The Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission will provide a significant opportunity to verify and potentially improve the ability of global circulation models (GCMs) 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 2026, FORUM will measure nadir-looking, 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 (FIR) 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). Climate model outputs only provide simulated energy fluxes integrated over the whole Earth emission spectrum making difficult the detection of biases and the identification of possible compensation errors in the estimation of the OLR. Conversely, comparing simulated to observed spectra, allows to point out the potential model criticalities in specific spectral bands which contain the signatures of particular climate variables. In order to extract simulated spectra from the climate model, EC-Earth has been equipped with 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, simulations provided by EC-Earth model equipped with the new COSP + ?-FORUM module have been performed with prescribed sea surface temperature and sea-ice cover every 6 hours, over a timeframe consistent with the availability of IASI METOP-A L1C data, from 2007 to 2016. 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 avoiding potential uncertainties related to application of retrieval methods. 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;Ugo Cortesi;Federico Fabiano;Piera Raspollini;Marco Ridolfi;
2021
Abstract
The Far-Infrared Outgoing Radiation Understanding and Monitoring (FORUM) mission will provide a significant opportunity to verify and potentially improve the ability of global circulation models (GCMs) 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 2026, FORUM will measure nadir-looking, 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 (FIR) 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). Climate model outputs only provide simulated energy fluxes integrated over the whole Earth emission spectrum making difficult the detection of biases and the identification of possible compensation errors in the estimation of the OLR. Conversely, comparing simulated to observed spectra, allows to point out the potential model criticalities in specific spectral bands which contain the signatures of particular climate variables. In order to extract simulated spectra from the climate model, EC-Earth has been equipped with 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, simulations provided by EC-Earth model equipped with the new COSP + ?-FORUM module have been performed with prescribed sea surface temperature and sea-ice cover every 6 hours, over a timeframe consistent with the availability of IASI METOP-A L1C data, from 2007 to 2016. 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 avoiding potential uncertainties related to application of retrieval methods. 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.
