Abstract. Understanding the atmospheric forcing from energetic particle precipitation (EPP) is important for climate simulations on decadal time scales. However, presently there are large uncertainties in energy flux measurements of electron precipitation. One approach to narrowing these uncertainties is by analyses of EPP direct atmospheric impacts and their relation to measured EPP fluxes. Here we use observations from the microwave limb sounder (MLS) and Whole Atmosphere Community Climate Model (WACCM) simulations, together with EPP fluxes from the Geostationary Operational Environmental Satellite (GOES) and Polar-orbiting Operational Environmental Satellite (POES) to determine the OH and HO2 response thresholds to solar proton events (SPEs) and radiation belt electron (RBE) precipitation. Because of their better signal-to-noise ratio and extended altitude range, we utilize MLS HO2 data from an improved offline processing instead of the standard operational product. We consider a range of altitudes in the middle atmosphere and all magnetic latitudes from pole to pole. We find that the nighttime flux limits for day-to-day EPP impact detection using OH and HO2 are 50–130 protonscm-2s-1sr-1 (E>10 MeV) and 1.0–2.5×104 electronscm-2s-1sr-1 (E = 100–300 keV). Based on the WACCM simulations, nighttime OH and HO2 are good EPP indicators in the polar regions and provide best coverage in altitude and latitude. Due to larger background concentrations, daytime detection requires larger EPP fluxes and is possible in the mesosphere only. SPE detection is easier than RBE detection because a wider range of polar latitudes is affected, i.e., the SPE impact is rather uniform poleward of 60∘, while the RBE impact is focused at 60∘. Altitude-wise, the SPE and RBE detection are possible at ≈ 35–80 and ≈ 65–75 km, respectively. We also find that the MLS OH observations indicate a clear nighttime response to SPE and RBE in the mesosphere, similar to the simulations. However, the MLS OH data are too noisy for response detection in the stratosphere below 50 km, and the HO2 measurements are overall too noisy for confident EPP detection on a day-to-day basis.
The paper focuses on the impact of energetic particle precipitation (EPP, both proton C1 ANGEOD Interactive comment Printer-friendly version Discussion paper and electron events) on the polar middle atmosphere. The overall goal is to determine the EPP flux thresholds at various altitudes and locations by using odd hydrogen species observed by MLS/Aura satellite and simulated by WACCM-D. Due to the significant uncertainties in satellite measurements of energetic particles, especially for electron precipitation, this study is useful. Although the study does not present critical advances, the paper is well written, the methodology is sound, and the results are in line with previous studies. Overall, I suggest publication subjected to address the following comments. Response to the general comments: We thank the reviewer for the constructive comments. We also appreciate the time devoted to the evaluation of our paper. Please try to make a more focused paper. Thirteen figures are too many for this study and make the reading difficult. It would be beneficial to try combining some of them. For example, three figures for showing the comparison of the climatology between MLS and WACCM are excessive. Other figures (at least Fig. 2 and Fig. 11) could be removed or included as supplementary information. We have removed Figures 5 and 11 to make paper more focused. Figure 2 we kept, because it is needed to demonstrate our methods. Figures 6-7 were also kept, as we would like to show comparisons of both day and night HO x. The text has been revised to accommodate the changes in the figures.
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