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Abstract. The development phase (DP) of the EUMETSAT Satellite Application Facility for Support to Operational Hydrology and Water Management (H-SAF) led to the design and implementation of several precipitation products, after 5 yr (2005)(2006)(2007)(2008)(2009)(2010) of activity. Presently, five precipitation estimation algorithms based on data from passive microwave and infrared sensors, on board geostationary and sun-synchronous platforms, function in operational mode at the H-SAF hosting institute to provide near real-time precipitation products at different spatial and temporal resolutions.In order to evaluate the precipitation product accuracy, a validation activity has been established since the beginning of the project. A Precipitation Product Validation Group (PPVG) works in parallel with the development of the estimation algorithms with two aims: to provide the algorithm developers with indications to refine algorithms and products, and to evaluate the error structure to be associated with the operational products.In this paper, the framework of the PPVG is presented: (a) the characteristics of the ground reference data available to H-SAF (i.e. radar and rain gauge networks), (b) the agreed upon validation strategy settled among the eight European countries participating in the PPVG, and (c) the steps of the validation procedures. The quality of the reference data is discussed, and the efforts for its improvement are outlined, with special emphasis on the definition of a ground radar Published by Copernicus Publications on behalf of the European Geosciences Union. S. Puca et al.:The validation service of the hydrological SAF geostationary products quality map and on the implementation of a suitable rain gauge interpolation algorithm. The work done during the H-SAF development phase has led the PPVG to converge into a common validation procedure among the members, taking advantage of the experience acquired by each one of them in the validation of H-SAF products. The methodology is presented here, indicating the main steps of the validation procedure (ground data quality control, spatial interpolation, upscaling of radar data vs. satellite grid, statistical score evaluation, case study analysis).Finally, an overview of the results is presented, focusing on the monthly statistical indicators, referred to the satellite product performances over different seasons and areas.

Previous works suggest that more El Niño-like conditions can be expected over the South American (SA) climate and atmospheric circulation because of the similarity of the predominately warm conditions in the sea surface temperature (SST) over the central-equatorial Pacific after the 1976/77 summer with those of the SSTs during El Niño events. Here, the summer (October to March) low-level atmospheric circulation over southern SA is studied in order to determine the specific changes that can be related with the global climate transition 1976/77. The rotated principal component analysis is applied to the daily 850-hPa geopotential height fields from the NCEP-NCAR reanalysis I for the periods before and after 1976/77. The second and third principal patterns reveal changes both in the order of explained variances and in some of their spatial features. They can be associated with an expansion of the subtropical South Atlantic anticyclone over SA and lower midlatitude cyclone activity after the 1976/77 summer. The latter is partly associated with the actual tendency toward the positive phase of the southern annular mode. The main patterns can even explain some changes in the observed precipitation over subtropical central-west Argentina as well as for other subtropical regions. Different inhomogeneity tests applied to the atmospheric circulation climatology support the changes. Results suggest that the atmospheric circulation change could be somewhat unique (not observed in the twentieth century) and, thus, it could not be thoroughly ascribed to the El Niño-like variability.