High-resolution zenith delay and tropospheric gradient fields track precipitation during heavy local-scale rainfall events

Global Navigation Satellite System (GNSS) meteorology has proven to be a useful tool for the study of weather phenomena and climate change. The sensitivity of GNSS signals to the distribution of water vapor and liquid water in the atmosphere has led to numerous applications of tropospheric delay data products, ranging from the evaluation of numerical weather prediction (NWP) models via data assimilation into NWP models, to the observation-driven analysis of rainfall events. In this study, we investigate the behavior of non-hydrostatic zenith delay (ZWD), integrated water vapor (IWV), and tropospheric gradients before, during, and after heavy short-duration local-scale convective precipitation events. The study area located in the WegenerNet 3D Open-Air Laboratory for Climate Change Research Feldbach Region (WEGN3D Open-Air Lab) is situated in the Alpine forelands of southeastern Austria and covers an extent of about 22 km by 16 km. The WEGN3D Open-Air Lab consists of a six-station GNSS network with baselines between 5 km and 10 km, 156 closely spaced meteorological stations, an X-band precipitation radar, and a microwave and broadband infrared radiometer for tropospheric profiling and cloud structure observations, respectively.  We generate non-hydrostatic zenith delay maps for the study region with a temporal resolution of 150 seconds by combining estimated ZWD and tropospheric gradients. These high-resolution ZWD maps are then used to derive IWV maps using surface meteorological measurements and tropospheric profile statistics. We further exploit the approximate relationship between the spatial derivatives of ZWD with tropospheric gradients to compute gradient fields for the entire ZWD map domain.  We compare the spatial patterns of these high-resolution datasets with X-band radar-derived precipitation during heavy convective precipitation events with small spatial extent and high spatial variability. In line with previous studies, we find that the location of precipitation cells is well reflected in the ZWD, IWV, and gradient maps before, during, and after the event, even for very localized, short-lived precipitation events with an extent of only a few kilometers. This shows that GNSS meteorology can provide insights into heavy precipitation events approaching the microscale.