|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 7
2
Scientific Objectives
i:
The following summary of the scientific objectives of solar and
space physics is taken from the NRC report An Implementation
Plan for Priorities in Solar and Space Physics (1985), which is
adapted from the Kennel report (Solar-System Space Physics in
the 1980~: A Research Strategy, 1980) with appropriate changes
and updates.
SOLAR PHYSICS
Major advances in our understanding of the Sun were made
.n the 1970s and the early 1980s (see Figure 2.la). Most, if not
all, of the magnetic flux that emerges from the convective zone is
subsequently compressed into small regions of strong (1200 to 2000
G) field, a fact that is still not understood theoretically. Obser-
vations confirmed earlier predictions that the 5-min photospheric
oscillation, discovered in the early 1960s, is a global phenomenon.
This discovery has made ~helioseismology" possible, by which the
depth of the convective zone and the rotation below the photo-
sphere have been inferred. In addition, by ruling out the classical
model of coronal heating by acoustic waves, observations from the
ground and from OSO-8 raised anew the question of what main-
tains the corona's high temperature. Coronal holes were among
7
OCR for page 8
8
the major discoveries of the 1970s. White-light, extreme ultravim
let, and x-ray observations suggested how coronal holes are related
to the convective zone and to the solar wind. Skylab observations
unambiguously identified magnetic arches as the basic structure
of coronal flares. This perception altered our theoretical picture
of solar flares and clarified the need for a coordinated multiin-
strument attack, which was initiated with the Solar Maximum
Mission.
To better understand all the processes linking the solar interior
to the corona, we need to study (see Figure 2.Ib) the following:
~ The Sun's global circulation how it reflects interior dy-
namics, is linked to luminosity modifications, and is related to the
solar cycle.
~ The interactions of solar plasma with strong magnetic
fields—active regions, sunspots, and fine-scale magnetic knots-
and how solar flare energy is released to the heliosphere.
~ The energy sources of the solar atmosphere and corona and
the physics of the Sun's large-scale weak magnetic field.
PHYSICS OF THE HE[IOSPHERE
The Sun is the only stellar exosphere where complex phe-
nomena common to aD stars can be studied in situ. Observations
of the Sun and the heliosphere (the plasma envelope of the Sun
extending from the corona to the interstellar medium) provide
the bash for interpreting a variety of phenomena ranging from
x-ray and gamma-ray radiation to cyclical activity and long-term
evolution. The Sun, together with the heliosphere and planetary
magnetospheres and atmospheres, makes up an immense labora-
tory that exhibits complex magnetohydrodynam~cal and plasma
physical phenomena whose study enhances our understanding of
basic physical laws as well as our understanding of the influences
of the Sun on our terrestrial environment.:
The solar wind has been studied near the Earth since 1961. At
the present time, measurements of the solar wind have primarily
been extended to within Mercury's orbit (0.3 AU) and past Pluto's
orbit but have been confined to near the ecliptic plane. Quantita-
tive models of high-speed solar wind streams and flare-produced
shocks have been developed and tested against data obtained near
the ecliptic. The realization that high-speed streams originate in
OCR for page 9
9
A SO LAR PtlYSICS--R ECENT ACCOh/lPLISHMENTS
IMPORTANCE OF STRONG
MAGN ETI C F I E LDS ~
ELEMENTAL AND ISOTOPIC ~ / ALES
DlFFERENTiATION /~
1C _~< CORONAL HEATING
At-_ ~
in_
/
I D E NTI F ICAT 10 N OF ~ H E Ll OSE I SMOLOG Y
SO LAR F LA R E G EOM ET R Y
B SOLAR PHYSICS—OBJECTIVES
How Do Global Circulation
and Surface Oscillations
Reflect Interior Dynamics?
What Are the
Corona's Energy
Sources?
-
~ ~q:_ ~
-
How Does Solar Plasma /
Interact with Strong
Magnetic Fields7 How Is
Solar Flare Energy
Released ?
C SOLAR PHYSICS—R ECU I R ED MEASU R EMENTS
How Is Solar
Wind Generated?
-
What Is the Physics of
the La rge Scale Weak
Magnetic Field?
