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9
Report of the Panel on Solar Wind-Magnetosphere Interactions
9.1 SUMMARY OF SWMI SCIENCE PRIORITIES AND IMPERATIVES
The magnetosphere is a central part of the solar and space physics system. Its various regions
globally interact in complex, nonlinear ways with each other, with the solar wind, and with the upper
atmosphere. These interactions occur by a number of fundamental physical processes that operate
throughout the universe. The resulting dynamic variations in the magnetospheric environment have
important practical consequences for human life and technology.
Over the past decade, significant progress has been made toward achieving the scientific
objectives laid out for solar wind-magnetosphere interactions in the previous decadal survey. This
progress has been achieved through a powerful combination of tools, including new data from satellites
launched during the decade or just before (e.g., Cluster, IMAGE, THEMIS, TWINS); analysis of data
returned from earlier missions; data from instruments flown on non-NASA operational satellites;
measurements from suborbital missions and from networks of ground-based observatories; greatly
improved numerical simulations; analytical theory; and laboratory work.
For the coming decade, the panel has identified a set of eight high-priority scientific goals for
research in solar wind-magnetosphere interactions, which follow naturally from the progress that has been
made, and will go a long way toward accomplishing the Decadal Survey Key Scientific Goals called out
for solar and space physics earlier in this report (Chapter 1). These critical scientific goals (which are not
prioritized) are:
SWMI Goal 1: Determine how the global and mesoscale structures in the magnetosphere respond
to variable solar wind forcing.
SWMI Goal 2: Identify the factors that control the dominant sources of magnetospheric plasma.
SWMI Goal 3: Understand how plasmas interact within the magnetosphere and at its boundaries.
SWMI Goal 4: Understand the balance of energetic particle acceleration, transport, and loss.
SWMI Goal 5: Discover how magnetic reconnection is triggered and modulated.
SWMI Goal 6: Understand the origins and effects of turbulence and wave-particle interactions.
SWMI Goal 7: Determine how magnetosphere-ionosphere-thermosphere coupling controls
system-level dynamics.
SWMI Goal 8: Identify the structures, dynamics, and linkages in other planetary magnetospheric
systems.
These are ambitious goals, and their accomplishment will require intelligent use of all the tools in
our research arsenal. Achieving some of them will require new measurements from strategic missions,
either already under development (MMS and RBSP) or to be started in the coming decade. Other
contributions toward accomplishing these goals will come from community-proposed Explorer missions,
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suborbital flights, CubeSats, operational satellites, and instruments flown on commercial platforms as
rides of opportunity. Studies that combine data from the numerous existing spacecraft (the “Heliophysics
Observatory”) will elucidate important aspects of global coupling, while analytical theory, laboratory
studies, and especially powerful numerical simulations will complement the various spacecraft
measurements in a synergistic attack on the science questions. However, because of budget constraints
and as-yet immature technology, a number of critical investigations must be deferred to a later decade,
requiring investments in the coming decade in the areas of technology innovation and development, as
well as in ways to more effectively couple theory and data.
In this chapter, the panel advocates a coherent and balanced program of research in solar wind-
magnetosphere interactions based on a prioritized set of imperatives that will enable a cost-effective
approach to accomplishing the critical science goals. These imperatives are sorted into three categories:
Missions, DRIVE-related initiatives, and Space Weather. While a given imperative may really apply to
more than one category, for simplicity the panel has simply assigned each to a single primary one. The
panel has prioritized the imperatives not only within but also across the three categories in order to
identify the most important and most cost-effective actions to accomplish its pressing science goals. The
five overall highest-priority imperatives that are developed in this chapter are the following:
SWMI Imperative 1: Enhance the resources dedicated to the Heliophysics Explorer program and
broaden the range of cost categories.
SWMI Imperative 2: Complete the strategic missions that are currently in development (MMS,
RBSP/ BARREL) as cost-effectively as possible.
SWMI Imperative 3: Initiate the development of a strategic mission, like MEDICI, to determine
how the magnetosphere-ionosphere-thermosphere system is coupled and responds to solar and
magnetospheric forcing.
SWMI Imperative 4: Ensure strong continued support for existing satellite assets that can still
contribute significantly to high-priority science objectives.
SWMI Imperative 5: Enhance and protect support for theory, modeling, and data analysis,
including research and analysis programs and mission-specific funding.
Within the three categories, the panel’s full set of prioritized imperatives is as follows. The numbering in
each category reflects each priority’s relative ranking among all three categories.
9.1.1 Missions
1. Enhance the resources dedicated to the Explorer program and broaden the range of cost
categories.
2. Complete the strategic missions that are currently in development (MMS, RBSP/ BARREL)
as cost-effectively as possible.
3. Initiate the development of a strategic mission, like MEDICI, to determine how the
magnetosphere-ionosphere-thermosphere system is coupled and responds to solar and
magnetospheric forcing
4. Ensure strong continued support for existing satellite assets that can still contribute
significantly to high-priority science objectives.
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9. Develop a mechanism within NASA to support rapid development and deployment of
science payloads on commercial vehicles and other missions of opportunity. NSF and DOD
efforts in this regard are also encouraged.
10. Through partnership between NASA’s Heliophysics Division and Planetary Division,
ensure that appropriate magnetospheric instrumentation is fielded on missions to other planets.
In particular, the panel’s highest priority in planetary magnetospheres is a mission to orbit
Uranus.
11. Partner with other space agencies to implement consensus missions, such as a multi-
spacecraft mission to address cross-scale plasma physics.
15. If resources permit, initiate a strategic mission like MISTE to simultaneously measure the
inflow of energy to the upper atmosphere and the response of the ionosphere-thermosphere
system to this input, in particular the outflow back to the magnetosphere.
9.1.2 DRIVE-Related Initiatives
5. Enhance and protect support for theory, modeling, and data analysis, including research
and analysis programs and mission-specific funding.
6. Ensure continuity of measurements of the upstream solar wind and interplanetary
magnetic field.
7. Invest significantly in developing the technologies to enable future high-priority
investigations.
8. Ensure strong multi-agency support for a broad range of ground-based assets that are a
vital part of magnetospheric science.
14. Strengthen workforce, education, and public outreach activities.
16. Create an interagency joint laboratory astrophysics program that addresses issues
relevant to space physics.
9.1.3 Space Weather
12. Encourage the creation of a complete architecture for the nation’s Space Weather
Program that would coordinate joint research, commercial, and operational space weather
observations and define agency roles for producing, distributing, and forecasting space weather
products. In addition all agencies are encouraged to foster interactions between the research and
operational communities and identify funding for maintaining a healthy Research-to-
Operations/Operations-to-Research program.
