Progress in 3D-Variational assimilation of total zenith delay at the Met Office

GPS total zenith delay (TZD) data have been assimilated into local area weather forecasting model using the Met Office's 3D variational assimilation system. The resulting analyses have been used as the initial conditions for a local area forecast model. Comparing model runs with and without GPS data assimilation shows that there is potential for GPS data to improve local area numerical weather forecasts. The expectation is that the largest forecast impact will be better seen in summer, non-dynamic weather conditions, rather than the winter cases presented here. The work shown here the current state of play; it is very much ongoing and so cannot represent definitive results. However it does show that GPS data can be assimilated into operational numerical weather prediction systems and shows some of the next steps that need to be taken, (C) 2001 Elsevier Science Ltd. All rights reserved.