Roles of the Inner Eyewall Structure in the Secondary Eyewall Formation of Simulated Tropical Cyclones

Qin, Nannan; Wu, Liguang; Liu, Qingyuan

doi:https://doi.org/10.5194/acp-2021-147

Preprints

https://doi.org/10.5194/acp-2021-147

Preprints

07 Apr 2021

| 07 Apr 2021

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

Roles of the Inner Eyewall Structure in the Secondary Eyewall Formation of Simulated Tropical Cyclones

Nannan Qin, Liguang Wu, and Qingyuan Liu

Abstract. It has been suggested that the inner eyewall structure may play an important role in the secondary eyewall formation (SEF) of tropical cyclones (TCs). This study is to further examine the role of the inner eyewall structure by comparing two numerical experiments, which were conducted with the same large-scale environment and initial and boundary conditions but different grid sizes. The SEF was simulated in the experiment with the finer grid spacing, but not in the other.

Comparing the eyewall structure in the simulated TCs with and without the SEF indicates that the eyewall structure can play an important role in the SEF. For the simulated TC with the SEF, the eyewall is more upright with stronger updrafts, accompanied by a wide eyewall anvil at a higher altitude. Compared to the simulated TC without the SEF, diagnostic analysis reveals that the cooling outside the inner eyewall is induced by the sublimation, melting and evaporation of hydrometeors falling from the eyewall anvil. The cooling also induces upper-level dry, cool inflow below the anvil, prompting the subsidence and moat formation between the inner eyewall and the spiral rainband. In the simulated TC without the SEF, the cooling induced by the falling hydrometeors is significantly reduced and offset by the diabatic warming. There is no upper-level dry inflow below the anvil and no moat formation between the inner eyewall and the spiral rainband. This study suggests that a realistic simulation of the intense eyewall convection is important to the prediction of the SEF in the numerical forecasting model.

Received: 25 Feb 2021 – Discussion started: 07 Apr 2021

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Nannan Qin, Liguang Wu, and Qingyuan Liu

Status: closed

RC1:
'Comment on acp-2021-147', Anonymous Referee #1, 06 May 2021
This study examined the role of inner eyewall structure in the formation of a secondary eyewall by performing two WRF simulations of (realistic or idealized unknown) tropical cyclones (TCs) with different horizontal grid spacings. The simulation with secondary eyewall formation (SEF) has stronger and deeper eyewall updrafts that produce more hydrometers falling out of anvil clouds outside the eyewall. The associated diabatic cooling helps induce a descending inflow beneath the outflow layer that is argued to contribute to the formation of a moat. In contrast, the simulation without SEF does not show the descending inflow and moat. The authors then emphasized the importance of accurately simulating the structure of the eyewall in the SEF.

I would like to appreciate the substantial efforts the authors made to diagnose the mechanism responsible for the formation of descending inflows outside the primary eyewall. However, after going through the paper, I fail to locate any solid evidence that can support the statement that the descending inflow outside the eyewall contributes to the SEF. The literature review is insufficient, and thus key findings from this study are mostly facts we have learned from previous studies. The model design is not clear and the experiment design with different horizontal grid spacings needs to be justified. The writing suffers from numerous grammatical errors. In some instances the grammatical issues were so severe that I could not discern the meaning of the authors. If the revised manuscript is not substantially improved to address these issues, then I will recommend rejection.

General comments:

The take-home message of this study is compared to non-SEF TCs SEF TCs have stronger intensity, and stronger upper-level inflows that descend into the boundary layer and contribute to a formation of moat. Is this a novel finding? A statistical analysis of Western North Pacific typhoons (Kuo et al. 2009) has shown that major typhoons are more likely to undergo SEF than weaker typhoons (see their Fig. 4). Additionally, a existed debate is the relative importance between strong strain flows that shear apart or suppress convection (Kossin et al. 2000; Rozoff et al. 2006) and subsidence, a component of the secondary circulation; the latter is argued to be the dominant factor by Wang et al. (2008). The related discussion is missing in the literature review. The inflow layer beneath the outflow layer for SEF TCs can be a response to momentum forcing, radiation, and many other factors, while authors only diagnosed the contribution of diabatic heating. Differences in TC structure and inflow strength between the two experiments are largely attributable to differences in TC intensity. I don’t understand the motive of revisiting these processes. Most importantly, please provide solid evidence to prove the descending inflow contributes to the SEF.

