Abstract
European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-Interim reanalysis total precipitation estimates are validated against ten years of in situ precipitation measurements onboard of ships over the Baltic Sea. A statistical analysis for binary forecasts and mean rain rates derived from all data show a good agreement with observations. However, a closer look reveals an underestimation of ERA-Interim total precipitation in spring and an overestimation in autumn, obviously related to stability. Deriving stability and evaporation by a bulk flux scheme it could be shown, in fact, that ERA-Interim underestimates precipitation for conditions with low evaporation and strongly overestimates it for conditions with high evaporation. Since ERA-Interim surface fields become too dry with increasing evaporation compared to independent synoptic ship observations, uncertainties in the ECMWF convection scheme may possibly cause these biases in seasonal precipitation.
Highlights
The Baltic Sea is a semi-enclosed sea, which is strongly influenced by human activities due to its location
All numbers are quite similar so it can be stated that ERA-Interim precipitation, despite to systematic deviations in the rain rates, shows, in general, a good agreement with observations for the Baltic Sea area
The comparison of the binary statistics based on the ERA-Interim product and collocated observations of rain, with results derived from simulated fields and observations based on weather radar reflectivities and the good agreement of the annual precipitation rates with observations, indicate that ERA-Interim precipitation is of sufficient accuracy over the Baltic Sea area
Summary
The Baltic Sea is a semi-enclosed sea, which is strongly influenced by human activities due to its location. There is a need to investigate the functioning of the marine system, for which the energy and water cycles determine the boundary conditions. Several efforts have been undertaken within the BALTEX (BALTic Sea EXperiment) research program [1,2] to improve our understanding of these cycles and their interconnections. Despite progress in Baltic Sea research, several gaps remain. [1] found that changes in ocean salinity are not fully understood and modelling of the hydrological cycle in atmospheric climate models is severely biased. They, concluded that more detailed investigations of regional precipitation and evaporation patterns are still needed
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