[P-EM16] Heliosphere and Interplanetary Space

[PEM16-P02] Study on the relationship between plasma upflow and solar wind using Hinode/EIS and IPS observations

Sora Nakada^1,2, *Kazumasa Iwai¹, Munetoshi Tokumaru¹, Ken'ichi Fujiki¹, Shinsuke Imada³ (1.Institute for Space–Earth Environmental Research (ISEE), Nagoya University, 2.Nagoya University Graduate School of Science, 3.Department of Earth and Planetary Science, Graduate School of Science, University of Tokyo)

Keywords:solar wind, solar corona, interplanetary scintillation

We analyzed the active region upflow observed by the Hinode satellite and the magnetic field structure around the upflow. The upflow is an upwelling of plasma in the solar corona and transition region above the active region, which is usually persistent for several days. The chemical composition of the upflow plasma measured by the EUV Imaging Spectrometer (EIS) on the Hinode satellite was found to be similar to that of the slow solar wind measured by in situ instruments near the Earth a few days later, suggesting that upflow may be a source of the slow solar wind. However, a comparison of in-situ measurements and EIS data, which can only provide solar wind parameters at a single point, does not confirm that upflow is a source of the slow solar wind. For upflow to be a source of the solar wind, the coronal upflow region must be connected to an open magnetic field extending into the interplanetary space. However, it has not yet been proven that upflow is connected to an open magnetic field, nor that it is connected to the slow solar wind. The purpose of this study is twofold. The first purpose is to test the hypothesis that upflow is the source of the slow solar wind. In this study, we use interplanetary scintillation (IPS) data observed by ISEE, Nagoya University in addition to EIS data, and the Potential Field Source Surface (PFSS) model to determine whether the upflow is connected to an open magnetic field and slow solar wind. The advantage of using IPS data is that the locations of the EIS-captured upflows can be compared with the global solar wind velocity distribution. Analysis of 13 active regions revealed that four active regions had upflows connected to open magnetic fields, three of which were connected to the slow solar wind. These upflow are likely to be the source of the slow solar wind. Although the upflows themselves were connected to closed magnetic fields in the five active regions, there were open magnetic field regions near the active regions. All of the magnetic fields for which solar wind velocities was observed by IPS were found to be connected to the slow solar wind. This result is consistent with the slow solar wind model, which assumes that upflow plasma moves into the open magnetic field lines due to magnetic interchange reconnection and is fed into the slow solar wind. In the four active regions, the upflow was connected to a closed magnetic field, and there were no open magnetic fields in the surrounding area. Without the presence of an open magnetic field, the upflow plasma could not flow out into interplanetary space and would be trapped in the solar corona by the closed magnetic loop. Thus, the results of this study indicate that not all upflows can be sources of solar wind. The second objective of this study is to investigate the characteristic of upflows connected to open and closed magnetic fields. We defined the analysis range in the upflow region connected to an open magnetic field and in the upflow region connected to a closed magnetic field, respectively, and compared the plasma characteristics obtained from the EIS data. The results show that the upflow connected to open magnetic fields has a larger excess spectral broadening called non-thermal velocity. This result suggests that the structure of the coronal magnetic fields and the mechanism of upflow generation may differ between the open and closed magnetic field regions, and is expected to provide new constraints on solar coronal heating models.