Séminaire
I will present work on two different aspects of the interaction between cloud-radiative effects and the large-scale circulation. The first part addresses the interaction between large-scale circulation and cloud-radiative effects (CRE)s on the long-term habitability of Earth-like planets. The second part focuses on the influence of CRE on the position on the inter-tropical convergence zone (ITCZ) using idealized aqua-planet simulations in a present-day Earth context.
In the first part of the talk, I will show results from simulations with the general circulation model ECHAM6 suggesting that a weakening large-scale circulation with increasing global-mean surface temperature leads to a cloud-induced climate instability at global-mean surface temperatures between 300 and 305 K. However, as the climate warms further, the CRE changes from strongly positive to strongly negative at global-mean surface temperatures above 330 K allowing eventually for the climate to attain a steady-state. In this new hot steady state the climate would be subject to a rapid loss of water to space and a planet in such a state would eventually become uninhabitable over geological time periods. This highlights the importance of interactions between cloud-radiative effects and the large-scale circulation on the long-term habitability of Earth-like planets.
In the second part, I will show ongoing work with idealized aqua-planet simulations with prescribed surface temperatures performed with a developmental version of the GFDL atmosphere model (AM) version 4. Aqua-planet simulations with prescribed surface temperatures are well known to produce two distinct ITCZs off the equator rather than one at the equator. Our results suggest that the longwave CRE pulls the ITCZ towards the equator whereas the shortwave CRE pushes the ITCZ away from the equator. The longwave CRE dominates the shortwave CRE such that the total CRE pulls the ITCZ equatorwards. Our work suggests a mechanistic understanding of how both longwave and the shortwave CRE affects the ITCZ position.