Carbon dioxide variations in the upper troposphere and lower stratosphere from GOSAT TANSO-FTS TIR profile data

Honda, Akihiro; Eguchi, Nawo; Saitoh, Naoko

doi:https://doi.org/10.5194/acp-2022-46

Preprints

https://doi.org/10.5194/acp-2022-46

Preprints

18 Feb 2022

| 18 Feb 2022

Status: this preprint was under review for the journal ACP but the revision was not accepted.

Carbon dioxide variations in the upper troposphere and lower stratosphere from GOSAT TANSO-FTS TIR profile data

Akihiro Honda, Nawo Eguchi, and Naoko Saitoh

Abstract. Carbon dioxide (CO₂) variations in the upper troposphere and lower stratosphere (UT and LS; pressure = 300–70 hPa) were investigated with profile data derived from the thermal infrared region (Band 4: 5.5–14.3 μm) of the Thermal And Near-infrared Sensor for carbon Observation (TANSO)–Fourier Transform Spectrometer (FTS) onboard the Greenhouse gas Observing SATellite (GOSAT). The vertical profile data (Level 2; version 1) of CO₂ mixing ratios were obtained by bias correction using the in situ aircraft data. Data with sufficient sensitivity were used for the analysis by selecting values with higher degrees of freedom. The analysis period is over four years from January 2010 to December 2013.

The increase of CO₂ mixing ratios obtained with the bias correction in the UT and LS was 1.8–2.4 ppmv year⁻¹ from 2010–2013, which is consistent with a previous observational study and almost the same as for the lower troposphere (LT). The seasonal variations in the UT and LS show that a maximum peak exists one or two months after the peak in the LT, and has an amplitude of 4–5 ppmv, which is less than that in the LT. The inter-annual variations observed in the tropical UT appear to be affected by ENSO events; higher (lower) CO₂ mixing ratios were observed during La Niña (normal/El Niño) periods. Intra-seasonal variations over the Asian summer monsoon region were associated with both vertical and horizontal motions owing to deep convection and monsoonal anticyclonic circulation, respectively.

Received: 17 Jan 2022 – Discussion started: 18 Feb 2022

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Akihiro Honda, Nawo Eguchi, and Naoko Saitoh

Status: closed

RC1:
'Comment on acp-2022-46', Xiaozhen Xiong, 29 Mar 2022

This investigation to the trend and variation of CO2 in UT-LS region is very important for global warming study, and our knowledge in this topic is limited due to the limited observations. Therefore, using GOSAT-FTS retrieval products is a novel approach. The method used is straight forward. The major concern to me is : if the derived trend and seasonal variation is largely from the a-priori used. Please check my comments in the attached file. With some more work, it can become a good paper to publish in this journal.

Citation: https://doi.org/10.5194/acp-2022-46-RC1
- AC1:
  'Reply on RC1', Nawo Eguchi, 14 Sep 2022
  Dear Dr. Xiong as Reviewer#1
  Thank you very much for reviewing our manuscript and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer) comments. Please check the following our reply(black) of each your comments (blue).
  In addition, we are sorry for late replaying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  Nawo Eguchi
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC1
- AC2:
  'Reply on RC2', Nawo Eguchi, 14 Sep 2022
  Dear Reviewer#2
  
  We would like to thank you very much for reviewing our manuscript carefully and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer’s) comments. Please check the following our reply (black) of each your comments (blue).
  In addition, we are sorry for late replying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC2
RC2:
'Comment on acp-2022-46', Anonymous Referee #2, 26 May 2022

Review of Honda et al.,

First of all apologies for my late comment, which was due to unforeseeable issues.

However I'm sorry to say, that I had a hard time reading the manuscript. The data set is very interesting and clearly of interest to the community. The discussion of the link to transport and dynamics is however misleading or partly wrong and neglects many aspects of transport (e.g.. the role of the tropopause as a barrier for transport and its effect on the CO2 cycle amplitude or phase, which has already been discussed in several papers).

The paper presents observations of CO2 from GOSAT from 2010 to 2013, which is analyzed at pressure levels of 500, 250, 150, and 100 hPa. The authors detrend the data by applying a simple linear empirical fit to build multiannual climatologies and anomalies.

