Magnetoacoustic surface gravity waves at a spherical interface
Magnetoacoustic surface gravity waves at a spherical interface
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DOI：
10.1051/0004-6361/201016075
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发表时间：
2011-03
影响因子：
6.5
通讯作者：
I. Ballai;E. Forgács-dajka;M. Douglas
中科院分区：
文献类型：
--
作者：
I. Ballai;E. Forgács-dajka;M. Douglas
目标。太阳大气中由磁场构成的等离子体是传播导磁波和磁声波的理想介质。众所周知，波传播的几何限制赋予了波的色散特性。此外，已知沿介质中的不连续面传播的波仍保持局域化。作为太阳和恒星条件下磁板和磁柱中导波理论的扩展，我们的目标是研究低太阳日冕(这里被认为是密度不连续)中磁声重力波在球形界面上的传播，模拟最近在日冕中观测到的EUV波长的全球波。方法：研究方法。利用界面上的守恒定律，我们导出了球面几何中的色散关系，在引力层结存在的情况下，球面几何中径向磁场扩展。考虑到传播发生在太阳表面附近，用近似方法导出了描述快速磁声-重力表面波的色散关系。结果。将本文得到的理论结果应用于研究EIT波在低电晕中的传播。波的频率随界面密度对比度的减小而增大。我们还表明，对于给定的方位波数，磁场对波的频率的影响很小。当相对于界面的位置(径向)绘制时，频率与距离成反比，而对于固定的密度比和界面位置，获得的频率定义在非常窄的区域内。
Aims. The plasma structured by magnetic fields in the solar atmosphere is a perfect medium for the propagation of guided magnetic and magnetoacoustic waves. Geometrical restriction of wave propagation is known to confer a dispersive character for waves. In addition, waves propagating along discontinuities in the medium are known to remain localized. As an extension to theories of guided waves in magnetic slabs and cylinders under solar and stellar conditions, we aim to study the propagation of magnetoacoustic-gravity waves at a spherical interface in the low solar corona (considered here as a density discontinuity), modelling global waves recently observed in the corona in EUV wavelengths. Methods. Using conservation laws at the interface we derive the dispersion relation in spherical geometry with a radially expanding magnetic field in the presence of gravitational stratification. The obtained dispersion relation describing fast magnetoacoustic-gravity surface waves is derived using an approximative method taking into account that propagation takes place near the solar surface. Results. Theoretical results obtained in the present study are applied to investigate the propagation of EIT waves in the low corona. The frequency of waves is shown to increase with decreasing density contrast at the interface. We also show that, for a given azimuthal wavenumber, the magnetic field has a very small effect on the value of the frequency of waves. When plotted against the location of the interface (in the radial direction) the frequency varies inversely proportional to the distance, while for a fixed density ratio and location of the interface the frequency is obtained to be defined in a very narrow region.