dinrichs et al. 
to 2010. Additionally, the BNSC is compared to the COSMO- 
REA6 reanalysis (Bollmeyer et al., 2015) from the DWD and 
the University of Bonn. COSMO-REA6 was calculated for the 
time period 1995 to 2015 and has a spatial resolution of 6km 
and an hourly temporal resolution. For the comparison, only 
monthly means are used. Before comparing the field, it is always 
interpolated onto the coarser grid. 
The compared station data are time series of sea level pressure 
of 10 different stations along the German coast. The data was 
provided by the DWD (www.dwd.de/cdc). For comparison, the 
nearest grid cell of the ERA-40 reanalysis, respectively, the 
3NSCatm, is used. 
in most comparisons, the monthly means are calculated 
and then a difference time series is created. Afterwards, these 
difference time series are averaged over the whole time period, 
single month or seasons. For the comparison of climatologies 
‚981-2010, a climatology for the same period is calculated 
from ERA Interim and this is monthly subtracted from the 
BNSCAatm climatology. 
14 Areas From Climatology of the Baltic Sea 
and ICOADS 
The BNSCatm was compared to available air and dew point 
temperature data in the Climatology of the Baltic Sea based on the 
[COADS-Data Set (1951-2000) by Schmager et al. (2008). They 
provide monthly means of air and dew point temperature for 14 
areas in the Baltic Sea. For the same areas and period, means were 
calculated for each month from the monthly means of air and 
dew point temperature of the BNSCatm. 
The hydrographic subset of the BNSC is compared to three 
data products: 
» the precursor of the BNSC, the KNSCv2 data set for the North 
Sea region (Bersch et al., 2016) 
the BALTIC ATLAS (Feistel et al., 2008) for the Baltic 
Sea region. 
(the latter two are based on in situ observations). 
a ihe BALTIC SEA PHYSICAL REANALYSIS PRODUCT (Axell 
and Liu, 2016). 
All three data products together with the applied comparison 
methods are described in the following. 
KNSCv2 
[The precursor of the data product presented here, the KLIWAS 
North Sea climatology (KNSCv2, Bersch et al., 2016) is used for 
comparison with time series of box-averages of the BNSC data 
product. The KNSCv2 product comes on altogether 179 depth 
levels on a horizontal grid with a box length of 0.5° (zonal) 
and 0.25° (meridional). It covers the period 1873-2013. For 
the comparison, the BNSC box averages in both annual and 
monthly resolution are used. Concerning the spatial resolution, 
BNSC is adapted to KNSCv2 by horizontally averaging the 
two BNSC boxes corresponding to one KNSCv2 box. BNSC 
values are linearly interpolated on KNSCv2 depth levels. In case 
rontiers in Earth Science | www.frontiersin.Ofu 
Baltic and North Seas Climatology 
of spatial and temporal correspondence, absolute differences 
are computed. 
BALTIC ATLAS 
The time series of monthly mean values for the Baltic Sea 
(BALTIC: Monthly Time Series 1900-2005, Feistel et al., 2008) is 
used for the comparison with the monthly BNSC box averages of 
temperature and salinity. The BALTIC grid has an edge length of 
L° and regularly spaced (10 m) depth levels. For the comparison, 
the BNSC product is horizontally averaged over the 16 boxes 
that correspond to one BALTIC box. Additionally, the BNSC 
values are linearly interpolated on the BALTIC depth levels. 
Absolute differences are then computed for every spatial and 
temporal correspondence between BALTIC and BNSC in the 
period 1900-2005. 
Baltic Sea Physical Reanalysis Product 
The BALTIC SEA PHYSICAL REANALYSIS PRODUCT, 
hereafter referred to as BSRA, provides, among others, 
temperature and salinity fields in monthly resolution. The 
horizontal grid has an edge length of 5km. BSRA has 50 
irregularly spaced depth levels with a distance of 4 m in the upper 
and a maximum distances of 40 m in the lower part of the water 
column. The period covered by the BSRA product is 1989-2015. 
For the comparison, the BSRA boxes corresponding to one 
BNSC box are spatially averaged and subsequently linearly 
interpolated to the BNSC depth levels. Absolute differences 
between the two data products are then computed. 
The BNSCatm data products are available from https://icdc. 
cen.uni-hamburg.de/1/daten/atmosphere/bnsc-met/ 
and should be cited as 
Jahnke-Bornemann, Annika; Sadikni, Remon (2018). Baltic 
and North Sea Climatology meteorological part (Version 2.0). 
World Data Center for Climate (WDCC) at DKRZ. https://doi.org/ 
10.1594/ WDCC/BNSClim_meteo_v2 
The BNSChydr data products are available from 
https://icdc.cen.uni-hamburg.de/1/daten/ocean/bnsc/ 
and should be cited as 
Hinrichs, Iris; Gouretski, Viktor (2018). Baltic and North Sea 
Climatology hydrographic part (Version 1.0). World Data Center 
for Climate (WDCC) at DKRZ. https://doti.0rg/10.1594/WDCC/ 
BNSClim_hydro_v1.0 
Free download as well as visual exploration of the data product 
is possible here. 
After first submission of this manuscript, an update of the 
BNSChydr product has taken place. The authors recommend 
to use the update, which can be found under the same above 
given link. Until no new DOI has been assigned, the above given 
citation remains. All analysis presented in this paper are based on 
BNSChydr v1.0. 
The spatial dimensions of the BNSC data products are 
described in Table 4. 
The BNSC data product itself is complemented by 
information about the distribution of sea and land in the 
BNSC region in order to be able to distinguish between the 
two spheres. 
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