Two annual cycles of the Pacific cold tongue under orbital precession

Chiang, John C. H., Atwood, Alyssa R., Vimont, Daniel J., Nicknish, Paul A., Roberts, William, Tabor, Clay R. and Broccoli, Anthony J. (2022) Two annual cycles of the Pacific cold tongue under orbital precession. Nature, 611 (7935). pp. 295-300. ISSN 0028-0836

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The Pacific cold tongue annual cycle in sea surface temperature is presumed to be driven by Earth’s axial tilt 1,2,3,4,5 (tilt effect), and thus its phasing should be fixed relative to the calendar. However, its phase and amplitude change dramatically and consistently under various configurations of orbital precession in several Earth System models. Here, we show that the cold tongue possesses another annual cycle driven by the variation in Earth–Sun distance (distance effect) from orbital eccentricity. As the two cycles possess slightly different periodicities 6, their interference results in a complex evolution of the net seasonality over a precession cycle. The amplitude from the distance effect increases linearly with eccentricity and is comparable to the amplitude from the tilt effect for the largest eccentricity values over the last million years (e value approximately 0.05) 7. Mechanistically, the distance effect on the cold tongue arises through a seasonal longitudinal shift in the Walker circulation and subsequent annual wind forcing on the tropical Pacific dynamic ocean–atmosphere system. The finding calls for reassessment of current understanding of the Pacific cold tongue annual cycle and re-evaluation of tropical Pacific palaeoclimate records for annual cycle phase changes.

Item Type: Article
Additional Information: Funding Information: We thank D. Battisti for providing the ICM code, W. Boos for providing code for the energy flux diagnostic, D. Pollard and M. Erb for providing code for the fixed-angle calendar conversion, S. White and R. Shen for advice on palaeoproxy records, and B. Raney and J. Bosmans for providing the GFDL and EC Earth model output, respectively. J.C.H.C. acknowledges support from a Visiting Professorship at Academia Sinica, funded by the Ministry of Science and Technology, Taiwan, under grant no. 110-2811-M-001-554. A.R.A. acknowledges support from National Science Foundation award 1903640. C.R.T. acknowledges funding from the National Center for Atmosphere Research Advanced Study Program postdoctoral fellowship. This research used the Savio computational cluster resource provided by the Berkeley Research Computing program at the University of California, Berkeley (supported by the UC Berkeley Chancellor, Vice Chancellor for Research and Chief Information Officer). High-performance computing support on Cheyenne ( was provided by NCAR’s Computational and Information Systems Laboratory, sponsored by the National Science Foundation.
Subjects: F700 Ocean Sciences
Department: Faculties > Engineering and Environment > Geography and Environmental Sciences
Depositing User: John Coen
Date Deposited: 30 Nov 2022 12:24
Last Modified: 09 May 2023 03:30

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