2024-03-28T14:06:11Z
https://nagoya.repo.nii.ac.jp/oai
oai:nagoya.repo.nii.ac.jp:00027269
2023-01-16T04:45:27Z
879:880:881
Comparative Study of Microwave Polar Brightening, Coronal Holes, and Solar Wind over the Solar Poles
Fujiki, Ken’ichi
89285
Shibasaki, Kiyoto
89286
Yashiro, Seiji
89287
Tokumaru, Munetoshi
89288
Iwai, Kazumasa
89289
Masuda, Satoshi
89290
Solar wind
Interplanetary scintillation
Radioheliograph
Coronal holes
Magnetic fields
Solar Cycle
We compared the long-term variation (1992–2017) in solar polar brightening observed with the Nobeyama Radioheliograph, the polar solar-wind velocity with interplanetary scintillation observations at the Institute for Space-Earth Environmental Research, and the coronal-hole distribution computed by potential-field calculations of the solar corona using synoptic magnetogram data obtained at the National Solar Observatory/Kitt Peak. First, by comparing the solar-wind velocity [V] and the brightness temperature [Tb] in the polar region, we found good correlation coefficients (CCs) between V and Tb in the polar regions, CC = 0.91 (0.83) for the northern (southern) polar region, and we obtained the V–Tb relationship as V=12.6(Tb−10,667)^1/2+432. We also confirmed that the CC of V–Tb is higher than those of V–B and V–B/f, where B and f are the polar magnetic-field strength and magnetic-flux expansion rate, respectively. These results indicate that Tb is a more direct parameter than B or B/f for expressing solar-wind velocity. Next, we analyzed the long-term variation of the polar brightening and its relation to the area of the polar coronal hole [A]. As a result, we found that the polar brightening matches the probability distribution of the predicted coronal hole and that the CC between Tb and A is remarkably high, CC = 0.97. This result indicates that the polar brightening is strongly coupled to the size of the polar coronal hole. Therefore, the reasonable correlation of V – Tb is explained by V – A. In addition, by considering the anti-correlation between A and f found in a previous study, we suggest that the V – Tb relationship is another expression of the Wang–Sheeley relationship (V – 1/f) in the polar regions.
ファイル公開:2020/03/01
journal article
Springer
2019-03
application/pdf
Solar Physics
3
294
30
0038-0938
1573-093X
https://nagoya.repo.nii.ac.jp/record/27269/files/Fujiki2019SolPhys_accepted.pdf
eng
https://doi.org/10.1007/s11207-019-1418-6
“This is a post-peer-review, pre-copyedit version of an article published in [Solar Physics]. The final authenticated version is available online at: http://dx.doi.org/10.1007/s11207-019-1418-6”.