Dynamical impact of total ozone observations in a four-dimensional variational assimilation

Impact dynamique des observations d'ozone total dans une assimilation variationelle quadri-dimensionnelle

Peuch, A. ; Thépaut, J.N. ; Pailleux, J.

Année de publication
2000

Observing-system simulation experiments (OSSEs) are performed to <br>investigate the dynamical impact of total-ozone data used in a <br>four-dimensional variational analysis in a numerical weather prediction <br>(NWP) model. Ozone columns are generated by the model at the location of<br> data retrieved by the National Environmental Satellite, Data, and <br>Information Service, from the measurements of the TIROS (Television <br>Infra-Red Observation Satellite) Operational Vertical Sounder (TOVS). <br>They are assimilated over a 12-hour period. In the present experiments, <br>ozone mixing ratio is considered to be a passive tracer, simply advected<br> by winds. The initial three-dimensional ozone field is not analysed. An<br> important positive impact is found in a fully idealized experiment, on <br>the flow analysis as well as on the temperature analysis. The ability to<br> derive thermodynamic information from ozone-column observations is <br>confirmed by an OSSE performed in a more realistic context. Moreover, <br>the information on wind fields supplied by ozone data may be in addition<br> to the information already provided by observations currently <br>assimilated in NWP models. Some conditions, needed to make the <br>information provided by ozone columns effective, are discussed, such as <br>the accuracy of the ozone measurements and the necessity of analysing <br>ozone in addition to the usual model variables.</div>

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