KLIWAS 
Seite 27 
possible for of easterly winds due to a lack of satellite data and corresponding 
observations at this wind direction. In a random selection of satellite observations the 
conditions regarding to the cloud state is not defined, therefore the temporal statistics 
is influenced by a seasonal dependency again. 
A further promising approach is the selection of the satellite scenes on pixel level and 
generating a uniform distribution with regard to the wind direction and the number of 
cloud-free observations. Due to time and budget restrictions this approach could not 
been realized in this project phase. In Fig. 12 we present some first results basing on 
the uniform distribution shown in Fig. 11. The Figures are based on AVHRR-sensor 
data of NOAA and MetOp satellites. 
Fig. 8: Frequency of geostrophic east (red) and west (blue) winds over the North Sea. Daily 
means for 1990-2011. 
Fig. 9: Relative monthly frequency of geostrophic east (red) and west (red) winds wind direction. 
Daily means for 1990-2011. Left: original distribution, right: after adjusting the seasonal 
distribution of westerly winds to that of easterly winds. 
KLIWAS 
Climatology 
of North Sea 
Fronts