Speaker
Description
Recent stellar observations have suggested that the Sun could switch to a high-activity regime, causing an increase in ultraviolet radiation with an amplitude about four times larger than that of an average solar activity cycle, together with a simultaneous decrease in total solar irradiance. We investigate the atmospheric response to the switch of the Sun to the high activity regime using the coupled chemistry–climate–ocean model SOCOLv3– MPIOM. To elucidate the role of different atmospheric processes, we employ dedicated forcing composites that separate photolysis (UV-driven chemistry) from direct radiative- energy changes affecting the surface energy balance. We quantify the responses of ozone, the key chemical families (NOx and HOx), and stratospheric water vapor to link composition changes to dynamics.
The simulations show a strong response in the middle atmosphere that is mainly driven by UV-induced chemistry: stratospheric ozone increases markedly (by up to 14% locally), and total ozone rises by up to 8%. The accompanying composition changes indicate weakened catalytic ozone loss: NOx decreases, reducing NOx-driven ozone destruction, and stratospheric water vapor also decreases, which tends to suppress HOx and further limits ozone loss. By contrast, changes near the surface are dominated by the reduced energy input from the Sun at longer wavelengths, leading to a patterned near-surface cooling that can reach about 1 K. This cooling weakens the Brewer–Dobson circulation, reduces the transport of water vapor from the troposphere into the stratosphere, and slows ozone transport from the tropics toward mid-latitudes that links the chemical and dynamical responses. Overall, our results highlight that a solar-regime shift would leave a clear atmospheric signature, with distinct and physically separable impacts on stratospheric composition, thermal structure, and large-scale transport.