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Produced by the NASA Center for Aerospace Information (CASI)
Semi-Annual Report

(For Period: April 1, 1983 - Sept 30, 1983)

1

f ^• n

_ 

75/3

PLASMA WAVE EXPERIMENT

FOR THE ISEF-3 MISSION

by

F. L. Scarf,

Principal Investigator

Prepared for

NASA Goddard Space Flight Center

Greenbelt, Maryland 20771

Contract No. NAS5-20682

9 November 1983

Bldg R-1, Rm 1176

Applied Technology Division

TRW Space and Technology Group

One Space Park

Redondo Beach, California 90278

(213) 536-2015

(.NASA-CR - 175132) PLASMA WAVE EXPERIMENT FOR N84 -15972

THE ISEE-3 MISSION Semiannual Report, 1

Apr. — 30 Sep. 1983 (TRW Space Techrolog,y

Labs.) 26 p HC A03/MF A01 CSCL 20I Unclas

G3/75 11303
APOfad Tiehnoloo^ One Space Park

Dinicion Redoudo Beach, CA 90278

TRW Space & Technology 213 535 4321

Group

TRW 23499.000

P241- 93-10664

10 November 1983

> TRW CONTRACTS - DATA TRANSMITTAL COVER SHEET

F

CONTRACT NO. NAS5-20682 - SEMI-ANNUAL REPORT, NO.

TITLE: PLASMA WAVE EXPERIMENT FOR THE ISEE-3 MISSION

DATE: 1 April thru 30 September 1983

c

COPIES ADDRESSEE

1 D. M. Burel, Code 286 (Contracting Officer

- 2 R. gales, Code 602 (Technical Officer)

1 Publications Branch, Code 253.1 4*w4K

1 Patent Counsel, Code 204

Letter AFPRO/TRW

ISEE Financial Analyst, Code 266

TRW INC.

SPACE & TECHNOLOGY GROUP

r ,^

D. M. Prescott

Contract Administrator

Applied Technology Division

Telephone: 213/536-3837

Mail Station: 01/1050

cc: F. L. Scarf, TRW Program Manager

} TRW Inc 
OF POOR QUALM t

I

TECHNICAL REMIT 1TANDARD TITLE PACE

ep•rt !h, 2.6•vrnnr•nf Accession file. 3, Recipieet's Catalog N•.

23499-6033-UT .CO

t ♦

and litiflo epeM ti

PLASMA WAVE EXPERIMENT FOR THE ISEE-3 MISSION 9 November 1983

6, h►firrn Code

^, Awfrar(ei 1. Performing argenirefi•n Ignri No

Frederick L. Scarf

1. Perforrninip Drgenitetien Name end Addreee 10, WeA Ueh lie.

Bldg R-1, Rm 1176

11, Contract •r grant me, TRW Space and Technology Group'

One Space Park NAS5-20682

17. Type of R•prt end Porled Covered

Semi-Annual Report

Rpdondo Roach, California 90279

12, Wrisoring Agency 049me end Address

4/1/83 - 9/30/83

4 5pons•ting Agency CoOt

1S, • ry Notes

L. Abstract

The objectio of this contract is to provide analysis of data from

a scientific instrument designed to study solar wind and plasma wave j

phenomena on the ISEE-3 Mission.

this report is the 7th Semi-Annual Report, submitted in compliance

with Modification 19 to Article XXI of Contract NAS5-20682, entitled, f

"Plasma Wave Experiment for ISEE-C (Heliocentric) flission dated

20 November 1974.

The purpose of this report is to summarize the performance of work

on the data analysis phase of the contract daring the period ca ,encin

1 April 1983 and ending 30 September 1983.

17. Key Yards (Selected h Auther(a)) 11, Distribution Statement

N. seewity Clessif, (of this ?pert) 20. Security Ciotti#, (•f this pelt) 21, Me. *fr*eps 22. Price*

Unclassified Unclassifiei 1 188

•For sale ►y the Clearioghouse for Federal Scientific and Technical Inf^rrarion, Sprinsfield, Vir/inii 22151.
1

PREFACE

1. OBJECTIVE

The purpose of this report is to summarize the performance of work

for the period 1 April 1983 through 30 Sept 1983, in compliance with

Modification 19 to Article XXI of Contract NAS5-20682, entitled "Plasma

Wave Experiment for ISEE-C (Heliocentric) Mission" dated 20 November 1974.

The objective of this contract is to provide analysis of data from

a scientific instrument designed to study solar wind and plasma wave phenomena

on the ISEE-3 Mission.

2. SCOPE OF WORK

Project activities during this past six months have included successful

return of data from the instrument, continuing analysis of all data, publication

of results, and deposit in National Space Science Data Center of the data.

3. CONCLUSIONS

Not applicable.

4. SUMMARY OF RECOMMENDATIONS

Not applicable.
1.d I)VTRODUCTION

The purpose of this report is to summarize the various activities

and tasks accomplished on the data analysis phase of the contract during the

last six months.

