Long-term Astroclimate Characterization of the Uluwati Site on the Pamir Plateau from ERA5 Reanalysis

We present a long-term astroclimatic assessment of the Uluwati high-altitude site on the eastern Pamir Plateau, southwestern Xinjiang, China, using reanalysis data. Six key nighttime atmospheric parameters relevant to optical and infrared astronomy are analysed: cloud cover, temperature, relative humidity, precipitable water vapour (PWV), wind properties, and aerosol optical depth (AOD). ERA5 data are validated against in situ measurements, demonstrating good agreement for temperature (R2 = 0.98) and relative humidity (R2 = 0.75), supporting their use for long-term analysis. The parameters are characterised across multiple timescales, including annual statistics, seasonal and monthly variations, daily variability, and long-term trends. The weighted annual mean cloud cover is ∼0.31 with a negligible long-term trend of less than 0.01 per decade. The mean nighttime temperature is −6.72 ○C, exhibiting a gradual warming of +0.18 ○C per decade. Relative humidity remains stable at ∼52 %, with a weak increase of +0.27 % per decade. The mean PWV is 3.13 mm, with a slight upward trend of +0.08 mm per decade. Upper-level winds (V200) exhibit strong seasonal modulation with a dominant annual periodicity, and vertical profiles reveal a coherent westerly flow. The AOD, derived from independent reanalysis data, exhibits a low annual mean value (∼0.081) with weak long-term variability, indicating clean and stable atmospheric conditions. Overall, the multi-parameter analysis demonstrates long-term stability of key astroclimatic parameters at the Uluwati site. These results provide a quantitative climatological baseline for telescope deployment, site monitoring, and comparative studies of high-altitude observatories in western China, supporting sustained ground-based optical and infrared observations.