Assessment of the contribution of IRS for the characterisation of ozone over Europe

Abstract. In the coming years, EUMETSAT’s Meteosat Third Generation – S (MTG-S) satellites will be launched with an instrument of valuable features on board. The MTG – Infrared Sounder (IRS) will represent a major innovation for the monitoring of the chemical state of the atmosphere, since, at present, observations of these parameters mainly come from in situ measurements (geographically uneven) and from instruments on board of polar-orbiting satellites (highly dependent on the scanning line of the satellite itself, which is limited, over a specific geographical area, to very few times per day). MTG-IRS will present many potentialities in the area of detecting different atmospheric species and will have the advantage of being based on a geostationary platform and to acquire data with a high temporal frequency (every 30 minutes over Europe), which makes easier to track the transport of the species of interest.

The present work aims to evaluate the potential impact, over a regional domain over Europe, of the assimilation of IRS radiances within a chemical transport model (CTM) Modèle de Chimie Atmosphérique de Grande Echelle (MOCAGE), operational in Météo-France.

Since IRS is not yet in orbit, observations have been simulated using the Observing System Simulation Experiment (OSSE) approach. Of the species to which IRS will be sensitive, the one treated along this study was the ozone.

The results obtained indicate that the assimilation of synthetic radiances of IRS always has a positive impact on the ozone analysis from the model MOCAGE. The relative average difference compared to the NR in the ozone total columns improves from -30 % (no assimilation) to almost zero when IRS observations are available over the domain. When considering tropospheric columns the improvement is also significant, from 15–20 % (no assimilation) down to 3 %.