Computer Science – Performance
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd...3e..44n&link_type=abstract
Solar Active Regions and 3D Magnetic Structure, 26th meeting of the IAU, Joint Discussion 3, 16-17 August, 2006, Prague, Czech R
Computer Science
Performance
Scientific paper
Solar corona is a highly structured medium and it is believed that the magnetic filed plays an important role in the performance, heating and the stability of these structures. Here, a magnetized flux tube of cylindrical geometry with the coordinates (r, z, φ) is considered. The tube is assumed to have the length L, the radius R and a uniform magnetic field B along the direction. A non-uniform density stratification of the form ρ=ρ_0 exp{-μsin(π z/L)} is assumed for the fluid inside the tube, where ρ_0 is the density at z=0 and μ=L/(π H)is the stratification parameter with H as the density scale height. If ξ is a displacement of a fluid element from equilibrium position it can be shown that the linearized equation of motion becomes ω^2 S=W, where ω is the frequency, S=intξ^* ρξ dη and W=int(1/ρ dPdρ δρ^*δρ+(γ-ρ/P dP/dρ) nabla.ξ^*nabla.ξ+1/4π δ B^* δ B) dη. P is the pressure, γ is the ratio of the specific heats at constant volume and pressure and the integrals are taken on the tube volume. Using a gauged version of Helmholtz' theorem the oscillation modes of the fluid are classified into p, g and t modes that are excited mainly by pressure, buoyancy and magnetic forces. By a suitable technique of modal analysis the wave propagation and possible motions of the fluid are investigated and the spectrum of eigen-frequencies are calculated for the different values of the magnetic field and the density stratification parameters. The effect of the presence of the magnetic field and the density stratification on the stability of the flux tube under coronal conditions are explored and commented on. The results obtained for the effect of the stratification on the frequencies of the fundamental and first overtone modes are in consistent with those obtained by Verwichte et al(2004 ). That is the fundamental mode frequency is independent of μ, while the first overtone mode frequency decreases by increasing μ.
Ebrahimi H.
Nasiri Sadolah
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