Interannual changes in length-of-day driven by a hydromagnetic core waves inside the fluid outer core

• Autores: Duan, P.; Huang, C.
• Año de publicación: 2025
• Idioma: inglés
• Tipo de recurso: documento de conferencia
• Materia: Ciencias Astronómicas; Length-of-day (LOD) variations; Core-mantle coupling; Magneto-Coriolis waves
• Institución: Universidad Nacional de La Plata

Variations in Earth rotation rate defined by length-of-day (LOD) on the intradecadal scales present two primary period (i.e., 6yr and 8.6yr) oscillations, the physical mechanisms for them are still uncertain. Based on the core surface flow data inferred from modern satellite magnetic observations for 1999 to the present, we calculate the electromagnetic torque exerting on the mantle from core flow motions and show that the torque also presents the same two period oscillations, providing new evidence to show that intradecadal LOD oscillations are driven by the core motions. Using the purely geostrophic core flow model described in the framework of torsional waves, this work shows that the predicted 6yr LOD result coincides well with the observation, while the observed 8.6yr LOD oscillation cannot be satisfactorily explained by this model due to the existing phase difference with ~ 2 years. This work further develops the novel model of LOD changes attributed to the quasi-geostrophic magneto-Coriolis (QG-MC) waves, suggesting that the QG-MC wave modes with cylindrical radial wave number ~4.8 and quality factor Q ~ 16 can provide a nice explanation for the 8.6yr LOD oscillation (including both amplitude and phase) and providing a new approach to infer the information of core dynamics via LOD changes.
Facultad de Ciencias Astronómicas y Geofísicas