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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
Assessment of Programs in Solar and Space Physics
1991
2
Status of Discipline
The assessment of the progress in meeting the objectives for the
discipline spelled out in the recent NRC reports is divided into two categories:
issues specific to each of the disciplines and issues common to all disciplines
concerned.
DISCIPLINE-SPECIFIC ISSUES
Solar Physics
The three major aspects involved in scientific studies of the Sun—the Sun
REPORT MENU
as a source of energy for the heliosphere, and in particular, for the Earth; the Sun
NOTICE
as a star; and the Sun as a laboratory for the study of basic physical
MEMBERSHIP
processes—are included in this assessment. The principal scientific goals of the
FOREWORD
solar physics program are as follows:
SUMMARY
CHAPTER 1
CHAPTER 2 Understanding the physical origin and effects of solar and stellar
CHAPTER 3
activity. Solar activity manifests itself in many forms, with time scales ranging
BIBLIOGRAPHY
from milliseconds to decades, and size scales from sub-arcsecond magnetic flux
ABBREVIATIONS AND
tubes to coronal streamers and mass ejections extending out to tens of solar
ACRONYMS
radii.
APPENDIX A
APPENDIX B
Using highly resolved observations of solar activity as a "laboratory" for
APPENDIX C
understanding widely applicable astrophysical and plasma processes.
Understanding the causes of variations in the radiative output of the
Sun. The active cavity radiometer irradiance monitor (ACRIM) experiment on the
Solar Maximum Mission (SMM) made the surprising discovery that the solar
bolometric irradiance varies with the sunspot cycle and with the appearance and
dissolution of individual sunspot groups.
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
Measuring the internal structure, dynamics, and composition of the
Sun. The principal tools for such measurements are helioseismology, the study of
solar neutrinos, and the study of the solar activity cycle.
Achieving the first three goals requires synoptic, high-resolution
observations of active regions, including small-scale magnetic and flow fields
(AMPS, 1983; SSB, 1985b; CPSMR, 1989). Ground-based Stokes polarimeters
have been constructed and are beginning to make progress in this area. The
critical tool, however, is the Orbiting Solar Laboratory (OSL). OSL is designed to
probe the fine-scale (100 to 300 km) structure that drives solar activity. Among
the large-scale consequences of small-scale processes are x-ray emission, solar
flares, mass ejections, and bolometric luminosity variations. We must look to the
Sun, the only highly resolved star, to place stellar x-ray astronomy on a firm
physical foundation. The observed magnitude of solar luminosity variations was
unanticipated and is a significant scientific problem in its own right. Recent
research, however, has shown that solar-type stars occasionally undergo even
larger (~l percent) luminosity variations. Because such a variation in the Sun
would cause global climate changes on Earth with catastrophic social
consequences, understanding the drivers of solar luminosity changes has been
given very high priority.
Flying in a fully sunlit orbit and carrying five major instruments to study the
full temperature range of the solar atmosphere at high angular resolution, OSL is
the most comprehensive and intensive solar physics mission ever developed.
The scientific objectives of OSL cannot be achieved by observations from the
ground because of the requirements for response in the ultraviolet and x-ray, for
a field of view large enough to encompass an entire active solar region, and for
continuous observations. While adaptive optics, although a promising but still
immature technology, may substantially increase our ground-based viewing
capabilities at visible wavelengths, the technique cannot provide, even in theory,
diffraction-limited images over the large field of view that OSL's instruments are
designed to image. OSL's instrumentation is state-of-the-art yet technically
proven. Despite the continuing delays in the implementation of this program, it
remains the highest priority new program for solar and space physics.
High-energy aspects of solar activity have been studied at length because
of the success of SMM and its repair mission. The impending SOLAR-A Satellite,
a Japanese mission using several U.S. instruments, will further expand our
knowledge of high-energy solar processes. The Geostationary Operational
Environmental Satellite (GOES) program funded by the National Oceanographic
and Atmospheric Administration (NOAA) will provide a substantial improvement
in routine imaging of solar soft x-ray and ultraviolet emissions; the Solar and
Heliospheric Observatory (SOHO) will furnish observations of coronal mass
ejections. Unfortunately, no imaging of high-energy x-ray emissions is planned for
the next solar maximum.
The Rosner report (CPSMR, 1989) recommended that National Science
Foundation (NSF) support activities leading to the definition and siting of a
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
modern telescope system for studying the physics of the Sun at small scales;
such a system would obtain data complementary to data from OSL. The report
pointed out that one option for pursuing this goal was for substantial U.S.
participation in the international consortium for the Large Earth-Based Solar
Telescope (LEST). To date, NSF has neither funded U.S. participation in LEST
nor pursued any alternative option.
Many past reports have recommended systematic long-term study of the
total solar irradiance (the "solar constant") and the solar ultraviolet spectral
irradiance (BASC, 1984; SSB, 1985b; CPSMR, 1989). National Aeronautics and
Space Administration (NASA) and NSF have reacted positively to these
recommendations, but the goal of obtaining long-term, uninterrupted
measurements has not been achieved because of program delays. SMM
reentered the atmosphere in early 1990, thereby halting the steady stream of
ACRIM bolometric irradiance data and making cross calibrations with any future
instruments impossible. Several solar variability monitors are included on Upper
Atmosphere Research Satellite (LIARS), but there will be at least a two-year gap
between the end of ACRIM and the beginning of LIARS measurements. NSF is
considering, but has not yet funded, a program of ground-based monitoring of
solar variability.
