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Spatially resolved evaluation of Earth system models with satellite column averaged CO2

Gier, Bettina and Buchwitz, Michael and Reuter, Maximilian and Cox, Peter and Friedlingstein, Pierre and Eyring, Veronika (2020) Spatially resolved evaluation of Earth system models with satellite column averaged CO2. Biogeosciences. Copernicus Publications. doi: 10.5194/bg-2020-170. ISSN 1726-4170.

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Official URL: https://bg.copernicus.org/preprints/bg-2020-170/

Abstract

Earth System Models (ESMs) participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) showed large uncertainties in simulating atmospheric CO2 concentrations. By comparing the simulations with satellite observations, in this study we find slight improvements in the ESMs participating in the new Phase 6 (CMIP6) compared to CMIP5. We utilize the Earth System Model Evaluation Tool (ESMValTool) to evaluate emission driven CMIP5 and CMIP6 simulations with satellite data of column-average CO2 mole fractions (XCO2). The satellite data are a combined data product covering the period 2003­-2014 based on the SCIAMACHY/ENVISAT (2003-2012) and TANSO-FTS/GOSAT (2009-2014) instruments. In this study the Observations for Model Intercomparisons Project (Obs4MIPs) format data product version 3 (O4Mv3) with a spatial resolution of 5° × 5° and monthly time resolution has been used. Comparisons of XCO2 time series show a large spread among the model ensembles both in CMIP5 and CMIP6, with differences in the absolute concentrations of up to approximately 20 ppmv relative to the satellite observations. The multi-model mean has a bias of approximately +10 and +2 ppmv in CMIP5 and CMIP6, respectively. The derived atmospheric XCO2 growth rate (GR) is typically slightly overestimated in the models, with a slightly better average and lower spread for CMIP6. The interannual variability of the growth rate is well reproduced in the multi-model mean. All models capture the expected increase of the seasonal cycle amplitude (SCA) with increasing latitude, but most models underestimate the SCA. Most models from both ensembles show a positive trend of the SCA over the period 2003-2014, i.e. an increase of the SCA with XCO2, similar to in situ ground-based measurements. In contrast, the combined satellite product shows a negative trend over this period. Any SCA derived from sampled data can only be considered an "effective" SCA, as sampling can remove the peaks or troughs. This negative trend can be reproduced by the models when sampling them as the observations. The average effective SCA in the models is higher when using the SCIAMACHY/ENVISAT instead of the TANSO-FTS/GOSAT mean data coverage mask, overall leading to a negative trend over the full period similar to the combined satellite product. Models with a larger difference in the average effective SCA between the two coverages also show a stronger trend reversal. Therefore, this trend reversal in the satellite data is due to sampling characteristics, more specifically the different data coverage of the two satellites that can be reproduced by the models if sampled the same way. Overall, the CMIP6 ensemble shows better agreement with the satellite data in all considered quantities (XCO2, GR, SCA and trend in SCA), with the biggest improvement in the mean XCO2 content of the atmosphere. This study shows that the availability of column-integral CO2 from satellite provides a promising new way to evaluate the performance of Earth System Models on a global scale, complementing existing studies that are based on in situ measurements from single ground-based stations.

Item URL in elib:https://elib.dlr.de/137612/
Document Type:Article
Title:Spatially resolved evaluation of Earth system models with satellite column averaged CO2
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Gier, BettinaUniv. Bremen und DLR, IPAUNSPECIFIED
Buchwitz, MichaelUniversity of BremenUNSPECIFIED
Reuter, MaximilianUniv. BremenUNSPECIFIED
Cox, PeterUniversity of Exeter, UKUNSPECIFIED
Friedlingstein, PierreCollege of Engineering, Mathematics and Physical Sciences, University of Exeter, Devon, UKUNSPECIFIED
Eyring, VeronikaDLR, IPAhttps://orcid.org/0000-0002-6887-4885
Date:June 2020
Journal or Publication Title:Biogeosciences
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In SCOPUS:Yes
In ISI Web of Science:Yes
DOI :10.5194/bg-2020-170
Publisher:Copernicus Publications
ISSN:1726-4170
Status:Published
Keywords:Earth system models, ESMs, C02, satellite, ESMValTool, CMIP
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Atmospheric and climate research
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Earth System Model Evaluation and Analysis
Deposited By: Langer, Michaela
Deposited On:17 Nov 2020 11:46
Last Modified:08 Dec 2020 12:50

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