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Title: Kink Waves in Non-isothermal Stratified Solar Waveguides: Effect of the External Magnetic Field

Abstract

We study the effect of an external magnetic field on the properties of kink waves, propagating along a thin non-isothermal stratified and diverging magnetic flux tube. A wave equation, governing the propagation of kink waves under the adopted model is derived. It is shown that the vertical gradient of temperature introduces a spatially local cut-off frequency ω {sub c}. The vertical distribution of the cut-off frequency is calculated for the reference VAL-C model of the solar atmosphere and for different values of a ratio of external to internal magnetic fields. The results show that the cut-off frequency is negative below the temperature minimum due to the negative temperature gradient. In the chromosphere the cut-off frequency at a given height is smaller for a stronger external magnetic field. For the appropriate range of a ratio B{sub e} / B{sub i}  ≈ 0–0.8, the cutoff lies in the range ω{sub c}  ≈ 0.003–0.010 s{sup −1} (periods 600 < P{sub c} < 2000 s). The estimate of the cut-off frequency in the transition region is provided as well. In the propagating wave regime, the effective wave energy flux in the non-isothermal diverging flux tubes is the same as in the straight and homogeneous cylindrical waveguides. Themore » obtained wave equation in the limit β  = 0 is used to study the kink oscillations of non-isothermal coronal loops. It is found that the gradient of temperature along the coronal loops reduces the frequency ratio of the first overtone to the fundamental mode, i.e., ω{sub 2}/ ω{sub 1} < 2. This reduction grows for a larger ratio of temperature at the loop top to the temperature at the footpoints. Moreover, the effect of reduction is most pronounced for the steeper temperature profiles.« less

Authors:
 [1];  [2]
  1. Ussuriisk Astrophysical Observatory, Russian Academy of Sciences (Russian Federation)
  2. Institute of Automation and Control Processes FEB RAS, Vladivostok (Russian Federation)
Publication Date:
OSTI Identifier:
22663152
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (Online); Journal Volume: 154; Journal Issue: 4; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CHROMOSPHERE; CYLINDRICAL CONFIGURATION; MAGNETIC FIELDS; MAGNETIC FLUX; MAGNETOHYDRODYNAMICS; OSCILLATIONS; SUN; TEMPERATURE GRADIENTS; TUBES; WAVE EQUATIONS; WAVEGUIDES

Citation Formats

Lopin, I., and Nagorny, I., E-mail: lopin78@mail.ru. Kink Waves in Non-isothermal Stratified Solar Waveguides: Effect of the External Magnetic Field. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA859E.
Lopin, I., & Nagorny, I., E-mail: lopin78@mail.ru. Kink Waves in Non-isothermal Stratified Solar Waveguides: Effect of the External Magnetic Field. United States. doi:10.3847/1538-3881/AA859E.
Lopin, I., and Nagorny, I., E-mail: lopin78@mail.ru. Sun . "Kink Waves in Non-isothermal Stratified Solar Waveguides: Effect of the External Magnetic Field". United States. doi:10.3847/1538-3881/AA859E.
@article{osti_22663152,
title = {Kink Waves in Non-isothermal Stratified Solar Waveguides: Effect of the External Magnetic Field},
author = {Lopin, I. and Nagorny, I., E-mail: lopin78@mail.ru},
abstractNote = {We study the effect of an external magnetic field on the properties of kink waves, propagating along a thin non-isothermal stratified and diverging magnetic flux tube. A wave equation, governing the propagation of kink waves under the adopted model is derived. It is shown that the vertical gradient of temperature introduces a spatially local cut-off frequency ω {sub c}. The vertical distribution of the cut-off frequency is calculated for the reference VAL-C model of the solar atmosphere and for different values of a ratio of external to internal magnetic fields. The results show that the cut-off frequency is negative below the temperature minimum due to the negative temperature gradient. In the chromosphere the cut-off frequency at a given height is smaller for a stronger external magnetic field. For the appropriate range of a ratio B{sub e} / B{sub i}  ≈ 0–0.8, the cutoff lies in the range ω{sub c}  ≈ 0.003–0.010 s{sup −1} (periods 600 < P{sub c} < 2000 s). The estimate of the cut-off frequency in the transition region is provided as well. In the propagating wave regime, the effective wave energy flux in the non-isothermal diverging flux tubes is the same as in the straight and homogeneous cylindrical waveguides. The obtained wave equation in the limit β  = 0 is used to study the kink oscillations of non-isothermal coronal loops. It is found that the gradient of temperature along the coronal loops reduces the frequency ratio of the first overtone to the fundamental mode, i.e., ω{sub 2}/ ω{sub 1} < 2. This reduction grows for a larger ratio of temperature at the loop top to the temperature at the footpoints. Moreover, the effect of reduction is most pronounced for the steeper temperature profiles.},
doi = {10.3847/1538-3881/AA859E},
journal = {Astronomical Journal (Online)},
number = 4,
volume = 154,
place = {United States},
year = {Sun Oct 01 00:00:00 EDT 2017},
month = {Sun Oct 01 00:00:00 EDT 2017}
}