The NRC recommended the establishment of an instrumentation and
theory program in helioseismology (BASC, 1984) to study the Sun's global
circulation and interior dynamics (SSB, 1985b), and the early completion and
operation of a global network of helioseismic observing stations (CPSMR, 1989).
In keeping with these recommendations, helioseismology has been relatively well
supported and its scientific promise is being realized. For example, the depth and
rotation profile of the solar convection zone have been determined. The Global
Oscillation Network Group (GONG) project is well under way, although it has
been funded well below the proposed profile. Observations continue from the
South Pole under the aegis of the polar research program, and space
observations will be made from SOHO of the European Space Agency (ESA)
with substantial U.S. participation.
Results from the new the Japan-U.S. Kamiokande II experiment suggest
already that the solution of the solar neutrino problem requires physics beyond
the standard electro-weak theory with zero neutrino masses. A critical test of
nonstandard theories will soon be provided by gallium detectors that measure the
low-energy neutrinos that directly probe the most energetically important nuclear
reactions in the solar core.
In summary, the SMM and the funding of ground-based Stokes
polarimeters have led to good progress in studies of irradiance variations, high-
energy emissions, and solar magnetism. Helioseismology and solar neutrino
studies are also progressing. The principal problem areas are the extraordinarily
long delay in achieving a new start for the Orbiting Solar Laboratory, multiyear
gaps in irradiance measurements, and lack of a funded plan for U.S. participation
in LEST.
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
Heliospheric Physics
Heliospheric physics has developed into an independent discipline during
the last decade, with its own set of scientific objectives:
Understanding the basic physical processes that heat the corona and
accelerate the solar wind. This objective can be accomplished by in situ
measurements, remote measurements of electromagnetic emissions originating
in or scattering from the solar wind source regions, and measurements of the
chemical and charge composition of the solar wind.
Understanding the large-scale structure and dynamics of the solar
wind. How does the stream structure imposed at the Sun and the global
morphology of the heliospheric magnetic-field shape the solar wind and influence
its interaction with the local interstellar medium?
Understanding fundamental microscopic and macroscopic plasma
processes, including the evolution of turbulence in the solar wind, the
acceleration and transport of energetic particles, and the pickup of ions in the
solar wind.
The three-dimensional structure of the heliosphere will be addressed by
the Ulysses Mission. After seven years of delay, the Ulysses spacecraft, built by
ESA, was successfully launched by NASA in October 1990 and is expected to
reach a solar southern latitude of 83° in July 1994 and a similar northern latitude
a year later. A key requirement for the success of this mission is the
simultaneous measurement of fields and particles in the solar wind near the
ecliptic by some combination of Interplanetary Monitoring Platform (IMP-8),
International Cometary Explorer (ICE), the wind component of the International
Solar-Terrestrial Physics (ISTP) program, Galileo, and perhaps the Soviet
Regatta Mission.
The heliospheric elements of the ISTP involve the Wind and SOHO
spacecraft. Wind will carry a set of instruments to monitor the interplanetary input
to the magnetosphere and will also study the solar wind per se, including
microphysical processes such as shock acceleration. Both missions will obtain
new data on the elemental abundances and ionization charge states of the solar
wind.
Extended missions for the large number of heliospheric spacecraft
(Voyagers 1 and 2, Pioneers 10 and 11, ICE, Pioneer Venus Orbiter, IMP-8,
Helios 1 and 2) still in full-time or occasional operation have been strongly
recommended (BASC, 1981, 1984; SSB, 1985b, 1988b). NASA has responded
to these recommendations by increasing the collection of data from IMP-8, which
is the only currently active solar-wind monitor near Earth, and has made great
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
efforts to obtain as much data as possible from the Pioneer and Voyager
spacecraft that are continuously moving into unexplored regions of the outer
heliosphere. There is grave concern, however, that the tracking time available on
the Deep Space Network is insufficient to support these spacecraft. efforts to
obtain increased funding for coordinated heliospheric studies using existing
spacecraft have so far been unsuccessful.
Previous reports also recommended advanced technology development
for a number of missions to be implemented after ISTP. The NRC has
consistently recommended (SSB, 1980, 1985b, 1988b) a Solar Probe mission
that will send a spacecraft into the region where the solar wind is accelerated.
The development of a nonablative heat shield to protect the spacecraft and
instruments at a distance of only 3 solar radii from the surface of the Sun has not
yet been adequately funded despite the fact that the heliospheric community
ranks the solar Probe as its highest priority new mission. Heliospheric missions
recommended (SSB, 1980, 1985b, 1988b) to follow the Solar Probe would all
benefit or be enabled by advanced propulsion (e.g., solar electric or nuclear
electric). These missions include the interstellar probe, a 1-astronomical unit
solar polar orbiter, and a heliosynchronous orbiter. We believe that such
propulsion systems are no closer to reality than they were when the
recommendations were first made (SSB, 1980).
In addition to space missions, the NRC has also recommended (BASC,
1981) continued use of interplanetary scintillation (IPS) and radio spectrometric
studies of coronal and interplanetary disturbances. The latter work, with the
exception of operational U.S. Air Force observations (radio solar telescope
network), ahs been discontinued. Recent IPS work has been limited to near-Sun
observations and occasional Deep Space Network doppler and phase scintillation
studies. To obtain the IPS data that it requires, NOAA has initiated cooperation
with other countries.
