DETECTION OF SUPERGRANULATION ALIGNMENT IN POLAR REGIONS OF THE SUN BY HELIOSEISMOLOGY

We report on a new phenomenon of 'alignment' of supergranulation cells in the polar regions of the Sun. Recent high-resolution data sets obtained by the Solar Optical Telescope on board the Hinode satellite enabled us to investigate supergranular structures in high-latitude regions of the Sun. We have carried out a local helioseismology time-distance analysis of the data and detected acoustic travel-time variations due to the supergranular flows. The supergranulation cells in both the north and south polar regions show systematic alignment patterns in the north-south direction. The south-pole data sets obtained in a month-long Hinode campaign indicate that the supergranulation alignment property may be quite common in the polar regions. We also discuss the latitudinal dependence of the supergranulation cell sizes; the data show that the east-west cell size decreases toward higher latitudes.