TRICE 2 Observations of Drifting Ion Upflows within the Northern Magnetospheric Cusp

On 08 December 2018 the Twin Rockets to Investigate Cusp Electrodynamics 2 (TRICE 2) sounding rocket mission carried two payloads through the northern magnetospheric cusp, a funnel shaped region of converging open magnetic field lines located near the Earths poles. Included on each payload was an ion electrostatic analyzer which measured ion distributions down to 13 eV with a full 360 field-of-view, electric field double-probes which measured the three-axis local DC electric field vector and the electric component of ELF/VLF plasma waves, as well as a commercial fluxgate magnetometer which measured the three-axis local magnetic field vector. During the TRICE 2 cusp traversal, the ion instrument measured upflowing low-energy ion distributions which peaked at pitch angles near ~135, near the poleward edge of the cusp. These upflowing ion distributions were correlated with broadband wave enhancements. The convection velocity calculated from the local DC electric and magnetic fields, in the spacecraft frame, also reveal a correlation between enhancements in the field-derived convection speed and the appearance of ion upflows. Plotting the ion data in pitch angle vs. rocket spin angle space reveals that the ion upflows were measured with a directional dependence, suggesting that these ion upflows were drifting. The measured velocity distributions show a drifting ion conic distribution, suggesting that the ion upflows were shifted into the field of view of the ion instrument by this drifting behavior. By performing a geometric 2D fit and approximating an appropriate ion conic distribution it was possible to obtain a lower bound to the drift speed needed to reproduce the measured velocity distribution. This study presents the TRICE 2 cusp observations and reports an ion-derived lower bound to the convection speed.