Impact of GPS and TMI precipitable water data on mesoscale numerical weather prediction model forecasts

Observation system experiments with JMA MesoScale model, were performed for precipitable water data derived from TMI (TRMM Microwave Imager) and ground-based GPS observation, by using a four-dimensional variational assimilation method. Since GPS data exists over land only, and TMI data are available only over ocean, use of both data can provide information about water vapor complementally over whole analysis domain. Although the number of experiments is not sufficient yet, the results so far suggest that the complementary use of TMI and GPS precipitable water data, can improve the precipitation forecast of the model.