the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Jul 2021
An improved carbon greenhouse gas simulation in GEOS-Chem version 12.1.1
Abstract. Understanding greenhouse gas–climate processes and feedbacks is a fundamental step in understanding climate variability and its links to greenhouse gas fluxes. Chemical transport models are the primary tool for linking greenhouse gas fluxes to their atmospheric abundances. Hence accurate simulations of greenhouse gases are essential. Here, we present a new simulation in the GEOS-Chem chemical transport model that couples the two main greenhouse gases: carbon dioxide (CO2) and methane (CH4), along with the indirect effects of carbon monoxide (CO), based on their chemistry. Our updates include the online calculation of the chemical production of CO from CH4 and the online production of CO2 from CO, both of which were handled offline in the previous versions of these simulations. We discuss differences between the offline (uncoupled) and online (coupled) calculation of the chemical terms and perform a sensitivity simulation to identify the impact of OH on the results. We compare our results with surface measurements from the NOAA Global Greenhouse Gas Reference Network (NOAA GGGRN), total column measurements from the Total Carbon Column Observing Network (TCCON) and aircraft measurements from the Atmospheric Tomography Mission (ATom). Relative to the standard uncoupled simulation, our coupled results show better agreement with measurements. We use the remaining measurement-model differences to identify sources and sinks that are over or underestimated in the model. We find underestimated OH fields when calculating the CH4 loss and CO production from CH4. Biomass burning emissions and secondary production are underestimated for CO in the Southern Hemisphere and we find enhanced anthropogenic sources in the Northern Hemisphere. We also find significantly stronger chemical production of CO2 in tropical land regions, especially in the Amazon. The model-measurement differences also highlight biases in the calculation of CH4 in the stratosphere and in vertical mixing that impacts all three gases.
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RC1: 'Comment on gmd-2021-173', Anonymous Referee #1, 01 Sep 2021
A new greenhouse gas simulation in GEOS-Chem is presented, which couples CO2, CH4 and CO. The paper presents a detailed evaluation of the new system and compares the model simulations to observations.
It seems likely that this new framework will be useful for inverse modelling studies in the future. The analysis is very thorough, although perhaps some aspects could be cut or moved to the Supplement to help streamline the text (which is quite long). However, I have some concerns about the experiment design and interpretation. I feel that the paper would suitable for publication in GMD after these concerns have been addressed.
General comments
Experiment design: The novel component of the paper is the description of the coupled CO2-CO-CH4 system. However, I found the discussion of the comparisons of the coupled and uncoupled systems very hard to follow in places. I think this is primarily because the various simulations were run with different OH fields and model resolutions (and with/without an OH diurnal cycle, although this doesn’t appear to have much impact). To partially address this, an additional OH run is carried out to test the sensitivity to OH, introducing another model into the mix. It seems that the reason for these inconsistencies is historical, although I wasn’t entirely sure from the text. It seems to me that this paper could be dramatically improved, streamlined and clarified by carrying out two sets of model runs, using the same OH field, the same resolution, one run coupled and one uncoupled. Given that it’s relatively cheap to run these simulations, I’m not sure why this wasn’t done. Can the authors explain? If it’s to maintain traceability back to earlier GEOS-Chem simulations, I’d argue that this should be a secondary consideration, compared to showing the improvement due to the new simulation setup.
Comparison to observations: The conclusions state that the new model improves the fit to the observations (L488 – 490). However, I don’t think that this can be concluded. Since we do not know the “true” flux magnitude for these gases, we can’t be sure that the coupled simulations are really improving the fit to the data, or just compensating for some bias(es) in the flux fields. For example, for methane, it is stated (L446) “The coupled-origOH results show a positive bias with overestimated CH4 values for all sites; however, using globally more abundant OH fields (v9-01-03) in the coupled simulation resolve this large bias”. However, it could well be that the new fields are simply compensating for some bias in the (highly uncertain) emission field.
Specific comments:
L107 (Eq. 2): I don’t think this equation works. For closure, I think there also needs to be a term representing the net flux from/to the troposphere.
L113: [OH] has already been defined.
L129 (Eq. 7): Again, need flux to/from the troposphere.
Figure 3: Is this figure relevant?
L226 – 227: Some of this inter-annual variability is present in the uncoupled simulation. Is the change really so marked in the coupled version?