The description for experiment design and model setup is not clear. Please inform readers whether these simulations use a realistic or an idealized TC. Reasons for performing simulations with different horizontal grid spacing are missing. Comparison of inner-core structure with different model grid spacing is not fair. The usage of a traditional PBL scheme at gray-zone resolutions (e.g., 333 m) is problematic. Given these issues, I would encourage the authors to perform ensemble simulations with 1-km horizontal grid spacing and compare the simulations with and without SEF.

Different types of descending inflows have been documented in literature, including the one mentioned in this study, the one coming from the stratiform region outward of the outer rainband (Didlake et al. 2018), and the one coming from the upper levels and outward of the outer rainband (Dai et al. 2019). I would encourage the authors to discuss whether these processes are intrinsic to the SEF or they are the results of SEF based on their numerical simulations. The inflow layer beneath the outflow layer has been discussed in modeling studies (e.g., Wang et al. 2020, https://doi.org/10.1002/qj.3856). Under which situation would the inflow layer descend into the boundary layer and contribute to the moat and SEF formation? These descending inflows typically locate within a confined region around the TC center, and how do they contribute to the symmetrization of outer rainband during the SEF? These open questions need to be addressed to some extent to advance our understanding of SEF.

There are numerous grammar mistakes in the text. I only list a few. Please carefully edit the text before resubmission.

Minor comments:

Line 25: “The SEF was simulated in the experiment …” ->”The experiment with … shows a SEF”

Line 30: “Compared to the simulated …, diagnostic analysis”. Rewrite this sentence.

Line 32: Could the outflow layer itself induce an inflow layer beneath it? A complete Sawyer-Eliassen equation diagnosis is needed.

Line 58: What is “stretching time”? Probably you mean filamentation time but that needs to be defined too.

Line 63: Did Kepert (2013) use an axisymmetric boundary layer model? You may be aware SEF is typically associated with an axisymmetrization of outer rainband. What insights would you think the axisymmetric framework can provide into this phenomenon?

Lines 81-82: I agree, and why not focus on this key scientific issue in this study?

Line 86: “since” -> due to

Lines 358-359: I may miss something. Did this study discuss under which situation would upper-level inflows descend into the boundary layer?
Citation: https://doi.org/10.5194/acp-2021-147-RC1
- AC1: 'Reply on RC1', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC1
RC2:
'Comment on acp-2021-147', Anonymous Referee #2, 07 Jun 2021

General Comments:

This study examined the influences of the inner eyewall structure on the moat development, spiral rainband and subsequent secondary eyewall using a pair of model simulations with only differing horizontal grid spacing. While I believe the manuscript provides a nice discussion on the role of the strength of the inner eyewall in modifying the diabatic cooling and upper-level inflow radially outward of the primary eyewall and beneath the anvil, I believe the analysis fails to connect this cooling to the boundary layer processes which are likely forcing the secondary eyewall formation. I also have specific concerns on the choice of comparing only two simulations with differing horizontal gird spacing, specifically the fact that the CTL simulation questionably uses a PBL parameterization in the ‘gray zone’ (0.3 km) and NSEF uses horizontal grid spacing of 1 km and a PBL parameterization.

