Distribution and Time Evolution of the Ozone Instantaneous Longwave Radiative Effect from IASI and TES Observations
Résumé
Ozone is the third most important greenhouse gas in terms of radiative forcing (0.4 W/m2) as a result of increases in ozone precursor emissions since pre-industrial times. Consequently, tropospheric ozone is recognized as one of the key atmospheric Essential Climate Variables by GCOS and WMO. Until recently, the ozone radiative forcing calculations were entirely model based, which led to significant discrepancies due to different model characteristics, as shown in the IPCC AR5. Satellite sounders operating in the infrared now offer the possibility to infer directly the Longwave Radiative Effect (LWRE) of ozone in the 9.6 micron band, with respect to its vertical distribution, allowing to better constrain model estimates of the ozone radiative forcing and its future predictions. Measurements of the ozone LWRE from the NASA Aura TES sounder have for instance been used to reduce intermodel RF uncertainty in the IPCC AR5.
In this presentation we calculate the ozone LWRE by exploiting the measurements of IASI on MetOp, which are performed at unprecedented temporal and spatial sampling and therefore allow investigating ozone radiative impacts on various scales. The calculation method, which we show to be more precise than previous methods based on an anisotropy correction for the angular integration, is very briefly presented. We then focus the presentation on the first daily global distribution of the LWRE from IASI and show also the first seasonal variations. The global variability of the LWRE and more local processes, such as stratospheric intrusions, are analyzed, considering also the impacts of surface temperature and humidity changes. Finally we present preliminary results of the comparison between IASI and TES/Aura. We show that IASI LWRE measurements continue and extend those of TES and that together they represent a robust dataset to benchmark future chemistry-climate model assessments, such as the Chemistry-Climate Model Initiative (CCMI).