They show the zonal mean distributions of CO2 and at the levels mentioned avbove to conclude on the transport processes, which cause the observed CO2 distributions, but neglect relevant literature (Boering, Andrews, Sawa, Hoor, ...).

For the troposphere they state a transport time of two months from the LT (lower troposphere) to the UT (upper troposphere) and a dampening of 50% of the seasonal cycle amplitude. They relate this to the "absolute mixing ratio decreasing with altitude and to a lesser extent mixing with low CO2 mixing ratio air mass".

Further they link troipcal CO2 mixing ratios to ENSO and identify interannual variability of the CO2 in the monsoon region to different relations of vertical transport by convection and horizontal transport "via anticyclonic circulation". The authors neglect relevant literature of CO2 and its seasonal cycle from aircraft observations.

The paper does not include any analysis of transport via e.g. Lagrangian methods, nor it shows links to surface observations or at least comparisons to the interannual variations of emissions or surface distributions or variability (zonally, globally or regionally, e.g. monsoon).

The authors further discuss transport and mixing particular at 250hPa, but do not even mention the term "subtropical jet", mixing barrier, isentropic transport, and consequently do not discuss their roles for the propagation of the seasonal cycle. The also state that Theta=370 K "indicates the physical surface of the tropopause", which is simply wrong. They fully dismiss the role of the extratropical tropopause as transport barrier, when discussing the timing of the seasonal cycle and its amplitude change at the barrier.

They state, that the role of seasonal CO2-cycles has not been studied and neglect significant corresponding work: For the stratosphere above 100 hPa: Andrews et al., 1999, Boering et al., 1994, 1996, Strahan et al., 1998.

For the UTLS and lower stratosphere: Hoor et al., 2004, Engel et al., 2007, Boenisch et al., 2009. For upper troposphere and the monsoon: Schuck et al., 2010, Gurk et al., 2008.

All in all there are too many speculations when linking transport and CO2 observations. I recommend to resubmit it focusing on the climatologies and the observations and carefully linking them to e.g. surface seasonal cycles from global observational network for the LT/MT data. For the UTLS there must be a correct treatment of the tropopause particularly for the 150 hPa and 250 hPa level. One could e.g. derive distinct seasonal cycles for tropospheric and stratospheric data, which can be compared to existing data sets (see references). Speculations about transport mechanisms should be removed.

Therefore I can't recommend the paper for publication in the current form.

I do highly suggest a resubmission with a different focus, since the data set as such is very valuable, but the discussion of potential links to transport and mixing is inappropriate. I encourage the authors for resubmission either sharpening the transport discusssion or just focusing on the climatologies.

Minor points: line 109: What is the vertical resolution and how do averaging kernels look like?

Fig. 1: Gradients appear at the tropopause. These were not accounted for.

The discussion of trends and Figure 1 illustrates an example of the coarse and insufficient discussions and speculations: The trend figure is discussed without any mentioning of the tropopause and its role for e.g. the mid-lat trend. The according table 1 provides trends for different latitude ranges, different altitudes without consideration or discussion of the tropopause. What shall one learn from this?

Fig.6 and related discussion (lines 261-268): The monsoon plays of course a role for the observed 250 hPa CO2 in Fig.6, but there is no disussion of potential surface emission variations, change of ENSO-related tropospheric circulation pattrens, change of emission patterns, the authors state without any supporting analysis, that the observed CO2 variability is related to variability of deep convection. How do the authors come to their conclusion? How is emission variability differentiated from large scale transport variability or convection?

Fig.2 : Concerning the bias correction, which is also mentioned in the manuscript: Which role does the isentropic CO2 gradient at the extratropcal and subtropical tropopause play for the bias correction? Did the authors consider the tropopause when calculating the bias?

Fig 2d) How do the cycles (e.g. at point Barrow and Mauna Loa) fit to the GOSAT observations at 500 hPa. Highest CO2 at high latitudes should occur later than at low latitudes, since biological activity is delayed. How does this fit to Fig.2d? also line 165-168.

l.184: The 370K isentrope defines the physical surface of the tropopause.

This statement is simply wrong. The tropopause is no way defined by isentropes (read Holton, 1995, Hoskins, 1991, Bethan, 1996...

Fig. 3: How well is the troposphere resolved in the CO2-data (vertical resolution, kernels, degrees of freedom)?

