V.";UCRL-51385

THE III ELECTRON AND PROTON SPECTROMETERON NASA'S ORBITING GEOPHYSICAL OBSERVATORY 5

(Final Report for Experiment 6)

H. I. West, Jr.R. M. Buck

J. R. Walton

May 29, 1973

Prepared for US. Atomic Energy Commission under contract No. W-7405-Eng-48

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LAWRENCE UVERMORE LABORATORY

UCRL-51385

THE ILL ELECTRON AND PROTON SPECTROMETERON NASA'S ORBITING GEOPHYSICAL OBSERVATORY 5

(Final Report for Experiment 6)

H. I. West, Jr.R. M. Buck

J. R. Walton

MS. date: May 29, 1973

Contents

Abstract . 1

Introduction .- 1

Instrument and Inflight Operation 2

Electron Spectrometer 2

Proton Spectrometer 5

Dynamic Range . ' 8

Magnetic Shielding 9

Pitch-Angle Scan Mechanism 9

Differential Discriminator and Proton Logic 11

Experiment Status and Failure 11

Raw Data Plots 12

Bibliography of Results 17

Reports 17

Talks . . . 1 8

Publications . . . 22

Resume of Results 24Inner Belt 24

Slot and Nearby Outer Belt .27

Pitch-Angle Distributions in the Outer Magnetosphere . . . . . 29

Plasma Sheet Boundary Motion During a Substorm 50

The April 1969 Solar Particle Event 54

The November 18, 1968 Solar Particle Event 56

Highly-Anisotropic Proton Distributions Observed Interplanetary . . . 58

Concluding Remarks 60

Acknowledgments . 61

References 62

-iii-

THE LLL ELECTRON AND PROTON SPECTROMETERON NASA'S ORBITING GEOPHYSICAL OBSERVATORY 5

(Final Report for Experiment 6)

Abstract

The LLL energetic electron and pro-

ton spectrometer on NASA's Orbiting

Geophysical Observatory 5 (OGO-5) oper-

ated successfully from launch — March 4,

1968—until retirement in August 1971.

Data recovery during this time was about

95 percent of the orbit except for the last

few months. The electron spectrometer

used a magnetic field for electron mo-

mentum selection which served also as

an electron broom for a proton range-

energy telescope. The energy range was

~60 to 2950 keV for electrons (seven

channels) and 0.10 to ~94 MeV for protons

(seven channels). The experiment was

scanned relative to the stabilized OGO-5

for obtaining directional information.

Excellent data were taken throughout the

magnetosphere and in the interplanetary

region (apogee 24 Rp). Studies were car-

ried out in the areas of equatorial pitch-

angle distributions, substorm dynamics

arid field topology, particle spectra (time

history), particle spatial distributions,and solar particle events. Excellent

data were available from other OGO-5

experiments for data correlation. This

report covers instrumentation features

that contributed significantly to the

experiment's success and also pre-

sents a resume of the experimental

results.

Introduction

NASA's Orbiting Geophysical Observa-

tory 5 (OGO-5), launched from the East-

ern Test Range at 0800 LT March 4, 1968,

operated successfully for nearly 3-1/2 yr.

Our experiment (E-06) ran continuously

during this period, with most of the ex-

periment working properly.

E-06 grew out of a 1962 experiment

(West, 1965) conducted on the U.S. Air-

force satellite STARAD (1962 |3K).to

assess the effects of the Starfish high-

altitude nuclear detonation on the earth's

radiation belts (West et al., 1965). This

experiment, consisting of a five-channelmagnetic beta-ray s p e c t r o m e t e r ,

worked well, giving three months of

data in the inner belt and high-latitude

regions of the outer belt. Because the

satellite was spinning, we were able

to measure pitch-angle distributions;

this was important in interpreting the

data.

-1-

In general, interpretation of the inner

belt data was hampered by a paucity of

pre-Starfish data. The STARAD results,

along with those emerging from studies

of the outer magnetosphere and the mag-

netotail by other investigators, pointed

up the need for studying magnetospheric

electrons with instruments able to make

unique measurements in well-defined

energy bins. Background effects would

have to be low or accurately measured.

Pitch-angle measurements would be re-

quired, particularly at the magnetic

equator where such measurements can

determine what is happening along the

field line on the time scale of the bounce

period; pitch-angle distributions also are

sensitive to effects at other longitudes on

the time scale of the azimuthal drift.To complete the picture provided by the

electrons, it was evident that low-energy

proton measurements would be needed. In

the OGO-5 experiment, this was accom-

plished by placing the proton detectors in-

side one of the electron-spectrometer

magnets so that the magnet served the

secondary purpose of an electron broom.

Other measurements on OGO-5 com-

plemented our results. Initially, low-

energy measurements were available via

two electrostatic analyzer experiments,

Unfortunately, these experiments met an

early demise. At times, the plasma-

wave measurements of Scarf et al. (dE/dt)

were valuable. However, for our pur-

poses, the most important information

was the magnetic vector data for our

pitch-angle studies, provided by the

UCLA flux-gate magnetometer experi-

ment. These were the major complemen-

tary data we needed for putting together

the physics.

In this final report, we first describe

the experiment's design and operation.

Although no new technology of a patent-

able nature was found, there are some

features of the instrumentation that mayinfluence future experiments. We then

present abstracts of pertinent reports,

talks, and publications. This is followed

by a resume of results. In the resume

we include a discussion of future work

that should be performed using the

OGO-5 data.

Instrument and Inflight Operation

The instrument report by West et al.

(1969) completely documents the LLL ex-

periment. In this final report, we merely

describe the instrument, emphasizing its

unique features and inflight operation.

The experiment consisted of an elec-

tronics package, located in the main body

of the satellite, and sensors on a boom

called the OPEP-2 (Orbital Plane Exper-

imental Package 2). Figure 1 shows the

electronic functional makeup of the exper-

iment. Figure 2 shows the important

features of the spacecraft, whose proper

orientation required that the solar pad-

dles look directly at the sun and the

OPEP shaft point to the earth's center.

Table 1 gives the characteristics of the

energy channels.

ELECTRON SPECTROMETER

The electron spectrometer used two

small permanent magnets for momentum

-2-

OPEP package

Impulse cmd turn on

Analog statuscommutator

Detector leakagecurrent monitors

Impulse cmd turn on

AmplifiersDiscriminators

Logic

»—|LV powerI I I I I ICounting data

Pulse generatorcontrol logic

Impulse cmd Shift register andHV selection

20 time-snared20-bit accumulatorsDigital

commutator

Inhibits for 52 redundant

floating-pointshift registers

digital words

Equipment group switch

Equipment groupOutputgatesEquipment group "2

Status and sync __ Main body package statusAnalogcommutatorStatus and sync "2 voltages, temp, cmds

OPEP status

FLg. 1. Block diagram of the electronics.

analysis (180-deg first-order focusing)

and solid-state detectors for particle

detection (see Figs. 3 and 4).

Accurate evaluation of backgrounds

was considered essential to the experi-

ment's success. The backgrounds for

-3-

Scan axis

OPEP-2

Magnetic field lineshowing trapped particle

Fig. 2. Orientation of the experiment in the sun-earth-satellitesystem. Note that the OPEP shaft always points towardsthe center of the earth and the solar paddles alwayspoint towards the sun. ,r

channels E. and E» were supplied by a

single detector between the E, and £„

detectors. For the other channels, indi-

vidual detectors were used in a multiplex-

ing arrangement. Figure 5 shows how

the multiplexed pulses were handled such

that the respective electron pulses and

background pulses were routed to their

respective scalars. The multiplexing

arrangement, which worked so well for

E~ through E?, was not used for E, and

E- because of the increase in electronic

noise that would have resulted.

An additional factor contributing to

background reduction was the use of

detectors thick enough to stop the. elec-

trons completely (at least for E through

Efi). Thus, a differential window could

be positioned over the peak in the pulse-

height distribution for the purpose of

eliminating backgrounds more effectively

(from bremsstrahlung and protons).

Other experimenters, by contrast, have

used thin solid-state detectors with a

wide window set to count the wide range

of pulse heights produced. While this is

attractive with respect to simplicity, it

results in a greater background, as

proved by an analysis of the background

spectrum.

The background evaluation procedure

worked extremely well for all regions of

space reached by OGO-5, including

measurements in the inner belt and in

-4-

the interplanetary region during solar-

particle events. In both cases, the major

background problem was penetrating pro-

tons. In using the background data, we

determined the sensitive-volume ratios

of the respective detectors (~10 percent)

before flight. These ratios were im-

proved to ~±2 percent through study of

penetrating galactic radiations during

periods of minimum solar activity when

OGO-5 was free from the influence of

magnetospheric radiations. Normaliza-

tion studies were made during 1968 and

1969, remaining quite constant during

that period.

PROTON SPECTROMETER

Proton data were acquired from an

array of proton detectors (range-energy

telescope and single detector) in one of

the electron spectrometer magnets. As

shown in Fig. 4, the array was in line

with the entrance aperture. Means were

provided for estimating the backgrounds

(by interchanged logic between detectors),

but the results were not of the high accu-

racy available for the electrons. The

electron-broom effect, provided by the

spectrometer magnet shown in Fig. 4,

was quite effective. E l e c t r o n or

Table 1. Spectrometer characteristics.

Channel

Electrons

ElE2E3E4E5E6E7

ProtonsP

P2P3P4

P.K*J

T^

Dp

7

Alpha

«1

Energy range

79 ± 23 keV

158 ± 36

266 ± 36

479 ± 52

822 ± 185

1530 ± 260

2820 ± 270

0.10 - 0.15 MeV

0.23 - 0.57

0.57 - 1.35

1.35 - 5.40

5.6 - 13.3

14.0 - 46

43 - 94

<~ 100

5.9 - 21.6 MeV

Geometry

0.180 cm2 keV sr

0.277

0.390

0.605

4.43

8.57 .

3.88

2.06 X, 10"3 cm2 sr

1.3 X 10"2

1.3 X 10"2

1.3 X 10"2

1.25 X 10"2_9

1.72 X 10_o

1.98 X 10 z

~0.6 X 4 TT cm

1.3 X 10"2 cm2 sr

Acceptanceangle(deg)a

7.6

5.9

4.7

3.5

5.3

4.1

2.5

12

12

12

12

12

12

12

omni

Effective full width at 50% acceptance in the scan plane.

-5-

1.726

4.800

Fig. 3. The low-energy electron spectrometer.

