Feedback of Atmosphere-Ocean Coupling on Shifts of the Intertropical Convergence Zone
It is well known that the Intertropical Convergence Zone (ITCZ) shifts in response to remote perturbations in the atmospheric energy balance, with shifts roughly in proportion to changes in the cross-equatorial atmospheric energy flux. However, atmospheric and oceanic energy fluxes in low latitudes are mechanically coupled, and the oceanic energy flux dominates the atmospheric energy flux. Here a quantitative framework is derived that shows how Ekman coupling of atmospheric and oceanic energy fluxes damps the perturbation response of the atmospheric energy flux, energy flux equator (EFE), and ITCZ. To first order, Ekman coupling alone mutes the response of EFE and ITCZ in the coupled atmosphere-ocean system by a factor γ = 1+O_0/NEI_0, where O_0 is the ocean energy uptake and NEI0 is the net energy input into the atmosphere at the equator. In the current climate in the zonal and annual mean, this factor is about γ≈3.
© 2017 American Geophysical Union. Received 19 JUL 2017; Accepted 24 OCT 2017; Accepted article online 30 OCT 2017. I thank Momme Hell for drawing Fig. 2, Karim Lakhani for calculating O_0 and NEI_0 from the CMIP5 models, and Ori Adam for helpful comments on a draft and help with Fig. 1. The National Center for Atmospheric Research (NCAR) provided the ERA-Interim energy budget products used in Fig. 1: https://climatedataguide.ucar.edu/climate-data/era-interim-derived-components. Part of the research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Published - Schneider-2017-Geophysical_Research_Letters.pdf
Accepted Version - grl56614.pdf