Analysis of the relation between GPS tropospheric delay and intense precipitation

The electromagnetic signal transmitted by the global navigation and positioning systems (GNSS) suffers a delay which is mainly caused by the water vapor in the atmosphere. Estimating the delay affecting the signal propagation, it is possible to estimate the water vapor column on the troposphere above each station. The aim of this study is to characterize the water vapor field on the troposphere over time by GNSS techniques. It is expected that can also come to assist in the Nowcasting particularly in the prediction of severe meteorological phenomena. Several events of strong, intense and short precipitation, observed in the Lisbon region throughout 2012 were analyzed. The choice of these events was based on the analysis of hourly precipitation given by a meteorological station located on Lisbon center. This region is monitored by a network of 15 GNSS stations covering about 100 square kilometers. The relationship between the GPS precipitable water vapor (PWV) and the hourly accumulated precipitation was evaluated over time (1D closest GPSmeteorological station plots) and spatially (2D maps) interpolated over the GNSS and meteorological stations. It was verified that there were a high and sudden increment of the GPS PWV prior to severe precipitation events. The PWV increment starts 6 to 10 hours before the rain and the value has increased between 57% and 75% relatively to the PWV value observed previously. In this study is shown that GPS data has good potential for forecasting severe rain events and high moisture flux situations.