2.0 WORK ACTIVITIES FOR THE SIX-MONTH PERIOD

2.1 Research

During the past six months, several papers have appeared in print,

new manuscripts have been completed and submitted for publication, and

intensive research on the ISEE-3 tail Measurements has started. In the

previous report (Oct 1, 82-Mar 30, 83) we described several pending

publications. The paper "Science Return from ISEE-3 Comet Giacobini-linner"

appeared in Cometary Exploration, Vol 2 (p.225). The paper "The Interplanetary

Shock Event of November 11112 1978-- A Comprehensive Test of Acceleration

Theory" appeared in Proceedings of the 18th International Cosmic Ray Conference

(p, 131). The paper "Plasma Boundaries and Shocks" appeared in Reviews of

Geophysics (21,449, 1983). The paper "Transfer of pulsation-related wave

activity across the magnetopause" appeared in Geophysical Research Letters (10,

659, 1983).

The new papers completed during this period include "Plasma Waves in Space"

by F. Scarf and "On the Relationship Between Collisionless Shock Structure and

Energetic Particle Acceleration" by C. Kennel (to be published in the Porceedings

of the Spring College on Radiation in Plasmas, International Centre for Theoretical

Physics), and "The Structure of Oblique Laminar Bow Shocks: ISEE 1 and 2" (submitte

to J. Geophysics Research) by M. Mellott and E. Greenstadt. Copies of these papers

are attached,

During this period, Dr. Kennel and his co-authors worked to restructure the

paper formerly entitled "Plasma and Energetic Particle Structure of a Collisionless

Quasi-Parallel Shock". This paper is being rewritten in several parts. Another

work that is underway is "Report of Working Group 10 on Collisionless Shock Waves

in the Solar Terrestrial Environment" (Greenstadt et al) prepared for the SolarTerrestrial Physics Workshop. Finally, Scarf, Coroniti and Gurnett are now

now writing papers on the new ISEE-3 tail data.
.' TRW Tech. Report No. 40789-6004-UT-00

PLASMA WAVES IN SPACE*

F. L. Scarf

Bldg R-1, Rm 1176

TRW Space and Technology Group

One Space Park

Redondo Beach, California 90278

USA

June 1983

*Invited lecture, Spring College on Radiation in Plasmas,

International Centre for Theoretical Physics, Trieste, Italy,

F 24 May - 17 June, 1983 (to be published in the Proceedings).

t
PLASMA WAVES IN SPACE

F. L. Scarf

TRW Space and Technology Group, Bldg R-1, Rm 1176, One Space Park,

Redondo Beach, rilifornia 90278, USA

ABSTRACT

During the first ten years of space exploration, spacecraft were

generally instrumented to measure properties of the local magnetic

field and characteristics of energetic particles, but during the

last fifteen years, plasma ph,lsics investigations have assumed

dominant roles in many space programs. Sensitive, high-resolution

plasma probes for analysis of the distribution functions and plasma

wave instruments for measurements of electromagnetic and electrostatic

wave modes are commonly flowp together to provide information on

plasma instabilities and wave-particle interactions. Spacecraft with

plasma physics payloads have now explored the magnetospheres of Earth,

Jupiter, and Saturn; the plasma environment of Venus; and the very-low

dens i ty interplanetary medium from within the orbit of Mercury to well

beyond Saturn's orbit. During the next few years, it will also be

possible to study at close range plasma waves W ^.izve-particle interactions that develop rear Uranus, Neptune, Comet GiacobinimZinner,

and Comet Halley.

These measurements of solar system plasma processes are of great

importance because they provide the only opportunity to acquire

in situ data that can be used to test theories developed to explain

ii't-r—opTysical observations. The measurements generally involve

parameter ranges that are not accessible in laboratory experiments,

and so the space plasma physics programs also serve to extend and

validate concepts developed in the laboratory. However, the

discipline of space plasma physics has some unique problems. For

instance, when local measurements are made from a small platform

that moves within the plasma, it is sometimes 4ifficult to separate

space and time variations, it is sometimes difficult to distinguish

spacecraft interference tones from ambient plasma waves, and it is

generally difficult to estimate the wavelengths of the plasma

oscillations with certainty. In some areas, however, space plasma

physics measurements have natural advantages. For instance, wall

effects are not important except at the surfaces of the spacecraft.

Plasma physics measurements in space are also unique because, here,

the plasma probes are able to measure fine details of the distribution function that are needed to understand how the observed waves

are generated. Finally, since many plasma waves in space have

characteristic frequencies that occur in the audio range, it is

possible to listen directly to the measurements of wave activity

in space plasmas.

1. Introduction

At the beginning of the space age, mission planners tacitly made

the assumption that th2 region above the ionosphere is a near-vacuum,

populated only by energetic particles trapped in the earth ' s magnetic
4~

field. In the early 60's, the confirmation of the existence of a

streaming solar wind showed that the region of influence of the

terrestrial magnetic field had to be finite, and the first series

of spacecraft to explore the earth's outer magnetosphere therefore

carried solar wind plasma probes, as well as instruments to measure

characteristics of the magnetic field and the energetic particles

trapped in the radiation belts. However, these missions continued

to ignore the possibility that plasma physics phenomena are of

importance within the magnetosphere.