In summary, the NRC recommendations concerning heliospheric physics
are generally being implemented, but with many delays (Ulysses, Wind). On the
positive side, outer heliospheric data continue to be received from the Pioneer
and Voyager spacecraft. Current concerns include advanced development of
technology required for future missions, oversubscription of Deep Space Network
tracking support, and the decline in support for ground-based radio observations
of the solar corona and solar wind.
Cosmic Ray Physics
The Field committee report (AMPS, 1983) has provided overall guidance
for the cosmic ray program during the 1980s. The scientific goals can be
organized under the following objectives:
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The origin and evolution of matter
Particle acceleration, transport, and interactions
The role of cosmic rays in galactic processes
The nature of the interstellar medium
In order to address these objectives, the following measurement goals
were identified for the 1980s (BPA, 1982; SSB, 1988c):
Isotopic composition of nuclei from H to Ni
Elemental composition of ultraheavy (Z > 30) cosmic rays
Elemental composition and origin of high-energy (,1015 Ev) cosmic
rays
Spectra of high-energy electrons, positrons, and antiprotons
Low-energy cosmic rays in the interstellar medium
Acceleration, propagation, and composition of solar energetic particles
Some of the highlights of cosmic ray physics in the 1980s were the
Voyager and Pioneer observations of the solar modulation of galactic cosmic
rays, further study of anomalous cosmic rays, and better understanding of the
mass spectrum of solar cosmic rays. At the same time, progress in cosmic ray
physics was limited by the cancellation of a Spacelab experiment to study high-
energy interactions and of re-flights of two experiments to measure cosmic ray
nuclei.
Two new cosmic ray Explorers were selected following the 1988
augmentation to the Explorer budget:
1. The Advanced Composition Explorer (ACE), which will measure the
elemental and isotopic composition of H through Ni nuclei over six decades in
energy/nucleon, from solar wind to galactic cosmic ray energies.
2. The Solar, Anomalous, and Magnetospheric Particle Explorer
(SAMPEX), which will measure low-energy solar, magnetospheric, and galactic
particles from 0.3 to 300 MeV/nucleon from a polar orbit. SAMPEX is the first of a
new series of Small Explorers that has been initiated to provide frequent access
to space for low-cost, focused experiments.
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
Several small experiments on "missions of opportunity" were also
successfully funded through the Explorer Program. On the negative side, cost
overruns in the current Explorer Program will apparently delay the launch of ACE
until at least 1997, ten years after it was proposed.
Another major recommendation (BPA, 1982; SSB, 1988c) was the
development of a superconducting magnetic spectrometer facility for the Space
Station, including instruments to extend particle and antiparticle spectroscopy into
the GeV and TeV energy ranges. Such a facility, named Astromag, was selected
for flight on the Space Station. In addition, a Heavy Nuclei Collector (HNC), which
would measure cosmic ray abundances of the heaviest elements in the periodic
table, was conditionally selected for Space Station. Unfortunately, funding for
these and all other attached payloads was recently suspended indefinitely. It will,
therefore, be necessary to explore other options to accomplish the important
objectives of Astromag and HNC.
Recently, the Positron Electron Magnetic Spectrometer (POEMS), was
tentatively selected for, and subsequently deleted from, the Earth Observing
System (EOS). POEMS would have measured electrons and positrons from the
Galaxy and the Sun as well as solar gamma rays and neutrons. Other means
must be found to pursue those important objectives.
Also recognized as important (BPA, 1982; SSB, 1988c) were laboratory
cross-section measurements to support the interpretation of cosmic ray data.
There has been considerable progress in the initiation of new cross-section
measurements at the BEVALAC, but this facility is unfortunately scheduled to
close in 1994.
The Twenty-First Century report (e.g., SSB, 1988b,c), which had a more
distant horizon, recommended the following additions to the cosmic ray program
for the years 1995-2015: (1) Interstellar Probe, a mission to traverse the
boundary of the heliosphere and to conduct in situ measurements in interstellar
space, (2) large detector arrays for very high energy (> 1015 eV) and ultra-heavy
(Z > 30) nuclei, and (3) experiments on polar platforms to measure positrons,
antiprotons, and the isotopes of ultra-heavy nuclei. Very little of the advanced
technology development required for these missions has been started.
If the recently selected SAMPEX, ACE, Astromag, and HNC missions are
indeed flown during the coming decade, we can expect major progress in studies
of the elemental and isotopic composition of energetic nuclei from the solar
system and galaxy, and in studies of antiprotons, electrons, positrons, and ultra-
heavy nuclei, although on a considerably longer schedule than envisioned by the
Field committee (AMPS, 1983). Although the cosmic ray program currently
scheduled for the 1990s will address in part all of the goals laid out for this
subdiscipline for the 1980s, it will not exhaust those goals that remain valid and
can be extended in a natural manner to nuclei in the upper two-thirds of the
periodic table and to higher energies. There are, however, two areas in which
these goals should be supplemented. There has been increasing interest in the
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
interface between astrophysics, particle physics, and cosmology, and in the use
of cosmic rays to test new theories in this field. The second area is the
investigation of particles accelerated within, or at the boundary of, the
heliosphere. The most significant of these is the so-called "anomalous" cosmic
ray component, apparently an accelerated sample of the neutral interstellar
medium.
In summary, although missions and experiments responsive to NRC
recommendations were started, many of them have been cancelled or indefinitely
postponed; others have been stretched to more than a decade. While there is
now promise of progress during the 1990's from missions such as SAMPEX and
ACE, there is also a danger that Astromag and HNC will repeat the cycle of
disappointments that characterized the 1980s.
