  We consider the effect of a random magnetic field in the convective zone of
the Sun superimposed to a regular magnetic field on resonant neutrino
spin-flavour oscillations. We argue for the existence of a field of strongly
chaotic nature at the bottom of the convective zone. In contrast to previous
attempts we employ in addition a model motivated regular twisting magnetic
field profile. In this scenario electron antineutrinos are produced through
cascades like $\nu_{eL}\to \nu_{\mu L}\to \tilde{\nu}_{eR}$, The expected
signals in the different experiments (SK,GALLEX-SAGE, Homestake) are obtained
as a function of the level of noise, regular magnetic field and neutrino mixing
parameters. Previous results obtained for small mixing and ad-hoc regular
magnetic profiles are reobtained. We confirm the strong suppression for large
part of the parameter space of the $\tilde{\nu}_{eR}$-flux for high energy
boron neutrinos in agreement with present data of the SK experiment. We find
that MSW regions ($\Delta m^2\approx 10^{-5}$ eV$^2$, both small and large
mixing solutions) are stable up to very large levels of noise (P=0.7-0.8) but
they are acceptable from the point of view of antineutrino production only for
moderate levels of it ($P\approx 0.95$). For strong noise and reasonable
regular magnetic field, any parameter region $(\Delta m^2, \sin^2 2\theta)$ is
excluded. As a consequence, we are allowed to reverse the problem and to put
limits on r.m.s field strength and transition magnetic moments by demanding a
particle physics solution to the SNP under this scenario.
