KLIWAS 
Seite 
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Summary 
The KLIWAS Project 1.03 analysed atmospheric near sea surface fields over the 
North Sea originating from the EU ENSEMBLES hindcast simulations forced with 
ERA-40 data. Since these atmospheric fields are used as boundary conditions for 
ocean models, these atmospheric parameters have great impact on the ocean state. It 
is therefore important to assess the bandwidth of these regional models which are also 
used in predicting the future oceanographic status of the North Sea, e.g. the water 
temperature and circulation patterns and, subsequently on the development of appro 
priate practical adaptation measures. This report presents the results of a comprehen 
sive assessment of a variety of relevant atmospheric parameters in comparison to the 
ERA-40 reanalysis data. A comparison against in-situ observations was not possible 
because of insufficient homogeneity of the long-term observational datasets of the 
North Sea. 
Seven meteorological parameters from 12 regional models were investigated, such as 
sea level pressure, wind speed and direction, air temperature, global radiation, cloud 
cover and precipitation. The comparisons were restricted to grid points at sea using 
the land-sea masks provided by the data base. For the whole North Sea climatological 
means and their standard deviations have been computed and plotted for the period 
1971-2000 as well as the differences between model results and ERA-40 for the an 
nual mean, January and July Frequency distributions have been constructed as well. 
For the latter two purposes the North Sea was divided into four sub regions. 
Sea level pressure: The deviations between the pressure fields of the regional climate 
models and ERA-40 show a variety of different patterns. The annual cycles for the 
four North Sea sub regions demonstrate good agreement of the ENSEMBLES RCMs 
with ERA-40 and, the ensemble mean reflects the ERA-40 picture very well. Only 
one RCM shows a permanent positive bias. The regional climate models thus follow 
to a great extent their driving model ERA-40. 
Wind speed: The differences between the monthly mean wind speed of ERA-40 and 
the RCMs show no systematic behaviour. There are no differences in the seasonal 
cycle and, there are positive as well as negative deviations. All of the selected RCMs 
agreed with ERA-40 considering the huge inherent variability of ERA-40 wind fields 
over the North Sea. 
Wind direction: For all sub regions in all wind speed and wind direction classes the 
frequencies of RCM wind directions differ from those of ERA-40. However, the larg 
est deviations of the wind direction frequencies of all RCMs from those of ERA-40 
are smaller than 7.6 %. Most RCMs agree with ERA-40 in southwest being the pre 
vailing and northeast the least frequent wind direction. 
Comparing 
meteorological 
fields of the 
Ensembles 
regional climate 
models with ERA- 
40-data over the 
North Sea