Inconsistency in Chinese solar radiation data caused by instrument replacement: Quantification based on pan evaporation observations

Abstract

Solar radiation determines our climate and hydrological cycle, and it has been widelymeasured by pyrometers at meteorological stations. In the early 1990s, a large-scale instrument replacement occurred across China, leading to inconsistent solar radiation observations. Fortunately, China has consistent pan evaporation (Epan) observations from Chinese micropans (with a diameter of 20 cm) from the 1950s to 2001. This study parameterized the PenPan-20 model for estimating Epan from these pans using a Bayesian approach. Furthermore, based on the PenPan-20 model, a shift in the solar radiation data (~1.4 ± 0.5 MJ/(dm2) or 16 ± 7W/m2) in the early 1990s was revealed; this change was likely due to the large-scale retrofitting of new instruments and irregular calibration operations.