the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Thermospheric nitric oxide NO during solar minimum modulated by O/O2 ratio and thermospheric transport and mixing
Abstract. The formation of NO by geomagnetic activity and EUV photoionization in the upper mesosphere and lower thermosphere and its subsequent impact on ozone contributes to the natural forcing of the climate system, and is recommended to be included in chemistry-climate model experiments since CMIP6. We compare NO concentrations simulated by five high-top chemistry-climate models – WACCM-X, EMAC, HAMMONIA, WACCM-D and KASIMA – in the mesosphere and thermosphere with satellite observations during a period of low geomagnetic and solar forcing from January to December 2010. While qualitatively the latitudinal and temporal variability of NO is captured by most models, we find disagreements of several orders of magnitude in high-latitude winter. Possible reasons are explored using snapshots at 12 UT on January 9, 2010. Two processes interacting with each other are identified as likely sources of these discrepancies, quenching of N(2D) by atomic oxygen in the mid-thermosphere, and meridional transport and mixing from the mid-thermosphere to the lower thermosphere. In the mid-thermosphere, the amount of atomic oxygen available from dissociation of molecular oxygen balances N(4S) and N(2D) via quenching of N(2D). N(4S) can then be transported or mixed into the lower thermosphere, where it efficiently reduces the lifetime of NO, leading to lower values of NO there. In high-latitude winter, meridional downward-poleward transport of N(4S) from the low-and midlatitude mid-thermosphere into the high-latitude lower thermosphere modulates the NO lifetime. This transport is affected by gravity waves, and therefore depends on the models gravity wave drag schemes and resolved gravity wave spectra.
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RC1: 'Comment on egusphere-2024-2256', Anonymous Referee #1, 12 Sep 2024
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Comments on the paper "Thermospheric nitric oxide NO during solar minimum modulated by O/O2 ratio and thermospheric transport and mixing" by Miriam Sinnhuber et al.
This study focused on the simulation of NO in the lower thermosphere by comparing 5 numerical models with observations. They concluded that “two processes interacting with each other are identified as likely sources of these discrepancies, quenching of N(2D) by atomic oxygen in the mid-thermosphere, and meridional transport and mixing from the mid-thermosphere to the lower thermosphere”. The results and conclusions will contribute to our knowledge on the variation of NO and also will contribute to further improve the first-principle based models in the future. However, there are some major issues to be addresses before it was considered to be published.Here are some detailed concerns and some suggestions:
- The structure of the paper lacks clarity, making it hard for readers to follow. I recommend having a native English speaker review and revise both the language and the logical flow to improve overall clarity.
- The title of the manuscript is difficult to understand. Please consider rewriting it for clarity.
- The font size of the text in the figures should be larger for better readability.
- Figure 7: The authors did not discuss why O/O2[N2] from HAMMONIA is lower than that from WACCMx, because both of which considered photodissociation of O2 in the SRBC.
- I recommend the authors add a table to list the advantage and disadvantage of these models before the Summary section to clarify the simulation results.
Citation: https://doi.org/10.5194/egusphere-2024-2256-RC1
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