Evidence for a Rotationally Driven Geodynamo From Laboratory Experiments and Measurements of Relative Paleointensity
Abstract
We model Earth's fluid core as a massive, low viscosity, contained, rotating fluid subjected to Luni-Solar strains. As long as the known strain rates, due to precession or semi-diurnal tide, exceed dissipation rates in the core, a rotating parametric instability (RPI) will cycle through growth and decay provided the Luni-Solar forcing continues. Laboratory measurements of RPI, observed over three decades, show faster growth than predicted in fluids contained by flexible boundaries which model the semi-diurnal tide. We report on recent experiments in a 30- cm diameter, flexible-walled sphere in which the retrograde period of semi-diurnal strain is allowed to depart from the prograde period of the container's rotation. A geodynamo driven by an RPI will leave a signature of the instability's growth and decay in the paleointensity record. We report on the properties of this signature obtained from measurements of relative paleointensity from several oceanic sites over the past decade. After averaging over individual cores to reduce the effect of errors in chronology, growth rates recovered from these observations are consistent with predictions from linear stability theory. Decay rates yield estimates of core viscosity similar to that of liquid metals.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2006
- Bibcode:
- 2006AGUSMDI52A..04B
- Keywords:
-
- 1507 Core processes (1213;
- 8115);
- 1510 Dynamo: theories and simulations;
- 1521 Paleointensity;
- 1560 Time variations: secular and longer;
- 3215 Instability analysis