Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmgp43a0790v&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #GP43A-0790
Astronomy and Astrophysics
Astronomy
1213 Earth'S Interior: Dynamics (1507, 7207, 7208, 8115, 8120), 1507 Core Processes (1213, 8115), 5744 Orbital And Rotational Dynamics (1221), 8130 Heat Generation And Transport
Scientific paper
Mantle precession and core oblateness have been suggested for support of geodynamo energy dissipation and fluid motions. Precession usually has been considered negligible. With a precession motion of 25,800 year/period and a period of 60x360 = 21,600 arc-minute, the motion is on the order of one arc-minute/year (little off by the sine of Earth's obliquity). The 'rigid' mantle changes its axis direction about one arc-minute each year. That is a major motion. Compare the sun's or the moon's apparent diameter of about 32 arc- minute. The CMB's oblateness is about (a-b)/a = 1/400. With (a-b) = 8.7 km, and estimates of its surface irregularities over 3 km, the CMB is neither smooth nor oblate. Between its 'calculated' oblate CMB and a 'calculated' included sphere, its very thin crescentoid interstice will generate turbulence and separation form drag with large dissipation energy rates. The actual core will not see the CMB but an effective smaller fluid sphere. Precession is an important feature of a geodynamo, but 1/400 oblateness is less pertinent. The core axis lags the precessing mantle axis by a small angle. This misalignment daily rubs the core against the mantle and produces major energy dissipation rates. The liquid core maintains its average lagging location by coupling drag and core internal flows. A correct analysis will use a 'rigid-sphere' model (1972 ref.) for energy, geodynamo, and coupling motion. The outer core is a melt whose temperature and heat are well known but not its cause. Some will be residual heat, but much of it will be generated by precession and radioactivity. Rigid-sphere energy (J. Appl. Mech. 1972, v39, 18-24). Geodynamo precession (Geo. Astro. Fluid Dyn. 1991, v59, 209-234). Turbulent laminar flow (Geophys. J. Intl., 1995, v121, 136-142). Concentric cylinders (Geophys. J. Intl., 2000, v142, 409-425). Core mantle coupling (Geophys. J. Intl., 2004, v158, 470-478). Theory and data (Rotating Fluids", 2001, Dover, Figs. 4.5, 4.10 and pp. 326, 397).
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