Interactive comment on “Diagnostics of the Tropical Tropopause Layer from in-situ observations and CCM data”

This study compares recent aircraft measurements of ozone and water vapour in the tropical tropopause region with data from the chemistry climate model ECHAM/MESSy in free running mode using different recently developed diagnostics mainly for use in the extra-tropics. The application of these diagnostics to tropical aircraft data is new and interesting not only from a model-measurement comparison point of view and makes the study certainly worth publishing. The manuscript, however, needs some improvement before I can recommend publication in ACP. In particular, the authors need to be clearer in their conclusions about what the new results are and where their results just conﬁrm already published results. E.g. they should clearly state, what we learned about the model’s performance, and if the diagnostics previously applied to the

extratropics are also valuable for validation in the TTL. In particular I would try to get an answer, if their approach to use the QBO phase instead of a multi-annual mean helps to improve the comparison.
Improvements are needed along the comments stated below along with a list of technical comments, asking for some changes in the language used, but which is far from being complete.
Specific comments: P11660 L22-26: This sentence to me belongs into the introduction, so to motivate why you perform this analysis. Here in the abstract, on the other hand, you rather need to say based on your results, if the model does represent the TTL structure accurately, or if the application of the new diagnostics can be regarded as useful or not.
P11663 L20-23: I do not think you investigate and show with your evaluations that these couple tracer profiles are representative for the whole TTL mean fine scale structure. Rather your results seem to show that the measurements are influenced by the particular sampling during the aircraft campaigns. You need to either improve your evaluations or take this claim out of the manuscript. (see also comment further below) P11665 L12: add '...along with their accuracy and precision' P11666 L22: I did not really follow your approach here. First, 'temporal location' sounds awkward. Rather use something like 'temporal sequence'. However, the campaigns are not marked in their real temporal sequence (TH and TR should be before SC). Is this because of your selection according to the QBO? P11667: Methodology section: this section might be improved by structuring it a little more. E.g. different subsections for different diagnostics used plus a section on how you handle the data (QBO-classification).
P11670 L16-26: I think this is an interesting approach to sample according to the QBO phase. Has this been done before? If so give references, if not, you should explain C2538

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Interactive Discussion Discussion Paper your motivation for using this approach.
P116672 L6-8: This seems unnecessary/wrong information. The profiles are plotted relative to the tropopause heights, so the dashed-dotted line corresponds to the thermal tropopause of both, the measurements and the models. You did plot the model data also relative to the thermal tropopause, no?
P11672 L10-14: Interesting, and you can see the same feature even in the N2O profiles, where the N2O values are higher than expected across the tropopause. A crosslink between this finding and the N2O section would be helping the reader to tie the conclusions together. Also, rather than just describing what Hector is, the manuscript would improve if you said more directly, that ECHAM Messy just can't resolve this particular feature. In the end the conclusion here tells me that the SCOUT -Darwin measurements are not representative for the mean fine-scale structure of the tropics, so you might want to add or change this in the conclusions.
P11674 L25-30: This is written in an obscured way. It is well-know that there is a seasonal cycle in tropopause/lower stratospheric H2O due to the seasonal cycle in temperature. Please include some refrence.
P11675 L2: The main sink of N2O (90 percent) is photolysis. Please add a statement.
P11676 L18: I suggest trying to color the data points according to potential temperature bins. This is because 12 hPa at different altitudes may span different widths in km due to differences in the mean height of the tropopause, which may make your comparison worse than it really is.
P11677 L0-4: I think this is also not a new finding, please include some references. Discussion Paper P11680 L5-12: this sounds contradictory to the findings of Gettelman and Birner, you need to point out that you refer to the fine scale mean and not the large scale structure, which they found most of the models were capable of resolving.
P11680 L23-26: This comment is just a matter of presentation. As it is written now, one could get the sense that you discovered the TTL (this is a problem found throughout the manuscript to some extent). Since the TTL is already known to exist you may rather write something along these lines: 'indeed the diagnostics used formerly in the extratropics can also be used to capture the TTL'. P11681 L20-24: I don't think this statement is true. The campaigns with strong convection show clear differences between model and measurements (e.g. Troccinox N2O profiles, SCOUT-Darwin/AMMA O3 profiles). This is likely due to the strong effect of convection as you interpret earlier. This finding has to be clearly stated. It is not pejorative of your results, rather adds an interesting angle to your evaluations, namely that the aircraft measurements may show a sampling bias (since they were designed to look into convection). Along this line, also add a caveat to your last statement 11682 L4-7, namely that the specific focus of the different campaigns may have influenced the outcome of the model-measurement comparison.