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Appendixes
The appendixes that follow are reports or excerpts of reports
that resulted from workshops conducted by NASA In support of
the present study. These efforts are an important part of the study
and are included here in order to make the task group report
complete.
The four workshops were conducted by different organiza-
tions and in different manners. Thus, the resulting reports are
very different in character. What follows are four documents that
represent, at least, the essential features of these reports:
A. Workshop on Unaging of the Earth's Magnetosphere.
This workshop was convened by the task group at the NAS Woods
Hole study center during the task group meeting of July 1985.
Appendix A represents the complete report.
B. Jupiter Polar Orbiter Workshop. Appendix B is a sum-
mary of the report of the workshop held at UCLA in July 1985.
C. Workshop on Plasma Physics Research on the Space Sta-
tion. Appendix C is taken from a review paper describing the
results of the workshop held in May 1985 in Alabama.
D. High-Resolution Observations of the Sun. Appendix D
represents the complete report of the workshop held at the Na-
tional Solar Observatory in Tucson, Arizona, in January 1986.
57
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Appendix A
Workshop on Imaging of the Earth's
Magnetosphere
WORKSHOP PARTICIPANTS
Lyle Broadfoot, University of Arizona
Andrew Cheng, Johns Hopkins University/Applied Physics
Laboratory
Paul Feldman, Johns Hopkins University
David Gorney, Aerospace Corporation
Warren Moos, Johns Hopkins University
Edward Roelof, Johns Hopkins University
Donald Shemansky, University of Arizona
Donald Williams, Johns Hopkins University/Applied Physics
I.aboratory
so
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60
CONTENTS
A.1 ~troducUon, 61
AN Imaging of the Aurora Oval: Present Status and
Future Needs, 64
A.3 Prospects far Extreme Ultraviolet Dogleg ~ Plums in
the ~agnetospbere, 66
A.4 Prospects far Neutral Particle Imaging of Planetary
~agnetospberes, 72
A.S Conclusions and Recommendatlons, 77
l
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61
A.1 INTRODUCTION
Our present knowledge about the structure of the Earth's
magnetosphere has been formed over the years largely on the bash
of local measurements from spacecraft that move along trajectories
that are molated in space and time. However, even these limited
observations show that the magnetosphere is essentially a dynamic
system with large configuration changes driven both by direct
variations in the solar wind and by more indirect processes that
trigger large-ecale instabilities associated with substorms.
Because of their enormous sizes and because there are large-
scale variations in both space and time, planetary magnetospheres
pose major challenges to scientists attempting to understand global
behavior an understanding that ~ necessary in a program aimed
at developing quantitative predictive models of these systems.
Since single-po~nt observations from an molated satellite within
the magnetosphere are obviously inadequate for this task, the ini-
tial response to the challenge of studying global behavior has
been to conduct sunultaneous multmatellite observations within
the magnetospheric system. For example, the International Mag-
netospheric Study (IMS) program was based on use of the ESA
GEOS satellites in geostationary orbits, the NASA ISE~3 space-
craft at the sunward libration powt, ~d the NASA-ESA space-
craft ISE~1 and ISE~2 in the same elliptical orbit with apogee of
23 earth radii. This program was highly successful, and it provided
definitive information on the structure of various thin boundaries
and on localized plasma physics phenomena—a soccer due to the
small reparation between ISE~! and ISE~2 and due to their
coordinated observing schedules. However, the program was not
nearly as successful in its thrust toward studies of global dynamics.
This was due both to the lack of coordinated observing schedules
for the primary IMS spacecraft and to the fact that the satellite
trajectories were not chosen to optimize global studies.
Thus, even after the IMS, a number of different theories ex-
isted to explain global observations, but definitive choices could
not always be made on the basis of available data. One example ~
the controversy between boundary layer and reconnection modem
of substorm-related phenomena in the Earth's magnetotail. An-
other example is the question of whether energy is stored for long
periods in the magnetota~} and then released suddenly to cause a
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62
substorm, or whether a substorm is caused by a transient increase
in energy input from the solar wind.
