Understanding energetic particle injections and their effect on Earth's outer radiation belt electrons using multipoint observations

About Our ISSI Team Project

**Figure:** Terminology and basic concepts of energetic particle injections. Credit: D. L. Turner

Energetic particle injections involve the sudden inward transport of energetic ions and electrons (typically 10s to 100s of keV) from the plasma sheet in Earth’s magnetotail into the inner magnetosphere, where the particles become quasi-stably trapped in the ring current and outer radiation belt. Injections occur regularly (many times per day) and are thought to be important for introducing the “seed population” of electrons into the outer electron radiation belt and the subsequent acceleration of these electrons to relativistic energies (up to several MeV). Particle injections are also considered important for introducing the populations of energetic ions and electrons that contribute to the build-up of the ring current, which can result in geomagnetic storms, and that are responsible for generating various plasma waves, which can then interact with outer radiation belt electrons and contribute to acceleration and loss of those particles. For these reasons, energetic particle injections are particularly interesting from a scientific standpoint, since they represent cross-energy and –species processes in which acceleration and loss of relativistic electrons are affected by the dynamics of lower energy electrons and various ion species.

There is currently only limited and/or indirect observational evidence in support of several of the key concepts and theories to explain energetic particle injections and their effects on Earth's ring current and outer radiation belt electrons. Major outstanding questions remain as to the nature of the injections themselves (e.g., the azimuthal extent and shape of injection fronts), how the upper energy thresholds and penetration depths of such injections vary with solar wind and geomagnetic activity, and the subsequent effect these injections have on the outer belt electron population. However, we now have an unprecedented level of in situ measurements of energetic particles in Earth’s inner magnetosphere that can be used to study energitic particle injections and their effects on Earth's ring current and radiation belts.

**Figure:** A classic example of a dispersed energetic electron injection from RBSP-B MagEIS. Colors correspond to different energies, labeled in keV. Credit: D. L. Turner

Thanks to support from ISSI, we have assembled a team of international scientists and space physics experts to systematically investigate how energetic particle injections affect Earth’s outer radiation belt electrons. Our team is comprised of outstanding researchers hailing from top institutes based in five different European nations, the United States, Canada, Japan, Korea, and China. Each of the members is an expert on the missions, instruments, and analysis techniques used to make and interpret observations of particles and waves in Earth’s radiation belts.

**Figure:** Spacecraft used in our studies. Credit: NASA SSCWeb 3D

The time period we have chosen to investigate starts at the beginning of NASA's Van Allen Probes (RBSP) science observations in September 2012 and spans up to the present time. From this period, we will use a collection of data sets to establish a database of events and develop case studies and statistics on: the azimuthal location and width of injection sites; the penetration depth (in L-shell) of injections; the upper energy thresholds of injected particles (ions and electrons) as a function of L-shell; differences between ion and electron injections; waves associated with distributions of injected particles; precipitation losses of electrons associated with injections; and evidence of acceleration from outer belt distributions observed by Van Allen Probes. We will incorporate data from: i) NASA's THEMIS and ESA's Cluster missions, which are capable of observing the source of these injections in the near-Earth plasma sheet; ii) geosynchronous spacecraft (i.e., LANL, GOES) that observe the injected particles as they are entering the outer belt zone; and iii) NASA's Van Allen Probes, which directly observe the effects injections have on the outer belt; iv) low-altitude spacecraft and balloon campaigns (e.g., POES/MetOp, CSSWE, BARREL) and ground-based observatories (GBOs) that provide observations required to understand losses from the system.

In 2015, ISSI will host two 1-week meetings for our team in Bern, Switzerland. At these meetings, our team will work together in person to develop and/or establish concepts and theories of energetic particle injections, plan and conduct focused studies of energetic particle injections, and coordinate for continued studies and result dissemination in the interim period. The goal of this team is to conduct a series of observational studies on these main points and share our results with the greater scientific community via a series of peer-reviewed journal publications.

