KLIWAS 
Seite 18 
KLIWAS 
Project 1.03: 
Atmospheric and 
Oceanic Reference 
Data and Climate 
Projections for 
Coastal and Open 
Sea Areas 
The evaluation of the RCM data suggests a higher risk of storm surges compared to 
ERA-40 data. 
A comparison of wind direction measurements at the station FINOl, about 40 km 
north of the German island of Borkum and satellite data for the time period 2005 - 
2008 in Badger et al. (2010) shows a similar distribution of directions of both in-situ 
and satellite data compared to ERA-40 data in sub region southwest in Fig. 3.4.5. 
Larsen et al. (2009) compared wind direction from two offshore stations (FINO 1, 
Horns Rev) in the southeastern part of the North Sea with results from two REMO 
runs with two different grid resolutions of 10 km and 50 km. For frequency distribu 
tions of wind directions both resolutions were in good agreement with the data meas 
ured. 
3.5 Air Temperature 
Off the coasts, the air temperature of the lower atmosphere is mainly determined by 
the temperature of the sea surface. For the North Sea, there is a significant influence 
of the two branches of the North Atlantic current entering the sea area through the 
English Channel and through the Fair Isle Channel between Scotland and the Shet 
land Islands. Additionally, the air temperatures are influenced by the adjacent Euro 
pean land masses and the geographical latitude. The air temperature at sea is of par 
ticular interest because it allows estimates of the stability of the temperature stratifica 
tion in lower air levels, which can provide information about e.g. cloud formation and 
mixing processes. Air temperature has a pronounced vertical gradient, especially 
close to the ground. 
In the analyses carried out here air temperatures refer to 2 m above the sea surface. 
The map of mean air temperatures of the ERA-40 reanalysis for the period of 1971- 
2000 over the North Sea shows a distinct zonal gradient with values of about 11 °C in 
the south and 7-8 °C in the north (Fig. 3.5.1). The maxima (about 12-13 °C) are lo 
cated within the southwest region, connected with the inflow of warm North Atlantic 
Current water through the English Channel eastward into the North Sea. 
Temperatures in the ENSEMBLES regional models show a similar pattern, with 
higher values in the south western parts, and lower values north of the British Islands 
(Fig. 3.5.2). Differences between all RCM and ERA-40 temperatures over the North 
Sea are relatively small (about 1 K), with an increasing tendency near the coast in the 
winter months (up to 4 K; Fig. 3.5.4, January). This feature can be seen in all RCMs 
and is due to better spatial resolution of the ENSEMBLE regional models. The spatial 
resolution of the RCMs is five times higher than that of the ERA-40 reanalysis and 
thus, RCMs resolve the coastline much better, whereas the coarser ERA-40 grid fields 
extends the land/sea gradient further towards the sea in mixed land/sea grid boxes. 
There is a significant difference in the RCM behaviour compared to ERA-40 between