Subsequent developments conclusively demonstrated the need to

start making direct measurements of microscopic plasma processes in

space. The strong dissipation and particle acceleration associated

with the collisionless bow shock surrounding the magnetosphere clearly

could not be explained without invoking localized plasma instabilities

and wave-particle interactions,. In addition, detailed theoretical

analysis showed that the electrons in the earth's radiation belts

have characteristics consistent witi, operation of a gyroresonant

plasma instability driven by thermal anisotropies. These advances

in the mid-60's convinced mission planners in several space agencies

of the need to include sensitive plasma probes and plasma wave instruments in the payloads of spacecraft traversing the terrestrial magnetosphere; somewhat later, plasma physics instruments were also routinely

placed on planetary missions.

These spacecraft measurements of plasma processes were designed

to provide basic physical understanding of local phenomena (in the

magnetospheres of Earth, Jupiter, and Saturn; the plasma environment

of Venus; and the interplanetary medium), and in all of the spatial

regior;s explored to date, very important interaction phenomena have

been detected. Specifically, it has been discovered that the collisionless plasmas in space generally have non-Maxwellian distribution

functions, with characteristics that strongly affect the growth of

plasma waves. The detailed measurements of local particle characteristics show that many mechanisms operate to produce a complex variety

of non-equilibrium plasma distributions in the earth's ionized

environment. Within the magnetosphere thermal anisotropies with

Tl q T Oevelop because of: (a) inward plasma diffusion and convection with conservation of u; (b) cyclotron and betatron acceleration
effects; and (c) selective pitch angle scattering into the loss cone.

The observed magnetospheric distributions with T > T are probably II 1

s

associated with inward motion and conservation of the longitudinal

action invariant, while similar distributions in the solar Mind are

thought to be connected with conservation of u, as the interplanetary

field strength in the expanding plasma, continuously declines. Other

thermal anisotropies that are significant with respect to plasma

instabilities involve heat flux and higher order moments, and these

perturbations can be associated with parallel electric fields,

Y currents, particle beams, and heat conduction.

c It has also become clear in recent years that the natural plasmas

are locally non-Maxwell'ian in the sense that there are significant

peaks and dips yin the energy distributions. These fluctuations arise

because: (a) the solar wind and the ionosphere are more or less

independent sources of warm and cool magnetospheric plasma; (b) varying gradient drifts selectively remove trapped particles in restricted

energy ranges from the magnetosphere and they leave residual quasitrapped distributions with deep flux ripples; (c) collisionless

acceleration processes apparently provide enhanced fluxes at certain

energies; and (d) resistive dissipation and heat conduction (and perhaps runaway) contribute to the observed non-thermal tail populations.

The original fairly narrow application of the two-stream instability has also been greatly generalized in recent years. Suprathermal

flows are commonly detected within the magnetosphere (i.e., in the

polar cusp and in the tail during large substprm events), and it is

known that the equivalent electron-proton drift speed in the solar

wind and magnetosheath has a significant contribution associated with

electron heat conduction. Current-driven instabilities are found to

be important at field-merging regions in the magnetosheath, as well

as the bow shock, and the field-aligned currents associated with

pressure gradients in the magnetosphere, the cusp boundary, and the

high latitude ionosphere can involve streaming instabilities.

These solar system measurements of plasma distributions and waveparticle interactions have also proven to be of grist value in terms

of general plasma physics. In essence, the space observations provide
e bCCU 

Of

F

the only way to gain direct information on the characteristics of

plasma processes that are commonly invoked by theoreticians who

offer explanations of astrophysical measurements. In addition, the

space observations are of great importance because they allow the

plasma and wave investigations to bsa conducted with unique and

important advantages. The measurements are made from small platforms

that move freely within the plasma, and the particle analyzers can

measure the distribution functions with very high resolution in

velocity, angle, ion mass, etc., while the wave investigators can

utilize electric antennas having sale sizes small canNared to Debye

lengths. Since the space measurements also generally involve parameter ranges that are not accessible in the laboratory, these programs

provide important information for all plasma physicists.

In this review, we focus attention on (a) electrostatic instabilities associated with currents, drifts and particle beams, and (b)

electromagnetic instabilities associated with thermal anisotropies.

Extensive measurements of wave-particle interactions have now been

made in the magnetospheres of Earth, Jupiter, and Saturn (Figure 1

shows the relative sizes of these three magnetospheres), in the solar

wind from within 0.4 AU (Helios) to beyond 15 AU (Voyager), and in the

plasma interaction regions surrounding Venus (Pioneer Venus Orbiter)

SHOCK MA TOPAUSE

s

WAN

 ^.

am « c31n

^-- 3 M 108 km --^

EARTH JUPITER SATURN

Figure 1. This scale drawing shows how the nominal sizes of the

Earth, Jupiter, and Saturn magnetospheres compare with

each other and with the solar disk. Only the sunward

sections of the magnetospheres are depicted, but the

magnetic tails extend very far downstream;, instruments

on Voyager 2 detected the Jovian tail more than 630

million kiolmeters behind the planet, demonstrating that

the tail actuAlly extends beyond the orbit of Saturn.
and Titan (Voyager); we use data from many of these locations to

illustrate advances derived from observations of space plasma physics

processes.

