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variability was concentrated at a period of about eight
years which slightly shifted to longer periods.
Figure 2. Wavelet analysis of air temperature at Kiel
lighthouse and NAO DJFM winter indices. The thick
black contour designates the 5% significance level
against red noise and the cone of influence where edge
effects might distort the picture is shown in lighter shade.
Additionally to the changes in temperature there is also a
change in prevailing winds for the periods under
consideration. Figure 3 shows the decrease in frequency
of wind from westerly directions for autumn (SON) and
an increase for winter (DJF). This shift in wind directions
is associated also with a decrease of strong wind events
during autumn and a corresponding increase in winter.
Figure 1. Frequency of wind events for autumn
SON (left) and winter DJF (right) for the periods
1970-1987 (blue) and 1988-2008 (red).
From NCEP/NCAR reanalysis MSLP data, we calculated
the first EOF for DJF for both periods (Fig. 4).
Comparing the first with the second period reveals an
intensification of the NAO/AO pattern and a slight shift
to the east of the centers of action.
Hilmer and Jung (2000) observed a similar shift of the
NAO pattern to the east when comparing the periods
1958-1977 and 1978-1997. Cassou et al. (2004)
explained the shift by the asymmetry of the NAO pattern.
For positve phases the NAO is located more easterly than
for negative phases.
Figure 2. First EOF of MSLP data for DJF calculated
from NCEP/NCAR reanalysis data for the period 1970-
1987 and 1988-2008.
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