演講資訊

摘要：

Solar magnetic fields are the main driver of many observed activities on the Sun and in the interplanetary space. How the magnetic fields are generated and why they change polarity every 11 years have been one of the most important subjects in the solar physics. However, the signal of the magnetic field below the surface is weak and difficult to detect because the gas pressure is much larger than the magnetic pressure inside the Sun. In this study, the aim is to probe the variation of the magnetic fields below the surface using solar meridional flows. Solar meridional flows are axisymmetric flows on the meridional planes, and exist in the entire convective zone. We use SOHO/MDI helioseismic data from 1996 to 2010, which includes two solar minima and one maximum. The time-distance method is first applied to the data to determine the travel-time difference between northward and southward propagating waves. The travel-time difference is then related to the meridional flow based on the ray path theory. Finally, an inversion procedure is applied to the travel- time difference to obtain the meridional flow speed at the solar minimum and maximum. The results show that the flow pattern in the entire convective zone changes significantly from solar minimum to maximum and that the flow change is related to the active latitudes, which are the centroid locations of the surface magnetic fields. This suggests that the change of the meridional flow pattern is closely related to the change of the magnetic fields. Therefore, the solar cycle variation of the meridional flow is a promising tool to probe the solar cycle variation of the solar magnetic fields in the convective zone.