To create a homogeneous dataset, consisting of monthly values of
air temperature, precipitation, air pressure, cloud cover and
number of days with snow cover from 70 climatological stations in
the North Atlantic area (50º N--80º N, 40º E--60º W)
covering the period 1890 - 1990.
Instrumental records covering the most recent 100-300 years are
being digitized and will go through various types of quality
control procedures in order to remove sporadic errors such as
miscalculations and typing errors.
The time series will be homogeniety tested using a varity and
statistical procedures. The first step will include an internal
relative homogeneity test which will detect changes in formula,
time of observation, coding system etc. Next step will include a
spatial relative homogeneity test, which will detect relocation
of stations, change of instruments etc. The third step will
include a spatial absolute homogeneity test, which should be able
to detect inhomogeneities related to nation-wide changes in the
The project will also develop a standardized metadata concept for
storing and retrieving information about relocations, change of
formula, change of instrument etc.
Adjustment of series due to detected inhomogeneities will be done
when there is physical evidence of a non-climatic change in the
station history or metadata-files. The adjustment figures will
be verified, if possible, by using parallel observations from a
nearby station or parallel observations of related climatic
elements from the same station or by using parallel series of
proxydata from data sparse regions.
The NACD-project will compare the dataset with existing
single-element datasets which have global coverage. Comparisons
have been planned for gridded sea surface temperature data, but
also comparison with cloud- and snow cover datasets will be
Another task is to merge the NACD with selected historical time
series reaching back several hundred years before systematic
instrumental observations began. This task will serve the
purpose of describing the long-term preindustrial natural
variability in the North Atlantic region.
The homogenous dataset will be analyzed with respect to regional
climatic trends of natural and/or anthropogenic origin. Finally
the NACD will be available for validation of output from climate
models and could also be used for model-based statistical
projections of the future climate.
Funding SchemeCSC - Cost-sharing contracts
3730 AE De Bilt
RG12 2SZ Bracknell
601 76 Norrkoeping