Validation of ECMWF and DWD model analyses with buoy measurements over the Norwegian Sea

Abstract

As part of the Lofote Cyclone experiment (Lofoten Zyklonen Experiment) 21 drift buoys were deployed in a 700 km × 400 km area of the Norwegian Sea situated to the west of the Lofote Islands. The buoys measured sea-level pressure (SLP), surface air temperature (SAT), and sea surface temperature (SST) at hourly intervals for a 6-month period from March to August 2005. This unique data set is used to validate the operational model analyses of the European Centre for Medium-Range Weather Forecasts (ECMWF) and the German Weather Service [Deutscher Wetterdienst (DWD)]. Comparisons were performed in both time and space. Generally, biases are small and amount to 0.2 hPa for SLP and −0.2 K for SAT. Temporal correlations are higher than 0.99 for SLP and 0.93 for SAT. Spatial correlations as a measure of pattern coincidence are lower then for temporal correlations, but still amount to values higher than 0.97 for SLP and 0.76 for SAT on average. SST, which is externally prescribed and not a model variable, shows surprisingly large and persistent errors of up to 6 K for latitudes above 76°N. This points towards basic errors in the SST source for both models. Taking all comparisons (SLP, SAT, and SST) together, agreement is slightly worse for DWD than for ECMWF.