Chapter 12
IMPORTANCE OF DATA: A
METEOROLOGICAL PERSPECTIVE
Florence Rabier
Météo-France, CNRM, Toulouse, France
Abstract:
The importance of data in meteorological data assimilation can be quantified
in the context of re-analyses performed at Numerical Weather Prediction
centres. The increasing quality and quantity of satellite data is seen to play a
major role in the improvement of forecast performance, particularly in the
Southern hemisphere. Further optimisation of the use of observations is
possible through proper evaluation of the data impact, optimisation of the
amount of data to be assimilated and of their error characteristics, and a
relevant selection of data based on information content concepts. A more
interactive forecasting system including an adaptive observation component is
a new challenge to bring additional improvement in the forecasting of highimpact weather.
Keywords: Observations, Numerical Weather Prediction, data assimilation, observation
targeting, data impact, optimisation, data selection, information content.
1.
Introduction
Atmospheric data assimilation consists in combining information coming
from a forecast model together with available observations. It is usually
performed in a sequential way, with a time series of “assimilation cycles”
including a model integration and a correction due to observations. As a
new set of observations becomes available every six or twelve hours, a
short-range forecast (so-called “background”) is updated with the new set of
data into a new “analysis” of the atmosphere. This analysis is then
propagated in time with the forecast model to provide a new background
field for the next “assimilation cycle”. This series of steps in the data
assimilation process shows that the atmospheric model is the basic
ingredient which allows time continuity in our evaluation of the atmospheric
flow. It also means that the observations are the crucial elements allowing to
343
E. P. Chassignet and J. Verron (eds.), Ocean Weather Forecasting, 343-360.
© 2006 Springer. Printed in the Netherlands.
IMPORTANCE OF DATA: A
METEOROLOGICAL PERSPECTIVE
Florence Rabier
Météo-France, CNRM, Toulouse, France
Abstract:
The importance of data in meteorological data assimilation can be quantified
in the context of re-analyses performed at Numerical Weather Prediction
centres. The increasing quality and quantity of satellite data is seen to play a
major role in the improvement of forecast performance, particularly in the
Southern hemisphere. Further optimisation of the use of observations is
possible through proper evaluation of the data impact, optimisation of the
amount of data to be assimilated and of their error characteristics, and a
relevant selection of data based on information content concepts. A more
interactive forecasting system including an adaptive observation component is
a new challenge to bring additional improvement in the forecasting of highimpact weather.
Keywords: Observations, Numerical Weather Prediction, data assimilation, observation
targeting, data impact, optimisation, data selection, information content.
1.
Introduction
Atmospheric data assimilation consists in combining information coming
from a forecast model together with available observations. It is usually
performed in a sequential way, with a time series of “assimilation cycles”
including a model integration and a correction due to observations. As a
new set of observations becomes available every six or twelve hours, a
short-range forecast (so-called “background”) is updated with the new set of
data into a new “analysis” of the atmosphere. This analysis is then
propagated in time with the forecast model to provide a new background
field for the next “assimilation cycle”. This series of steps in the data
assimilation process shows that the atmospheric model is the basic
ingredient which allows time continuity in our evaluation of the atmospheric
flow. It also means that the observations are the crucial elements allowing to
343
E. P. Chassignet and J. Verron (eds.), Ocean Weather Forecasting, 343-360.
© 2006 Springer. Printed in the Netherlands.