Magnetospheric Physics
The Kennel report (SSB, 1980) cited six critical regions of the terrestrial
magnetosphere that needed to be better understood in order to advance
quantitative understanding of the time-dependent exchange of energy and
plasma between the solar wind and the magnetosphere, and called for
simultaneous studies of plasma processes in those regions. The regions cited
were (1) the Earth's extended magnetic tail, (2) the upstream solar wind, (3) the
mid-magnetosphere equatorial plane, (4) well above the polar cap, (5) the low-
altitude region observable from the ground, and (6) the atmospheric regions. The
Friedman-Intriligator report (BASC, 1981) expressed strong agreement with the
recommendations of the Kennel report, and made a series of recommendations
that emphasized the need to understand the coupling between the critical
regions, in addition to understanding local processes within each region.
Specifically, Friedman-Intriligator recommended programs to study energy and
momentum transfer between the solar wind and magnetosphere; energy transfer
between the magnetosphere, ionosphere, and atmosphere in magnetic field line
regions passing through the auroral zone, polar caps, and geomagnetic tail; and
global coupling of the magnetosphere, ionosphere, and atmosphere system.
The decade of the 1980s witnessed both a substantial, steady growth in
our understanding of magnetospheric processes and a series of major
accomplishments that provided new perspectives on the magnetosphere and its
dynamics. The following list, although not complete, is illustrative of the major
changes that came about in the 1980s in magnetospheric physics:
Global auroral imaging provided a remarkable initial step to obtaining a
global perspective of magnetospheric processes.
New observations, notably from Dynamics Explorer (DE) and Active
Magnetospheric Particle Tracer Experiment (AMPTE), definitively showed that
the ionosphere is a major source of magnetospheric particles.
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Assessment of Programs in Solar and Space Physics 1991 (Chapter 2)
The composition and charge state of the ring current were measured
for the first time.
The first measurements of the deep tail were made showing surprising
correlations with inner magnetosphere activity and the existence of plasma
configurations, called plasmoids, traveling at high velocity away from the Earth.
New observations demonstrated the importance of magnetospheric
boundary layers in the transport of plasma through the magnetosphere and
possibly in the dynamics of the magnetosphere.
The development of a new model of the Earth's bow shock and
foreshock regions provided a better understanding of many of the available
observations.
Suggested methods for achieving further progress were put forth by the
Intriligator report (BASC, 1984) in 1984, and by the Krimigis report (SSB, 1985b)
in 1985. The Intriligator report recommended an international solar-terrestrial
physics program and an increase in annual solar-terrestrial research funding
above 1984 levels. The Krimigis report recommended a coordinated program of
multisatellite observations aimed at providing simultaneous information from the
six critical regions as recommended in the Kennel report. In essence, this was
the ISTP program.
Several concerns stem from the program delays and major program
restructuring. For example, the deep-tail and near-equatorial ISTP spacecraft
were removed from the NASA program. The Japanese have provided a deep-tail
spacecraft, Geotail (which includes NASA-funded instruments), and the Air Force
has provided an equatorial spacecraft named the Combined Release and
Radiation Effects Satellite (CRRES). Geotail fulfills the need for deep-tail
observations, but CRRES does not fulfill the need for observations in the vital
equatorial mid-magnetospheric region at altitudes above 6 earth radii. The
CSSP/CSTR endorses NASA's current efforts to re-establish those crucial
equatorial observations and reaffirms their need in the ISTP science program. A
further concern is that the various programs will be spread out in time to the
extent that there will be little simultaneity, thereby directly impacting a most
important aspect of the earlier recommendations, i.e., the need for simultaneous
observations in the key magnetospheric regions. Although ISTP has the highest
priority within the magnetospheric community, the Krimigis report also
recommended a series of active experiments to study plasma processes in the
magnetosphere either by optical observation of tracer gases or by measuring the
response of the magnetosphere to artificial disturbances such as injections of
waves or energetic particles. Although CRRES is performing some chemical
releases, most of the active experiments developed for the Shuttle have been
seriously descoped or delayed.
In summary, response to magnetospheric science and implementation
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recommendations has been positive but slow. The slowness has resulted in
programmatic restructuring that has worked against some key aspects of the
recommendations, the most serious being the decrease in temporal overlap of
the ISTP spacecraft.
Middle- and Upper-Atmosphere Physics
A comprehensive program investigating the global neutral atmosphere,
the characteristics of its distinct altitude regions, long-term and solar-cycle
variability, and the coupling and interaction between regions were defined as the
focus for research in the 1980s in several NRC reports (SSB, 1980; BASC, 1981,
1984). Specific scientific topics included:
The effects of variable photon and particle fluxes.
The significance of forcing from the magnetosphere.
The energy balance, chemistry, and dynamics of the thermosphere,
mesosphere, and stratosphere.
A better understanding of the global electric circuit.
The NRC reports emphasize continuing observation and analyses
combined with a broad range of specific new missions. Increased annual funding,
continued support for mission operations and data analysis, technology
development, coordinated campaigns, and a continuing suborbital program were
to form a basis for studies of the thermosphere, middle atmosphere, and global
electric circuit. Support for the Middle Atmosphere Program (MAP), UARS, the
Solar Mesosphere Explorer (SME), a middle atmosphere tether mission, and the
Shuttle-based Solar Terrestrial Observatory (STO) were recommended.
Significant advances in understanding dynamical, radiative, chemical, and
coupling processes were made through participation of U.S. scientists in MAP.
