Gravitational torque on the inner core and decadal polar motion

Details Gravitational torque on the inner core and decadal polar motion Gravitational torque on the inner core and decadal polar motion

Mar 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008geoji.172..903d&link_type=abstract

Geophysical Journal International, Volume 172, Issue 3, pp. 903-920.

Astronomy and Astrophysics

Astronomy

8

Earth Rotation Variations, Dynamo: Theories And Simulations, Mantle Processes, Elasticity And Anelasticity

Scientific paper

A decadal polar motion with an amplitude of approximately 25 milliarcsecs (mas) is observed over the last century, a motion known as the Markowitz wobble. The origin of this motion remains unknown. In this paper, we investigate the possibility that a time-dependent axial misalignment between the density structures of the inner core and mantle can explain this signal. The longitudinal displacement of the inner core density structure leads to a change in the global moment of inertia of the Earth. In addition, as a result of the density misalignment, a gravitational equatorial torque leads to a tilt of the oblate geometric figure of the inner core, causing a further change in the global moment of inertia. To conserve angular momentum, an adjustment of the rotation vector must occur, leading to a polar motion. We develop theoretical expressions for the change in the moment of inertia and the gravitational torque in terms of the angle of longitudinal misalignment and the density structure of the mantle. A model to compute the polar motion in response to time-dependent axial inner core rotations is also presented. We show that the polar motion produced by this mechanism can be polarized about a longitudinal axis and is expected to have decadal periodicities, two general characteristics of the Markowitz wobble. The amplitude of the polar motion depends primarily on the Y12 spherical harmonic component of mantle density, on the longitudinal misalignment between the inner core and mantle, and on the bulk viscosity of the inner core. We establish constraints on the first two of these quantities from considerations of the axial component of this gravitational torque and from observed changes in length of day. These constraints suggest that the maximum polar motion from this mechanism is smaller than 1 mas, and too small to explain the Markowitz wobble.

Affiliated with

Also associated with

No associations

Rating

Gravitational torque on the inner core and decadal polar motion does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Gravitational torque on the inner core and decadal polar motion, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gravitational torque on the inner core and decadal polar motion will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-957082