The quality of the ASCAT winds has been assessed before, mostly over the large areas of oceans using comparisons with buoy measurements (Verhoef & Stoffelen 2009). The present study attempts

to assess whether the same quality and uncertainty characteristics apply to the narrow, almost enclosed Baltic Sea basin as well. The comparison further aims to assess the quality and uncertainty range of HIRLAM NWP model predictions, as its output is often used for driving marine models in operational forecasting and hindcasting regimes. Two different resolutions of the NWP model are compared to see whether the resolution increase can play a significant role in forecasting over the selleck chemicals enclosed Baltic Sea. In the present study the EARS ASCAT 12.5-km gridded wind speed and wind direction were studied during the two-month period from 01.10 to 03.12.2009. The period was chosen to represent the stormy season over the Baltic Sea. HIRLAM forecasts from the archive of operational runs at the EMHI for the same period were used for comparison. Unfortunately, buoy measurements from the Baltic Sea were not available for inclusion in the study. The NWP environment at EMHI is based on HIRLAM version 7.1.2 and consists of two modelling areas, ETA_II and ETB_II, with different grids. _II refers to EMHI’s in-house second generation of modelling areas

and will be omitted further on in the current manuscript for ease of reading. Figure 2 illustrates the HIRLAM modelling areas and their Sirolimus geographical Doxacurium chloride location. The ETA modelling domain has a horizontal grid distance of 11.1 km and the smaller ETB model domain has a 3.3 km grid. It should be noted that the HIRLAM has a rotated-pole

latitude-longitude grid (here, the south pole is located at 30°S and 0°E). The boundary fields for the HIRLAM ETA model are provided by the European Centre for Medium-Range Weather Forecasting (ECMWF) model, and the boundary fields for the ETB model are provided by the ETA forecasts. The 54-hour forecasts of the ETA model are calculated four times a day with forecast starting-points at 00, 06, 12 and 18 UTC. For the ETB domain the 36-hour forecasts are calculated twice a day with starting-points at 00 and 12 UTC. To maintain the analysis cycle, 6-hour forecasts at 06 and 18 UTC are calculated for ETB as well. Forecast fields are available with a 3-hour time resolution. Further properties of models and the parameterization schemes applied in the NWP environment at EMHI can be found in the paper by Keevallik et al. (2010). The physical definition of the ASCAT winds is that of equivalent neutral winds. In the most common definition, equivalent neutral wind speed is the mean wind speed that would be observed if there was neutral atmospheric stratification (Geernaert & Katsaros 1986). The only difference between neutral and real ASCAT winds is a bias of +0.