GPS observations of precipitable water dynamics associated with typhoon Zeb (1998)

Spatial and temporal distributions of precipitable water (PW) during the passage of a typhoon are monitored by ground-based GPS (Global Positioning System) receivers deployed by Central Weather Bureau (CWB) of Taiwan. GPS-observed PW time series demonstrate an expected trend that the PW amount is in general high before and during the occurrence of the typhoon, and low after the typhoon event. That is, PW increased from about 5 cm on DoY (Day of Year) 285 (October 13) to near 8 cm or so on DoY 288 (October 16) when Typhoon Zeb was striking Taiwan, and, then, decreased to 2-3 cm after passage of Zeb. GPS-observed PW is compared with that predicted by the Penn State-NCAR nonhydrostatic mesoscale model version 5 (MM5). With an acceptable assumption that GPS-observed PW is regarded as reference, MM5-predicted PW mimics that observed by GPS except that there are some discrepancies between them. This indicates that assimilation of GPS-observed PW into atmospheric circulation models is potentially helpful to numerical weather prediction (NWP) models.