-6-

Light baffles - Al

Armco iron

Electrons

Absorbers

Pole pieces'—Gold case

te

\\

JL

rnmog V

3

'yXI

slsS^ • ^1

B

11

II.

IH

|4

\/ f

f t f f J ' l

(

l.C

Fig. 4. The larger electron spectrometer and the proton detectionsystem. The field of the electron spectrometer acts as anelectron broom for the proton detection system. The fieldin the magnet is high enough to bend low-energy protonsabout 5 deg so the true geometry for the small side detectoris greater than the apparent optical geometry.

-7-

u4)

I - HV

z s

- <

Electron+ background pulses

J^-

2"

II

\Preamp

/II

5 VBackground pulses

To detector leakagecurrent- monitors

To scalar

!Background pulses

Electron+background

pulses

To scalar

Fig. 5. Multiplexing arrangement for the detectors in the magnetic electron spectrom-eters. This procedure ensures that the background normalization, oncedetermined, will be constant.

bremsstrahlung background was never a

problem. However, penetrating protons

were troublesome when we tried to acquire

data in the inner belt and during relativ-

istic solar-particle events. The proton

data channels we used are listed in

Table 1. Some other channels were pro-

vided (West et al., 1969), but these were

not properly calibrated or used and will

not be discussed here.

DYNAMIC RANGE

The geometric factors for the electron

spectrometer were near optimum for

most of the mission. For example, the

maximum counting rates for E., E0, and5Eo in the inner belt got to 10 counts/

second, only on occasion. For these

rates, count rate corrections could be

properly made. By contrast, a factor-

of-10 increase in the geometry for E» or

an equivalent reduction in background

would have been preferred for the inner

belt. Larger geometry would have been

desirable, at times, in the magnetotail.

It was'not realistic, however, with this

type of instrumentation, to try to meas-

ure electrons in excess of about 1 MeV

in the plasma sheet. The instrument was

quite effective during solar particle

events for E.-Eg. Obviously, greater

geometry would have been desirable.

For example, it was only during the

April 1969 solar electron event (the

largest in the history of space measure-

ments) that Eg and E? provided useful

data.

Because of the wide variation in pro-

ton fluxes and energies encountered, it is

difficult to design a proton spectrometer

that works well throughout the magneto-

sphere. A serious count-rate problem

was encountered in measuring protons

mirroring near the equatorial regions in

the heart of the outer belt. The high

-8-

count rates in P. and P5 were enough to

cause partial paralysis of P_ and P3.

The paralysis produced minima near

90 deg in the pitch-angle distributions for

these channels. The paralysis was quite

consistent. It was only with some reluc-

tance, following studies with Flight

Unit 2, that we had to abandon the result.

The experiment provided good meas-

urements in most of the outer magneto -

sphere. Results in the magnetotail were

confined to P-, and P2< and P,. During

solar particle events, P..-P,. were effec-

tive, with occasional significant results

in Pfi and P?. Alpha channel a. provided

good data during solar particle events.

However, due to a pulse-pileup problem,

a, results were of no value for L £ 4, at

least in the region of appreciable trapped

proton populations.

MAGNETIC SHIELDING

The magnetic field of the larger elec-

tron spectrometer magnet between pole

pieces was about 2700 G; the field of the

smaller spectrometer magnet was about

860 G. The magnets were so mounted

that their external dipoles partially can-

celled. Because the cancellation did not

reduce the stray field adequately, we

installed additional shielding: a singleJ;

sheet of 4-mil Conetic about 1/2 in.

from the spectrometers. The Conetic

had to be annealed carefully before

^Conetic is a trade name, product ofthe Magnetic Shield Division, PerfectionMica Company. Reference to a companyor product name does not imply approvalor recommendation of the product by theUniversity of California or the U. S.Atomic Energy Commission to the exclu-sion of others that may be suitable.

assembly and not "work hardened" after-

wards. The package "depermed" to a

residual field of about 12 7 at 1 ft, which

was quite acceptable for the mission.

PITCH-ANGLE SCANMECHANISM

Because OGO-5 was oriented with

respect to the earth and the sun, the

aperture of the experiment had to be

scanned relative to the spacecraft. The

OPEP's were scannable at 1.5 deg/sec as

a normal spacecraft function, but thiscapability generally could not be used

because OPEP-1 and -2 were tied to-

gether rigidly; all OPEP experiments

would have scanned as a consequence.

Hence a special mechanism had to be

provided on OPEP-2 for scanning our$$experiment. It operated almost contin-

uously during the 3-yr mission with no

evident sign of malfunction. On alternate

orbits inside 4 R^, the mechanism was

turned off so a companion experiment on

the same scan platform could look for-

ward in the plane of the orbit (the OPEP

"gyro mode"). This reduced our inner-

belt data coverage by half.

We encountered a serious problem

with respect to the spacecraft scan mech-

anism. The requirement that our exper-

iment viewing-direction be tied into the

coordinate system of the vector magne-

tometer to ±1 deg did not seem to be fully

understood by the spacecraft people. The

spacecraft system determined the shaft

**This mechanism was supplied throughthe efforts of R. Browning, and laterH. Burdick, of the NASA-Goddard SpaceFlight Center.

-9-

PIN i

QlJN559

Q2ZH930 ZN559

Q5 Q6Its JI9I+ ZN325I

PtM*V OUTPUT

1. M.L TRANilbTORS. PEKLES 116-va

2. * • DENOTti MtTALPER MIL ^PtC f OR, RN'b'iCOR

Fig. 6. Differential discriminator. This LLL circuit design is capable of zerostandby power and wide operating temperature; it is fast and cannot be trickedby overload pulses, even those lasting tens of microseconds.

ANTI -COINCIDENCE -

PITA 14 ciwo

Fig. 7. Typical proton logic circuit. The anticoincidence portion of the circuit(CR1, Q3, Rg, R^, R^, Rg, R-j) is identical in principle to that used inthe discriminator (Fig. 6).

-10-

angle through the use of seisin angle re-

solvers. This system, capable of frac-

tional degree accuracy, was calibrated at

best to 5 deg. Thus, we had to effect an

inflight calibration using trapped particle

fluxes in predictable regions. Part of

this calibration effort is still going on.

DIFFERENTIAL DISCRIMINATORAND PROTON LOGIC

A circuit designed at LLL prior to the

start of the OGO-5 work proved invalu-

able in implementing our experiment

design. Figures 6 and 7 show its use.

The circuit uses zero standby power, is

fast, and cannot be tricked by overload

pulses. Although it has been reported

(McQuaid. 1966; West et al., 1969). it

does not seem to be widely used.

A differential discriminator (Fig. 6),

which is easily expandable to multichan-

nel use, was employed in the electron

system. Negative pulses are supplied to

integral discriminators 1 (CR1.Q1) and 2

(CR2, Q2). Tripping discriminator 1

results in anticoincidence of the differ-

entiated pulse from discriminator 2 (the

output comes in the trailing edge of the

pulse from discriminator 2); this occurs

through the tripping of tunnel diode CR3,

which in turn saturates transistor Q3.

Note that once CR3 is tripped, via cur-

rent through R6 and R7, it stays in con-

duction until discriminator 2 is turned off

(the current through R7 is sufficient to

maintain the tripped condition). Thus,

long saturating pulses at the input cannot

produce an output. Also note that Q3 is

in hard conduction when CR3 is on; this

means a delay of ~0.7 /usec before Q3

comes out of conduction, so that the anti-

coincidence function is maintained for

this period. The tunnel diode and tran-

sistor are temperature-compensating,

ensuring that the delay is constant over a

wide temperature range.

Figure 7 shows a similar system used

in the proton logic. Ql, Q2, and Q6 form

a standard series-coincident circuit.

CR1 and Q3 form the anticoincidence

logic, which operates as previously dis-

cussed. In this case, current through R9

plus current from either R4, R5, R6, or

R7 results in anticoincidence.

EXPERIMENT STATUSAND FAILURES

A large amount of housekeeping data

were brought out of the experiment in

order to keep track of its status. Once

every orbit, near apogee, an inflight

pulse generator was exercised to check

out the system. This test always gave

positive results, an important factor in

establishing the credibility of the data.

Some partial failures were observed.

In August 1968, we discovered that noise

associated with the Goddard Space Flight

Center (GSFC) scan mechanism was get-

ting into the bottom channels of the proton

telescope. The problem was most pro-

nounced in P« and usually could be local-

ized to a small range of scan angles.

For the first few weeks of OGO-5's

operation, we encountered occasional

problems in the electronically associated

channels E_, EB?, O., and O™. Noise,

seldom lasting more than 10 min at a

time, was being generated, probably as

a result of bulk or surface leakage in

either the E? or EB_ detector. After

the first few weeks, this noise disap-

peared and was never a problem

afterwards.

-11-

In the Spring of 1971, a detector prob-

lem appeared in the associated channels

E,, and EB« (the two detectors were mul-b otiplexed into the same preamplifier). The

channels became noisy. However, Eg

responded to outer belt fluxes and, based

on the resulting spectrum, appeared to

give correct results. We found that just

prior to this time, OGO-Operations had

turned off the experiment; in restoring it,

personnel had failed to turn on the experi-

ment's high voltage. After the high volt-

age had been on for a few weeks, the

noise disappeared. We cite this as the

kind of solid-state detector failure that

can occur after prolonged operation in a

space environment (3 yr).

RAW DATA PLOTS

We used two plotting schemes for rou-

tine examinations of our data: a 20-min

plot and a 2-hr plot. Many of these, for

1963 and 1969, are available at the

National Space Science Data Center.

Figure 8 is a 20-min plot of E, data*)

obtained at the heart of the inner belt.

The I's are the electron data (4.6-sec

averages) and the O's are backgrounds

(4.6-sec averages, counted only one-

quarter of the time). The zig-zag pat-

tern gives the magnetic aspect angle,

which is read from the scale at the upper

right of the plot. The normalization of

the background to the electron data is

1.01 ± 0.02. The electron-to-background

ratios in the inner belt for the lower en-

ergy channels (Ej-E.) are considerably

better than for the E- data. Figure 9

shows P0 data obtained the same time as£

the E,- data; the background normalization

is 1.0.

Figure 10 shows E- data in a 2-hr plot

overlapping the time period of Fig. 8.

The electron data are 4.6-sec averages,

and the background data are 73.7-sec

averages. Because of the long averages

for the background, some of the back-

ground structure has been averaged out.