Individual components of the magnetosphere such as the field-
aligned current systems near the Earth, the plasma sheet distri-
butions, and the high-energy radiation belts have been relatively
well measured separately but are poorly understood as interact-
ing parts of a whole. Fundamental controversies on the nature of
global dynamic phenomena such as substorms are a natural re-
sult. Indeed, significant advances have recently occurred in one of
the areas cited above aurora and field-aligned currents near the
Earth precisely because of the advent of global auroral imaging
in the ultraviolet with simultaneous charged particle and magnetic
field measurements on the Dynamic Explorer mission. Examples
of these very significant observations are shown in Figure A.1.
The International Solar-Terrestrial Physics (ISTP) program
represents a major new thrust in our attempt to understand global
magnetospheric dynamics. This program, specifically designed for
global studies, will place appropriately instrumented satellites in
key magnetospheric locations, and simultaneous auroral imaging
will be utilized to obtain data on the magnetospheric energy de-
position into the atmosphere. A strong theory, modeling, and
computer simulation effort has been incorporated into ISTP from
the beginning, thus assuring the development of global models to
be used with the ISTP data base. Finally, since ISTP has been
designed as a global studies program from the outset, the partic-
ipating space agencies (NASA, the European Space Agency, and
the Japanese Institute for Space and Astronautical Sciences) have
agreed on full coordination of observing schedules to maximize
simultaneous coverage from the ISTP spacecraft. They will also
establish a common central data base facility through which all
ISTP researchers will have access to all ISTP data.
A major result of the ISTP program will involve the develop
ment and initial qualitative testing of the first truly global mode!
of the Earth's magnetosphere. More accurate tests will certainly
be needed as the community attempts to move the modeling effort
into a quantitative predictive phase. Ordinarily this requires a
dense grid of observing platforms. However, for a system as vast
as the terrestrial magnetosphere, it would not be economically
feasible to provide a sufficiently dense grid using local spacecraft
observations alone. A new and innovative approach is required,
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hL
- ~ -
FIGURE A.1 Ultraviolet auroral images from Dynamics Explorer.
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64
and recent measurements suggest that this approach should in-
volve development of an imaging capability for the magnetosphere
as a whole.
This report summarizes the topics discussed at the Workshop
on Imaging of the Earth's Magnetosphere, which was held at the
NAS Study Center in Woods Hole, Massachusetts, on July 30 and
31, 1985, under the auspices of the Solar and Space Physics Task
Group of the Space Science Board's study: Space Science in the
Twenty-First Century.
In the next section is a brief description of the science return
from the present programs involving topside imaging of the auroral
oval at atmospheric altitudes and expectations for improvement.
The third section contains a discussion of the prospects for ex-
treme ultraviolet imaging of the relatively dense and coo! plasma
of the plasmsphere, magnetopause, bow shock, and storm-time
plasma sheet. The use of energetic neutral (generated by charge
exchange) for imaging of high-temperature plasma regions (e.g.,
the ring current and outer radiation belt) is discussed in the fourth
section, and the conclusions and recommendations are contained
in the final section.
A.2 IMAGING OF THE AURORAL OVAL: PRESENT
STATUS AND FUTURE NEEDS
Auroral zone observations of visible, ultraviolet, and x-ray
emissions generated by the precipitation into the atmosphere of
energetic particles streaming downward along the geomagnetic
field have provided extremely important means for remote sensing
of dynamical phenomena that develop In the magnetosphere. The
auroral region has been compared to a television screen that allows
us to view the end effects of very remote magnetospheric processes.
For years we looked upward toward the aurora from the ground
and we were able to observe parts of the auroral displays, but the
ground-based observations were limited" in space and they were
also restricted to the visible part of the spectrum.
Early results from the low-altitude polar-orbiting Defense Me-
teorological Satellite Program (DMSP) provided a large data base
of broadband visible auroral imagery. from this data set much
was learned about the large- and small-scale morphology of the
aurora, the response to changing conditions in the solar wind,
and the occurrence of brief but energetic substorms. These early
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65
photographs from space were also very significant because they
provided a medium to tie together other satellite and ground-
based observations of the particles and fields responsible for and
resulting from the aurora. A major drawback of these early oh
servations was their scarcity the DMSP orbits provide auroral
images with temporal separations of 90 min.
