Observing water vapor variability during three super typhoon events in Hong Kong based on GPS water vapor tomographic modeling technique

Abstract

This paper for the first time numerically characterizes the water vapor spatial and temporal variation during the life cycle of super typhoons, using the 3D tomographic water vapor modeling method. Global Positioning System (GPS) data sets collected in Hong Kong were used to reconstruct the water vapor density field with a temporal resolution of 30 min during three super typhoon events in 2013 and 2014. The spatiotemporal variabilities of water vapor at five altitude layers (<0.8, 0.8–1.6, 1.6–3.0, 3.0–5.2, and 5.2–8.5 km) were examined. It was found that in the lower troposphere (<1.6 km), the precipitable water vapor (PWV) had only minor fluctuation during typhoon events. But significant PWV increase was observed at altitude above 1.6 km, and PWV kept increasing with the altitude, leading to the increase of the total water vapor. Hong Kong's PWV was observed to increase as the typhoons were about 795 to 821 km away from Hong Kong. The PWV spatial (distance) increase rate was 0.031–0.037 mm/km in the upper layers (1.6–8.5 km) and temporal increase rate was 12.710–24.272 mm/day in the upper layers (1.6–8.5 km). The typhoons had the largest impact on the PWV variation in the top layer (layer 5, 5.2–8.5 km). Prior to typhoon impact, PWV in layer 5 accounts for only 12.77% to 13.68% in the upper layers (1.6–8.5 km). With the typhoon impact, the PWV in layer 5 accounts for 21.28% to 26.38%. This work has demonstrated the potential to use water vapor tomographic technique to study water vapor evolution during super typhoons.