Specific Comments:

1) The choice of comparing two simulations with different innermost grid spacing (0.3 km vs 1 km) is odd to me. For one, grid spacing of 0.3 km is within the turbulent ‘gray zone’ so the choice of using a PBL parameterization is questionable (e.g., Green and Zhang 2015 and Honert et al. 2020). In addition, the finest resolved eddies will be different between the two simulations, and it is not clear to me how to interpret these differences in terms of the results presented. This is especially true in comparing with the results of Green and Zhang (2015). Green and Zhang showed that the development of the secondary eyewall in their simulations (ranging in horizontal grid spacing from 111 m – 3 km) was sensitive to how the turbulence was parameterized. More specifically, they noted that none of the simulations without a planetary boundary layer parametrization simulated the development of a secondary eyewall, suggesting strong sensitivity of secondary eyewall formation to the parameterization of turbulence in the ‘gray zone’. I think it is important that the authors reconsider their choice in comparing two simulations with different horizontal grid spacing in order to more easily interpret their results.

Honnert, R., Efstathiou, G., Beare, R., Ito, J., Lock, A., Neggers, R., et al. (2020). The atmospheric boundary layer and the “gray zone” of turbulence: A critical review. Journal of Geophysical Research: Atmospheres, 125, e2019JD030317. https://doi.org/10.1029/2019JD030317

Green, B. W., and F. Zhang (2015), Numerical simulations of Hurricane Katrina (2005) in the turbulent gray zone, J. Adv. Model. Earth Syst., 07, doi:10.1002/2014MS000399.

2) Partially related to my first comment, I am not convinced that the differences in secondary eyewall formation can be completely attributed to the differences in the inner eyewall structure and not other differences related to the varying horizontal grid spacing between the two simulations and small-scale boundary layer perturbations, potentially related to differences in the model representation of turbulence. As one example, Zhang et al. (2014) demonstrated that secondary eyewall formation is sensitive to very small differences in initial conditions. As a result, I recommend the authors consider revisiting the role of the inner eyewall structure in secondary eyewall formation using a small ensemble with the same model set up.

Zhang, F., D. Tao, Y. Q. Sun, and J. D. Kepert (2017), Dynamics and predictability of secondary eyewall formation in sheared tropical cyclones, J. Adv. Model. Earth Syst., 9, 89–112, doi:10.1002/2016MS000729.

3) One additional aspect lacking in the current analysis is a connection between the increased cooling radially outward of the inner eyewall and the mechanisms forcing the secondary eyewall formation. As an example, the authors should try and link this cooling to the boundary layer processes commonly discussed in secondary eyewall formation (e.g., Chen and Wu 2018, Fischer et al. 2020, Wang and Tang 2020) or describe some other relevant process (e.g., Trabing and Bell 2021). It was difficult for me to discern how, or if, the boundary layer forcing changed between these two simulations leading up to secondary eyewall formation and, if so, how that is related to the increased cooling radially outward of the primary eyewall. I suggest the authors take a closer look at any changes in the boundary layer forcing, such as convergence in the vicinity of the secondary eyewall and/or differences in the surface fluxes, and relate these differences back to inner eyewall structure and the cooling already discussed in the manuscript.

Cheng, C.-J., and C.-C. Wu (2018), The role of WISHE in Secondary Eyewall Formation, J. Atmos. Sci., 11, 3823–3841, doi:10.1175/JAS-D-17-0236.1

Fischer, M. S., R. F. Rogers, and P. D. Reasor (2020), The rapid intensification and Eyewall Replacement Cycles of Hurricane Irma, Mon. Wea. Rev., 3, 981–1004, doi:10.1175/MWR-D-19-0185.1

Wang, Y.-F., and Z.-M. Tan (2020), Outer Rainbands-Driven Secondary Eyewall Formation of Tropical Cyclones, J. Atmos. Sci., 6, 2217–2236, doi:10.1175/JAS-D-19-0304.1

Trabing, B. C., & Bell, M. M. (2021). The sensitivity of eyewall replacement cycles to shortwave radiation. Journal of Geophysical Research: Atmospheres, 126, e2020JD034016. https://doi. org/10.1029/2020JD034016

4) I recommend adding column labels for ‘CTL’ and ‘NSEF’ on Figures 2–4, similar to that in Figure 8.

