An Empirical Model for Estimating Precipitable Water Vapor on the Tibetan Plateau

Abstract

Using the ground meteorological and radiosonde data of 122 atmospheric stations from 1958 to 2008 all over China, excellent numerical correlations between precipitable water vapor (PWV) and ground humidity parameters such as ground water vapor pressure (e) have been derived; by introducing two parameters, latitude φ and altitude H, we establish an empirical model for estimating the total amount of PWV from e in different climatic areas in China, especially on the vast Tibetan Plateau with complex topography. In the validation, we make use of the ground meteorological data of the atmospheric weather station from 2016 July 12 to December 22 at the Ali observatory (32.°30N, 80.°05E, 5050 m above sea level), which is located in the most western part of the Tibetan Plateau, to obtain the total amount of PWV by the empirical model; compared with the PWV derived from radiosonde observations at Ali, the model shows a very good performance estimating PWV, and presents very well the seasonal and diurnal variations of PWV. The total amount of PWV derived from the empirical model at the observatory agree with that from radiosonde observations very well, with the correction coefficient R = 0.958 and the root mean square error RMSE = 1.04 mm; the errors between the model and observations are a bit larger in summer when PWV is rich, and small in winter when PWV values are usually less than 2.0 mm. Based on the empirical model, the median PWV value in 2017 at the Ali observatory was about 2.9 mm, and the values were less than 2.0 mm for half the 2017. Overall, the total amount of PWV derived from the empirical model is proved to be reliable, and the empirical model is excellent and accurate, allowing it to be implemented as an operational tool for estimating PWV at an astronomical site.