Water Vapor Retrieved from Ground-Based GNSS and its Applications in Lightning Weather in Hong Kong

Abstract

As an important parameter in meteorological research, precipitable water vapor (PWV) can reflect atmospheric water vapor variations. PWV obtained through the inversion of global navigation satellite systems (GNSS) has the advantages of high accuracy, low cost, and high spatial-temporal resolution. In Hong Kong, frequent lightning activity is observed due to topographic and climatic conditions, and GNSS PWV can be used to analyze the lightning activity. GAMIT can derive accurate atmospheric information from GNSS observations. First, the zenith total delay (ZTD) of six IGS stations worldwide were calculated at different satellite elevation cutoff angles. It was found that the highest precision of ZTD was obtained at a satellite elevation cutoff angle of 10°, with an average RMSE (MAE) of 2.94mm (2.28 mm) for the six IGS stations. Second, when using GAMIT to calculate PWV, different mapping functions can yield different results. The PWV is solved by using the satellite observation data of HKSC station in Hong Kong, and it is found that the highest accuracy of PWV is obtained when using VMF1, and its RMSE (MAE) is 2.43 m (1.79 mm). Third, a study of 63 lightning events in the vicinity of HKSC and HKKT stations from May to October 2021 in the Hong Kong region reveals that the onset of lightning is usually preceded by a decreasing process of PWV. It was found that there is typically a decrease in PWV before the occurrence of lightning. Among the studied lightning events, 60.32% were associated with a decrease in PWV, while 39.68% were associated with an increase in PWV. Moreover, 73% of lightning events occurred within three hours before or after the lowest point of PWV during this decrease process. These results show that GNSS PWV has great potential for short-term proximity prediction of lightning in Hong Kong.