'Caption': Replace 'vertical velocity' with 'pressure tendency' - they have different signs.

Fig.4b)c): The data at 250 hPa are affected by the tropopause location, which inhibits quasi-horizontal (quasi-isentropic) transport. The phase propagation therefore is differnt from 100 hPa or 500 hPa (see Sawa et al., 2008, Hoor et al., 2004). Please add the (mean) 2 PVU and 4 PVU contour (also Fig. 6a)-d) and Fig.5 a)

l.208/209: Which vertical gradient? Please calculate or plot (e.g. for diffenet latitudes).

l.210: This statement holds for any tracer and is very unspecific - the distribution of anything in the UTLS depends on vertical and horizontal transport in the troposphere.

Fig.5: 500 hPa shows a trend of the anomaly at higher latitudes. Is this due to the (possibly wrong) linear trend estimate to derive the anomaly (eqn.1)?

Also Figure 7: Why is the CO2 maximum related to deep concvection? Why do the data not show any accumulation effect inside the anticyclone (see e.g. Baker, 2013, Schuck, 2010?

-------------------------------------------

Refernces:

Andrews et al., Empirical age spectra for the lower tropical stratosphere from in situ observations of CO2: Implications for stratospheric transport, JGR, 194, 26581-26595, 1999.

Boering, K. A., Wofsy, S. C., Daube, B. C., Schneider, J. R., Loewenstein, M., Podolske, J. R., and Conway, T. J.: Stratospheric mean ages and transport rates from observations of CO2 and N2O, Science, 274, 1340–1343, 1996 (and reference to Boering 1994, therein)

H. Bönisch, A. Engel, J. Curtius, Th. Birner, and P. Hoor, Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF6 and CO2, Atmos. Chem. Phys., 9, 5905–5919, https://doi.org/10.5194/acp-9-5905-2009, 2009.

Engel, A., B Ìonisch, H., Brunner, D., Fischer, H., Franke, H.,G Ìunther, G., Gurk, C., Hegglin, M., Hoor, P., K Ìonigstedt, R.,Krebsbach, M., Maser, R., Parchatka, U., Peter, T., Schell, D.,Schiller, C., Schmidt, U., Spelten, N., Szabo, T., Weers, U.,Wernli, H., Wetter, T., and Wirth, V.: Highly resolved observations of trace gases in the lowermost stratosphere and upper troposphere from the Spurt project: an overview, Atmos. Chem.Phys., 6, 283–301, 2006.

Gurk, Ch., Fischer, H., Hoor, P., Lawrence, M. G., Lelieveld, J., and Wernli, H.: Airborne in-situ measurements of vertical, seasonal and latitudinal distributions of carbon dioxide over Europe, Atmos. Chem. Phys., 8, 6395–6403, https://doi.org/10.5194/acp-8-6395-2008, 2008.

Hoor, P., Gurk, C., Brunner, D., Hegglin, M. I., Wernli, H., and Fischer, H.: Seasonality and extent of extratropical TST derived from in-situ CO measurements during SPURT, Atmos. Chem. Phys., 4, 1427–1442, 2004, http://www.atmos-chem-phys.net/4/1427/2004/.

T. J. Schuck, C. A. M. Brenninkmeijer, A. K. Baker, F. Slemr, P. F. J. von Velthoven, and A. Zahn, Greenhouse gas relationships in the Indian summer monsoon plume measured by the CARIBIC passenger aircraft, Atmos. Chem. Phys., 10, 3965–3984, https://doi.org/10.5194/acp-10-3965-2010, 2010.

Strahan, S. E., Douglass, A. R., Nielsen, J. E., and Boering, K. A.: The CO2 seasonal cycle as a tracer of transport, J. Geophys. Res., 103, 13 729–13 741, 1998.

