Alfven waves in the inner polar coronal hole


PEKUNLU E., BOZKURT Z., AFSAR M., SOYDUGAN F. , SOYDUGAN F.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, cilt.336, ss.1195-1200, 2002 (SCI İndekslerine Giren Dergi) identifier identifier

  • Cilt numarası: 336 Konu: 4
  • Basım Tarihi: 2002
  • Doi Numarası: 10.1046/j.1365-8711.2002.05849.x
  • Dergi Adı: MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
  • Sayfa Sayıları: ss.1195-1200

Özet

We investigate the Alfven wave propagation characteristics in the inner zone (r < 1.35R(.)) of the North Polar Coronal Hole. The linear, incompressible magnetohydrodynamic (MHD) approximation reveals two wave modes with different phase velocities. Alfven 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 Alfven 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 Alfven 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 10(6) 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 Si VIII data taken by the Solar Ultraviolet Measurements of Emitted Radiation instrument on board Solar and Heliospheric Observatory. Si VIII lines like many other ionic lines show nonthermal broadening. The observed radial profile of the non-thermal line-of-sight velocity of Si VIII 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 Alfven waves causes the plateau formation in Si VIII non-thermal line-of-sight velocity profile.