The scatter of points in the electron data

is due, of course, to the scan modulation

of the data.

Figure 11 shows P? data in a 2-hr plot

covering the same period as the E- data.

Note that saturation effects are occurring

for the period 1724 to 1820 UT.

-12-

OGO V DETECTOR ORBIT YEAR MONTH DAY YDAY LSAV HOUR HIM. SEC. RUN REEL FiLE RECORD KBIT i-C- R£: ?X, SEC ritUlT. E5 3 58 HAR 9 09 5 19 3 8.9 50 2 6 1 IPS 3 3FitiAL EB5 19 22 47.4 8 2 15

__ _ _<Sfc»5 .8.

1912

1.6951.6575.49

193.719.4

201.410.2

1918

1.9822.003

9.83201.3

27.7211.7

14.0

1920

2.0782.12210.952S3.5

29.9214.6

15. C

«GSE«GSH«5SK

Fig. 8. £5 inner-belt data in a 20-min plot. The flags are electron data and the O'sbackground. The background normalization is close to 1.00. These data aretypical of the EI - E5 data in the inner belt where background due to highenergy penetrating protons is a potential problem. The coordinates along theabscissa are: universal time, R in RE, L in RJT, ^m (magnetic latitude),

(solar ecliptic azimuth), 0QSE (elevation above the ecliptic plane),(s°lar magnetospheric azimuth), and 0GSM (s°lar magnetospheric

elevation).

-13-

OGO V DETECTOS 3R8IT YEAR MONTH DAY Yt'AY LDAY HOUR H!N. SEC. RUN REEL TILE RECORD KBIT i-0 RiC YJ.', ?l'. *iINI7. P2 3 68 HAR 9 65 5 19 3 8.9 50 2 6 ! !P8 3 3FINAL P82 is 22 47.4 a 2 :s

._, T r Km..».1 jl_.._ T • - .8-.

w

g«Jyy

E-01.

HOURHIN.RLXH•GSE«CS£»GSM9GSM

19"2

1.2631.220-6.72176.4

-3.6175.1

-1.4

194

1.3401.280-3.67180.6

2.2181.6

1.6

196

1.4231.357-0.93184.3

7.3187.4

4.3

198

1.5111 .4491.49

187.711.9

192.56.6

1910

1.6021.5503.62

190.815.8

197.28.5

1912

1.6951.6575.49

193.719.4

201.410.2

1914

1.7901.7707.13

196.422.5

205.111.7

1916

1.8861.8868.56

198.925.2

208.612.9

1918

1.9822.0039.83

201.327.7

211.714.0

1920

2.0782.1221C. 95203.5

29.9214.6

15.0

1922

2.1742.24115.942C5.63!. 8

217.215.8

!92-J

2.2732.36:12.82237.7

33.5219.7

16.5

Fig. 9. ?2 inner-belt data in a 20-min plot,to 1.00.

The background normalization is close

-14-

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-15-

OGO VINIT.

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Fig. 11. in a 2-hr plot.

-16-

Bibliography of Results

REPORTS

The LRL Electron and Proton Spectrometer on NASA'sOrbiting Geophysical Observatory V(E) '

(Instrumentation and Calibration)

H. I. West, Jr., J. H. Wujek, J. H. McQuaid, N. C. Jenson,R. G. D'Arcy, Jr., R. W. Hill, and R. M. Bogdanowicz

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Lawrence Livermore Laboratory Report UCRL-50572, June 1969

The design, construction, and calibration of the LLL electron arid proton experi-

ment on the OGO-V satellite are described. A brief account of postlaunch results is

included. The electron spectrometer consists of two small permanent magnets used

for energy analysis with electron detection provided by solid-state detectors. Back-

ground detectors are also provided. The energy range covered is approximately 60 to

2950 keV in 7 differential energy channels. Geometrical factors vary from 0.18 to

8.6 cm2-keV-sr.

The proton spectrometer consists of a single solid-state detector and a range

energy telescope of four solid-state detectors situated in line with the entrance aper-

ture of the larger of the electron spectrometer magnets. The energy range is 0.1 to

94 MeV in 7 differential energy channels. The geometrical factor for the lowest energy-3 2

channel (0.1 to 0.15 MeV) is 2.06 X 10 cm -sr and for the rest of the proton channels_2 2

1.3 to 1.9 X 10 cm -sr. Data handling in the experiment is primarily digital using a

binary floating-point compressional scheme. The experiment apertures are scanned

relative to the stabilized spacecraft for obtaining pitch-angle distributions.

The LLL Electron and Proton Spectrometer on NASA'sOrbiting Geophysical Observatory V

(The data user's guide to the microfilm records)

H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Lawrence Livermore Laboratory Report UCRL-51037, June 1972

This report provides background for using data from the LLL energetic-particle

experiment conducted on OGO-5. These data have been plotted on both 20-min and 2-hr

We give the abstracts of reports here because this information is not as readilyobtainable as the talks and publications that follow. Also, the latter information issummarized in the resume of results.

-17-

scales. Data from the UCLA magnetometer experiment have been plotted to the 20-min

scale for correlative purposes. In addition, tables of pertinent attitude-orbit data have

been plotted. Many of these data are available on microfilm from the National Space

Science Data Center.

The LLL Electron and Proton Spectrometer on NASA'sOrbiting Geophysical Observatory V(E):

The Three-Way Merged Tape(An Archival Data Base)

M. M. Zeligman and J. R. Walton

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Lawrence Livermore Laboratory Report UCRL-51314, November 1972

This is a description of a data base that can be used for archival records. The

data are combined from three sources and thus the name of the resultant tape: The

Three-Way Merged Tape.

The data contained on these tapes came from the following sources:

The LLL Electron and Proton Spectrometer (Experiment E-06)on NASA's Orbiting Geophysical Observatory V(E).

Attitude-orbit tapes containing the satellite ephermeris providedby Goddard Space Flight Center.

Magnetometer tapes provided by Drs. Paul J. Coleman andC. T. Russell with data from the Triaxial Fluxgate MagnetometerExperiment (Experiment E-14) on OGO-5.

TALKS

Observations of Energetic Electrons and Protons on OGO-V

Harry I. West, Jr., Raymond G. D'Arcy, Richard W. Hill,John R. Walton, and G. Allen McGregor

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

International Symposium on the Physics of the MagnetosphereWashington, D. C., September 3-13, 1968

-18-

Electron and Proton Pitch Angle Distributionsin the Outer Magnetosphere

Harry I. West, Jr., Richard W. Hill, John R. Walton,and Richard M. Buck

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Raymond G. D'Arcy, Jr.

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

EOS Trans., Amer. Geophys. Union 50, 659, 1969

Observations of Magnetopause Crossings by OGO-5

K. W. Ogilvie and J. D. Scudder

NASA-Goddard Space Flight CenterGreenbelt, Maryland

H. I. West

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

EOS Trans., Amer. Geophys. Union 50_, 661, 1969

Anisotrppic Angular Distribution of Protons and Electronsfrom the Cosmic Ray Solar Flare of November 18, 1968~

Raymond G. D'Arcy

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

Harry I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

EOS Trans. Amer. Geophys. Union j31_, 410, 1970

Simultaneous Measurementsof Solar Flare Electron Spectra in Interplanetary Space

and Within the Earth's Magnetosphere

Harry I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

A. L. Vampola

Space Physics Laboratory, The Aerospace CorporationEl Segundo, California

EOS Trans., Amer. Geophys. Union 5^, 411, 1970

-19-

Electron Spectra in the Slot and the Outer Radiation Belt

H. I. West, Jr., R. M. Buck, and J. R. Walton

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

EOS Trans., Amer. Geophys. Union 5L, 806, 1970

Evidence for Thinning of the Plasma Sheet During' the August 15, 1968 Substorm

R. M. Buck and H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

R. G. D'Arcy, Jr.

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

EOS Trans., Amer. Geophys. Union 51. 810, 1970

' • .OGO-5 Observationsof Substorm-Associated Energetic Electrons

on 15 August 1968

Margaret G. Kivelson and Thomas A. Farley

Institute of Geophysics and Planetary Physics, University of CaliforniaLos Angeles, California

Harry I. West, Jr.

'e Laboratory, Univvermore, Californi

EOS Trans., Amer. Geophys. Union 51, 810, 1970

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

The Butterfly Pitch Angle Distributionof Electrons in the Postnoon to Midnight Region

ofthe Outer Magnetosphere as Observed on OGO-5

H. I. West, Jr., R. M. Buck, and J. R. Walton

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

EOS Trans. , Amer. Geophys. Union 53, 486, 1972

-20-

Energetic Protons as Probesof Magnetospheric Particle Gradients

R. M. Buck and H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, .California

R. G. D'Arcy

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

EOS Trans., Amer. Geophys. Union 53, 486, 1972

Energetic Particles Near the Noon Magnetopausea s Observed o n O G Q - 5 ~

R. M. Buck and H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

American Geophysical Union meetingWashington, D. C., Spring 1973

Inner Belt Electrons in 1968 Observed on OGO-5

H. I. West, Jr. and R. M. Buck

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

American Geophysical Union meetingWashington, D. C., Spring 1973

A Unified View of Electron Pitch-Angle Distributionsin the Equatorial Regions'

of the Outer Magnetosphere—OGO-5 Observations

H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Invited paper, American Geophysical Union meetingWashington, B.C., Spring 1973

-21-

PUBLICATIONS

Simultaneous Observations of Solar-Flare Electron Spectrain Interplanetary Space and Within Earth's Magnetosphere

H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

A. L. Vampola

Space Physics Laboratory, The Aerospace CorporationLos Angeles, California

Phys. Rev. Lett. 26, 458, 1971

Energetic Electrons and Protons Observedon OGO-5, March 6-10, TWTS

H. I. West, Jr., J. R. Walton, and R. M. Buck

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

R. G. D'Arcy, Jr.

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

Solar Geophys. Data ESSA Report UAG-12, 124, 1971

Shadowing of Electron Azimuthal-Drift MotionsJear theNoon Magnetopause

H. I. West, Jr., R. M. Buck, and J. R. Walton

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Nature Phys. Sci. 240. 6, 1972

Energetic Electron and Proton Solar Particle Observationson OGQ-5, January 24-30, J97T~

H. I. West, Jr., R. M. Buck, and J. R. Walton

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

R. G. D'Arcy, Jr.

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

Solar Geophys. Data ESSA UAG Report UAG-24, Part 1, 113, 1972

-22-

Electron Pitch-Angle DistributionsThroughout the Magnetosphere as Observed on OGO-5

