Geoscience Reference
In-Depth Information
As far as conventional observations are concerned, it is possible to distinguish
the following three types of observations:
- surface observations are delivered by meteorological stations over land, by
ships and buoys. The most useful measurements for numerical weather prediction
are pressure, wind speed and direction at 10m, temperature and humidity at 2m
above surface;
- radiosonde observations are generally carried out twice a day at precise times
(00 and 12 UTC), and provide the models with information on vertical profiles of
temperature, humidity and wind up to altitudes of approximately 30 km;
- airborne observations on board commercial airplanes, generally made by
automatic systems, provide temperature and wind information along the flight route,
and during take off and landing.
Amongst the satellite observations, it is possible to distinguish between the
following types of observations:
- observations from atmospheric sounders aboard orbiting satellites: radiometric
measurements (called radiances) provide information e.g. on the vertical profiles of
temperature and humidity;
- wind observations using geostationary satellite (such as Meteosat) imagery are
generally derived from monitoring the displacement of certain types of clouds.
The above mentioned observations are used by most of numerical forecast global
models. As an example, the ECMWF is producing global analyses four times a day
at 00, 06, 12, and 12 UTC, and 10-day forecasts from analyses made at 00 and 12
UTC.
The assimilation scheme performs the following operations:
Global
analysis of:
Wind, temperature, surface pressure, humidity and ozone (4D variational
assimilation called 4D-VAR which is carried out over 12 hour periods).
Surface parameters: surface temperature from National Centers for
Environmental Predictions (NCEP); sea ice derived from SSM/I satellite
data; soil water content; snow depth and ocean waves.
In-situ conventional data over land and the ocean (SYNOP for the surface,
TEMP and PILOT for upper-air profiles measured by radiosondes or
rawinsondes, and tracked Pilot balloons; drifting buoys DRIBU data;
AIREP, ACARS and AMDAR data from airliners and wind profilers)
Satellite data (NOAA ATOVS eadiances; AIRS radiances; AMSU-A
radiances; radiances from geostationary satellites and displacement vectors
(derived e.g. from the displacement of clouds); surface wind from
scatterometers; SSM/I radiances; ENVISAT total ozone column; SBUV
ozone profiles)
ENVISAT ASAR data for the oceanic wave model; JASON and ENVISAT
altimetric data
Data used
Table 4.2.
Analyzed parameters and data used in the
operational ECMWF assimilation scheme
