Effect of Foreshortening on Center-to-Limb Variations of Measured Acoustic Travel Times

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• 作者：Junwei Zhao ; Andrey Stejko ; Ruizhu Chen
• 关键词：Sun ; helioseismology ; Sun ; oscillations
• 刊名：Solar Physics
• 出版年：2016
• 出版时间：March 2016
• 年：2016
• 卷：291
• 期：3
• 页码：731-739
• 全文大小：1,594 KB
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• 作者单位：Junwei Zhao (1)
  Andrey Stejko (1) (2)
  Ruizhu Chen (1) (3)
  
  1. W.W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, 94305-4085, USA
  2. Department of Physics, New Jersey Institute of Technology, Newark, NJ, 07102, USA
  3. Department of Physics, Stanford University, Stanford, CA, 94305-4060, USA
  
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Astronomy
  Extraterrestrial Physics and Space Sciences
  Astrophysics
  
• 出版者：Springer Netherlands
• ISSN：1573-093X

文摘

We use data observed near the solar disk center by the Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) to mimic observations at high-latitude areas after applying geometric transform and projection. These data are then used to study how foreshortening affects the time–distance measurements of acoustic travel times. We find that foreshortening reduces the measured mean travel-times through altering the acoustic-power weighting in different harmonic degrees, but the level of reduction and the latitude dependence are not as strong as those measured from the observation data at the same latitude. Foreshortening is not found to be accountable for the systematic center-to-limb effect in the measured acoustic travel-time differences, which is an essential factor for a reliable inference of the Sun’s meridional-circulation profile. The differences in the acoustic power spectrum between the mimicked data and the observation data in high-latitude areas suggest that the optical spectrum-line formation height or convection cells in these areas may be the primary cause of the center-to-limb effect in helioseismic analyses.