Night-time measurements of astronomical seeing at Dome A in Antarctica

Bin Ma (), Zhaohui Shang (), Yi Hu (), Keliang Hu, Yongjiang Wang, Xu Yang, Michael C. B. Ashley, Paul Hickson and Peng Jiang
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Bin Ma: Chinese Academy of Sciences
Zhaohui Shang: Chinese Academy of Sciences
Yi Hu: Chinese Academy of Sciences
Keliang Hu: Chinese Academy of Sciences
Yongjiang Wang: Chinese Academy of Sciences
Xu Yang: Chinese Academy of Sciences
Michael C. B. Ashley: University of New South Wales
Paul Hickson: University of British Columbia
Peng Jiang: MNR, Polar Research Institute of China

Nature, 2020, vol. 583, issue 7818, 771-774

Abstract: Abstract 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 arcseconds1–3. Sites on the Antarctic plateau are characterized by comparatively weak turbulence in the free atmosphere above a strong but thin boundary layer4–6. The median seeing at Dome C is estimated to be 0.23–0.36 arcseconds7–10 above a boundary layer that has a typical height of 30 metres10–12. 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.

Date: 2020
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DOI: 10.1038/s41586-020-2489-0

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