/
V -
2. IN SITU MEASUREMENTS
OF CORONAL PLASMA
PROCESSES NEAR SOLAR
/ A) \ WIND CRITICAL SURFACE
. HIGH RESOLUTION (0.1")
SH UTTL E OBSE RVAT IONS
OF ACTIVE REGIONS,
SM A L L SCAL E F I E LDS
AN D F LAR ES
3. SURVEY OBSERVATIONS OF
SURFACE OSCILLATIONS,
LARGE SCALE MAGNETIC
F I E L D, LU M I NOSITY VAR I AT 10 N
FIGURE 2.1 Solar physics: status, objectives, and recommendations. In
this series of sketches of the Sun and its coronal magnetic field some recent
accomplishments in solar physics are illustrated. (A) Questions that can
be fruitfully attacked in the 1980s and l990s. (B) The principal research
programs needed to answer these questions. (C) The Sun and solar corona
within 5 solar radii. The influence of the processes occurring within this
region extends throughout interplanetary space via the solar wind.
OCR for page 10
10
the rapidly diverging magnetic-flux tubes of coronal holes has re-
oriented much solar wind research. The sector structure of the
solar wind has been unambiguously related to a magnetic neu-
tral sheet of solar system scale that connects to the large-scale
magnetic field of the rotating Sun. Finally, microscopic plasma
processes have been shown to regulate solar wind thermal conduc-
tion and diffusion and, possibly, local acceleration of particles in
solar wmd structures.
To understand better the transport of energy, momentum,
energetic particles, plasma, and magnetic field through interplan-
etary space, we need to study the following:
~ First and foremost, the solar processes that govern the
generation, structure, and variability of the solar wind.
The three-dimensional properties of the solar wind and
heliosphere.
~ The plasma processes that regulate solar wind transport
and accelerate energetic particles throughout the heliosphere.
MAGNETOSPHERIC PHYSICS
New processes regulating Earth's magnetic interactions with
the solar wind were Recovered in the 1970s and early 1980s (see
Figure 2.2a). For example, unsteady plasma flows that apparently
originate deep in the geomagnetic tad! en c] deposit their energy
in the inner magnetosphere and polar atmosphere were observed.
Observations of impulsive energetic particle acceleration suggested
that the cros~tai! electric field is also highly unsteady. The dis-
covery of energetic ionospheric ions in the near-tai! and inner
magnetosphere forced a reevaluation of our ideas concerning the
origin and circulation of magnetospheric plasma. The 1982-1983
ISE~3 reconnaissance of the geotai} out to 150 Re provided sig-
nificant first-order information on tad! dynamics during quiescent
and substorm conditions.
Our understanding of many individual processes became more
quantitative. The coupling of magnetospheric motions and energy
fluxes to the thermosphere was observed and modeled. Currents
flowing along the Earth's magnetic field and connecting the polar
ionosphere to the magnetosphere were found to create strong lo-
calized electric fields at high altitudes. These fields may accelerate
the electrons responsible for intense terrestrial radio bursts and
OCR for page 11
11
A MAGNETOSPHERIC PHYSICS—RECENT ACCOMPLISHMENTS
ELECTR IC Fl ELDS
ACCELERATING
AURORAL PARTICLES
DISCOVERY OF ENERGETIC /
IONS OF IONOSPHERIC ORIGIN /~
IN MAGNETOSPHERE. '/ ~>
\N ~ / magnetopause
\\/~= ~
MOC)ELLING OF
THERMOSPHERIC ~
WINE) GENERATION / ~ X> shocked solar wind
UNSTEADY PLASMA FLOWS, So//
ELECTR IC F I E LDS AND '$~°n/ess ~
PARTICLE ACCELERATION IN °iVs~Ock
GEOMAGNETIC TAIL
E] MAGNETOSPHERIC PHYSICS—OBJECTIVES
What is Origin and Fate of
Magnetospheric Plasmas?
How Does Solar
Wind Couple to
Magnetosphere?
magne~opause
-
How Does Magnetosphere c /'
Couple with Atmosphere Sail _
and ionosphere? °~s,,Ock
C SIX CRITICAL REGIONS OF MAGNETOSPHERIC PHYSICS
AURORAL FIELD An'
ON THE LINES An'
GROUND /, ~
~ magnetopause
How is Energy Stored
and Released in
Magnetic Tail?
DEEP IN
SOLAR 'I=---- GEOMAGNETIC
W I ND (,~ ~ ~ TA t Is
/ ~ ~ ~ shocked solar wind
Ml DMAGNETOSPHE R E \ cO// ~
ECU ATO R I A L P LA N E \ °~/e`S O ~
IN THE POLAR Elk
UPPER ATMOSPHERE
FIGURE 2.2 MagDetospheric physics: status, objectives, and recommenda-
tions. Shown here is the Earth's magnetosphere—the cavity formed by the
interaction of the solar wind with the Earth's magnetic field. A collisionless
bow shock stands upstream of the magnetopause, the boundary separating
shocked solar wind from the magnetosphere proper. The Moon is 60 earth
radii from the Earth; the Earth's magnetic tail is thought to extend some
thousand earth radii downstream. (A) Some recent achievements in mag-
netospheric physics. (B) Objectives that can motivate research programs in
the 1980s and 1990~. (C) The six critical regions where simultaneous studies
are needed to help construct a global picture of magnetospheric dynamics.