2. Instabilities Associated with Currents, Drifts, and Beams

From a plasma physics viewpoint, space measuremen U of strong

wave-particle interactions associated with current-driven instabilities are particularly valuable because the significant interactions

are highly localized, and the scale lengths are extremely small;

magnetic structures and dissipation lengths are on the order of

c/fp+ , c/fp- (c is the speed of light, and fp-, fp+ are the electron

and ion plasma frequencies) * and wavelengths as small as 2wAD (AD is

the Debye length) play important roles in providing dissipation.l)

These small scale sizes can, how.w;ver, be readily studied from spacecraft, since the spacecraft (z meters) is very small in comparison

with the shock scale sizes (hundreds of meters to kilometers).

The most extensive measurements in space tare related to studies

of the collisionless bow shock in front of the Earth, and Figure 2

shows some characteristic plasma wave phenomena detected on October

18 9 1982, when ISEE-3 crossed the shock surface on its way to start

the initial exploration of the Earth's distant magnetic tail. The

figure shows the total magnetic field (bottom panel), the magnetic

field wave levels in six bandpass channels covering the range 18 Hz

to 311 Hz (center panel), and the electric field wave levels in sixteen channels covering the range 18 Hz to.100 kHz (top panel). The

shock Jump (near 0600) is associated with a peak in the turbulence

levels for the E and B components of the plasma waves, but it can be

seen that significantly enhanced wave levels persist throughout the

downstream magnetosheath. Figure 2 also shows presursor wave activity

in the upstream region (the foreshock), and we identify 31 kHz emissions as electron plasma oscillations. The broadbanded mid-frequency

(311 Hz to 5.6 kHz) electric field bursts detected between 0200 and

'0400 are thought to be short-wavelength Doppler-shifted ion acoustic

waves generated by supersonic ions streaming back from the bow shock.

These signals are very impulsive, and Figure 2 shows that the peakto-average ratio is very large (for each channel in Figure 2, the

vertical scale corresponds to an amplitude range of 4} orders of
OF

G

 

Norj^

..^ QuRtl7"1►

ISEE-3 OCTOBER 18, 1982

EAK

VERAGE

100kHz

56

31

18

10

5,6

3.1

1.8

1.0

562 Hz

311

178

E 100

56

31

18

311H2

178

100

B 56

31

18

20-

B, 7

10

0

1^ 1

ptI"" l

BOW SHOCK

0400 0800 1200 1600 UT

Figure 2. Magnetic field profile (bottom panel) and B and E wave

levels (upper panels) measured on October 18, 1982, when

ISEE-3 crossed the Earth's bow shock. This figure shows

the full range of shock-associated phenomena, including

enhanced wave levels within the narrow shock layer (near

0600), upstream electron plasma oscillations and ion

acoustic waves, as well as high turbulence levels in the

downstream region (magnetosheath).

- 4 e
magnitude).

The tow-frequency electromagnetic waves detected at the shock and

in the magnetosheath are readily identified as right-hand polarized

whistler mode signals. In these regions, the higher-frequency E-field

waves are again customarily identified as ion acoustic oscillations,

and this suggests thLt the turbulence peak at the shock Jump is

associated with an ion sound instability driven by the currents that

produce the AB/AX. The resulting anomalous resistivity can then, in

principle, account for the shock dissipation.2)

Although this general concept of the microstructure for a thin

collisionless (laminar) shock was put forth at an early stage,

detailed investigations of shock processes have continued to occupy

the forefront of space plasma physics for more than a decade. The

right-hand drawing in Figure 3 contains a sketch that is now thought

to represent a "snapshot" of the solar wind-magnetosphere interface

region. For a fixed field orientation, the thin quasi-perpendicular

shock develops on one side of the magnetosphere, while the other side

has thirk quasi-parallel shock structures, with an extensive foreshock

re9 0 ,: 11Ja t contains suprathermal electrons and ions and enhanced wave

lervs. This picture was originally constructed using single-point

measurements from isolated spacecraft, together with occasional data

from multiple spacecraft in the same general region. However, a longstanding problem of great importance involved determination of the

shock speed with respect to the spacecraft, so that the actual thickness of the shock layer (and the current) could be evaluated. The

left-hand side of Figure 3 shows how the problem was recently solved

using two spacecraft in nearly the same orbit; ISEE I and 2 measurements, such as those plotted here, provided information that allowed

space and time variations to be distinguished, so that AB/AX could be

evaluated with confidence.3)

In recent years, the measurements of plasma physics phenomena

have been extended to Venus, Jupiter, and Saturn, and Figure 4 contains characteristic bow-shock turbulence spectra detected on Pioneer

Venus, IMP-6, and Voyager I and 2. In order to allow spectral shifts

to be assessed with respect to the changes in plasma characteristics,

the average values for the electron and proton plasma frequencies ( fpe, fpi ), the electron cyclotron frequency (f Ce ), and the Buneman 4)
77,000

76,000

II, km

75,000

74,900

«0

191

S, Somme 40

20

0

60 ISEE 1

s, Sammy 40

20 y^^

ORIGINAL PAGE 13

OF POOR QUALITY

ISEE Z

SMOCK TRAJECTORY

ISEE i

IEEE

0 "

OP46 0248 UT 0250 , OCT. 27, 1977

Figure 3. Right side: Conceptual snapshot of the interface between

the streaming solar wind and the terrestrial magnetosphere.

