Three-dimensional distribution of water vapor estimated from tropospheric delay of GPS data in a mesoscale precipitation system of the Baiu front

Three-dimensional distributions of water vapor in a mesoscale precipitation system, which developed on 7 July 1996 in the Baiu front, were estimated d irectly from the GPS data of 'GPS Earth Observation Network' (GEONET) of th e Geographical Survey Institute. In estimating the three-dimensional distri bution of water vapor from the GPS data, we used the tropospheric delays al ong each path from GPS satellites to GPS receivers on the ground. The resul t showed that the moist air extended up to the height of 6 km in the precip itation region in the early stage of the precipitation system and that a dr y air intruded into the precipitation system from the northwest in the midd le-level (from 3 km to 5 km altitude) in the later stage. This dry air intr usion in the middle-level was supported by numerical simulations.