Characterization and implications of intradecadal variations in length of day
Résumé
Variations in Earth's rotation (defined in terms of length of day) arise
from external tidal torques, or from an exchange of angular momentum
between the solid Earth and its fluid components(1). On short timescales
(annual or shorter) the non-tidal component is dominated by the
atmosphere, with small contributions from the ocean and hydrological
system. On decadal timescales, the dominant contribution is from angular
momentum exchange between the solid mantle and fluid outer core.
Intradecadal periods have been less clear and have been characterized by
signals with a wide range of periods and varying amplitudes, including a
peak at about 6 years (refs 2-4). Here, by working in the time domain
rather than the frequency domain, we show a clear partition of the
non-atmospheric component into only three components: a decadally
varying trend, a 5.9-year period oscillation, and jumps at times
contemporaneous with geomagnetic jerks. The nature of the jumps in
length of day leads to a fundamental change in what class of phenomena
may give rise to the jerks, and provides a strong constraint on
electrical conductivity of the lower mantle, which can in turn constrain
its structure and composition