Reconstructing High-Cadence Ion Velocity from MMS Trigger Mode Data: Enabling Extended Analysis of Magnetosheath Wave Phenomena

During MMS fast mode intervals FPI operates continuously in the burst mode, of which only a few percent of the burst mode is downloaded. Four ion moments (ion density, ion flux) termed trigger mode are continuously computed onboard from the burst data at a 150 msec cadence and telemetered over the entire fast mode interval. Before the trigger data is telemetered the sign bits of the 3 ion flux components are dropped so ion velocity can't be computed on the ground. Using 4 s FAST mode data and minimization methods, we reconstruct the sign bits of the ion flux and compute ion velocity. As a validation check we compare the trigger velocity with the available burst mode velocity over multiple fast mode magnetosheath intervals (~100 of burst mode comparisons). We demonstrate the scientific usefulness of the trigger derived density and velocity in the magnetosheath by analysis of ~1-hour long interval consisting of highly coherent ion cyclotron waves. The velocity perturbations when compared to the magnetic field perturbations of the ICW are consistent with linear dispersion theory in both amplitude and phase. We also demonstrate that the velocity perturbations are highly correlated with the magnetic field curlometer derived current of the ICW. Our goal is to create a public archive at the SPDF of calibrated sign bit reconstructed ion trigger density and velocity for all magnetosheath and boundary layer intervals over the MMS mission.