Solar Wind Dynamics

Click on image for larger version.

Polar Plume Simulation

Polar plumes are being modelled by Steve Suess, Shyamsundar Parhi, and Martin Sulkanen. Plumes are bright rays in coronal holes, visible between one and several solar radii. They are denser and slower compared to interplume plasma and are modelled here as jets or wakes. The plasma is considered compressible and ideal (no viscous dissipation, thermal diffusion, or electrical resistance). A jet is introduced with a perscribed flow speed and an internal magnetic field. The surroundings are at rest and are also permeated by a magnetic field but with a different field strength. The simulations are described in a paper titled "Can Kelvin-Helmholtz instabilities of jet-like structures and plumes cause solar wind fluctuations at 1 AU?" by Parhi, Suess, and Sulkanen. The paper appears in the July 1, 1999 issue of the Journal of Geophysical Research, Vol. 104, No. A7, pages 14,781 to 14,787.

Click on image for animation.

Click on image for animation.

The animations presented here are performed with the computer code Zeus-3D which solves the equations of ideal magnetohydrodynamics explicitly on a Eulerian grid. Open boundary conditions are considered at all boundaries of the simulation domain. The evolution of the Kelvin-Helmholtz instability is studied when a velocity perturbation of less than 1% of the jet flow speed is imposed at the origin of the preexisting jet. In the upper animation, where magnetic shear is low, the effect of the instability is less apparent than in case of strong shear as in the lower panel. This instability helps set up a process of mixing between plumes and interplumes, accompanied with the formation of shocks and plasma entrainment. This suggests that the instability thus generated at a few solar radii can account for the smooth fast solar wind and reduced velocity shear between plumes and interplumes as observed beyond 0.3 astronomical units (about the orbit of the planet Mercury).

Web Links

Return to Solar Physics Home