Analysis of waves surrounding foreshock cavitons

Cavitons have been recently discovered in the Earth’s foreshock. Foreshock cavitons have first been predicted by global hybrid simulations and later structures with similar properties were discovered in observational data from the Cluster mission. Cavitons are observed as simultaneous depressions of the magnitude of the magnetic field and plasma density (δB/B, δn/n⩾0.2) that commonly last ⩽30 s and are surrounded by a rim of enhanced values of B and n. They are always immersed in a sea of compressive low frequency waves. Numerical simulations results suggest that the cavitons are produced by the interaction of foreshock sinusoidal plasma waves with perpendicularly propagating compressive fast mode waves. Here we present a study of the waves that were observed in the immediate neighborhood or inside two foreshock cavitons detected by the Cluster I spacecraft. We analyze the frequency, polarization, direction of propagation and compressibility of the waves.