Comparison of General Circulation Models of the Venus upper atmosphere

In the context of future Venusian missions, it is crucial to improve our understanding of Venus upper atmosphere through 3D modelling, notably for spacecraft orbit computation. This study compares three General Circulation Models (GCMs) of the Venusian atmosphere up to the exosphere: The Venus Planetary Climate Model (Venus PCM; Lebonnois et al., 2010; Martinez et al. 2024), the Venus Thermospheric Global Model (VTGCM; Brecht et al., 2021) and the Tohoku University GCM (TUGCM; Hoshino et al., 2013), focusing on their nominal simulations (e.g. composition, thermal & dynamic structures and heating/cooling rates).

Similarities and discrepancies among them are deeply discussed in Martinez et al. (2026), together with data-models comparison. Despite similar large-scale features, significant differences are identified among the models (see Figure 1). All three GCMs reproduce a warm dayside thermosphere and a cold nightside cryosphere, driven by a balance between solar extreme ultraviolet heating, near-infrared heating, radiative cooling by CO₂ at 15-μm, thermal conduction, and dynamical effects. However, the magnitude and vertical distribution of temperatures differ substantially, particularly in the upper thermosphere. Comparisons with Pioneer Venus, Venus Express, and Magellan observations reveal that the nominal simulations systematically overestimate daytime exospheric temperatures. This bias is consistently linked to an underestimation of atomic oxygen densities, which reduces radiative cooling efficiency at high altitudes.

   

Figure 1: Diurnal structure of the temperatures for equatorial latitude (30°S–30°N) for Venus PCM, VTGCM and TUGCM at high solar activity (leftside) and at low solar activity (rightside). The approximate altitude of each model for each solar period is marked in white for pressure levels of 10, 1, 0.1, 10⁻², 10⁻³, 10⁻⁴ and 10⁻⁵ Pa.

Based on the findings of the article, a list of recommendations is proposed aiming at improving the modelling of Venus’ upper atmosphere, among them: 1. Standardize the EUV-UV solar spectrum input. 2. Update the near-infrared heating scheme with Venus Express-Era data. 3. Reassess Radiative cooling schemes. 4. Investigate the underestimated atomic Oxygen abundance.

References:

Brecht, A. S., Bougher, S. W., Shields, D., Liu, H.‐L., & Lee, C. (2021). Planetary‐Scale Wave Impacts on the Venusian Upper Mesosphere and Lower Thermosphere. In Journal of Geophysical Research: Planets (Vol. 126, Issue 1). American Geophysical Union (AGU). https://doi.org/10.1029/2020je006587

Lebonnois, S., Hourdin, F., Eymet, V., Crespin, A., Fournier, R., Forget, F., 2010. Superrotation of Venus’ atmosphere analyzed with a full general circulation model. J. Geophys. Res. (Planets) 115, 6006. https://doi.org/10.1029/2009JE003458.

Martinez, A., Chaufray, J.-Y., Lebonnois, S., Gonzàlez-Galindo, F., Lefèvre, F., & Gilli, G. (2024). Three-dimensional Venusian ionosphere model. In Icarus (Vol. 415, p. 116035). Elsevier BV. https://doi.org/10.1016/j.icarus.2024.116035

Martinez A., Karyu H., Brecht A., Gilli G., Lebonnois S., Kuroda T., Stolzenbach A., Gonzalez-Galindo F., Bougher S. and Fujiwara H. (2026). Comparison of General Circulation Models of Venus upper atmosphere. Icarus, 116901, 0019-1035, https://doi.org/10.1016/j.icarus.2025.116901

Hoshino, N., Fujiwara, H., Takagi, M., Kasaba, Y., (2013), Effects of gravity waves on the day-night difference of the general circulation in the Venusian lower thermosphere, J. Geophys. Res. (Planets), 118, pp. 2004-2015, doi:10.1002/jgre.20154