C51

Presentation Title:	Evolution of the open flux extended from the sunspot groups during solar maximum
Author(s):	Minami Yoshida, Toshifumi Shimizu, Shin Toriumi, Haruhisa Iijima

Abstract:

The open magnetic flux extended from the photosphere produces the interplanetary magnetic field (IMF), and that of global structure changes over the solar cycle. The coronal magnetic field is mainly extended from the polar regions during the solar minimum, while complicated due to locally closed magnetic fields during the solar maximum. Understanding the evolution of open flux leads to understanding the structure of the background magnetic field in the heliosphere. One of the serious problems is the "open flux problem," in which the near-Earth magnetic field estimated from photospheric magnetic field observations is underestimated by a factor of 2-5 compared with in-situ observations in interplanetary space. The systematic bias in the polarimetric magnetic field observation was focused as one of the causes of this. As another idea, Yoshida et al. (2023) suggest that the low-latitude magnetic field in the photosphere is a main component of producing the IMF evolution.
In this study, we investigate how low-latitude active regions during the solar maximum contribute to the evolution of the open flux. We simulate the time evolution of photospheric and coronal magnetic structure from a bipolar magnetic group, using the surface flux transport model and the potential field source surface model. After inserting a new bipolar magnetic group, the open flux increases until 3-4 months later, depending on the sunspot tilt angle and the latitude of emergence. Further analysis shows that the simulated increase in open flux is produced by the equatorial magnetic dipoles, which are in turn formed by a largely tilted sunspot group sheared by the differential rotation. Further analysis is needed to understand the evolution of the sunspot as a primary source of the open flux.

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