removal of heat from the core by the convecting mantle drives the
geodynamo that generates the Earth's magnetic field. Much
recent progress has been made in modeling the dynamo process, yet
much remains to be understood. How is the magnetic field evolving
on annual to decadal time scales? For how much longer will the current
rate of decay of the field, sufficiently rapid to eliminate the
dipole in 2000 years, be maintained? What role does the core play
in the angular momentum balance of the Earth on decadal time scales?
How important is the magnetic field in modulating the possible effects
of space weather on the atmosphere, and hence on climate?
magnetic measurements are essential for mapping and understanding
not only the main part of the Earth's magnetic field generated
in the Earth's liquid outer core, but also the crustal field,
the external field, and currents induced in the mantle by the external
field. The combination of satellite-based measurements with numerical
modeling promises to lead to a new level of understanding of the
generation of Earth's magnetic field.