Citation: https://doi.org/10.5194/acp-2022-46-RC2
- AC2:
  'Reply on RC2', Nawo Eguchi, 14 Sep 2022
  Dear Reviewer#2
  
  We would like to thank you very much for reviewing our manuscript carefully and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer’s) comments. Please check the following our reply (black) of each your comments (blue).
  In addition, we are sorry for late replying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC2
- AC1:
  'Reply on RC1', Nawo Eguchi, 14 Sep 2022
  Dear Dr. Xiong as Reviewer#1
  Thank you very much for reviewing our manuscript and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer) comments. Please check the following our reply(black) of each your comments (blue).
  In addition, we are sorry for late replaying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  Nawo Eguchi
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC1

Status: closed

RC1:
'Comment on acp-2022-46', Xiaozhen Xiong, 29 Mar 2022

This investigation to the trend and variation of CO2 in UT-LS region is very important for global warming study, and our knowledge in this topic is limited due to the limited observations. Therefore, using GOSAT-FTS retrieval products is a novel approach. The method used is straight forward. The major concern to me is : if the derived trend and seasonal variation is largely from the a-priori used. Please check my comments in the attached file. With some more work, it can become a good paper to publish in this journal.

Citation: https://doi.org/10.5194/acp-2022-46-RC1
- AC1:
  'Reply on RC1', Nawo Eguchi, 14 Sep 2022
  Dear Dr. Xiong as Reviewer#1
  Thank you very much for reviewing our manuscript and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer) comments. Please check the following our reply(black) of each your comments (blue).
  In addition, we are sorry for late replaying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  Nawo Eguchi
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC1
- AC2:
  'Reply on RC2', Nawo Eguchi, 14 Sep 2022
  Dear Reviewer#2
  
  We would like to thank you very much for reviewing our manuscript carefully and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer’s) comments. Please check the following our reply (black) of each your comments (blue).
  In addition, we are sorry for late replying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC2
RC2:
'Comment on acp-2022-46', Anonymous Referee #2, 26 May 2022

Review of Honda et al.,

First of all apologies for my late comment, which was due to unforeseeable issues.

However I'm sorry to say, that I had a hard time reading the manuscript. The data set is very interesting and clearly of interest to the community. The discussion of the link to transport and dynamics is however misleading or partly wrong and neglects many aspects of transport (e.g.. the role of the tropopause as a barrier for transport and its effect on the CO2 cycle amplitude or phase, which has already been discussed in several papers).

The paper presents observations of CO2 from GOSAT from 2010 to 2013, which is analyzed at pressure levels of 500, 250, 150, and 100 hPa. The authors detrend the data by applying a simple linear empirical fit to build multiannual climatologies and anomalies.

They show the zonal mean distributions of CO2 and at the levels mentioned avbove to conclude on the transport processes, which cause the observed CO2 distributions, but neglect relevant literature (Boering, Andrews, Sawa, Hoor, ...).

For the troposphere they state a transport time of two months from the LT (lower troposphere) to the UT (upper troposphere) and a dampening of 50% of the seasonal cycle amplitude. They relate this to the "absolute mixing ratio decreasing with altitude and to a lesser extent mixing with low CO2 mixing ratio air mass".

Further they link troipcal CO2 mixing ratios to ENSO and identify interannual variability of the CO2 in the monsoon region to different relations of vertical transport by convection and horizontal transport "via anticyclonic circulation". The authors neglect relevant literature of CO2 and its seasonal cycle from aircraft observations.

The paper does not include any analysis of transport via e.g. Lagrangian methods, nor it shows links to surface observations or at least comparisons to the interannual variations of emissions or surface distributions or variability (zonally, globally or regionally, e.g. monsoon).

The authors further discuss transport and mixing particular at 250hPa, but do not even mention the term "subtropical jet", mixing barrier, isentropic transport, and consequently do not discuss their roles for the propagation of the seasonal cycle. The also state that Theta=370 K "indicates the physical surface of the tropopause", which is simply wrong. They fully dismiss the role of the extratropical tropopause as transport barrier, when discussing the timing of the seasonal cycle and its amplitude change at the barrier.

They state, that the role of seasonal CO2-cycles has not been studied and neglect significant corresponding work: For the stratosphere above 100 hPa: Andrews et al., 1999, Boering et al., 1994, 1996, Strahan et al., 1998.

For the UTLS and lower stratosphere: Hoor et al., 2004, Engel et al., 2007, Boenisch et al., 2009. For upper troposphere and the monsoon: Schuck et al., 2010, Gurk et al., 2008.

All in all there are too many speculations when linking transport and CO2 observations. I recommend to resubmit it focusing on the climatologies and the observations and carefully linking them to e.g. surface seasonal cycles from global observational network for the LT/MT data. For the UTLS there must be a correct treatment of the tropopause particularly for the 150 hPa and 250 hPa level. One could e.g. derive distinct seasonal cycles for tropospheric and stratospheric data, which can be compared to existing data sets (see references). Speculations about transport mechanisms should be removed.

