Concurrent Astronomical Observations for Studying Continental Drift, Polar Motion, and the Rotation of the Earth

Markowitz, Wm.

doi:10.1017/s0074180900019240

Cited by 14 publications

(13 citation statements)

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“…The Markowitz wobble is a somewhat irregular polar motion with a magnitude of roughly 20 to 50 milliarcseconds (mas) (Markowitz 1960(Markowitz , 1968. Until recently, the existence of this oscillation was in doubt for several reasons, including changes in the star catalogues and modifications in data processing techniques (e.g.…”

Section: Introductionmentioning

confidence: 99%

Inner core tilt and polar motion

Dumberry

Bloxham

2002

Geophysical Journal International

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Summary A tilted inner core permits exchange of angular momentum between the core and the mantle through gravitational and pressure torques and, as a result, changes in the direction of Earth's axis of rotation with respect to the mantle. We have developed a model to calculate the amplitude of the polar motion that results from an equatorial torque at the inner core boundary which tilts the inner core out of alignment with the mantle. We specifically address the issue of the role of the inner core tilt in the decade polar motion known as the Markowitz wobble. We show that a decade polar motion of the same amplitude as the observed Markowitz wobble requires a torque of 1020 N m which tilts the inner core by 0.07 degrees. This result critically depends on the viscosity of the inner core; for a viscosity less than 5 × 1017 Pa s, larger torques are required. We investigate the possibility that a torque of 1020 N m with decadal periodicity can be produced by electromagnetic coupling between the inner core and torsional oscillations of the flow in the outer core. We demonstrate that a radial magnetic field at the inner core boundary of 3 to 4 mT is required to obtain a torque of such amplitude. The resulting polar motion is eccentric and polarized, in agreement with the observations. Our model suggests that equatorial torques at the inner core boundary might also excite the Chandler wobble, provided there exists a physical mechanism that can generate a large torque at a 14 month period.

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Section: Introductionmentioning

confidence: 99%

Inner core tilt and polar motion

Dumberry

Bloxham

2002

Geophysical Journal International

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“…With such a data set, it is possible to evaluate the trend in polar motion and to investigate possible low-frequency periodic motions, which have been suggested previously (Hattori 1959;Markowitz 1960Markowitz , 1968Markowitz , 1970. Early investigations, which used optical astronomical data, were plagued by the possibility of systematic errors in the proper motions contained in the star 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000 (1988) concluded that the low-frequency oscillation was caused by systematic effects a t the individual stations.…”

Section: Introductionmentioning

confidence: 99%

“…To investigate the nature of the very low-frequency polar motion, it is necessary to assemble a series of polar-motion observations that are consistent within one reference system. With such a data set, it is possible to evaluate the trend in polar motion and to investigate possible low-frequency periodic motions, which have been suggested previously (Hattori 1959;Markowitz 1960Markowitz , 1968Markowitz , 1970. Early investigations, which used optical astronomical data, were plagued by the possibility of systematic errors in the proper motions contained in the star 1920 1940 1960 1980 2000 1900 1920 1940 1960 1980 2000 catalogues and by the fact that some of the ILS stations did not observe continuously [see Yumi & Wako (1965) and Lambeck ( 1 980,].…”

Section: Introductionmentioning

confidence: 99%

Path of the Mean Rotational Pole From 1899 to 1994

McCarthy

Luzum

1996

Geophysical Journal International

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S U M M A R YHistorical sources of polar motion are analysed together with modern data in order to compile a set of coordinates of the mean pole in a reference system consistent with that of the International Earth Rotation Service. The trend and quasi-periodic motion of the pole are investigated, and we find that the rotational pole appears to be moving at the rate of 0.333 arcsec century-' in the direction of 75.0" west longitude. Modern data also appear to be consistent with the possible existence of very low-frequency periodic motion (Markowitz wobble).

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“…In particular, Adhikari and Ivins (2016) demonstrated that the continent-ocean mass transport and the terrestrial water storage can explain the observed polar motion departure from a secular trend (excited by GIA) since 2000. Nevertheless, these obviously do not well explain the majority of the decadal polar motion, including the ∼30 year Markowitz wobble (e.g., Gross, 2015;Markowitz, 1968;Schuh et al, 2001;Vicente & Wilson, 2002). In addition, Chao (2017) in his recent studies asserted two rotational modes in the Earth system, namely, the axial torsional libration and the inner core wobble, owing to the mantle-inner core gravitational torques (Buffett, 1996).…”

Section: Introductionmentioning

confidence: 99%

Decadal Polar Motion of the Earth Excited by the Convective Outer Core From Geodynamo Simulations

2017

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Long time geodetic observation records show that the orientation of the Earth's rotation axis with respect to the terrestrial reference frame, or polar motion, changes on a broad range of timescales. Apart from external torques from the luni‐solar tides, these changes are excited by interactions among different components of the Earth system. The convective fluid outer core has long been conjectured a likely contributor to the observed polar motion on timescales upward of decades, such as the ∼30 year Markowitz wobble. We investigated the electromagnetic coupling scenario across the core‐mantle boundary via numerical geodynamo simulation for different geodynamo parameters (Rayleigh numbers and magnetic Rossby numbers). Our simulated polar motion varies strongly with the dynamo parameters, while its excitation on decadal timescales appear to converge asymptotically within the adopted range of numerical Rossby numbers. Three strongest asymptotic modes emerge from numerical results, with periods around 30, 40, and 60 years for the prograde excitation and around 24, 30, and 60 years for the retrograde excitation. Their amplitudes are all larger than 5 × 10−8, or approximately 10 milliseconds of arc. The results suggest that the electromagnetic core‐mantle coupling could explain a substantial portion, if not all, of the observed decadal polar motion. In particular, the predicted 60 year polar motion deserves special attention for future observations and studies.

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Concurrent Astronomical Observations for Studying Continental Drift, Polar Motion, and the Rotation of the Earth

Cited by 14 publications

References 1 publication

Inner core tilt and polar motion

Inner core tilt and polar motion

Path of the Mean Rotational Pole From 1899 to 1994

Decadal Polar Motion of the Earth Excited by the Convective Outer Core From Geodynamo Simulations

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