Multi-scale Processes of Energetic Particles (PEP) in the Inner Magnetosphere
Overarching Goal
Use the synergy of multi-spacecraft datasets and modeling to develop system-wide understanding of the
energetic particle environment and cross-scale interactions in Earth’s inner magnetosphere during geomagnetic
storms.
Topic
The highly variable energetic particle environment at Earth comprises several components including
electrons and ions in the ring-current (keV range) and radiation belts (MeV range). During geomagnetic storms a
large volume of ions is injected into the inner magnetosphere where they are energized to ring-current energy
levels such that their pressure becomes the dominant driver of the electrodynamics of the magnetosphere–
ionosphere system. Pressure-driven currents determine the distribution of magnetic field across the inner
magnetosphere, which in turn governs the motion of radiation belt particles. Hot plasma also provides the
energy source for multiple instabilities generating wave modes that drive local acceleration and loss as well as
radial transport of radiation belt particles.
During enhanced geomagnetic activity, electron intensities across the radiation belts may vary by multiple
orders of magnitude on the time scales from minutes to days. Global variability of radiation belt intensities is
controlled by the shifting balance among multiple acceleration and loss mechanisms, which sculpt particle
intensities by affecting their motion at various spatial and temporal scales. Local mechanisms interact with the
fast gyromotion and usually operate over a fraction of a drift orbit. They include resonant interaction with ULF/
VLF plasma waves such as ion cyclotron and whistler-mode waves as well as particle scattering at sharp
inhomogeneities in the magnetic field such as created by thin current sheets. Global mechanisms, on the other
hand, interact with the slow longitudinal drift motion around Earth. For example, large-scale ULF oscillations
drive radial transport of radiation belt electrons by resonantly interacting with their drift motion. Radial transport
can also be caused by the coupling of particle drift and bounce motion associated with the day–night asymmetry
in the geomagnetic field.
Charged particle energization and transport are fundamental physical processes operating in all astrophysical
plasmas. The Earth’s inner magnetosphere is a unique natural laboratory for developing our understanding of
general energization and transport processes which operate across the universe, and it is an opportune time to
study this system. With both the unprecedented number and quality of in situ spacecraft and the current level of
sophistication of global models now available, it is possible to thoroughly analyze the cross-scale energy and
interspecies interaction processes that drive variability in the ring current and radiation belts.
Understanding dynamic variability of the energetic particle environment is also of great practical
importance, since increased energetic particle intensities create hazardous space weather conditions. Penetrating
ions and relativistic electrons in the magnetosphere can disable orbiting spacecraft and provide lethal levels of
radiation for humans in space. Increasing dependence on space based communication and navigation systems
demands improved modeling capability and understanding of energetic particle populations in space.
We propose this new GEM Focus Group to combine data from multiple ongoing and recent constellation
missions, ground-based observatories and state-of-the-art models to develop a better understanding of how
energetic particle populations in the inner magnetosphere evolve during geomagnetic storms with the emphasis
on cross-energy, -scale and -species interactions. We will use the meeting sessions and group challenges to
address the most compelling science questions of the energetic particle processes in the inner magnetosphere
including: 1) What are the basic mechanisms of the ring current buildup during storms? 2) What are the relations
of ring current injections with dropout/enhancements of radiation belt electrons during storm main/recovery
phase? 3) How are various wave modes are generated or enhanced during the storm and feed back into the
energetic particle populations via wave-particle interactions?
Timeliness
While many key mechanisms important to particle acceleration and transport in Earth’s magnetosphere have
been identified by previous observations and analysis, some processes remain poorly characterized, and it is still
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unknown how these processes interact with each other under varying geomagnetic conditions to generate the
real space environment as observed at any given time. Profound mysteries remain because historic observations
were insufficient to resolve complex multi-scale interactions governing the global state of the system.