5) (L137–140) Are these fluctuations in Vmax in CTL associated with the azimuthal mean structure (wavenumber-0) or predominantly higher wavenumbers? My speculation is these gusts are likely related to higher wavenumber structures simulated in CTL but please clarify in the manuscript if possible.

6) I am confused by the buoyancy perturbation analysis discusses (e.g., L209–214 and Eq. 1). How are the wavenumber 0 and 1 components of the perturbation field calculated? Are these related to the full wind field or only the right of shear quadrant? Also, it appears that A₀ is simply a 2d average. I would recommend refining this term as so as not be confused with the wavenumber 0 component.

7) Why was only the upshear-right quadrant chosen to discuss/show in the manuscript? Please clarify in the manuscript or consider also adding some discussion on other shear-relative quadrants.

8) I strongly recommend changing Figures 11 and 14 to clearly depict/highlight the quadrants in a shear relative coordinate system, as opposed to the cardinal directions currently used.

9) It is not clear how Eq. (2) is being solved. Please clarify in the manuscript.

Technical Corrections:

L22: change “is to further examine” to “further examines”

L23: The sentence appears incomplete I suggest adding “in the secondary eyewall formation” after “the role of the inner eyewall structure”

L46–48: Please be more descriptive here on what you mean by “a consensus has not been reached”, in terms of what?

L85–87: This sentence appears incomplete, please revise.

L203: Suggest changing “encircle” to “axisymmetrize”

L207–209: This sentence is unclear, please revise.

L262–263: Change “much diabatic warming” to “more diabatic warming”.

L346–347: This sentence is unclear, please revise or remove it.

Citation: https://doi.org/10.5194/acp-2021-147-RC2
- AC2: 'Reply on RC2', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC2
RC3:
'Comment on acp-2021-147', Anonymous Referee #3, 18 Jun 2021

I have no problem waiving my anonymity.

Michael Montgomery

Citation: https://doi.org/10.5194/acp-2021-147-RC3
- AC3: 'Reply on RC3', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC3
RC4:
'Comment on acp-2021-147', Anonymous Referee #4, 23 Jun 2021

Overall Evaluation:

I recommend major revision. In short, I am concerned about the use of two grid configurations to study secondary eyewall formation (SEF) in tropical cyclones. That a simulation with smaller grid spacing produces SEF vs the coarser simulation is not surprising considering other studies on the topic. However, grid spacing fundamentally impacts the nature of turbulence and convection, thereby making the investigation of SEF a more complex problem experimentally. I suggest fixing grid spacing and either a small ensemble approach or set of well designed sensitivity experiments. The paper does a nice job examining the formation of a moat in the control simulation, but it is not clear how valuable the coarser resolution experiment is in comparison for fundamentally understanding SEF. With a small ensemble, or sensitivity experiments with fixed grid spacing, assuming there's a wide enough variance in SEF properties, then more emphasis can be put into getting into the valuable questions on the importance of mesoscale and microphysical impacts on moat formation, descending inflow jets, etc in SEF. At the moment, it is difficult to determine whether the current manuscript adds to our existing knowledge of SEF and moat formation.

Citation: https://doi.org/10.5194/acp-2021-147-RC4
- AC4: 'Reply on RC4', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC4-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC4

Status: closed

RC1:
'Comment on acp-2021-147', Anonymous Referee #1, 06 May 2021
This study examined the role of inner eyewall structure in the formation of a secondary eyewall by performing two WRF simulations of (realistic or idealized unknown) tropical cyclones (TCs) with different horizontal grid spacings. The simulation with secondary eyewall formation (SEF) has stronger and deeper eyewall updrafts that produce more hydrometers falling out of anvil clouds outside the eyewall. The associated diabatic cooling helps induce a descending inflow beneath the outflow layer that is argued to contribute to the formation of a moat. In contrast, the simulation without SEF does not show the descending inflow and moat. The authors then emphasized the importance of accurately simulating the structure of the eyewall in the SEF.

