How Does Cloud-Radiative Heating over the North Atlantic Change with Grid Spacing, Convective Parameterization, and Microphysics Scheme?
Abstract. Cloud-radiative heating (CRH) within the atmosphere and its changes with warming affect the large-scale atmospheric wind patterns in a myriad of ways, such that reliable predictions and projections of circulation require reliable calculations of CRH. In order to assess sensitivities of upper-tropospheric midlatitude CRH to model settings, we perform a series of simulations with the Icosahedral Nonhydrostatic Model (ICON) over the North Atlantic using six different grid spacings, parameterized and explicit convection, and one- versus two-moment cloud microphysics. While sensitivity to grid spacing is limited, CRH profiles change dramatically with microphysics and convection schemes. These dependencies are interpreted via decomposition into cloud classes and examination of cloud properties and cloud-controlling factors within these different classes. We trace the model dependencies back to differences in the mass mixing ratios and number concentrations of cloud ice and snow, as well as vertical velocities. Which frozen species are radiatively active and the coupling of microphysics and convection schemes turn out to be crucial factors in altering the modeled CRH profiles.
Sylvia Sullivan et al.
Status: open (until 25 Apr 2023)
- RC1: 'Reviewer comment on egusphere-2023-109', Anonymous Referee #1, 22 Feb 2023 reply
- CEC1: 'Comment on egusphere-2023-109', Astrid Kerkweg, 14 Mar 2023 reply
- RC2: 'Comment on egusphere-2023-109', Anonymous Referee #2, 22 Mar 2023 reply
Sylvia Sullivan et al.
Model Dependencies of Cloud-Radiative Heating over the North Atlantic [postprocessed dataset] https://doi.org/10.5281/zenodo.7236564
Sylvia Sullivan et al.
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This study explores the sensitivity of model representation of atmospheric cloud radiative heating profiles over the North Atlantic to changes in grid resolution, atmospheric convection (explicit or parameterized), and microphysics scheme within the ICON model. While grid resolution is only found to play a small role, cloud radiative heating profiles are highly sensitive to the model representation of convection and microphysics. In particular, the role of cloud ice mass mixing ratio appears to play a critical role.
This manuscript provides a good discussion of the factors governing atmospheric cloud radiative heating profiles at midlatitudes in the ICON model. Technically, the manuscript is sound and just needs some minor corrections/clarifications (detailed below). However, my general impression in reading this paper is that I’m not sure GMD is really the right journal for this work. The manuscript is using the model output data set from a previous study (Senf et al. 2020) and really not describing fundamentally new methods, rather just extending the authors’ previous work from the tropics to the midlatitudes. I'll leave it to the editor to decide whether GMD is the appropriate venue for this work.
Lines 9-10: Isn’t this point (coupling of microphysics and convection schemes) just a hypothesis provided at the end of the paper (Line 352-360)? If so, it doesn’t belong in the abstract as a statement of certainty. I don’t see any formal evidence presented to support this conjecture.
Lines 23-25: Lu et al. (2007) do not discuss cloud-radiative impacts, and models do not agree on whether the presence of cloud radiative effects drive a poleward circulation shift (see discussion in Voigt et al. 2020 review). For example, Li et al. (2015) do not find a poleward expansion of the circulation due to the presence of cloud radiative effects, and they actually show that cloud-radiative effects decrease the static stability in the tropics.
Line 32: The intensification of ENSO due to cloud radiative effects is again a model dependent result. Middlemas et al. (2019) found a differing effect on ENSO.
Lines 136-137: More detail probably needs to be provided here to explain this conclusion, as the numbers in Table S1 do in fact look quite sensitive to the particular thresholds used.
Lines 146-155: It also seems important to note/discuss here that the altitude of the lower and upper tropospheric cooling peaks differs fairly significantly by model.
Lines 169-170: Also convective heating rates appear to be important in this layer
Lines 172-173: Also, the cooling peak appears to be slightly higher in altitude in the one-moment scheme
Line 180, typo: Change “Then” to “The”
Lines 184-185: Also, a large heating peak develops at lower altitudes, which is not present in the simulations with the deep convective parameterization
Lines 221-227: Good to double check the percentage values quoted in this paragraph. They appear to match what is shown in Fig. S3, not Fig. 7.
Lines 230-232: Can you provide a physical explanation for why the isolated high clouds warm and the deeper clouds cool?
Line 243 (and hereafter): The term “higher grid spacing” could be confusing and could imply coarser resolution to some readers. I would either say “higher resolution” or “finer grid spacing”.
Line 269: It doesn’t look like a factor of four. At best, it looks like a factor of two.
Line 271: The relative increase actually appears stronger in the thin cloud layers.
Lines 317, 325: This citation structure is confusing. Initially, I was looking for Fig. 10a and Table 2 in this paper. Please clarify that this figure and table are in the Sullivan et al. (2022) paper, and not this paper.
Line 328: I think you need to elaborate more on why you choose “supersaturation generated by vertical velocity” as one of your cloud controlling factors. The other two are obvious from the above equations, but this one is less obvious.
Line 384, typo: boundary
Figure 1 caption: North Africa, as well
Code and data availability: available is misspelled.
Li, Y., Thompson, D. W. J., & Bony, S. (2015). The influence of atmospheric cloud radiative effects on the large-scale atmospheric circulation.
Journal of Climate, 8, 7263–7278. https://doi.org/10.1175/JCLI-D-14-00825.1
Middlemas, E. A., Clement, A. C., Medeiros, B., & Kirtman, B. (2019). Cloud radiative feedbacks and El Niño–southern oscillation. Journal
of Climate, 32(15), 4661–4680. https://doi.org/10.1175/JCLI-D-18-0842.1