For any fixed B-field orientation, it is expected that

thick quasi-parallel shocks will develop in some regions,

while thin quasi-perpendicular shocks will be present in

other locations.

Left side: Simultaneous measurements from the ISEE 1 and 2

spacecraft allow space and time variations to be distinguished.

i

frequency (f B = [me /mi ]'fpe ), 0.7 9 1.0, 5.0, and 9.2 AU, are shown

at the tops of the individual panels. These measurements suggest very

significant changes in spectral shape with changing heliocentric distances. Scarf, Gurnett, and Kurth S) attribued the variatio^is to'

changes in the average Mach number from the range of 5-6 (mean Alfven

Mach r:umber for Earth, Venus) to the range 11-21 (Jupiter and Saturn).
ORIGINAL PAG1 1.-,

OF POOR QUA67Y

10'5

10.11

.

., 10.10

N

10'12

V'10.11

10.16

10.1eL

10 103 105 101

EARTH

IMP-6

105

101

103

FREQUENCY (HERTZ)

VENUS

PIONEER ORBITER

1 101103 105

Figure 4. Comparison of bow-shock plasma wave spectra measured

at Saturn, Jupiter, Earth, and Venus.

These results are of interest because they suggest that in situ studies in the distant solar system provide direct information on supercritical shock phenomena.

Multi-planet observations also provide very significant informa-

+fi tion on the variable nature of post-shock plasma conditions. At

Earth, it is known that the magnetosheath is characterized by enhanced

turbulence (see Figure 1), and these measurements form the basis for

certain astrophysical theories of shock-induced particle acceleration

involving wave-particle interactions in the pre-shock and the postshock regions. At Venus, the downstream sheath region is found to be

even more turbulent than at Earth. In fact, Figure 5 shows that in a

related situation, where Titan's exosphere-ionosphere interacts with

the corotating plasma of Saturn's magnetosphere, very intense turbulence levels were detected, although the Mach number was so love that

only a slow-mode shock might have developed.6)

Since the post-shock turbulence levels at Venus, Earth, and Titan

were found to be so high, one could assume that this result is universally true. However, the Voyager 1 and 2 measurements in the magnetosheath regions of Jupiter and Saturn revealed extremely low turbulence levels for f x 10 Hz. It is possible that with those high Mach

number shocks, strong downstream wave activity occurs only for

f << fCe [Prognoz 8 measurements show enhanced wave levels at the

lower hybrid resonance (f = f Ce/43) during crossings of the terres.` 5 • Y' OR^O 01Rp,1,1"C1^

OF

DA( 317 NOVEMBER 12, 1980

POSSIBLE

SLOW MODE

SHOCK

562

31,1

17.8

IQO

5.62

3.1 I

1.78

1.00

.562

.311

.178

.100

.056

x031

.018

.010

+ g 6

v

6 T

1 1

-sRT

^ 1 1

MI N M2

6 i 1I

4 1L

i 2

' LI i

0

0330 0510 0550

.3

.5

-5

-5

-5

— U H R EMISSIONS '•5

-5

ar

-5

-5

W SHEATH

.52

-5

-5

.5

LOBE

-5

.5

.5

Figure 5. Magnetic field and plasma wave measurements obtainer! as

Voyager 1 passed behind Titan. The high-frequency wave

observations yield the electron density profile, and the

B-field data show the locations of the magnetotail boundaries

(M1 , M2 ) and the neutral sheet (N), between the two tail

lobes (L I , 1. 2 ). The very intense low-frequency waves are

interpreted as ion acoustic oscillations in the sheath and

plasma sheet.
trial bow shock; such electrostatic waves. presumably associated with

the lower hybrid drift instability, could not gave been detected on

Voyager]. It is also possible that post-shock flow can be extremely

quiescent for some ranges of astrophysical plasma parameters; if

this is true, it may be necessary to search for acceleration mechanisms that do not depend on the presence of strong wave-particle

interactions downstream from collisionless shocks.

Bow-shock phenomena illustrate the diverse range of plasma waves

associated with instabilities driven by currents, plasma beams, suprathermal particles, and heat conduction. However, these instabilities

are not uniquely associated with the solar wind-magnetosphere interface region. Field-aligned currents are also of considerable importance within the magnetosphere, and the OGO-5 investigators first

described the detection of strong electrostatic turbulence together

with field-aligned currents in the polar cusp and on the plasma sheet

boundary.)

The plasma turbulence associated with current-driven instabilities

produces changes in the distribution functions, and the process can

be described in terms of an anomalous or turbulent resistivity. As

discussed by several authors, the effective collision frequency, "eff'

is approximately given by 2)

v

eff ' 327rT fpe (E0

E 2

/2NKTe ) 1

(1)

and, in principle, the anomalous resistivity can be evaluated directly

by measuring the local plasma wave turbulence amplitude and the electron moments. For instance, for a typical terrestrial bow shock, ueff

turns out to be approximately 30-60 collisions per second using

Equation (1) with Te = 2 x 10 50 K. and the anomalous conductivity,

o - Ne2/m veff, can account for the shock dissipation.

