The Rapid Variability of Wave Electric Fields Within and Near Quasiperpendicular Interplanetary Shock Ramps: STEREO Observations

We present STEREO observations within 1500 proton gyroradii of 12 quasiperpendicular interplanetary shocks, with long-duration burst mode electric field acquisition by S/WAVES enabling observation of the evolution of waves throughout the entire ramp of interplanetary shocks. The shocks are low Mach number (Mf ∼ 1-5), with beta (β) ∼0.2-1.8. High variability in frequency, amplitude, and wave mode is observed upstream, downstream, and in shock ramps. Observations in every region include ion acoustic-like waves, electron cyclotron drift instability (ECDI) driven waves, electrostatic solitary waves, and high frequency whistler mode waves. We also show for the first time the existence of electrostatic waves with frequencies in the ion acoustic range, which are frequency dispersed in time and the first observations of ECDI-driven waves at interplanetary shocks. The waves are bursty, large amplitude (∼5->200 mV m−1), and seen in all three regions. All wave modes are more commonly observed downstream than upstream.