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?