13. Implement a program to determine, based on past observations, the optimum set of
measurements that are required to drive high-fidelity predictive models of the environment.
Implementation of these imperatives will enable the achievement of the exciting and high-priority
science goals laid out in this report, providing a strong foundation for the accomplishment of the long-
term actions described earlier in this decadal survey. To summarize, eight overarching SWMI science
goals motivate sixteen, prioritized actionable imperatives that are required to enable the goals (these
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prioritized imperatives and their mapping to decadal categories from Part I are shown in a table at the end
of Chapter 9).
9.2 INTRODUCTION TO SWMI SCIENCE
In this section a brief introduction to the magnetosphere and its interactions with the solar wind
and the upper atmosphere is given. This provides a context for the subsequent discussion of the past
decade’s accomplishments and important unanswered questions, leading to the panel’s critical science
goals for the coming decade and the initiatives necessary to accomplish them.
9.2.1 What Is the Magnetosphere?
The magnetosphere (Figure 9.1) is a vast, highly coupled system governed by fundamental
physical processes and characterized by complex, nonlinear linkages between its different parts. It is
formed by the interaction of the solar wind plasma stream and its embedded magnetic field with Earth’s
intrinsic magnetic field. Earth with its field is an obstacle in the solar wind flow, carving out a separate
plasma domain where Earth’s field has dominant control over the motions of the electrically charged
particles trapped there. These charged particles come from both the solar wind and Earth’s upper
atmosphere. This region of dominance, the “magnetosphere,” extends out to approximately 10 Earth radii
on the sunward side of Earth and, in a long “magnetotail,” extends to well beyond the moon on the side
away from the Sun. The shape of the magnetosphere is determined by the balance between the pressure
exerted by the solar wind plasma and interplanetary magnetic field (IMF) and the pressure of Earth’s
plasma and magnetic field. Earth is only one of six of the Sun’s planets (Mercury, Earth, Jupiter, Saturn,
Uranus, and Neptune) that are known to have a magnetosphere by virtue of their intrinsic magnetic fields.
Ganymede, one of Jupiter’s satellites, also has its own tiny magnetosphere embedded within Jupiter’s
giant one.
FIGURE 9.1 Schematic diagram of the magnetosphere, with various regions indicated. SOURCE:
Adapted from L.A. Weiss, P.H. Reiff, R.V. Hilmer, J.D. Winningham, and G. Lu, Mapping the auroral
oval into the magnetotail using dynamics explorer plasma data, Journal of Geomagnetism and
Geoelectricity, 44(12):1121, 1992.
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9.2.1.1 Regions
The magnetosphere is made up of regions with different plasma characteristics. As illustrated in
Figure 9.1, the shape of the underlying geomagnetic field lines governs the morphology of these various
regions. Nearest Earth, there is a relatively cold and dense region called the plasmasphere. The
plasmasphere contains plasma that has escaped from the ionosphere, the ionized region of Earth’s upper
atmosphere. Coincident with the plasmasphere or residing at slightly larger radial distances are higher-
energy charged-particle populations called the ring current and radiation belts. Ring-current particles drift
azimuthally around Earth because of the strong magnetic field gradients, with positively charged ions
drifting west and electrons drifting east, producing an electrical current large enough to modify
substantially the global magnetic field. At still higher energies, the similarly drifting radiation-belt
population possesses tremendous energy per particle, but because of its very low density, carries little net
current. Beyond the ring current and radiation belt is a low-density, hot plasma called the plasma sheet,
extending to large distances into the magnetotail and serving as the reservoir for much of the plasma that
ultimately feeds the inner magnetosphere ring-current and radiation-belt populations. The high latitude
magnetic flux regions that are nearly devoid of plasma and that extend down the magnetotail from the
polar caps are called the tail lobes. The magnetopause is the boundary of the magnetosphere, which
separates it from the surrounding regions dominated by the solar wind and its magnetic field. Upstream
from the magnetopause there is a standing shock wave, the bow shock, at which the supersonic solar wind
is slowed and heated, enabling it to flow around the magnetospheric obstacle. The transition region of
shocked solar wind between the bow shock and the magnetopause is known as the magnetosheath. A
final region, beyond the bow shock, is called the foreshock, in which fast particles move upstream along
the IMF and perturb the supersonic flow of the incoming solar wind. Another term that is often used
synonymously with the magnetosphere-ionosphere system is “geospace.”
9.2.1.2 Physical Processes
Several primary physical processes produce the rich phenomenology of the structured, time-
dependent magnetospheric system. “Magnetic reconnection” is the process by which energy stored in
magnetic fields is converted to plasma thermal energy, plasma bulk flow energy, and energized particles
through a topological magnetic field reconfiguration. Charged particles in general conserve certain
quantities of motion called adiabatic invariants, which relate aspects of the particle motion to magnetic
field parameters and can lead to reversible energy changes. “Wave-particle interactions” (WPI) refers to
the general and broad process by which electromagnetic waves and charged particles exchange energy
and momentum. “Turbulence” describes the flow state of a fluid (including magnetized fluids) that is
chaotic and stochastic. Turbulent media provide a rich opportunity for WPI. These same physical
processes, determining the structure and dynamics of Earth’s coupled solar wind-magnetosphere system,
also govern other planetary magnetospheres; by studying these fundamental processes in our own
neighborhood universally applicable knowledge is gleaned.
9.2.1.3 Coupling to the Ionosphere and Solar Wind
The magnetosphere is physically bounded by the ionosphere and solar wind at its lower and upper
extents, respectively. Earth’s magnetosphere has no internal plasma sources, so these boundary regions
are the two major sources of magnetospheric plasma. The solar wind is a large source of protons and
electrons into the magnetosphere, while the ionosphere contributes not only protons but also heavy ion
species like oxygen, helium, and nitrogen, and their accompanying electrons. Furthermore, the solar wind
and IMF, through magnetic reconnection and viscous interaction, drive convective flow throughout the
magnetosphere. The ionosphere, with its high conductance, regulates and modulates this convective flow.
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In addition, the neutral gas of the upper atmosphere, known as the thermosphere, can also influence
magnetospheric flow through ion-neutral collisions.
9.2.1.4 Space Weather and the Magnetosphere
Space weather is the name given to the time-dependent conditions and changes that occur in near-
Earth space to the magnetospheric plasmas and fields. These include changes in the plasma density,
temperature, and spatial distributions, from the cold plasmasphere to the very energetic radiation belts. In
particular, “space weather” implies changes that have significant impact on technology and society. For
example, the variable ionosphere and plasmasphere alter geolocation signals from GPS and transmissions
from communication spacecraft; strong magnetospheric currents create geomagnetically induced currents
in power distribution systems; energetic particles cause radiation damage to microelectronics and space-
farers; and substorm-related satellite charging causes malfunctions and surface degradation.
