Benchmarking climate model top-of-atmosphere radiance in the 9.6 micron ozone band compared to TES and IASI observations
Résumé
Tropospheric ozone has the third highest radiative forcing (RF) for anthropogenic greenhouse gases since pre-industrial times, but high uncertainties and a large spread in model values remain in the IPCC AR5. These uncertainties, along with recent studies comparing climate models and satellite observations of tropospheric ozone provide motivation to benchmark the model-to-satellite differences in TOA ozone band flux and flux sensitivity. The TOA flux for the 9.6 micron ozone band is a fundamental quantity which is predicted by IPCC chemistry-climate models but has never been tested directly against satellite measurements. We also compute the sensitivity of TOA (top of atmosphere) flux to the vertical distribution of ozone, or Instantaneous Radiative Kernel (IRK), for both the Aura-TES and MetOP-IASI instrument. The IRK explicitly accounts for more dominant radiative processes such as clouds and water vapor due to the spectrally resolved absorption features and allows attribution of changes in ozone RF to vertical changes in ozone and ozone precursor emissions. The continuation of the TES record of infrared ozone spectra, TOA flux and IRKs 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. Here we present initial comparisons of satellite observed TOA ozone band fluxes and IRKs with RRTMG (Rapid Radiative Transfer Model-GCM applications) in the NCAR CAM-chem chemistry/climate model and with the GISS radiative transfer model.