Rotationally Driven Geodynamo: Evidence from Laboratory Observations and Paleomagntic Intensity

Fluctuations in the paleomagnetic field with observed duration of order 10kyr are modeled as growths and decays due to excitation and collapse of rotational parametric instabilities (RPI) in Earth's fluid core. Theoretical calculation and experimental evidence over the past three decades have shown that RPI will exist in a contained, rotating fluid undergoing continuous straining of streamlines. In Earth's fluid core, elliptical strain is produced by the luni-solar tide and predominantly shear strain from precession of the mantle. The signature of RPI in Earth's fluid core has been found in paleomagnetic intensity records from oceanic sediment cores that is consistent with the growth times expected from the luni-solar tide and precession. This result is also consistent with our recent laboratory work where a tide-like perturbation is imposed at the outer boundary of a flexible spheroidal container both with and without an inner core. RPI has been identified near the diurnal period. Results of a search for instabilities at neighbouring tidal periods will be reported.