The chromosphere is a key atmospheric layer, bridging the stellar interior, where energy is generated, to the outer space, where this energy is ultimately injected. As such, it plays a central role in shaping the interplanetary environment, and by extension, the conditions for life. Yet, its complex and dynamic nature remains one of the least understood aspects of the solar atmosphere, due to strong observational and theoretical challenges.
In this talk, I will argue why the chromosphere is of prime importance, not just as a passive layer, but as an active, dynamic engine regulating how energy, mass, and magnetic structures are transferred from the solar interior to the corona and beyond. I will more especially present recent advances we've made on the solar case, using high-resolution simulations to investigate how shocks and reconnecting current sheets sustain the chromosphere temperature. How these processes behave and inject energy higher up is further key to understand the non-monotonic response of higher parts, establishing a crucial links to solar wind formation and ultimately to space weather forecasting.
Through this scope, I aim to convince you that the chromosphere emerges not only as a site of fascinating plasma dynamics, but also fundamentally as a cornerstone for understanding how stars connect to, and influence, their cosmic surroundings.
