ERA5-based long-term capacity and availability assessment of a satellite-to-ground laser downlink communication channel

Atmospheric variability strongly affects satellite-to-ground laser communication, making long-term capacity and availability assessment important for communication window selection and site evaluation. This paper develops an ERA5-based clear-sky channel capacity assessment framework for a satellite-to-ground intensity-modulated/direct detection (IM/DD) laser link at Tashkurgan, Xinjiang, China. Hourly ERA5 profiles from 2015 to 2025 are used to calculate MODTRAN5 clear-sky transmittance, diagnose turbulence-related quantities using a general turbulence model (GTM)-inspired parameterization, and estimate capacity at four elevation angles. The median capacity estimate increases from 187.56 Gbps at 30° to 233.72 Gbps at the zenith. Threshold exceedance probabilities show lower occurrence frequencies of median- and upper-quartile capacity states in summer and generally higher frequencies in autumn. Joint group permutation identifies relative humidity as the strongest meteorological predictor group, with an importance of 0.650. These results provide a meteorology-driven reference for clear-sky link assessment and communication window evaluation at high-altitude optical ground station candidates.