9.2.1.5 Magnetospheric Questions That Flow from the Motivations
The motivations underlying the study of solar and space physics apply directly to the study of
Earth’s magnetosphere and its interaction with the solar wind and upper atmosphere: Earth’s
magnetosphere (and those of other planets) is a fascinating, complex system, in which fundamental
physical processes that operate throughout the universe combine with unique conditions of plasma
sources, sinks, and drivers to create dynamic conditions that can affect humans and the technologies they
depend on in space and sometimes on the ground.
• Motivation 1. Understand our home in the solar system: The fundamental motivation of
wanting to understand the fascinating Sun-Earth system drives the desire to learn what determines the
dynamically changing charged-particle environment of the magnetosphere, from the lowest-energy
particles emerging from the upper atmosphere, to the hazardous high-energy particles of the radiation
belts. What exactly are the relationships between the different magnetospheric regions, and how are these
regions coupled to the solar wind and upper atmosphere? How do these linkages determine
magnetospheric dynamics? And what new insights do are gained from examining the similarities and
differences in these regions and processes at other planets?
• Motivation 2. Predict the changing space environment and its societal impacts: A thorough
understanding of this complex and highly coupled system will enable scientists to predict its behavior
under a variety of changing conditions, allowing conditions that are adverse to human life and technology
to be anticipated and recognized. Within the magnetosphere, scientists are particularly interested in how
damaging particle populations and electrodynamic fields can be evaluated and predicted.
• Motivation 3. Reveal universal processes: The geospace system comprises a laboratory for
exploring a wide variety of processes that operate throughout the universe. These include the ways in
which ionized outflows can be driven from planetary atmospheres; how waves and particles provide
coupling between disparate plasma regions; how plasmas interact with neutral materials; how magnetic
reconnection occurs and how it energizes particles; how collisionless shock waves work; and how plasma
turbulence is generated and dissipated and affects other dynamical processes.
In the following sections, recent progress made toward addressing the fundamental questions
raised by these motivations is outlined. The outstanding problems where significant progress can be
accomplished in the near future is then outlined, leading to the identification of specific science goals for
the coming decade. Finally, the panel lays out the imperatives for actions that are needed to meet those
goals.
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9.3 SIGNIFICANT ACCOMPLISHMENTS OF THE PREVIOUS DECADE
9.3.1 Scientific Progression
The science of solar wind-magnetosphere interactions was established near the dawn of the space
age, only 50 years ago. Since that time, knowledge of the magnetosphere has grown tremendously,
progressing from discovery to understanding.
Early research focused on the discovery and exploration of the different regions that lie above
Earth’s atmosphere: the radiation belts, the plasmasphere, the plasma sheet, and the solar wind. As these
regions and the particle populations that define them were discovered, scientists sought to identify and
understand the physical processes that accelerate and transport the particles. It has also been found that
the system is not static, but rather exhibits substantial variability with identifiable patterns. It became
clear that different regions are not independent, but are intimately linked, and the variability and
processes in one region can be clearly related to those in other regions.
Scientists now appreciate that the magnetosphere is a vast, highly coupled system, which involves
a wide array of fundamental physical processes and complex linkages between different regions. In the
last decade this system’s impact on human technology and society has also come to be appreciated:
Storms and other disturbances in geospace have significantly disrupted and disabled spacecraft and
ground-based power grids. Finally, as mankind has reached out to explore the solar system, scientists
have discovered that other solar system bodies possess magnetospheres that exhibit many of the same
processes found near Earth, but frequently manifested in different ways, and producing very different
structure and dynamics.
FIGURE 9.2 A schematic of the temporal progression of scientific research into solar wind-
magnetosphere interactions, with time increasing upwards.
Thanks to observations from new satellite missions, new analyses of data from previous missions,
and improved numerical modeling capabilities, substantial progress has been made in the past decade to
advance the field along the progression illustrated in Figure 9.2. Here the panel reviews some of these
significant accomplishments. This review is by no means comprehensive, but serves to illustrate the
progress that continues to be made across a broad front of scientific endeavors. These accomplishments
lay the foundation for what needs to be done in the future to continue the progression towards a
comprehensive and actionable understanding of the SWMI system.
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9.3.2 Regions
9.3.2.1 Statistical Description of Magnetospheric Properties
The decades-long reconnaissance of magnetospheric structure and dynamics has culminated in
new statistical descriptions of plasma properties in the magnetosphere, particularly their systematic
variation in response to solar wind drivers. For example, using data sets that extend over more than a
solar cycle, the activity-dependent spatial distribution of plasma-sheet fluxes was found to be well-
described by a relatively simple convection model coupled with losses. These and similar results have
solidified the statistical picture of the structure of the inner magnetosphere, but they do not capture the
dynamic evolution of these regions, nor the coupling with the rest of the system.
9.3.2.2 Measuring Invisible Populations
During the past decade, several new techniques were exploited for measuring the plasma density
over more extended regions than allowed by single-point, in situ measurements. On the ground,
observations of field-line resonances enabled instantaneous determination of the equatorial plasma
density over a broad spatial domain. In space, active radio sounding techniques probed the density
variation along magnetic field lines, and both radio sounding and Extreme Ultraviolet (EUV) images
revealed not only the dynamics of the boundaries of the plasmasphere, but actual global plasmaspheric
density distributions. These advances enabled for the first time the observation of the global evolution of
the plasmasphere in response to variable driving of the magnetosphere.
Energetic neutral atom (ENA) imaging established itself as a valuable tool in determining the
global scale configuration, dynamics, and composition of the ring current (e.g., Figure 9.6 below). It was
found that the peak of the ring-current proton distribution during the main phase of magnetic storms could
lie not in the historically expected afternoon location, but in the early morning sector, revealing that the
coupling with the ionosphere can very strongly alter the behavior of magnetospheric plasmas. In addition,
the hydrogen component of the ring current builds up and decays gradually throughout a magnetic storm,
but the oxygen component rises and falls impulsively. These variations in Oxygen are often correlated
with substorm injections highlighting the coupling between the magnetosphere and ionosphere. These
results represent not just a huge leap forward in system-level knowledge of the ring current; they also
offer a tantalizing hint of the dynamic magnetospheric behavior that could be uncovered with higher-
resolution, continuous and global imaging.
9.3.3 Processes
9.3.3.1 Magnetic Reconnection
The recent decade has witnessed substantial progress in understanding how magnetic
reconnection works. For example, increased computing power has allowed full-physics simulations
describing the essential physics and structure of the diffusion region, the key region where magnetic field
lines break and reform. The decoupling of ion and electron motions plays a key role, accelerating the
energy release, creating high-speed electron beams, and warping the magnetic field. These predictions
have facilitated the first direct detections of the ion diffusion region in the magnetosphere (see Figure 9.3)
and in the laboratory, as well as glimpses of the much smaller electron diffusion region. The observations
in the vicinity of the diffusion region revealed surprisingly that electrons can be accelerated by
reconnection to hundreds of keV.
