LIQUID MZTAL MHD AND THE GEODYNAMO

ABSTRACT. The magnetic field of the Earth is generated by dynamo action arsociated with the upwelling ot buoyant material in the liquid outer core. It is argued that this upwelling occurs in the form ot mushroom-shaped blobs of material released from the mushy zone at the inner core boundary (ICE), and having a very small denrity defect 6p/p. The rise of buoyant material with velocity W is compenaated by the slow rate of growth of the solid inner core. The resulting maas balaace, combined with approximate geortrophic force balance in the core leada to estimates 6 p / p- 3 x 10- ~ ,- 2 x I O- ~ ~ / S. Each riring blob drives a Taylor column, and the helicity and O-effect Mrociated with thir flow is estimated. A mean-field dynamo driven by thir a-effect in conjunction with differential rotation geuarstsa a magnetic field whore strength is determined in order of magnitude byr)he plaurible urumption of magnetoatrophic equilibrium. I