I would like to appreciate the substantial efforts the authors made to diagnose the mechanism responsible for the formation of descending inflows outside the primary eyewall. However, after going through the paper, I fail to locate any solid evidence that can support the statement that the descending inflow outside the eyewall contributes to the SEF. The literature review is insufficient, and thus key findings from this study are mostly facts we have learned from previous studies. The model design is not clear and the experiment design with different horizontal grid spacings needs to be justified. The writing suffers from numerous grammatical errors. In some instances the grammatical issues were so severe that I could not discern the meaning of the authors. If the revised manuscript is not substantially improved to address these issues, then I will recommend rejection.

General comments:

The take-home message of this study is compared to non-SEF TCs SEF TCs have stronger intensity, and stronger upper-level inflows that descend into the boundary layer and contribute to a formation of moat. Is this a novel finding? A statistical analysis of Western North Pacific typhoons (Kuo et al. 2009) has shown that major typhoons are more likely to undergo SEF than weaker typhoons (see their Fig. 4). Additionally, a existed debate is the relative importance between strong strain flows that shear apart or suppress convection (Kossin et al. 2000; Rozoff et al. 2006) and subsidence, a component of the secondary circulation; the latter is argued to be the dominant factor by Wang et al. (2008). The related discussion is missing in the literature review. The inflow layer beneath the outflow layer for SEF TCs can be a response to momentum forcing, radiation, and many other factors, while authors only diagnosed the contribution of diabatic heating. Differences in TC structure and inflow strength between the two experiments are largely attributable to differences in TC intensity. I don’t understand the motive of revisiting these processes. Most importantly, please provide solid evidence to prove the descending inflow contributes to the SEF.

The description for experiment design and model setup is not clear. Please inform readers whether these simulations use a realistic or an idealized TC. Reasons for performing simulations with different horizontal grid spacing are missing. Comparison of inner-core structure with different model grid spacing is not fair. The usage of a traditional PBL scheme at gray-zone resolutions (e.g., 333 m) is problematic. Given these issues, I would encourage the authors to perform ensemble simulations with 1-km horizontal grid spacing and compare the simulations with and without SEF.

Different types of descending inflows have been documented in literature, including the one mentioned in this study, the one coming from the stratiform region outward of the outer rainband (Didlake et al. 2018), and the one coming from the upper levels and outward of the outer rainband (Dai et al. 2019). I would encourage the authors to discuss whether these processes are intrinsic to the SEF or they are the results of SEF based on their numerical simulations. The inflow layer beneath the outflow layer has been discussed in modeling studies (e.g., Wang et al. 2020, https://doi.org/10.1002/qj.3856). Under which situation would the inflow layer descend into the boundary layer and contribute to the moat and SEF formation? These descending inflows typically locate within a confined region around the TC center, and how do they contribute to the symmetrization of outer rainband during the SEF? These open questions need to be addressed to some extent to advance our understanding of SEF.

There are numerous grammar mistakes in the text. I only list a few. Please carefully edit the text before resubmission.

Minor comments:

Line 25: “The SEF was simulated in the experiment …” ->”The experiment with … shows a SEF”

Line 30: “Compared to the simulated …, diagnostic analysis”. Rewrite this sentence.

Line 32: Could the outflow layer itself induce an inflow layer beneath it? A complete Sawyer-Eliassen equation diagnosis is needed.

Line 58: What is “stretching time”? Probably you mean filamentation time but that needs to be defined too.

Line 63: Did Kepert (2013) use an axisymmetric boundary layer model? You may be aware SEF is typically associated with an axisymmetrization of outer rainband. What insights would you think the axisymmetric framework can provide into this phenomenon?

Lines 81-82: I agree, and why not focus on this key scientific issue in this study?