H. I. West, Jr., R. M. Buck, and J. R. Walton

.vermore Laboratory, University iLivermore, California

J. Geophys. Res. 78, 1064, 1973

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

Satellite Studies of Magnetospheric Substorms on August 15, 19687. OGO-5 Energetic Proton Observations — Spatial Boundaries

R. M. Buck and H. I. West, Jr.

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

R. G. D'Arcy, Jr.

Bartol Research Foundation, Franklin InstituteSwarthmore, Pennsylvania

J. Geophys. Res. 78, 3103, 1973

Satellite Studies of Magnetospheric Substorms on August 15, 19686. OGO-5 Energetic Electron Observations —

Pitch-Angle Distributions in the Nighttime Magnetosphere

H. I. West, Jr., R. M. Buck, and J. R. Walton

Lawrence Livermore Laboratory, University of CaliforniaLivermore, California

J. Geophys. Res. 78, 3093, 1973

-23-

Resume of Results

Initially, the perigee of OGO-5 was

291 km and apogee was ~24 R,-,. TheHiorbit inclination was 31 deg at launch

(March 1968), increasing slowly to

54 deg in 1971. The orbital period was

~2-l/2 days. The experiment obtained

useful data throughout the orbit. During

most of 1968 and part of 1969, OGO-5

made many inbound passes during which

it stayed close to the geomagnetic equa-

tor from about 15 R_ into 4 R,-,. This,is ±LJcoupled with the fact that OGO-5 pro-

vided about 95 percent data coverage

during the mission, meant that we were

able to do an extraordinarily good job of

acquiring data in the equatorial regions

of the magnetosphere.

During most of the time that the pitch-

angle scan mechanism was in operation,

our experiment scanned so as to look out

perpendicular to the earth's radius (the

choice was dictated by the operational

makeup of the spacecraft). Consequently,

our angular coverage in much of the mag-

netosphere varied from 90 deg to the dip

angle of the local magnetic field. Equa-

torial coverage thus meant complete

pitch-angle coverage and, of course,

equatorial pitch-angle measurements

also meant a complete knowledge of what

was going on along the field lines. Away

from the equator, in a dipole-like field,

the coverage was largely limited to pitch

angles near 90 deg. Near the noon mag-

netopause, however, the field configura-

tion is close to being circular and here,

even at high latitudes (45 deg geomag-

netic), good pitch-angle coverage was

available. Conversely, in the magneto-

tail during substorm growth phases, the

magnetic field approached the radial

direction. During these times, the pitch-

angle coverage could be as limited as

90 ± 20 deg. When needed, complemen-

tary electron data from the UCLA scintil-

lation counter experiment were available.^

As will be seen later, the limited pitch-

angle coverage in the magnetotail had its

compensations; it was ideal for using the

proton east-west effect in the study of the

plasma sheet boundary during substorms.

The experimental results are dis-

cussed below in terms of the inner belt,

the slot and near-by outer belt, pitch-

angle results in the outer magnetosphere,

plasma sheet boundary during substorms,

and solar particles. Some of this work

is published or in publication, while the

rest is in process of completion.

INNER BELT

Data were studied in the inner belt

region for those orbits during which the

experiment scanned. The values of j. at

discrete L-shell crossings were obtained

and were plotted in terms of j. vs X ,

(here, X , is the magnetic latitude as

determined from the dipole equations

B/B Q = (I/cos 6X d ) (4-3 cos2Xd)1 /2 .

Figure 12 shows an example of the

ordering of the data. To a good order of•j, -j*

approximation, we and others (e.g.,

Pfitzer et al., 1966) find that the shape of

This experiment, conducted byT. Farley and M. Kivelson, consisted ofsix scintillation counters looking in differ-ent directions.

* *_This is a reasonable approximation

well away from the loss cone.

-24-

£•078e

E»0888

E»OS88

E«0388

E«0286

£•01

Q.CCLJa

CALC. LAMBDA M L= 2.00RUN 3/27 LINEAR LAMBDA TIME FIT DAYS 69-293

Fig. 12. EI j±-fluxes for L = 2 in 1968 plotted as a function of Xd. Note that the Xdused here is derived from the dipole equation. These low-energy electronsshowed little decay during 1968 whereas the higher energies showedappreciable changes (especially E$ and £5).

the distribution (j -vs-X , being equivalent

to jj-vs-equatorial-pitch-angle) is inde-

pendent of energy. This finding has

allowed us to order the data in terms of

equatorial j, - values.

L-plots of equatorial fluxes for 1968

and early 1969 are shown in Fig. 13. The

curves starting at L = 1.3 indicate the

flux in early 1968. All energies except

E, decayed slowly until the large inner-

belt injection during the October 31-

November 1, 1968, magnetic storms.

The poststorm radiation belt rearrange-

ment effects also are indicated in Fig. 13;

-25-

10'

u0)

<U

-*I

U

O

O0)

10'

CO

0>

I 10C

H 10in

10

. , I

288,293,303

288,293,303

288,293,303 -4

288,293,303 -

1.0 1.5 2.0

L-shell

2.5 3.0

Fig. 13. Equatorial j^-values for 1968 plotted as a function of L.Major inner-belt injection occurred on Days 305 and306. The various curves show the rearrangementeffects that occurred following injection.

unfortunately, the perigee crossing was

at L = 1.8 on November 1, so that deep

inner-belt coverage was not possible.

It is surprising how stable the E^

fluxes are. They did not rise appreciably

during the major injection even though the

fluxes of the next higher energy channel

(£„) rose above those in Ej. Conversely,

we are fascinated by the relatively rapid

changes in E. and E&. We believe the

data in Eg (Fig. 13) to be a Starfish resid-

ual. The E? fluxes were of comparable

-26-

10J

CN

u0)

0_yi

o

•5 10'

West (STARAD)

Pfitzer(OGO-l)

-Pfitzer :OGO-3)

West (OGO-5)

• L = 1.4 equatorial flux, 1 , 1 , 1 , 1 , 1

1962 1964 1966Year

1968

Fig. 14. Long-term decay of 2-MeVelectrons at L = 1.4. All datapoints were determined bymagnetic electron spectrom-eters. The data sources areindicated on the figure.

level but are not plotted in Fig. 13 due to

the greater difficulty in extracting these

data.

With our 1968 data, we combined

earlier data obtained in 1962 by West

(1965), in 1964 by Pfitzer (1968) andPfitzer et al. (1968), and in 1966 and

1967 by Vampola (private communication).

An energy of 2 MeV, which seems well

above the electron energies involved in

the usual inner belt dynamics, is chosen

for the L = 1.4 data plotted in Fig. 14.

The e-fold decay rate is ~370 days. Star-

fish electrons are no longer important in

radiation belt dynamics.

Electron spectra typical of the mid-

latitude regions are shown in Fig. 15 for

the period before the major injection

event. The data are normalized to point

out the spectral hardening as we approach

the earth. The spectrum changed greatly

as a result of the October-Novemberinjection.

SLOT AND NEARBYOUTER BELT

In the inner belt, the pitch-angle dis-

tributions are largely independent ofenergy. In the outer belt, by contrast,we find a marked energy dependence. A

good example of data we acquired is pre-

sented in Lyons et al. (1972), their Fig. 6;

these authors used our data as a point-in-

proof of their electron pitch-angle diffu-

sion theory. The pitch-angle data, along

10'

JH8

_Q

O

I 3_ 103

102

10'

NormalizedequatorialspectraDays 69 - 1841968

10' 102 103 104

Energy — keV

Fig. 15. Typical inner-belt electronspectra in the period March 4to October 31, 1968. Thespectra are normalized tofacilitate comparison. Major .changes occurred in the spectrafollowing injection onOctober 31-November 1.

-27-

with the theoretical comparisons, are

shown in Fig. 16. Other examples are

shown in Fig. 17. Salient features of

these results are the flat pitch-angle dis-

tributions prevailing at the higher ener-

gies and the appearance of what may be

described as a bell-shaped distribution

sitting on a broader flat distribution for

the lower energy electrons. At present,

it has not been established whether these

features are time-independent; possibly

some of them evolve during storm time

injection and are modified later. The

resolution of this point is the subject of

further investigation. Unfortunately, the

OGO-5 equatorial data coverage in this

region is not as complete as we would

like.

We have carried out a study of storm-

time injection and decay. The data were

obtained during a relatively mild storm

(peak DST = -94y ) on June 11, 1968.

Preliminary results were presented by

West et al. (1970). Pitch-angle correc-

tions based on studies described in the

previous paragraph still need to be made;

hence, we still consider the results

preliminary.

Plots of j .-vs-L provide part of the

picture. Figures 18 and 19 show data

from Day 158, 1968, obtained three days

before the storm. Figure 20 presents

storm-time data for Day 163. Figure 21

shows data on Day 176, 13 days after the

storm. At this time, the outer belt is

believed to have been in diffusive equi-

librium.

Taking j, from such plots as Figs. 18

through 21, we have prepared the time

plots shown in Figs. 22 and 23 for L = 3.5

and L = 4.5. No pitch-angle cor-

rections have been made; this may

account for some of the scatter in the

data. Features to be specially noted are

90 1800 90Equatorial pitch angle — deg

Fig. 16. Electron equatorial pitch-angle distributions obtained April 25, 1968, com-pared with theory (solid line). [After Lyons et al. (1972)]. Lyons et al.calculate a combination of cyclotron and Landau resonant diffusion cTrfven bythe average observed band of plasmaspheric whistler-mode radiation (hiss).There can be no doubt that they have pinpointed the major effects controllingthe energetic electron fluxes in this region of space.

-28-

March 30, 1968

10L=3.89

>GSM~356°

X =-1.0m

E 4 ~10. & E . < 10°5 o

60 90 0 30 . 60 90

Fig. 17. Electron pitch-single distributions obtained March 30, 1968. This is anotherexample of slot-region pitch-angle data similar to that shown in Fig. 16.For perspective, note the corresponding radial profile data in Fig. 26.

the drop in the high energy fluxes during

storm time and the rise of the low-energy

fluxes; the relatively rapid decay of E0,ft

E«, and E .; and the growth of E,., Ec, and*3 4 • O D

£„ followed by slow decay. Obviously,

the decay rates are energy-dependent.

For shells ~3 to 4.5, the lower energy

channels E, - E. have e-fold decay rates

of 1.4 to 3 days. The decay rates for Ej.J

are 3 to 4 days, for Eg are 6 to 7 days,

and for E? are 10 to 14 days.

