  The possibility of non-axisimmetric (kink) instabilities of a toroidal field
seated in the tachocline is much discussed in the literature. In this work, the
basic properties of kink and quasi-interchange instabilities, produced by mixed
toroidal and poloidal configuration, will be briefly reviewed. In particular it
will be shown that the unstable modes are strongly localized near the Equator
and not near the Poles as often claimed in the literature. Based on the results
of recent numerical simulations, it is argued that a non-zero helicity can
already be produced at a non-linear level. A mean-field solar dynamo is then
constructed with a positive $\alpha$-effect in the overshoot layer localized
near the Equator and a meridional circulation with a deep return flow. Finally,
the possibility that the solar cycle is driven by a $\alpha\Omega$ dynamo
generated by the negative subsurface shear in the supergranulation layer will
also be discussed.