The last decade has also witnessed surprises regarding the triggering and modulation of
reconnection: Theoretical studies using fully three dimensional simulations revealed that the added
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dimension facilitates plasma instabilities which can disrupt the diffusion region, making reconnection
highly turbulent. Observationally, reconnection seems to behave differently in different regions. On the
dayside magnetopause, as well as recently discovered in the solar wind, magnetic reconnection can be
quite steady in time and extended in space. In the magnetotail, however, reconnection is most often
patchy and bursty, producing narrow flow burst channels. Using multi-spacecraft observations, these
reconnection-generated flow channels have now been demonstrated to initiate magnetospheric substorms.
FIGURE 9.3 The center figure is a schematic of the magnetospheric indicating the regions where
magnetic reconnection usually occurs. The lower panel is a simulation result of the quadrupolar magnetic
field topology in the ion diffusion region, and the left and right panels are observations of these field
topologies by the Polar and Wind spacecraft, respectively. For comparison, the relative motions of the
two spacecraft through the reconnection region are indicated on the simulation result panel. The Hall
field arises from the decoupling of the ions from the electrons. SOURCE: Left: Adapted from F.S. Mozer,
S.D. Bale, and T. D. Phan, Evidence of Diffusion Regions at a Subsolar Magnetopause Crossing, Phys.
Rev. Lett. 89:015002, 2002. © 2002 The American Physical Society. Middle, top: C. Day, Spacecraft
probes the site of magnetic reconnection in Earth’s magnetotail, Physics Today 54:10, 2001. Middle,
lower: Adapted from Phan, T. D.; Drake, J. F.; Shay, M. A.; Mozer, F. S.; Eastwood, J. P. Evidence for
an elongated (>60 ion skin depths) electron diffusion region during fast magnetic reconnection, Phys. Rev.
Lett. 99:255002, 2007. © 2007 The American Physical Society. Right: Adapted from M. Øieroset, T. D.
Phan, M. Fujimoto, R.P. Lin, and R.P. Lepping, In situ: detection of collisionless reconnection in the
Earth’s magnetotail. Nature 412:414-417, 2001, doi:10.1038/35086520.
9.3.3.2 Wave-Particle Interactions
A delicate balance between acceleration and loss caused by wave-particle interactions controls
the variability of radiation belt fluxes during geomagnetic storms. Understanding of magnetospheric
plasma waves and their role in radiation belt dynamics has increased significantly during the last decade.
Statistical analyses of satellite wave data have led to the development of global models of the wave
environment. These have then been used to quantify the rates of energization and scattering loss to the
atmosphere. Time-dependent two-dimensional and three-dimensional models for the radiation belts and
the ring current, which incorporate the effects of wave-particle scattering, have been developed and are
beginning to provide a more realistic picture of storm-time particle dynamics.
Satellite observations of peaks in the radial profiles of radiation-belt electrons have demonstrated
that local acceleration due to WPI may at times dominate over traditionally accepted acceleration
associated with diffusive radial transport. Diffusive radial transport may actually lead to enhanced losses
at the magnetopause, causing a decrease in trapped flux rather than an increase. Particle interactions with
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“chorus” waves in particular have been shown to provide a major probable source of local acceleration.
The source of plasmaspheric hiss, another wave mode known to be responsible for strong losses of
radiation belt electrons near the edge of the plasmasphere, has been shown to be discrete chorus emissions
generated in the low-density region outside the plasmapause (see Figure 9.4). Chorus emissions have also
been shown to be the dominant cause of scattering of plasma sheet electrons, leading to their precipitation
into the atmosphere, where they produce the diffuse aurora. Intriguingly, recent observations of extremely
large-amplitude waves suggest that non-linear wave-particle physics may play an important role in
radiation belt dynamics.
FIGURE 9.4 Ray path calculations showing how discrete whistler-mode chorus emissions generated
outside the plasmapause can be refracted into the plasmasphere, become trapped, and eventually merge to
form incoherent plasmaspheric hiss. SOURCE: J. Bortnik, R.M. Thorne, and N.P. Meredith, The
unexpected origin of plasmaspheric hiss from discrete chorus emissions, Nature 452:62-66, 2008,
doi:10.1038/nature06741.
9.3.3.3 Turbulence
In the past decade the presence of large-amplitude MHD fluctuations in the magnetotail plasma
sheet has been established by spacecraft measurements, and the spatial scales (~1 RE) and time scales (~1
minute) of the fluctuations have been determined. Global simulations of the solar-wind-driven
magnetosphere are reaching high-enough spatial resolutions in the magnetotail to enable them to predict
irregular vortical flows at these scales and to statistically match the properties of the vortical flows to
observed fluctuations. However, the dynamical nature of these fluctuations, what causes them, and their
influence on the behavior of the magnetosphere has not been determined. Fluid turbulence provides one
pathway by which energy moves across scale sizes from large to small where energy can be dissipated in
the form of heating. When and where turbulent processes play a significant role in magnetospheric
dynamics remains unclear.
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9.3.4 Linkages
9.3.4.1 Coupling with the Solar Wind
The variable solar wind drives a wide range of variations in magnetospheric behavior. Over the
past decade, continuous measurements of the solar wind combined with observations throughout
geospace have enabled significant advances in identifying which specific large- and mesoscale solar-wind
properties produce different modes of magnetospheric response (e.g., storms, steady magnetospheric
convection events, sawtooth events). For example, studies have linked variations in the solar wind
dynamic pressure to radiation-belt loss and energization processes. Other studies quantified that the
strength of geomagnetic storms depends on both the electrodynamic coupling between the solar wind and
the magnetosphere and plasma loading of the magnetosphere, including both ionospheric and solar wind
sources. Spacecraft observations and numerical simulations reveal that solar-wind plasma entry into the
magnetosphere is surprisingly efficient under “quiescent” conditions of northward interplanetary
magnetic field. This plasma in turn participates as a substantial element of the storm-time ring-current
development when southward interplanetary magnetic fields couple with and energize the magnetosphere.
Additional progress has also been made in delineating the effects of smaller-scale solar wind variations on
magnetospheric behavior. While some of the specific processes that mediate this coupling with the solar
wind were clarified in the past decade, major questions remain regarding the spatial extent over which
they operate and the conditions that control their relative importance (such as small-scale solar wind
dynamic pressure variations and how they drive ULF waves regionally and globally in the
magnetosphere).
