Kinetic Modeling of Ionospheric Outflows Observed by the VISIONS Sounding Rockets

Plasma escape from the high-latitude ionosphere (ion outflow) serves as a significant source of heavy plasma to the magnetospheric plasma sheet and ring current regions. Outflow can significantly alter mass density and reconnection rates, hence global responses of the magnetosphere. The VISIONS-1 (VISualizing Ion Outflow via Neutral atom imaging during a Substorm) sounding rocket was launched on Feb. 7, 2013 at 8:21 UTC from Poker Flat, Alaska, into an auroral substorm with the objective of identifying the drivers and dynamics of nightside ion outflow at altitudes where it is initiated, below 1000km. Energetic ion data from the VISIONS-1 polar cap boundary crossing show evidence of an ion ``pressure cooker'' effect whereby ions energized via transverse heating in the topside ionosphere travel upward and are impeded by a parallel potential structure at higher altitudes. VISIONS-1 was also instrumented with an energetic neutral atom (ENA) detector which measured neutral particles (~50-100 eV energy) produced by charge-exchange with the energized outflowing ions. The purpose of this instrument was to try to detect and understand ENAs produced by ion outflow and to investigate ENAs as a means to remotely sense ionospheric outflow.

This investigation focuses on better understanding the connections of ion outflows and ENAs and the use of ENA detections for understanding ion outflows. We develop a new kinetic model which traces large numbers of individual macro-particles, using a guiding-center approximation, in order to facilitate calculation of ion distribution functions and moments. For the present study we include mirror and parallel electric field forces, ambipolar electric field, charge-exchange, and a parameterized source of ion cyclotron resonance (ICR) wave heating, thought to be central to the transverse energization of ions. The model is initiated with a steady-state ion density altitude profile and Maxwellian velocity distribution characterizing the initial phase-space conditions for multiple particle trajectories. This document outlines the design and implementation of our kinetic outflow model and shows initial applications of this model to simulate outflow representative of conditions observed during the VISIONS-1 campaign. This project provides quantitative means to interpret VISIONS data and related remote sensing approaches to studying ion outflow and serves to advance our understanding of the drivers and particle dynamics in the auroral ionosphere and to improve data analysis for future sounding rocket and satellite missions.