Copyright © National Academy of Sciences. All rights reserved.
Solar and Space Physics: A Science for a Technological Society
REPORT OF THE PANEL ON SOLAR WIND-MAGNETOSPHERE INTERACTIONS
231
tions with various plasma waves and shock fronts, which cause a violation of one or more of the adiabatic
particle invariants, leading to loss to the atmosphere, exchange of energy between waves and particles, or
radial transport. Waves responsible for such processes either are generated naturally during the injection
of medium-energy particles into the inner magnetosphere, or are excited by macroscopic changes in the
system caused by solar wind variations, interplanetary shocks, or substorm activity. Accurate modeling of
the energetic particle source and loss processes thus requires a global understanding of all important waves,
or shock characteristics, and the variability of their power spectra. Moreover, several of these important
waves attain amplitudes at which nonlinear scattering occurs, but it is not yet known how pervasive such
conditions are, nor how to incorporate them in global radiation belt models.
The radiation belt population is strongly coupled to changes in the medium-energy ring current and
plasma-sheet populations, which provide a reservoir of both source particles and energy needed to accelerate a fraction of the lower-energy particles to radiation-belt energies. In this regard, RBSP stands to benefit
from existing missions of the Heliophysics Systems Observatory. Electrons in the outer radiation belt are
undoubtedly seeded by lower energy particles injected from beyond geostationary orbit. Missions such as
Geotail, Cluster, and THEMIS provide these higher-altitude measurements needed to augment RBSP’s local
studies of acceleration and heating in the radiation belts. Improvements in understanding how the radiation belts respond to changes in the solar wind will require the development of numerical codes capable
of simulating the development of these populations and the magnetic field distortions they produce, the
incorporation of physically realistic particle scattering and diffusion into such codes, and further detailed
in situ observations to establish the exact nature of the scattering. Improved measurements of the spatial
distribution of the radiation belt population are needed to discriminate between wave-driven energization
processes that occur locally and energization that occurs via spatial diffusion. Further observations of the
prompt acceleration of electrons and ions by interplanetary shocks penetrating into the magnetosphere
are also required to establish the significance of this process.
Understanding the energization of the radiation belts was one of the top-level science objectives identified in the 2003 decadal survey 5 and led not only to the impressive advances described in Section 9.3 but
also to NASA’s RBSP. It is expected that RBSP will provide definitive answers to many of the outstanding
questions in this area, but since it has not yet launched, the SWMI panel reiterates the enduring importance
of those questions and endorses anew the science objectives of the RBSP mission.
Predicting the variability of the highly energetic and thus hazardous populations of our space environment is a central part of decadal survey key science goal 1. Since this variability is explicitly determined
by processes operating within the magnetosphere in response to solar wind input, this goal also enables a
significant portion of decadal survey key science goal 2. Those processes, as described above, are fundamental ones that presumably operate throughout the universe, including in other planetary magnetospheres,
and so accomplishing this goal will also contribute significantly to decadal survey key science goal 4.
The second critical SWMI science goal related to universal physical processes is goal 5.
9.4.2.2 SWMI Science Goal 5. Discover How Magnetic Reconnection Is Triggered and Modulated
Digging Deeper
Magnetic reconnection is a ubiquitous process in plasmas in which magnetic field lines break and
reform, causing an explosion powered by magnetic field annihilation. Examples of its fundamental role
include releasing the energy that drives solar flares and coronal mass ejections, coupling the solar wind
5 National Research Council, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, The
National Academies Press, Washington, D.C., 2003; and National Research Council, The Sun to the Earth—and Beyond: Panel
Reports, The National Academies Press, Washington, D.C., 2003.
Solar and Space Physics: A Science for a Technological Society
REPORT OF THE PANEL ON SOLAR WIND-MAGNETOSPHERE INTERACTIONS
231
tions with various plasma waves and shock fronts, which cause a violation of one or more of the adiabatic
particle invariants, leading to loss to the atmosphere, exchange of energy between waves and particles, or
radial transport. Waves responsible for such processes either are generated naturally during the injection
of medium-energy particles into the inner magnetosphere, or are excited by macroscopic changes in the
system caused by solar wind variations, interplanetary shocks, or substorm activity. Accurate modeling of
the energetic particle source and loss processes thus requires a global understanding of all important waves,
or shock characteristics, and the variability of their power spectra. Moreover, several of these important
waves attain amplitudes at which nonlinear scattering occurs, but it is not yet known how pervasive such
conditions are, nor how to incorporate them in global radiation belt models.
The radiation belt population is strongly coupled to changes in the medium-energy ring current and
plasma-sheet populations, which provide a reservoir of both source particles and energy needed to accelerate a fraction of the lower-energy particles to radiation-belt energies. In this regard, RBSP stands to benefit
from existing missions of the Heliophysics Systems Observatory. Electrons in the outer radiation belt are
undoubtedly seeded by lower energy particles injected from beyond geostationary orbit. Missions such as
Geotail, Cluster, and THEMIS provide these higher-altitude measurements needed to augment RBSP’s local
studies of acceleration and heating in the radiation belts. Improvements in understanding how the radiation belts respond to changes in the solar wind will require the development of numerical codes capable
of simulating the development of these populations and the magnetic field distortions they produce, the
incorporation of physically realistic particle scattering and diffusion into such codes, and further detailed
in situ observations to establish the exact nature of the scattering. Improved measurements of the spatial
distribution of the radiation belt population are needed to discriminate between wave-driven energization
processes that occur locally and energization that occurs via spatial diffusion. Further observations of the
prompt acceleration of electrons and ions by interplanetary shocks penetrating into the magnetosphere
are also required to establish the significance of this process.
Understanding the energization of the radiation belts was one of the top-level science objectives identified in the 2003 decadal survey 5 and led not only to the impressive advances described in Section 9.3 but
also to NASA’s RBSP. It is expected that RBSP will provide definitive answers to many of the outstanding
questions in this area, but since it has not yet launched, the SWMI panel reiterates the enduring importance
of those questions and endorses anew the science objectives of the RBSP mission.
Predicting the variability of the highly energetic and thus hazardous populations of our space environment is a central part of decadal survey key science goal 1. Since this variability is explicitly determined
by processes operating within the magnetosphere in response to solar wind input, this goal also enables a
significant portion of decadal survey key science goal 2. Those processes, as described above, are fundamental ones that presumably operate throughout the universe, including in other planetary magnetospheres,
and so accomplishing this goal will also contribute significantly to decadal survey key science goal 4.
The second critical SWMI science goal related to universal physical processes is goal 5.
9.4.2.2 SWMI Science Goal 5. Discover How Magnetic Reconnection Is Triggered and Modulated
Digging Deeper
Magnetic reconnection is a ubiquitous process in plasmas in which magnetic field lines break and
reform, causing an explosion powered by magnetic field annihilation. Examples of its fundamental role
include releasing the energy that drives solar flares and coronal mass ejections, coupling the solar wind
5 National Research Council, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, The
National Academies Press, Washington, D.C., 2003; and National Research Council, The Sun to the Earth—and Beyond: Panel
Reports, The National Academies Press, Washington, D.C., 2003.