Fredricks et al. 

7) first used we a and particle measurements from

OGO-5 to argue that during storms anomalous resistivity near the

boundaries of the earth's polar cusp allows large-scale parallel

electric fields to develop. Other aspects of the high-latitude

measurements are consistent with an anomalous resistivity interpreta-

'tion. In the cusp region, electron spectral plots show a depletion

in low-energy population and appearance of suprathermal particles as

the spacecraft encounters the current system and its associated

turbulence; these changes could be explained by resistive heating
}

R i

associated with the wave particle interactions. It is noteworthy

that field-aligned currents and related electrostatic turbulence are

also frequently detected above the Venus ionosphere (see Figure 6).

This suggests that even in the absence of a permanent planetary magnetic field, microscopic plasma processes that yield anomalous resistivity readily develop; in all of these cases, the dynamical processes

cannot be well described in terms of conventional mhd fluid theories,

and the plasma physics phenomena &ctually control the large-scale

configuration changes, as well as the local particle distribution

functions.

3. Gyroresonant Interactions

The original concept that electromagnetic whistler mode turbulence

leads to precipitation of radiation belt particles was developed into

a self-consistent theory by Kennel and Petschek 8) ; this was based on

use of a natural gyroresonance instability mechanism for the wave

growth (amplification associated with trapped particle T > T i , pitchangle distributions) and the concept of turbulent pitch-angle diffusion arising from the local wave-particle interactions. The Kennel

and Petschek 8) theory predicted stable trapping limits and precipitation patterns that agreed well with terrestrial observations, and

this pioneering effort has since stimulated an enormous amount of

more detailed analytical activity; improved self-consistent theories

for electron whistler and ion cyclotron mode turbulence were developed,

these ideas were applied to analyze lightning whistler amplification

processes, numerical simulation studies were performed, and the basic

concepts were used in attempts to explain localized plasmapause phenomena as varied as ring current decay, SAR arc formation, and the

development of an energetic electron "slot."

For relativistic electrons, the interaction can be well described

in terms of whistler mode waves that propagate parallel to the B-field,

with an index of refraction (n) given by

f 2

C
-4

-6

-4

-6

ORIGINAL- PI^G

? TY OF POOR QUAI-1

The waves resonate with electrons having

v Cfes fc

(3)

-4

-6

LOG 10 E,

V/m(Hz)1 /2

-4

-6

Bx

0

-40

B

40

Y 0

-40

BZ 40 .. ..

0

-40

BT 40 .. .......... . ..... , ..

0

Time (UT) 0151 0154 0157

Alt (km) 1872 1284 1005

Figure 6. Field-aligned currents and intense electrostatic turbulence

detected on August 24, 1981, as the Pioneer Venus Orbiter

was inbound on the night side of the planet.
ORIGINAL PAQIw f t

•.. OF POOR QUALITY

and the resultant diffusion coefficient, 

Da., 

is 

c

Recently, this theory has also been applied to explain radiation

belt observations at Jupiter. Figure 7 shows how Voyager detected

electromagnetic chorus emissions together with a low-frequency hiss

band as the spacecraft moved through the high-density to plasma torus.

Scarf et al. 

9) and Thorne and Tsurutani 10) 

demonstrated that the measured whistler mode turbulence would produce significant tosses of

radiation belt electrons. Subsequently, Coroniti et al." )identified

a Jovian chorus structure, and they showed that these waves precipitate

12

i

 *4 81

I (kHz) 6

j

3

1 i .e a l l __

0 — loll

0620:36

1 keV

IE-- 5 keV

1-10 keV ELECTRON

ENERGY

50 keV

100 keV

I— I WV

0621 :24

10 L-SHELL 

0912

MAGNETIC

; ;1 i;i;.;i;ii;;ii:iiiE. EQUATOR ii!= 

_ _ 0620

'ii;iiii?Ej. ,?^ r: ,,•.^,;i:•s'ii^i^i=i=i is

10 PLASMA VOYAGER-1

TORUS MARCH 5, 1979

Figure 7. Frequency-time diagram showing chorus and hiss detected as

Voyager crossed Jupiter's magnetic equator and entered the

to plasma torus. The resonant electron energies shown on

the right side are derived using Equations (2) and (3).
/ 1 

into the atmosphere about 6 ergs/cm2 sec of electrons with energies on

` the order of a few keV. Thus, it has been established that at Jupiter

pitch-angle diffusion and precipitation associated with whistler mode

wave-particle interactions are dynamically important. Chorus was also

detected at Saturn, but here the electron fluxes are very low in comparison with the stable trapping limit, and the whistler mode waveparticle interactions have a negligible effect.

The low-frequency hiss band in Figure 7 was originally interpreted

in terms of electromagnetic whistler mode turbulence, and Equations (2)

and (3) show that such waves would resonate with very energetic electrons. Recently, other interpretations have been considered, and it

has been conjectured that these Jovian waves are ion cyclotron modes

or even lower hybrid resonance emissions.

