Simulations of Ozone Feedback Effects on the Equatorial Quasi-Biennial Oscillation with a Chemistry–Climate Model
Round 1
Reviewer 1 Report
See attached file.
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer_1
(1) There is no direct comparison of the modeled QBO (the standard or ST case) with the observed QBO. How well does the zonal-mean zonal wind evolution shown in Figure 1b agree with observations? In particular, does your QBO descend down into the lower stratosphere as low as is seen in observations (about 100 hPa)? This may have been covered already in prior publications but it would be good to cover it again at least briefly here. Adding a figure comparing the zonal wind evolution in Figure 1b with the observed evolution during 1975-1985 would be helpful.
Rply(R): Added a panel of the zonal wind evolution of observation (ERA-40) in Figure 1.
(2) Does the MRI-CCM used here include a coupled ocean? The stated model integration methods (lines 104-108) seem to imply that only observed SSTs were applied at the lower boundary. Would including a coupled ocean substantially modify the results of this study?
In lines 89-91, it says that only a brief description of the model is given here because it has been already described in another paper (Shibata and Lehman, 2020). However, when I look up this paper, it also says that only a brief description is provided because it has already been described in a paper by Shibata and Deushi (2008). So maybe a reference to the latter paper is also needed.
R: An adjective “atmospheric” was added such as “The dynamics module of MRI-CCM is an atmospheric spectral global model…”
R: Shibata and Deushi (2008) was referred to.
(3) It is disappointing that no suggestions or hypotheses are advanced as to why increasing the calculated ozone input to the dynamical module produces a longer QBO period while not affecting the QBO amplitude. It is only speculated (lines 329-331) that “the QBO period is forced to change so as to hold the QBO amplitude nearly unchanged as manifested in the time series of the QBO forcings of EPD and GWF” (i.e., the two dynamical wave forcings that drive the QBO winds). “However, to address the mechanism of this response of the QBO is beyond the scope of this study using a CCM. Future studies using mechanistic models are preferable ...” A possible mechanism that may contribute to the period lengthening is indicated by the time-height cross sections of zonal-mean ozone in the tropical stratosphere shown in Figure 5. Comparing the P (a) plot with the N (c) plot,
it is seen that the ozone in the lower stratosphere is stronger and extended further in time in plot (a) than in plot (c). This could be at least partly because the strengthened residual meridional circulation produces stronger downwelling near the 20 hPa level, which extends the lower stratospheric ozone anomaly in time. If the lower stratospheric ozone anomaly is further extended in time, the QBO period could be lengthened. This is just a thought but you might want to mention this as a possible hypothesis to be tested in the future using mechanistic models.
R: I added Figure 12 depicting the time series of w* and u at 20 hPa, which showed w* to be also very similar in the three runs, indicating w* associated with the QBO was not the cause of the variations in the QBO period. Further, I added a Table showing the climatological (background) w*, in which the background w* monotonically increased with the intensity of the ozone feedback above 50 hPa. So, I added one sentence in the last paragraph in Section 4: “One plausible mechanism for this response is the changes in the background upwelling w* above middle stratosphere of 50 hPa such that stronger (weaker) background upwelling retards (advances) the downward propagation of zonal wind, resulting in lengthening (shortening) of the QBO period.”
More minor corrections or suggested additions:
(4) In the abstract (line 11), the altitude or pressure range in the stratosphere where ozone changes were imposed is not mentioned. Later the pressure range is stated to be 100 to 10 hPa. Please modify to say lower to middle stratosphere or give the actual pressure range in the abstract.
R: The actual pressure range was added such as “… equatorial stratosphere from 100 to 10 hPa …..”
(5) Lines 72-73: “This paper is to investigate the ozone radiative feedback on the QBO with a CCM thoroughly holding the interaction between chemistry and dynamics.” The meaning of this is not clear. I think you mean that the ozone change is calculated first in the chemistry module and then this ozone change is input to the dynamics module with no further feedback to the chemistry module. Please explain more clearly here what is new about the current approach as compared to previous CCM studies of the same issue.
R: Added a sentence “That is, ozone is always treated interactively throughout the investigation, being in high contrast to the previous studies of the comparison between interactive and non-interactive ozone simulations [16-18].”
(6) Lines 79-83. These are results and should not be put in the Introduction.
R: These lines are briefly describing important results, and this is within permissible range in the variations of Introduction styles.
(7) Typos and English corrections. Line 49: dimensional.
R: Corrected.
Line 109: In addition to the standard run, ...
R: Changed as suggested.
Line 122: G(P).
R: Corrected.
Lines 205-206: “ozone tendency due to transport” Maybe re-word this as “ozone transport timescale”?
R: Changed as suggested.
Figure 11 caption: from 10S to 10N.
R: Corrected.
Line 293: referred to as gravity-wave forcing.
R: Corrected.
Line 329: In other words.
R: Corrected.
Reviewer 2 Report
General comments
It is an interesting and topical work. However, since it is the application of a model, it is difficult to find the scientific contribution of the manuscript.