The recent Dynamics Explorer (DE) satellite remedied this
problem by imaging the aurora continuously from a high-altitude
elliptical orbit. Figure A.l shows a set of examples from DE, taken
consecutively at ultraviolet wavelengths. Auroral unages of this
type are also available with somewhat diminished quality under
sunlight illumination (as demonstrated by observations from the
low-altitude HILAT spacecraft). We now have continuous global
images from the auroral region, and they have yielded extremely
significant new information on auroral forms and morphology.
Scientifically, auroral imagery could provide even greater quan-
titative information if sunultaneous multispectral Nonages were
available. Such mult~pectral techniques are now being developed
to derive quantitatively the characteristics of the perturbations of
the neutral and ionized atmosphere due to the aurora.
X-ray imaging of the aurora from space also offers promise
for quantitative remote sensing of low-altitude processes since the
x-ray emissions (bremsstrahIung) occur directly as a result of ener-
getic auroral electrons colliding with atmospheric constituents. A
number of successful imaging x-ray instruments have been flown in
low-altitude polar orbit. Although the low-altitude observations
have provided an opportunity to test the analysis techniques and
instrumentation, they have not provided an adequate combination
of spatial resolution, energy resolution, and aperture to perform
true quantitative global imaging of the aurora.
The full potential of x-ray imaging demands instrumentation
based at high altitude in order to view the entire polar region. The
system must also be capable of providing adequate measurements
of x-ray spectra on reasonable time scales and Figure A.2 shows
the integration time needed to produce a quantitative x-ray image
as a function of altitude and spatial resolution within the aurora;
here an aperture of 100 cm2 Is assumed.
The ISTP polar spacecraft will carry multispectral auroral
imagers that will cover visible, ultraviolet, and x-ray wavelengths,
and the payload will also include advanced instrumentation for
measurements of local plasma physics phenomena.
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66
DMSP,
NOAA,
SHUTTLE TIROS
1000
A
-
O 100
-
o
Oh
LL
A:
~ 10
oh
1
GEOSYNCHRONOUS LUNAR
MOLNIYA ORBIT
,c,G /~
oils
-
'//?
1 00 1 000
10K
ALTITUDE (km)
100K 1M
FIGURE A.2 Temporal and spatial resolution as a function of distance
from source to x-ray detector. Required integration time A = lOO cm2.
A.3 PROSPECTS FOR EXTREME ULTRAVIOLET
IMAGING OF PLASMA IN THE
MAGNETOSPHERE
Plasma temperatures above about 40,000°K generally pro-
duce ions with resonance transitions into the EUV region of the
spectrum. In this temperature regime, energy lost by racliative
processes is then dominantly in the EUV, and study of emissions
at the short wavelengths can yield accurate diagnostic Formation
about the plasma. An example of EUV plasma imaging involves
the data provided by the Voyager spectrograph as it detected the
plasma torus of Jupiter's moon, To. Successive sweeping of the
field of view of this one-dimensional imaging system has yielded
the three-dimensional image of the jovian system shown in Figure
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67
INTERSTELLAR
WIND H Ly ~
so
~ on
INTERSTELLAR
WIND He 5" A
AURORAL
H. BANDS
. .,
~~A ~ ,'
PLANETARY
H Low
>a lV- rev
..rA\J~
~,f,f~ (A
-C~05
FIGURE A.3 Spatially and spectrally resolved image of Jupiter and the lo
plasma torus obtained by the Voyager EUV spectrometer.
A.3. These observations have provided many pictorial views of
the integrated emission from the plasma torus. The measurement
of the characteristics of the EUV source (size, shape, spectral in-
tensity, etc.) allows the identification of the ion species, and the
deterniination of the number density and electron temperature
distributions.
