Summary: Quasigeostrophic models of convection in rotating spherical
Institut for Geophysics of the University of Goettingen, Herzberger Landstrasse 180, Goettingen 37075, Germany
Nicolas Gillet and Philippe Cardin
Laboratoire de Ge´ophysique Interne et Tectonophysique, Observatoire de Grenoble, B.P. 53, 38041 Grenoble, France
 The use of a quasigeostrophic, two-dimensional approximation in the problem of convection in a
rapidly rotating spherical shell has been limited so far to investigations of the qualitative behavior of the
solution. In this study, we build a quasigeostrophic model that agrees quantitatively with full three-
dimensional solutions of the onset of convection in the case of differential heating. Reducing the
dimensionality of the problem also permits the simulation of finite amplitude regimes of convection, up to
quasigeostrophic turbulence. The nonlinear behavior of the system is studied in detail and compared to
ultrasonic Doppler velocimetry measurements performed in a convecting, rapidly rotating spherical shell
filled with water and liquid gallium. The results are quantitatively satisfactory and open the way to less
computer-demanding, and still accurate, simulations of the geodynamo.
Components: 8168 words, 13 figures, 1 table, 2 dynamic content.
Keywords: Geodynamo; convection; quasigeostrophic numerical models.
Index Terms: 1507 Geomagnetism and Paleomagnetism: Core processes (8115); 1510 Geomagnetism and Paleomagnetism: