Effects of transient stellar emissions on planetary climates of tidally-locked exo-earths

Abstract: Space weather in exoplanetary systems, driven by transient stellar emissions such as flares, coronal mass ejections, and stellar proton events, can significantly influence planetary habitability and the long-term evolution of atmospheres. These time-dependent phenomena also complicate the remote characterization of exoplanets by altering the abundance of key chemical species and modulating atmospheric brightness temperatures. While prior studies have largely focused on photochemical effects, surface UV dosages, and spectral consequences, here we extend the analysis using three-dimensional general circulation models coupled with interactive photochemistry. We simulate the climate and chemical responses of TRAPPIST-1e-like, synchronously rotating planets subjected to stellar energetic particle events and periodic UV flux enhancements. Using statistical methods, we evaluate impacts across spatial and temporal scales. Our results show that abrupt thermospheric cooling occurs via radiative emissions from NO and CO2, while warming in the middle and lower atmosphere arises from increased infrared absorbers, including N2O and H2O. In moderately active stellar regimes, atmospheric temperature changes are strongly modulated by O3 variability. Cumulative effects depend on flare frequency, while instantaneous responses are sensitive to the spectral energy distribution of the flare. Notably, intense flares can dynamically energize the middle atmosphere, enhancing wind speeds by up to 40 m/s on the substellar nightside at altitudes of 30 to 50 km. These findings suggest that repeated, high-energy eruptive events from young stars may play a critical role in shaping atmospheric dynamics on temperate terrestrial exoplanets.