  We present a study of disorder origination and growth inside an ordered phase
processes induced by the presence of multiplicative noise within mean-field
approximation. Our research is based on the study of solutions of the nonlinear
self-consistent Fokker-Planck equation for a stochastic spatially extended
model of a chemical reaction. We carried out numerical simulation of the
probability distribution density dynamics and statistical characteristics of
the system under study for varying noise intensity values and system parameter
values corresponding to a spatially inhomogeneous ordered state in a
deterministic case. Physical interpretation of the results obtained that
determines the scenario of noise-induced order-disorder transition is given.
Mean-field results are compared with numerical simulations of the evolution of
the model under study.
  We find that beginning from some value of external noise intensity the
"embryo" of disorder appears inside the ordered phase. Its lifetime is finite,
and it increases with growth of noise intensity. At some second noise intensity
value the ordered and disordered phases begin to alternate repeatedly and
almost periodically. The frequency of intermittency grows with the increasing
of noise intensity. Ordered and disordered phase intermittency affects the
process of spatial pattern formation as a consequent change of spatial
inhomogeneity configurations.