Satellite observations and parallel theoretical efforts have played a central
role in facilitating rapid progress. Observations by the Stratospheric and
Mesospheric Sounder (SAMS) and the Limb Infrared Monitor of the Stratosphere
(LIMS) provided data on atmospheric composition and dynamics on a global
scale. SME made global measurements of ozone and other minor constituents in
the middle atmosphere, as well as measurements of temperature over a period of
several years. Observations of ozone and aerosols from the Stratospheric
Aerosol and Gas Experiment (SAGE) and of total ozone content from the Total
Ozone Mapping Spectrometer (TOMS) have also played an important role,
especially in recent studies of polar ozone depletion. Spacecraft observations
have also determined the response of ozone concentrations to 27-day and solar-
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cycle variations in solar ultraviolet radiation, but the effect on the lower
atmosphere remains to be determined. At greater heights, DE has revealed much
new information on the dynamics of and coupling between the magnetosphere,
ionosphere, and thermosphere.
A partial list of theoretical advances stimulated by these satellite-based
observational programs includes an increased understanding of the processes
that control the thermal budget and the distribution of minor constituents in the
middle atmosphere; the importance of transport by planetary and gravity waves;
the interaction among dynamics, photochemistry, cloud microphysics, and
radiative transfer in the development of the Antarctic ozone hole; and the
formation and redistribution of volcanic aerosols by atmospheric motions, and the
possible impact of such aerosols on stratospheric chemistry and ozone depletion.
The funding agencies also have made a concerted effort to support
ground- and aircraft-based research on transport and chemistry in the
stratosphere. In particular, there has been strong support for investigations of the
polar ozone problem. NSF support has also helped focus research on the
thermosphere and its coupling to the ionosphere and mesosphere through the
program on Coupling, Energetics, and Dynamics of Atmospheric Regions
(CEDAR). Ground-based experiments, with support from various agencies and
from CEDAR have revealed a number of important dynamical, radiative,
chemical, and coupling processes, as well as their influences on the circulation,
structure, and variability of the middle atmosphere. Particularly interesting in this
regard have been the insights gained through observational and theoretical
efforts addressing relatively small-scale motions, and the extent to which such
motions influence the circulation and thermal structure of the middle atmosphere
on both small and global scales.
A clearer understanding of the global electrical circuit has been achieved.
Progress has been made toward quantifying the relationship between lightning
flash rate and the Maxwell current output above thunderstorms and into the
global electric circuit. Atmospheric electric fields and ion mobilities have been
measured using balloons and rockets. NASA is also supporting work on modeling
the global electric circuit and the Lightning Imaging Sensor (LIS) has been
selected to fly on the first platform of the Earth Observing System (EOS-A). On
the other hand, little or no progress has been made in elucidating how global
cloud distributions or pollution in the boundary layer affect the global electric
circuit.
In summary, response to many of the recommendations concerning the
middle and upper atmosphere has been positive, and great strides have been
made in advancing our understanding of the processes and interactions taking
place in those regions. However, delays in the implementation of satellite-borne
observing systems combined with inattention to some scientific problems have
limited the progress anticipated at the time the recommendations were made.
Areas of concern include repeated postponements of the launching of UARS,
uncertain prospects for the rapid implementation of other, simpler satellite
missions in the period between the launching of UARS and that of EOS-A, the
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lack of a vigorous research program on the effects of solar activity on the middle
atmosphere, and the neglect of certain aspects of the global electric circuit
problem.
Solar-Terrestrial Coupling
Since the early 1980s, recommendations in the solar-terrestrial area have
focused on the development of a quantitative understanding of the cause-effect
chain of events linking solar variations to effects in the Earth's environment.
Related studies address of the interplay between solar radiation, the solar
corona, solar wind, magnetosphere, ionosphere, and atmosphere. To this end,
specific recommendations (see SSB, 1980, 1985b; BASC, 1981, 1984) have
been made:
To provide simultaneous measurements on as many of the links as
possible in the coupling of the Sun to the Earth;
To develop and test increasingly comprehensive models of these
processes; and
To determine the effect of solar luminosity and spectral irradiance
variations on weather and climate.
In response to NRC recommendations to study solar wind-
magnetosphere-ionosphere coupling at polar latitudes (BASC, 1981), the
Chatanika incoherent scatter radar was relocated to Sondrestrom, Greenland.
Magnetosphere-ionosphere coupling was a focus of the CEDAR program, and
the expanded theory programs led to greatly improved models of the ionosphere
and ionosphere-thermosphere coupling. Some specific programs required for
implementation of the solar-terrestrial coupling goals have been approved,
notably UARS, ISTP, CEDAR, Geospace Environment Modeling (GEM), CRRES,
the Solar-Terrestrial Theory Program (STTP), and a revitalization of the Explorer
program. Many of these programs remain under development with
implementation several years away. Further, some have been descoped owing to
budgetary constraints. Therefore, the NRC recommendations formed in the early
1980s are as valid today as then.
Major gaps that still remain in previously recommended scientific studies
include solar variability and its impact on weather and climate, and the global
electric circuit and its role in the solar-terrestrial coupling process. A further
hampering of progress in this area results from a baseline program (e.g.,
research and analysis, theory, rockets, balloons, and ground-based) that barely
has maintained an adequate level of effort and in some areas actually has eroded
during the past decade.
