Earth's emitted energy in the wavelength range 4 ?m-100 ?m is commonly termed Outgoing Longwave radiation (OLR) and its accurate measurement is a first-priority requirement to assess the energy balance of the planet. Integrated broadband OLR fluxes provided by CERES energy balanced and filled (EBAF) dataset constitutes the standard reference to study the Earth's energy budget and consequently represents the target values of energy fluxes at top of atmosphere (TOA) for climate models tuning. Even if tuning operations guarantee a good agreement on a global basis between observed and simulated OLR at TOA, large regional biases are present all over the globe and a significant spread exists between different climate model simulations. The Far-Infrared Outgoing Radiation and Monitoring (FORUM) mission, planned for launch in 2026, will provide nadir-looking spectrally resolved radiance measurements of the Earth's emission spectrum at TOA from 100 to 1600 cm-1 (6.25 ?m-100 ?m) with a resolution better than 0.50 cm-1. For the first time FORUM measurements will fill the existing observational gap in the far-infrared (FIR) radiation range from 100 to 667 cm-1 (15 ?m-100 ?m) also providing spectrally resolved OLR fluxes (level 2 data product). In anticipation of FORUM measurements, we want to quantify the potential improvement of climate models in simulating OLR fluxes at TOA due to the future availability of spectrally resolved fluxes data from FORUM, extending to the Far InfraRed. At this stage, we focus on the analyses of simulations provided by EC-Earth (version 3.3.2), a new climate model developed by the joint effort of 27 research institutes of 10 European countries which has directly contributed to Coupled Model Intercomparison (CMIP) in its phases 5 and 6. The EC-Earth model is based on ECMWF's Integrated Forecasting System (IFS) for the atmosphere-land component and the ocean model NEMO, including sea ice (LIM2) and land surface components. Atmospheric profiles and information on the surface and on the clouds produced by EC-Earth simulations in realistic but simplified conditions are provided in input to SIGMA-IASI, a radiative transfer model able to calculate spectral radiances compatible with those that will be measured by FORUM. From these synthetic measurements, we estimate OLR fluxes by applying angular distribution models (ADM) of increasing complexity. The comparison between the OLR fluxes provided by the EC-Earth simulation and those calculated from synthetic FORUM measurements may allow to identify potential improvements for the parametric radiative module included in EC-Earth to estimate the OLR radiative fluxes.
The potential contribution of FORUM mission to the evaluation and improvement of OLR fluxes estimation in EC-Earth climate model
Stefano Della Fera;Ugo Cortesi;Federico Fabiano;Piera Raspollini;Marco Ridolfi;
2020
Abstract
Earth's emitted energy in the wavelength range 4 ?m-100 ?m is commonly termed Outgoing Longwave radiation (OLR) and its accurate measurement is a first-priority requirement to assess the energy balance of the planet. Integrated broadband OLR fluxes provided by CERES energy balanced and filled (EBAF) dataset constitutes the standard reference to study the Earth's energy budget and consequently represents the target values of energy fluxes at top of atmosphere (TOA) for climate models tuning. Even if tuning operations guarantee a good agreement on a global basis between observed and simulated OLR at TOA, large regional biases are present all over the globe and a significant spread exists between different climate model simulations. The Far-Infrared Outgoing Radiation and Monitoring (FORUM) mission, planned for launch in 2026, will provide nadir-looking spectrally resolved radiance measurements of the Earth's emission spectrum at TOA from 100 to 1600 cm-1 (6.25 ?m-100 ?m) with a resolution better than 0.50 cm-1. For the first time FORUM measurements will fill the existing observational gap in the far-infrared (FIR) radiation range from 100 to 667 cm-1 (15 ?m-100 ?m) also providing spectrally resolved OLR fluxes (level 2 data product). In anticipation of FORUM measurements, we want to quantify the potential improvement of climate models in simulating OLR fluxes at TOA due to the future availability of spectrally resolved fluxes data from FORUM, extending to the Far InfraRed. At this stage, we focus on the analyses of simulations provided by EC-Earth (version 3.3.2), a new climate model developed by the joint effort of 27 research institutes of 10 European countries which has directly contributed to Coupled Model Intercomparison (CMIP) in its phases 5 and 6. The EC-Earth model is based on ECMWF's Integrated Forecasting System (IFS) for the atmosphere-land component and the ocean model NEMO, including sea ice (LIM2) and land surface components. Atmospheric profiles and information on the surface and on the clouds produced by EC-Earth simulations in realistic but simplified conditions are provided in input to SIGMA-IASI, a radiative transfer model able to calculate spectral radiances compatible with those that will be measured by FORUM. From these synthetic measurements, we estimate OLR fluxes by applying angular distribution models (ADM) of increasing complexity. The comparison between the OLR fluxes provided by the EC-Earth simulation and those calculated from synthetic FORUM measurements may allow to identify potential improvements for the parametric radiative module included in EC-Earth to estimate the OLR radiative fluxes.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