Therefore I can't recommend the paper for publication in the current form.

I do highly suggest a resubmission with a different focus, since the data set as such is very valuable, but the discussion of potential links to transport and mixing is inappropriate. I encourage the authors for resubmission either sharpening the transport discusssion or just focusing on the climatologies.

Minor points: line 109: What is the vertical resolution and how do averaging kernels look like?

Fig. 1: Gradients appear at the tropopause. These were not accounted for.

The discussion of trends and Figure 1 illustrates an example of the coarse and insufficient discussions and speculations: The trend figure is discussed without any mentioning of the tropopause and its role for e.g. the mid-lat trend. The according table 1 provides trends for different latitude ranges, different altitudes without consideration or discussion of the tropopause. What shall one learn from this?

Fig.6 and related discussion (lines 261-268): The monsoon plays of course a role for the observed 250 hPa CO2 in Fig.6, but there is no disussion of potential surface emission variations, change of ENSO-related tropospheric circulation pattrens, change of emission patterns, the authors state without any supporting analysis, that the observed CO2 variability is related to variability of deep convection. How do the authors come to their conclusion? How is emission variability differentiated from large scale transport variability or convection?

Fig.2 : Concerning the bias correction, which is also mentioned in the manuscript: Which role does the isentropic CO2 gradient at the extratropcal and subtropical tropopause play for the bias correction? Did the authors consider the tropopause when calculating the bias?

Fig 2d) How do the cycles (e.g. at point Barrow and Mauna Loa) fit to the GOSAT observations at 500 hPa. Highest CO2 at high latitudes should occur later than at low latitudes, since biological activity is delayed. How does this fit to Fig.2d? also line 165-168.

l.184: The 370K isentrope defines the physical surface of the tropopause.

This statement is simply wrong. The tropopause is no way defined by isentropes (read Holton, 1995, Hoskins, 1991, Bethan, 1996...

Fig. 3: How well is the troposphere resolved in the CO2-data (vertical resolution, kernels, degrees of freedom)?

'Caption': Replace 'vertical velocity' with 'pressure tendency' - they have different signs.

Fig.4b)c): The data at 250 hPa are affected by the tropopause location, which inhibits quasi-horizontal (quasi-isentropic) transport. The phase propagation therefore is differnt from 100 hPa or 500 hPa (see Sawa et al., 2008, Hoor et al., 2004). Please add the (mean) 2 PVU and 4 PVU contour (also Fig. 6a)-d) and Fig.5 a)

l.208/209: Which vertical gradient? Please calculate or plot (e.g. for diffenet latitudes).

l.210: This statement holds for any tracer and is very unspecific - the distribution of anything in the UTLS depends on vertical and horizontal transport in the troposphere.

Fig.5: 500 hPa shows a trend of the anomaly at higher latitudes. Is this due to the (possibly wrong) linear trend estimate to derive the anomaly (eqn.1)?

Also Figure 7: Why is the CO2 maximum related to deep concvection? Why do the data not show any accumulation effect inside the anticyclone (see e.g. Baker, 2013, Schuck, 2010?

-------------------------------------------

Refernces:

Andrews et al., Empirical age spectra for the lower tropical stratosphere from in situ observations of CO2: Implications for stratospheric transport, JGR, 194, 26581-26595, 1999.

Boering, K. A., Wofsy, S. C., Daube, B. C., Schneider, J. R., Loewenstein, M., Podolske, J. R., and Conway, T. J.: Stratospheric mean ages and transport rates from observations of CO2 and N2O, Science, 274, 1340–1343, 1996 (and reference to Boering 1994, therein)

H. Bönisch, A. Engel, J. Curtius, Th. Birner, and P. Hoor, Quantifying transport into the lowermost stratosphere using simultaneous in-situ measurements of SF6 and CO2, Atmos. Chem. Phys., 9, 5905–5919, https://doi.org/10.5194/acp-9-5905-2009, 2009.

