Compilation of Summaries 
26 
System Nordsee 
contrast to monthly distributions, they are usually found in close accord with climato 
logical reference states. Notable exceptions are the S-ly meridional flow in winter 2006 
and the sharply enhanced SW-ly flow throughout the fall of the same year. In com 
parison, particularly striking intraseasonal circulation contrasts in summer 2006 and 
winter 2007 expressed themselves in inverse month-to-month surface air temperature 
anomalies across the entire land mass within temperate latitudes of the Northern 
Hemisphere. This hemispheric response clearly shows that large-scale atmospher 
ic circulation anomalies are integrated into the mid-latitudes’ earth-girding system of 
waves and eddies. 
The widely used North Atlantic Oscillation index does not always provide a useful 
indication of atmospheric flow in the North Sea region. The enhanced SW-ly flow in 
September and October 2006, for example, was associated with a correspondingly 
strong positive mode of the East Atlantic Pattern, while, at the same time, various NAO 
indices were suggestive of (incompatibly) weak zonal circulation. 
The switch of the database to NCEP/NCAR reanalyses made obvious the problem 
of pressure reduction to mean sea level in mountain regions in general, and in the 
Norwegian Scandes in particular. In comparison to previously used MSLP fields of the 
UK Met Office, the NCEP/NCAR fields were found to be noticeably distorted here in 
fall and winter. This deformation usually corresponds to an artificial SE deflection of 
the wind. MSLP distributions are solely employed here in diagnostic analyses, which 
in the end are based on the weather-typing scheme. As this technique did not yield 
unbearably compromised results on any relevant time scale, no attempts were made 
to correct the NCEP/NCAR fields for this artefact. 
North Sea Wind (p. 85 sqs.) 
Being proportional to the wind index of the weather-typing scheme, the geostrophic 
>North Sea Wind< characterizes wind speed and direction across the North Sea. Us 
ing daily wind vectors wind probability ellipses and virtual displacement trajectories 
were constructed as to visualize seasonal states and day-to-day evolution of wind 
conditions in 2006 and 2007. Monthly, seasonal, and annual means of both, vector and 
scalar wind speeds, wind direction and directional stability are reported among other 
tabulated statistics. 
In either year, the prevalence of westerly winds is reflected in a W:E ratio of the zonal 
wind of nearly 3:1. At 3:2 the S:N ratio of the meridional wind in 2006 was markedly 
less balanced than usual or in 2007 (1:1). The proportion of vector to scalar wind 
speed measures directional stability or persistence. Proportions close to 1:2 are typi 
cal of annual and seasonal means - excepting spring, when persistence falls to about 
1:4. Substantial deviations occurred in winter (1:4), spring (1:2), and fall 2006 (3:4). At 
60% high winds (> 10 m/s) were much more frequent in fall/winter 2006/07 than in 
winter 2006 or fall 2007 (40% each). High wind frequencies in spring (13%) and sum 
mer 2007 (30%) were У2 and 3 times as large as in corresponding seasons of 2006. 
Seasonal shifts in the influence of Icelandic Low and Azores High are apparent from 
the climatological virtual trajectory of >North Sea Wind<. Uniformly strong WSW winds 
from October through March are typical of the cold season, which abruptly gives way 
to a period of stagnation in April and May when winds are changeable and may blow 
from any direction. With progressing spring season, the influence of the Azores High 
eventually prevails. Weak WNW winds at its northern edge from early June character 
ize average North Sea summer weather.