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ON ESTIMATING FORCE-FREENESS BASED ON OBSERVED MAGNETOGRAMS
Zhang, X. M.1,2; Zhang, M.1; Su, J. T.1
2017
Source PublicationASTROPHYSICAL JOURNAL
Volume834Issue:1
AbstractIt is a common practice in the solar physics community to test whether or not measured photospheric or chromospheric vector magnetograms are force-free, using the Maxwell stress as a measure. Some previous studies have suggested that magnetic fields of active regions in the solar chromosphere are close to being force-free whereas there is no consistency among previous studies on whether magnetic fields of active regions in the solar photosphere are force-free or not. Here we use three kinds of representative magnetic fields (analytical force-free solutions, modeled solar-like force-free fields, and observed non-force-free fields) to discuss how measurement issues such as limited field of view (FOV), instrument sensitivity, and measurement error could affect the estimation of force-freeness based on observed magnetograms. Unlike previous studies that focus on discussing the effect of limited FOV or instrument sensitivity, our calculation shows that just measurement error alone can significantly influence the results of estimates of force-freeness, due to the fact that measurement errors in horizontal magnetic fields are usually ten times larger than those in vertical fields. This property of measurement errors, interacting with the particular form of a formula for estimating force-freeness, would result in wrong judgments of the force-freeness: a truly force-free field may be mistakenly estimated as being non-force-free and a truly non-force-free field may be estimated as being force-free. Our analysis calls for caution when interpreting estimates of force-freeness based on measured magnetograms, and also suggests that the true photospheric magnetic field may be further away from being force-free than it currently appears to be.
SubtypeArticle
KeywordSun: Magnetic Fields Sun: Photosphere Sunspots
WOS HeadingsScience & Technology ; Physical Sciences
Funding OrganizationNational Natural Science Foundation of China(11125314 ; National Natural Science Foundation of China(11125314 ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; U1531247) ; U1531247) ; National Natural Science Foundation of China(11125314 ; National Natural Science Foundation of China(11125314 ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; U1531247) ; U1531247)
DOI10.3847/1538-4357/834/1/80
WOS KeywordMAGNETIC-FIELD MEASUREMENTS ; RECONSTRUCTION
Indexed BySCI
Language英语
Funding OrganizationNational Natural Science Foundation of China(11125314 ; National Natural Science Foundation of China(11125314 ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; U1531247) ; U1531247) ; National Natural Science Foundation of China(11125314 ; National Natural Science Foundation of China(11125314 ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; Strategic Priority Research Program of the Chinese Academy of Sciences(XDB09000000) ; U1531247) ; U1531247)
WOS Research AreaAstronomy & Astrophysics
WOS SubjectAstronomy & Astrophysics
WOS IDWOS:000392152700009
Citation statistics
Document Type期刊论文
Identifierhttp://ir.bao.ac.cn/handle/114a11/8290
Collection空间科学研究部
Affiliation1.Chinese Acad Sci, Natl Astron Observ, Key Lab Solar Act, A20 Datun Rd, Beijing 100012, Peoples R China
2.Univ Chinese Acad Sci, Beijing, Peoples R China
Recommended Citation
GB/T 7714
Zhang, X. M.,Zhang, M.,Su, J. T.. ON ESTIMATING FORCE-FREENESS BASED ON OBSERVED MAGNETOGRAMS[J]. ASTROPHYSICAL JOURNAL,2017,834(1).
APA Zhang, X. M.,Zhang, M.,&Su, J. T..(2017).ON ESTIMATING FORCE-FREENESS BASED ON OBSERVED MAGNETOGRAMS.ASTROPHYSICAL JOURNAL,834(1).
MLA Zhang, X. M.,et al."ON ESTIMATING FORCE-FREENESS BASED ON OBSERVED MAGNETOGRAMS".ASTROPHYSICAL JOURNAL 834.1(2017).
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