Excitation of proton cyclotron waves at interplanetary travelling shocks: ACE/MAG and SOHO/CELIAS observations

The quasi-linear theory on self-consistent wave generation and ion acceleration upstream of an interplanetary travelling shock by M.A. Lee (1983) applies for strongly super-Alfvenic ions amplifying pure Alfven waves in the solar wind. Spacecraft data from the ACE magnetometer and from the CELIAS/HSTOF sensor on board SOHO indicate that weakly super-Alfvenic ions generate ion whistler waves. This is a natural consequence of the dispersion relation of Alfven waves which enters the ion whistler branch if the wave frequency approaches the proton gyro-frequency. We extend the theory by Lee (1983) to apply for weakly super-Alfvenic ions and for self-generated ion whistler (ion cyclotron) waves.