  Thermalization and heating of plasma flows at shocks result in unstable
charged-particle distributions which generate a wide range of electromagnetic
waves. These waves, in turn, can further accelerate and scatter energetic
particles. Thus, the properties of the waves and their implication for
wave-particle interactions are critically important for modeling energetic
particle dynamics in shock environments. Whistler-mode waves, excited by the
electron heat flux or a temperature anisotropy, arise naturally near shocks and
foreshock transients. As a result, they can often interact with supra-thermal
electrons. The low background magnetic field typical at the core of such
transients and the large wave amplitudes may cause such interactions to enter
the nonlinear regime. In this study, we present a statistical characterization
of whistler-mode waves at foreshock transients around Earth bow shock, as they
are observed under a wide range of upstream conditions. We find that a
significant portion of them are sufficiently intense and coherent to warrant
nonlinear treatment. Copious observations of background magnetic field
gradients and intense whistler wave amplitudes suggest that phase trapping, a
very effective mechanism for electron acceleration in inhomogeneous plasmas,
may be the cause. We discuss the implications of our findings for electron
acceleration in planetary and astrophysical shock environments.
