Particle precipitations due to nonlinear wave-particle interactions in the magnetosphere.

We have studied chaos and nonlinear dynamics of a bouncing proton in the presence of a kinetic Alfven wave in the magnetosphere. We traced the particle motion numerically in phase space using Poincare' surface of section technique. With suitable initial conditions we obtained particle trajectories (under paraxial approximation) for various values of the wave amplitudes. The trajectories show chaotic behavior at the finite amplitude of the wave. The threshold electrostatic field computed for the onset of chaos is less than expected electric field accompanied with kinetic Alfven wave in the magnetosphere. We believe that kinetic Alfven wave can lead to proton precipitation near the equatorial region.