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

TL;DR

This study analyzes optical turbulence at Muztagh-ata, revealing how turbulence parameters vary with height and conditions, and suggesting the site’s potential for astronomical observations due to favorable turbulence conditions.

Contribution

The paper provides detailed measurements of optical turbulence parameters at Muztagh-ata and links turbulence behavior to environmental factors, highlighting the site's suitability for astronomy.

Findings

Nighttime seeing median of 0.24 arcseconds at 6-30m height

Optical turbulence decreases exponentially with height during the night

Temperature inversion improves seeing conditions

Abstract

In this paper, we conducted a detailed analysis of optical turbulence in the Atmospheric Surface Layer (ASL) at Muztagh-ata site during on-site testing. We utilized ultrasonic anemometers positioned on a 30-meter tower to collect and process data at five height levels, obtaining data from October 1, 2021 to the present. We investigated the behavior of optical turbulence parameters (\(C_n^2\) and seeing \(\varepsilon\)) in the ASL. Nighttime \(C_n^2\) 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 arcseconds at nighttime and 0.48 arcseconds at daytime between 6-30m. 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 Muztagh-ata site has the potential to be an outstanding optical astronomical observatory in the western plateau of china.