  Chaotic evolution of structures in Coupled map lattice driven by identical
noise on each site is studied (a structure is a group of neighbouring
lattice-sites for whom values of dynamical variable follow certain predefined
pattern). Number of structures is seen to follow a power-law decay with length
of the structure for a given noise-strength. An interesting phenomenon, which
we call stochastic coherence, is reported in which a rise of bell-shaped type
in abundance and lifetimes of these structures is observed for a range of
noise-strength values.
