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[1] We present Polar observations of high frequency (100 Hz ≲ f ≲ 4000 Hz) electrostatic (ES) waves at Earth's bow shock under extreme solar wind conditions. Although solitary waves are observed, the most prevalent structures in the magnetic ramp are coherent, large-amplitude (up to 80 mV/m) ES wave packets, which last 10–30 cycles, and propagate at varied obliquities relative to the magnetic field. The ES wave power is well correlated with maxima in the magnetic ramp substructure, suggesting that these maxima are important source regions. Detailed interferometric based analysis of waveforms show that they have wavelengths of a few hundred meters (e.g., ∼20λD ∼ 0.5ρe) and phase speeds at the acoustic speed, suggesting that they are ion acoustic waves (IAW)s. The IAWs, having potentials ≲1 V with no net change, are not likely to affect bulk plasma energization, though they may scatter the plasma and thus affect plasma thermalization.