Astronomical seeing with DIMM and wind-speed distributions with ERA5 data at the Muztagh-Ata site on the Pamir Plateau

ABSTRACT The Muztagh-Ata site, situated in the eastern Pamir Plateau of south-western Xinjiang, China, has been identified as a promising high-altitude location for astronomical observations, with systematic monitoring of atmospheric and observational parameters conducted since 2017. This study analyses 6 yr (2017–2022) of Differential Image Motion Monitor data, revealing exceptional stability in the site’s seeing conditions, with a median value of 0.89 arcsec and a mean value of 0.96 arcsec, following a lognormal distribution. Most seeing values fall between the 25th and 75th percentiles (0.72–1.12 arcsec), indicating minimal anomalies and confirming the site’s potential for high-resolution optical astronomy. Seasonal and monthly variations demonstrate notable stability, with months that have larger sample sizes, such as November, showing more stable conditions, while months with smaller sample sizes exhibit greater variability. Additionally, wind speed characteristics were analysed using 24 yr (2000–2023) data of ERA5, the fifth edition of the European Centre for Medium-Range Weather Forecasts. The wind speed distribution reveals an inverse relationship with atmospheric pressure, with stronger winds observed at higher altitudes and during winter months. Wavelet and autocorrelation analyses of upper level wind data ($V_{200}$) indicate periodicities at 0.5-, and 1-yr intervals, corresponding to seasonal and climatic cycles. A moderate positive correlation between seeing and $V_{200}$ suggests that high-altitude atmospheric dynamics influence turbulence, though ground-layer effects and seasonal variations also contribute. This study offers essential insights for enhancing the observational capabilities of the existing telescopes at the Muztagh-Ata site and for advancing future research in adaptive optics.