On the basis of these points of reference we can make a reason-
able deterniination of our ability to image the terrestrial magneto-
sphere with EUV radiation. It is currently technically feasible to
measure emission brightness at the level of 0.01 Rayleigh, within
a reasonable tune frame of about 100 s. On this basis an im-
age of Earth's magnetosphere in the resonance fluorescence of the
He+ 304 ~ line, for example, would provide an isophote map to
a distance of 10 Re geocentric. Arguments at a sunilar level can
be made for the detection of other species in emissions produced
by collisions and by fluorescence. The workshop participants con-
clude that the mapping of the plasmasphere and magnetosphere
in EUV emission is an obtainable goal.
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68
Plasmaspheric and Magnetospheric Boundaries
The dominant ion in the plasmasphere capable of producing
EUV emission is He+. As noted above, the principal emission
feature of this species is at 304 A, and this is produced primarily
by resonance fluorescence of the solar line. Knowledge of the solar
differential flux distribution and the spectral shape of the scattered
radiation allows diagnostics of bulk motion of the plasma as well as
plasma temperatures. The image of the terrestrial plasmasphere
obtained by a photometer coupled to an array detector is illus-
trated in Figure A.4; these profiles have been calculated using a
specific mode! of the He+ distribution derived from Dynamics Ex-
plorer observations, as shown in Figure A.5. The ability to measure
EUV emission at the level of 0.01 Rayleigh in an imaging system
is entirely possible In the near future. Recent AMPT~CCE ob-
servations of Hey suggest that the magnetopause boundary could
also be imaged. Moreover, it ~ known that the distant plasma
sheet is populated by Hey (and O+) during storms, and hence
imaging of dynamical tail phenomena during substorms should
also be possible.
Other less extensive species having lower abundances, such as
0, 0+, N. and N+, could be observed with an imaging spectrome-
ter and would provide measurement of the nature of the interface
between the magnetosphere and the ionosphere. In general, these
species are excited by both plasma electrons and fluorescence of
solar lines. Spectral analysis of the emissions from these species
are diagnostic of basic plasma properties; composition, density,
and temperature of both ions and electrons.
The analysis technique has been used in astrophysics for many
years (for instance, in the study of gaseous nebula), and it is
equally suited to the study of the plasma environments of Venus,
the outer planets, and comets, provided that suitable atom and
molecular transitions are chosen for each particular system. A col-
umn abundance of 10~°/cm2 of Oll ions interacting with electrons
having typical auroral energies could be detected by present-day
instrument design with a 100~8 integration time, for example.
Given somewhat larger integration times, processes at the bow
shock and magnetosheath should be observable. Bulk motions in
the magnetotai} may be traced through successive measurements
of structural features and through high-resolution spectral line
shape measurements.
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69
/ 0.~- -in :~N
0;1 0 \ 1 ¢~40~_~ ~ >
\
FIGURE A.4 He+ 304 ~ isophote~ for distribution model 1 (see Figure
A.5), as seen from two views: (top) a point on the Earth-Sun line in the
plane of the magnetic equator, and (bottom) a point on the noon meridian
at a magnetic latitude of 35°.
These global observations of the magnetosphere must clearly
be linked to direct parallel measurements of solar activity, and
followed through a time scale of one or more major solar cycles.
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70
3.0
+
1: 2 . 0
Cal
o
1.0
0.0
_
.'''''
"am\ ~
~ ~ Model ~
~ a.
\Model I
. . . . . . .
1 2 3 4 5 6 7 8 9
L SHELL
FIGURE A.5 Model He+ distributions derived from Dynamics Explorer
observations.
Locations for Observing Stations
Earth's magnetosphere can be unaged from a range that allows
the whole system to be continuously ~ the field of view of the
imager. This can be done from the I.1 I,agr~gian point, as a
control monitor, with spacecraft at the L4 and L5 Lagrangian
points or an instrument on a lunar base to provide stereoscopic
capability.
