[P-EM14] Heliosphere and Interplanetary Space

[PEM14-01] Yearly variation of the Sun’s polar regions during Solar Cycle 24 observed with Hinode

*Daikou Shiota¹, Masumi Shimojo² (1.National Institute of Information and Communications Technology (NICT), 2.National Astronomical Observatory of Japan (NAOJ))

Keywords:solar cycles, photospheric magnetic field, coronal magnetic field

Observations of the magnetic fields in the Sun’s polar regions are of crucial importance to understand the long-term variation of solar magnetism. As a consequence of the magnetic variation the three-dimensional structure of global solar corona and solar wind also show a drastic long-term variation and, as a result, fast solar wind emanates from the polar regions around solar minima. The first Hinode observation of the polar region reveals the fine structure of photospheric vector magnetic fields of the polar areas: the existence of many patchy magnetic concentrations with intrinsic field strengths of over 1kG distributed across the entire polar region (Tsuneta et al. 2008) around the solar minimum. Following the first polar observation, the monitoring of the polar regions has been continued for 12 years. Since 2012, which was before the solar maximum of this cycle, the time variations in the distribution of the whole polar regions during the polarity reversal period have been monitored with periodic SP observations during a month at the proper timing (March for the south pole and September for the north pole). At September 2020, Solar Cycle 25 Prediction Panel, an international group of experts co-sponsored by NASA and NOAA, announced that solar minimum occurred in December 2019. This means that Hinode succeeded to observe the Sun’s polar regions during whole of Solar Cycle 24.
In this study, we investigated the yearly variation in magneitc field distribution of both Sun’s polar regions obtained in the monitoring during Solar Cycle 24. We also combined the polar magnetic field data with HMI/SDO synoptic map. Using the maps, we calculated the three-dimensional coronal magnetic field with potential field source surface model. We will report yearly variation in the coronal magnetic field structure associated with the variation in the polar magnetic field.