Physics & Astronomy/Thayer Plasma Seminar - Matina Gkioulidou, JHUAPL

Dartmouth Events

Physics & Astronomy/Thayer Plasma Seminar - Matina Gkioulidou, JHUAPL

Title: "Outflow off the Beaten Path: Low Energy (< keV) O+ Outflow Directly Into the Inner Magnetosphere as Observed by the Van Allen Probes"

Tuesday, May 22, 2018
Wilder 202
Intended Audience(s): Public
Categories: Lectures & Seminars

Abstract: The heavy ion component of the low-energy (eV to hundreds of eV) ion population in the inner magnetosphere, also known as O+ torus, is crucial for various aspects of magnetospheric dynamics. Yet, although the effects of high latitude and cusp ionospheric O+ outflow and its subsequent transport and acceleration within the magnetotail and plasma sheet have been extensively studied, the source of low-energy O+ within the inner magnetosphere (already observed by the Dynamic Explorer 1 spacecraft in the 80s) remains a compelling open question. The HOPE instrument aboard each of the Van Allen Probes (in highly elliptical, equatorial orbits with apogee of 5.8 RE) has repeatedly detected low-energy O+ field-aligned enhancements. We present a comprehensive study of a low energy (<keV) O+ outflow event directly into the inner magnetosphere, within L = 4, occurring during the main phase of geomagnetic storm. Bi-directional field-aligned intensity enhancements of O+ ions of few eV to 2 keV energy were observed, with the energy spectrograms exhibiting multiple bands of these enhancements with energy dispersion. A simple 2-D particle tracing simulation demonstrated that the observed features are due to O+ ions outflowing from both hemispheres of the night-side ionosphere directly into the magnetosphere within L = 3 - 4, and subsequently bouncing from one hemisphere to the other. These outflows are associated with field-aligned Poynting flux enhancements and field-aligned electron beams, as observed at the Van Allen Probes location, revealing energy transport from the magnetosphere to ionosphere as well as simultaneous field-aligned electron heating. During the same time interval, partial number densities from the HOPE instrument reveal that, due to the outflow population, the O+ density in the region outside plasmapause was significantly higher than the H+ one, indicating the possible formation of O+ torus. The ubiquity of such events in the Van Allen Probes data during geomagnetically active times might reveal one of the sources for the O+ torus.

For more information, contact:
Tressena Manning

Events are free and open to the public unless otherwise noted.