Wave power studies of cusp crossings with the Polar satellite

Abstract

Burst data from the electric field instrument (EFI) on the Polar satellite are used to classify cusp wave properties and the association of the observed waves with particle populations. The most intense wave type (most commonly triggering burst mode data collection) are the broadbanded waves which are then studied in detail using the three‐dimensional resolution of the EFI. Finite wavelength effects are removed using two techniques: time‐shifting of the sphere potentials to a spacecraft body reference time and spin angle selection. The corrected electric field signal exhibits a uniform spectrum in two dimensions. The wave properties are consistent with two‐dimensional turbulence, with phase velocities smaller than the spacecraft velocity and frequency as low as (or lower than) the oxygen gyrofrequency. Owing to their low frequency, we conclude that these waves cannot resonate with and thus heat the ions. The broad k‐spectrum and very low frequency in the plasma frame points toward drift or shear instabilities for wave excitation.