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Three-phase Evolution of a Coronal Hole. II. The Magnetic Field
被引:20
作者:
Heinemann, Stephan G.
[1
]
Hofmeister, Stefan J.
[1
]
Veronig, Astrid M.
[1
]
Temmer, Manuela
[1
]
机构:
[1] Karl Franzens Univ Graz, Inst Phys, Univ Pl 5, A-8010 Graz, Austria
关键词:
Sun: corona;
Sun: magnetic fields;
Sun: photosphere;
SOLAR-WIND SPEED;
ORIGIN;
DYNAMO;
FLUX;
FUNNELS;
FLOWS;
CYCLE;
D O I:
10.3847/1538-4357/aad095
中图分类号:
P1 [天文学];
学科分类号:
0704 ;
摘要:
We investigate the magnetic characteristics of a persistent coronal hole (CH) extracted from EUV imagery using Heliospheric and Magnetic Imager filtergrams over the period 2012 Febmary-October. The magnetic field, its distribution, and the magnetic fine structure in the form of flux tubes (FTs) are analyzed in different evolutionary states of the CH. We find a strong linear correlation between the magnetic properties (e.g., signed/unsigned magnetic field strength) and the area of the CH. As such, the evolutionary pattern in the magnetic field clearly follows a three-phase evolution (growing, maximum, and decaying) as found from EUV data (Part I). This evolutionary process is most likely driven by strong FTs with a mean magnetic field strength exceeding 50 G. During the maximum phase they entail up to 72% of the total signed magnetic flux of the CH, but only cover up to 3.9% of the total CH area, whereas during the growing and decaying phases, strong FTs entail 54%-60% of the signed magnetic flux and cover around 1%-2% of the CH's total area. We conclude that small-scale structures of strong unipolar magnetic field are the fundamental building blocks of a CH and govern its evolution.
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页数:10
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