Engel, A., B Ìonisch, H., Brunner, D., Fischer, H., Franke, H.,G Ìunther, G., Gurk, C., Hegglin, M., Hoor, P., K Ìonigstedt, R.,Krebsbach, M., Maser, R., Parchatka, U., Peter, T., Schell, D.,Schiller, C., Schmidt, U., Spelten, N., Szabo, T., Weers, U.,Wernli, H., Wetter, T., and Wirth, V.: Highly resolved observations of trace gases in the lowermost stratosphere and upper troposphere from the Spurt project: an overview, Atmos. Chem.Phys., 6, 283–301, 2006.

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Citation: https://doi.org/10.5194/acp-2022-46-RC2
- AC2:
  'Reply on RC2', Nawo Eguchi, 14 Sep 2022
  Dear Reviewer#2
  
  We would like to thank you very much for reviewing our manuscript carefully and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer’s) comments. Please check the following our reply (black) of each your comments (blue).
  In addition, we are sorry for late replying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC2
- AC1:
  'Reply on RC1', Nawo Eguchi, 14 Sep 2022
  Dear Dr. Xiong as Reviewer#1
  Thank you very much for reviewing our manuscript and giving us many useful comments.
  We agree your almost all of comments and suggestions, therefore the manuscript has been revised along your (and another reviewer) comments. Please check the following our reply(black) of each your comments (blue).
  In addition, we are sorry for late replaying because it takes time to repair the data server which was broken down.
  
  The major points that we deal with in the revised manuscript are as follows:
  Figures were updated or removed.
  Adding 2PVU (potential velocity unit) and OLR (outgoing longwave radiation) as the indicator of deep convection to Figures 1, 2, 3 and 5 of the revised manuscript, and zonal wind to Figure 2 of the revised manuscript
  
  Figure 1 (plot of latitudinal distribution of increasing rate) in the previous manuscript was removed because Table 1 was enough information on it.
  
  Figure 3d (time-latitude cross section for 4-year at 250 and 500hPa) of the revised manuscript was drawn by the corrected data, because the previous figure was drawn by the data without the bias correction.
  
  Figure 5 (time-latitude cross section of inter-annual variation) in the previous manuscript was removed from the revised manuscript.
  
  The discussion on CO₂ variation related with ENSO was moved to section of Discussion and Summary. Therefore the section name was changed to “Summary and Conclusion” to “Discussion and Summary” in the revised manuscript.
  
  Many references recommended by reviewers were added to mainly the section of Introduction related with the in situ observational studies.
  
  The reply on each your comments are in the file of supplement. Please read that.
  Nawo Eguchi
  
  Citation: https://doi.org/10.5194/acp-2022-46-AC1

Akihiro Honda, Nawo Eguchi, and Naoko Saitoh

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Cumulative views and downloads (calculated since 18 Feb 2022)

Month	HTML	PDF	XML	Total
Feb 2022	141	40	5	186
Mar 2022	56	12	3	71
Apr 2022	18	14	0	32
May 2022	15	6	3	24
Jun 2022	16	12	2	30
Jul 2022	12	6	0	18
Aug 2022	17	10	0	27
Sep 2022	31	11	3	45
Oct 2022	12	14	1	27
Nov 2022	19	5	0	24
Dec 2022	14	6	0	20
Jan 2023	46	13	1	60
Feb 2023	32	16	1	49
Mar 2023	49	14	1	64
Apr 2023	37	10	0	47
May 2023	37	9	2	48
Jun 2023	36	6	0	42
Jul 2023	31	15	1	47
Aug 2023	38	12	1	51
Sep 2023	24	6	2	32
Oct 2023	24	8	0	32
Nov 2023	20	6	6	32
Dec 2023	14	4	2	20
Jan 2024	25	9	0	34
Feb 2024	16	10	1	27
Mar 2024	19	13	0	32
Apr 2024	37	7	1	45

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Short summary

The intra-seasonal, seasonal and inter-annual variations of carbon dioxide (CO₂) at the upper troposphere and lower stratosphere (UTLS) are investigated by the CO₂ profile data derived from the thermal infrared spectra of TANSO-FTS instrument onboard GOSAT satellite, for understanding of the missing sink of CO₂ and detail exchange process between UT and LS. There are new findings on the intra-seasonal and inter-annual variations associated with Asian summer monsoon and ENSO, respectively.


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Carbon dioxide variations in the upper troposphere and lower stratosphere from GOSAT TANSO-FTS TIR profile data

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