A Partial Coupling Method to Isolate the Roles of the Atmosphere and Ocean in Coupled Climate Simulations

• Published in: Journal of Advances in Modeling Earth Systems
• Main Authors: Oluwayemi A. Garuba, Philip J. Rasch
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union (AGU) 2020
• Subjects: partial coupling; coupled climate modeling; ocean‐atmosphere interaction; air‐sea interaction; ocean general circulation; passive tracers; Physical geography; GB3-5030; Oceanography; GC1-1581; Sea ice
• Online Access: https://doi.org/10.1029/2019MS002016; https://doaj.org/article/1fd26c72b8d04a28b34e117bc72e5cd3

Abstract This study describes the formulation and application of a partial coupling method that disentangles the coupling between the atmosphere and ocean and isolates the atmosphere‐ and ocean‐driven components of the coupled climate interactions. In contrast to strategies using stand‐alone simulations with prescribed atmosphere or ocean states, the climate components in the partially coupled method remain coupled, but the impact of ocean circulation changes is removed from the air‐sea interaction using temperature‐like tracers. The partially coupled simulation thereby suppresses the ocean‐driven interaction and isolates an atmosphere‐driven interaction only. The ocean‐driven component can be inferred by comparing climate response in the partially coupled simulation with that of a standard fully coupled one. The partial coupling approach is applied to decompose the fully coupled climate response to CO2 quadrupling into atmosphere‐ and ocean‐driven components. The linearity of the decomposition is validated by simulating the ocean‐driven response using another complimentary partially coupled simulation forced only with the atmosphere‐driven anomalous surface fluxes. A comparison of the two partially coupled simulations with the fully coupled simulation indicates that the sum of the atmosphere‐ and ocean‐driven components accurately describes the fully coupled response. The decomposition identifies several robust atmosphere‐ and ocean‐driven features of the global warming and provides new insights into the impacts of atmospheric feedbacks on the Atlantic overturning circulation and sea ice response to CO2 increase.