Ocean Dynamics 
Ô Springer 
-FCOO_GETM 
DMI_DKSS 
BSH_CMOD 
BSH_HBM 
SMHI_HIROMB_NS03 _ 
SMHI_HIROMB_BS01 
- FMI_HBM_hirlam 
FMI_HBM_ec 
« DMI_HBM 
■ MME mean 
a) 
ja 
E 
■ ■ ■ MME median 
Feb Mar Apr May 
Aug Sep 
Nov Dec 
Fig. 18 Daily spatial averages of SSS from the MME mean, MME median (black lines), and the individual forecasts in the Baltic Sea in 2014, except for 
the forecast from MSI. The ensemble spread is indicated by the yellow-shaded field. The number of forecasts is marked as blue plus signs 
by comparatively higher displacements at most transects during 
winter months, mainly in region V. This period is followed by 
distinct lower values in spring. Compared to the other forecasts, 
BSH CMOD is in the normal range of displacements. In con 
trast, DMIHBM exhibits the highest values at most transects 
in both regions, the Central Baltic Sea and the Gulf of Finland. 
Forecasts with lowest values differ between transects. The 
greatest range of displacements occurs at Tr50 varying between 
4.8 km (SMHIHIROMBNS03) and 10 km (DMI HBM). 
The displacements in the Baltic Sea, where maximum values 
range from 9 to 11 km, are low in comparison to the North Sea 
with maximum displacements varying between 10 and 30 km 
depending on the region. This is due to generally higher SSC in 
the North Sea than in the Baltic Sea. 
General difficulties in comparing SSC in region IV, the 
Skagerrak and Kattegat, occur due to different model resolu 
tions. In these highly dynamic areas, higher resolution of all 
forecast models would be necessary to obtain more convinc 
ing results for comparison of SSC. Therefore, this region is not 
evaluated here. 
The relative deviation of SSC magnitude gives more infor 
mation about the spread between the forecasts (Fig. 21). 
Higher deviations between North Sea forecasts occur in region 
III, thus at those transects located in the outflow area of the 
Baltic Sea. Low deviations occur at transects situated in the 
central North Sea, German Bight, and English Channel where 
SSC are often highest. Regarding the deviation between Baltic 
Sea forecasts, comparatively high values appear at all tran 
sects, indicating a strong spread between the forecasts in the 
whole area. The same pattern is reflected in Fig. 20, where 
transects with strong differences in final displacements are 
correlated with high deviation in Fig. 21, e.g., Tr4, Trl3, 
Tr9, Tr21, and Tr22. In contrast, Tr30, Tr49, and Tr50, char 
acterized by large spreads in Fig. 20, exhibit low relative de 
viations in Fig. 21 which might be due to the fact that the 
deviation in current magnitude is lower compared to the de 
viation of current components. Nevertheless, the relative de 
viation displayed in Fig. 21 gives more information about the 
real spread between the models, while Fig. 20 gives the im 
pression that the spread at the Baltic Sea transects is very 
small. The reason is that the statistics are dependent on the 
absolute SSC values, which are mostly lower in the Baltic Sea, 
resulting in lower displacements of PVDs. 
4.4 Regional pattern in model deviation for water 
transport 
The percentage occurrence of the CV categories are shown as 
bar plot at each transect in the North Sea (a) and the Baltic Sea 
(b) in Fig. 22. The distribution shows that the best category 1 
appears most with more than 65 % at most transects while 
category 3 appears less frequent. This indicates that the 
Table 3 Regions and groups of 
transects defined for the 
evaluation of sea surface currents 
and surface transports 
Number 
Name of region 
Number of transect 
I 
Inflow North Sea 
Tri, Tr4, Tr7, TrlO 
II 
English Channel, German Bight 
Tri5, Trl4, Trl3, Trl2, Trll, Trl9, Tr20 
III 
Norwegian Coastal Current 
Tr23, Tr22, Tr21, Tr9, Tr6, Tr5, Tr2 
IV 
Skagerrak, Kattegat 
Tr28, Tr27, Tr26, Tr25, Tr24 
V 
Gulf of Finland 
Tr46, Tr45, Tr44, Tr43 
VI 
Central Baltic Sea 
Tr52, Tr50, Tr49, Tr41, Tr36, Tr32, Tr30, Tr29 
VII 
Gulf of Riga 
Tr38, Tr42