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In summary, funding agencies have provided a generally positive
response to the scientific recommendations forged in solar-terrestrial physics in
the early 1980s. This positive response, however, has been negated by delays in
implementation, program restructuring, and inattention to a number of
recommendations. The net result is that the earlier scientific recommendations
remain valid and will not be implemented until more than a decade after their
formulation.
Comparative Planetary Studies
For the past decade, NRC committee reports (e.g., SSB, 1980, 1985b)
have underscored the basic importance of comparative studies of planetary
magnetospheres and have strongly recommended the inclusion of particle and
field instruments on all planetary missions. The spectacular successes of the
Voyager mission have dramatically demonstrated the veracity and importance of
those recommendations.
Although several new missions (Galileo and CRAF/Cassini) have
substantive particles and fields payloads, there is not an appropriate complement
of particles and fields instruments on the Mars Observer even though recent
USSR Phobos results have shown the existence of a dynamic particles and fields
environment around Mars.
Some progress has been made toward understanding the thermospheres
of planets other than Earth. The Pioneer-Venus mission has provided much new
information on the Venusian thermosphere and ionosphere; unfortunately, our
understanding of the thermospheres and ionospheres of other planets is still
rather poor.
The cometary plasma and neutral particle environments have been
studied, and the major advances have come from the Soviet, European, and
Japanese missions to Comet Halley. The major U.S. contribution concerned the
cometary plasma environment of Comet Giacobini-Zinner as sampled by the ICE
spacecraft-a mission of opportunity with a spacecraft not designed for cometary
observations.
In summary, the response to recommendations in this area has been
positive. However, major delays (Galileo, CRAF/Cassini), the absence of a U.S.
mission to Comet Halley, and the lack of plasma instrumentation on U.S.
missions to Mars have slowed progress significantly.
COMMON ISSUES
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Program Management
The Krimigis report (SSB, 1985b) recommended a reorganization of the
NASA Office of Space Science and Applications (OSSA) calling for the
establishment of a separate Space Physics Division. This recommendation has
been implemented and the resulting strong representation of the discipline of
space physics at NASA Headquarters has revitalized the field.
The Rosner Report (CPSMR, 1989) called for restructuring of the solar
physics related programs at NSF, noting that the discipline is split between the
Divisions of Astronomy and the Division of Atmospheric Sciences. This
recommendation is currently under consideration.
Several reports (BASC, 1981, 1984; CPSMR, 1988) recommended
paying more attention to interagency coordination of activities in the broad area of
solar-terrestrial research. This recommendation has become increasingly
important with the initiation of additional projects that draw on resources of
several agencies. The Interagency Coordinating Council for Solar-Terrestrial
Research (ICCSTR) was established as a mechanism for such consultation in
1984, but it has been inactive since 1987. The charter remains in effect and the
committee could be reactivated to serve as a mechanism for interagency
coordination. Despite the hiatus in ICCSTR activity, inter-agency consultation and
cooperation has been initiated in the area of Global Change, essential to the
effective development of this ambitious program.
Coordination of U.S. space programs with the programs of other nations
was called for in the Lanzerotti report (SSB, 1984c). One response to this
recommendation was the establishment of the Interagency Consultative Group
(IACG) that meets regularly to coordinate planning for space missions. In
addition, several international unions and scientific committees sponsor major
worldwide coordinated efforts in this field. An example is the current Solar
Terrestrial Energy Program (STEP) sponsored by the Scientific Committee on
Solar-Terrestrial Physics (SCOSTEP).
Data Archiving and Access
A number of NRC reports (BASC, 1988; CPSMR, 1988; SSB, 1982,
1984a, 1985b, 1986b, 1988a) have recommended increased attention to the
acquisition and storage of meaningful data in an accessible and understandable
format. They have pointed out that improved data archiving is important not only
for its own sake, but also because it facilitates good science. The science must
be an integral element of all the archiving efforts. Providing an accessible, well-
documented archive of solar-terrestrial data is essential for the future of the
science.
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The Shea-Williams report (SSB, 1984a) detailed a plan for solar-terrestrial
data access. It included the formation of a solar-terrestrial Central Data Catalog
and Data Access Network (CDC/DAN) and the establishment of a scientific
steering committee for oversight. The report called for all agencies sponsoring
solar-terrestrial research projects to configure their data systems to be
compatible with the CDC/DAN and recommended that it serve as a clearing
house for software. In addition, the report recommended that the funding
agencies offer incentives to encourage researchers to provide useful and
appropriate data sets and that projects identify resources needed for data
archiving at project initiation. Finally, the report recommended the formation of
data archival groups consisting of discipline specialists to review archival
activities and to help search for useful but non-archived data collections.
The needs discussed in the NRC committee reports remain unfulfilled
today. Some progress related to the recommendations has been made: greater
emphasis is being placed on the acquisition and storage of meaningful data in an
accessible form; program management no longer assumes that its responsibility
ends with the data acquisition and initial science analysis; NASA and NSF
support networking that aids the transport of smaller data sets; and missions
such as ISTP have initiated planning for the data system and archiving objectives
early in the mission plans. Unfortunately, the ISTP data distribution system has
not lived up to its early promise with respect to compilation and access to
reduced data. Although, the CDC/DAN has not been implemented, NASA has
organized a group of scientists to address the issues raised in the NRC reports.
Since the space physics data system activities are so new, the issues of science
oversight, interoperability, and software have not been addressed yet, and no
action has been taken by NASA to offer real incentives for solar-terrestrial
researchers to provide useful and appropriate data for archiving.