OCR for page 12
12
aurora] arcs. Thus, the problem of auroral particle acceleration is
nearing quantitative understanding. By contrast, the relationship
between energy circulating in the magnetosphere, the energy dis-
sipated in the atmosphere, and the concurrent state of the solar
wind has not been unambiguously quantified even today.
To understand better the tune-dependent interaction between
the solar wind and Earth, we need to study (see Figure 2.2b) the
following:
The transport of energy, momentum, plasma, and magnetic
and electric fields across the magnetopause, through the magneto-
sphere and ionosphere, and into or out of the upper atmosphere.
The storage and release of energy in the Earth's magnetic
tail.
The origin and fate of the plasmats) within the magneto-
sphere.
~ How the Earth's magnetosphere, ionosphere, and atmo-
sphere interact.
UPPER ATMOSPHERIC PHYSICS
The upper atmosphere has traditionally been divided into the
stratosphere, mesosphere, thermosphere (and ionosphere), and
exosphere, in order of increasing altitude. Recent research makes
it clear that these layers and their chemistry, dynamics, and
transport are coupled (see Figure 2.3a). For example, downward
transport from the thermosphere can provide a source of nitrogen
compounds to the mesosphere and possibly to the upper stratm
sphere. The catalytic reactions of odd hydrogen, nitrogen, and
chlorine compounds destroy ozone, thereby altering the absorb
tion of solar ultraviolet radiation. Results from three Atmospheric
Explorers, which largely quantified the photochemistry of the ther-
mosphere and ionosphere, also illustrate the strength of the elec-
trodynam~c coupling of the thermosphere to the magnetosphere.
Finally, understanding how the upper "d lower atmospheres af-
fect each other will be necessary to complete the description of the
chain of solar-terrestrial interactions. This will require consider-
able improvement in our understanding of the chemistry, dynam-
ics, and radiation balance of the mesosphere and stratosphere, as
well as of troposphere-stratosphere exchange processes.
To understand better the entire upper atmosphere as one
OCR for page 13
13
A UPPER ATMOSPHERIC PHYSICS—RECENT ACCOMPLISHMENTS
IMPORTANCE OF
ELECTRODYNAM IC
COUPLI NG
GENERAL REALIZATION
OF IMPORTANT COUPLINGS
BETWEEN LAYERS AND
THEIR CHEMISTRY,
DYNAMICS AND TRANSPORT
B UPPER ATMOSPHERIC PHYSICS—OBJECTIVES
How Do Energetics, Chemistry,
and Dynamics Interact to
Establish the Structure and
Variability of the Middle
Atmosohere? "
C
sax - .
USA`
AL
ATMOSPHERE EXPLORERS
, ~ , ~ QUANTIFI~DTHERMOSPHERE
A-o~a PHOTOCHEMISTRY ABOVE
~ 130 km
_: ~
How Do Variable Photon
and Particle Fluxes
Affect the Thermosphere,
Mesosphere, and Stratosphere?
So. `*'a~
U~n~.c tl - 'C - S
~ ~ ~ ·~< '~ ~ ~ .
~/~ —~
Off;
UPPER ATMOSPHERIC PHYSICS—REQUIRED MEASUREMENTS
A SERIES OF SPACE OBSERVATIONS
mesosphere and stratosphere
SELECTED HIGH RESOLUTION
OBSERVATIONS FROM
FREE FLYERS, PLATFORMS,
AND sHIJTTl F
What Are the World-Wide
Effects of the
Magnetosphere's Interaction
with the Upper Atmosphere?
MONITOR SOLAR LUMINOSITY
< as AND SPECTRAL IRRADIANCE,
Ados !` LONG-WAVP RAD IAT ION, CH EM ICAL
COMPOSITION, DYNAMICS, AND
FNFR~.FTIC PARTICLE INPUT
/~ := ~ `~.~ ^
FIGURE 2.3 Upper atmospheric physics: status, objectives, and recommen-
dations. Sketched in these figures are the layers into which the atmosphere
has traditionally been divided. Our studies of these layers, and the in-
teracting processes occurring within them, are becoming more integrated.
