Near-real-time GNSS tropospheric IWV monitoring system for South America

Abstract

Water vapor (WV) is a key component in the hydrological cycle. Changes in the distribution of WV and the rate of these changes influence the evolution of the climate. In addition, near-real-time (NRT) observations of WV have important applications through their assimilation into Numerical Weather Predictions (NWP). In South America, the only operational WV measurements have been those obtained by radiosonde (RS). Here we present a regional NRT WV monitoring system based on GNSS observations. It relies exclusively on data produced by existing geodetic and meteorological infrastructure, and uses only surface meteorological observations. Coverage extends from central Brazil to the Antarctic Peninsula, including Argentina and Uruguay, and produces hourly estimates of both Zenith Total Delay (ZTD) and Integrated Water Vapor (IWV). As part of the development of the system, we assessed the quality of the products by means of a comprehensive two-year comparison, between April 2018 and March 2020, with independent GNSS products, RS measurements, ECMWF Reanalysis v5 (ERA5) hourly estimates and Atmospheric Infrared Sounder (AIRS) observations. The obtained biases and inter-technique dispersions confirm the good quality of the NRT products. This is especially important since the development of this NRT monitoring system is ultimately aimed at generating an accurate product that could be used, by the regional meteorological services, in their NWP. In addition, a preliminary study was conducted on the representativeness of the NRT product during a mesoscale convective system event in the region, particularly associated with severe weather.