Open AccessInterannual oscillations in length of day: Implications for the structure of the mantle and core
Author(s) -
Mound J. E.,
Buffett B. A.
Publication year - 2003
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2002jb002054
Subject(s) - mantle (geology) , inner core , core–mantle boundary , angular momentum , physics , geophysics , earth's rotation , outer core , earth's internal heat budget , dynamo theory , geology , mantle convection , dynamo , magnetic field , classical mechanics , lithosphere , astronomy , quantum mechanics , paleontology , tectonics
An ∼6‐year variation in the length of day has been observed for which there is no corresponding signal in records of atmospheric angular momentum. We find that this signal can be explained by an exchange of angular momentum with the core arising from gravitational coupling between the mantle and inner core. We develop a theoretical model of the core‐mantle system that includes a combination of gravitational and electromagnetic couplings that allow angular momentum to be transferred between the solid inner core, fluid outer core, and mantle of the Earth. This model is used to calculate the natural period of interannual oscillations in the axial rotation of the core and mantle. The period and quality of the free oscillations depend on physical properties of the core and mantle. Time‐varying geodynamo processes produce torques on the inner core which are capable of exciting the predicted free oscillations to observable levels. The observed length‐of‐day variation is used to constrain the strength of gravitational coupling between the mantle and inner core and hence the degree 2, order 2 component of equipotential surfaces at the inner core boundary and core mantle boundary. This constraint has implications for models of mantle flow.