9.3.4.2 Magnetosphere-Ionosphere Coupling
Coupling between the magnetosphere and the ionosphere represents a key linkage in geospace.
Over the past decade, combined ground-based and space-based observations, theory, and modeling
greatly advanced understanding of this coupling as well as fostering new discoveries and new areas of
investigation. Empirical studies of spacecraft data established correlations between solar wind and
magnetosphere-ionosphere coupling parameters. For examples, solar wind density and dynamic pressure
increases lead to enhanced ionospheric outflow. Empirical relationships quantified how electromagnetic
energy flux into the ionosphere led to consequent outflow rates. Supporting theory has shown that
producing this outflow requires a multistep process involving a combination of WPI and electromagnetic
forcing. The important consequences this out-flowing ionospheric plasma has on the dynamic evolution
of the magnetosphere has also been realized. Observations have shown how this outflow merges with
plasmas of solar wind origin in the plasma sheet, creating a multi-species plasma. Theorists have shown
how differently reconnection behaves in multi-species plasmas, which in turn substantially modifies its
impacts on magnetospheric evolution and topology. Multi-fluid global scale simulations have confirmed
the major role ionospheric outflow plays in the creation of periodic substorm or so-called “sawtooth”
intervals (see Figure 9.5). While the basic correlations have been established and the fundamental
building blocks the creation of a complete theory of outflow and a detailed understanding of their
magnetospheric consequences remains a goal for the next decade.
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highlighted that can address these challenging objectives, but which require technology developments in
the coming decade to achieve feasible cost and readiness levels.
9.5.3.1 Magnetospheric Constellation Mission (MagCon)
Science Goals
Understanding the mass and energy transport at global and mesoscales in Earth’s magnetospheric
plasma sheet and reconnection regions of the near Earth magnetotail, plus the dayside and flanks of the
magnetopause and bow shock regions can be implemented using a multi-satellite in situ mission such as
the MagCon mission. The prime overarching objective of the mission is to determine how the
magnetosphere stores, processes, and releases energy in the magnetotail and accelerates particles that
supply the inner magnetosphere’s radiation belts. It would track the spatial-temporal plasma structures
and flows associated with the solar wind plasma entry across the magnetopause and transport within and
through the magnetotail. On the dayside and flanks the constellation would provide multipoint
measurements of the upstream solar wind input, the response throughout the magnetosphere, enabling
determination of how the entire system responds to variable solar wind driving. In the magnetotail it
would provide a map of the global plasma flows and field configurations, leading to determination of
whether they are internally developed or externally triggered. Throughout the mission, MagCon would
provide a global “picture” of these otherwise invisible regions of the magnetosphere.
Mission Concept
MagCon uses many satellites separated by mesoscale distances (~1-2 Re) that make magnetic
field plus plasma and energetic particle distribution function measurements at multiple points
simultaneously with relatively rapid cadence. The mission requires a significant number of spacecraft, 36
in the concept the panel evaluated, to achieve the mesoscale spacing while filling a significant fraction of
the near Earth space using orbits with perigees in the 7-8 Re range and apogees dispersed uniformly up to
25 Re with low inclination. The satellites would be simple ~30 kg class spin-stabilized vehicles with their
spin axes perpendicular to the ecliptic. Each spacecraft would carry a boom-mounted fluxgate
magnetometer, a three-dimensional ion-electron plasma analyzer, and simple energetic ion-electron
particle telescopes.
To implement such a constellation requires development of small satellite systems and
instruments that can be more cheaply manufactured and tested in a reasonable time frame (2-3 years) with
acceptable reliability levels, plus a better match between launch vehicle capabilities and constellation
mission needs.
9.5.3.2 Magnetospheric Constellation and Tomography (MagCat)
Science Goals
With science objectives similar in many respects to those of MagCon, MagCat would address
some of the most critical processes in Sun-Earth connections: plasma entry into the magnetosphere,
plasma-sheet formation and dynamics, and investigation of bow-shock structure, plasmaspheric plumes,
and other meso-scale structures that form in response to solar-wind variability. To achieve this objective
requires observations with a minimum spatial resolution of 0.5 Re at a minimum time cadence of 15s.
MagCat could provide those required measurements.
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Mission Concept
MagCaT is a 20-spacecraft mission that would provide a combination of two-dimensional images
of the equatorial outer magnetosphere and multi-point in situ observations made concurrently and in the
same imaged region. The spacecraft would be in two coplanar orbits that pass through critical regions in
the magnetotail, flank, and subsolar magnetosphere. Each satellite would transmit radio waves to all
others, obtaining 190 line-of-sight densities, enabling tomographic images of plasma density over large
regions with an average spatial resolution of 0.32 Re at 12s cadence. Each satellite would carry a suite of
plasma and field instruments that provide complementary in situ data throughout the imaged area for
ground truth as well as revealing the detailed plasma processes in the region. The nominal payload would
include a 3-axis fluxgate magnetometer, electrostatic analyzers that measure three-dimensional ion and
electron distributions, a relaxation sounder to determine the ambient density, and a radio tomography
instrument.
Like MagCon, the pre-CATE estimate for the MagCat mission was deemed beyond the scope of
the budget in the coming decade. Thus, there is a similar need in the coming decade to develop cost-
effective and efficient manufacturing procedures to mass produce a large number of spacecraft and
instruments.
9.5.4 International Partnerships
International partnerships involving a consortium of individual space agencies can be an effective
way to pool limited resources to achieve an outstanding science goal whose importance is agreed upon by
a consensus of these agencies. For example, determining the cross-scale coupling physics involved in key
plasma processes is believed to be crucial for complete understanding of the causes and consequences of
these processes. None of the past, current (e.g., Cluster and THEMIS), or planned missions (e.g., MMS)
are designed to address the cross-scale aspects of these processes. However, a mission concept has been
developed in Japan, Canada, and Europe that involves a fleet of spacecraft performing simultaneous in
situ measurements at electron, ion, and fluid scales. Such a mission can investigate how turbulence
transports and dissipates energy over multiple scales, how kinetic microscale instabilities are modulated
by macroscale properties of the plasma, as well as the relative role of global conditions versus microscale
physics in determining the structure and dynamics of magnetic reconnection. These are all important
aspects of goals 6 and 7. This and other international, cross-agency partnerships should be pursued when
available and possible.
SWMI Imperative: Partner with other space agencies to implement consensus missions, such as
a multi-spacecraft mission to address cross-scale plasma physics.
9.5.5 DRIVE-Related Initiatives
In this section, the panel expands on a number of issues that have a material impact on the
national ability to conduct an effective and productive research effort.
