Adinrichs et al. 
Baltic and North Seas Climatolog\ 
TABLE 6 | Overview. variables of the data product. 
Variable 
Explanation 
BNSChydr (para = temperature, salinity) 
Monthly and annual box averages 
para]_mean 
para]_stddev 
para]_noobs 
Decadal box averages 
para]_mean 
para]_stddev 
para]_year_mean 
para]_year_stddev 
para]_n_of_ys 
Interpolated fields 
para]_ocan 
para]_amd 
paral_nobins 
Mean value 
Standard deviation 
Number of observations 
Decadal monthly mean value 
Decadal standard deviation 
Mean year, lies in range of calendar years of respective decade 
Standard deviation corresponding to mean year 
Number of years that went into decadal mean 
Decadal monthly mean (interpolated)} 
Absolute median deviation (based on all neighboring boxes contributing to the optimal interpolation) 
Number of neighboring boxes included for the optimal interpolation, maximum 8. _nobins = 0 means corresp. value of the 
irst guess field is attributed to this box. 
“First guess”-value, corresponds to the long term mean of 1873-2015 
Relative interpolation error, values between 0 and 1 
Mean year, does not necessarily lie in the range of calendar years of respective decade; depends on mean year of decadal 
box averages or, if those are not sufficient for the optimal interpolation, on the “first guess”-field 
para]_mean_distance Mean distance of box center and the neighboring boxes considered for the optimal interpolation 
BNSCatm (para = air_pressure, dewpoint, airtemp) 
Time series of monthly + climatological mean values mean values 
para] Mean 
para]_stddev Standard deviation 
para]_noobs Number of observations (for the climatologies : average number of observations) 
climatological mean values 
para]l_boxcount 
time period, and monthly climatologies of the periods 1951- 
1980, 1961-1990, 1971-2000, and 1981-2010. The resulting data 
set contains mean values as well as standard deviations, and the 
mean number of observations per grid point. 
The present version includes time and area of the KNSC 
climatology, on the same grid, but some small improvements 
were applied in the production that caused differences. The 
differences are largest in air pressure (between —1.5 to 2 hPa) 
and especially its standard deviation (about —1 to 15 hPa) as 
this is calculated with a different method. The values of mean air 
(emperature and dew point temperature and associated standard 
deviations show only small changes of < 1 degree compared to 
the KNSC climatology. 
The monthly comparison between BNSCatm and ERA- 
Interim climatologies for the period 1981-2010 showed for mean 
pressure differences in the interval —2.2 hPa to +2.7 hPa. The 
mean 2m air temperature differences are between —2.1K and 
8K at a single point at the Norwegian coast, and if that is 
ignored, the maximum difference is below 2K. Most extreme 
values occur at the edges of the data field. A part of these 
differences can be explained by the so called “fair weather 
bias” which means that there are fewer measurements under 
severe weather conditions. This can cause a bias compared to 
the reanalysis results, which includes land stations and fills 
such gaps at sea with modeled data. But this inclusion of 
the land data leads in the analysis to mixed land/sea boxes 
chat arise on the coasts and tend to have higher values than 
the BNSC. 
The comparison between sea-level pressure in BNSCatm, 
ERA-Interim and ERA-40 climatology for 1979-2001 showed 
mean differences in the interval of —1.5 hPa and 1.5 hPa. 
Additionally the comparison with COSMOS-REA6 for 1995- 
2015 showed mean deviations between —1 hPa to 1 hPa. Highest 
absolute differences between the reanalysis and BNSCatm 
occur in winter and lowest in summer with better agreement 
over the open water and less good agreement close to 
the coast. 
An intercomparison between BNSCatm, the ERA-40 
reanalysis and observations based on station data was carried 
out. The mean deviations of both BNSCatm and ERA-40 from 
the observational data are within the range of uncertainty and 
show a regional pattern with the BNSC being closer to the 
observations at the North Sea coast and ERA-40 at the Baltic 
Sea coast. 
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