Potential uses of surface based GPS water vapour measurements for meteorological purposes

The current user requirements for relative humidity measurements in the atmosphere will be reviewed and the contribution which surface based GPS measurements can contribute to satisfying this requirement will considered. The potential of GPS data is discussed in view of some data assimilation, nowcasting/ synoptic and climate applications.

Some potential uses of GPS water vapour are considered, particularly in relationship to thunderstorm forecasting on occasions of potential instability. These depend on the ability of the forecaster to visualise the horizontal distribution of water vapour and to be able to compare this with satellite products on a very short time scale. In terms of potential operational GPS water vapour measurements it is suggested that in the UK, initial demonstration experiments concentrate on the problems of forecasting summertime convection over southern England.

The use of GPS water vapour measurements for climate change verification has been suggested in the past. The Hadley Centre Climate model data is used to estimate the magnitude and distribution of IWV changes over Europe to be expected in the next 50 years.

Some outstanding problems are highlighted, particularly the accuracy of the Ocean tide loading correction and the impact of errors in the total delay measurements in colder conditions. The latter has implications for the optimum distribution of GPS receivers for purely meteorological purposes in any planned network.