9.5.5.1 Solar Wind Monitor
Essentially the entire set of SWMI science objectives requires knowledge of the upstream solar
wind conditions, so an upstream solar wind monitor is crucial to accomplishing those objectives. These
conditions include the upstream solar wind properties, energetic particles, and the interplanetary magnetic
field; ideally a solar coronagraph could provide advanced indications of an upcoming solar wind event.
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Chapter 7 of Part I justifies the value of these measurements. The information provided by this spacecraft
would also be essential to any space weather forecasting system. The panel does not have a preference on
which agency conducts this mission, but these data must be available on a continuous basis throughout
the coming decade.
SWMI Imperative: Ensure continuity of measurements of the upstream solar wind.
9.5.5.2 Theory, Modeling and Data Analysis
Efforts related to advancing theoretical and modeling studies of geospace are another key
component of the solar and space physics research effort. The future of data analysis is becoming ever
more closely linked with modeling, and tools need to be developed to enable a broad segment of the
community to access and combine observations and model results. Currently, a great deal of the science
return from NASA missions and NSF ground-based measurements occurs through theory, modeling, and
data analysis supported in a portfolio of both NASA and NSF grants programs. The high productivity
and cost-effectiveness of these programs argue strongly that major increases in science output can be
achieved with modest funding increases. The panel therefore strongly encourages the agencies to
enhance the funding of R&A programs. In a constrained funding environment, this is one of the most
cost-effective ways to assure that the high-priority science objectives outlined in this survey will be
accomplished.
In addition, the panel supports funding enhancements to enable the creation of a new program
within NASA’s research portfolio to bring critical-mass multidisciplinary science teams together to
address grand challenge problems. However, these proposed Heliophysics Science Centers must not be
created at the expense of the current research programs, e.g., Heliophysics Theory Program. They must
also be competed regularly and be focused on addressing a key science question.
The panel also strongly affirms the vital role theory and modeling supported by mission funding
play in advancing the scientific objectives of the missions. The panel believes that this role should be
protected by requiring external reviews of the impacts of any theory-funding reductions on the ability of
the mission to fulfill its scientific objectives.
SWMI Imperative: Enhance and protect support for theory, modeling, and data analysis,
including research and analysis programs and mission-specific funding.
9.5.5.3 Innovation and Technology
In reviewing the white papers submitted from the community, the panel found that many relied on
tried and true measurement techniques. However, while much can be accomplished with new applications
of state-of-the art technology, it is also clear that to accomplish the most challenging science objectives of
the future, the development of new, innovative concepts will be necessary. Indeed, in an observation-
driven field such as solar and space physics, it is often new observations that point the way to the
scientific questions of the future.
As described in Section 9.5.3, advanced instrumentation for constellation missions is an area of
particular need if the science goals the panel has outlined are ultimately to be realized. Targeted research
on how to acquire, analyze, and display the simultaneous measurements from many spacecraft is also
needed. New ways to integrate global modeling and global observations also need to be developed.
Another area where technology development efforts could have a big scientific payoff is global
imaging systems, particularly systems that can stand off, well outside the magnetosphere’s bow shock,
and image its boundary structures using a range of techniques such as neutral atom imaging (ENA),
scattered light, and X-ray emission. New instrumentation with increased sensitivity and resolution is
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needed to achieve spatial resolutions (~0.5 Re) and image cadences (~15 min) sufficient to image the
boundaries and visualize their motions and structure. New techniques for reducing background noise are
also needed.
A number of the science goals outlined in Section 1.4 involve connecting phenomena and
signatures that occur in the ionosphere with their corresponding phenomena and signatures in the
magnetosphere. Because this connection occurs primarily via the geomagnetic field, which is strongly
distorted and highly variable due to currents flowing within the magnetosphere itself, an accurate
mapping between the ionosphere and magnetosphere for all relevant conditions is lacking. Current efforts
to relate magnetospheric and ionospheric physics thus typically rely on empirical models based on
statistical analysis of large data sets acquired over long times and under a variety of conditions.
Techniques to establish definitively the instantaneous mapping are thus urgently needed.
The SWMI panel feels that the current limited investment in technology development has
discouraged the development of new instrument concepts. The panel therefore strongly supports the
creation of a robust Heliophysics Instrument and Technology Development Program (HITDP) in the
context of the NASA ROSES. In the panel’s opinion, this program should be funded sufficiently to
support several grants at levels significantly larger than is possible at present through SR&T.
Moreover, the missions of the future will require new satellite and systems technologies. Such
technologies are most appropriately pursued by the Office of the Chief Technologist, in close consultation
with HPD so that real mission needs are addressed. Possible technology development needs noted by the
panel include, but are not limited to, techniques that make it feasible to produce and deploy large numbers
of identical spacecraft at an affordable price, high radiation tolerance, solar sails, advanced propulsion
and power, low-cost launch vehicles, mass-production techniques, component miniaturization, and
wireless communications within a satellite.
Another area where near-term investments will help reduce the risk and long-term cost of new
instruments is in raising the technology readiness level (TRL) of the instruments of the future, particularly
in the area of providing in-space operating experience. The panel believes that suborbital flights are cost-
effective ways to mature instrument technologies for future science applications, even if no immediate
science can be obtained from flying suborbitally. Thus, while the panel applauds and supports the science
output of the suborbital program, it also encourages the utilization of suborbital flights for increasing the
TRL of instruments with long-term science applications, but not necessarily science output from the flight
itself.
SWMI Imperative: Invest significantly in developing the technologies to enable future high-
priority investigations.
9.5.5.4 Ground-Based Instrumentation
Since the science objectives established by this panel emphasize a global view of the coupled
MIT system the panel strongly supports networks of ground-based instruments. For example, the
MEDICI mission will be greatly enhanced by the data from magnetometer arrays and the SuperDARN
network, and both MISTE and MEDICI benefit from the data provided by incoherent scatter radars (ISRs)
and networks of all-sky cameras. The panel concludes that existing facilities, e.g., ISRs, SuperDARN,
magnetometer arrays, should continue to be supported, upgraded and perhaps enhanced. Moreover, the
increasing access to data from these instrument suites via the Internet would greatly benefit from the
development of standards for data collection and access.
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FIGURE 9.15 Composite auroral image constructed from the THEMIS All-sky Imager network.
SOURCE: Courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio; available at
http://www.youtube.com/watch?v=GEebRsRnwm0.
The panel takes note of successful NASA contributions in the past decade to ground-based assets
that directly support their space missions, e.g., the THEMIS all-sky-camera network, for which an
example image is shown in Figure 9.15. The panel encourages continuation and expansion of these
efforts. The panel also notes that DOD supports a number of ground-based observatories that contribute
significantly to the science objectives outlined above and encourages continued sponsorship of those
facilities as well. The panel further supports negotiation of international agreements to enable
coordination and collaboration with non-U.S. ground-based capabilities.