Finally, NASA, in cooperation with several other agencies in the United
States, Canada, Europe, and Japan, has developed a master directory to data
repositories of geophysical interest. A group of discipline coordinators is charged
with verifying the contents of the directory and locating unique but nonarchival
data collections. NASA has also appointed an advisory group to consider the
problems associated with making data directories and catalogs interoperable.
In summary, the start of the solar-terrestrial data systems is encouraging,
but a great deal needs to be done.
Explorer Program
In 1984 the CSSP became concerned that the capability of the Explorer
program was in danger of serious erosion as a result of escalating costs and
mission complexity. In an effort to revitalize the Explorer program as a viable
research tool, a study was initiated; the resulting report (SSB, 1984b)
recommended the following:
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A return to small, simple missions.
An average of one Explorer per year for solar and space physics,
along with augmentation of the Explorer budget if necessary.
Use of a two-stage selection process based on an Announcement of
Opportunity mechanism, with selection for definition, followed, if warranted, by
selection for development.
Near this same time frame, strong recommendations for an augmented
and revitalized Explorer program were offered by the Astronomy Survey
Committee (AMPS, 1983) and the Committee on Space Astronomy and
Astrophysics (SSB, 1986a).
Within the past three years all of these recommendations have been
addressed to some extent by NASA, beginning with a significant augmentation to
the Explorer budget in 1988. A principal result of this budget increase was the
establishment of a new Small Explorer (SMEX) program aimed at providing
frequent (approximately one launch per year) access to space for low-cost (< $30
million), focused experiments. The first two SMEX missions to be selected are
from the Space Physics Division: SAMPEX, scheduled for launch in 1992, and
Fast Auroral Snapshot Explorer, scheduled for launch in 1993. In addition, in
response to a 1986 call for proposals for an Explorer Concept Study, four new
Delta-class Explorer concepts were selected for Phase-A study, including two
from space physics.
As the above progress indicates, NASA has been generally responsive to
the recommendations from NRC reports, and this important program has indeed
been revitalized. Unfortunately, cost overruns in the current Explorer program
continue to cause delays, and it now appears that the first of the new Delta-class
Explorers will not be launched until more than 10 years after it was proposed.
The overwhelming response of Explorer proposals (more than 40 Delta-
class Explorer concepts and more than SO SMEX proposals) confirms the
continuing value of these small missions to the space physics community.
Coordinated Programs and Synoptic Observations
Solar-terrestrial research deals with time-varying phenomena spanning
several regions of space and scientific disciplines. Coordinated programs,
encompassing observations and theory covering the interrelated areas, are
necessary to address these complex research problems adequately. Just as
three-dimensional, time-varying magnetospheric characteristics can be
addressed by simultaneous equatorial, polar, and tail observations, coordinated
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measurements of the Earth's polar upper atmosphere and the overlying
magnetosphere are needed to determine the linkage between the solar wind and
terrestrial upper atmospheric winds. To facilitate coordinated research, the ISTP
program was strongly recommended (see BASC, 1984; SSB, 1985b) as was a
program of coordinated ground-based campaigns to study the coupling of
atmospheric regions. The program of World Days or SCOSTEP campaigns
triggered by specific events was recommended, including incremental funding of
$2M per year (BASC, 1984).
Several initiatives have been proposed in response to these needs,
including ISTP and CEDAR. Incremental funding for CEDAR has been supported
by the Global Change program. NSF has also gone forward with the GEM
initiative that consists of coordinated observational campaigns and theoretical
studies of specific regions. The first target of the GEM program is the
magnetosphere boundary layer.
Synoptic observations of the fundamental parameters that characterize
the solar-terrestrial system underlie the wide range of specific investigations in
the field. Such studies reveal trends and long-term variability not evident in
studies of isolated events (BASC, 1981, 1988). It has been recommended that
unmanned spacecraft, space platforms (BASC, 1988), and ground-based
facilities (BASC, 1984) provide continuing measurements of solar (including total
radiance, spectral, particle, and magnetic field), interplanetary (solar wind
particles, magnetic field, and energetic particles), magnetospheric (aurora,
current, and electric fields and particles), and thermospheric (circulation,
temperature, and energy resources) parameters. Incremental funding in the
amount of $4 M/year was recommended. Analysis of historical and archival data
sets was also recommended (CPSMR, 1988; BASC, 1988). To date, there is no
national program or policy in response to those recommendations. An effort was
made, however, to provide additional solar wind and interplanetary magnetic field
data from IMP-8, resulting in >50 percent coverage.
Research and Analysis
The perceived erosion of the base research program is currently receiving
a lot of attention by both NASA and NRC committees. This section briefly
addresses some of the issues specific to solar and space physics.
Theory and Modeling
A major review of the field of space plasma physics by the SSB in the late
1970s Space Plasma Physics: The Study of Solar System Plasma, (National
Academy of Sciences, 1978—the Colgate report) emphasized that theory should
play a central role in the planned development of space plasma physics. The
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SSB research strategy for this field—the Kennel report (SSB, 1980)—reiterated
this conclusion and stressed the need for quantitative modeling in every
subdiscipline of the field. Subsequent reports (BASC, 1981, 1984; SSB, 1985b)
echoed the same theme.
On the positive side, theoretical support is now "built-in" on many flight
missions. Those mission-associated theory efforts have the advantage of being
closely coupled to observational campaigns and the disadvantage of having to
cope with scheduling delays and other upsets that typically accompany flight
missions (e.g., CRRES, ISTP).
