Comparison of precipitable water obtained from SAFNWC/MSG and GPS

Abstract

The Spinning Enhanced Visible and Infrared Imagery (SEVIRI) instrument, on board the Meteosat Second Generation (MSG), is a radiometer with eight infrared (IR) spectral bands. Layer Precipitable Water (LPW) from MSG SEVIRI, over the northern hemisphere area covered by MSG (MSG N), has been developed by INM within the EUMETSAT SAFNWC (Satellite Application Facility on support to Nowcasting and Very Short-Range Forecasting) framework. Seven of the SEVIRI IR channels are used to retrieve the LPW (Layer Precipitable Water) using neural networks. The Total Precipitable Water (LPW(TPW)) is one of the LPW parameters. The LPW(TPW) is routinely generated every fifteen minutes at a satellite horizontal resolution of 3 km in nadir on clear air pixels. Total column Integrated Water Vapor data derived from Zenith Total Delay GPS (Global Positioning System) data (GPS_IWV) and surface measurements/NWP estimations, are provided by eleven different ground based GPS data processing centres participating in the TOUGH EU Project in near real time (NRT). A set of LPW(TPW) values co-located with GPS_IWV stations has been added to NRT GPS data that are being routinely introduced in passive mode in the Hirlam 3DVar Assimilation system operational at INM. This paper will show an intercomparison of total column integrated water vapor from the HIRLAM first guess for the 3DVar analysis, the NRT GPS_IWV data and the LPW(TPW) product.