Solar ultraviolet photons deposit their energy largely in the stratosphere
and above. The magnetosphere interacts with the upper atmosphere both
through energetic plasma deposition and through electric fields, which are
generated by magnetospheric motions. Plasma heating and electric fields
both couple to upper atmosphere wince.
OCR for page 14
14
dynamic, radiating, and chemically active fluid, we should study
(see Figure 2.3b) the following:
The radiant energy balance, chemistry, and dynamics of
the mesosphere and stratosphere and their interactions with at-
mospheric layers above and below.
.
The worldwide effects of the magnetosphere's interaction
with the polar thermosphere and mesosphere and the role of elec-
tric fields in the Earth's atmosphere and space environment.
~ The effects of variable photon and energetic particle fluxes
on the thermosphere and on chemically active minor constituents
of the mesosphere and stratosphere.
SO[AR-TERRESTRIAl COUPLING
Solar-terrestria] coupling is concerned with the interaction of
the Sun, the solar wind, and the Earth's magnetosphere, ions
sphere, and atmosphere, with particular emphasis on the response
of the system to solar variability. For example, a solar flare pros
duces both a strong solar wind shock that initiates a magnetic
storm when it passes over the magnetosphere and energetic pro-
tons that penetrate deep into the polar atmosphere. Studies of
such solar-terrestrial phenomena are of considerable practical im-
portance.
To understand better the effects of the solar cycle, solar ac-
tivity, and solar wind disturbances upon Earth, we need to do the
following:
models of these processes.
~ Provide, to the extent possible, simultaneous measure-
ments on many links in the chain of interactions coupling solar
perturbations to their terrestrial response.
Create and test increasingly comprehensive quantitative
Whereas 10 years ago it was generally believed that signifi-
cant effects of solar variability penetrate only as far as the upper
atmosphere, some scientists now believe that they also reach the
lower atmosphere and so affect weather and climate in ways not
yet completely understood. For example, it has recently been sug-
gested that the mean annual temperature in the north temperate
zone followed long-term variations of solar activity over the past
70 centuries.
OCR for page 15
15
To clarify the possible solar-terrestrial influence on Earth's
weather and climate, we need to do the following: ;
· Determine if variations in solar luminosity and spectral
irradiance sufficient to modify weather''and cInnate exist, and
understand the solar physics that controb these variations.
. Ascertain whether any processes involving solar and mag-
netospheric variability can cause measurable changes in the Earth's
lower atmosphere.
. Strengthen correlation studies of solar-terrestrial, climato-
logical, and meteorological data.
COMPARATIVE PLANETARY STUDIES
Comparative studies of the interaction of the solar wind with
planets and comets highlight the physics pertinent to each and
put solar-terrestrial interactions in a broader scientific context.
The solar system has a variety of magnetospheres sufficient to
make their comparative study fruitful. Because the planets and
their satellites have different masses, magnetic fields, rotation peri-
ods, surface properties, and atmospheric chemistry, dynamics, and
transport, comparative atmospheric and magnetospheric studies
can help us to understand these processes in general and possibly
to identify terrestrial processes that might otherwise be missed.
In the 1970s, Pioneer and Voyager spacecraft made flyby stud-
ies of Jupiter's atmosphere and magnetosphere, the largest and
most energetic in the solar system. Pioneer 11 and the Voyagers
encountered Saturn in 1979, 1980, and 1981. Mariner 10 flybys
discovered an unexpected, highly active magnetosphere at Mer-
cury. Pioneer Venus results suggest that the strong interaction
between the solar wind and the upper atmosphere of Venus plays
a significant role In the evolution of the atmosphere.
To understand better the interactions of the solar wind with
solar system bodies other than Earth, and from their diversity to
learn about astrophysical magnetospheres In general, we need to
do the following:
. Investigate in situ Mars's solar-wind interaction in order
to fill an important gap in comparative magnetospheric studies;
previous missions provided little such information.
· Make the first in situ measurements of the plasma, mag-
netic fields, and neutral gases near a comet.
OCR for page 16
16
~ Secrete our underst~dlog of rapidly rotating magneto
spheres Evolving strong stmospberic ~d sateDite interactions.
~ Determine the role of at~spberes in substor~ Id other
magnetospber~ processes by orbits studies ~ ~e~ury-tbe only
known m~ne~zed planet without ~ dyn~caDy d~c~t Tam
sphere.
Representative terms from entire chapter:
upper atmosphere
