ENSO driven inter-annual variability of the OLR from satellite observations

Feedback mechanisms are an important component of the climate system radiative response to surface and atmospheric processes that shape the Earth’s climate. However, global climate models still show a consistent spread in feedback estimates, which affects the reliability of their future climate projections. A possible way ahead is represented by satellites observations of the top-of-atmosphere radiative budget to both improve our knowledge of feedback mechanisms and evaluate climate models simulations. Here, we focus on the Outgoing Longwave Radiation (OLR), the energy released by Earth’s climate system to achieve the thermal equilibrium, and its inter-annual variability driven by El-Niño Southern Oscillations (ENSO), the most important variability mode of the climate system on this time scale. An assessment of the OLR response to ENSO-driven variability is first performed on a subset of atmosphere-only and coupled historical simulations of climate models participating to the Coupled Model Intercomparison Project phase 6 (CMIP6) project through the comparison against broadband OLR satellites observations of the CERES instrument. The second part of the work exploits the use of spectral OLR satellite observations to deeper investigate the physical processes beyond the radiative response to ENSO and unravel possible climate models biases masked by error compensation associated to different spectral regions. We also relied on spectral radiative kernels to separately evaluate the radiative response associated to the Planck surface and atmospheric, water vapor and ozone feedback. In this work, we show the main feedback mechanisms behind the longwave radiative response to ENSO, from a spectral point of view, and use this information to improve our understanding of climate models biases in reproducing this relationship.