The electron spectrum can change

markedly as a function of time. Fig-

ures 24 and 25 show the post-recovery

diffusion effects for L = 3.5 and L =4.5.

The curves are annotated to show the

number of days after the storm. Fig-

ure 26 shows the changes in spectrum as

a function of L-shell for Day 181. Note

the evolution of a marked high-energy

peak in the slot region. This is charac-

teristic of the slot at weeks to months

after injection.

PITCH-ANGLE DISTRIBUTIONSIN THE OUTER MAGNETOSPHERE

We have had a major preoccupation

with these data; accounts of our efforts

are to be found in West et al. (1969) and

West et al. (1972 a,b,; 1973 a,b). We

-29-

10C

oo>

0)-XI

CMEo.

u<0

10"

10

I02

10

10

10-1

June 6, 1968Day 158

m19.6 30.0

26.0°

GSM

'GSM

35.0°

121.4

41.8°

5

38.0' 39.0 41.1'

135.1

48.7'

41.9' 42.. 2

Fig. 18. Outbound radial flux profile on Day 158, 1968. This quiet-timedata (also Fig. 19) sets the stage for the changes that occurredduring the storm on Day 163, 1968.

-30-

I • . IJune 6, 1968Day 158 .

\ -37.9° -45.5° -23.9° -15.9° -11.8° -9.3° -7.7 -6.8

GSM 280.6° . 263.8°

GSM -26.6° -8.1°

Fig. 19. Inbound radial flux profile on Day 158, 1968.

-31-

June 11, 1968Day 163

27.0

GSM

GSM

Fig. 20. Outbound radial flux profile on Day 163, 1968.

-32-

10"

o 10

r

ioEo

o£ 10'

_Q)

4)

10'

10-1

I ' IJune 24, 1968Day 176

m

2 3

11.0° 20.2

^GSM

GSM

4 5

24.2° 26.0°

107.7°

33.8°

26.9°

7

26.9°

130.2°

46.4°

8

26.4°

9

25.5°

Fig. 21. Outbound radial flux profile on Day 176, 1968. The electronsshould be in a state of diffusive equilibrium at this time.

-33-

10 15 20 25 30

-100

Fig. 22. TLme history of j,-fluxes on L-shell 3.5 before,during and after the June 11, 1968, magnetic storm(Day 163). These data are preliminary since pitch-angle corrections have not been made.

-34-

10-1

5 10 15 20 25 30 5 10 15

-100

Fig. 23. Time history of the j^-fluxes on L-shell 4.5 before,during, and after the June 11, 1968, magnetic storm(Day 163). These data are preliminary since pitch-angle corrections have not been made.

-35-

10C

10'

o4)

(I)

cp

u0>

IO5

10'

10'

Day UT

o!58 0419• 163 0847o 163 1018o!66 0040• 168 1525• 171 0540*173 1842A 176 1039o 179 0047

Xm

-32.7-10.222,836.822.031.6

-28.222.6.36.9

+ 3

+ 5

10° 10"

Energy — keV

Fig. 24. Changes in spectra at L-shell3.5 as a function of time afterthe June 11, 1968, storm. Thevarious spectra are labeled,to show number of days follow-ing the storm.

have studied the equatorial pitch-angle

distributions of electrons at all local

times throughout the magnetosphere. As

a result, we have acquired an overall

view we wish to present. We have also

10'

10'

r 10'

4)J*

CM

^ 10'V)

iu

4)

I 10*

10

10

Day UT* 163 0819« 163 1049a 165 2309* 171 0346* 176 1056° 181 1530

1 '""IX

IT)

-3.326.3

-29.9-17.925.425.8

+ 18

10' 10" 10° . 10*Energy — keV

Fig. 25. Changes in spectra at L-shell4.5 as a function of time afterthe June 11, 1968, storm. Thevarious spectra are labeled toshow number of days followingthe storm.

studied the proton pitch-angle distribu-

tions. These data are more subjective

than the electron results, not as well

understood, and, hence, discussed more

briefly.

-36-

We start in the prenoon magnetosphere.

The electron pitch-angle distributions in

this region are always normal. (Here we

are referring to distributions that are

symmetrical and peaked at 90 deg and

have a loss cone. They are often shaped

like the normal probability distribution

and are encountered all the way to the

magnetopause.) The radial profile of

jj-vs-L for March 30, 1968 (Fig. 27) pro-

vides perspective for presenting some

pitch-angle data. Figures 17, 28, and 29

show the pitch-angle results acquired.

These results are quite typical of this

region of the magnetosphere.

As electrons drift through the noon

magnetosphere at extended distances,

changes can occur as a result of drift-

shell splitting. Assuming adiabaticity,

we find that the equatorially mirroring

particles follow contours of constant B.

Constant-B contours obtained by Fairfield

(1968) for an average magnetosphere are

shown in Fig. 30. Conversely, as shown

by Roederer (1967, 1969), particles with

small equatorial pitch-angles, drift so as

to keep the length of their bounce path

approximately constant, all-the-while

maintaining a constant mirror field. If,

for example, we examine data at 9 R_,Jtii

and 0900 local time and contrast themwith data at 9 R^ and 1500 local time, wetiimight expect to find changes in electron

fluxes having pitch-angles near 90 deg.

An effect indeed occurs, as exemplified;

by the radial profile data in Fig. 31 and

the pitch-angle data in Fig. 32. We call

these pitch-angle distributions with min-

ima near 90 deg "butterfly" distributions.

We consistently find this effect of "mag-

netopause shadowing" in the equatorial

region beyond roughly the constant-B

10C

Q) "J

-* 10

Eo

o

10'

10i

: 4.5,-8.0-/

r-4.0,-10.8

June 29, 19681233-1414 UTDay 181

I I

10 10 10

Energy — keV

10"

Fig. 26. Changes in spectra as a functionof L-shell on June 29, 1968.

contour that maps from noon to about

7 RE at local midnight (see Fairfield's

data in Fig. 30).

Starting near dusk, as we go into the

nighttime magnetosphere, another aspect

of drift-shell splitting comes into play.

The appearance of a tail-like magnetic

field further contributes to the generation

of the butterfly distribution. This effect,

which we call "configuration-change

drift-shell splitting," is well known. By

contrast, the effect of magnetopause

-37-

o0)

o_*i

10"

iof

10

CM

iot/lcs

10*"

10-1

i r i i rMarch 30, 1968

1 79 kev

3 4 5 67 8 9 10 11 12

X -35.6° -0.3° 6.9° 10.2 11.2 10.3m -8.3° 4.0° 8.9° 10.9 10.9

GSM

VGSM

337°

-4.4°

322°

•10°

Fig. 27. Radial flux profile on March 30, 1968.

-38-

March 30, 1968

*GSM~330°

L = 8.38 X =10.5°

><u-*i

10C

105

It»_ooI 10*

10'

1 = 6.93 X =8.8° L=5.41 X =5.4°m m

. E7

I30 60 90 0 30 60 90 0 30 60 90

Pitch angle — deg

Fig. 28. Typical outer-belt pitch-angle distributions obtained on themorning side of the earth March 30, 1968.

<u-fCM

March 30, 1968

""GSM"3220

L=10.98 X =11.0° L=10.14 X =11.2° L = 9.18 X =11.0°m m m

10-1 _L30 60 90 0 30 60 90 0 30 60 90

Pitch angle —deg

Fig. 29. Typical pitch-angle distributions near the morning magneto-pause obtained March 30, 1968.

-39-

GM12 10 8 0 -2 -4 -6 -8 -10-12-14-16-18-20

Fig. 30. Contours of constant equatorial-B for an average magneto-sphere [after Fairfield (1968)] . Equatorially mirroring particlesdrift at constant-B as long as the first adiabatic invariant re-mains conserved.

shadowing is an original discovery of this

experiment.

An example of the effects we obtained

in a quiet magnetosphere is shown in

the radial profiles of Fig. 33 and the

corresponding pitch-angle distributions

in Fig. 34. Inside ~9 R~, we attribute

most of the butterfly distribution to

configuration-change drift-shell splitting;

beyond roughly 9 Rp,, the results are due

to the combined action of both shell-

splitting effects. As indicated earlier,

we might expect to find the crossover

point of these effects more in the range 7

to 8 Rp,. Although some other data are

more in agreement with this expectation,

there seems to be a discrepancy indicat-

ing an area of future work. Serlimitsos

(1966) and Haskell (1969) have also

observed the butterfly distribution deep

in the nighttime magnetosphere. They

attribute the distribution to configuration-

change drift-shell splitting only, over-

looking the effect of magnetopause

shadowing.

The almost complete dropout in the

perpendicular fluxes beyond 9 RF, .as

shown in Fig. 33, is quite typical of the

premidnight outer magnetosphere during

periods of magnetic quiet. During dis-

turbed periods, some disruption of the

butterfly distribution occurs. The filling

in of the perpendicular fluxes occurs

more readily for the lower energies; how-

ever, in general, it is electrons, showing

the deep dropout in j., which drift into the

substorm region. For our purposes, this

is ~2300 ± 2 local time. The transition to

-40-

10°E I

10°iv

o

1 101

10-1

in \ i rJanuary 7, 1969

J_1 L 2 3 4 5 6 7 8 9 1 0 1 1 1 2

A -8.2° -31.3° -19.1° -8.0° -0.3° 5.0C

m

"GSMIGSM

-30.1° -26.1° -13.0°. -3.9° 2.6°

67.1° 40.5°

-17.3° 13.7°

Fig. 31. Radial profile of electrons in the afternoonmagnetosphere obtained January 7, 1968.Note beyond 8.5 RJT that j± is no longer thedominate flux in pitch angle. The relativelylarge fluctuations in ji may be due to thefact that these electrons in their eastwardazimuthal drift were closer to the magneto-pause than were the peak fluxes (at ~50-degpitch angles).

a tail-like field in the regions near mid-

night can mean the demise of the butterfly

distribution. We attribute this change to

a transition from guiding-center motion

of the electrons to one in which they get

caught up in the field reversals of the

neutral sheet (Speiser, 1965, 1967, 1971).

