Wavelet bicoherence analysis of strong plasma turbulence at the Earth’s quasiparallel bow shock

Nonlinear interactions in strong plasma turbulence have been investigated in the vicinity of the Earth’s quasiparallel bow shock by making use of magnetometer data from the AMPTE–UKS (Active Magnetospheric Particle Tracer Explorers–United Kingdom Subsatellite) spacecraft. Using a new and more robust estimator of the bicoherence, it is shown that the large-amplitude monolithic magnetic structures observed upstream the shock front interact with the whistler wave trains that accompany them. A unified picture emerges, in which the whistlers progressively grow from these soliton-like structures through nonlinear interaction, similarly to the dynamical evolution of step-like profiles in the Korteweg–de Vries equation.