ESC seminar No. 43

Geodynamo simulations in low viscosity regime

Date
September 26 (Fri.), 2008, 14:30 - 15:30
Place
Seminar Room. 1F, Earth Simulator Research Building, YES
Speaker
Dr.Akira Kageyama (Earth Simulator Center, JAMSTEC)
Language
Japanese

Abstract

One of the difficulties in simulating the geodynamo arises from the small viscosity of the outer core, which is characterized by a non-dimensional parameter called Ekman number. The Ekman number of the earth's outer core is of the order of 10-15.

Following the initial computer simulations of the geodynamo about a decade ago, the Ekman number achieved has been steadily decreasing, with recent geodynamo simulations performed with the Ekman number of the order of 10-6. We have perfomed a geodynamo simulation with an Ekman numberof the order of 10-7 by the highest-resolution simulation yet achieved, making use of 4,096 processors of the EarthSimulator.

We have found that both the convection flow and magnetic field structures are qualitatively different from those found in larger Ekman-number dynamos. The convection takes the form of sheet plumes or radial sheet jets, rather than the columnar cell structures that are usually found.

We have found that this sheet plume convection is an effective dynamo and the generated current is organized as a set of coils in the shape of helical springs or at times as a torus. An advanced visualization system based on the virtual reality technology plays key roles in analyzing three-dimensional structure of various vector fields.

Contact

Dr. Shigenobu Hirose
Earth Simulator Center
TEL: 045-778-5783
e-mail: shirose