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https://doi.org/10.5194/esd-2017-52
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
18 Jul 2017
Review status
This discussion paper is under review for the journal Earth System Dynamics (ESD).
Atmospheric Torques and Earth's Rotation: What Drove the Millisecond-Level Length-of-Day Response to the 2015–16 El Niño?
Sébastien B. Lambert1, Steven L. Marcus2, and Olivier de Viron3 1SYRTE, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, LNE, Paris, France
2Independent Researcher, Santa Monica, California, USA
3Littoral, Environnement et Sociétés (LIENSs), Université de La Rochelle and CNRS (UMR7266), La Rochelle, France
Abstract. El Niño/Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east-west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–83 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015–16 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that: (i) as a mixed Eastern/Central Pacific event, the 2015–16 mountain torque was smaller than for the 1982–83 and 1997–98 events which were pure Eastern Pacific events, and (ii) the smaller mountain torque was augmented by positive friction torques arising from an enhanced Hadley-type circulation in the Eastern Pacific, leading to similar AAM/LOD signatures for all three extreme ENSO events. The 2015–16 event thus contradicts the dominant paradigm that mountain torques cause the Earth rotation response for extreme El Niño events.

Citation: Lambert, S. B., Marcus, S. L., and de Viron, O.: Atmospheric Torques and Earth's Rotation: What Drove the Millisecond-Level Length-of-Day Response to the 2015–16 El Niño?, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2017-52, in review, 2017.
Sébastien B. Lambert et al.
Sébastien B. Lambert et al.
Sébastien B. Lambert et al.

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Short summary
We explain how the extreme 2015–16 El Niño event lengthened the day by 0.8 ms. The 2015–16 event was a Niño of different type compared to previous extreme events, so that we expected different mechanisms of coupling with the solid Earth. We showed that the atmospheric torque on the American topography, usually acting alone during classical Niños, was, in 2015–16, augmented by a friction torque over the Pacific ocean and inherent to the different nature of this particular event.
We explain how the extreme 2015–16 El Niño event lengthened the day by 0.8 ms. The 2015–16...
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