The Moon and the L4 and L5 points have many good features
as sites for these measurements. The L4 and L5 points are at lunar
distance, preceding and following the Moon at 60° to the Earth-
Moon line. The 120° aspect angle is almost ideal for stereoscopic
studies of discrete plasma motions of detached plasmas. The lunar
orbital rate is slow enough to aDow correlated studies over several
days. The time scale is also about right for the study of typical
solar-magnetospheric interactions. The changing aspect of the
lunar orbit is important for viewing interface regions such as the
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71
magnetopause and bow shock surfaces. These interfaces need to be
investigated with long optical paths that occur when the viewing
direction is nearly tangent to the surface. For instance, the bow
shock should be viewed tangentially over an arc-shaped region of
the sky. The tangent line progresses so as to result in a comnIete
survey of the complete bow shock in each lunar period.
Simultaneous imaging of the magnetospheric system from the
L1 point is also required. This ~ an important viewing station
because whereas L4, L5, and the Moon orbit the Earth, the L1 view
is stable and stationary with respect to the Sun's direction. The
solar wind can also be measured continuously from the L1 station,
allowing detailed study of the effect of solar wind variability on the
magnetospheric system. From here one could also study changes
in the solar flux spectrum and intensity; this information is of
importance for atmospheric analysis, and it is also needed for
the complete interpretation of the resonance emissions from the
magnetospheric plasma.
~ .
[id"
Lasers can be used to excite emissions from the constituents
of the ionospheric and magnetospheric plasma, as well as the at-
mosphere. This lidar technique involves the excitation of ions and
atoms by a light source with highly controlled characteristics, and
this, in turn, leads to precise Formation on species concentra-
tion, location, and velocities. NASA ~ developing such a lidar
system for remote sensing of the rniddIe atmosphere from the
Space Shuttle and Space Station, with planned operations in the
1990~. Although the densities of magnetospheric particles are very
low in comparison with atmospheric densities, the path lengths are
long, and therefore acceptable signals may be generated. The ma-
jor obstacle to applying this technique to magnetospheric remote
sensing is the lack of a laser with reasonable efficiencies to oper-
ate at ultraviolet wavelengths. However, DOD requirements could
lead to development of an ultraviolet laser, and NASA should
be prepared to take advantage of such advances and utilize laser
technology for remote mapping of the magnetospheric plasma.
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72
A.4 PROSPECTS FOR NEUTRAL PARTICLE DIALING
OF PLANETARY MAGNETOSPHERES
Background
A new window into magnetospheric physics has been opened
with the detection of energetic neutral particles (50 keV) emanat-
ing from the magnetospheres of Earth, Jupiter, and Saturn. These
measurements directly point the way toward an innovative class
of instruments devoted to global imaging of magnetospheric neu-
tral particle emissions. Energetic neutrals are created within the
magnetosphere by charge exchange reactions between fast magne-
tospheric ions and ambient neutral atoms or molecules (see Figure
Am. Since the resulting fast neutrals escape from the magneto-
sphere on rectilinear trajectories, they can be used to image the
neutral-particle-emitting regions of the magnetosphere. The re-
sulting images provide the only known means for remote sensing
on a global scale of the magnetospheric energetic charged particle
populations.
In this way energetic neutral images are complementary to ul-
traviolet and optical images of the magnetosphere, which remotely
sense only the low-energy (~5 keV) charged particle populations.
Unlike conventional spacecraft observations of charged particles
that are essentially single-point measurements that sample only
very small regions at any time, energetic neutral particles can im-
age the entire complex magnetospheric system at a single instant.
Charged particle measurements sample only a region comparable
to the mean free path if scattering occurs; otherwise they sample
only a flux tube of radius comparable to the gyroradius. Both
length scales are much smaller than global length scales. Some
very low frequency plasma waves are observed after propagation
from global distances, but these are of such long wavelength that
little or no directional information can be obtained.
Expected Results
Global imaging of neutral particle emissions from Earth's mag-
netosphere will yield a completely new global view of dynamic
processes such as changes in plasma sheet configuration, growth
and decay of the ring current, and auroral zone charged parti-
cle precipitation. Imaging studies of the interrelationships among
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73
IMAGING NEUTRAL PARTICLE DETECTOR
ATOM ~
~ CHARGE EXCHANGE
(7=
r ION
FIGURE A.6 Energetic neutral particle imaging of the fast ion and ambient
neutral population. An energetic trapped ion captures an electron from an
ambient neutral in a charge exchange reaction, becoming an energetic neutral
atom, which then escapes the magnetosphere to the detector along a direction
determined by the ion's velocity at the time of the reaction.
these processes on a global scale should resolve the long-standing
debates concerning the nature of geomagnetic substorms.
