| Presentation Title: | Hinode observation of long-term variation of magnetic fields in the Sun’s polar regions during Cycle 24-25 |
| Author(s): | D. Shiota(1,2), M. Kubo(3), Y. Katsukawa(3), M. Shimojo(3), H. Iijima(2), T. Matsumoto(2), S. Masuda(2)
1. National Institute of Information and Communications Technology, Japan
2. Institute for Space-Earth Environmental Research, Nagoya University, Japan
3. National Astronomical Observatory of Japan, Japan |
Abstract:
Observations of the magnetic fields in the Sun’s polar regions are known to be very important for understanding the long-term variation of the solar magnetism. Furthermore fast solar wind emanates from the large coronal holes formed in polar regions around solar minima. The understanding the fluctuation of the solar polar magnetic field is also an important element for improving the accuracy of space weather forecasts.
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 1 kG 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 17 years. Since 2012, the monitoring of the whole polar regions has begun as HOP 206: Periodic SP observations during a month at the proper timing (March for the south pole and September for the north pole). The monitoring covers the period longer than one solar cycle and revealed that the distributions of large magnetic patches show variations associated with the solar activity cycle while small magnetic patches do not change as shown in the previous study (Shiota et al 2012).
In this study, we present Hinode observation of long-term variation of magnetic fields in both Sun’s polar regions. Since the beginning of Cycle 25 in December 2019, the Sun becomes more active toward the maximum, which is expected to reach in 2025. At the same time, the polarity reversal of the magnetic fields of both the Sun’s polar regions seems to rapidly proceed in HMI observation. Hinode observation revealed that in the South polar region magnetic fields also are rapidly weakening but still keep the same negative polarity in March 2024 and therefore the polarity reversal process has not yet finished.