Speaker
Description
Space Weather (SWE) has a profound impact on Earth’s atmospheric chemistry and climate. Compared to the present-day Sun, the young Sun was more magnetically active and experienced more frequent extreme space weather events, such as coronal mass ejections (CMEs) and solar energetic particles (SEPs), which steadily bombarded Earth’s upper atmosphere. These particles enhanced atmospheric chemistry, potentially resulting in large amounts of kinetically produced greenhouse gases, such as CO, H$_2$, N$_2$O, and HCN. Here, we used a chain of three models – (i) a thermochemical and photochemical kinetic model [Locci et al., 2022], (ii) a radiative-convective model (EOS) [Simonetti et al., 2022], and (iii) an energy balance model (ESTM) [Vladilo et al., 2015; Biasiotti et al., 2022] – to explore the impact of an extreme SWE event on Earth’s atmosphere, in terms of variation of atmospheric species and the consequences on Earth’s climate. Specifically, we tested whether the Sun-Earth interaction could address the Faint Young Sun Paradox (FYSP), as proposed by Airapetian et al. (2016).
To conduct this analysis, first we used the thermochemical and photochemical kinetics model to simulate the interaction between atmospheric gases and ionizing stellar radiation. By integrating stellar particle interactions, the model yields detailed vertical chemical profiles of atmospheric components. These vertical profiles are then used as inputs to our radiative-convective model, which calculates the outgoing longwave radiation and the top-of-atmosphere albedo for a set of atmospheric columns with different surface pressures and chemical compositions. The radiative lookup tables compiled by EOS are included in ESTM to derive the seasonal evolution of surface temperature. We also applied this modeling pipeline to the present-day Earth atmosphere to assess the potential impact of a prolonged period of intense solar activity.
First, we found that for each atmosphere considered, due to the dissociation of N$_2$ by SEPs, N(2D) is produced, giving rise to a rich chemistry that results in the production of greenhouse gases such as N$_2$O and HCN. H$_2$ is also produced. Additionally, another greenhouse gas, CO, is thermochemically produced. Finally, we observed that in the case of secondary atmospheres, the chemical abundances of the species are dominated by SEP-driven chemistry, while high-energy radiation plays a marginal role. Second, for an Archean Earth-like atmosphere of 90% N$_2$, 10% CO$_2$, and trace amounts of either CH$_4$ or H$_2$, the two most abundant species produced are CO and H$_2$. In this condition, the surface temperature increase is no larger than 0.3 K, which makes this solution to the FYSP unviable. Notably, the contribution of nitrogen species (N$_2$O and HCN) to this temperature increase is negligible. Even when the SEP flux is enhanced by a factor of 10 with respect to Carrington-like conditions, the chemical composition of the atmosphere remains unchanged. This indicates that even under stronger space weather conditions, the impact on the planetary thermal state is minimal. Lastly, under present-day conditions, the cumulative effects of a prolonged period of intense solar activity, in terms of frequent Carrington-like SEP events, would decrease the surface temperature by ∼4 K.
