Phase speed of magnetized Rossby waves that cause solar seasons

We demonstrate that phase propagation is a typical characteristic of tachocline nonlinear oscillations that are created by unstable MHD Rossby waves, responsible for producing solar seasons.

For toroidal field bands placed at latitudes between 5° and 75°, we find that phase velocities occur in a range similar to the observations, with more retrograde speeds (relative to the solar core rotation rate) for bands placed at higher latitudes, just as coronal holes have at high latitudes compared to low ones. The phase speeds of these waves are relatively insensitive to the toroidal field peak amplitude. Rossby waves for single bands at 25° are slightly prograde.