A Comparison of GPS- and NWP-derived PW Data over the Korean Peninsula

Precipitable Water (PW) derived from Global Positioning System (GPS)measurements and numerical weather prediction (NWP) model analysis data werecompared to further evaluate the efficacy of applying GPS-derived PW to theNWP model. The spatial and temporal variations of GPS-derived PW during arainfall event were also examined.GPS-derived PW measurements show good agreement with the behavior of watervapor at a high spatial resolution during the analysis period. Temporalanomalies of GPS-derived PW moving along with the front are successfullydetected by the GPS array. Large positive anomalies of GPS-derived PW areindicated immediately before a rainfall event, and the intensity of thesepositive anomalies do not seem to decrease significantly as theprecipitation system passes. These results indicate that the Korean GPSnetwork may have great potential as a PW sensor over the Korean Peninsula.In contrast with GPS-derived PW, NWP-derived PW shows negative biases. Thesebiases appear to stem mainly from the differences between modeled and actualGPS site elevations, as GPS sites were generally located at elevations lowerthan those employed by the NWP model. However, there still exists adiscernable dry bias after a PW correction is applied to NWP-derived PW.GPS-derived PW better reflects the spatial and temporal moisture variationsof precipitation systems, as compared to NWP-derived PW. These resultsprovide entirely new information for improving the regional NWP system,since GPS-derived PW produced with data from the Korean GPS network may beincorporated into the NWP model to improve rainfall forecasts.