It is expected that the electrons can alter-

nate between these two modes until they

either precipitate or drift out of the inter-

action region. Figures 35 and 36 show

data acquired during the famous substorm

of 0714 UT, August 15, 1968. (For the

pitch-angle data see West et al., 1973;

this was part of a nine-paper substorm

study.) Prior to the start of the substorm

growth phase, the field was close enough

to a dipole configuration to maintain the

butterfly distribution. As the substorm

developed, the higher-energy electrons

changed to isotropy, followed by the lower-

energy electrons on a time scale of a few

-41-

10

o .<u ln4V 10

« 10"

E o< ]°2

Mc

o 101

j>(U

" 10°

10

January 7, 1969

*GSM=40-7°

R = 9.87. X = -0.6°,5 m

R = 9.38X =-2.2°

m

R=8.98X =-3.6°

m

30 60 90 0 30 60 90 0 30 60

Equatorial pitch angle — deg

XGSM=8 '3

R = 8.01\ =-7.3°

m

90 0 30 60 9'J

Fig. 32. Pitch-angle distribution of electrons ppstnoon in the distant magnetosphereJanuary 7, 1968. These pitch-angle distributions were transformed to themagnetic equator under the assumption that the position of the dipole equatoris still meaningful this close to the magnetopause.

minutes, Substorm expansion occurred

at 0714 UT. With the resulting occur-

rence of a dipole-like magnetic field,

fresh electrons showing the butterfly dis-

tribution drifted in from dusk. Magnetic

and wave-particle effects disturbed the

distributions so that the undisturbed

butterfly distribution was not observed

until about 0740 UT, which is near the

end of the substorm recovery phase.

Another example of substorm effects

is shown in Fig. 37. Here we show data

obtained near midnight. The data have

been plotted to 4.6-sec averages and are

shown in time sequence without any selec-

tion of angle. The pitch angles of the

particles being detected are indicated by

the panel marked "scan." Of course, only

qualitative pitch-angle information can be

obtained from these plots. By virtue of

the experiment-satellite orientation, the

outer envelope of "scan" is equal to the

field inclination and its complement; when

the envelope is narrow, we have a tail-

like field and when wide, a dipole-like

field.

In the bottom four panels we show the

UCLA magnetometer data in geocentric

solar magnetospheric (GSM) coordinates.

Four well-defined substorms occurred on

this inbound pass; expansion onsets

occurred at 1700, 2012, 2255, and

0108 UT as the field direction began to

rotate to a more dipolar direction. The

-42-

September 18, 1968

60°

40°

20°

uc

-20°

105

usI

0)_*I 10W

£ 10'uV

10V

6Xm -4.5°

*GSM 170°

ZGSM -1.43

(B meas - B dipole)/B dipole

7

-1.0°

-20°

-40°

8 9

1.9° 4.1°

161°

-0.85

10

5.8°

155°

0.07

11

6.9°

12

7.4°

151°

1.21

Fig. 33. The radial flux profile for September 18, 1968. Thefluxes labeled ji, are in reality the peak fluxes in thebutterfly distribution at pitch angles of 20 to 40 deg.Beyond about 9.5 Rjr, the magnetic field becamesomewhat tail-like, so the physical constraints placedon the field of view of our spectrometer meant we couldnot view at much less than 25 deg. The lower energydistributions peaked at higher angles than the higherenergies, accounting for the more complete coveragein jii at low energies. The dashed curves indicate someextrapolation in the data. K = 0+.

-43-

September 18, 1968

R=9.03

10*

± 10V

0)

J 102

I*»uJi 10(!)

0.1

*GSM=158°

R=8.07

1 ' r I ' ^El

I

R = 7.01

X =-0.9° <t>m

=164

30 60 90 0 30 60 90 0

Pitch angle — deg

30 60 90

Fig. 34. Pitch-angle distributions obtained just before midnight September 18, 1968.These distributions inside roughly 9 Rjp are typical of the entire nighttimesector.

electron pitch-angle effects are made

evident by the degree of modulation. Iso-

tropy shows as no modulation except for

statistical scatter. When we observe

modulation in this region of the magneto-

sphere, it is always due to the butterfly

distribution. Following the 2012 UT sub-

storm, we note the onset of enhanced

modulation in E2 at ~2100 UT and in E.

at ~2110 UT. A new substorm growth

period began as the field started to

become more tail-like; at ~2210 UT, we

note the abrupt transition from the butter-

fly distribution to isotropy. Following

the onset of expansion of the 0108 UT sub-

storm, we note the emergence of the but-

terfly distribution in £„ at ~0124 UT and

in E1 at ~0200 UT. It will be noted that

the proton fluxes P. also reflect substorm

effects. The pitch-angle distributions of

the protons are generally isotropic and do

not show the reemergence of the butterfly

during expansion. The butterfly distribu-

tion, however, is usually found in the

nighttime magnetosphere at roughly 6 to

9 Rg. Modulation in the proton fluxes in

Fig. 37 is to be noted, but, as discussed

later, this is due to plasma sheet gra-

dient effects.

Even during a quiet period, electrons

cannot drift through the nighttime mag-

netosphere to dusk without a considerable

modification occurring in the butterfly

distributions. Figure 38 shows data

-44-

80

10

10-

406

10"uSI

r 10°>01

lio2

I

lio1

10-2 _J I I

0600 UT 0700

8I7

0800

Universal time and radial distance

Fig. 35. Perpendicular and parallel electron flux during the0714 UT substorm on August 15, 1968. The electronenergy channels Ej, Eg, and Eg are centered at 79,266, and 822 keV, respectively. The jn shown dottedprior to -0655 UT was obtained from the UCLAexperiment and tacked onto the LLL data. The errorbars are an estimate of the uncertainty in this pro-cedure. The flux, jn, is actually the peak flux in theangular range 135 t'o 150 deg with respect to B. Thetotal magnetic field in the top panel was obtained fromthe UCLA magnetometer experiment.

-45-

80

o

10

406

oVV)

I 'O3

I

<0

10

1 101

JB(1)

10-1

10-20600 UT 0700

I9 R r 8

0800

Universal time and radial distance

Fig. 36. Perpendicular and parallel electron flux during the. 0714 UT substorm on August 15, 1968. This is the

same as for Fig. 34 except the electron channels£2, E4, and Eg are 158, 479, and 1530 keV, re-spectively.

-46-

3

4

3

2

1

0,\

4

3

f 2

•o i

i «8. -i1 *\I $

^ 4

i0

4

3

2

1

0

-1+ OA°

Inc no

Dec Q°

-90° 50

B,-v 251 n

isn"

Scan 9QOI

n«

UT

REX

m

*GSMXGSM

— i r i . . . . } . . . . t . . . . i , . . . .

1 1 1 1 1 1

. . / I '!/&,.... „ : -.. rtkf tt illSS5^ J - ^Sfe x..vV,;.-^ :. ..-..— "7 ""~..' " - ••_--—-_': -^; ^7j; ; >p ._.^r — ',m!17Ii " ^-2 ' • . » • • • "j . 'r- '"-^ • **.*•"' .*. «"

i I I i

pl

^?*£t-j •'•..;.•:•.•.•:..>•'.• .•'.-.•' /..'•.•.V^Vf^^^.j-A *•>'.'•••' -.-. •'••..!• • :-..••'.•.— ••; • •••' .••'.- •.'>•'«.".''.'.>.>•.->.• .'A.-.:...' .•'.•).••' .vX'-". '

i i i i

P2 -

^^r -•'•"••" •'"-;•;••• ~ •^r~-----*~~-:* "i '• ;-' v '""•-'"'"••" ":"•!".''' " ' ' " ' /s"% V .'V .'.

~-J--.Jjryv^— k t~~'V*Av^v .±~^—*± -.- " -- _L

^-Dipole inclination

__,A.,4 i . _.^ .Au*. «*.^ . -...- !• - jf ' ••

^ _____ ^ ^^-^ ^-^__x-'^'txV — '

•*!f*r*~^ ^~ !"IV~^~T"~~. ~ — ~\~ v^~--~^ (

— htttti — i i].i.m.imi i --m— - — -ThhitinyitiitiiitmnmnrniiiiiiiiiiumnifrnnniviniTiTTiiiiiiiiiiiiiiiiiiBiiriiiiiiiiriTmmtijiiiiiininimiiiifivTmpiiiiiiininiiiniimiiiiigeigtiMuiiuiiuiiiauin:inrainniiiirain]niiiniMjimi.*j.iiiiiii.ii Jiiiijjii>EtiituiBjii!iai]iiiiijii!iiiiiiiiM»iuiiniu>tmujujij-tiTniimTOnTiinra-jiiiiiau'cuuiujMLunrivram'tmiiiiiiBjiiuijiiuJiijiiiMiimM 'niMiwiiiiii'uiu

|"|' p| I I I I I 1 1 11 I1" ' I 'ilHWl"!

1 I I I 11700 1800 1900 2000 2100 2200 2300 2400 0100 0200I I I I I I I

18 17 16 15 14 13 12 11 10 9 8•2.8° -3.1° -2.4° -1.3° -0.1° 1.0° 1.8° 2.3° 2.2° 1.6° 0.5°

180° 190°23.0° 13.9°

Fig. 37. Scatter plot of data acquired during an inbound pass near midnight August 9,1968. The small dots show the data at 4.6-sec averages obtained at all pitchangles reached by the experiment scan, whereas the large dots indicate thebackgrounds. The panel labeled "scan" shows the range of pitch angles ob-served by the experiment; the outer envelope is equivalent to the field in-clination and its complement. The data show four well-defined substorms.

-47-

Os:

I

coU

4

3210

-1

5

43

1

0-1

..,,;..;.,.,-^:A^:^ .. ,_.£.>

54

3211

01

1 1 1 1 1 P i i i i-

^-JSBW*""—

- -'-- w'|.n ^, ->->->

. • : • - . :a.>iVi .«'.""*'^Tv^yftgy; r^v^:. ^spp - . '' •>..- •' ,•• " ''•"'y/l''"" ,

Yooo

4321

0-1

1 i i i i i i 1 ' ' 1 1

-_ ,.fj^SS.p ...^tf-gSs**

1 .,, ;0$^j( .;;.;:;-;. .:.;v-,-/i

;

•..•..:<^ f!H{.3$<!i®*&'*l*i'*'"t"*'"*~

.jf*^^^ fj.'*r

-..•:.. . , .-. •.ri-i-^Vx:ia^*-v£^iir:th;rf' . : ''"''"~I7'' ••.•a'.'J.' J. .- ''. V'-. ^" ' • '•'•V/'v'~'.":vrj:;; •_'."•'•'• '.'• '.' r.'"' •'• •"..''.•: .V '"'-•-' "''AV .'•'".'_'••''••'•'•' f'1 .'•'..'".•.' , ,

180°V

§ 90'1/1

0°vraniiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiHiiiiiiiiiiiiiMiiiiuiiiiiiiiiiiiiiiiiiiiiiii'iiiiiniiuiiiiiiiiiiiiiiiiiimiiiiiiiiiiiiuiiiiiiiiuiiiiiiiiiiiiiliiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiniiintiif'

250

250

250

50250

UT

m

18001

17

19001

16

3.4°

2000I

15

-2.1°

2100I

14

2200I

13

-4.6°

2300 24001

12I

11

-5.7°

110

010019

02001 1 18 7 6

0300

-6.9° -8.9"

GSMLGSM

I250°

14.0°

I255°0.4°

Fig. 38. Scatter plot of data during an early morning inbound pass whilein the plasma sheet June 5, 1968. See Fig. 37 for an explana-tion of the plots. The electron data are annotated to show thecharacter of the pitch-angle distributions evident in the variousregions.

