals A Thermal Catastrophe in a Resonantly Heated Coronal Loop

1983 ◽  
Vol 102 ◽  
pp. 397-400
Author(s):  
P.C.H. Martens ◽  
M. Kuperus
Keyword(s):  
Magnetic Field ◽  
Thermal Stability ◽  
Coronal Loop ◽  
Coronal Loops ◽  
Natural Explanation ◽  
X Ray ◽  
Magnetic Field Topology ◽  
Coronal Rain ◽  
The Magnetic Field ◽  
Thermal Stability Of

A theory for the thermal stability of hot coronal loops is presented, which is based on the resonant electrodynamic heating theory of Ionson (1982) and the evaporation/condensation scenario of Krall and Antiochos (1980). The theory predicts that gradual changes in the length of a loop or in its magnetic field strength can trigger catastrophic changes in the X-ray visibility of the loop, without the need for a change in the magnetic field topology.A natural explanation is thereby given for the observations of X-ray brightenings in loops and loop evacuations with coronal rain.

scholarly journals Comparing extrapolations of the coronal magnetic field structure at 2.5R⊙with multi-viewpoint coronagraphic observations

2019 ◽  
Vol 627 ◽  
pp. A9 ◽  
Author(s):  
C. Sasso ◽  
R. F. Pinto ◽  
V. Andretta ◽  
R. A. Howard ◽  
A. Vourlidas ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Solar Corona ◽  
Large Scale ◽  
Solar Rotation ◽  
Coronal Holes ◽  
Coronal Magnetic Field ◽  
Central Meridian ◽  
Fast Method ◽  
The Many ◽  
The Magnetic Field

The magnetic field shapes the structure of the solar corona, but we still know little about the interrelationships between the coronal magnetic field configurations and the resulting quasi-stationary structures observed in coronagraphic images (such as streamers, plumes, and coronal holes). One way to obtain information on the large-scale structure of the coronal magnetic field is to extrapolate it from photospheric data and compare the results with coronagraphic images. Our aim is to verify whether this comparison can be a fast method to systematically determine the reliability of the many methods that are available for modeling the coronal magnetic field. Coronal fields are usually extrapolated from photospheric measurements that are typically obtained in a region close to the central meridian on the solar disk and are then compared with coronagraphic images at the limbs, acquired at least seven days before or after to account for solar rotation. This implicitly assumes that no significant changes occurred in the corona during that period. In this work, we combine images from three coronagraphs (SOHO/LASCO-C2 and the two STEREO/SECCHI-COR1) that observe the Sun from different viewing angles to build Carrington maps that cover the entire corona to reduce the effect of temporal evolution to about five days. We then compare the position of the observed streamers in these Carrington maps with that of the neutral lines obtained from four different magnetic field extrapolations to evaluate the performances of the latter in the solar corona. Our results show that the location of coronal streamers can provide important indications to distinguish between different magnetic field extrapolations.

Large-Scale Coronal Magnetic Structure and Its Variations during an 11-year Solar Cycle

1994 ◽  
Vol 144 ◽  
pp. 35-39
Author(s):  
E. V. Ivanov
Keyword(s):  
Magnetic Field ◽  
Solar Cycle ◽  
Large Scale ◽  
Heliospheric Current Sheet ◽  
Reference Points ◽  
Source Surface ◽  
Solar Cycles ◽  
Dipole Component ◽  
Global Magnetic Field ◽  
Main Components

AbstractMaps of coronal magnetic fields at different heights calculated under potential approximation, have been used to reconstruct the corona shape in different phases of solar cycles 21 and 22. The shape of the solar corona depends on the maximum heliolatitudes and the structure of the heliospheric current sheet (HCS) that, in turn, are determined by space-time variations of the 3 main components of the global magnetic field of the Sun: 1) the axial dipole component; 2) the inclined dipole component; and 3) the quadrupole component. Variations of theHCSmaximum heliolatitudes and the width of the corona at 2.5R⊙during a solar cycle are compared with variations of the global magnetic field indices in the photosphere and at the source surface. The role of the solar cycle reference points and the global magnetic field indices in the corona shape variations over a solar cycle are discussed.

Mapping the global magnetic field in the solar corona through magnetoseismology

2021 ◽  
Author(s):  
Zihao Yang ◽  
Christian Bethge ◽  
Hui Tian ◽  
Steven Tomczyk ◽  
Richard Morton ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Solar Corona ◽  
Phase Speed ◽  
Magnetic Coupling ◽  
Active Regions ◽  
Coronal Magnetic Field ◽  
Spectral Lines ◽  
Mhd Waves ◽  
Global Magnetic Field

<p>Magnetoseismology, a technique of magnetic field diagnostics based on observations of magnetohydrodynamic (MHD) waves, has been widely used to estimate the field strengths of oscillating structures in the solar corona. However, previously magnetoseismology was mostly applied to occasionally occurring oscillation events, providing an estimate of only the average field strength or one-dimensional distribution of field strength along an oscillating structure. This restriction could be eliminated if we apply magnetoseismology to the pervasive propagating transverse MHD waves discovered with the Coronal Multi-channel Polarimeter (CoMP). Using several CoMP observations of the Fe XIII 1074.7 nm and 1079.8 nm spectral lines, we obtained maps of the plasma density and wave phase speed in the corona, which allow us to map both the strength and direction of the coronal magnetic field in the plane of sky. We also examined distributions of the electron density and magnetic field strength, and compared their variations with height in the quiet Sun and active regions. Such measurements could provide critical information to advance our understanding of the Sun's magnetism and the magnetic coupling of the whole solar atmosphere.</p>

scholarly journals Magnetic structure of sunspot under the photosphere

2009 ◽  
Vol 5 (H15) ◽  
pp. 351-351
Author(s):  
Elena A. Kirichek ◽  
Alexandr A. Solov'ev
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Large Scale ◽  
Propagation Speed ◽  
Theoretical Models ◽  
Flux Tubes ◽  
Magnetoacoustic Waves ◽  
Deep Layers ◽  
Magnetic Flux Tubes ◽  
Wave Propagation Speed

In recent years, the local helioseismology has become a highly effective tool for investigating subphotospheric layers of the Sun, which can yield fairly detailed distributions of the subphotospheric temperatures and large-scale plasma flows based on the spectra of the oscillations observed at the photospheric layers and the observed peculiarities of propagation of magnetoacoustic waves in this medium (Zhao et al. (2001), Kosovichev (2006)). Unfortunately, the effects of temperature and the magnetic field on the wave propagation speed have not yet been separated Kosovichev (2006), so that the structure of the sunspot magnetic field in deep layers, beneath the photosphere, remains a subject of purely theoretical analysis. In his analysis of some theoretical models of the subphotospheric layers of sunspots based on recent helioseismological data, Kosovichev (2006) concluded that Parker's (“spaghetti”) cluster model Parker (1979) is most appropriate. In this model, the magnetic flux in the sunspot umbra is concentrated into separate, strongly compressed, vertical magnetic flux tubes that are interspaced with plasma that is almost free of magnetic field; the plasma can move between these tubes.

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