Solitary waves in coronal holes-predicted signatures close to the sun
Abstract
Coronal holes are well known sources of the high speed solar wind, however, the exact acceleration mechanism of the wind is still unknown. We find that solitary waves may be generated in coronal holes nonlinearly by Alfvén waves. The solitary waves may efficiently accelerate the fast solar wind in addition to thermal conduction. We solve numerically the time-dependent, nonlinear, resistive 2.5-D MHD equations in spherical geometry with azimuthal symmetry to model solar wind acceleration by waves in coronal holes. Torsional Alfvén waves are driven at the base of the model coronal hole and propagate into the corona. Ohmic heating layers are found to occur at the coronal hole boundaries due to phase-mixing of the torsional Alfvén waves. The nonlinear coupling of the perpendicular (to the background magnetic field) components of the velocity and the magnetic field to the radial component of the momentum equation leads to the acceleration of the solar wind in the radial direction and to the generation of solitary waves. The solitary wave phase velocity was found to be above the sound speed in the coronal hole, with the driving Alfvén wave amplitude vd~25 km s-1, and plasma β=2.5%. We discuss the implication of our results to the proposed in-situ observations in the region r<10Rs with the future solar probe mission.
- Publication:
-
Robotic Exploration Close to the Sun: Scientific Basis
- Pub Date:
- January 1997
- DOI:
- 10.1063/1.51760
- Bibcode:
- 1997AIPC..385..227O
- Keywords:
-
- 96.60.Ly;
- 96.60.Pb;
- 95.30.Qd;
- Helioseismology pulsations and shock waves;
- Magnetohydrodynamics and plasmas