Even at Earth, a very significant uncharted area involves ion

wave modes and ring current loss mechanisms. Near the terrestrial

plasmapause, the local phenomenology of the electromagnetic ioi cyclotron instability is unclear, and knowledge about heavy ion electromagnetic modes and positive ion electrostatic modes near the equator is

fragmentary (GEOS wave measurements are providing very significant

information from one location). The losses of 1 . 100 keV ions are not

well understood, although it appears that auroral protons are on strong

diffusion. In future programs, we expect that sensitive equatorial

wave measurements will be combined with comprehensive local measurements of particle distribution functions and with simultaneous coordinated information from other spacecraft to yield definitive information about ring current formation and decay processes, the origins of

SAR arcs and the proton aurora, the variations with storm effects, and

the role of the cold dense plasmasphere in modulating these processes.

4. Electrostatic Cyclotron Harmonics

At Earth, some of the most intense waves with frequencies related

to the local electron gyrofrequency, fCe , are the (n + 1/2) fCe emissions first discussed by Kennel et al. 12) Several analyses suggested

that these strong emissions (which very frequently have amplitudes as

high as 10 millivolts/meter) are substorm related, and Gurnett and

Shaw 13) verified that the modes are electrostatic. The most common
R(RS)

15

10

5

0

VOYAGER-2 AUGUST 25-26,1981 LATITUDE

--, 30°

0

-30°

-3

-6

-6

-6

-6

-6

-6

-6

-6

-6

1600

r

^E

W

0

0O

o¢h uA►

.rrt.

' OF POQR observation of this mode is at f r 3 fCe/2. These waves were also

readily detected at Jupiter and at Saturn. Figure 8 contains Voyager

2 observations centered about the Saturn magnetic equator/ring plane

crossing, and the drawing clearly shows intense 3 f Ce/2 waves, along

with upper hybrid resonance emissions.

A definitive analysis of the effects of (n + 1/2) f Ce emissions

on terrestrial magnetospheric particle distributions was carried out

by Lyons, 14) who demonstrated that a turbulence amplitude of 1-10 mV/m

is sufficient to put electrons with energies of several kilovolts in

strong diffusion. Lyons' calculations also verified that 100 mV/m

waves would indeed lead to strong diffusion for 100 keV electrons, and

showed that some detailed low-altitude (rocket) measurements of 1-20

keV electron energy spectra in the loss cone can be very well explained

on the assumption that moderate amplitude (a few mV/m) 3 fCe /2 waves

produce strong diffusion near the equator. It now seems certain that

at Earth the (n + 1/2) fCe modes play a very important role in provid56.2

= 31.1

17.8

10.0

z 5.62

3.11

0 1.78

1.00

0.56

1600 2000 0000 \ 0400 0800 1200

CHORUS AND HISS

Figure 8. Electromagnetic and electrostatic waves detected in the

inner magnetosphere of Saturn, as Voyager 2 crossed the

ring plane and magnetic equator.

w^
A s ing the source of high-latitude electron precipitation fluxes, especially during geomagnetically active periods.

Several theories for the origin of the (n + 112) f Ce waves have

been proposed. The waves commonly grow in regions where cold and hot

particles are both present, but Gurnett and Frank 

15) 

reported that the

emissions appear to be quenched whenever the density of vevy low energy

thermal plasma exceeds a small fraction (on the order of 5 percent) of

the suprathermal plasma density. This suggests that the generation

mechanism for these modes involves a hump in the energy distribution

as well as a thermal anisotropy. Recently, Kurth et al. 16) 

showed that

intense electrostatic wave activity involving both the (n + 112) modes

and the upper hybrid resonance is associated with a positive slope in

the perpendicular distribution (i.e., for v perpendicular to B). They

suggested that strong electrostatic waves can be generated by a wide

variety of distribution functions which have a source of free energy

and a considerable population of cold electrons. The convective

properties of the waves result in large spatial growth rates or a nor,-

convective instability. The waves could heat the cold electrons forming the basis of a nonlinear saturation mechanism. Kurth et al. 16)

also noted that anisotropy in the cold electron distribution might

actually provide the free energy for the instability.

Magnetospheric measurements of intense electrostatic upper hybrid

and (n + 112) fCe emissions are of great interest because it appears

that some non-linear process allows electromagnetic waves to be generated in those regions where f(UHR) = (n + 1/2) f Ce . Thus, the in situ

study of these waves and the wave-wave interactions provide unique information on phenomena related to the origin of radio emissions from a

magnetized plasma.

5. Discussion

The preceding sections contain brief descriptions of some of the

most prominent types of plasma instabilities and wave-particle interactions that have been studied in space. It should be clear that the

space environment provides a very important laboratory for the study of

general plasma physics. It should also be apparent that only the

strongest and most obvious interactions have been analyzed carefully

It
to date. In particular, the study of ion cyclotron plasma waves is

quite incomplete, although recent measurements of magnetospheric ions

show complex compositions (hydrogen, helium, and oxygen ions at Earth

and Venus; hydrogen, sulphur, and oxygen at Jupiter; possibly nitrogen

at Saturn; etc.). Thus, there are many cyclotron and hybrid resonances

at very low frequencies, and high resolution wave measurements in this

spectral region are needed.

