Alfvén waves in the inner polar coronal hole

Details Alfvén waves in the inner polar coronal hole Alfvén waves in the inner polar coronal hole

Nov 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002mnras.336.1195p&link_type=abstract

Monthly Notice of the Royal Astronomical Society, Volume 336, Issue 4, pp. 1195-1200.

Astronomy and Astrophysics

Astronomy

7

Mhd, Waves, Sun: Corona

Scientific paper

We investigate the Alfvén wave propagation characteristics in the inner zone (r < 1.35 Rsolar) of the North Polar Coronal Hole. The linear, incompressible magnetohydrodynamic (MHD) approximation reveals two wave modes with different phase velocities. Alfvén wave with the slower phase velocity is quickly damped; in other words it cannot propagate in the coronal plasma. On the other hand, the higher phase velocity Alfvén waves can propagate along the magnetic field lines. Mechanical energy flux density of these waves is found to be high enough to replace the coronal energy which is lost via optically thin emission and through heat conduction to the chromosphere below. We show that Alfvén waves propagating along the magnetic flux tubes go through refraction and get damped via viscous dissipation and resistivity. The energy flux density of the waves is of the order of 106 erg cm-2 s-1. The radial profile of the energy flux density in the region 1.05-1.35 R shows a rise until about 1.15 R where it peaks and further on declines less steeply than rising arm. This result is used to interpret SiVIII data taken by the Solar Ultraviolet Measurements of Emitted Radiation instrument on board Solar and Heliospheric Observatory. SiVIII lines like many other ionic lines show non-thermal broadening. The observed radial profile of the non-thermal line-of-sight velocity of SiVIII shows a plateau which coincides with the peak of the energy flux density we derived. We claim that this coincidence is not accidental but indicates the fact that the decrease in the energy flux density of damped Alfvén waves causes the plateau formation in SiVIII non-thermal line-of-sight velocity profile.

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