Optical turbulence in the atmospheric surface layer at the Pamir Plateau Muztagh-ata site

ABSTRACT In this paper, we conducted a detailed analysis of optical turbulence in the atmospheric surface layer (ASL) at the Muztagh-ata site during on-site testing. We utilized ultrasonic anemometers positioned on a 30-m tower to collect and process data at five height levels, obtaining data from 2021 October 1 to the present. We investigated the behaviour of optical turbulence parameters ($C_n^2$ and seeing $\varepsilon$) in the ASL. Night-time $C_n^2$ primarily fluctuated in the range of $10^{-16}$ to $10^{-14}$, exhibiting an exponential decrease with height. During the day, it showed a $h^{-0.82}$ dependency, while at night, it displayed a $h^{-0.48}$ dependency. Additionally, we presented the distribution of seeing across different layers within the ASL, showing a gradual decrease with increasing height, with a median seeing of 0.24 arcsec at night-time and 0.48 arcsec at daytime between 6 and 30 m. We investigated the relationship between surface temperature inversion, seeing in the ASL, and wind speed at the site. Our results show that under temperature inversion conditions, seeing significantly improves and is often accompanied by low to moderate wind speeds, while high wind speeds are usually associated with poorer seeing. Preliminary calculations and observational results, combined with the high altitude and unique geographical location, suggest that the Muztagh-ata site has the potential to be an outstanding optical astronomical observatory in the western plateau of China.