15 May 2014 
DANGENDORF ET AL. 
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Januar 2007 [days] 
Fig. 1. Visualization of (top) the daily meteorological situation during January 2007 and (bottom) the related daily storm surges 
measured at the Cuxhaven tide gauge. In the vector plots (top), the colored contours represent areas of similar pressure, while the vectors 
show the wind speed and direction. For presentation purposes, only the first 25 days are shown. In the graph (bottom), daily surges (black) 
and daily NSCI index (blue; see also section 3; based on 20CRv2 data) are shown. The red line marks the long-term (1843-2012) 95th 
percentile of daily (skew) surges, while the gray areas represent single events exceeding this threshold. 
When using hourly values, astronomical tidal water 
levels are subtracted from contemporaneous observed 
water levels. When using only two tidal high and low 
water levels per day, astronomical peaks are subtracted 
from the nearest observed peaks. The two may be up to 
a few hours apart from each other due to the wind in 
fluence, and therefore the resulting surges are known as 
“skew surges." Hence, we first evaluated whether the 
skew surges (averaged to daily means) differ in the long 
term from original surges (or nontidal residuals) derived 
from hourly values for the overlapping period from 1918 
to 2008 (Fig. 2). For that purpose, we have computed 
different annual percentiles (0.1%, 1%, 2%, 5%, 10%, 
20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 95%, 
98%, 99%, and 99.9%; Fig. 2a)—the percentiles are com 
puted for each year separately—and the corresponding