the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 14 Mar 2024
Influence of mid-latitude Sea Surface Temperature Fronts on the Atmospheric Water Cycle and Storm Track Activity
Abstract. The climatological mean turbulent air-sea heat exchange maximises along midlatitude sea surface temperature (SST) fronts that anchor midlatitude storm tracks. This implies a crucial role of the air-sea latent heat exchange along the SST fronts on the atmospheric water cycle and storm tracks through the intensification of atmospheric cyclones and their associated precipitation. We investigate the sensitivity of the atmospheric water cycle to the SST front through a set of aqua-planet experiments. Varying the latitude of a zonally symmetric midlatitude SST front, the midlatitude atmospheric water cycle responds through distinct changes in surface latent heat fluxes, precipitation, as well as atmospheric moisture fluxes, whereas the tropical latitudes remain largely unchanged. As storm tracks are self-maintained through the diabatic generation of eddy available potential energy, the position of the storm track is diabatically anchored at the SST front. While the position of the SST front determines the position of the eddy moisture convergence and thus the diabatic heating that energises the storm track, the underlying SST determines the general strength of the water cycle and thus the intensity of the storm track. The strong connection identified between the eddy moisture flux and the SST front implies a diabatic pathway of latent heating to anchor the storm track along SST fronts.
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- RC1: 'Comment on egusphere-2024-735', Anonymous Referee #1, 21 Apr 2024
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CC1: 'Comment on egusphere-2024-735', Justin Small, 12 May 2024
Review of Ogawa and Spengler, “Influence of mid-latitude Sea Surface Temperature fronts on the atmospheric water cycle and storm track activity” submitted to EGUsphere.
This paper investigates the effect of diabatic processes at SST fronts on the water cycle and Extratropical storm track. The tool is an aqua-planet model which has been often used in previous studies, but still provides some useful insight. By necessity, the experiments are idealized. The analysis, of moisture budgets and Lorenz energy cycle, is sophisticated and thorough, and the interpretation very reasonable. They find that the latitude of the SST front plays a key role in determining the Extratropical water cycle and storm track, extending previous work by Sampe, H. Nakamura and Ogawa that focused on more basic storm track metrics. The hydrologic cycle is a key aspect of climate state and climate variability, and I think this novel work should be published subject to the revisions suggested below. I indicate Major Revisions because it may take some time to address some of my points including figure re-plotting, but I do not have major disagreements on the main points.
Justin Small, NCAR
Main Comments
Line 45 and line 225-227 . The low level baroclinicity is not really discussed further in the paper. Can you say something about the relative role of the diabatic processes discussed in this paper vs the baroclinicity? Can you relate it to the Lorenz energy cycle, perhaps?
Line 251. I am thinking that your global “+/-5K” simulations also significantly warm/cool the Tropics, which may teleconnect to Extratropics. Can you think of an experiment to focus on SST changes in Extratropics only? (This may be difficult as it is likely to add an artificial meridional gradient of SST).
Other comments
Fig. 2. The line plots are all dominated by the signal in the Tropics, and this is quite similar between cases, as you describe. You could have one panel with the full fields (F45 or REF), and other panels are differences from that case.
Line 2. “implies a crucial role”-> “suggests”. The first sentence only noted a spatial correspondence which is not conclusive in itself.
Line 18 “maximize in the Extratropics” – as you must be excluding the ITCZ in this sentence.
Line 58. Add a sentence describing convective and large-scale parameterizations, as these are analyzed in the paper.
Equations 9-22 are quite extensive! In my copy, I did not see where CZ is defined. Maybe Q is not defined, and DAPE and DKIN.
Line 138. In practice, there is usually some small trend, either drift or interannual variability.
Lines 175-179. Please specify where you are talking about Fig. 3a or Fig. #c.
Line 181 For reference to C_m, should this be” (black line, Fig. 2b)”
Line 190. “(Fig. 2b)” ?
Lines 191-197. Consider first discussing the REF experiment, which has biggest difference to F45, before discussing the other latitude cases. You might also point out that F_m looks very similar between F45 and REF.
Line 199. Convergence of F -> “(Fig. 3a and Fig. 3c)” i.e. F is the total.
Fig. 8. Typos in caption, should be F45+5 etc.
The shaded fields in Fig. 3 and 4 are all parts of the moisture budget. Would it be useful to show all on the same color bar, as they should balance? This may be difficult as I note Figs 4e,f are on a much larger range color bar (meaning there must be substantial cancellation, probably by convective param., which presumably saturates the color bar).
Line 229. 850hPa to 200hPa – why not from surface?
Line 238. CA does change significantly in the REF experiment – I think this is consistent with Sampe et al. 2010, and should be mentioned.
