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

Observing-system simulation experiments (OSSEs) are performed to investigat e the dynamical impact of total-ozone data used in a four-dimensional varia tional analysis in a numerical weather prediction (NWP) model. Ozone column s are generated by the model at the location of data retrieved by the Natio nal Environmental Satellite, Data, and Information Service, from the measur ements of the TIROS (Television Infra-Red Observation Satellite) Operationa l Vertical Sounder (TOVS). They are assimilated over a 12-hour period. In t he present experiments, ozone mixing ratio is considered to be a passive tr acer, simply advected by winds. The initial three-dimensional ozone field i s not analysed. An important positive impact is found in a fully idealized experiment, on the flow analysis as well as on the temperature analysis. Th e ability to derive thermodynamic information from ozone-column observation s is confirmed by an OSSE performed in a more realistic context. Moreover, the information on wind fields supplied by ozone data may be in addition to the information already provided by observations currently assimilated in NWP models. Some conditions, needed to make the information provided by ozo ne columns effective, are discussed, such as the accuracy of the ozone meas urements and the necessity of analysing ozone in addition to the usual mode l variables.