The establishment of the STTP in 1979 was a very positive response to
NRC recommendations. STTP, now called the Space Physics Theory Program
(SPTP), was and is intended to support efforts characterized by a "critical mass"
of collocated personnel and to provide "attractive and secure opportunities to
young theorists.." (STTP Announcement of Opportunity, 1979). The program was
started with $2.25 M, with awards up to ~$450K and an average award of
~$200K. The current program supports a larger number of groups with roughly
twice the original total funds covering the full scope of the Space Physics
Division, but with an average award of ~$275K. This is a good deal less than the
original level of support when 11 years of inflation is taken into account. This
steady erosion of constant-dollar grant size jeopardizes the "critical mass" feature
of the program, and taxes the ability to support senior researchers and still
provide the "attractive and secure opportunities to young theorists. . .". NSF, with
fewer resources to devote to solar-terrestrial research, has used its re-sources
more effectively in supporting theory, with reasonable-sized grants and a
reasonable level of commitment to seeing ongoing efforts through to completion.
The NASA Research & Analysis program (now called the Supporting
Research & Technology Program) has moved even farther in the direction of
offering large numbers of awards of ever-decreasing size. These declines in
support are at odds with the recommendation (BASC, 1981) that "As [solar-
terrestrial] research matures, the need for theoretical work and modeling grows;
an appropriately balanced program must provide for such an effort." This
recommendation is certainly still valid. A dramatic strengthening of and
recommitment to the original principles of SPTP are needed. NASA's Research
and Analysis program is even more in need of reassessment. NSF activities in
this area are now heavily constrained by the mandate to support the Global
Change program, but the same principles apply.
Supercomputing
Supercomputers are especially important for global modeling of the solar
corona, the heliosphere, the magnetosphere of the Earth and other planets, and
the terrestrial and planetary atmospheres and ionospheres. The Krimigis report
(SSB, 1985b) recommended support for a program of computer modeling,
including access to supercomputers.
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Three major elements are required to undertake modeling on
supercomputers: (1) the supercomputer itself, (2) access to the computer via
electronic networks, and (3) digestion of the results (including graphics) at the
home institution by means of small computers and workstations.
Response to the modeling and supercomputing recommendation has
been very good overall. In particular, the response to the three major elements
has been as follows.
1. The NSF set up four supercomputing institutions across the country,
and the supercomputer facility at the National Center for Atmospheric Research
(NCAR) has continued to be supported and upgraded. NASA has
supercomputing facilities available at several NASA centers, although for off-site
researchers the NASA facilities have been more difficult to use than the NSF
centers. The military also has supercomputers on which space science work is
done, but access to those facilities is restricted.
2. The NSF Internet and NASA Space Physics Analysis Network (SPAN)
electronic networks are available for access to the "national" supercomputers.
These networks had problems during their initial phase several years ago, but
they have improved greatly.
3. Small machines or workstations of relatively modest cost (<$10,000)
are required to analyze and display the output produced by the supercomputers,
as well as to initiate communication over the networks with the supercomputer
facilities. This linkage is now the limiting factor for many scientists. Requests for
funds for small computers are too often frowned upon by agency program
directors during times of fiscal constraints.
Suborbital and Spartan Programs
The Suborbital program, which includes balloon, rocket, and aircraft
payloads, is essential for addressing quick turn-around science objectives,
development and testing of new instrumentation, more rapid testing of theoretical
ideas, and training students in experimental techniques. The strengthening and
augmentation of such projects was strongly endorsed by both the Intriligator and
Krimigis committees (BASC, 1984; SSB, 1985b).
During the mid-1980s, the Balloon program floundered because of faulty
balloon material. NASA made special efforts to correct that situation, and by 1986-
1987, the Balloon program was enjoying great success. Currently, the Balloon
program is sized at ~50 flights/year, which is adequate to meet the demand, but
some additional funding is required for improved balloon electronics, including
more sophisticated location devices (e.g., Global Positioning System (GPS)
receivers). The biggest problem is lack of funding to support payload
development. Because approximately two-thirds of the proposals are not funded
and because of a trend to larger, more expensive payloads, there has been a
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decline in the frequency of flights in the last few years. An example of the
devastating effect of limited funding is the collapse of the balloon component of
the MAX'91 Long Duration Program because no funding could be found for the
three instruments that had been selected for flight.
Important advances in soft x-ray and extreme ultraviolet imaging of the
Sun have been achieved through NASA's Rocket program. Overall, however, the
Rocket program declined in the 1980s because inflation was not covered from
1987 through 1989, active experiments were removed from the program, and
Rocket program money was spent on development of a fine-pointing capability
for the Spartans.
The Spartan program was designed to provide relatively long flights (~40
hours) for rocket-type payloads by using the Shuttle for release and retrieval. The
Krimigis report (SSB, 1985b) recommended that some Rocket program funding
be used to support the Spartan program. The Spartan program was effectively
terminated by the Challenger disaster in 1986. In retrospect, the resources
expended for the Spartan program adversely affected the rocket-type science it
was meant to help. NRC recommendations to strengthen the Suborbital program
are still valid and generally unfulfilled. Education
Recommendations to enhance university participation and to increase
graduate student support appear in several NRC reports (e.g., SSB, 1985a;
CPSMR, 1989). To date, only a few programs have set aside specific funds to
support educational components of their activities. CEDAR is a notable example
of support for educational endeavors, with student attendance at their annual
workshop increasing from six participants in 1986 to 107 students in 1990.
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