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Séminaire LATMOS-Jussieu, salle 411, Mardi 10 juin 2014, 11H

Orateur: Helen Worden (NCAR)

Using TES and IASI satellite observations to test climate model predictions of ozone radiative forcing hydrological cycle on ozone RF.

Recent international assessments have demonstrated the co-benefits of controlling tropospheric ozone for both near-term climate change and air quality. However, strategies for targeting ozone precursor emissions require accurate model predictions of ozone radiative forcing (RF). Tropospheric ozone has the third highest RF for anthropogenic greenhouse gases since pre-industrial times, but high uncertainties and a large spread in model values remain in the IPCC AR5. We will show how TES observations of ozone and the sensitivity of TOA (Top Of Atmosphere) radiative flux to ozone have been used to reduce the uncertainty in the mean estimate of tropospheric ozone RF from the ACCMIP (Atmospheric Chemistry and Climate Model Intercomparison Project) reported in the IPCC AR5. We also present the results of combining TES TOA flux sensitivity and the GEOS-chem adjoint to determine the radiative effect of ozone precursor emissions NOx, CO and NMHC (non-methane hydrocarbons). This study showed a large spatial dependence for radiative forcing from ozone as a function of where the precursors were emitted. For example, NOx emissions from Chicago have to be more than 3 times larger than Atlanta emissions to have the same forcing. These previous TES results provide motivation for new work to benchmark the model-to-satellite differences in TOA ozone band flux and flux sensitivity. The TOA flux for the infrared ozone band is a fundamental quantity which is predicted by IPCC chemistry-climate models but never tested directly against satellite measurements. The continuation of the TES record of infrared ozone spectra with long-term IASI data will allow accurate predictions of future ozone forcing and an assessment of the feedback from changes in the hydrological cycle on ozone RF.