Interactive comment on “ Global stratospheric hydrogen peroxide distribution from MIPAS-Envisat full resolution spectra compared to KASIMA model results ” by S .

MIPAS-ENVISAT full resolution spectra were analyzed to obtain a global distribution of hydrogen peroxide (H2O2) in the stratosphere. H 2O2 acts as reservoir gas for the HOx family (= H+OH+HO2) and thus, observations of H 2O2 provide a better understanding of the HO x chemistry in the atmosphere. A retrieval approach based on constrained least squares fitting was developed and applied to small dedicated spectral analysis windows with maximum H 2O2 information and minimum contribution of interfering gases. Due to a low signal to noise ratio in the measured spectra single profiles cannot be used for scientific interpretation and about 100 profiles have to be averaged temporally or spatially. Our retrievals of H2O2 from MIPAS measurements provide meaningful results between approximately 20 and 60 km. A possible impact by the high uncertainty of the reaction rate constant for HO2 + HO2→H2O2 + O2 in our 3D-CTM KASIMA is discussed. We find best agreement between model and observations for applying rate constants according to Christensen et al. (2002), however, a mismatch in vertical profile shape remains. The observations were compared to the model results of KASIMA focusing on low to mid latitudes. Good agreement in spatial distribution and in temporal evolution was found. Highest vmr of H 2O2 in the stratosphere were observed and modeled in low latitudes shortly after equinox at about 30 km. The modelled diurnal cycle with lowest vmr shortly after sunrise and highest vmr in the afternoon is confirmed by the MIPAS observations.


General Comments -
The paper presents new retrieval results of global H2O2 distribution in the middle atmosphere from MIPAS instrument on board Envisat. Considering the importance of HOx chemistry in the middle atmosphere and the role of H2O2 as a reservoir species for HOx, the unique H2O2 data set from space-borne instrument helps provide valuable information about the hydrogen budget. The discussions of H2O2 diurnal and intraannual variations based on the comparison of model results and MIPAS data are also interesting. Such topic should be of interest to the science community of Atmospheric Chemistry and Physics. I recommend it to be published if the authors can address the Since the signal to noise ratio if very low, it would be very important to see the retrieval residual and compare with the H2O2 spectral lines to ensure that the residual is random in nature.
2) P33519, Line 8-16: about the negative values in the profile Does the negative feature present in both daytime and nighttime profiles of MIPAS H2O2? Does the negative feature change with latitude or change with time of year? These may be useful information for the reader as well. Also, it may help evaluate whether it is a consistent bias of the measurement.
3) P33521, Line 8-10: Is the "daily mean vmrs from MIPAS data" here refers to daytime zonal mean only? If so, please specify it and please mention the satellite overpass time at the corresponding latitudes as well. A few pages later, when discussing the diurnal variation, the authors do mention the 10am and 10pm times, but here the description is not clear. Fig 7: The MIPAS profiles does not show the uncertainty (or error bars). I understand that the error bars might be very big and dominating. But this is important information to be included in the comparison plots (or at least mentioned in the caption and the text). Also the model results should include some uncertainty

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Interactive Discussion Discussion Paper ranges as well. A good way to do it is to use the recommended uncertainty ranges of the key chemical reaction in the several kinetic references. This uncertainty in reaction rate should produce a corresponding uncertainty in the model results. With these "error bar" information included in Fig 7, the discussion will be more meaningful.
More importantly, the authors didn't address the different vertical profiles of H2O2 before MIPAS and various model calculations at the near polar regions in both southern and northern hemispheres. The shapes, not only the values, are different. And I suspect that such difference in profile shape can not be explained by adjusting one simple chemical reaction rate. Fig 9, the annual variation Since the H2O2 mostly follows the overhead sun, it's the best to overplot the corresponding SZA (solar zenith angle) so that it can be easily shown.

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6) P33525, Line 6: The authors avoid discussions on the discrepancies at polar region in Fig 9 by saying that it may be affected by the "energetic particle precipitation". But the "energetic particle precipitation" does not penetrate as deep as 30 km to affect H2O2 in Fig 9. It's influences are mostly in the mesosphere. I think the discrepancy here is again related to the unresolved/undiscussed discrepancy between modeled and retrieved H2O2 vertical profiles (as shown in Fig 7). It is fine that if the authors can not make any solid conclusions on it. But it is worth mentioning it in the conclusions. P33523, Line15: "whole time period of MIPAS" Again, the authors mentioned earlier that they only use data before the resolution change in 2004. So the statement here is confusing. Please explain.
"3d-Chemical Transport Model" in a number of places in the text: I assume it means "3 dimensional". Suggest to use "3D (3 dimensional) " when it's first introduced.