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Solar and Space Physics: A Science for a Technological Society
RECOMMENDATIONS
107
3. How is solar wind energy partitioned into dynamical and chemical effects in the IT system, and
what temporal and spatial scales of interaction determine this partitioning?
4. How are these effects modified by the dynamical and energetic variability of the ionosphere-upper
atmosphere introduced by atmospheric wave forcing from below?
The observational problem is such that global dynamics cannot be captured by any number of probes
on a single satellite. When averaged over a sufficiently long period of time, data from a single satellite
provide a useful climatology as a function of latitude and longitude. However, such data are static and
do not show the physical coupling inherent in the continuously evolving density and velocity patterns
(dynamics) as they respond at all local times to the many drivers of the AIM system.
For example, electromagnetic flux and energetic particle precipitation are highly structured and
variable in latitude and local time. The dynamical response includes hydrodynamic atmospheric waves
propagating from high to low latitudes, but differently during day and night due to the large difference in
neutral-ion drag. During major storms, the large-scale upper atmospheric wind patterns are greatly disturbed
and constantly altered by the penetrating and dynamo electric fields that exhibit strong local time variations. Further, the chemical mixing of the upper atmosphere by auroral heating expands to low latitudes
and depletes the ionospheric plasma, reducing an important source of fuel for a geomagnetic storm, but
again in a highly local-time-dependent manner. These phenomena exemplify why a new approach must
be taken to advance understanding of the AIM system and how Earth’s upper atmosphere and ionosphere
regulate the response of geospace to significant solar wind energy inputs.
GDC would be a constellation of identical satellites in low Earth orbit providing simultaneous, global
observations of the AIM system over roughly the range of local times over which magnetospheric drivers
(and thus AIM responses) are organized. The satellites would have high-inclination circular orbits in the
300- to 450-km altitude range. Table 8.1 in Chapter 8 summarizes the science objectives, science merit,
and space weather relevance of GDC and how it relates to the overall decadal survey strategy.
GDC Mission Concept
The nominal plan for GDC is to have six identical satellites that will be spread individually into equally
spaced orbital planes separated by 30° longitude, thus providing measurements at 12 local times, with a
resolution of 2 hours local time, as shown in Figure 4.10. The satellites will nominally have an inclination of 80°, in order to use precession to help separate the local time planes, while maintaining adequate
coverage of the high-latitude region.
GDC Contributions to the HSO
GDC will make measurements critical to understanding how the IT system regulates the response of
geospace to external forcing (Table 4.6). The constellation of satellites will provide a complete picture of
the dynamic exchange of energy and momentum that occurs between ionized and neutral gases at high
latitudes, providing the HSO a critical capability for measuring the response and electrodynamic feedback
of Earth’s IT system to drivers originating in the solar wind and magnetosphere. GDC will also determine
the global response of the IT system to magnetic activity and storms and expose how changes in the system
at different locations are related. Finally, it will determine the influence of forcing from below on the IT
system, by measuring the global variability of thermospheric waves and tides on a day-to-day basis with
the spatial resolution that only a constellation of satellites can provide.
Solar and Space Physics: A Science for a Technological Society
RECOMMENDATIONS
107
3. How is solar wind energy partitioned into dynamical and chemical effects in the IT system, and
what temporal and spatial scales of interaction determine this partitioning?
4. How are these effects modified by the dynamical and energetic variability of the ionosphere-upper
atmosphere introduced by atmospheric wave forcing from below?
The observational problem is such that global dynamics cannot be captured by any number of probes
on a single satellite. When averaged over a sufficiently long period of time, data from a single satellite
provide a useful climatology as a function of latitude and longitude. However, such data are static and
do not show the physical coupling inherent in the continuously evolving density and velocity patterns
(dynamics) as they respond at all local times to the many drivers of the AIM system.
For example, electromagnetic flux and energetic particle precipitation are highly structured and
variable in latitude and local time. The dynamical response includes hydrodynamic atmospheric waves
propagating from high to low latitudes, but differently during day and night due to the large difference in
neutral-ion drag. During major storms, the large-scale upper atmospheric wind patterns are greatly disturbed
and constantly altered by the penetrating and dynamo electric fields that exhibit strong local time variations. Further, the chemical mixing of the upper atmosphere by auroral heating expands to low latitudes
and depletes the ionospheric plasma, reducing an important source of fuel for a geomagnetic storm, but
again in a highly local-time-dependent manner. These phenomena exemplify why a new approach must
be taken to advance understanding of the AIM system and how Earth’s upper atmosphere and ionosphere
regulate the response of geospace to significant solar wind energy inputs.
GDC would be a constellation of identical satellites in low Earth orbit providing simultaneous, global
observations of the AIM system over roughly the range of local times over which magnetospheric drivers
(and thus AIM responses) are organized. The satellites would have high-inclination circular orbits in the
300- to 450-km altitude range. Table 8.1 in Chapter 8 summarizes the science objectives, science merit,
and space weather relevance of GDC and how it relates to the overall decadal survey strategy.
GDC Mission Concept
The nominal plan for GDC is to have six identical satellites that will be spread individually into equally
spaced orbital planes separated by 30° longitude, thus providing measurements at 12 local times, with a
resolution of 2 hours local time, as shown in Figure 4.10. The satellites will nominally have an inclination of 80°, in order to use precession to help separate the local time planes, while maintaining adequate
coverage of the high-latitude region.
GDC Contributions to the HSO
GDC will make measurements critical to understanding how the IT system regulates the response of
geospace to external forcing (Table 4.6). The constellation of satellites will provide a complete picture of
the dynamic exchange of energy and momentum that occurs between ionized and neutral gases at high
latitudes, providing the HSO a critical capability for measuring the response and electrodynamic feedback
of Earth’s IT system to drivers originating in the solar wind and magnetosphere. GDC will also determine
the global response of the IT system to magnetic activity and storms and expose how changes in the system
at different locations are related. Finally, it will determine the influence of forcing from below on the IT
system, by measuring the global variability of thermospheric waves and tides on a day-to-day basis with
the spatial resolution that only a constellation of satellites can provide.