The two spacecraft comprising the recently launched Van Allen Probes mission (RBSP) provide
simultaneous multi-scale measurements of the ring current and radiation belts in the heart of the inner
magnetosphere where most particle acceleration, transport and loss processes take place. The probes are
discovering new and unexpected behaviors of the energetic particle environment such as coherently ordered
multiple structures in the electron belt, the buildup of the storm-time ring current by localized ion injections
deep into the inner magnetosphere, and organization of the inner belt electrons in regular patterns. In the
following five years of the mission, the synergy between RBSP and recent and ongoing missions/observational
capabilities presents an unprecedented opportunity to develop a new system-wide understanding of dynamic
processes that sculpt Earth’s energetic particle environment. Some of the elements include:
BARREL
- Global characterization of energetic particle losses into the atmosphere
SAMPEX, POES
- Atmospheric losses, pitch-angle scattering
THEMIS
- Magnetopause losses, radiation belt seed population, ion injections
GOES, LANL-GEO
- Energetic particle environment at the geosynchronous orbit
SuperDARN, AMPERE
- Global electrodynamics
Relevance to GEM
GEM Challenges
Inner magnetospheric dynamics during Solar Cycle 24 have been characterized by a series of moderate
storms with highly dynamic and unexpected responses of the ring current and radiation belt intensities including
sudden dropouts, large enhancements, and the development of interesting structures. Event studies are
particularly useful because they bring together narrowly focused studies, encouraging a system-wide approach.
We will use the storms of Solar Cycle 24 as “GEM challenges” to facilitate close collaboration of data analysts
and modelers in working towards the goals of this group.
Workshop Style
An increasing number of GEM Summer Workshop participants and growing interest in radiation belt and
ring current physics present both challenges and opportunities. A primary goal will be to maintain the workshopstyle operation essential to GEM. A Focus Group organization centered on specific events/challenges will help
facilitate a workshop-style operation centered on discussion rather than formal presentations. A large number of
diverse studies will provide the opportunity for the development of system-wide understanding, including many
opportunities for joint topics with other, existing Focus Groups. Participation by all will be encouraged in
discussions.
Broad Community Involvement
In addition to mini-GEM and the Summer Workshop meetings, we will engage the community throughout
the year by soliciting contributions towards the goals of this group in the GEM messenger and the SPA
Newsletter.
Promoting Young Scientists
For many young scientists, GEM provides an indispensable introduction to the broader space science
community and to geospace research outside our own institution. In turn, young scientists bring energy and new
perspective to the field. We will support the education goals of GEM by giving the priority to students and
young scientists in all Focus Group activities (brief oral presentations/discussion/enabling collaborations).
Relation to Existing Focus Groups
This Focus Group has strong connections to existing Focus Groups, which will enable collaboration and
natural integration into the GEM structure. Our goal is to support the ongoing Focus Group activities as well as
to provide new research avenues through the proposed Focus Group operation. The connections to the existing
groups include:
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1) Radiation Belt and Wave Modeling (RBWM) (2010-2014). The main goal of RBWM is to develop the
model of waves and their impacts on radiation belt particles. The radiation belt environment is one of the central
components of the proposed Focus Group. A particular area of expected collaboration is the application of
models developed by the RBWM community to the analysis of Solar Cycle 24 events and including the model
runs into our deliverable datasets. This activity will help to understand the extent to which the existing models
of wave-particle interactions are capable of explaining highly dynamic variability of the radiation belt
environment.
2) Scientific Magnetic Mapping & Techniques (2011-2015). System mapping is essential for understanding
dynamic variability and losses throughout the near-Earth energetic particle environment. Determination of the
global context of simultaneous measurements made at low and high latitudes requires the knowledge of their
magnetic conjugacy. The exact knowledge of magnetic coordinates is essential to computing the adiabatic
invariants of trapped energetic particles, important for understanding mechanisms that sculpt their intensities.
We expect to have joint sessions with the Mapping Group and to work closely in developing the most accurate
techniques for mapping the energetic particle measurements.
3) Tail-Inner Magnetosphere Interaction (TIMI) (2012-2016). The main goal of TIMI is to understand how
plasma is transported and accelerated from the tail into the inner magnetosphere, including addressing the
relative role of meso-scale processes such as dipolarization fronts, bursty-bulk flows and low entropy bubbles.
These questions are essential for understanding both the buildup of the storm-time ring current, the source
populations of ULF/VLF waves like chorus and EMIC waves, and the seed population for the radiation belts.
We will work closely with the TIMI community in joint sessions and creating a data set of conjugate tail-inner
magnetosphere events and their analysis to determine the relation of transport and acceleration processes in the
tail and the inner magnetosphere.
4) Storm-Time Inner Magnetosphere-Ionosphere Convection (STIMIC) (2013-2017). Our collaboration with
STIMIC will include compilation of combined data sets of global ionospheric/low-altitude measurements such
as SuperDARN, AMPERE, and SuperMAG with in situ energetic particle measurements to determine the role of
global electrodynamics in buildup of stormtime ring current and radiation belts.