-48-

acquired in the plasma sheet on an in-

bound pass at -0500 local time, during

which K was 2 . Figures 39 and 40

show the corresponding pitch-angle dis-

tributions. Note that as we approach

dawn, the change in the field configurar

tion leads to the demise of the butterfly

distribution inside radial distances of

about 9 Rp. Beyond this distance, the

loss of the butterfly distribution is due to

the disruptive influence of tail-like mag-

netic fields and plasma sheet noise.

Figure 41 provides a resum6 of the pitch-

angle results.

We believe this resume of our pitch-

angle results provides the proper overall

view of the effects occurring to the elec-

o0)

icr

o/

O

oV

-H 10'

1 ' I 'June 5, 1968Electron channel E

2209 UT

1938 UT

1758 UT

2026-2052 UT

I

1803 UT

30 60

Pitch angle — deg

90

Fig. 39. Pitch-angle distributions forEj at various times during theinbound pass June 5, 1968.

trons as they drift eastward around the

earth. The story is not complete, how-

ever. An area of major interest is the

noontime magnetopause (noon plus or

minus a few hours and plus or minus

about 50 deg in magnetic latitude). Here

there are questions about the mechanisms

that produce the magnetopause shadowing

effects we observe from a. few hours past

noon extending into the nighttime magneto-

sphere. It may be that the near

equatorially-mirroring particles leave

the magnetosphere directly at the mag-

netopause. Or it may be that they are

scattered by wave activity near the mag- .

netopause so as either to enhance the

fluxes at small pitch angles or cause them

to leave the trapping regions. There is

the possibility also that the equatorial

drift paths for electrons, rather than

mapping to the magnetopause near noon,

may split north and south through regions

of minimum B (that is, through minima in

B along the field line which are not at the

equator) and then come back together an

hour or two past noon. The possibility of

this mechanism was suggested by

Shabansky (1971) and discussed by

Roederer (1969) in his presentation of

field models. Roederer pointed out that

these high-latitude regions have not been

shown to connect topologically to the rest

of the magnetosphere; however, we find

copious quantities of electrons mirroring

in what would appear to.be high-latitude

minimum-B regions, judging from the

experimental results of Sugiura et al.

(1971). The population of the regions is

associated with a general high-latitude

buildup of fluxes near the magnetopause

for both electrons and protons. Our guess

is that the action of the minimum-B paths

-49-

June 5, 1968

2215 UT 2302 UT

105

104

. oT

J[ 103

V

SJ

E 90 1Q*

""x.«/)

iU |

•1 'o1

1

" 10°

in"1

R = 1 2 . 5 8 11.66X =-4.9 -5.4°m

i i | . i | , i i.

f 2302 UTC1

s^ *>r^-— . -^^^^ 2215 UT

E2 ^

s- -^

' ^^X^m

1 , 1 , . ! . .

2345 UTR= 10.75\ = -5.8°

T

, o 2357 UT' R=10.49

X = -5.9°m"1—T

i i I I i

0 30 60 90 0 30 30 90 0 30 60 90

Pitch angle — deg

Fig. 40. Pitch-angle distributions for E^, £3, and £3 at various times during theinbound pass June 5, 1968.

is important in determining the particle

motions.

Proton data may provide some insight

into the problem of azimuthal particle

drift by the noon magnetopause. One

would expect to find magnetopause shad-

owing effects in the prenoon magneto-

sphere. Although these effects are occa-

sionally found and become pronounced at

~0600 LT and earlier (that is, in the

nighttime magnetosphere), they do not

show in the same convincing way as for

electrons. For example, at 9 RF at

0900 LT, the typical pitch-angle distri-

bution is a narrow "normal" distribution

sitting on an isotropic background. We

have a very real problem in reconciling

the proton data to the clear effects of

magnetopause shadowing obtained for the

electrons.

PLASMA SHEET BOUNDARYMOTION DURING A SUBSTORM

The plasma sheet boundary motion was

was studied in detail during the 0714 UT,

August 15, 1968, substorm (Buck et al.,

1973). Figure42 shows the geometry

existing at the start of this substorm's

growth phase. The experiment scanned

looking out perpendicular to the earth's

radius vector, looking alternately from

west to east. It saw particles whose

-50-

YGSMEquatorial pitch angledistributions

15

15 --10 - V ~ /\

GSM

A Normal

f\f\ Butterfly

Isotropic

Fig. 41. . Survey of equatorial pitch-angle distributions throughout themagnetosphere. In those nighttime regions beyond ~9 Rgwhere a mixture of distributions prevail, the results arestatistical.

Plasma

IRe

0640 UT

Anticipated neutral

sheet position

GSM equator

Fig. 42. Scale drawing in the XQSM " ZGSM Plane showing thesituation at the start ofthe growth phase of the August 15,1968, substorm. The magnetic field had almost doubledby the end ofthe growth phase, so at that time the protonorbits were about half the size shown here.

-51-

80

CO

u0)r

O

OO

ClI

40

107

10C

r10g

rIO5

rIO

10"

-102 103

0600 UTI

9 R £

0700 0800

8

Universal time and radial distance

Fig. 43. East and west proton fluxes measured during the0714 UT August 15, 1968, substorm. The toppanel shows the scalar magnetic field variationduring the substorm. jie and jxw are the peakfluxes (average energies Pj =0 .12 MeV,?2 = 0.33 MeV, and P, = 0.81 MeV) measuredperpendicular to I? in the approximate east andwest directions. JQ is the value of the flux at theradial position of OGO-5 at pitch angles of about110 deg. .

-52-

gyro centers varied in position from

above the spacecraft to below the space-

craft. The complete scan took about

1 min; hence, every minute or so we

were able to generate a flux gradient by

assigning the measured fluxes to their

average position of motion. For perspec-

tive we show, in Fig. 43, a radial profile

of fluxes measured below the spacecraft

(j ), at the spacecraft (jQ), and above

the spacecraft (j. ). The flux gradient

history is shown in Fig. 44. The e-fold

boundary lengths and boundary velocities

are given in Figs. 45 and 46, respectively.

These data indicate that, in the region of

the midnight cusp where these data were

taken, the plasma sheet virtually col-

lapsed just prior to substorm expansion.

This observation has led to the sugges-

tion by McPherron et al. (1973) that

reconnection near the midnight cusp may

be the causitive factor in the initiation of

the substorm's expansive or explosive

phase.

We studied boundary motions during

several other substorms; a preliminary

account was presented by Buck et al.

(1972). In these studies, a steepening

XD

I'0'o

<u~° •£ «•O C I-

10"

• - 3 8 O IT) CO•fe <u or^-o>oLLI C— OO O

+1.0

10'

10

>,0706 AN^

i\ Vx0709

X0712

+0.5 -0.5

Z B~ R E

Fig. 44. Proton flux profile evolution during the substorm. Each set of curvesis a profile obtained from one full scan of the experiment aperture atthe indicated times. The thinning wave at the plasma sheet boundarybecame apparent about 0656 UT. The anticipated position of the neutralsheet (magnetic equator) is indicated at various times to the left. Thedata are representative of the flux in Pj in units of protons/cm^-sr-sec.The heavy line is Pj; the light lines are Po and P-$, the latter beinglonger. The P3 data after 0650 UT are deleted from the plots.

-53-

and thinning of the boundary always oc-

curred. However, in each case, OGO-5

was too high above the expected position

of the neutral sheet to determine the

extent of sheet collapse. Also, OGO-5

was deeper in the magnetotail than for

the 0714 UT August 15 substorm. These

data are not inconsistent, however, with

the suggestion that reconnection near the

midnight cusp may be the causitive factor

in substorm expansion.

THE APRIL 1969 SOLARPARTICLE EVENT

This interesting event (the largest

electron event ever recorded) was due to

a flare on April 10, 1969, behind the sun's

east limb. Figure 47 shows the time his-

tory of the electrons as observed on

10

: Well inside 5 §: sheet

IQ

0.1

0.01

}}•Boundary regionion I

»Thinning wave

0610 0630 0650 0710

Universal time

Fig. 45. The characteristic e-fold lengthsof the boundary. The data showboth the slowly varying regiondeep in the sheet and the boundarywave that-became appar'ent at-0656 UT.

E

i1c.9t3o>

rf\

Nc

*™

£"o_o

*oc3

£

Fig.

109

8

7

6

5

4

3

2

10

1 I . I 1 1Q

4lmsr

a r i n

/

a —

_

— D —a

— aa —

— —

— —

— —

I I 1 1 10630 0640 0650 0700 0710 0720 0730

Universal time

46. Boundary velocity perpendiculaito B (ZB-direction). The slowvariation is associated with thevariations deep in the sheetduring the early growth phase,whereas the rapid variationnear the end is associated withthe advance of the thinning.wave. The velocity in the•ZGSM direction was -0.9 ofthat shown in this figure.

OGO-5. Similar data have been obtained

for protons, but as yet we have done noth-

ing with these data. In contrast to west-

limb events, where the particles can take

advantage of the spiraling interplanetary

magnetic field in their transport to Earth,

the particles from this east-limb event

had to arrive at Earth by indirect means

(diffusion, convection, drift, etc.). It

would appear that this event is perfect for

the diffusive analysis of electron trans-

port, but our early attempts to this end

have not been successful. Possibly some

of the more recent theoretical formula-

tions will work.

