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Solar and Space Physics: A Science for a Technological Society
50
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
chaotic dynamics, or “emergent” behavior, that could never have been predicted without knowledge of
the coupling physics.
The electrodynamic coupling between the magnetosphere and ionosphere modifies the simple dissipative response in dramatic ways. The interaction of the ring current with the ionosphere severely distorts
inner magnetospheric convection, which feeds back on the ring current itself, skewing its peak toward
dawn. Duskside flow channels arising from ionospheric coupling remain long past periods of peak solar
wind driving. These studies shattered the notion that the inner magnetosphere is well shielded from the
outer magnetosphere and is quiescent.
It is now established that storm-time acceleration and injection of the ring current depend on pre-storm
loading of the magnetosphere from the solar wind. Spacecraft observations and numerical simulations
reveal that solar-wind plasma entry into the magnetosphere is surprisingly efficient under “quiescent” conditions of a 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. The plasmasphere in turn controls whether ring current injections act to
enhance or deplete energetic particle populations, overturning the decades-old idea of a passive, quiescent
plasmasphere. The overlap of freshly injected, hot, ring current plasma with the dense plasmasphere produces local instabilities. The resulting waves scatter radiation belt particles, depleting the radiation belts.
The predictions that cold dense plasma facilitates the acceleration of energetic electrons to relativistic
energies were also confirmed by observations. Thus, it has been established that pre-injection dynamics
are critical in establishing the state of the plasmasphere and governing the radiation belt storm response.
The ionosphere can also be a significant source of plasma for the magnetosphere over the past decade.
The understanding of ionospheric ion outflow advanced significantly, and the conditions promoting extraction of ionospheric plasma to high altitudes and into the magnetosphere were established. Solar wind density and dynamic pressure increases were shown to lead to enhanced ionospheric outflow, but the greatest
outflow rates were also closely correlated with the electromagnetic energy flux into the ionosphere. The
energy flux from the solar wind yields intense ionospheric ion outflows supporting the theoretical predictions that this outflow requires a multistep process involving a combination of local heating by waves and
electromagnetic forcing. It was also demonstrated that ionospheric outflow has dramatic consequences
for the dynamic evolution of the magnetosphere. Outflows merge with plasmas of solar wind origin in the
plasma sheet, creating a multi-species plasma that alters the dynamics of magnetic reconnection. Multifluid global simulations confirmed the major role that ionospheric outflow plays in the creation of periodic
substorms or so-called sawtooth intervals.
The discoveries of preconditioning interactions and of efficient pathways for magnetosphere-ionosphere coupling, and the identification of the dynamics that emerge, provide the basis for a program of
research to achieve a quantitative, predictive understanding of system behavior under extreme conditions.
Magnetospheres of Other Planets
The past decade saw many advances in understanding the structure, dynamics, and linkages in other
planetary magnetospheres or systems with magnetospheric-like aspects. For the terrestrial planets, they
range from insights on atmospheric loss at Mars and the identification of Venus lightning from high-altitude
radio wave measurements to observations of magnetospheric dynamics at Mercury that reflect dramatically
stronger solar wind-magnetosphere coupling than that at Earth. There have also been advances in theoretical understanding and observational tests of the impact of solar wind dynamic pressure variations on Jovian
auroral emissions, and significant progress in understanding magnetospheric interactions with Jupiter’s
satellites, especially Io. ENA imaging demonstrated that an extensive torus of neutral gas from Europa has
Solar and Space Physics: A Science for a Technological Society
50
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
chaotic dynamics, or “emergent” behavior, that could never have been predicted without knowledge of
the coupling physics.
The electrodynamic coupling between the magnetosphere and ionosphere modifies the simple dissipative response in dramatic ways. The interaction of the ring current with the ionosphere severely distorts
inner magnetospheric convection, which feeds back on the ring current itself, skewing its peak toward
dawn. Duskside flow channels arising from ionospheric coupling remain long past periods of peak solar
wind driving. These studies shattered the notion that the inner magnetosphere is well shielded from the
outer magnetosphere and is quiescent.
It is now established that storm-time acceleration and injection of the ring current depend on pre-storm
loading of the magnetosphere from the solar wind. Spacecraft observations and numerical simulations
reveal that solar-wind plasma entry into the magnetosphere is surprisingly efficient under “quiescent” conditions of a 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. The plasmasphere in turn controls whether ring current injections act to
enhance or deplete energetic particle populations, overturning the decades-old idea of a passive, quiescent
plasmasphere. The overlap of freshly injected, hot, ring current plasma with the dense plasmasphere produces local instabilities. The resulting waves scatter radiation belt particles, depleting the radiation belts.
The predictions that cold dense plasma facilitates the acceleration of energetic electrons to relativistic
energies were also confirmed by observations. Thus, it has been established that pre-injection dynamics
are critical in establishing the state of the plasmasphere and governing the radiation belt storm response.
The ionosphere can also be a significant source of plasma for the magnetosphere over the past decade.
The understanding of ionospheric ion outflow advanced significantly, and the conditions promoting extraction of ionospheric plasma to high altitudes and into the magnetosphere were established. Solar wind density and dynamic pressure increases were shown to lead to enhanced ionospheric outflow, but the greatest
outflow rates were also closely correlated with the electromagnetic energy flux into the ionosphere. The
energy flux from the solar wind yields intense ionospheric ion outflows supporting the theoretical predictions that this outflow requires a multistep process involving a combination of local heating by waves and
electromagnetic forcing. It was also demonstrated that ionospheric outflow has dramatic consequences
for the dynamic evolution of the magnetosphere. Outflows merge with plasmas of solar wind origin in the
plasma sheet, creating a multi-species plasma that alters the dynamics of magnetic reconnection. Multifluid global simulations confirmed the major role that ionospheric outflow plays in the creation of periodic
substorms or so-called sawtooth intervals.
The discoveries of preconditioning interactions and of efficient pathways for magnetosphere-ionosphere coupling, and the identification of the dynamics that emerge, provide the basis for a program of
research to achieve a quantitative, predictive understanding of system behavior under extreme conditions.
Magnetospheres of Other Planets
The past decade saw many advances in understanding the structure, dynamics, and linkages in other
planetary magnetospheres or systems with magnetospheric-like aspects. For the terrestrial planets, they
range from insights on atmospheric loss at Mars and the identification of Venus lightning from high-altitude
radio wave measurements to observations of magnetospheric dynamics at Mercury that reflect dramatically
stronger solar wind-magnetosphere coupling than that at Earth. There have also been advances in theoretical understanding and observational tests of the impact of solar wind dynamic pressure variations on Jovian
auroral emissions, and significant progress in understanding magnetospheric interactions with Jupiter’s
satellites, especially Io. ENA imaging demonstrated that an extensive torus of neutral gas from Europa has