Stochastic ion heating at the magnetopause due to kinetic Alfven waves

The magnetopause and boundary layer are typically characterized by large amplitude transverse wave activity with frequencies below the ion cyclotron frequency. The signatures of the transverse waves suggest that they are kinetic Alfven waves with wavelength on the order of the ion gyroradius [Johnson and Cheng, 1997a; Johnson et al., 2001]. We investigate ion motion in the presence of large amplitude kinetic Alfven waves with wavelength the order of pi and demonstrate that for sufficiently large wave amplitude (deltaB(perpendicular to)/B-0 > 0.05) the particle orbits become stochastic. As a result, low energy particles in the core of the ion distribution can migrate to higher energy through the stochastic sea leading to an increase in T-perpendicular to and a broadening of the distribution. This process can explain transverse ion energization and formation of conics which have been observed near the magnetopause in both the magnetosheath and low-latitude boundary layer.