The paper does not have a conclusion section. It is not possible to find the scientific contribution of the results presented.
Lines 46-48
It is said that it is of great importance to take into account the dynamic characteristics of the QBO. However, it seems that the model used does not take into account the altitudinal variation.
Line 50
It is also mentioned that it is important to consider the variation that occurs due to the vertical position that causes local heating anomalies .....
Line 94-95 and 98-99
.... so why use a model that does not consider the orographic event?
Line 114-116
However, it is mentioned that an altitudinal function G(P) is taken into account. The wording and basic conditions of the model are very confusing.
Line 210-212
Why is it said that the MRI-CCM correctly reproduces the ozone QBO? Where is this evidence in the manuscript? Are you referring to Figure 11?
Line 260 Figure 9.
Very interesting results are shown in the cross-sections of the mean vertical velocity of the anomalies at 20hPA. However, the analysis and discussion of the results in the time aspect are questionable.
The results and discussion is focused on the aspect of specific point values, as shown in Table 1. If the results are shown in the form of a time series, at a minimum a correlation or time significance analysis (correlogram) should be presented. Where appropriate, also a time-series break analysis to ensure the stationarity of the series.
Author Response
Response to Reviewer_1
Comments and Suggestions for Authors
General comments
It is an interesting and topical work. However, since it is the application of a model, it is difficult to find the scientific contribution of the manuscript.
Reply(R): Numerous papers dealing simulation results by a model have been published and contributed to science, in particular, the atmospheric science.
The paper does not have a conclusion section. It is not possible to find the scientific contribution of the results presented.
R: Since Conclusions Section is not mandatory in “Climate”, I included the findings in 4. Summary and Discussion.
Lines 46-48
It is said that it is of great importance to take into account the dynamic characteristics of the QBO. However, it seems that the model used does not take into account the altitudinal variation.
R: The altitudinal variation is taken into account, because all the prognostic and diagnostic variables in the model depend on altitude, latitude, and longitude.
Line 50
It is also mentioned that it is important to consider the variation that occurs due to the vertical position that causes local heating anomalies .....
R: Below about 20 hPa the ozone QBO is due to the vertical transport of ozone and the resultant ozone anomalies produce local radiative heating anomalies.
Line 94-95 and 98-99
.... so why use a model that does not consider the orographic event?
R: In tropics the major source of gravity waves is not orography but convective activity.
Line 114-116
However, it is mentioned that an altitudinal function G(P) is taken into account. The wording and basic conditions of the model are very confusing.
R: Please see the response to comment of Lines 46-48.
Line 210-212
Why is it said that the MRI-CCM correctly reproduces the ozone QBO? Where is this evidence in the manuscript? Are you referring to Figure 11?
R: I described that the QBO is realistically simulated in the ST run in Section 2: “, in which the QBO was realistically simulated in zona wind and ozone [21].”
Line 260 Figure 9.
Very interesting results are shown in the cross-sections of the mean vertical velocity of the anomalies at 20hPA. However, the analysis and discussion of the results in the time aspect are questionable.
R: The analysis of the results in the time aspect is certain. Discussion was so modified that Figure 12 and Table 1 were added. Previous Table 1 was renumbered to Table 2.
The results and discussion is focused on the aspect of specific point values, as shown in Table 1. If the results are shown in the form of a time series, at a minimum a correlation or time significance analysis (correlogram) should be presented. Where appropriate, also a time-series break analysis to ensure the stationarity of the series.
R: Table 2 (previous Table 1) tabulates values averaged for long time (~10 years), which is to concisely summarize time series (Figures 1, 2, and 11) which include broad frequencies within the QBO.
Round 2
Reviewer 2 Report
Reply(R): Numerous papers dealing simulation results by a model have been published and contributed to science, in particular, the atmospheric science.
Totally agree. Then I suppose that the authors will be able to detail the scientific achievements of the work they present. The model is not being questioned, the scientific contributions that the authors provide with the use of the model are being questioned. The authors have not yet responded to this request.
R: Since Conclusions Section is not mandatory in “Climate”, I included the findings in 4. Summary and Discussion.
The results and discussion were correctly included. However, in any scientific work, the conclusions of the research are required. And although there is no specific section, the authors must conclude on their results.
Author Response
Response to Reviewer 2 (round 2)
Reply (R, round 1): Numerous papers dealing simulation results by a model have been published and contributed to science, in particular, the atmospheric science.
Totally agree. Then I suppose that the authors will be able to detail the scientific achievements of the work they present. The model is not being questioned, the scientific contributions that the authors provide with the use of the model are being questioned. The authors have not yet responded to this request.
Reply (R2, round 2): Please see the Reply 2 below.
R: Since Conclusions Section is not mandatory in “Climate”, I included the findings in 4. Summary and Discussion.
The results and discussion were correctly included. However, in any scientific work, the conclusions of the research are required. And although there is no specific section, the authors must conclude on their results.
R2: Conclusions were included in the last two paragraphs of 4. Summary and Discussion.
