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Solar and Space Physics: A Science for a Technological Society
46
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
unexpected dynamics associated with plasma convection, particle acceleration, and particle transport. Key
advances were made on the underlying fundamental physical processes that govern the nonlinear dynamics of the system, including reconnection, wave-particle interactions, and turbulence. Observations and
simulations of the dramatically different magnetospheres of Jupiter and Saturn provided key tests of current
understanding and highlight the great variety of behavior exhibited by different systems.
These advances were enabled by combining a wide array of observations in concert with theory, laboratory plasma experiments, and revolutionary computational models. Critical observations were returned
from instruments on suborbital rockets and balloons, and from an extensive ground-based network of
radars, lidars, imagers, magnetometers, and riometers. Instrumental to these advances were spacecraft
observations returned from new satellites launched during the decade or just before (e.g., Cluster, IMAGE,
THEMIS, TWINS) as well as data returned from earlier missions and data collected by instruments flown
on non-NASA satellites.
Global Dynamics
The global dynamics of the magnetosphere are controlled by the changing north-south component of
the interplanetary magnetic field (IMF), which drives global circulation in the magnetosphere, as shown
in Figure 2.4. Changes in the IMF and solar wind dynamic pressure produce storms, light up the aurora,
and drive a host of other global responses.
Global imaging of heretofore invisible plasma populations of the magnetosphere was used to identify
its large-scale response to this variable solar wind forcing. The plasmasphere, which is the region of cooldense plasma that co-rotates with Earth, was imaged in the extreme ultraviolet. Observations revealed
that strong storms strip off the outer part of the plasmasphere in plumes, which convect outward to the
dayside magnetopause (Figure 2.5) and map to produce ionospheric density enhancements of the type
shown in Figure 3.3.
The magnetospheric equatorial ring current is enhanced during geomagnetic storms, and it perturbs
the strength of the magnetic field at Earth’s surface. Understanding its dynamics is crucial for establishing a predictive capability of the response of geospace to storms. The injections of ring current ions were
imaged for the first time, establishing their configuration and composition. Numerical models and global
ENA imaging revealed that the ring current is highly asymmetric during the main phase of storms, which
suggests a strong coupling with the ionosphere. The peak of the ring-current proton distribution during
the main phase of magnetic storms was shown to occur consistently in the early morning and not in the
afternoon as had been expected. This can happen only if the ionosphere feedback fundamentally alters
the electric field that is responsible for magnetospheric convection.
Fundamental Physical Processes: Magnetic Reconnection and Wave-Particle Interactions
The understanding of fundamental physical processes that govern system-level dynamics advanced on
a number of fronts over the past decade. Substantial progress was made in understanding how magnetic
reconnection works. The first quantitative predictions of detailed magnetic and plasma flow signatures
were spectacularly confirmed with in situ observations. Similarly, sophisticated kinetic simulations finally
yielded a consistent understanding of signatures of the onset of magnetic reconnection in the tail.
Increased computing power has facilitated simulations of the essential physics and structure of the
diffusion region, where magnetic field lines 3 reconnect and change their connectivity (Figure 1.4). It was
3 Field lines are a convenient construct for understanding magnetic field connectivity and topology.
Solar and Space Physics: A Science for a Technological Society
46
SOLAR AND SPACE PHYSICS: A SCIENCE FOR A TECHNOLOGICAL SOCIETY
unexpected dynamics associated with plasma convection, particle acceleration, and particle transport. Key
advances were made on the underlying fundamental physical processes that govern the nonlinear dynamics of the system, including reconnection, wave-particle interactions, and turbulence. Observations and
simulations of the dramatically different magnetospheres of Jupiter and Saturn provided key tests of current
understanding and highlight the great variety of behavior exhibited by different systems.
These advances were enabled by combining a wide array of observations in concert with theory, laboratory plasma experiments, and revolutionary computational models. Critical observations were returned
from instruments on suborbital rockets and balloons, and from an extensive ground-based network of
radars, lidars, imagers, magnetometers, and riometers. Instrumental to these advances were spacecraft
observations returned from new satellites launched during the decade or just before (e.g., Cluster, IMAGE,
THEMIS, TWINS) as well as data returned from earlier missions and data collected by instruments flown
on non-NASA satellites.
Global Dynamics
The global dynamics of the magnetosphere are controlled by the changing north-south component of
the interplanetary magnetic field (IMF), which drives global circulation in the magnetosphere, as shown
in Figure 2.4. Changes in the IMF and solar wind dynamic pressure produce storms, light up the aurora,
and drive a host of other global responses.
Global imaging of heretofore invisible plasma populations of the magnetosphere was used to identify
its large-scale response to this variable solar wind forcing. The plasmasphere, which is the region of cooldense plasma that co-rotates with Earth, was imaged in the extreme ultraviolet. Observations revealed
that strong storms strip off the outer part of the plasmasphere in plumes, which convect outward to the
dayside magnetopause (Figure 2.5) and map to produce ionospheric density enhancements of the type
shown in Figure 3.3.
The magnetospheric equatorial ring current is enhanced during geomagnetic storms, and it perturbs
the strength of the magnetic field at Earth’s surface. Understanding its dynamics is crucial for establishing a predictive capability of the response of geospace to storms. The injections of ring current ions were
imaged for the first time, establishing their configuration and composition. Numerical models and global
ENA imaging revealed that the ring current is highly asymmetric during the main phase of storms, which
suggests a strong coupling with the ionosphere. The peak of the ring-current proton distribution during
the main phase of magnetic storms was shown to occur consistently in the early morning and not in the
afternoon as had been expected. This can happen only if the ionosphere feedback fundamentally alters
the electric field that is responsible for magnetospheric convection.
Fundamental Physical Processes: Magnetic Reconnection and Wave-Particle Interactions
The understanding of fundamental physical processes that govern system-level dynamics advanced on
a number of fronts over the past decade. Substantial progress was made in understanding how magnetic
reconnection works. The first quantitative predictions of detailed magnetic and plasma flow signatures
were spectacularly confirmed with in situ observations. Similarly, sophisticated kinetic simulations finally
yielded a consistent understanding of signatures of the onset of magnetic reconnection in the tail.
Increased computing power has facilitated simulations of the essential physics and structure of the
diffusion region, where magnetic field lines 3 reconnect and change their connectivity (Figure 1.4). It was
3 Field lines are a convenient construct for understanding magnetic field connectivity and topology.