Coarse global images of Earth's ring current using neutral
particle emissions have already been obtained. Analysis of ISE~1
and IMP 7,8 data has revealed energetic neutral particle emissions
from charge exchanges between ring current ions and hydrogen
atoms of Earth's geocorona.
Figure A.7 is an example (constructed from an eigh~pixe!
ISE~1 image near the midnight meridian at 20 Re) of the energetic
neutral particle emission during the recovery phase of a magnetic
storm; the emission comes from the magnetic equatorial region
of the ring current (3 S ~ < 5), and it is strongly asymmetrical,
being concentrated in the dusk-m~dnight section.
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74
Sun
April 18, 1978
/
\
( 7th ) ~
O Spin 21
sector 6
Cad
Magnetic pole
{04 UT)
\
/
-
:: . -
.,\
:: ;
. . .\ ,., - wq I jam
FIGURE A.7 Energetic neutral particle emission pattern during the re-
covery of a geomagnetic storm ISEE-1 near the midnight meridian at 20
Re. Ranking of the pixel intensity (in lozenges marking the center of each
pixel) indicates the greatest intensity from the late evening quadrant of the
magnetic equatorial region (3 < L ~ 5~.
Figure A.8 shows how a high-resolution neutral imager could
provide much more information. The top pane} contains the "im-
age~ expected from an ideal energetic neutral atom detector lo-
cated at X—-8Re, Y = 0, Z = 5Re. For simplicity a dipole
magnetic field, a nearly isotropic equatorial pitch angle d~tribu-
tion with empty loss cone, and an azimuthally symmetric ring
current are assumed. The bottom pane! of Figure A.S then shows
the line-of-sight ion flux column density for the main phase ring
current distribution deduced from the measured neutral atom in-
tensity profile in the bottom panel.
Energetic neutral particles also contain specific information
on the composition of the magnetospheric energetic ions. For
example, from Table A.! the decay time and the energy spectrum
of the neutral particle emissions observed during the recovery
phase of a small magnetic storm are given; here it was deduced
that O+ was a significant component of the ring current. Thm
illustrates the strong need for composition resolution capability in
this new class of instruments.
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75
_CR~
-
_ ~~
1 ~
~ o
US ·—
._ ~
I
so
·m
o
·_
~ -
o
._
Co' ~
., ._
o A,
~ ._
o
3
o
Ce Cal b,O
Al ~
._ ~
L.
so oo
~ lo.
4.
L.
oo
Cot
P4
·=
— Cot
X d :^
1~ moo
._
go. ~ ~
~ ~ X
_ ~ ~
a
_I
Go ~
{i] at,'—
08
O ~
O
=_'
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76
TABLE A.1 Nominal Neutral Particle Intensities from Various Components of
Earth's Magnetosphere
E ~ 40 keV
Proton Hydrogen Energetic Neural Count Rate per
Intensity Column Density Intensity1 (cm ~ Pixel, Angular
(cm Her (cm ) so keV) Resolution
keV)~
Near-Earth 104 lolo 0.01 0.1/sec,-10°
Plasma Sheet
Quiet Time 2 x 104 5 x 1011 1a O.s/~,a -2O
Radiation Belh
Storm Time 3x 105 5 x 1011 1Sa 7.5/s,a -2O
Ring Current
aEnergetic neutral intensities and count rates up to an order of magnitude greater are
predicted if O dominates rather than protons.