L231 and Figure 5 caption: The figure shows the CO production, not the “Changes of the CO production”. The change can be inferred from the figure, but is not directly shown.
Figure 4: Add an x-axis. Also, it’s not clear why a bar chart is the best way to present this. How about a line graph?
L244: “Hemispheric” seems preferable to “regional” to describe the table.
Figure 7: Perhaps move this, and the discussion, to the Supplement. I’m not sure it adds too much.
L340: I think a comma would be preferable to a semi-colon between “seasons” and “but”.
L431: The offset in the modelled values will lead to a small difference in the CO production, etc., compared to the real atmosphere (i.e. CO production from CH4 will be over-estimated, since the model spin up leads to higher CH4). Is this effect important?
L449: “resolves”, rather than “resolve” (although, see general comment… I don’t agree with this statement!)
L464 / 465: Notwithstanding the issues around flux magnitudes, these differences seem very small compared to all the other uncertainties in the system. I think it’d also be fair to say that the model changes had a negligible impact on the comparison with the observations here.
L488 – 491: I think these lines in particular (and many others throughout) need to be revised in light of my general comment regarding the potential impact of uncertain fluxes.
L593: I don’t think you can say that the v5-07-08 fields are incorrect based on this analysis, given the emissions uncertainty.
L607 – 609: As above, I think this conclusion needs to be removed.
Appendix A: Titled as “Appendix A: Appendix A”
Citation: https://doi.org/10.5194/gmd-2021-173-RC1 - AC1: 'Reply on RC1', Beata Bukosa, 22 Oct 2021
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RC2: 'Comment on gmd-2021-173', Anonymous Referee #2, 08 Sep 2021
Review of "An improved carbon greenhouse gas simulation in GEOS-Chem version 12.1.1" by Beata Bukosa et al.
This paper simulated CO2, and CO2 production by oxidation of CH4 and CO using 3 different types of OH fields. The topic of research is important for better estimation of CO2 sources and sinks on the Earth's surface. The distribution of OH is heavily concentrated over the tropical region, where CO2 would be added to the atmospheric CO2 due to oxidation of CO and CH4. If ignored this CO2 chemical production, biased source of CO2 is needed from the tropical land and ocean regions by inverse modelling. I very much liked the idea of this research, but unfortunately wasn't able to read through the whole manuscript due to poor execution of the research idea, in my opinion. Thus I cannot recommend publication of this work in Geoscientific Model Development in the present form or anything close to this. It is better to rerun the model and submit a newly prepared manuscript.
Here are some of my major concerns:
Table 1: For eaxmple, "Coupled only" : I do not understand - are all CO are produced from CH4 oxidation ? If so you are going to underestimate CO. If not, is CO in L(CO) and P(CO)ch4 are different entities, then there is a good chance of double counting
Formulation of Eq. 1 & 2 (also for CO): Not correct !!, I think Eq. 1 and Eq. 2 are not separable in a chemistry-transport model, except for “tagging”. Please clarify or rectify errors
Figure 2: Quite large differences in OH. Acceptable? May be you should run CH3CCl3 tracer of checking your OH.
Figure 5 (left column): the P(CO)ch4 and P(CO2) are apparently not consistent with the OH fields in Figure 2.
This where I had to stop going forward or read the text carefully. I am extremely sorry, but this has to be solved first before interpreting the results.
You have about 20% higher OH for the red and purple lines, compared to blue, both at the surface and at 500 mb when averaged over a year (Fig. 2).
But here in Fig. 5, we find the blue line is close to purple than the red line for P(CO2), and also I cannot explain the relative values of P(CO)ch4 as expected from the OH fields.
I understand that the OH level is affecting the concentrations of CO and CH4 and then you get very mixed pictures for P(CO) or P(CO2). But these are not realistic, because we only have one state of CO and CH4 concentration distributions (strictly).
If you are checking the effect of OH then design experiments accordingly, and so on. Please consider.Citation: https://doi.org/10.5194/gmd-2021-173-RC2 - AC2: 'Reply on RC2', Beata Bukosa, 22 Oct 2021
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RC3: 'Comment on gmd-2021-173', Anonymous Referee #3, 13 Sep 2021
Review of the manuscript: “An improved carbon greenhouse gas simulation in GEOS-Chem version 12.1.1” by B. Bukosa et al.
