Seeing—the angular size of stellar images blurred by atmospheric turbulence—is a critical parameter used to assess the quality of astronomical sites at optical/infrared wavelengths. Median values at the best mid-latitude sites are generally in the range of 0.6–0.8 arcseconds1,2,3. Sites on the Antarctic plateau are characterized by comparatively weak turbulence in the free atmosphere above a strong but thin boundary layer4,5,6. The median seeing at Dome C is estimated to be 0.23–0.36 arcseconds7,8,9,10 above a boundary layer that has a typical height of 30 metres10,11,12. At Domes A and F, the only previous seeing measurements have been made during daytime13,14. Here we report measurements of night-time seeing at Dome A, using a differential image motion monitor15. Located at a height of just 8 metres, it recorded seeing as low as 0.13 arcseconds, and provided seeing statistics that are comparable to those at a height of 20 metres at Dome C. This indicates that the boundary layer was below 8 metres for 31 per cent of the time, with median seeing of 0.31 arcseconds, consistent with free-atmosphere seeing. The seeing and boundary-layer thickness are found to be strongly correlated with the near-surface temperature gradient. The correlation confirms a median thickness of approximately 14 metres for the boundary layer at Dome A, as found from a sonic radar16. The thinner boundary layer makes it less challenging to locate a telescope above it, thereby giving greater access to the free atmosphere.
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The seeing and weather data at Dome A in 2019 that support the findings of this study are available in the China-VO Paper Data Repository, http://paperdata.china-vo.org/BinMa/DomeA-seeing2019.zip. The weather data in 2015 have been published18 and are available in http://aag.bao.ac.cn/klaws/downloads/. The data are also displayed on a public website, http://aag.bao.ac.cn/klsite/klaws2g.php.
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We are grateful to the 35th Chinese National Antarctic Research Expedition team supported by the Polar Research Institute of China and the Chinese Arctic and Antarctic Administration. We also thank Z. Li, F. Du, Z. Hu, T. Song, E. Aristidi and K. Agabi for their help in the development of the KL-DIMMs. We thank the Chinese Antarctic Center of Surveying and Mapping for providing the map of Antarctica in Extended Data Fig. 1. This work is supported by the National Natural Science Foundation of China under grant numbers 11733007, 11673037 and 11873010, and is partly supported by the Operation, Maintenance and Upgrading Fund for Astronomical Telescopes and Facility Instruments, budgeted from the Ministry of Finance of China (MOF) and administrated by the Chinese Academy of Sciences (CAS). The tower for KL-DIMMs was funded by Tianjin Normal University, and implemented by Tianjin University. P.H. acknowledges support from the Natural Sciences and Engineering Research Council of Canada, RGPIN-2019-04369, the Canada Foundation for Innovation, and the Chinese Academy of Sciences (CAS), President’s International Fellowship Initiative, 2017VMA0013. M.C.B.A. acknowledges support from the Australian Antarctic Division and NCRIS funding through Astronomy Australia Limited.
The authors declare no competing interests.
Peer review information Nature thanks Marc Sarazin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
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Extended data figures and tables
The red dots indicate locations of Dome A (Chinese Kunlun Station), Dome C (French–Italian Concordia Station), Dome F (Japanese Dome Fuji Station) and the South Pole (United States Amundsen–Scott Station), respectively. Map drawn using CorelDRAW and used with permission from Xiaoping Pang and Shiyun Wang (2020).
a, Seeing (black) and Sun elevation (red). b, Air temperature T at heights of 12 m, 8 m and 0 m. c, Wind speed U at heights of 12 m, 8 m and 2 m. d, Wind direction at a height of 8 m. Dotted vertical lines mark times when seeing either increased or decreased rapidly.
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Ma, B., Shang, Z., Hu, Y. et al. Night-time measurements of astronomical seeing at Dome A in Antarctica. Nature 583, 771–774 (2020). https://doi.org/10.1038/s41586-020-2489-0