Peter L. Olson

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We analyse *50 3-D numerical calculations of hydrodynamic dynamos driven by convection in a spherical shell. We examine rigid and stress-free boundaries, with Prandtl number 1, magnetic Prandtl numbers in the range 0.5^5, Ekman numbers E~10{3^10{4 and Rayleigh numbers to 15 times critical. No parametrizations such as hyperviscosities are used. Successful(More)
Results of thermal convection experiments in a rotating uid with a geometry similar to the Earth's core tangent cylinder are presented. We nd four di erent regimes of convection. In order of increasing heat ow, these are: (1) subcritical (no convection), (2) helical plumes (hetons) around the tangent cylinder, (3) hetons throughout the tangent cylinder, and(More)
The four most recent large mass extinction events in the Phanerozoic – the Cretaceous–Tertiary (KT), the Triassic–Jurassic (TJ), and the Permo-Triassic (PT) and Guadalupian–Tatarian (GT) doublet – are associated with a major flood basalt eruption, with the timing of peak volcanic activity corresponding within measurement uncertainties to the extinction(More)
Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including(More)
Seismic waves sampling the top 100 km of the Earth's inner core reveal that the eastern hemisphere (40 degrees E-180 degrees E) is seismically faster, more isotropic and more attenuating than the western hemisphere. The origin of this hemispherical dichotomy is a challenging problem for our understanding of the Earth as a system of dynamically coupled(More)
Short-lived isotope systematics, mantle siderophile abundances and the power requirements of the geodynamo favour an early and high-temperature core-formation process, in which metals concentrate and partially equilibrate with silicates in a deep magma ocean before descending to the core. We report results of laboratory experiments on liquid metal dynamics(More)
We present numerical dynamo models which qualitatively reproduce some structural characteristics of the present-day geomagnetic field. Timedependent convection in an electrically conducting, rotating spherical shell at Ekman numbers 1 3 x l0 -4 generates dipole-dominated magnetic fields, which exhibit distinct bundles of strong radial flux at high(More)
The dipole moment of Earth’s magnetic field has decreased by nearly % MathType!Translator!2!1!AMS LaTeX.tdl!TeX -- AMS-LaTeX!% MathType!MTEF!2!1!+-% feaaeaart1ev0aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9%(More)