Rotation of the Sun, coordinate systems
Key points
- Rotation introduces issues to within the equations of the internal structure. The radial energy transfer equations can't be fulfilled when rotation exists -- the von Zeipel paradox. Meridional circulation solves the problem. Effective mainly at hotter stars (A-type or so), which usually have hot poles.
- Solar meridional circulation exists, but is of a different origin. Turbulent pumping play a role.
- Solar rotation is differential (both in latitude and in depth), is effective only in the convection zone. The radiative interior rotates as a rigid body.
- The measurements are not easy to intepret, different methods yield different results.
- There is a solar cycle related varying component of both the differential rotation (=torsional oscillations) and the meridional circulation. It can be found around activity belts. The model of circulating flows (geostrophic flow) around magnetic regions (low-pressure regions) may provide an explanation. Unfortunately this explanation is problematic at the beginning of the solar cycle, when no sunspots exist and yet, the torsional oscillations are observed.
- There are many coordinate systems being used in solar physics, Carrington coordinate mesh (=rigid rotation) is the reference one. Today, no one will code the coordinate transforms once again. It is adviced to use the available libraries. In astronomy, those libraries within the WCS (World Coordinate System) are available here. They are often integrated within larger packages, such as SunPy for Python.