General Comments
The authors present coupled greenhouse gas simulations with GEOS-Chem focusing on CO2/CH4/CO and its global chemical interactions. Such simulations will be definitively needed towards a consistent description of long-term atmospheric chemistry and for realistic assessment of climatic change by earth system models. I fully acknowledge the work done here and I am convinced that the new developments implemented in GEOS-Chem are a big step towards these goals. When reading the abstract, I got the impression that the paper follows a clear outline by first comparing coupled and uncoupled simulations and then evaluate the new model version with observational data. The authors present a sound and informative introduction to the scientific and computational problem of consistent chemistry simulations, which comprise processes representing a broad range of timescales as well as trends and interannual variability. I also liked the detailed budget term quantification as presented in Table 2. Unfortunately, I got lost after different versions of the OH input fields were introduced. For me it remained unclear why the authors are not able to stick to a single OH field which then can be used for both, the uncoupled and the coupled simulations. In the discussion part of the manuscript, the introduction of a third simulation (coupled-origOH) lead to unnecessary confusion and an overload with information details which made it hard for me to extract the major conclusions. Overall, I would not recommend to publish the paper in its current form but I encourage the authors to submit a revised manuscript based on more consistent coupled and uncoupled simulations.
Specific Comments
Line 49: What do you mean by “outside source regions”?
Lines 49-56: For CO budget terms you can also refer to Stein et al. (2014).
Line 51: Publication year is missing.
Lines 52-54: It would be interesting to see also the numbers for the chemical production by NMVOCs (used as input for your simulations).
Lines 60-63: Can you give a reference here?
Lines 82-84: Is the spin-up time sufficient? You doubt this later on (Lines 506-508).
Lines 96-97: I would expect that a single reference full chemistry simulation is used for all simulations presented here.
Line 134: How does GEOS-Chem handle Biomass burning emissions? It is known that such emissions need to be emitted throughout the troposphere following a vertical profile.
Line 295: Exchange “tropospheric column” by “mid troposphere”.
Lines 348-349: I would expect to have the same P(NMVOC) for all model runs. Give numbers!
Table 1: Publication year is missing.
Figure 1: I like this figure. It could even improve if you orient your coupled and uncoupled flows from left to right.
Figure 4: From your description I would expect that P(CO)CH4 (for all years) and P(CO2) (for 2010-2017) remains exactly constant for the uncoupled runs (except for leap years).
Figure 7(b): This reads like “Surface Loss” as parameter.
References:
Stein, O., Schultz, M. G., Bouarar, I., Clark, H., Huijnen, V., Gaudel, A., George, M., and Clerbaux, C.: On the wintertime low bias of Northern Hemisphere carbon monoxide found in global model simulations, Atmos. Chem. Phys., 14, 9295-9316, doi:10.5194/acp-14-9295-2014, 2014.
Citation: https://doi.org/10.5194/gmd-2021-173-RC3 - AC3: 'Reply on RC3', Beata Bukosa, 22 Oct 2021
Status: closed
-
RC1: 'Comment on gmd-2021-173', Anonymous Referee #1, 01 Sep 2021
A new greenhouse gas simulation in GEOS-Chem is presented, which couples CO2, CH4 and CO. The paper presents a detailed evaluation of the new system and compares the model simulations to observations.
It seems likely that this new framework will be useful for inverse modelling studies in the future. The analysis is very thorough, although perhaps some aspects could be cut or moved to the Supplement to help streamline the text (which is quite long). However, I have some concerns about the experiment design and interpretation. I feel that the paper would suitable for publication in GMD after these concerns have been addressed.
General comments
Experiment design: The novel component of the paper is the description of the coupled CO2-CO-CH4 system. However, I found the discussion of the comparisons of the coupled and uncoupled systems very hard to follow in places. I think this is primarily because the various simulations were run with different OH fields and model resolutions (and with/without an OH diurnal cycle, although this doesn’t appear to have much impact). To partially address this, an additional OH run is carried out to test the sensitivity to OH, introducing another model into the mix. It seems that the reason for these inconsistencies is historical, although I wasn’t entirely sure from the text. It seems to me that this paper could be dramatically improved, streamlined and clarified by carrying out two sets of model runs, using the same OH field, the same resolution, one run coupled and one uncoupled. Given that it’s relatively cheap to run these simulations, I’m not sure why this wasn’t done. Can the authors explain? If it’s to maintain traceability back to earlier GEOS-Chem simulations, I’d argue that this should be a secondary consideration, compared to showing the improvement due to the new simulation setup.