Line 86: “since” -> due to

Lines 358-359: I may miss something. Did this study discuss under which situation would upper-level inflows descend into the boundary layer?
Citation: https://doi.org/10.5194/acp-2021-147-RC1
- AC1: 'Reply on RC1', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC1
RC2:
'Comment on acp-2021-147', Anonymous Referee #2, 07 Jun 2021

General Comments:

This study examined the influences of the inner eyewall structure on the moat development, spiral rainband and subsequent secondary eyewall using a pair of model simulations with only differing horizontal grid spacing. While I believe the manuscript provides a nice discussion on the role of the strength of the inner eyewall in modifying the diabatic cooling and upper-level inflow radially outward of the primary eyewall and beneath the anvil, I believe the analysis fails to connect this cooling to the boundary layer processes which are likely forcing the secondary eyewall formation. I also have specific concerns on the choice of comparing only two simulations with differing horizontal gird spacing, specifically the fact that the CTL simulation questionably uses a PBL parameterization in the ‘gray zone’ (0.3 km) and NSEF uses horizontal grid spacing of 1 km and a PBL parameterization.

Specific Comments:

1) The choice of comparing two simulations with different innermost grid spacing (0.3 km vs 1 km) is odd to me. For one, grid spacing of 0.3 km is within the turbulent ‘gray zone’ so the choice of using a PBL parameterization is questionable (e.g., Green and Zhang 2015 and Honert et al. 2020). In addition, the finest resolved eddies will be different between the two simulations, and it is not clear to me how to interpret these differences in terms of the results presented. This is especially true in comparing with the results of Green and Zhang (2015). Green and Zhang showed that the development of the secondary eyewall in their simulations (ranging in horizontal grid spacing from 111 m – 3 km) was sensitive to how the turbulence was parameterized. More specifically, they noted that none of the simulations without a planetary boundary layer parametrization simulated the development of a secondary eyewall, suggesting strong sensitivity of secondary eyewall formation to the parameterization of turbulence in the ‘gray zone’. I think it is important that the authors reconsider their choice in comparing two simulations with different horizontal grid spacing in order to more easily interpret their results.

Honnert, R., Efstathiou, G., Beare, R., Ito, J., Lock, A., Neggers, R., et al. (2020). The atmospheric boundary layer and the “gray zone” of turbulence: A critical review. Journal of Geophysical Research: Atmospheres, 125, e2019JD030317. https://doi.org/10.1029/2019JD030317

Green, B. W., and F. Zhang (2015), Numerical simulations of Hurricane Katrina (2005) in the turbulent gray zone, J. Adv. Model. Earth Syst., 07, doi:10.1002/2014MS000399.

2) Partially related to my first comment, I am not convinced that the differences in secondary eyewall formation can be completely attributed to the differences in the inner eyewall structure and not other differences related to the varying horizontal grid spacing between the two simulations and small-scale boundary layer perturbations, potentially related to differences in the model representation of turbulence. As one example, Zhang et al. (2014) demonstrated that secondary eyewall formation is sensitive to very small differences in initial conditions. As a result, I recommend the authors consider revisiting the role of the inner eyewall structure in secondary eyewall formation using a small ensemble with the same model set up.

Zhang, F., D. Tao, Y. Q. Sun, and J. D. Kepert (2017), Dynamics and predictability of secondary eyewall formation in sheared tropical cyclones, J. Adv. Model. Earth Syst., 9, 89–112, doi:10.1002/2016MS000729.

3) One additional aspect lacking in the current analysis is a connection between the increased cooling radially outward of the inner eyewall and the mechanisms forcing the secondary eyewall formation. As an example, the authors should try and link this cooling to the boundary layer processes commonly discussed in secondary eyewall formation (e.g., Chen and Wu 2018, Fischer et al. 2020, Wang and Tang 2020) or describe some other relevant process (e.g., Trabing and Bell 2021). It was difficult for me to discern how, or if, the boundary layer forcing changed between these two simulations leading up to secondary eyewall formation and, if so, how that is related to the increased cooling radially outward of the primary eyewall. I suggest the authors take a closer look at any changes in the boundary layer forcing, such as convergence in the vicinity of the secondary eyewall and/or differences in the surface fluxes, and relate these differences back to inner eyewall structure and the cooling already discussed in the manuscript.

