Influence of cloud-radiation effects on the location of the intertropical convergence zone

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The intertropical convergence zone (ITCZ) is a central element of Earth's climate system. Its location determines the distribution of tropical rainfall and clouds. The ITCZ has experienced large meridional shifts in Earth's history, and will likely show such shifts in response to anthropogenic climate change. Although the ITCZ has been the subject of many studies, the role of cloud-radiative effects has received little attention. Motivated by this gap as well as recent simulations with the atmosphere model ECHAM6, the project investigates how and through which mechanisms cloud-radiative effects influence the ITCZ location. The two following questions are addressed. First, how strong is the influence of cloud-radiative effects on the ITCZ location in comparison to the wind-evaporation-sea-surface-temperature feedback? Second, do cloud-radiative effects amplify or damp meridional ITCZ shifts? These two questions are answered by the coordinated use of four different atmosphere models with interactive sea-surface temperatures. Comparing the four models provides the opportunity to separate robust from non-robust model behavior, to relate robust model behavior to physical mechanisms, and to connect non-robust model behavior to model differences in cloud-radiative effects. The project will be carried out during a 6-month visit to the Laboratoire de Meteorologie Dynamique in Paris. This will allow the applicant to closely collaborate with Dr. Sandrine Bony and Dr. Jean-Louis Dufresne, to apply the LMD atmosphere models, and to compare the LMD models to the atmosphere models of the Max Planck Institute for Meteorology, Hamburg.