  We report in details the observations of structures in coupled map lattice
during its chaotic evolution, both in one and two dimension, driven by
identical noise on each site (by a structure we mean a group of neighboring
lattice-sites for whom values of dynamical variable follow certain prespecified
pattern). It is observed that the number of these structures decays with their
size following a power-law, for a given noise-strength. The number of
structures decays with their lifetime following a stretched exponential. We
have seen an interesting phenomenon, which we call stochastic coherence, in
which the average length as well as the average lifetime of these structures
exhibit bell-shaped maxima for some intermediate range of noise-strength
values. Similar features have also been observed for `spatio-temporal
structures'.