The neutral particle intensity from charge exchanges in the
Earths magnetosphere is estimated from the integral along the line
of sight of the product of the ion intensity, the charge exchange
cross section, and the neutral density. Table A.! gives nominal
estimates of neutral particle intensities at E ~ 40 keV from the
near-Earth plasma sheet, the quiet time radiation belts, and the
storm time ring current. The first of these refers to an equatorial
line of sight near 10 Re through the plasma sheet. Both quiet
time radiation belt and storm time ring current refer to lines of
sight near ~—4. A 2~keV energy band is assumed, and a charge
exchange cross section equal to 10-~6 cmi2 (appropriate for 5~
keV protons incident on hydrogen) is used. The charge exchange
cross section and predicted neutral intensities are about 10 tunes
greater if O+ ions are assumed to dominate protons, since the
charge exchange crow section is 10-~5 cm2 for ~100 keV OF ions
near incident on hydrogen.
Nominal count rates per pixel are shown in Table A.~. These
rates apply to pixel whose fields of view are filled by the respec-
tive emitting regions. This new class of instruments will be able to
image the quiet tune radiation belts and the storm tune rug cur-
rent with high angular resolution (2°) and high time resolution (13
to 200 s). They also unage the near-Earth plasma sheet at lower
resolution. These studies will revolutionize our understanding of
global dynamic processes such as magnetic substorms, because we
will, for the first time, be able to see the entire magnetosphere in
one image. Energetic neutral particle imaging can revolutionize
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77
our understanding of planetary magnetospheres In general. The
Voyager spacecraft detected energetic charge exchange neutrals
from both Jupiter and Saturn, but the instruments could not pro-
duce images. At Jupiter, energetic neutral imaging fulfills a unique
role. It is the only known way of continuously sampling the very
intense charged particle population in the innermost region of
the Jovian radiation belts, where particle detectors are saturated
(and heavily damaged) by the penetrating radiation. We still do
not know if there are magnetic storms at Jupiter and Saturn (or
Uranus) similar to those at Earth. Global anages of their ener-
getic ion populations offer the means to answer this question and
perhaps to discover a new generalization of the concept of mag-
netic store=. Remote sensing, particularly from a high-~nclination
orbit, could be compared directly with earth-based optical and
ultraviolet torus images and radio observations of synchrotron
radiation.
A.5 CONCLUSIONS AND RECOMMENDATIONS
The exploration of the Earth's environment has been highly
incomplete in the sense that we have not yet developed the tech-
nology to determine the complete dependence of atmospheric and
magnetospheric dynamics on solar activity. Our understanding
of the behavior of the Sun's emissions over a solar cycle ~ rudi-
mentary, and our knowledge of the global response of the Earth's
magnetosphere on both a short- and a long-term basis ~ very
incomplete.
The workshop participants have investigated the future needs
of the discipline and conclude that the full ISTP program will
provide an excellent data base for the development of one or more
dynamic global models of the Earth's magnetosphere. They aLso
conclude that in the post-ISTP era, a new approach will be needed
to ensure that the correct mode} is adopted, and to verify its
accuracy.
The workshop discussions strongly suggest that the only prac-
tical post-ISTP approach to testing of global magnetospheric mod-
els Is one that utilizes techniques to provide global images of the
magnetosphere. Fortunately, the workshop deliberations also sug-
gest that this imaging concept ~ a realistic one. It was demon-
strafed (using Voyager data from Jupiter) that atomic lines are
excited by ambient electrons with sufficient intensity to provide
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78
images of coo} dense plasma boundaries. For Earth the Hey 304
~ line appears to be the best candidate for unaging the plasma-
sphere, the bow shock and magnetopause region, and (during
storm conditions) the plasma sheet in the geomagnetic tail; how-
ever, this is currently a theoretical concept, since a terrestrial He+
304 ~ imager has not been flown.
The more energetic plasmas (ring current, auroral region, and
so on) are best ~imaged" by searching for energetic neutral atoms
produced by charge exchange. The very low resolution results
already obtained with the ISE~1 energetic particle analyzer verify
the concept and show the power of this technique, but they also
point to the need for development of instruments with higher
resolution.
The workshop participants urge NASA to support the devel-
opment and testing of suitable sensitive high-resolution magneto-
spheric imaging instruments with the aim of establishing a full-
fledged magnetospheric imaging my - ion in the post-ISTP time
frame.
Representative terms from entire chapter:
energetic neutral
