TORSIONAL OSCILLATION, MERIDIONAL FLOWS, AND VORTICITY INFERRED IN THE UPPER CONVECTION ZONE OF THE SUN BY TIME-DISTANCE HELIOSEISMOLOGY

摘要

By applying time-distance helioseismology measurements and inversions to Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager (MDI) dynamics campaign data, we obtain synoptic maps of subsurface plasma-flow fields at a depth of 0- 12 Mm for seven solar Carrington rotations, covering the years 1996-2002, from solar-activity minimum to maximum. Vorticity distribution and both zonal and meridional flows are derived from such synoptic flow maps, which contain an enormous amount of information about solar dynamics. The results for the zonal flows agree well with previous results. The meridional flows of an order of 20 m s~(-1) are found to remain poleward during the whole period of observations. In addition to the poleward meridional flows observed at the solar minimum, extra meridional circulation cells of flow converging toward the activity belts are found in both hemispheres, which may imply plasma downdrafts in the activity belts. These converging flow cells migrate toward the solar equator together with the activity belts as the solar cycle evolves. The vorticity distributions are largely linear with latitude, and the deviations from the vorticity caused by the mean differential rotation are presented. Patterns of large-scale flows are investigated for a large active region at different depths. Converging flows toward the center of the active region are found near the solar surface, and divergent flows in this large active region are found to be rooted much deeper than similar flows observed in individual sunspots. We conclude that the extremely rich and complicated dynamics of the upper convection zone reveal remarkable organization on the large scale, which can be correlated with the magnetic activity zones.