Comparison to observations: The conclusions state that the new model improves the fit to the observations (L488 – 490). However, I don’t think that this can be concluded. Since we do not know the “true” flux magnitude for these gases, we can’t be sure that the coupled simulations are really improving the fit to the data, or just compensating for some bias(es) in the flux fields. For example, for methane, it is stated (L446) “The coupled-origOH results show a positive bias with overestimated CH4 values for all sites; however, using globally more abundant OH fields (v9-01-03) in the coupled simulation resolve this large bias”. However, it could well be that the new fields are simply compensating for some bias in the (highly uncertain) emission field.
Specific comments:
L107 (Eq. 2): I don’t think this equation works. For closure, I think there also needs to be a term representing the net flux from/to the troposphere.
L113: [OH] has already been defined.
L129 (Eq. 7): Again, need flux to/from the troposphere.
Figure 3: Is this figure relevant?
L226 – 227: Some of this inter-annual variability is present in the uncoupled simulation. Is the change really so marked in the coupled version?
L231 and Figure 5 caption: The figure shows the CO production, not the “Changes of the CO production”. The change can be inferred from the figure, but is not directly shown.
Figure 4: Add an x-axis. Also, it’s not clear why a bar chart is the best way to present this. How about a line graph?
L244: “Hemispheric” seems preferable to “regional” to describe the table.
Figure 7: Perhaps move this, and the discussion, to the Supplement. I’m not sure it adds too much.
L340: I think a comma would be preferable to a semi-colon between “seasons” and “but”.
L431: The offset in the modelled values will lead to a small difference in the CO production, etc., compared to the real atmosphere (i.e. CO production from CH4 will be over-estimated, since the model spin up leads to higher CH4). Is this effect important?
L449: “resolves”, rather than “resolve” (although, see general comment… I don’t agree with this statement!)
L464 / 465: Notwithstanding the issues around flux magnitudes, these differences seem very small compared to all the other uncertainties in the system. I think it’d also be fair to say that the model changes had a negligible impact on the comparison with the observations here.
L488 – 491: I think these lines in particular (and many others throughout) need to be revised in light of my general comment regarding the potential impact of uncertain fluxes.
L593: I don’t think you can say that the v5-07-08 fields are incorrect based on this analysis, given the emissions uncertainty.
L607 – 609: As above, I think this conclusion needs to be removed.
Appendix A: Titled as “Appendix A: Appendix A”
Citation: https://doi.org/10.5194/gmd-2021-173-RC1 - AC1: 'Reply on RC1', Beata Bukosa, 22 Oct 2021
-
RC2: 'Comment on gmd-2021-173', Anonymous Referee #2, 08 Sep 2021
Review of "An improved carbon greenhouse gas simulation in GEOS-Chem version 12.1.1" by Beata Bukosa et al.
This paper simulated CO2, and CO2 production by oxidation of CH4 and CO using 3 different types of OH fields. The topic of research is important for better estimation of CO2 sources and sinks on the Earth's surface. The distribution of OH is heavily concentrated over the tropical region, where CO2 would be added to the atmospheric CO2 due to oxidation of CO and CH4. If ignored this CO2 chemical production, biased source of CO2 is needed from the tropical land and ocean regions by inverse modelling. I very much liked the idea of this research, but unfortunately wasn't able to read through the whole manuscript due to poor execution of the research idea, in my opinion. Thus I cannot recommend publication of this work in Geoscientific Model Development in the present form or anything close to this. It is better to rerun the model and submit a newly prepared manuscript.
Here are some of my major concerns:
Table 1: For eaxmple, "Coupled only" : I do not understand - are all CO are produced from CH4 oxidation ? If so you are going to underestimate CO. If not, is CO in L(CO) and P(CO)ch4 are different entities, then there is a good chance of double counting
Formulation of Eq. 1 & 2 (also for CO): Not correct !!, I think Eq. 1 and Eq. 2 are not separable in a chemistry-transport model, except for “tagging”. Please clarify or rectify errors
Figure 2: Quite large differences in OH. Acceptable? May be you should run CH3CCl3 tracer of checking your OH.