Line 246. “in winter but not in summer (Fig. 6c)”
Fig. 7 – consider showing as differences, F45+5 minus F45 etc.
Fig. 8a – CA does not change much because the baroclinicity is not changed when adding/subtracting a fixed SST?
Citation: https://doi.org/10.5194/egusphere-2024-735-CC1 -
AC1: 'Comment on egusphere-2024-735', Fumiaki Ogawa, 14 Jun 2024
Please find the supplement where replies to both RC1 and CC1 are found.
- AC2: 'Reply on AC1', Fumiaki Ogawa, 14 Jun 2024
Status: closed
- RC1: 'Comment on egusphere-2024-735', Anonymous Referee #1, 21 Apr 2024
-
CC1: 'Comment on egusphere-2024-735', Justin Small, 12 May 2024
Review of Ogawa and Spengler, “Influence of mid-latitude Sea Surface Temperature fronts on the atmospheric water cycle and storm track activity” submitted to EGUsphere.
This paper investigates the effect of diabatic processes at SST fronts on the water cycle and Extratropical storm track. The tool is an aqua-planet model which has been often used in previous studies, but still provides some useful insight. By necessity, the experiments are idealized. The analysis, of moisture budgets and Lorenz energy cycle, is sophisticated and thorough, and the interpretation very reasonable. They find that the latitude of the SST front plays a key role in determining the Extratropical water cycle and storm track, extending previous work by Sampe, H. Nakamura and Ogawa that focused on more basic storm track metrics. The hydrologic cycle is a key aspect of climate state and climate variability, and I think this novel work should be published subject to the revisions suggested below. I indicate Major Revisions because it may take some time to address some of my points including figure re-plotting, but I do not have major disagreements on the main points.
Justin Small, NCAR
Main Comments
Line 45 and line 225-227 . The low level baroclinicity is not really discussed further in the paper. Can you say something about the relative role of the diabatic processes discussed in this paper vs the baroclinicity? Can you relate it to the Lorenz energy cycle, perhaps?
Line 251. I am thinking that your global “+/-5K” simulations also significantly warm/cool the Tropics, which may teleconnect to Extratropics. Can you think of an experiment to focus on SST changes in Extratropics only? (This may be difficult as it is likely to add an artificial meridional gradient of SST).
Other comments
Fig. 2. The line plots are all dominated by the signal in the Tropics, and this is quite similar between cases, as you describe. You could have one panel with the full fields (F45 or REF), and other panels are differences from that case.
Line 2. “implies a crucial role”-> “suggests”. The first sentence only noted a spatial correspondence which is not conclusive in itself.
Line 18 “maximize in the Extratropics” – as you must be excluding the ITCZ in this sentence.
Line 58. Add a sentence describing convective and large-scale parameterizations, as these are analyzed in the paper.
Equations 9-22 are quite extensive! In my copy, I did not see where CZ is defined. Maybe Q is not defined, and DAPE and DKIN.
Line 138. In practice, there is usually some small trend, either drift or interannual variability.
Lines 175-179. Please specify where you are talking about Fig. 3a or Fig. #c.
Line 181 For reference to C_m, should this be” (black line, Fig. 2b)”
Line 190. “(Fig. 2b)” ?
Lines 191-197. Consider first discussing the REF experiment, which has biggest difference to F45, before discussing the other latitude cases. You might also point out that F_m looks very similar between F45 and REF.
Line 199. Convergence of F -> “(Fig. 3a and Fig. 3c)” i.e. F is the total.
Fig. 8. Typos in caption, should be F45+5 etc.
The shaded fields in Fig. 3 and 4 are all parts of the moisture budget. Would it be useful to show all on the same color bar, as they should balance? This may be difficult as I note Figs 4e,f are on a much larger range color bar (meaning there must be substantial cancellation, probably by convective param., which presumably saturates the color bar).
Line 229. 850hPa to 200hPa – why not from surface?
Line 238. CA does change significantly in the REF experiment – I think this is consistent with Sampe et al. 2010, and should be mentioned.
Line 246. “in winter but not in summer (Fig. 6c)”
Fig. 7 – consider showing as differences, F45+5 minus F45 etc.
Fig. 8a – CA does not change much because the baroclinicity is not changed when adding/subtracting a fixed SST?
Citation: https://doi.org/10.5194/egusphere-2024-735-CC1 -
AC1: 'Comment on egusphere-2024-735', Fumiaki Ogawa, 14 Jun 2024
Please find the supplement where replies to both RC1 and CC1 are found.
- AC2: 'Reply on AC1', Fumiaki Ogawa, 14 Jun 2024
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