Deliverables
Datasets
We will select a number of the most interesting and well-sampled storms of Solar Cycle 24 as GEM Challenges.
For each of the storms a comprehensive data set will be combined and made available for the community.
Datasets will include (but are not restricted to):
1) All available RBSP measurements
2) Additional near-equatorial in situ measurements of energetic particles, plasma, and fields including: THEMIS,
GOES, LANL-GEO
3) Low altitude particle and field measurements including: SAMPEX, POES
4) Precipitation measurements from BARREL
5) Global measurements such as SuperDARN, AMPERE, SuperMAG
The data sets will also include all model runs produced in the process of Focus Group operation.
Publications
The most fully analyzed events will be selected as the topics of one or more special issues on dynamic
variability of the energetic particle environment at Earth that we plan on publishing in JGR or a similar journal.
Co-chairs
-Brian Kress (bkress@dartmouth.edu): Experience includes test-particle radiation belt modeling. Development
of a real-time data-driven geomagnetic cutoff model currently running at the NASA Langley Research Center.
-Drew Turner (drew.lawson.turner@gmail.com): Research scientist on the THEMIS team specializing in
energetic particles in space plasmas and system-wide data analysis with large datasets including THEMIS,
ARTEMIS, RBSP, GOES, LANL-GEO, and POES.
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-Sasha Ukhorskiy (ukhorskiy@jhuapl.edu): Co-I of the RBSPICE experiment. Ring current and radiation belt
test-particle modeling. Data analysis of wave - particle interaction. Empirical magnetic field modeling.
Research Area
Our primary research area is Inner Magnetosphere and Storms (IMS). We also have strong connections to
Tail, including plasma transport and heating from the tail to the inner magnetosphere, and MagnetosphereIonosphere Coupling (MIC), including the analysis of global electrodynamics effects on energetic particles in
the inner magnetosphere.
Term
Five years (2014 - 2018)
Expected Activities
Following are a possible set of activities for the duration of the proposed Focus Group term. Since GEM is a
community driven forum, it is expected that the Focus Group operation will be defined by our participants and
the interactions with the ongoing and future Focus Groups. This list should be considered only as a guide to the
proposed Focus Group direction.
Year 1 – During our first year we introduce the Focus Group to the rest of the GEM community and reach out to
the other Focus Groups for collaborative work and joint sessions. During the Summer Workshop, we will
include: i) an introductory session, in which we detail the goals for the new Focus Group; ii) a broader topics
session, including short, informal presentations on relevant work; and iii) at least one session to review the
storms and active periods during Solar Cycle 24 and identify at least one event of interest for focused study
throughout the following year. The challenge will include drastic variations in the ring current and radiation
belts while allowing for multipoint observations from spacecraft and ground-based observatories throughout the
system. Our “kick-off” challenge will consist of detailed analysis and modeling of this event, the results of
which will be presented at the Summer Workshop the following year. Challenge participants will be able to
provide updates on their studies and compare initial results at the Mini-GEM workshop before the AGU Fall
Meeting 2014.
Year 2 – During the 2015 Summer Workshop we will review results from the “kick-off” challenge. We will
then devote a session to developing a set of diagnostic criteria to identify other events in which similar processes
may have dominated the observed ring current and radiation belt variability. During this session, we will also
announce Year 2’s challenge: to identify then analyze and/or model two different storms, one dominated by
similar processes to the first and one that is driven by different processes. In Year 2, we will also set the tone of
our Focus Group for future years by having an open session on relevant topics (i.e., studies not related to the
Focus Group challenge) and one joint session with another of the Focus Group’s listed above. Challenge
participants will again be able to provide updates on their work at the Mini-GEM workshop in December.
Year 3 – In the first session of the 2016 Summer Workshop, we will review the results of the Year 2 challenge.
This year will be focused on joint topics with other Focus Groups, and we will devote the majority of the
sessions to joint topics and chose a new joint challenge. Also, we will have another open session on relevant
topics.
Year 4 – Discussion of new broader challenges including possible joint challenges with parallel Focus Groups.
Outlining publications for a Special Issue.
Year 5 - This will be the “wrap-up” period, when we pull together all that was learned as a result of the Focus
Group’s efforts. Open session on relevant topics including joint sessions with ongoing Focus Groups.
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