Monitoring the Migration of Water Vapor Using Ground-Based GNSS Tropospheric Products

Water vapor (WV), as an essential climate variable, its content and migration process have significant implications for determining the intensity, time, and extent of various weather extremes. Hence, it is essential to conduct continuous, timely, and accurate monitoring of WV, especially its migration. Nowadays, the ground-based global navigation satellite systems (GNSSs) tropospheric sounding technique has been effectively applied to sensing WV content. To advance its application, a new method for monitoring WV migration using GNSS-derived zenith total delay (ZTD) and tropospheric gradients is developed. The utility of the method was evaluated in the context of New Zealand (NZ) to monitor the rapid migration of WV resulting from cyclone cody and the eruption of the Hunga Tonga-Hunga Ha'apai (HTHH) volcano over the period January 15 and 16, 2022. By using the products obtained from a dense GNSS network with 40 stations, the determined isochrones clearly depict the migration direction and speed of WV. Results indicated that the WV moved southwestward and southeastward over the North and South Islands of NZ, respectively. It took about 15 h for the WV to pass over the study region, with a mean speed of 79.79 km/h.