Cheng, C.-J., and C.-C. Wu (2018), The role of WISHE in Secondary Eyewall Formation, J. Atmos. Sci., 11, 3823–3841, doi:10.1175/JAS-D-17-0236.1

Fischer, M. S., R. F. Rogers, and P. D. Reasor (2020), The rapid intensification and Eyewall Replacement Cycles of Hurricane Irma, Mon. Wea. Rev., 3, 981–1004, doi:10.1175/MWR-D-19-0185.1

Wang, Y.-F., and Z.-M. Tan (2020), Outer Rainbands-Driven Secondary Eyewall Formation of Tropical Cyclones, J. Atmos. Sci., 6, 2217–2236, doi:10.1175/JAS-D-19-0304.1

Trabing, B. C., & Bell, M. M. (2021). The sensitivity of eyewall replacement cycles to shortwave radiation. Journal of Geophysical Research: Atmospheres, 126, e2020JD034016. https://doi. org/10.1029/2020JD034016

4) I recommend adding column labels for ‘CTL’ and ‘NSEF’ on Figures 2–4, similar to that in Figure 8.

5) (L137–140) Are these fluctuations in Vmax in CTL associated with the azimuthal mean structure (wavenumber-0) or predominantly higher wavenumbers? My speculation is these gusts are likely related to higher wavenumber structures simulated in CTL but please clarify in the manuscript if possible.

6) I am confused by the buoyancy perturbation analysis discusses (e.g., L209–214 and Eq. 1). How are the wavenumber 0 and 1 components of the perturbation field calculated? Are these related to the full wind field or only the right of shear quadrant? Also, it appears that A₀ is simply a 2d average. I would recommend refining this term as so as not be confused with the wavenumber 0 component.

7) Why was only the upshear-right quadrant chosen to discuss/show in the manuscript? Please clarify in the manuscript or consider also adding some discussion on other shear-relative quadrants.

8) I strongly recommend changing Figures 11 and 14 to clearly depict/highlight the quadrants in a shear relative coordinate system, as opposed to the cardinal directions currently used.

9) It is not clear how Eq. (2) is being solved. Please clarify in the manuscript.

Technical Corrections:

L22: change “is to further examine” to “further examines”

L23: The sentence appears incomplete I suggest adding “in the secondary eyewall formation” after “the role of the inner eyewall structure”

L46–48: Please be more descriptive here on what you mean by “a consensus has not been reached”, in terms of what?

L85–87: This sentence appears incomplete, please revise.

L203: Suggest changing “encircle” to “axisymmetrize”

L207–209: This sentence is unclear, please revise.

L262–263: Change “much diabatic warming” to “more diabatic warming”.

L346–347: This sentence is unclear, please revise or remove it.

Citation: https://doi.org/10.5194/acp-2021-147-RC2
- AC2: 'Reply on RC2', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC2
RC3:
'Comment on acp-2021-147', Anonymous Referee #3, 18 Jun 2021

I have no problem waiving my anonymity.

Michael Montgomery

Citation: https://doi.org/10.5194/acp-2021-147-RC3
- AC3: 'Reply on RC3', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC3-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC3
RC4:
'Comment on acp-2021-147', Anonymous Referee #4, 23 Jun 2021

Overall Evaluation:

I recommend major revision. In short, I am concerned about the use of two grid configurations to study secondary eyewall formation (SEF) in tropical cyclones. That a simulation with smaller grid spacing produces SEF vs the coarser simulation is not surprising considering other studies on the topic. However, grid spacing fundamentally impacts the nature of turbulence and convection, thereby making the investigation of SEF a more complex problem experimentally. I suggest fixing grid spacing and either a small ensemble approach or set of well designed sensitivity experiments. The paper does a nice job examining the formation of a moat in the control simulation, but it is not clear how valuable the coarser resolution experiment is in comparison for fundamentally understanding SEF. With a small ensemble, or sensitivity experiments with fixed grid spacing, assuming there's a wide enough variance in SEF properties, then more emphasis can be put into getting into the valuable questions on the importance of mesoscale and microphysical impacts on moat formation, descending inflow jets, etc in SEF. At the moment, it is difficult to determine whether the current manuscript adds to our existing knowledge of SEF and moat formation.

