Oscilações MHD ideal em tubos de fluxo magnetico com variação radial ; : aplicações em fisica solar

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

In this work, we present the ideal magnetohydrodynamic (MHD) spectral analysis of a two-layered magnetic flux tube with radial variations. The two layers represent two regions with different physical characteristics and find many applications in astrophysical systems. Here we concentrate our attention on the study of solar magnetic flux tube oscillations. A numerical code was developed in order to obtain the solutions of the Hain-Lüst equation with appropriate boundary conditions. This equation results from the linearization of the ideal MHD equations in cylindrical coordinates when the static equilibrium profiles depend only on the radius. The discrete modes can exhibit different MHD nature (Alfvén, slow or fast magnetosonic) and also distinct evanescent/oscillatory character in each plasma layer. This results in a wide variety of combined modes, where emphasis is given to the new modes called Alfvén surface-fast magnetosonic modes. They appear in between the two branches of the Alfvén continuum and present oscillatory behaviour only in the outer layer . Applications to sunspot and coronal loop oscillations are presented. In the former, the two layers represent the umbra and penumbra, and in the latter, the coronal loop and surrounding fainter magnetic flux tubes. We treat two distinct sunspot regions coherently in one composite structure in contrast to previous works. The umbral and penumbral oscillations are then described as composite oscillation modes. Two regimes are investigated: low and high b regimes. Good results are also obtained for coronal oscillations in the range of some seconds, which are observed in the solar corona. In both applications, we discuss the inftuence of the boundary conditions on the results

ASSUNTO(S)

analise espectral manchas solares ondas magnetoidrodinamicas

ACESSO AO ARTIGO

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