  One of the key questions in solar physics that remains to be answered
concerns the strength and the distribution of the magnetic fields at the base
of the convection zone. The flux tube dynamics requires that toroidal fields of
strength as large as 100 kilogauss be present at the base of the convection
zone. The kinetic-magnetic equipartition argument leads to smaller field
strengths. For possible detection of these relatively small (compared to
pressure effects) fields by helioseismic methods it is important to know the
range of the field strengths and their distribution.
  We estimate a range for the toroidal magnetic field strengths at the base of
the convection zone using dynamo simulations in a spherical shell. These
simulations involve the distribution of rotation provided by helioseismic
inversions of the GONG and MDI data. Combining the simulations with the
observed line-of-sight surface poloidal field we extract the spatial pattern
and magnitude of the mean toroidal magnetic field at the base of the convection
zone.