Our ISSI Team

Our team's first group dinner at the Altes Tramdepot. From center-left going clockwise around the table: Mark Clilverd, Christine Gabrielse, Jacob Bortnik, Jean-François Ripoll, Yoshi Miyoshi, Ondřej Santolík, Junga Hwang, Iannis Dandouras, Elena Kronberg, Lauren Blum, Geoff Reeves, Xinlin Li, Sasha Ukhorskiy, Robyn Millan, Emma Spanswick, Drew Turner, and Matina Gkioulidou

Young Scientists:
Team Members:	Institutes:	Countries:	Areas of Expertise:
Dr. Jacob Bortnik	University of California, Los Angeles	USA	Theory and observations of the plasma waves and wave-particle interactions
Dr. Iannis Dandouras	Research Institute of Astrophysics and Planetology (IRAP)	France	Cluster bulk plasma observations and analysis
Dr. Junga Hwang	Korea Astronomy and Space Science Institute	South Korea	POES/MetOp energetic particle observations and analysis
Dr. Elena Kronberg	Max Planck Institute for Solar System Research	Germany	Cluster energetic particle observations and analysis
Prof. Xinlin Li	Laboratory for Atmospheric and Space Physics, University of Colorado	USA	CSSWE, THEMIS, RBSP, and GEO wave, fields, energetic particle observations and analysis
Prof. Robyn Millan	Dartmouth College	USA	BARREL baloon observatories and campaigns
Prof. Yoshi Miyoshi	Nagoya University	Japan	ERG, POES/MetOp, and GEO wave, fields, and energetic particle observations and analysis
Dr. Geoff Reeves (team co-leader)	Los Alamos National Laboratory	USA	RBSP and LANL-GEO wave, fields, energetic particle observations and analysis
Prof. Ondřej Santolík	Institute of Atmospheric Physics	Czech Republic	Cluster and Van Allen Probes waves and fields observations and analysis
Dr. Emma Spanswick	University of Calgary	Canada	Ground based observatories (riometers, all-sky imagers, magnetometers)
Dr. Drew Turner (team co-leader)	The Aerospace Corporation	USA	THEMIS, RBSP, POES/MetOp, and GEO energetic particle observations and analysis
Dr. Sasha Ukhorskiy	Johns Hopkins Applied Physics Laboratory	USA	Theory of energetic particle dynamics and Van Allen Probes energetic particle observations
Dr. Lauren Blum	Space Sciences Laboratory, University of Califorina, Berkeley	USA	EMIC waves and precipitation of radiation belt electrons and CSSWE observations and analysis
Dr. Christine Gabrielse	University of California, Los Angeles	USA	Theory of energetic particle injections and THEMIS observations and analysis
Dr. Matina Gkioulidou	Johns Hopkins Applied Physics Laboratory	USA	Theory of ring current dynamics and Van Allen Probes observations and analysis
Dr. Eva Macúšová	Institute of Atmospheric Physics	Czech Republic	Theory of plasma waves and Cluster observations and analysis
External Advisors:
Dr. Mark Clilverd	British Antarctic Survey	United Kingdom	Ground based observations and analysis of VLF waves
Prof. Wenlong Liu	Beihang University	China	THEMIS, GOES, and Van Allen Probes waves and fields observations and analysis
Dr. Jean-François Ripoll	French Alternative Energies and Atomic Energy Commission (CEA)	France	Theory and observations of energetic particles and wave-particle interactions in the inner magnetosphere
Dr. Matt Taylor	European Space Agency	Netherlands	Observations and analysis of energetic particles in the inner magnetosphere

Meetings

First Meeting: 26–30 January 2015, Bern, Switzerland
Second Meeting: 21–25 September 2015, Bern, Switzerland

**Meeting 1:** Sun and snow on Bern's Old City during our first team meeting. Photo by: D. L. Turner

About Our ISSI Team Project

Our ISSI Team

Meetings

Publications (team member authors in bold)

Understanding energetic particle injections and their effect on Earth'souter radiation belt electrons using multipoint observations

Publications
(team member authors in bold)

Understanding energetic particle injections and their effect on Earth's
outer radiation belt electrons using multipoint observations