Articles | Volume 25, issue 3
https://doi.org/10.5194/acp-25-1477-2025
© Author(s) 2025. This work is distributed under the Creative Commons Attribution 4.0 License.
Technical note: Recommendations for diagnosing cloud feedbacks and rapid cloud adjustments using cloud radiative kernels
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- Final revised paper (published on 03 Feb 2025)
- Preprint (discussion started on 12 Sep 2024)
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- RC1: 'Comment on egusphere-2024-2782', Anonymous Referee #1, 04 Nov 2024
- RC2: 'Comment on egusphere-2024-2782', Anonymous Referee #2, 09 Nov 2024
- AC1: 'Comment on egusphere-2024-2782', Mark Zelinka, 22 Nov 2024
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AR by Mark Zelinka on behalf of the Authors (22 Nov 2024)
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ED: Publish as is (22 Nov 2024) by Matthew Lebsock
AR by Mark Zelinka on behalf of the Authors (23 Nov 2024)
Cloud radiative feedbacks and rapid adjustments, both prime sources of climate model uncertainty, are increasingly diagnosed in climate models and observations using the cloud radiative kernel (CRK) technique. A limitations of how CRKs are typically applied is that they rely on either passive satellite data or model output that mimics passive satellite data which, in either case, can provide a misleading representation of the low cloud behavior as the passively sensed high clouds obscure lower level changes. Likewise, nonlow cloud radiative changes can be misinterpreted when the observation/simulator is misrepresenting the low cloud state.This technical note addresses this issue, providing a guide and code for overcoming this issue as best as possible. It then demonstrates the extent to which this obscuration effect can bias the magnitude (and in some cases sign) of the low and nonlow cloud feedbacks (or adjustments). This manuscript is well written, very polished, and timely, as the passive satellite simulators needed to apply this method in models figure to play a large role in the upcoming CMIP7. I have a few comments below I hope the authors can address, but otherwise this manuscript is in good shape for publication.
Equation 1 and surrounding text: If I understand correctly, framing of fractionally unobscured, or clear-sky fraction, is really only relevant in the context of grid-scale histograms,. Whereas, at the actual satellite pixel-level, we can’t really differentiate between fractions of cloudiness/obscuration. I think it’s worth clarifying if so that this is specifically applicable to the use of CRKs /joint histograms and not pixel-level analysis.
Section 3: One can imagine a scenario where high cloud fraction changes between the perturbed and control state while a low cloud appears in the perturbed state that truly was not present in the control state. How is this scenario differentiated from the scenario in Figure 1 where it is assumed there is no low cloud in the control state even though it is present and just fully obscured? The former scenario is a covariance term case while the latter is an obscuration term case, but can output provided by the simulator actually distinguish between the two?
Page 8 footnote: The text mentions that the ISCCP retrieval algorithm reports a single cloud type using the optical depth integrated across all cloud types, including a lower-level cloud beneath an upper-level cloud. Does this suggest a disconnect between the model simulator, which would know a low-cloud is present as generated by the model subcolumn, vs. an actual ISCCP passive satellite retrieval which could not see the low level cloud and thus would not be accounting for any low cloud in the optical depth/integrated extinction estimate? Or am I missing something?
Line 240-248: Total feedback magnitude is conserved with these corrections as they are essentially just moving radiative changes from one category to another, but is total feedback inter-model spread not conserved? If both low and noncloud cloud amount feedback spread are reduced as noted in this paragraph, that must mean either total feedback spread is able to decrease, or it means another type of cloud feedback’s spread is increasing after these corrections in order for total cloud feedback inter-model spread to remain the same.