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Solar and Space Physics: A Science for a Technological Society
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SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
in the magnetosphere to the ionosphere can vary among models by more than 100 km, so ionospheric
signatures cannot be properly attributed to the associated magnetospheric regions and processes. Since
strong and variable currents significantly distort the magnetospheric magnetic field by different amounts
under different conditions, determining this mapping is a challenging but important problem.
There are numerous examples of how magnetosphere-ionosphere-thermosphere coupling plays out in
the system-level response, both through electrodynamics and through mass coupling.
On the electrodynamic side, the strength of the convective motion in the ionosphere saturates for high
levels of solar wind driving. The exact physical mechanisms for this saturation effect remain unclear, but
ionospheric conductance certainly plays a key role. As another example, the electrodynamic coupling
with the magnetosphere extends down into the thermosphere, where the ionospheric convection can drive
neutral-particle motions that in turn influence ionospheric drifts after the solar wind driving is reduced.
These plasma drifts then are communicated back into the magnetosphere, where they affect the shape
and evolution of the plasmasphere. Because the plasmasphere dominates the inner magnetospheric mass
content and therefore the plasma wave properties, the location of the plasmaspheric edge dramatically
influences the acceleration and loss processes of the ring current and radiation belts. Furthermore, it has
been shown that strong field-aligned currents closing the partial ring current near the plasmasphere boundary can lead to the formation of SAPS, which have significant impacts throughout the system, including
disturbances that propagate in the thermosphere down to equatorial latitudes. Finally, “slippage” between
the intrinsic field of the rotating Earth and the magnetosphere is of fundamental interest but still limited
basic understanding, perhaps with applications to concepts in coronal physics of interchange reconnection.
On the mass coupling side, it is known that ionospheric plasma is a vital component of the magnetosphere. Observations have shown that the ionosphere can be a dominant mass source for the energetic
ring current during magnetospheric storms. Theoretical results indicate that this plasma will alter the wave
processes as well as the rates of magnetic reconnection. How this plays out in the macroscopic evolution
of the system, and whether it helps determine the global mode of magnetospheric behavior, are not fully
understood.
Understanding the dynamic behavior of the coupled system is central to completing decadal survey
key science goal 2 and undergirds the ability to make quantitative predictions about the space environment, making this goal also relevant to decadal survey key science goal 1. Furthermore, understanding
system-level dynamics will help advance knowledge of the fundamental processes that couple the regions
of geospace, providing a connection to decadal survey key science goal 4 as well.
9.4.4 Comparative Magnetospheres
Fifty years of robotic exploration of the solar system have led to flybys of all the major planets and
orbital insertion around all but Uranus and Neptune. 6 Researchers have found intrinsic magnetospheres
at Mercury, Jupiter, Saturn, Uranus, Neptune, and Ganymede; induced magnetospheres at Venus and
comets; and mini-intrinsic magnetospheres on Mars. Pathfinder magnetospheric observations have been
made for all of these planets, but comprehensive measurements have been made only at Jupiter and Saturn
and presently at Mercury by the MESSENGER mission. Even for Jupiter and Saturn, fundamental magnetospheric questions remain unanswered, including the degree of solar wind influence on the structure and
dynamics. For the other planets, especially the outer ice giants, nothing is known about the dynamics
or variability. A comprehensive understanding of magnetospheric physics requires measurements from a
complete suite of magnetospheric instruments from satellites in orbit around other planets, ideally with
6 Pluto is no longer considered a major planet; a flyby of Pluto is anticipated in January 2015 by NASA’s New Horizons spacecraft.
Solar and Space Physics: A Science for a Technological Society
234
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
in the magnetosphere to the ionosphere can vary among models by more than 100 km, so ionospheric
signatures cannot be properly attributed to the associated magnetospheric regions and processes. Since
strong and variable currents significantly distort the magnetospheric magnetic field by different amounts
under different conditions, determining this mapping is a challenging but important problem.
There are numerous examples of how magnetosphere-ionosphere-thermosphere coupling plays out in
the system-level response, both through electrodynamics and through mass coupling.
On the electrodynamic side, the strength of the convective motion in the ionosphere saturates for high
levels of solar wind driving. The exact physical mechanisms for this saturation effect remain unclear, but
ionospheric conductance certainly plays a key role. As another example, the electrodynamic coupling
with the magnetosphere extends down into the thermosphere, where the ionospheric convection can drive
neutral-particle motions that in turn influence ionospheric drifts after the solar wind driving is reduced.
These plasma drifts then are communicated back into the magnetosphere, where they affect the shape
and evolution of the plasmasphere. Because the plasmasphere dominates the inner magnetospheric mass
content and therefore the plasma wave properties, the location of the plasmaspheric edge dramatically
influences the acceleration and loss processes of the ring current and radiation belts. Furthermore, it has
been shown that strong field-aligned currents closing the partial ring current near the plasmasphere boundary can lead to the formation of SAPS, which have significant impacts throughout the system, including
disturbances that propagate in the thermosphere down to equatorial latitudes. Finally, “slippage” between
the intrinsic field of the rotating Earth and the magnetosphere is of fundamental interest but still limited
basic understanding, perhaps with applications to concepts in coronal physics of interchange reconnection.
On the mass coupling side, it is known that ionospheric plasma is a vital component of the magnetosphere. Observations have shown that the ionosphere can be a dominant mass source for the energetic
ring current during magnetospheric storms. Theoretical results indicate that this plasma will alter the wave
processes as well as the rates of magnetic reconnection. How this plays out in the macroscopic evolution
of the system, and whether it helps determine the global mode of magnetospheric behavior, are not fully
understood.
Understanding the dynamic behavior of the coupled system is central to completing decadal survey
key science goal 2 and undergirds the ability to make quantitative predictions about the space environment, making this goal also relevant to decadal survey key science goal 1. Furthermore, understanding
system-level dynamics will help advance knowledge of the fundamental processes that couple the regions
of geospace, providing a connection to decadal survey key science goal 4 as well.
9.4.4 Comparative Magnetospheres
Fifty years of robotic exploration of the solar system have led to flybys of all the major planets and
orbital insertion around all but Uranus and Neptune. 6 Researchers have found intrinsic magnetospheres
at Mercury, Jupiter, Saturn, Uranus, Neptune, and Ganymede; induced magnetospheres at Venus and
comets; and mini-intrinsic magnetospheres on Mars. Pathfinder magnetospheric observations have been
made for all of these planets, but comprehensive measurements have been made only at Jupiter and Saturn
and presently at Mercury by the MESSENGER mission. Even for Jupiter and Saturn, fundamental magnetospheric questions remain unanswered, including the degree of solar wind influence on the structure and
dynamics. For the other planets, especially the outer ice giants, nothing is known about the dynamics
or variability. A comprehensive understanding of magnetospheric physics requires measurements from a
complete suite of magnetospheric instruments from satellites in orbit around other planets, ideally with
6 Pluto is no longer considered a major planet; a flyby of Pluto is anticipated in January 2015 by NASA’s New Horizons spacecraft.