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Solar and Space Physics: A Science for a Technological Society
SOLAR AND SPACE PHYSICS: RECENT DISCOVERIES, FUTURE FRONTIERS
51
a significant impact on Jupiter’s magnetosphere. Io-genic plasma is transported outward by flux-tube interchange processes on the dayside but by centrifugal instabilities and plasmoid ejection in the evening and
at night. Intense bursts of energetic particles are accelerated in regions ~200 Jupiter radii down the tail on
the dusk flank. These discoveries demonstrate the great range of physical processes that the Jovian system
exhibits, presenting an enormous opportunity for advancing understanding of magnetospheric dynamics.
A major highlight of the decade came from the extensive measurements of Saturn’s highly structured
magnetosphere and satellite system by the Cassini spacecraft. Plumes of water gas and ice crystals emanate from rifts in the south polar region of Enceladus (Figure 2.7). Flux tube interchange in the middle
magnetosphere followed by plasmoid release in the magnetotail was revealed as the primary transport
mechanism for cold Enceladus plasma.
Solar wind pressure variations strongly modulate the activity in the outer magnetosphere, including
Saturnian kilometric radio emission and the acceleration of energetic particles in Saturn’s ring current. These
results remain a challenge to explain and demonstrate the critical role the study of these other systems has
in advancing magnetospheric physics.
Atmosphere-Ionosphere-Magnetosphere Interactions
A broad range of national, international, and multiagency programs facilitated major advances in
the science of Earth’s ionosphere and thermosphere and their interactions with the magnetosphere and
the lower atmosphere. A major surprise is that the ionosphere-thermosphere system exhibits unexpected
structuring during solar-quiet conditions. New Global Positioning System (GPS)-based assets from ground
and space led to fundamental discoveries of dynamics of the global ionospheric density. Reactive feedback
processes of thermospheric upwelling and intense ionospheric ion outflows were demonstrated to occur
in new ways and were shown to have profound consequences for magnetospheric dynamics. The stormtime response of the system is now better characterized than ever before, and key gaps in understanding
of the linkages between drivers and responses have been identified. Finally, tropospheric forcing from
below was discovered to play a surprisingly strong role in the dynamics and structure of the ionosphere
and thermosphere.
It is worth noting here the importance of international and cross-agency support that has made these
scientific discoveries possible. For example, the COSMIC mission—a six-satellite joint U.S.-Taiwanese mission to improve understanding of both weather and space weather—carries instruments developed by JPL
and the Naval Research Laboratory and was launched by the U.S. Air Force (USAF), and the data it collects
are downloaded at NOAA and NASA facilities and processed at the NSF-supported National Center for
Atmospheric Research (NCAR). The C/NOFS mission is another more recent example of scientifically productive cooperation between the USAF and NASA. Perhaps not surprisingly, several scientific discoveries
involve physical processes that extend across the regions of interest of these agencies, and across nations.
Active Ionosphere During Solar Minimum
Gradual changes in solar activity, solar wind, solar EUV radiation, and Earth’s magnetic field play a
significant role in defining the long-term variation in the geospace environment. The most recent solar
minimum produced a prolonged period of low solar EUV fluxes and corresponding heating rates. At the
same time, the thermospheric densities dropped to anomalously low levels, lower than any observed in the
past four solar cycles. No numerical model has yet been able to predict or reproduce the density observations, which are thought to have resulted from some combination of low solar and geomagnetic activity,
cooling from increasing greenhouse gas concentrations, and possibly additional chemical or dynamical
Solar and Space Physics: A Science for a Technological Society
SOLAR AND SPACE PHYSICS: RECENT DISCOVERIES, FUTURE FRONTIERS
51
a significant impact on Jupiter’s magnetosphere. Io-genic plasma is transported outward by flux-tube interchange processes on the dayside but by centrifugal instabilities and plasmoid ejection in the evening and
at night. Intense bursts of energetic particles are accelerated in regions ~200 Jupiter radii down the tail on
the dusk flank. These discoveries demonstrate the great range of physical processes that the Jovian system
exhibits, presenting an enormous opportunity for advancing understanding of magnetospheric dynamics.
A major highlight of the decade came from the extensive measurements of Saturn’s highly structured
magnetosphere and satellite system by the Cassini spacecraft. Plumes of water gas and ice crystals emanate from rifts in the south polar region of Enceladus (Figure 2.7). Flux tube interchange in the middle
magnetosphere followed by plasmoid release in the magnetotail was revealed as the primary transport
mechanism for cold Enceladus plasma.
Solar wind pressure variations strongly modulate the activity in the outer magnetosphere, including
Saturnian kilometric radio emission and the acceleration of energetic particles in Saturn’s ring current. These
results remain a challenge to explain and demonstrate the critical role the study of these other systems has
in advancing magnetospheric physics.
Atmosphere-Ionosphere-Magnetosphere Interactions
A broad range of national, international, and multiagency programs facilitated major advances in
the science of Earth’s ionosphere and thermosphere and their interactions with the magnetosphere and
the lower atmosphere. A major surprise is that the ionosphere-thermosphere system exhibits unexpected
structuring during solar-quiet conditions. New Global Positioning System (GPS)-based assets from ground
and space led to fundamental discoveries of dynamics of the global ionospheric density. Reactive feedback
processes of thermospheric upwelling and intense ionospheric ion outflows were demonstrated to occur
in new ways and were shown to have profound consequences for magnetospheric dynamics. The stormtime response of the system is now better characterized than ever before, and key gaps in understanding
of the linkages between drivers and responses have been identified. Finally, tropospheric forcing from
below was discovered to play a surprisingly strong role in the dynamics and structure of the ionosphere
and thermosphere.
It is worth noting here the importance of international and cross-agency support that has made these
scientific discoveries possible. For example, the COSMIC mission—a six-satellite joint U.S.-Taiwanese mission to improve understanding of both weather and space weather—carries instruments developed by JPL
and the Naval Research Laboratory and was launched by the U.S. Air Force (USAF), and the data it collects
are downloaded at NOAA and NASA facilities and processed at the NSF-supported National Center for
Atmospheric Research (NCAR). The C/NOFS mission is another more recent example of scientifically productive cooperation between the USAF and NASA. Perhaps not surprisingly, several scientific discoveries
involve physical processes that extend across the regions of interest of these agencies, and across nations.
Active Ionosphere During Solar Minimum
Gradual changes in solar activity, solar wind, solar EUV radiation, and Earth’s magnetic field play a
significant role in defining the long-term variation in the geospace environment. The most recent solar
minimum produced a prolonged period of low solar EUV fluxes and corresponding heating rates. At the
same time, the thermospheric densities dropped to anomalously low levels, lower than any observed in the
past four solar cycles. No numerical model has yet been able to predict or reproduce the density observations, which are thought to have resulted from some combination of low solar and geomagnetic activity,
cooling from increasing greenhouse gas concentrations, and possibly additional chemical or dynamical