Estimates of core-mantle torques from rotational and gravitational data

Details Estimates of core-mantle torques from rotational and gravitational data Estimates of core-mantle torques from rotational and gravitational data

Mar 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001geoji.144..532d&link_type=abstract

Geophysical Journal International, Volume 144, Issue 3, pp. 532-538.

Astronomy and Astrophysics

Astronomy

1

Core-Mantle Coupling, Gravitational Data, Rotational Fluctuations, Torques

Scientific paper

In this study, the amount of core participation in rotational accelerations of the mantle is used to infer the strength of core-mantle coupling at various tidal periods. Determining the role of the core in rotational fluctuations depends on our ability to quantify the contributions by the oceans, solid earth and atmosphere to the rotational signals. At lunar tidal nine-day and fortnightly periods, estimates of core participation are taken from the analysis of length-of-day data by Dickman & Nam (1995), which incorporated theoretical predictions of the oceanic and solid-earth contributions. Maximum torques at these two periods consistent with observation are estimated to be 1.5×1016 and 2.4×1017 Nm, respectively. At seasonal periods, a novel approach is presented that employs time-dependent gravitational data to quantify all of the mass redistributions that excite seasonal changes in the length of day. Combined with rotational data, our efforts to constrain core participation meet with only limited success at the annual period, as a result of larger-than-optimal uncertainties in both the gravity data and especially the rotational signal. Because those error bars should improve over time, our gravitational approach can eventually be expected to provide useful bounds on annual axial torques between the core and mantle. At the semi-annual period, in contrast, all uncertainties are much smaller but the gravity data are not yet reliable.

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