5:15 PM - 7:15 PM
[PEM14-P08] Connection of the Magnetic Field between the Sun and the Earth
Keywords:Interplanetary magnetic field, Photospheric magnetic field, Open flux, Space weather
The global magnetic field structure of the Sun (coronal magnetic field) changes over the 11-year solar cycle. The solar magnetic field is a good indicator of solar activity, as represented by sunspots, which have positive and negative fluxes that appear in the solar surface (photosphere). The coronal magnetic field extended from the photosphere includes “closed” and “open” magnetic fluxes. The open flux extends into interplanetary space with the solar wind, the plasma flow from the Sun. During the solar minimum (low solar activity), the coronal magnetic structure is a dipole and the magnetic field extends from the unipolar polar regions into the interplanetary space. During the solar maximum (high solar activity), coronal structures change and are complicated due to the emergence of sunspots in low latitudes. Understanding how the solar magnetic field extends and forms the IMF is the basis of space weather, which provides insight into how solar activity affects the Earth.
However, our understanding of the magnetic field structure between the Sun and the Earth is developing. One of the serious issues is the Open Flux Problem (Linker et al., 2017; Wallace et al., 2019). IMF can be estimated by extrapolating from the photospheric magnetic field, but the estimation is underestimated compared with the in-situ observation at the L1 point over the solar cycle. This lack of understanding interferes with research on the connection between the Sun and the Earth. It is difficult to correctly estimate the near-Earth impacts associated with space weather. For example, the solar wind model SUSANOO requires constant multiplication of extrapolated solar magnetic field as input values. Therefore, the open flux problem is a severe issue that is deeply related to utility such as space weather forecasting.
In this study, we focus on long-term variations of the open flux and IMF. We set the goal to connect the global magnetic fields of the Sun and IMF. We investigate which components of the solar magnetic field produce the IMF evolution by comparing the evolution of the IMF with that of the solar magnetic field. We extrapolate the coronal magnetic structures from the solar photospheric magnetic field observed by the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) and Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) spacecraft with the potential field source surface (PFSS) model from May 2010 to October 2021. Then, the coronal magnetic field is decomposed into components (l, m) by spherical harmonic function, where the component with l=1 is the dipole flux and the components with l>1 are the non-dipole flux and compared with IMF.
As a result, we found the IMF near the Earth peaks half a month or 1 year later than the sunspot maximum. Furthermore, it suggests that the solar equatorial dipole flux (l, m)=(1,±1) is dominant during the IMF maxima, and the axial dipole flux (l, m)=(1, 0) is the main component of IMF, while nondipole flux (l≧2) produces IMF variation during solar minima. Therefore, it is expected that we focus on the mid-and low-latitude magnetic field in the solar photosphere.
These results are based on the analysis during Cycle 24 in Yoshida et al. (2023), and we found that the results are common in other solar cycles. The consideration of the connectivity in terms of the magnetic field is the basis for the understanding of the solar wind and space weather, the impact of the sun on the Earth.
However, our understanding of the magnetic field structure between the Sun and the Earth is developing. One of the serious issues is the Open Flux Problem (Linker et al., 2017; Wallace et al., 2019). IMF can be estimated by extrapolating from the photospheric magnetic field, but the estimation is underestimated compared with the in-situ observation at the L1 point over the solar cycle. This lack of understanding interferes with research on the connection between the Sun and the Earth. It is difficult to correctly estimate the near-Earth impacts associated with space weather. For example, the solar wind model SUSANOO requires constant multiplication of extrapolated solar magnetic field as input values. Therefore, the open flux problem is a severe issue that is deeply related to utility such as space weather forecasting.
In this study, we focus on long-term variations of the open flux and IMF. We set the goal to connect the global magnetic fields of the Sun and IMF. We investigate which components of the solar magnetic field produce the IMF evolution by comparing the evolution of the IMF with that of the solar magnetic field. We extrapolate the coronal magnetic structures from the solar photospheric magnetic field observed by the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) and Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory (SOHO) spacecraft with the potential field source surface (PFSS) model from May 2010 to October 2021. Then, the coronal magnetic field is decomposed into components (l, m) by spherical harmonic function, where the component with l=1 is the dipole flux and the components with l>1 are the non-dipole flux and compared with IMF.
As a result, we found the IMF near the Earth peaks half a month or 1 year later than the sunspot maximum. Furthermore, it suggests that the solar equatorial dipole flux (l, m)=(1,±1) is dominant during the IMF maxima, and the axial dipole flux (l, m)=(1, 0) is the main component of IMF, while nondipole flux (l≧2) produces IMF variation during solar minima. Therefore, it is expected that we focus on the mid-and low-latitude magnetic field in the solar photosphere.
These results are based on the analysis during Cycle 24 in Yoshida et al. (2023), and we found that the results are common in other solar cycles. The consideration of the connectivity in terms of the magnetic field is the basis for the understanding of the solar wind and space weather, the impact of the sun on the Earth.