Geoscience Reference
In-Depth Information
inhomogenities from statistical evaluation of the differences or ratios to a reference
series computed from neighboring stations in similar climate conditions considering
statistical significance of breakpoint. Absolute homogenity tests fail to differentiate
between climatic and non-climatic inhomogenities.
Figure 1.9 summarizes the procedure of climate time series homogenization used
by most of the homogenization tools used in climatology. Also the procedure varies
with the different homogenization tools; however, it is laborious work, independent
of the method used. Reference series are not only used for detection of breakpoints
but also for adjustment of breaks. A useful summary of available homogenization
methods (for both the breakpoint detection and the adjustment procedure) is given
by [AGU 03].
It is important for homogenization work to consider the underlying statistical
distribution of data to be analyzed. Non-normally distributed datasets need other
approaches compared with datasets with normally distributed data.
Figure 1.10 shows results from homogenization of a multiple climate dataset for
the GAR. It can be concluded from this figure that climate networks contains
systematic changes of the network inherent to all stations and that averaging over a
larger sample of climate series can not remove inhomogenities.
1.3. Metadata: documenting quality and usability
1.3.1.
Short characteristic of metadata from a climate data perspective
Information on data, known as metadata, enables the operator of an observing
system to take the most appropriate preventive, corrective, and adaptive actions to
maintain or enhance data quality. Metadata, therefore, include detailed information
on the observing system itself and, in particular, on all changes that occur during the
time of its operation. Within the WMO, the role of ISO 19115 is stressed as the
metadata standard for describing meteorological and climatological data. This
standard has been developed for the geographical community, but it is also useful
for meteorology as both disciplines deal with spatial data. Whereas the
documentation of metadata related to the quality of the data is well established in
meteorology and climatology, the description of the context of the data (e.g. access
rules) is much less developed. Detailed and standardized metadata are increasingly
important in the case of data access via the internet.
Elements of a metadata database (according to [WMO 08]):
A metadata database contains initial set-up information together with updates
whenever changes occur. Major elements include the following:
(a) Network information:
(i) the operating authority, and the type and purpose of the network;
(b) Station information:
