Modelling of atmospheric optical turbulence with the Weather Research and Forecasting model at the Ali observatory, Tibet

Abstract

ABSTRACT In this study, we make use of a meso-scale numerical model to obtain the parameters of atmospheric optical turbulence at the Ali observatory above the Tibetan Plateau. These parameters are essential for ground-based optical observations and some adaptive optics techniques. We present the characterization of the vertical distributions of atmospheric optical turbulence Cn2 and the main integral parameters, such as coherence time τ0, isoplanatic angle θ0 and seeing ε0 derived from Cn2. Meanwhile, the measurement of Cn2 obtained with a radiosonde instrument is used to quantify the model performance on reconstructing the optical turbulence above the site. This shows a high level of agreement and provides a reliable tool for astronomical site testing. The results presented in this paper demonstrate the good behaviour of the atmospheric optical turbulence condition at Ali, particularly during the summer half of the year. We find yearly median values of seeing ε0 = 0.47 arcsec, isoplanatic angle θ0 = 4.35 arcsec and atmospheric coherence time τ0 = 5.52 ms in 2016, and we also provide independent confirmation of the potential of the Ali site in adaptive optics. Moreover, it has been proven that meso-scale models can provide reliable estimations of atmospheric optical turbulence conditions above an astronomical site on the Tibetan Plateau.