Estimating the potential cooling effect of cirrus thinning achieved via the seeding approach

Liu, Jiaojiao; Shi, Xiangjun

doi:https://doi.org/10.5194/acp-21-10609-2021

Articles | Volume 21, issue 13

https://doi.org/10.5194/acp-21-10609-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/acp-21-10609-2021

© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 21, issue 13

Research article

|

14 Jul 2021

Research article |

| 14 Jul 2021

Estimating the potential cooling effect of cirrus thinning achieved via the seeding approach

Jiaojiao Liu and Xiangjun Shi

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Final revised paper (published on 14 Jul 2021)
Preprint (discussion started on 01 Mar 2021)

Interactive discussion

Status: closed

RC1:
'Comment on acp-2021-148', Blaž Gasparini, 22 Mar 2021

The comment was uploaded in the form of a supplement: https://acp.copernicus.org/preprints/acp-2021-148/acp-2021-148-RC1-supplement.pdf

Citation: https://doi.org/10.5194/acp-2021-148-RC1
- AC1: 'Reply on RC1', Jiaojiao Liu, 29 May 2021
  
  We thank the reviewer for the helpful comments. Point-to-point responses are uploaded as a supplement in this post.
  
  Citation: https://doi.org/10.5194/acp-2021-148-AC1
RC2:
'Comment on acp-2021-148', Anonymous Referee #2, 22 Apr 2021

Review of "Estimating the potential cooling effect of cirrus thinning achieved via

the seeding approach" by Liu and Shi

This manuscript documents experiments with variable ice nucleation number, by adjusting the ice concentration in a GCM to prevent homogenous freezing and thin cirrus clouds as a form of geo engineering. The manuscript is well written and thought out. It should be publishable in ACP with minor revisions.

My major concern is a lot of the effects are from liquid and mixed phase clouds that the method is not directly perturbing. Or should not be directly perturbing. But the mechanism is not explained well in the text. It is not clear if the compensating effects for mixed and liquid clouds from adding ice crystals to pure ice clouds is an artifact of the model, or has a solid physical basis. This should be detailed further in the discussion of the cases and the conclusions. It may require a bit more in depth analysis.

Specific comments:

Page 1, L11: is cooling positive or negative? Do the values in lines 10 and 11 with different signs represent the same direction? Please clarify: if the same direction then should be the same sign.

Page 1, L14: cirrus clouds typically do not contain liquid, so why would cirrus seeding impact mixed phase clouds?

Page 1, L16: could yield. Also, what sign is intended here?

Page 3, L80: this seems like a pretty significant change to shut off homogeneous freezing below 205K. What is the impact of that?

Page 4, L97: I think the formulas are an important part of the study, and should be in the main text.

Page 5, L134: if you add ice number do you have to worry about conservation or inconsistencies? Not for number, but do such affects bleed into humans.

Page 5, L140: does the ice added feedback through the microphysics ?

Page 10, L226: for clarity maybe you could pull out the global mean values into a table or a set of histograms.

Page 10, L240: please name and make a formal equation for the seeding effectiveness.

Page 12, L274: can you comment more on the mechanism: why does adding ICs impact mixed phase and liquid clouds? Is this a real effect or a feature of the model formulation?

Page 12, L283: can you explain in a sentence or so why N increases with decreasing R?

Page 12, L284: which experiments are “these”?

Page 12, L285-7: Im lost here. I thought the point of seeding was not to reach Sihom? Please clarify.

Page 14, L314: can you explain why? Does it have to do with liquid and mixed phase clouds?

Page 14, L324: but don’t you need INP to make IC?

Page 15, L311: This is attributed to...

Page 15, L342: what is the mechanism for the effects on liquid and mixed phase clouds? You need to figure out of this is real or an artifact of the bulk model physics.

Page 15, L353: is sedimentation the mechanism then? Can you test that?

Page 17, L388: you say ICs increase W, but then contradict that in the next phase. This is confusing and unclear.

Citation: https://doi.org/10.5194/acp-2021-148-RC2
- AC2: 'Reply on RC2', Jiaojiao Liu, 29 May 2021
  
  We thank the reviewer for the helpful comments. Point-to-point responses are uploaded as a supplement in this post.
  
  Citation: https://doi.org/10.5194/acp-2021-148-AC2

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Jiaojiao Liu on behalf of the Authors (29 May 2021) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (01 Jun 2021) by Martina Krämer

RR by Anonymous Referee #2 (02 Jun 2021)

RR by Blaž Gasparini (12 Jun 2021)

ED: Publish as is (15 Jun 2021) by Martina Krämer

AR by Jiaojiao Liu on behalf of the Authors (17 Jun 2021)

Short summary

Cirrus thinning, which reduces the warming effect of cirrus clouds, has been investigated as a new geoengineering approach. In this study, a flexible seeding method is used to exploit the potential cooling effect of cirrus thinning. Simulation results show that the seeding method is essential for estimating the cooling effect. Cirrus thinning with the flexible seeding method could produce a considerable cooling effect, which is much stronger than the fixed seeding method.