Assessment of thermospheric nitric oxide NO formation and loss in high-top chemistry-climate models

Kurzfassung

Geomagnetic forcing is considered part of the natural forcing of the climate system, and recommended to be included in chemistry-climate model experiments since CMIP6. The starting point is the formation of NO mainly in the lower thermosphere by energetic electron precipitation from the aurora and radiation belts and EUV radiation. We compare results of NO from five high-top chemistry-climate models in the mesosphere and thermosphere with satellite observations for low geomagnetic forcing throughout the year 2010. While qualitatively, the latitudinal and temporal variability is well captured by all models compared with the observations, we find disagreements between models reaching several orders of magnitude in the winter-time high-latitude lower thermosphere. Possible reasons are explored using snapshots of one day, and two main drivers of the large differences are tentatively identified: the treatment of neutral chemistry on the one hand, and an impact of the thermospheric circulation in the winter hemisphere driven by sub-scale gravity waves