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Published June 4, 2019 | Published + Supplemental Material
Journal Article Open

Modelling CO_2 weather – why horizontal resolution matters


Climate change mitigation efforts require information on the current greenhouse gas atmospheric concentrations and their sources and sinks. Carbon dioxide (CO_2) is the most abundant anthropogenic greenhouse gas. Its variability in the atmosphere is modulated by the synergy between weather and CO_2 surface fluxes, often referred to as CO_2 weather. It is interpreted with the help of global or regional numerical transport models, with horizontal resolutions ranging from a few hundreds of kilometres to a few kilometres. Changes in the model horizontal resolution affect not only atmospheric transport but also the representation of topography and surface CO_2 fluxes. This paper assesses the impact of horizontal resolution on the simulated atmospheric CO_2 variability with a numerical weather prediction model. The simulations are performed using the Copernicus Atmosphere Monitoring Service (CAMS) CO_2 forecasting system at different resolutions from 9 to 80 km and are evaluated using in situ atmospheric surface measurements and atmospheric column-mean observations of CO_2, as well as radiosonde and SYNOP observations of the winds. The results indicate that both diurnal and day-to-day variability of atmospheric CO_2 are generally better represented at high resolution, as shown by a reduction in the errors in simulated wind and CO_2. Mountain stations display the largest improvements at high resolution as they directly benefit from the more realistic orography. In addition, the CO_2 spatial gradients are generally improved with increasing resolution for both stations near the surface and those observing the total column, as the overall inter-station error is also reduced in magnitude. However, close to emission hotspots, the high resolution can also lead to a deterioration of the simulation skill, highlighting uncertainties in the high-resolution fluxes that are more diffuse at lower resolutions. We conclude that increasing horizontal resolution matters for modelling CO_2 weather because it has the potential to bring together improvements in the surface representation of both winds and CO_2 fluxes, as well as an expected reduction in numerical errors of transport. Modelling applications like atmospheric inversion systems to estimate surface fluxes will only be able to benefit fully from upgrades in horizontal resolution if the topography, winds and prior flux distribution are also upgraded accordingly. It is clear from the results that an additional increase in resolution might reduce errors even further. However, the horizontal resolution sensitivity tests indicate that the change in the CO2 and wind modelling error with resolution is not linear, making it difficult to quantify the improvement beyond the tested resolutions. Finally, we show that the high-resolution simulations are useful for the assessment of the small-scale variability of CO_2 which cannot be represented in coarser-resolution models. These representativeness errors need to be considered when assimilating in situ data and high-resolution satellite data such as Greenhouse gases Observing Satellite (GOSAT), Orbiting Carbon Observatory-2 (OCO-2), the Chinese Carbon Dioxide Observation Satellite Mission (TanSat) and future missions such as the Geostationary Carbon Observatory (GeoCarb) and the Sentinel satellite constellation for CO_2. For these reasons, the high-resolution CO_2 simulations provided by the CAMS in real time can be useful to estimate such small-scale variability in real time, as well as providing boundary conditions for regional modelling studies and supporting field experiments.

Additional Information

© Author(s) 2019. This work is distributed under the Creative Commons Attribution 4.0 License. Received: 20 Feb 2019 – Discussion started: 27 Feb 2019 – Revised: 07 May 2019 – Accepted: 08 May 2019 – Published: 04 Jun 2019. This research was generated using Copernicus Atmosphere Monitoring Service (2018) information. Anna Agustí-Panareda has been partly funded by the CHE project. The CHE project has received funding from the European Union's Horizon 2020 Research and Innovation programme under grant agreement no. 776186. Frédéric Chevallier received funding from the Copernicus Atmosphere Monitoring Service, implemented by the European Centre for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Commission. Thanks are given to all the station principal investigators from the numerous individual stations and networks like NOAA, ICOS, AEMET, AGH, CSIRO, ECCC, ECN, EMPA, FMI, HMS, LSCE, NCAR, JMA, MPI-BGC, NIWA, SAWS, TU, UBA-SCHAU, UEA, UHEI-IUP, UR, UBremen-IUP, BIRA-IASB, Caltech, KIT, NASA, JAXA, NIES and UOW that contributed their CO_2 observations to the cooperative GLOBALVIEWplus (ObsPack , 2015) product and TCCON which are fundamental for the evaluation of the model simulations. The ClimaDat Network has received funding from the "la Caixa" Foundation, under agreement 2010-002624. We are grateful to many colleagues at ECMWF for their support and fruitful discussions, particularly to Gabor Radnoti, Thomas Haiden and Martin Janouseck for their technical support in the evaluation of the winds; Miha Razinger for his technical support in the production of Fig. 1; Johannes Flemming and Zak Kipling for their support in the implementation of the additional CO_2 tracers in the IFS model; Sylvie Malardel for her support and discussions on the general aspects of atmospheric tracer modelling in the IFS; and Gianpaolo Balsamo, Souhail Boussetta, Zak Kipling and Johannes Flemming for their technical support in the implementation of a bug fix in the CTESSEL model of biogenic emissions. Many thanks are given to Paul Wennberg (Caltech) for his advice on the use of the TCCON data; Martin Krol (Wageningen University) for his suggestions on the evaluation of the daily maximum CO_2; and Britton Stephens (NCAR) for his comments on the mountain site evaluation which helped improve the description of the vertical sampling strategy and emphasise the importance of high resolution at mountain sites. This research has been supported by the Copernicus Atmospheric Monitoring Service and by the European Commission (CHE project, grant no. 776186). Author contributions. The simulations were performed by AAP. The coding of the mass fixer required for the high-resolution transport in the IFS was done by MD. The concept and ideas to design the high-resolution simulations were devised by FC, AAP, MD, SM and JMS in discussion with RE and VHP. RML, ZL, JAM and RC provided additional observations at crucial sites and guidance on the evaluation of the simulations. CR and DW provided data and input on the interpretation of the model evaluation at the TCCON site of Pasadena. The CO2 validation tools have been developed by SM and AAP. The paper was prepared by AAP with input and feedback from MD, SM, FC, JMS, JB, RE, BL, RML, ZL, JAM, MP, VHP, MR, CR, ATV, TW Data availability. The data are accessible by contacting the corresponding author (anna.agusti-panareda@ecmwf.int). The supplement related to this article is available online at: https://doi.org/10.5194/acp-19-7347-2019-supplement. The authors declare that they have no conflict of interest. Review statement. This paper was edited by Christoph Gerbig and reviewed by two anonymous referees.

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August 19, 2023
August 19, 2023