The Far-Infrared Outgoing Radiation and Monitoring (FORUM) mission will provide an unprecedented opportunity to verify and potentially improve the ability of global circulation models (GCM) in simulating the Outgoing Longwave Radiation (OLR). Accurate simulation of the OLR is in fact crucial to better constrain the different radiative feedbacks. Planned for launch in 2027, FORUM will measure spectrally resolved radiances of the Earth's emission spectrum at the top of the atmosphere (TOA) from 100 to 1600 cm-1 filling the existing observational gap of the far-infrared region, from 100 to 667 cm-1. In addition, FORUM will fly in loose formation with IASI-NG, which will continue to cover the middle infrared range of IASI from 675 to 2760 cm-1. In anticipation of FORUM measurements, we aim at comparing IASI existing observations to synthetic radiances extracted from the EC-Earth GCM (version 3.3.2), a recent European model 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 (1). Tuning operations linked to the sub-grid physical parametrization in climate models guarantee a very good global agreement between simulated and observed (CERES - EBAF 4.1) OLR broadband fluxes, but the study limited to the energy fluxes integrated over the whole Earth emission spectrum makes difficult the detection of biases and the identification of potential spectral compensation errors in climate models. Conversely, comparing simulated to observed spectra, allows to point out the potential model criticalities in given spectral bands which contain the signatures of specific climate variables. In order to extract simulated spectra from the climate model, EC-Earth has been used along with the Cloud Feedback Model Intercomparison Project (COSP), a simulator package able to map the model state into synthetic observations from different satellite-borne active (CloudSat (radar) and CALIPSO (lidar)) and passive (ISCCP, MISR and MODIS) (2) sensors. We have further developed the package by implementing inside COSP the radiative transfer model ?-FORUM, a monochromatic code able to reproduce synthetic radiances in the Far-Infrared and Mid-Infrared regions compatible with future FORUM and existing IASI observations (3). Due to the high computation cost of the operation, the efficiency of the EC-Earth model equipped with the new COSP module has been improved by modifying the ?-FORUM original code structure and by reducing the original resolution of the model. Therefore, on-line simulations provided by EC-Earth equipped with the new COSP + ?-FORUM module have been performed in clear-sky conditions with prescribed sea surface temperature and sea-ice cover every 6 hours, over a timeframe consistent with the availability of IASI data. Meanwhile, the IASI clear-sky radiance climatology has been built starting from the METOP-A L1C data provided by EUMETSAT through the European Weather Cloud (EWC) infrastructure. Systematic comparison between observational data and model outputs have been performed over spectral bands of 10 cm-1 on a global and regional scale by distinguishing the types of surface (land, sea) of the emitted radiances in order to address the existing biases in different spectral bands to specific climate variables. The long term analysis shows a warm bias of the climate model in the CO2 absorption band, which represents a strong evidence of model bias in the upper-troposphere and stratosphere. Moreover, a warm bias in the roto-vibrational water vapour bands and a cold bias in the atmospheric window over land occur in the model suggesting the existence of spectral compensation errors in the computation of the broadband flux. The comparison between nadir radiances simulated by the EC-Earth climate model and the climatology built from ten years of IASI observations represents a very high confidence test for the direct verification and improvement of the GCM. The same approach could be extended to other climate models and, in the near future, it will involve FORUM measurements for a comprehensive analysis of the climate model ability in reproducing the whole Earth emission spectrum. References 1. Hazeleger, Wilco, et al. "EC-Earth: a seamless earth-system prediction approach in action." Bulletin of the American Meteorological Society 91.10 (2010): 1357-1364. 2. Bodas-Salcedo, Alejandro, et al. "COSP: Satellite simulation software for model assessment." Bulletin of the American Meteorological Society 92.8 (2011): 1023-1043. 3. Amato, Umberto, et al. "Corrigendum to: "The sigma-IASI code for the calculation of infrared atmospheric radiance and its derivatives" [Environmental Modelling & Software (2002) 17 (7) 651-667]." Environmental Modelling and Software 18.1 (2003): 97
A FORUM simulator in the EC-EARTH climate model: implementation and verification against IASI measurements
