From a general turbulence model, useful properties of the bicoherence
gamma(omega1,omega2) are derived: Let S = SIGMA(omega') gamma(omega,om
ega-omega')2, then S less-than-or-equal-to 1 for near-Gaussian fluctua
tions (S almost-equal-to 1 if the turbulent broadening is small), and
S may be > 1 for turbulence dominated by coherent structures. These re
gimes of increasing nonlinear coherence are demonstrated through analy
sis of data from a toroidal plasma device.