Helioseismology Study of Subsurface Dynamics in the Polar Regions of the Sun

Details Helioseismology Study of Subsurface Dynamics in the Polar Regions of the Sun Helioseismology Study of Subsurface Dynamics in the Polar Regions of the Sun

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.s32a..03n&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #S32A-03

Astronomy and Astrophysics

Astrophysics

[7522] Solar Physics, Astrophysics, And Astronomy / Helioseismology

Scientific paper

We report on our time-distance helioseismology study of the subsurface dynamics in the polar regions of the Sun. It is generally difficult to observe the polar regions in details because of severe foreshortening. The high-resolution data obtained by Solar Optical Telescope (SOT) onboard the Hinode satellite, however, enabled us to investigate dynamics in the regions with up to 80 degrees in latitude. The measurements are obtained by calculating the cross-covariance function of the random solar oscillations observed as fluctuations of intensity of the Ca II H line, and by fitting a Gabor-wavelet function for estimating the phase and group travel times of solar acoustic waves. We obtain the maps of subsurface velocity field by inverting the differences of the phase travel times, calculated for the cross-correlations with positive and negative lag times, using a ray-path approximation. Among the subsurface dynamical processes in the polar region, we focus on supergranulation in this study. Supergranules are thought to be one of convective cells in the convective envelope of the Sun. Typical temporal and spatial scales of supergranular cells are 1 day and 30 Mm, respectively. The supergranulation is considered to play important roles in the magnetic flux transport and formation of the magnetic network. However, we still do not have sufficient knowledge of their origin and properties. In our study, we have observed a curious alignment of the supergranular cells in the polar regions approximately in the North-South direction. The alignment was seen in both northern and southern polar regions. We discuss properties and temporal evolution of the supergranular structures in the region, as well as the possibilities of measuring the differential rotation and meridional flows in the polar regions, which are critical for the solar dynamo theories.

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