Damping of magnetohydrodynamic waves by resonant absorption in the solar atmosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 433-446 ◽  
Author(s):  
M Goossens ◽  
J Andries ◽  
I Arregui
Keyword(s):  
Resonant Absorption ◽  
Mhd Waves ◽  
Coronal Loops ◽  
Two Dimensional ◽  
Heliospheric Observatory ◽  
Magnetohydrodynamic Waves ◽  
One Dimensional ◽  
Magnetic Structures ◽  
Different Types ◽  
Kink Waves

In the last decade we have been overwhelmed by an avalanche of discoveries of magnetohydrodynamic (MHD) waves by the Solar and Heliospheric Observatory and Transition Region and Coronal Explorer observatories. Both standing and propagating versions of fast magnetoacoustic and slow magnetoacoustic MHD waves have been detected. Information on the damping times and damping distances of these waves is less detailed and less accurate than that on periods and amplitudes. Nevertheless, observations show the damping times and damping lengths are often short. Also, different types of MHD waves in different types of magnetic structures likely require different damping mechanisms. The phenomenon of fast damping is well documented for the standing fast magnetosonic kink waves in coronal loops. This paper concentrates on standing fast magnetosonic waves. It reports on results on periods and damping times due to resonant absorption in one-dimensional and two-dimensional models of coronal loops. Special attention is given to multiple modes.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: II. Viscous Effects

1994 ◽  
Vol 144 ◽  
pp. 506-508
Author(s):  
R. Erdélyi ◽  
M. Goossens
Keyword(s):  
Stress Tensor ◽  
Resonant Absorption ◽  
Mhd Waves ◽  
Larmor Radius ◽  
Coronal Loops ◽  
Viscous Effects ◽  
Viscous Stress Tensor ◽  
Magnetohydrodynamic Waves ◽  
Finite Larmor Radius ◽  
Viscosity Coefficients

AbstractResonant absorption of MHD waves in coronal loops is studied in linear, viscous MHD. Viscosity is described by Braginskii’s viscosity stress tensor. The dependence of the process of resonant absorption on the viscosity coefficients is studied. The compressive viscosity and viscosity due to the finite Larmor radius do not produce absorption. Shear viscosity produces absorption and is a viable candidate for heating coronal loops. The width of the dissipation layer is found to be proportional to, whereη1is the shear viscous coefficient of the full viscous stress tensor.

scholarly journals Seismology of kink oscillations in coronal loops: Two decades of resonant damping

2007 ◽  
Vol 3 (S247) ◽  
pp. 228-242 ◽  
Author(s):  
Marcel Goossens
Keyword(s):  
Wave Theory ◽  
Resonant Absorption ◽  
Mhd Waves ◽  
Coronal Loops ◽  
Equilibrium Models ◽  
Kink Waves ◽  
The Common ◽  
Uniform Equilibrium ◽  
Transverse Oscillations ◽  
Alfven Velocity

AbstractThe detection of rapidly damped transverse oscillations in coronal loops by Aschwanden et al. (1999) and Nakariakov et al. (1999) gave a strong impetus to the study of MHD waves and their damping. The common interpretation of the observations of these oscillations is based on kink modes. This paper reviews how the observed period and damping time can be reproduced by MHD wave theory when non-uniform equilibrium models are considered that have a transversal variation of the local Alfven velocity. The key point here is that resonant absorption cannot be avoided and occurs as natural damping mechanism for kink waves in non-uniform equilibrium models. The present paper starts with work by Hollweg & Yang (1988) and discusses subsequent developments in theory and their applications to seismology of coronal loops. It addresses the consistent use of observations of periods and damping times as seismological tools within the framework of resonant absorption. It shows that within the framework of resonant absorption infinitely many equilibrium models can reproduce the observed values of periods and damping times.

Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: I. The Code and Test Cases

1994 ◽  
Vol 144 ◽  
pp. 503-505
Author(s):  
R. Erdélyi ◽  
M. Goossens ◽  
S. Poedts
Keyword(s):  
Resonant Absorption ◽  
Numerical Code ◽  
Mhd Waves ◽  
Test Cases ◽  
Numerical Accuracy ◽  
Element Discretization ◽  
Flux Tubes ◽  
Magnetohydrodynamic Waves ◽  
Viscosity Coefficients ◽  
Magnetic Flux Tubes

AbstractThe stationary state of resonant absorption of linear, MHD waves in cylindrical magnetic flux tubes is studied in viscous, compressible MHD with a numerical code using finite element discretization. The full viscosity tensor with the five viscosity coefficients as given by Braginskii is included in the analysis. Our computations reproduce the absorption rates obtained by Lou in scalar viscous MHD and Goossens and Poedts in resistive MHD, which guarantee the numerical accuracy of the tensorial viscous MHD code.

Excitation and damping of disturbances in cylindrical coronal loops

2005 ◽  
Vol 364 (1839) ◽  
pp. 547-550 ◽  
Author(s):  
Jaume Terradas ◽  
Ramón Oliver ◽  
José Luis Ballester
Keyword(s):  
Boundary Layer ◽  
Coronal Loop ◽  
Normal Mode Analysis ◽  
Resonant Absorption ◽  
Time Dependent ◽  
Mode Analysis ◽  
Coronal Loops ◽  
Two Dimensional ◽  
Magnetohydrodynamic Equations ◽  
Kink Mode

The excitation and damping of transversal coronal loop oscillations is studied using one-and two-dimensional models of line-tied cylindrical loops. By solving the time-dependent magnetohydrodynamic equations it is shown how an initial disturbance generated in the solar corona induces kink mode oscillations. We investigate the effect of the disturbance on a loop with a non-uniform boundary layer. In particular, a strong damping of transversal oscillations due to resonant absorption is found, such as predicted by previous works based on normal mode analysis.

scholarly journals The damping of transverse oscillations of prominence threads: a comparative study

2013 ◽  
Vol 8 (S300) ◽  
pp. 48-51 ◽  
Author(s):  
Roberto Soler ◽  
Ramon Oliver ◽  
Jose Luis Ballester
Keyword(s):  
Comparative Study ◽  
Thermal Conduction ◽  
Resonant Absorption ◽  
Radiative Cooling ◽  
Magnetohydrodynamic Waves ◽  
Physical Mechanisms ◽  
Solar Prominences ◽  
Kink Waves ◽  
Conduction Cooling ◽  
Transverse Oscillations

AbstractTransverse oscillations of thin threads in solar prominences are frequently reported in high-resolution observations. The typical periods of the oscillations are in the range of 3 to 20 min. A peculiar feature of the oscillations is that they are damped in time, with short damping times corresponding to few periods. Theoretically, the oscillations are interpreted as kink magnetohydrodynamic waves. However, the mechanism responsible for the damping is not well known. Here we perform a comparative study between different physical mechanisms that may damp kink waves in prominence threads. The considered processes are thermal conduction, cooling by radiation, resonant absorption, and ion-neutral collisions. We find that thermal conduction and radiative cooling are very inefficient for the damping of kink waves. The effect of ion-neutral collisions is minor for waves with periods usually observed. Resonant absorption is the only process that produces an efficient damping. The damping times theoretically predicted by resonant absorption are compatible with those reported in the observations.

Real-Time Text Detection in Color Images Based on Color Projection

2011 ◽  
Vol 480-481 ◽  
pp. 84-88
Author(s):  
Jian Jie Wu ◽  
Yu Hui Zhang
Keyword(s):  
Real Time ◽  
Production Line ◽  
Color Image ◽  
Detection Algorithm ◽  
Text Detection ◽  
Color Images ◽  
Two Dimensional ◽  
Defect Inspection ◽  
One Dimensional ◽  
Different Types

In SMT production line, different types of components may have the same shape but providing different functions. The only difference between these components is the text on surface of a component indicating its type. Therefore, not only geometry defect inspection but also text detection is needed in component inspection to avoid wrong use of components. Traditional algorithms based on pixel comparison of text image are time consuming and sensitive to tiny change of the text as well. A concise text detection algorithm based on color projection is proposed. The algorithm transfers two-dimensional color image to one-dimensional curve for comparison by projection of the text image, which greatly reduces the computing amount, increases speed and makes the algorithm less sensitive to displacement or rotation of the text. Experiments show that the algorithm can ensure effective real-time text detection.

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