Debye‐scale bipolar structures and their role in the electron trajectory instability at the bow shock

A number of mechanisms have been suggested to operate within the terrestrial bow shock to redistribute energy contained in the incoming solar wind flow. The majority of mechanisms involve the generation of turbulence while some are based on particle motion alone. In this paper, we investigate the possible occurrence of the Electron Trajectory Instability, that results from short scale electric field gradients. Spike-like bipolar features in electric field measurements are a commonly observed signature within the terrestrial bow shock. They are usually associated with the passage of electrostatic solitary waves associated with phase space holes in the particle distribution. Using electric field measurements, we compare different interferometric methods to determine the propagation direction, velocity, and spatial scale of these features. Based on these results, it appears that the instability criterion for the Electron Trajectory Instability is fulfilled and the electron trajectories will diverge in the presence of these structures.