This is the slightly revised version 2 of the Baltic and North Sea Climatology (BNSC) for the Baltic Sea and the North Sea in the range 47 ° N to 66 ° N and 15 ° W to 30 ° E. It contains the monthly average of air temperature, pressure and dew point on a 1 ° x 1 ° grid for the period from 1950 to 2015.
For the calculation of the mean values, all available quality-controlled data of the DWD (German Meteorological Service) of ship observations and buoy measurements were taken into account during this period. For each month additional climatologies were calculated for the standard periods 1951-1980, 1961-1990, 1971-2000 and 1981-2010. As a prerequisite for the calculation of the 30-year-climatology, at least 25 out of 30 (five-sixths) valid monthly averages had to be present in the respective grid box. For the long-term climatology from 1950 to 2015, at least four-fifths valid monthly means had to be available.
Two methods were used (in combination) to calculate the monthly averages, despite the small number of measurements per grid box and their uneven spatial and temporal distribution:
1. For parameters with a detectable annual cycle in the data (air temperature, dew point temperature), a 2nd order polynomial was fitted to the data to reduce the intra-month variation and reduce the uncertainty of the calculated averages. In addition, for the mean value of air temperature, the daily temperature cycle was removed from the data. In the case of air pressure, which has no annual cycle, in version 2 per month and grid box no data gaps longer than 14 days were allowed for the calculation of a monthly mean and standard deviation. This method differs from version 1, where mean and standard deviation were calculated from 6-day windows means.
2. If the number of observations fell below a specified threshold value (which was for the air temperature and the dew point temperature 20 values per grid box and month, for the air pressure 500 per box and month), the data of the neighboring boxes were used in two steps (only 8, if not sufficiently the next 16) to calculate the mean value. Thus, the spatial resolution of the parameters is reduced at certain points and, instead of 1 ° x 1 °, if neighboring values are taken into account, data from an area of 5 ° x 5 ° can also be considered, which are then averaged into a grid box value. This was especially used for air pressure, where the 24 (= 8 + 16) values of the neighboring boxes were included in the averaging for most grid boxes.
The mean value, the number of measurements, the standard deviation and the number of grid boxes used to calculate the mean values are available as parameters in the products.
The calculated monthly and annual means were allocated to the centers of the grid boxes:
Latitudes: 47.5, 48.5, ...
Longitudes: -14.5, -13.5, …
In order to remove any existing values over land, a land-sea mask was used, which is also provided in 1 ° x 1 ° resolution.
In version 2 of the BNSC, a slightly different database was used, which resulted in small changes in the range of tenths of degrees in the averages and standard deviations of the 2-meter air temperature and the 2-meter dew-point temperature. In addition, the parameter names and units have been adjusted to meet the CF 1.6 standard.
The hydrographic part of BNSC can be found here.