| Projection Effects on Physical Parameters Obtained from Solar Vector Magnetograms |
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| 作者姓名： | Hui Li Purple Mountain Observatory Chinese Academy of Sciences Nanjing National Astronomical Observatories Chinese Academy of Sciences Beijing |
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| 作者单位： | Hui Li Purple Mountain Observatory，Chinese Academy of Sciences，Nanjing 210008 National Astronomical Observatories，Chinese Academy of Sciences，Beijing 100012 |
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| 基金项目： | 国家自然科学基金，国家重点基础研究发展计划(973计划) |
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| 摘 要： | 1 INTRODUCTION Magnetic field plays an important role in solar activity. The stressing and subsequent partialrelaxation of magnetic fields in the active regions are generally accepted to be the energy sourceof solar flares. To quantitatively study the extent of stressed magnetic field as distinct from itspotential field, Hagyard et al. (1984) defined a magnetic shear angle膖he azimuth differencebetween the observed transverse magnetic field vector and the computed potential field vectorth…
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| 关 键 词： | 太阳 磁场 太阳活动 光球 物理参数 |
Projection Effects on Physical Parameters Obtained from Solar Vector Magnetograms |
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| Hui Li Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing National Astronomical Observatories,Chinese Academy of Sciences,Beijing .Projection Effects on Physical Parameters Obtained from Solar Vector Magnetograms[J].Chinese Journal of Astronomy and Astrophysics,2002,2(2):174-182. |
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| Authors: | Hui Li |
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| Institution: | PurpleMountainObservatory,ChineseAcademyofSciences,Nanjing210008 |
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| Abstract: | Projection effects in Huairou solar vector magnetograms are corrected by transferring or mapping the observed vector magnetogram in the image plane to the heliographic plane (planar correction) and to the heliospheric coordinate system (spherical correction). The magnetograms after the correction are considerably different. The planar correction and the spherical correction lead to slightly different magnetic configurations, especially when the active region involved is far from the disk center. We also discuss the effects of the corrections on magnetic activity parameters, such as magnetic shear, current helicity, etc. It is shown that the neutral line is obviously distorted after the mapping. The mapping generally decreases the average shear angle on the neutral line by several degrees when the active region is in the eastern hemisphere, and increases it when in the western hemisphere. In most of the cases studied, the correction reduces the current helicity imbalance, and sometimes even changes its sign. It is found that the current helicity imbalance may change its sign in its evolution when there are apparent fluxes emerging from the lower photosphere. The corrections increase the noise level of Bz greatly, and decrease the noise level of Bt slightly. The accuracy of the magnetic field measurement at Huairou is estimated to be better than 20 G and 150 G for the longitudinal and the transverse component, respectively. |
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| Keywords: | Sun: magnetic fields - Sun: activity - Sun: photosphere |
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