SWMI Imperative: Ensure strong multi-agency support for a broad range of ground-based assets
that are a vital part of magnetospheric science.
9.5.5.5 Laboratory Studies
The panel endorses the recommendation in the Plasma Science Decadal Survey that the
Department of Energy be the prime steward for laboratory plasma science. However, to enable research
on basic plasma physics that will be of greater utility to SWMI science objectives, the panel supports the
creation of an interagency joint laboratory astrophysics program. This program should be competed on a
regular basis, include selection criteria that focus on issues relevant to space physics, contain a
mechanism for outside investigators to have access to supported facilities, and be open to proposals from
any institution.
SWMI Imperative: Create an interagency joint laboratory astrophysics program that addresses
issues relevant to space physics.
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9.5.5.6 Education and Workforce
At the most basic level, the field of solar and space physics needs a robust, well-trained, and
talented workforce to accomplish its science goals, as well as an educated populace that recognizes the
value of addressing these exciting scientific challenges. The panel therefore endorses curriculum
development efforts across all academic levels, as well as faculty development programs. The panel
notes in particular the success of the NSF FDSS program and strongly supports its continuation and
enhancement throughout the coming decade. The panel further endorses funded training opportunities for
both undergraduate and graduate students, especially for participation in the development of flight
hardware. Such opportunities could be provided by science grant augmentations, stand-alone E/PO grants,
and mission-related funding.
SWMI Imperative: Strengthen workforce, education, and public outreach activities.
9.5.6 Space Weather
The long-term vision of this Decadal Survey is to have the knowledge to ensure the well-being of
a society dependent on space. Actionable knowledge of space environment effects involves the ability to
characterize conditions anywhere in the system at any time in the past, as well as to predict future
conditions with good fidelity. This requires an understanding of the full, coupled solar-terrestrial system
that encompasses all the regions, processes, and coupling described above, across spatial scales from
meters to hundreds of Earth radii. It includes understanding the fundamental microscopic physics as well
as the global system behavior in response to variable driving. The ultimate objective in solar wind-
magnetosphere interactions is to know how solar and solar-wind input at various spatial and temporal
scales determine the nature and behavior of magnetospheric populations, structures, and processes and to
be able to predict those that have significant space weather impacts. There are three aspects of
accomplishing this long-term vision:
1. Establishment of the foundation of comprehensive scientific understanding;
2. Development of sound, validated space environment models;
3. Fielding the optimum operational assets to drive those models.
The scientific program laid out above will put in place some of the tools needed to achieve this
vision, particularly by defining outstanding questions that still inhibit a comprehensive scientific
understanding.
The development of sound, validated space environment models requires a healthy R20/O2R
program. This in turn clearly necessitates communication and coordination between research-oriented
agencies and operational agencies with end-use requirements so that a robust and adequately funded
process exists for transitioning scientifically sound and operationally useful models between the two
emphases.
Observations are critical for an effective space weather program because they support research
and development of models and they drive models in their operational phase. Space weather observations
are available from government research and some operational programs as well as from the commercial
sector. Currently, each group in isolation develops observational requirements and observing systems to
fulfill those requirements. To make more effective use of limited resources, these observations should be
nationally coordinated, allowing research groups to provide input and possibly additional payloads to
operational or commercial endeavors. Similarly, coordination would allow operational and commercial
entities to guide and use research observations. It is highly desirable that the National Space Weather
Program (NSWP) be augmented to provide a mechanism for coordinating space weather observations,
allowing for input to mission definition and payloads from all groups. The panel encourages the
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placement and coordination of space-weather-related observing systems on research, commercial, and
government platforms to the greatest extent possible. The panel also supports development of
mechanisms for real-time data acquisition and distribution from all available platforms.
More generally, to make the most of limited resources, an effective space weather program must
be accomplished through coordinated activities within the government as well as with the commercial
sectors. Currently several commercial and government groups provide various forms of space weather
products with some limited coordination, yet many functions overlap. The panel urges that the NSWP be
enhanced and clarified in order to delineate the roles for each agency, e.g., NASA, NOAA, NSF, the U.S.
Geological Survey, DOD, and DOE, in producing and distributing data and models providing forecasting
and space weather related products. The panel strongly endorses the undertaking of a high-level study to
design a more complete overarching architecture for the NSWP that would define agency roles and
coordinate observations.
SWMI Imperative: Encourage the creation of a complete architecture for the nation’s Space
Weather Program that would coordinate joint research, commercial, and operational space
weather observations and define agency roles for producing, distributing, and forecasting space
weather products. In addition the panel encourages all agencies to foster interactions between the
research and operational communities and identify funding for maintaining a healthy R2O/O2R
program.
For the long-term future vision of this decadal survey, the optimum set of operational
observations need to be identified to drive models that will enable specification and prediction of the
environment throughout the magnetosphere. This may ultimately require an operational “great
observatory” of satellites in appropriate orbits for monitoring crucial aspects of the input from and
response to solar wind variability. Such an observatory would not only provide the input necessary for
high-fidelity environmental specifications, but would also provide routine context information for future
targeted science experiments, much as magnetospheric activity indices are used today. Potential elements
of such a space weather observatory could include: a solar wind monitor (including IMF, energetic
particle, and corongraphic measurements, too) high-altitude synoptic imaging of the aurorae, ring current,
plasmasphere, and of the outer magnetospheric boundary; constellation observations of plasma entry and
global tail structure; low-altitude, DMSP-like satellites to observe the magnetospheric input into the
ionosphere and its response; multiple geosynchronous measurements of plasma, energetic particles, and
magnetic field; RBSP-like monitors of the inner magnetospheric radiation environment; and a fine mesh
of appropriate ground measurements. One important near-term investment is to determine, based on past
observations of this nature, the optimum set of measurements that are required to drive high-fidelity
predictive models of the environment.
SWMI Imperative: Implement a program to determine, based on past observations, the optimum
set of measurements that are required to drive high-fidelity predictive models of the environment.
9.5.7 Prioritization
These imperatives would all greatly enhance scientists’ ability to accomplish the science goals the
panel has outlined, thereby providing the foundation needed for addressing the Decadal Survey Science
Goals. However, the panel realizes that in times of constrained budgets, it may not be possible to enact
all of these imperatives, so the panel has undertaken a prioritization process to help identify which of
these are the most important. The panel’s prioritization is based on the overarching objective to identify
initiatives that will most cost-effectively enable the science of the future. Accordingly, the panel has
adopted the following criteria:
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General considerations for prioritization
• Focus on elements that are directly relevant to the SWMI science objectives identified.
• Consider historical evidence about contributions of various elements to scientific progress.
• Consider the cost of an imperative versus its likely return.