The highest resolution wave data from spacm are transmitted to

Earth using wideband amplifiers, and since most ff the characteristic

frequencies are in the audio band, it is possible to listen directly

to these measurements, so that the plasma wave inilruments act as

"robot ears." The audio link is also frequently e, ,tt.reme`iy useful as

a scientific tool. Some of the signals that have bean identified with

certainty only by listening to the sounds include lightning whistlers

(Earth and Jupiter), chorus (Earth, Jupiter, and Saturn), dust impacts

(Saturn), and various interference tones.

Acknowledgments

The research described here has been supported in part by NASA

Headquarters (NASW-3690 and NASW-3504), the Voyager Project at the Jet

Propulsion Laboratory (954012), the ISEE Project at Goddard Space

Flight Center (NAS5-20682), and the Pioneer Venus Project at Ames

Research Center (NAS2-9482).

References

1) Fredricks, R. W., G. M. Crook, C. F. Kennel, I. M. Green, F. L.

Scarf, P. J. Coleman, and C. T. Russell, J. Geophys. Res., 75,

3751, 1970.

Rodriguez, P., and D. A. Gurnett, J. Geophys. Res., 80, 19, 1975.

Morse, D. L., and E. W. Greenstadt, J. Geophys. Res., 81, 1791,

1976.

2) Kadonitsev, B. B., Plasma Turbulence, Acad. Press, London, N.Y.,

1965.

Sagdeev, R. Z., Proc. Symp. Applied Math, 18, 281, 1967.

Biskamp, D., Nucl. Fusion, 13, 719, 1973.

Papadopoulos, K., and T. Coffey, J. Geophys. Res., 79, 1558, 1974.

3) Russell, C. T., and E. W. Greenstadt, Space Science Reviews, 23, 3,

D. Reidel Pub. Co., Dordrecht, Holland, 1979.

i
t .

t

Greenstadt, E. W., C. T. Russell, J. T. Gosling, S. J. Bame,

G. Paschmann, G. K. Parks, K. A. Anderson, F. L. Scarf, R. R.

Anderson, D. A. Gurnett, R. P. Lin, C. S. Lin, and H. Reme,

J. Geophys. Res., 85, 2124 0 1980.

4) Buneman, 0., Phys. Rev. Lett., L. 8, 1958.

5) Scarf, F. L., D. A. Gurnett, and W. S. Kurth, Nature, 292, 747,

1981.

See also:

Gurnett, D. A., W. S. Kurth, and F, L. Scarf, Science, 212, 235,

1981.

Scarfs F. L., D. A. Gurnett, and W. S. Kurth, Science, 204, 9919

1979.

Scarf, F. L., D. A. Gurnett, W. S. Kurth, and R. L. Poynter,

Nature, 280, 796 9 1979.

Rodriguez, P., and D. A. Gurnett, J. Geophys. Res., 81, 2871, 1976.

Scarf, F. L., W. W. L. Taylor, C. T. Russell, and R. C. Elphic,

J. Geophys. Res., 85, 7599, 1980.

6) Gurnett, D. A., F. L. Scarf, and W. S. Kurth, J. Geophys. Res., 87,

1395 0 1982.

f) Fredricks, R. W., F. L. Scarf, and C. T. Russell, J. Geophys. Res.,

78, 2133, 1973.

Scarf, F. L., R. W. Fredricks, I. M. Green, and C. T. Russell,

J. Geophys. Res., 77, 2274, 1972.

Scarf, F. L., R. W. Fredricks, C. T. Russell, M. Kivelson,

M. Neugebauer, and C. R. Chappell, J. Geophys. Res., 78, 21500

1973.

8) Kennel, C. F., and H. F. Petschek, J. Geophys. Res., 71, I t 1966.

9) Scarf, F. L., F. V. Coroniti, D. A. Gurnett, and W. S. Kurth,

Geophys. Res. Lett., 6, 653, 1979.

10) Thorne, R. T., and B. T. Tsurutani, Geophys. Res. Lett., 6, 649,

1979.

_

11) Coroniti, F. V., F. L. Scarf, C. F. Kennel, W. S. Kurth, and D. A.

Gurnett, Geophys. Res. Lett., Z. 45 9 1980.

12) Kennel, C. F., F. L. Scarf, R. W. Fredricks, J. H. McGehee, and

F. V. Coroniti, J. Geophys. Res., 75, 6136$ 1970.

13) Gurnett, D. A., and R. R. Shaw, J. Geophys. Res., 78, 8136 0 1973.

14) Lyons, L. R., J. Geophys. Res., 79, 575 9 1974.

15) Gurnett, D. A., and L. A. Frank, J. Geophys. Res., 79, 2355, 1974.
1

16) Kurth, W. S., L. A. Frank, M. Ashour-Abdalla. D. A. Gurnett, and

B. G. Burek, Geaphys. Res. Lett., 7, 293 0 1980.

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