| 29 Aug 2025
The impact of electron precipitation on Earth's thermospheric NO production and the drag of LEO satellites
Abstract. We investigate the response of space weather events on Earth's upper atmosphere over the polar regions by studying their effect on the drag of the CHAMP and GRACE satellites. Increasing solar activity that results in heating and the expansion of the upper atmosphere threatens low Earth orbit (LEO) satellites. Auroral events are closely related to the stellar energy deposition of solar EUV radiation and precipitating energetic electrons, which influence photochemical processes such as the production of nitric oxide (NO) in the upper atmosphere. To study the production of NO molecules and their influence on the thermospheric structure and satellite drag, we first model Earth’s background thermosphere structure with the 1D upper atmosphere model Kompot by considering the incident X-ray, EUV, and IR radiation during selected space weather events. For investigating the effect of electron precipitation in the production of NO molecules in the polar thermosphere, we apply a Monte Carlo model that takes into account the stochastic nature of collisional scattering of auroral electrons in collisions with the surrounding N2-O2 atmosphere, including the production of suprathermal N atoms. The observed effect of the atmospheric drag on the CHAMP and GRACE spacecraft during the two studied events indicates that a sporadic enhancement of NO molecule production in the polar thermosphere and its IR-cooling capability, which counteracts thermospheric expansion and can lead to an "overcooling" with decreased density after the space weather event, can have a protective effect on LEO satellites. Their production efficiency, however, is highly dependent on the energy flux of the precipitating electrons.
Review report on the manuscript “The impact of electron precipitation on Earth’s thermospheric NO production and the drag of LEO satellites”, submitted to ANGEO by Scherf et al. for the consideration of publication.
Manuscript summary
The authors combine 1D Kompot thermosphere runs (background atmosphere) with a kinetic Monte-Carlo model of precipitating electrons (Shematovich et al. approach) to estimate NO production during two CME-drive storm events and examine consequences for thermospheric cooling and satellite drag. They compare Kompot-only results vs. calculations including electron precipitation and compare with SABER observations and CHAMP/GRACE density-derived orbital decay.
Overall manuscript recommendation
This is an interesting and valuable manuscript. The modelling approach and the data comparisons are appropriate, and the results are relevant for satellite drag/space-weather forecasting communities. The main scientific message — that precipitation-driven NO can cause overcooling and can therefore affect thermospheric densities and subsequent satellite orbital decay — is supported by the modelling and SABER/accelerometer evidence. However, I recommend minor–major revisions before acceptance: the authors should (i) explicitly connect the results to empirical models and storm recovery mechanics (see Major point #1), (ii) discuss possible NO cooling timing on model predictions, and (iii) clarify the use of SABER data..
Major comments
In this case, I recommend the authors add a short subsection in Discussion explicitly entitled something like “Implications for empirical models and storm recovery” that explains why omission of precipitation-driven NO leads to errors specifically during the recovery phase (timing: NO lifetime/diffusion ~1 day is mentioned and important). Also, if possible, provide a short numerical estimate or point to literature values (see below) on how big the cooling bias can be and whether it systematically moves empirical model outputs relative to observations.
There has been previous work done on NO cooling effects on empirical models. For example, Oliveira and Zesta (2019) noted that the lack of NO information in the Jacchia-Bowman 2008 (JB2008) model is most likely a major source for density errors during recovery phase of storms, particularly during extreme events. Licata et al. (2021) also observed the same features with CHAMP and GRACE data, but they noted that the HASDM (High Accuracy Satellite Drag Model) was able to capture cooling effects due to NO (recovery) and CO2 (pre-storm) phases. Oliveira et al. (2021) also noted with a superposed epoch analysis that HASDM was able to capture NO effects and even an overcooling effect supported by observations (CHAMP and GRACE), but JB2008 failed miserably during the recovery phase of the storm. One more. Zesta and Oliveira (2019) were able to quantify the timing of such cooling effects, noting that the thermosphere heats and cools faster for the more extreme geomagnetic storms. I think the NRL-MSIS results showed by the authors are expected, since the lack of NO effects also have profound impacts on model results during storm recoveries in the case of JB2008. I think this discussion should be added to support the authors’ conclusion stating that, e.g., “[…] NO molecules have [not has] protective effect on LEO satellites.” (line 367)
Licata, R. J., Mehta, P. M., Tobiska, W. K., Bowman, B. R., & Pilinski, M. D. (2021). Qualitative and Quantitative Assessment of the SET HASDM Database. Space Weather, 19, e2021SW002798. https://doi.org/10.1029/2021SW002798
Oliveira, D. M., Zesta, E., Mehta, P. M., Licata, R. J., Pilinski, M. D., Kent Tobiska, W., & Hayakawa, H. (2021). The current state and future directions of modeling thermosphere density enhancements during extreme magnetic storms. Frontiers in Astronomy and Space Sciences, 8 (764144). https://doi.org/10.3389/fspas.2021.764144
Zesta, E., & Oliveira, D. M. (2019). Thermospheric heating and cooling times during geomagnetic storms, including extreme events. Geophysical Research Letters, 46 (22), 12,739-12,746. https://doi.org/10.1029/2019GL085120
Knipp, D. J., Pette, D. V., Kilcommons, L. M., Isaacs, T. L., Cruz, A. A., Mlynczak, M. G., Hunt, L. A., & Lin, C. Y. (2017). Thermospheric nitric oxide response to shock-led storms. Space Weather, 15 (2), 325-342. https://doi.org/10.1002/2016SW001567
Minor comments
Caption of figure 2: repectively respectively.
Caption of Table 1. “TIMMED/SEE” TIMED/SEE.
Line 378. “author’s” authors.
Spell out DMSP the first time it is mentioned. The same for LST.