For mission-related imperatives
• How well does the mission address the high-priority science objectives?
• Is it highly focused or does it address a broader range of the objectives?
• How feasible is it?
• Will it fit within the expected budget?
• What is the science return for the cost?
• Does it require technology development?
• What is the broader impact (other panels, space weather, etc.)?
For other capabilities
• How central is the capability to the accomplishment of the science objectives?
• Is it currently in danger?
• Could it make a much bigger contribution with a modest enhancement?
Using these criteria, the panel has prioritized the imperatives not only within but across the three
categories in order to identify the most cost-effective approach to accomplishing the panel’s critical
science goals. The full set of prioritized imperatives, with their mapping to the three categories, is
presented in Table 9.4.
TABLE 9.4 Summary of SWMI Imperatives
Rank Imperative Missions DRIVE Space
Weather
1 Enhance the resources dedicated to the Explorer program and broaden
the range of cost categories.
2 Complete the strategic missions that are currently in development
(MMS and RBSP/BARREL) as cost-effectively as possible.
3 Initiate the development of a strategic mission, like MEDICI, to
determine how the magnetosphere-ionosphere-thermosphere system is
coupled and responds to solar and magnetospheric forcing.
4 Ensure strong continued support for extended missions that can still
contribute significantly to high-priority science objectives.
5 Enhance and protect support for theory, modeling, and data analysis,
including research and analysis programs and mission-specific funding.
6 Ensure continuity of measurements of upstream solar wind, IMF, and
energetic particles that are necessary for solar wind-magnetosphere
interaction science.
7 Invest significantly in developing the technologies to enable future
high-priority investigations.
8 Ensure strong multi-agency support for a broad range of ground-based
assets that are a vital part of magnetospheric science.
9 Develop a mechanism within NASA to support rapid development,
deployment, and utilization of science payloads on commercial vehicles
and other missions of opportunity. NSF and DOD efforts in this regard
are also encouraged.
10 Through partnership between NASA’s Heliophysics Division and
Planetary Division, ensure that appropriate magnetospheric
instrumentation is fielded on missions to other planets. In particular,
our highest priority in planetary magnetospheres is a mission to orbit
Uranus.
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Rank Imperative Missions DRIVE Space
Weather
11 Partner with other space agencies to implement consensus missions that
address the high-priority science objectives identified in this report,
such as a multi-spacecraft mission to address cross-scale plasma
physics.
12 Encourage the creation of a complete architecture for the nation’s
Space Weather Program that would coordinate joint research,
commercial, and operational space weather observations and define
agency roles for producing, distributing, and forecasting space weather
products. In addition the panel encourages all agencies to foster
interactions between the research and operational communities and
identify funding for maintaining a healthy R2O/O2R program.
13 Implement a program to determine the optimum set of measurements
that are required to drive high-fidelity predictive models of the
environment, and put in place a plan to ensure that the optimum set of
observational capabilities is maintained.
14 Strengthen workforce, education, and public outreach activities.
15 If resources permit, initiate a strategic mission like MISTE to
simultaneously measure the inflow of energy to the upper atmosphere
and the response of the ionosphere-thermosphere system to this input,
in particular the outflow back to the magnetosphere.
16 Create an interagency joint laboratory physics program that addresses
issues relevant to the high-priority science objectives identified in this
report.
9.6 CONNECTIONS TO OTHER PANELS OR DISCIPLINES
9.6.1 Solar and Heliospheric
It is clear from the foregoing discussion that the variable solar wind is the dominant driver of
magnetospheric dynamics. In order to fully understand the way in which both long-term solar variations
as well as short-term eruptive events such as solar flares or coronal mass ejections can produce dramatic
effects of importance to humans at Earth, solar wind measurements upstream of Earth’s magnetosphere
are essential. At present a nearly continuous record of measurements of the solar wind flow velocity,
density and temperature is available from the very early days of the space program up to the present time.
Any interruption in the continuity of these measurements would have serious consequences on scientists’
ability to study the effects that solar variations have on Earth’s magnetosphere, ionosphere, and
atmosphere, and on the ability to forecast significant societal impacts.
9.6.2 Atmosphere and Ionosphere
The past decade has significantly reinforced appreciation of the key influences the ionosphere has
on magnetospheric behavior and of the importance of magnetospheric driving for ionospheric behavior.
It is thus impossible to understand one without taking into account the two-way coupling with the other.
While this decadal survey separates the two regions for ease of discussion, it is clear from both chapters
that they must be understood as a coupled system. During the coming decade one of the most important
emphases of space physics research will be to clarify quantitatively the coupling of these elements in
order to enable progress toward a predictive understanding of both.
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9.6.3 Planetary Science
The magnetospheres of other planets display not only certain close similarities, such as the
formation of bow shocks and radiation belts, but also many processes that are markedly different, such as
the source of charged particles within the radiation belts, which can vary from a mixture of the solar wind
and ionosphere at Earth, to lava volcanoes and water geysers on small moons at Jupiter and Saturn. This
rich diversity has provided surprising discoveries of the breadth of expression of fundamental physical
processes that play important roles in the acceleration of charged particles and the generation of magnetic
fields in planetary magnetospheres. Both planetary and magnetospheric understanding is thus enriched by
the comparative study of magnetospheres. With orbital missions at many of the solar system’s other
planets, comparative magnetospheric studies should increasingly provide insights into the diversity of
magnetospheric processes and how they couple to the planets themselves.
9.6.4 Physics and Astrophysics
Many of the processes and phenomena that determine magnetospheric behavior act throughout
the universe in settings as diverse as laboratory plasmas and supernova shock waves. The ability to
observe and diagnose these processes in situ, with no interference from walls, is a powerful tool to enable
basic understanding with broad applicability. Examples of such processes include magnetic reconnection,
shock acceleration of charged particles, and the physics of rapidly rotating magnetized bodies. Moreover,
the study of comparative magnetospheres not only elucidates the behavior of magnetized planets in our
solar system, but also points the way to the potential breadth of behavior of magnetized bodies throughout
the universe.
9.6.5 Complex Nonlinear System Studies
Eruptive solar processes such as solar flares and spontaneously occurring episodic dynamical
variations in planetary magnetospheres known as “magnetic substorms” involve highly nonlinear systems.
Similarly, planetary radiation belts evolve through a complicated and nonlinear combination of wave-
particle processes that accelerate particles to very high energies, transport them throughout the system,
and cause their loss. Although many of these phenomena are at best poorly understood, their study serves
as an important driver for furthering the understanding of the mathematical analysis of complex nonlinear
systems. Predicting the behavior of the vast, coupled, multi-scale, and nonlinear Sun-magnetosphere-
atmosphere system presents a major challenge to mathematical and computational methods.
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