Séminaire ISTerre

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Variations in length of day on the subdecadal scales and their potential mechanisms

vendredi 1er décembre 2023 - 11h00

Pengshuo Duan  - Shanghai Astronomical Observatory - Institute of Geodesy and Geophysics
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Variations in Earth rotation rate defined by length-of-day (LOD) on the subdecadal scales present two primary periodic (i.e., 6yr and 8.6yr) oscillations, the former reflects the signatures of torsional Alfvén waves, while the latter origin is still unclear. Modern observations also show that the fast fluctuations in geomagnetic acceleration and fluid core surface flow motions own the 8.6yr period component on the subdecadal scales, and these core motions seemingly mainly occur at the equatorial regions, which may arise from the rapidly hydromagnetic waves atop the Earth’s core. Using the core surface flow data inferred from recent satellite magnetic observations, we compute the electromagnetic torque exerting on the mantle from the fluid outer core (FOC), from which two obviously periodic (i.e., 6yr and 8.6yr) oscillatory components are extracted in time domain by the normal wavelet analysis method, further supporting the existence of the core waves with the same periods. Moreover, we explore the potential mechanisms for these periodic LOD oscillations from the excited hydromagnetic waves and the equatorial Magnetic-Archimedes-Coriolis modes as well as the inner core gravitational oscillation model. Studying the subdecadal LOD changes can provide an effective approach to constrain (or infer) the dynamic information within the Earth deep interiors, which cannot be directly observed from the Earth surface.

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Equipe organisatrice : Géodynamo

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères