Measuring vortical flows in the solar interior

In this thesis, an observational approach is taken to study the effects of rotation on solar convection at the length scales of supergranulation and larger. Solar rotation drives vortical flows through the Coriolis force. Such vortical flows were measured via the techniques of timedistance helioseismology and local correlation tracking of granules, using images from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) spacecraft. In particular, the vertical vorticity of the flows associated with the average supergranule was spatially resolved by coaligning thousands of individual supergranules in a given latitude band. It was found that in the northern hemisphere outflows are on average associated with a clockwise circulation. The signal vanishes at the equator and has opposite sign in the southern hemisphere. Inflow and outflow regions have vertical vorticity of opposite sign, as expected from predictions based on the effects of the Coriolis force. Furthermore, the magnetic field around the average supergranule (in the inflow regions) was studied at the equator. An anisotropy in the average magnetic field strength was discovered; the field is stronger in the west (prograde) than in the east. This surprising result adds to the mystery of solar supergranulation.