COST-716 demonstration project for the near real-time estimation of integrated water vapour from GPS

Abstract

The operational potential of ground-based GPS data to the fields of climate and Numerical Weather Prediction (NWP) is investigated in the European COST-716 action. To demonstrate the operational potential for NWP a near real-time trial was started in March 2001 involving several analysis centres, each processing a GPS network and delivering estimates of zenith total delay (ZTD) to a gateway at the UK Met Office in a standard meteorological data format. The network consisted July 2002 of 150 GPS stations in Europe, of which several are processed by more than one of the six analysis centres. The algorithms, dataflow, formats and assimilation into Numerical Weather Prediction (NWP) models have been tested on 15 days of GPS data which were processed off-line, but to near-real time quality, for the period of June 9–23, 2000. The overall consistency between the solutions is about 5–6 mm in the zenith delay, which is about 1 kg/m 2 in terms of integrated water vapour (IWV). Comparisons with radiosonde data showed an agreement at the 10–15 mm level in terms of ZTD. The performance of the near real-time trial is satisfactory. Several of the analysis centres are already capable of delivering ZTD within the requirement of 1 h and 45 min, and the performance continues to improve with time. Although ZTDs are routinely converted into IWV at KNMI, the best way hitherto for NWP is to assimilate zenith total delay (ZTD). First results from assimilation trials and a couple of applications of the near real-time data are discussed in this paper as well.