Climate Responses Under an Extreme Quiet Sun Scenario.

Fundamental understanding of the climate responses to solar variability is obscured by the large and complex climate variability. This long‐standing issue is addressed here by examining climate responses under an extreme quiet sun (EQS) scenario, obtained by making the sun void of all magnetic fields. It is used to drive a coupled climate model with whole atmosphere and ocean components. The simulations reveal significant responses, and elucidate aspects of the responses to changes of troposphere/surface forcing and stratospheric forcing that are similar and those that are different. Planetary waves (PWs) play a key role in both regional‐scale responses and the mean circulation changes. Intermediate scale stationary waves and regional climate respond to solar forcing changes in the troposphere and stratosphere in a similar way, due to similar subtropical wind changes in the upper troposphere. The patterns of these changes are similar to those found in a warming climate, but with opposite signs. Responses of the largest scale PW during northern hemisphere and southern hemisphere winters differ, leading to hemispheric differences in the interplay between dynamical and radiative processes. The analysis exposes remarkable general similarities between climate responses in EQS simulations and those under nominal solar minimum conditions, even though the latter may not always appear to be statistically significant. Plain Language Summary: Understanding how climate may change under different solar conditions is both interesting and important. However it is difficult to clearly identify solar signal from the very large climate variability on broad time scales. In this study, we tackle this problem by providing a lower bound of the solar minimum condition according to our current understanding of solar physics. By specifying this extremely low solar minimum condition in a climate model that takes into consideration of the effects of ocean and middle atmosphere, we are able to identify significant climate responses, which are very different between the northern and southern hemispheres. We gain an understanding of the processes driving these responses, including how the lower and upper atmospheric processes may enhance/offset each other. By comparing these climate responses to those under nominal solar minimum conditions, we expose climate patterns that are hidden under the large climate variability in the latter. Key Points: Climate simulations under extreme quiet sun conditions reveal significant responsesHemispheric differences in the interplay between dynamical and radiative processes identifiedQuantify tropospheric/surface and stratospheric responses that are similar or different [ABSTRACT FROM AUTHOR]