Variations in solar irradiance are known to influence the composition and dynamics of the Earth’s atmosphere, which can impact modern technologies such as radio communication, GPS accuracy, and satellite drag. However, the consequence of increases in solar radiation during solar flares on the Earth’s ionosphere is still not fully understood. Our team will comprise experts in solar flares and ionospheric aeronomy, two interconnected areas that have been studied quite separately historically. We will determine how the ionosphere responds to flares of different magnitudes, spectral properties, locations, at different times of year and solar cycle. This will help us understand how and why ionisation rates, particle temperatures and densities vary during ionospheric disturbances caused by solar flares. To comprehensively study this solar-terrestrial connection, we will combine solar flare observations from a range of space-borne instruments, as well as spectral irradiance and radiative hydrodynamic models, with ionospheric measurements and theoretical predictions. Our findings will piece together the physical mechanisms responsible for producing geoeffective emission during flares and the impact those emissions have on various layers of the Earth’s ionosphere. Obtaining a comprehensive understanding of the relevant physical processes, and improving our predictive capability, is increasingly important in space weather research.