Abstract
Typhoons can be serious natural disasters for the sustainability and development of society. The development of a typhoon usually involves a pre-existing weather disturbance, warm tropical oceans, and a large amount of moisture. This implies that a large variation in the atmospheric water vapor over the path of a typhoon can be used to study the characteristics of the typhoon. This is the reason that the variation in precipitable water vapor (PWV) is often used to capture the signature of a typhoon in meteorology. This study investigates the usability of real-time PWV retrieved from global navigation satellite systems (GNSS) for typhoons’ characterizations, and especially, the following aspects were investigated: (1) The correlation between PWV and atmospheric parameters including pressure, temperature, precipitation, and wind speed; (2) water vapor transportation during a typhoon period; and (3) the correlation between the movement of a typhoon and the transportation of water vapor. The case study selected for this research was Super Typhoon Mangkhut that occurred in mid-September 2018 in Hong Kong. The PWV time series were obtained from a conversion of GNSS-derived zenith total delays (ZTDs) using observations at 10 stations selected from the Hong Kong GNSS continuously operating reference stations (CORS) network, which are also located along the path of the typhoon. The Bernese GNSS Software (ver. 5.2) was used to obtain the ZTDs; and the root mean square (RMS) of the differences between the GNSS-ZTDs and International GNSS Service post-processed ZTDs time series was less than 8 mm. The RMS of the differences between the GNSS-PWVs (i.e., the ZTDs converted PWVs) and radiosonde-derived PWVs (RS-PWVs) time series was less than 2 mm. The changes in PWV reflect the variation in wind speed during the typhoon period to a certain degree, and their correlation coefficient was 0.76, meaning a significant positive correlation. In addition, a new approach was proposed to estimate the direction and speed of a typhoon’s movement using the time difference of PWV arrival at different sites. The direction and speed estimated agreed well with the ones published by the China Meteorological Administration. These results suggest that GNSS-derived PWV has a great potential for the monitoring and even prediction of typhoon events, especially for near real-time warnings.
Highlights
Tropical cyclones (TCs) are frequent and extreme weather events and have often caused significant damages in property and severely threatened the safety of human life [1]
The characteristics of the variations in precipitable water vapor (PWV) time series retrieved from global navigation satellite systems (GNSS) measurements were investigated for the detection of typhoon extreme weather events since GNSS data have the advantages of low cost and high spatio-temporal resolution in comparison with the sparsely distributed RS data
The GNSS-zenith total delays (ZTDs) time series over 10 stations selected from the Hong Kong regional GNSS continuously operating reference station (CORS) network in the three periods—before, during, and after the typhoon period—were assessed by comparing them against these from the International GNSS Service (IGS) precise products
Summary
Tropical cyclones (TCs) are frequent and extreme weather events and have often caused significant damages in property and severely threatened the safety of human life [1]. Traditional water vapor detection technologies including radiosonde (RS), microwave radiometer, solar photometer, and satellite remote sensing, have some technology-specific disadvantages [5,6,7,8], e.g., low spatial and temporal resolutions, and uneven accuracy These disadvantages often lead to difficulties in monitoring rapid variations of water vapor, especially when extreme weather events occur. Real-time high accuracy GNSS-derived precipitable water vapor (GNSS-PWV) can be achieved through the recent advances in International GNSS Service (IGS) real-time products. This makes it possible to predict short-term extreme weather events. Numerous studies have shown that the variations in PWV can reflect information of a typhoon’s landing [19,20,21], hardly any mathematical models established for the correlation between PWV and a typhoon’s movement can be found
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