Citation: https://doi.org/10.5194/acp-2021-147-RC4
- AC4: 'Reply on RC4', Nannan Qin, 14 Aug 2021
  
  The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-147/acp-2021-147-AC4-supplement.pdf
  
  Citation: https://doi.org/10.5194/acp-2021-147-AC4

Nannan Qin, Liguang Wu, and Qingyuan Liu

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May 2021	53	11	1	65
Jun 2021	76	20	3	99
Jul 2021	27	13	2	42
Aug 2021	42	14	6	62
Sep 2021	35	21	1	57
Oct 2021	33	92	0	125
Nov 2021	31	51	0	82
Dec 2021	21	11	0	32
Jan 2022	15	7	1	23
Feb 2022	14	5	0	19
Mar 2022	12	7	0	19
Apr 2022	17	8	0	25
May 2022	3	5	1	9
Jun 2022	3	1	1	5
Jul 2022	6	4	0	10
Aug 2022	9	4	0	13
Sep 2022	16	3	0	19
Oct 2022	9	2	0	11
Nov 2022	5	7	0	12
Dec 2022	16	6	0	22
Jan 2023	61	13	0	74
Feb 2023	55	23	1	79
Mar 2023	60	11	0	71
Apr 2023	62	8	0	70
May 2023	55	4	2	61
Jun 2023	58	10	0	68
Jul 2023	44	19	1	64
Aug 2023	51	6	0	57
Sep 2023	13	10	1	24
Oct 2023	12	5	0	17
Nov 2023	10	5	3	18
Dec 2023	15	4	1	20
Jan 2024	16	4	0	20
Feb 2024	25	8	2	35
Mar 2024	30	9	0	39
Apr 2024	45	1	1	47

Cumulative views and downloads (calculated since 07 Apr 2021)

Month	HTML	PDF	XML	Total
Apr 2021	147	36	4	187
May 2021	53	11	1	65
Jun 2021	76	20	3	99
Jul 2021	27	13	2	42
Aug 2021	42	14	6	62
Sep 2021	35	21	1	57
Oct 2021	33	92	0	125
Nov 2021	31	51	0	82
Dec 2021	21	11	0	32
Jan 2022	15	7	1	23
Feb 2022	14	5	0	19
Mar 2022	12	7	0	19
Apr 2022	17	8	0	25
May 2022	3	5	1	9
Jun 2022	3	1	1	5
Jul 2022	6	4	0	10
Aug 2022	9	4	0	13
Sep 2022	16	3	0	19
Oct 2022	9	2	0	11
Nov 2022	5	7	0	12
Dec 2022	16	6	0	22
Jan 2023	61	13	0	74
Feb 2023	55	23	1	79
Mar 2023	60	11	0	71
Apr 2023	62	8	0	70
May 2023	55	4	2	61
Jun 2023	58	10	0	68
Jul 2023	44	19	1	64
Aug 2023	51	6	0	57
Sep 2023	13	10	1	24
Oct 2023	12	5	0	17
Nov 2023	10	5	3	18
Dec 2023	15	4	1	20
Jan 2024	16	4	0	20
Feb 2024	25	8	2	35
Mar 2024	30	9	0	39
Apr 2024	45	1	1	47

Viewed (geographical distribution)

Total article views: 1,709 (including HTML, PDF, and XML) Thereof 1,709 with geography defined and 0 with unknown origin.

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Latest update: 23 Apr 2024

Short summary

Understanding of the secondary eyewall formation is a critical issue to improve the prediction of tropical cyclone intensity. Numerical experiments are conducted to explore the roles of the inner eyewall structure in the secondary eyewall formation. It is found that the inner eyewall structure plays an important role in the secondary eyewall formation of the simulated tropical cyclone.


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