Figure 5 (left column): the P(CO)ch4 and P(CO2) are apparently not consistent with the OH fields in Figure 2.
This where I had to stop going forward or read the text carefully. I am extremely sorry, but this has to be solved first before interpreting the results.
You have about 20% higher OH for the red and purple lines, compared to blue, both at the surface and at 500 mb when averaged over a year (Fig. 2).
But here in Fig. 5, we find the blue line is close to purple than the red line for P(CO2), and also I cannot explain the relative values of P(CO)ch4 as expected from the OH fields.
I understand that the OH level is affecting the concentrations of CO and CH4 and then you get very mixed pictures for P(CO) or P(CO2). But these are not realistic, because we only have one state of CO and CH4 concentration distributions (strictly).
If you are checking the effect of OH then design experiments accordingly, and so on. Please consider.Citation: https://doi.org/10.5194/gmd-2021-173-RC2 - AC2: 'Reply on RC2', Beata Bukosa, 22 Oct 2021
-
RC3: 'Comment on gmd-2021-173', Anonymous Referee #3, 13 Sep 2021
Review of the manuscript: “An improved carbon greenhouse gas simulation in GEOS-Chem version 12.1.1” by B. Bukosa et al.
General Comments
The authors present coupled greenhouse gas simulations with GEOS-Chem focusing on CO2/CH4/CO and its global chemical interactions. Such simulations will be definitively needed towards a consistent description of long-term atmospheric chemistry and for realistic assessment of climatic change by earth system models. I fully acknowledge the work done here and I am convinced that the new developments implemented in GEOS-Chem are a big step towards these goals. When reading the abstract, I got the impression that the paper follows a clear outline by first comparing coupled and uncoupled simulations and then evaluate the new model version with observational data. The authors present a sound and informative introduction to the scientific and computational problem of consistent chemistry simulations, which comprise processes representing a broad range of timescales as well as trends and interannual variability. I also liked the detailed budget term quantification as presented in Table 2. Unfortunately, I got lost after different versions of the OH input fields were introduced. For me it remained unclear why the authors are not able to stick to a single OH field which then can be used for both, the uncoupled and the coupled simulations. In the discussion part of the manuscript, the introduction of a third simulation (coupled-origOH) lead to unnecessary confusion and an overload with information details which made it hard for me to extract the major conclusions. Overall, I would not recommend to publish the paper in its current form but I encourage the authors to submit a revised manuscript based on more consistent coupled and uncoupled simulations.
Specific Comments
Line 49: What do you mean by “outside source regions”?
Lines 49-56: For CO budget terms you can also refer to Stein et al. (2014).
Line 51: Publication year is missing.
Lines 52-54: It would be interesting to see also the numbers for the chemical production by NMVOCs (used as input for your simulations).
Lines 60-63: Can you give a reference here?
Lines 82-84: Is the spin-up time sufficient? You doubt this later on (Lines 506-508).
Lines 96-97: I would expect that a single reference full chemistry simulation is used for all simulations presented here.
Line 134: How does GEOS-Chem handle Biomass burning emissions? It is known that such emissions need to be emitted throughout the troposphere following a vertical profile.
Line 295: Exchange “tropospheric column” by “mid troposphere”.
Lines 348-349: I would expect to have the same P(NMVOC) for all model runs. Give numbers!
Table 1: Publication year is missing.
Figure 1: I like this figure. It could even improve if you orient your coupled and uncoupled flows from left to right.
Figure 4: From your description I would expect that P(CO)CH4 (for all years) and P(CO2) (for 2010-2017) remains exactly constant for the uncoupled runs (except for leap years).
Figure 7(b): This reads like “Surface Loss” as parameter.
References:
Stein, O., Schultz, M. G., Bouarar, I., Clark, H., Huijnen, V., Gaudel, A., George, M., and Clerbaux, C.: On the wintertime low bias of Northern Hemisphere carbon monoxide found in global model simulations, Atmos. Chem. Phys., 14, 9295-9316, doi:10.5194/acp-14-9295-2014, 2014.
Citation: https://doi.org/10.5194/gmd-2021-173-RC3 - AC3: 'Reply on RC3', Beata Bukosa, 22 Oct 2021
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