Geoscience Reference
In-Depth Information
GPS measurements. In addition to the spatial reference in geographical coordinates
according to WMO, there are still a great number of national reference systems in
use. However, the increasing use of the UTM system will overcome this variety of
spatial reference systems in the future. Problems from different national reference
systems could appear in the case of merging datasets (especially gridded fields)
from different data holders, which could result in certain differences in overlapping
areas.
In addition to altitude, several other vertical coordinate systems are used in
meteorology including pressure, isentropic, or terrain-following coordinates, which
are used for upper-air observations or for weather and climate models. Beside
upper-air observations, such coordinated systems are used for weather and climate
models. Such systems are not established in the traditionally predominately two-
dimensional GIS world [WOO 05]. Providing the full richness of vertical coordinate
systems will be an important requirement for full integration of GIS in meteorology
and climatology, and thus, an important area of OGC activity.
1.1.6.
Climate reanalysis data
Climate reanalysis aims to produce meteorologically consistent datasets of the
atmosphere covering the entire Earth with state-of-the-art methods. In particular,
they combine the full set of meteorological observations, including, e.g. surface
stations, radio sounds, and satellite data with weather forecast models using data
assimilation methods. Climate reanalysis datasets are among the most important
climate datasets in climate research, including climate impact studies. Standard data
formats for climate reanalysis are GRIB or NetCDF. Due to the NetCDF data
format, these datasets are already standardized for direct use in GIS applications
(see section 1.1.4). Climate reanalysis data are provided in Europe by the ECMWF
(European Center for Medium-range Weather Forecast, UK) from the following
projects: ERA15 covering the period 1979-1993 and ERA40 covering the period
1957-2002. In the USA, reanalysis projects have been run by the NOAA and NASA
within: NOAA-NCEP covering the period 1948 onwards and NASA/DAO covering
the period 1980-1995, and from Japan Meteorological Agency: JRA-25 covering the
period 1979 onwards.
New reanalysis projects are currently under way (ERA interim) or planned
(NCEP, JRA). In addition to meteorological consistency, the most important product
of reanalysis data is their full spectrum of data covering the entire atmosphere in
similar way as weather forecast models in high temporal resolution (e.g. 6 hourly
fields for ERA40), but also with similar spatial resolution of the gridded fields.
Climate reanalysis is derived by data assimilation methods, which is today a
four-dimensional (4D) variational analysis in the case of ERA [AND 08]. 4D-Var
performs a statistical interpolation in space and time between a distribution of
meteorological observations and an
a priori
estimate of the model state (the
background). This is done in such a way that the dynamics and physics of the