Stefano Della Fera;Piera Raspollini;Flavio Barbara;Marco Ridolfi;Federico Fabiano;
2022
Abstract
The Far-Infrared Outgoing Radiation and Monitoring (FORUM) mission will provide an unprecedented opportunity to verify and potentially improve the ability of global circulation models (GCM) in simulating the Outgoing Longwave Radiation (OLR). Accurate simulation of the OLR is in fact crucial to better constrain the different radiative feedbacks. Planned for launch in 2027, FORUM will measure spectrally resolved radiances of the Earth's emission spectrum at the top of the atmosphere (TOA) from 100 to 1600 cm-1 filling the existing observational gap of the far-infrared region, from 100 to 667 cm-1. In addition, FORUM will fly in loose formation with IASI-NG, which will continue to cover the middle infrared range of IASI from 675 to 2760 cm-1. In anticipation of FORUM measurements, we aim at comparing IASI existing observations to synthetic radiances extracted from the EC-Earth GCM (version 3.3.2), a recent European model 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 (1). Tuning operations linked to the sub-grid physical parametrization in climate models guarantee a very good global agreement between simulated and observed (CERES - EBAF 4.1) OLR broadband fluxes, but the study limited to the energy fluxes integrated over the whole Earth emission spectrum makes difficult the detection of biases and the identification of potential spectral compensation errors in climate models. Conversely, comparing simulated to observed spectra, allows to point out the potential model criticalities in given spectral bands which contain the signatures of specific climate variables. In order to extract simulated spectra from the climate model, EC-Earth has been used along with the Cloud Feedback Model Intercomparison Project (COSP), a simulator package able to map the model state into synthetic observations from different satellite-borne active (CloudSat (radar) and CALIPSO (lidar)) and passive (ISCCP, MISR and MODIS) (2) sensors. We have further developed the package by implementing inside COSP the radiative transfer model ?-FORUM, a monochromatic code able to reproduce synthetic radiances in the Far-Infrared and Mid-Infrared regions compatible with future FORUM and existing IASI observations (3). Due to the high computation cost of the operation, the efficiency of the EC-Earth model equipped with the new COSP module has been improved by modifying the ?-FORUM original code structure and by reducing the original resolution of the model. Therefore, on-line simulations provided by EC-Earth equipped with the new COSP + ?-FORUM module have been performed in clear-sky conditions with prescribed sea surface temperature and sea-ice cover every 6 hours, over a timeframe consistent with the availability of IASI data. Meanwhile, the IASI clear-sky radiance climatology has been built starting from the METOP-A L1C data provided by EUMETSAT through the European Weather Cloud (EWC) infrastructure. Systematic comparison between observational data and model outputs have been performed over spectral bands of 10 cm-1 on a global and regional scale by distinguishing the types of surface (land, sea) of the emitted radiances in order to address the existing biases in different spectral bands to specific climate variables. The long term analysis shows a warm bias of the climate model in the CO2 absorption band, which represents a strong evidence of model bias in the upper-troposphere and stratosphere. Moreover, a warm bias in the roto-vibrational water vapour bands and a cold bias in the atmospheric window over land occur in the model suggesting the existence of spectral compensation errors in the computation of the broadband flux. The comparison between nadir radiances simulated by the EC-Earth climate model and the climatology built from ten years of IASI observations represents a very high confidence test for the direct verification and improvement of the GCM. The same approach could be extended to other climate models and, in the near future, it will involve FORUM measurements for a comprehensive analysis of the climate model ability in reproducing the whole Earth emission spectrum. References 1. Hazeleger, Wilco, et al. "EC-Earth: a seamless earth-system prediction approach in action." Bulletin of the American Meteorological Society 91.10 (2010): 1357-1364. 2. Bodas-Salcedo, Alejandro, et al. "COSP: Satellite simulation software for model assessment." Bulletin of the American Meteorological Society 92.8 (2011): 1023-1043. 3. Amato, Umberto, et al. "Corrigendum to: "The sigma-IASI code for the calculation of infrared atmospheric radiance and its derivatives" [Environmental Modelling & Software (2002) 17 (7) 651-667]." Environmental Modelling and Software 18.1 (2003): 97I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
