Copyright © National Academy of Sciences. All rights reserved.
Solar and Space Physics: A Science for a Technological Society
ENABLING DISCOVERY IN SOLAR AND SPACE PHYSICS
25
age. Yet, despite increasingly accurate measurements of the flows beneath the solar surface and more
sophisticated models of the dynamo that drives the activity, scientists cannot confidently make a physical
prediction of the emergence of a strong sunspot, let alone the level of activity that will be present at the
end of the coming decade. The missing information will come, in part, from measurements of the hardto-view solar poles. The deep, ponderous flows that carry patterns of magnetic flux to the poles regulate
the seeding of the deep-seated dynamo that generates subsequent solar cycles.
While large-scale dynamics drive cyclic solar changes, the actual mechanisms of variability—brightness, heating, mass flow—depend also on the summation of the myriad interactions that take place on
the smallest scales. Against that seething background of continual small-scale activity, global structures
store immense energy on a vast scale. The build-up of magnetic stress can be modeled, but not observed
directly. What triggers catastrophic energy release in a flare or CME remains a puzzle. Only by sensing
the solar wind directly with a probe near the Sun will it be possible to distinguish what accelerates the
ordinary wind and more energetic particles.
Key Science Goal 2
Key Science Goal 2. Determine the dynamics and coupling of Earth’s magnetosphere, ionosphere, and
atmosphere and their response to solar and terrestrial inputs. The regions of Earth’s space environment are coupled by interactions among neutral gas, electrically charged particles, and plasma waves
occurring over a range of spatial and temporal scales. The transport of energy and momentum through
this environment exhibits varying degrees of feedback and complexity, requiring research approaches
that treat it as a coupled system.
The space environment of Earth is profoundly affected by the solar wind. When the entrained solar
wind magnetic field encounters Earth’s magnetic field where the two magnetic fields are pointing in
opposite directions, they can annihilate through the process of magnetic reconnection. (See Figure 1.4.)
Magnetic reconnection drives convection that carries energetic particles toward Earth where they are
injected and trapped in orbits around Earth to form the outer radiation belt. Although the broad view of
how reconnection takes place and drives convection in the magnetosphere is now well established, the
underlying physics of magnetic reconnection in the magnetosphere is not yet understood well enough to
predict when, where, and how fast this process will occur and how it contributes to the transport of mass,
energy, and momentum. Understanding charged-particle acceleration, scattering, and loss, which control
the intensification and depletion of the radiation belts, is therefore a priority of solar and space physics.
During magnetic storms intense ion upwelling from the ionosphere—the inner boundary of the magnetosphere—into the magnetosphere is so strong that it can alter magnetospheric dynamics by modifying
magnetic reconnection both on the dayside and on the nightside. The ionosphere is also the site of fundamental plasma-neutral gas interactions that must be unraveled to understand the dynamics of the neutral
atmosphere-ionosphere system. When magnetospheric currents are disrupted, it is the ionosphere that
provides the alternate path for magnetospheric currents to flow, heating Earth’s atmosphere.
Research and observations are clearly needed to understand energy transport, cooling, and structuring across this system. The intense energy input from the magnetosphere, reaching up to a terawatt or
more, typically occurs in regions spanning less than 10 degrees in latitude, but during storms energy is
redistributed throughout the polar regions and down to middle latitudes. Theory still cannot explain how
the global thermosphere “inflates” several hours after the onset of high-latitude heating, nor have studies
yet captured the subsequent cooling with the fidelity that is needed to predict changes in satellite orbits
occurring during magnetic storms.
Solar and Space Physics: A Science for a Technological Society
ENABLING DISCOVERY IN SOLAR AND SPACE PHYSICS
25
age. Yet, despite increasingly accurate measurements of the flows beneath the solar surface and more
sophisticated models of the dynamo that drives the activity, scientists cannot confidently make a physical
prediction of the emergence of a strong sunspot, let alone the level of activity that will be present at the
end of the coming decade. The missing information will come, in part, from measurements of the hardto-view solar poles. The deep, ponderous flows that carry patterns of magnetic flux to the poles regulate
the seeding of the deep-seated dynamo that generates subsequent solar cycles.
While large-scale dynamics drive cyclic solar changes, the actual mechanisms of variability—brightness, heating, mass flow—depend also on the summation of the myriad interactions that take place on
the smallest scales. Against that seething background of continual small-scale activity, global structures
store immense energy on a vast scale. The build-up of magnetic stress can be modeled, but not observed
directly. What triggers catastrophic energy release in a flare or CME remains a puzzle. Only by sensing
the solar wind directly with a probe near the Sun will it be possible to distinguish what accelerates the
ordinary wind and more energetic particles.
Key Science Goal 2
Key Science Goal 2. Determine the dynamics and coupling of Earth’s magnetosphere, ionosphere, and
atmosphere and their response to solar and terrestrial inputs. The regions of Earth’s space environment are coupled by interactions among neutral gas, electrically charged particles, and plasma waves
occurring over a range of spatial and temporal scales. The transport of energy and momentum through
this environment exhibits varying degrees of feedback and complexity, requiring research approaches
that treat it as a coupled system.
The space environment of Earth is profoundly affected by the solar wind. When the entrained solar
wind magnetic field encounters Earth’s magnetic field where the two magnetic fields are pointing in
opposite directions, they can annihilate through the process of magnetic reconnection. (See Figure 1.4.)
Magnetic reconnection drives convection that carries energetic particles toward Earth where they are
injected and trapped in orbits around Earth to form the outer radiation belt. Although the broad view of
how reconnection takes place and drives convection in the magnetosphere is now well established, the
underlying physics of magnetic reconnection in the magnetosphere is not yet understood well enough to
predict when, where, and how fast this process will occur and how it contributes to the transport of mass,
energy, and momentum. Understanding charged-particle acceleration, scattering, and loss, which control
the intensification and depletion of the radiation belts, is therefore a priority of solar and space physics.
During magnetic storms intense ion upwelling from the ionosphere—the inner boundary of the magnetosphere—into the magnetosphere is so strong that it can alter magnetospheric dynamics by modifying
magnetic reconnection both on the dayside and on the nightside. The ionosphere is also the site of fundamental plasma-neutral gas interactions that must be unraveled to understand the dynamics of the neutral
atmosphere-ionosphere system. When magnetospheric currents are disrupted, it is the ionosphere that
provides the alternate path for magnetospheric currents to flow, heating Earth’s atmosphere.
Research and observations are clearly needed to understand energy transport, cooling, and structuring across this system. The intense energy input from the magnetosphere, reaching up to a terawatt or
more, typically occurs in regions spanning less than 10 degrees in latitude, but during storms energy is
redistributed throughout the polar regions and down to middle latitudes. Theory still cannot explain how
the global thermosphere “inflates” several hours after the onset of high-latitude heating, nor have studies
yet captured the subsequent cooling with the fidelity that is needed to predict changes in satellite orbits
occurring during magnetic storms.