One of the world’s fastest computers
DOI: 10.1063/1.4797225
Tackles one of the world’s toughest problems: the generation of Earth’s magnetic field. The field arises from the planet’s fluid outer core. There, according to the prevailing picture, convection and rotation drive a dynamo that generates and sustains the field. Because the underlying equations are nonlinear and complex, modeling any magnetohydrody-namical system is tough. Earth’s dynamo poses an additional challenge: Many of the features that geophysicists want to understand, such as the field’s sporadic reversals of polarity, occur over tens of millennia, with the fluid’s viscosity close to that of water. To work at all, computer models of Earth’s dynamo must artificially raise the viscosity. The first comprehensive model, published 10 years ago, relied on a boost factor of a million and yielded one tentative field reversal (see Physics Today, January 1996, page 17 ). Now, using Japan’s powerful Earth Simulator computer (shown in the photo), Futoshi Takahashi of Japan’s Institute of Space and Astronautical Science and Masaki Matsushima and Yoshimori Honkura of Tokyo Institute of Technology have reduced the required boost factor to a relatively modest 100. In their simulation, which runs over 400 000 years, reversals begin when strong, high-latitude patches of magnetic flux drift toward the poles and fade away. Patches of reversed polarity then emerge at low and mid latitudes and drift poleward to complete the reversal. (