By chance, during the course of the*

event, a similar magnetic spectrometer

A. L. Vampola, Space Physics Labo-ratory, The Aerospace Corporation, LosAngeles, California.

-54-

o(U

I>J

Ies

u

u0)

102

10

10-1

79keV

11 12 13 14 15

April 1969

16 17 18

Fig. 47. The time history of the April 1969 solar-particle event asobserved by the magnetic electron spectrometer on OGO-5.Data obtained in the magnetosphere that clearly representedtrapped radiation are excluded from this plot. Normally, thesolar fluxes could be identified well inside the magnetosphere,with no sign of discontinuity at the magnetospheric boundaryexcept for the superposition of trapped radiation.

was collecting data on the polar orbiting

Airforce Satellite OV1-19. This experi-

ment provided for good data correlation

(West and Vampola, 1971) between the

polar caps and the interplanetary region.

The two experiments tracked j. values

during the event's history. A compari-

son at the peak of the event is shown in

Fig. 48.

To summarize these observational data

data, we have:

(1) Absolute flux intensities and

energy spectra: There was tracking of

fluxes and spectra between the interplan-

etary region and over the north and south

polar caps during the entire history of the

event.

(2) Pitch-angle distributions: (a) The

interplanetary pitch-angle distributions

were isotropic. (b) The pitch-angle dis-

tributions over the polar caps were iso-

tropic except for the single loss cone

when looking towards Earth, (c) Sharp

discontinuities were observed in pitch-

angle distribution (energy-independent)

when transiting from the quasitrapping

region (double loss cone) to the polar

caps (single loss cone) on the sunward

-55-

IU

103

o4>

in1

-* 101CM

E0

«/>c20 10V

1•H

1

-110

: 1 — i — i i i 1 1 1 1 1 — i — i i i 1 1 1 1 1 — i — i i i 1 11.; April 13, 1969 :

i \ ' • i\X

: \, :: \ :r V . -- x "

- - *b ;

0910-0925 UT *

- o OGO-V \

: « QV1-19 V :

South polar cap \

1050-1 105 UT \

; • OGO-V ? '-+ ovi-i9 \ ' :

North polar capt ! | ! , ( ) , , ,

10 102 103 104

Energy — keV

Fig. 48. Comparison of electron-spectrometer data obtained onOGO-5 and OV1-19 near thepeak of the solar-particleevent on April 13, 1969. Forthe 0910-0925 UT data, OV1-19was over the south polar cap,altitude >4 500 km; for the1050-1105 UT data, it was overthe north polar cap, altitude<2000 km.

side of Earth, (d) Sharp discontinuities

were observed in pitch-angle distribution

(energy-independent) when transiting

from the outer zone to the polar cap at

local midnight.

(3) Polar flux profiles: (a) Uniform

particle distributions were observed over

the polar caps, (b) There were sharp dis-

continuities of particle fluxes in transit-

ing from quasitrapping region to polar

caps,

(4) Solar magnetic-field sector bound-

ary effects: No particle effects were

obvious at OGO-5 or OV1-19 during the

~1140 UT, April 13 interplanetary solar

magnetic sector crossing.

Observations 1, 2a, 2b, 2c, 3a, and

3b can be explained through a picture of

adiabatic motion. We allow the polar

field lines to connect to the solar field in

the interplanetary medium. The elec-

trons are expected to start off in the

interplanetary region where they are in

diffusive equilibrium, to spiral along the

field lines to the region over the polar

caps, then to mirror and return to the

interplanetary region. This picture is in

strong support of the model of the "open"

magnetosphere.

The pitch-angle and flux discontinuity

at the polar plateau (observations 2c and

3b) would at first glance appear to be a

crowning achievement of the "open" mag-

netosphere model. However, one would

anticipate no energy dependence in the

latitude of the pitch-angle discontinuity

(observation 2d), as .is found to occur

near local midnight. On April 13, near

the peak of the event, the transition

occurred at 64.89 ± 0.05'deg invariant

latitude for 50-keV electrons and 64.43

± 0.05 deg for 1.1-MeV electrons. Also,

there was no obvious effect in the OV1-19

data during the April 13 interplanetary

sector crossing, which occurred near the

peak of the particle event. In the pres-

ence of appreciable direct connection, we

would expect to find an effect due to re-

arrangement of the magnetic-field config-

uration. These two observations weaken

the arguments for the "open" magneto-

sphere model.

THE NOVEMBER 18, 1968SOLAR PARTICLE EVENT

A preliminary account of this work

was presented by D'Arcy et al. (1970).

-56-

This solar particle event was the result

of a west-limb flare. Relativistic pro-

tons were observed on Earth by neutron

monitors. OGO-5 was on the dusk side

of Earth, in position to observe the

scatter-free propagation of electrons and

protons along the spiraling interplanetary

magnetic field leading from the sun to the

vicinity of Earth. The early arrival is

shown in Fig. 49 by the scatter plot of the

EX electrons (79 keV). The data points

are shown in time sequence as the exper-

iment scanned about an axis (the earth's

radius vector, inclined about 34 deg to the

plane of the ecliptic), so that the experi-

ments aperture viewed largely in the

north-to-south direction. The experiment

looked somewhat west of the sun when

060 V DETECTOR ORBIT YEAR MONTH DAT YDAY LOAY HOUR flIN. SEC. RIMINIT. El 100 68 NOV 18 323 259 9 51 41.2 WFINAL CB> 12 9 M.I

«a riii «EcoR8 air A-O NEC nit RECi 11 ts itt 2 o

12 5 tO 940 0

8-

E+Oj

(4

w

gE*H

64

E»OJ

E-OtL * 4 8MfM ^ ^

HOURWH.RLMlKSEICSE•CSM•CSX

9"24

23.32823.545

5.2272.635.975.711.4

936

23.32623.543

5.2072.855.775.811.1

948

23.32223.542

5.2072.935.675.910.9

to0

23.31725.541

5.2373.035.576.010.7

1012

23.31125.542

5.2975.155.376.110.6

1024

23.30425.545

5.5873.235.276.110.4

1036

23.29523.545

5.4973.535.176.210.3

to48

23.28523.548

5.6273.534.976.310.3

I t0

23.27425.551

5.7875.634.876.410.3

M12

23.26123.556

5.9773.734.776.410.3

It24

23.24823.562

6.1773.834.576.510.3

1136

23.23323.568

6.4073.934.476.610.3

t t48

23.21623.577

6.6574.134.376.710.4

120

23.19925.588

6.9374.234.176.710.5

1212

0.0.0.

0.0.0.0.

Fig. 49. E, fluxes obtained during the early time history of the November 18, 1968,solar particle event.

-57-

viewing in the ecliptic plane. The upper

envelope of the data is due to electrons

arriving from the direction of the sun;

the lower envelope is the back-scattered

component. These data, including proton

data, are being analyzed by workers at

the Bartol Research Foundation, Swarth-

more, Pennsylvania.

HIGHLY -ANISOTROPIC PROTONDISTRIBUTIONS OBSERVEDINTERPLANETARY

Our experiment made numerous meas-

urements of highly-anisotropic proton

distributions in the interplanetary medium.

Some of these observations are associated

with a well-defined solar particle event;

OCO V DETECT*IN1T. PIFINAL PBt

ORBIT YEAR HONTH W YWY LOiY HOUR HIN. SEC. RUN REEL FILE RECORD KBIT A-0 REC MAC REC PACE94 68 HOY t 306 242 21 44 37.7 296 4 2 257 8KB 1 4 11

22 4 17.2 520 306 78

E-OI,

HOUR 21 "KIN. 44R 15.668L 26.947Ml 40.21WSE 66.0ICSE 52.1*SSH 69.1ICSH 45.6

2146

15.69626.948

40.1566.152.169.145.6

2148

15.72326.948

40.0966.252.069.245.6

2150

15.75126.94740.0366.352.069.345.6

fi13.77926.94639.9766.352.069.345.6

|i15.10626.94539.9166.431.969.445.5

fi15.13326.94339.1566.551.969.445.5

15.86126.94039.7966.651.969.545.5

220

15.18!26.93639.7366.751.869.645.5

22

15.91526.93239.6666.751.869.645.5

22

15.94226.92839.6066.851.869.745.4

226

15.96926.92339.5366.951.769.745.4

Fig. 50. Example of highly directed solar protons obtained on OGO-5. Note thatthese low energy protons (~100-150 keV) are directed along the field line.

-58-

KO V DETECTOR ORBIT YEAR HONTH DAT YDAY U)AY HOUR KIN. SEC. RUN RED. FILE RECORDINIT. PI 94 68 NOV 1 306 242 23 59 50.1 296 5 4 118FINAL FBI 25 59 29.6 iat

BJBO

KBIT A-0 REC HAG REC PACE8KB 1 4 6

363 9086400

E-01,

HOUR 23"HIM. 38R 17.142L 26.152XH 35.92•CSE 70.1•CSE 50.2•GSM 72.5«CSH 43.4

2340

17.16626.12635.83

70.150. t72.643.4

23

17J8926.10135.74

70.2S0.172.643.3

2344

17.21326.07935.64

70.350.172.743.3

2346

17.237235$

70.350.072.843.2

t17.26126.02339.46

70.450.072.843.1

1117.2152S.996J5.J7

70.550.072.943.1

17.301vs70.550.072.943.0

2354

17.33225.943

39.1870.649.973.042.9

2396

17.35525.91715.01

70.649.973.142.9

2358

17.57925.89034.99

70.749.975.142.8

240

0.0.0.0.0.0.0.

Fig. 51. Example of highly directed solar protons obtained on OGO-5. Note thatthese low energy protons (~100-150 keV) are directed along the field line.

a

I

Sa

others seem to be isolated bursts of .

protons lasting from minutes to tens

of minutes. During a well-defined solar

particle event, we find the usual in-

crease in anisotropy as we go to lower

energies. The lowest-energy channels,

however, can show high degrees of

anisotropy. In the cases we examined,

the protons may be observed coming

from roughly the solar direction. Other

examples of large anisotropy are shown

in Figs. 50 and 51. These data were

acquired during the solar particle event

accompanying the intense magnetic

storms of October 31- November 1,

1968.

-59-

Concluding Remarks

This experiment made significant

advances in several areas:

• The electron distributions and

dynamics of the inner belt were

provided for 1968 and 1969. These

data will be useful in studying the

diffusive transport of particles in

the inner magnetosphere.

• A partial study was carried out

covering the electron pitch-angle

distributions and dynamics of the

slot and outer belt regions.

• A rather complete survey was

made of the electron pitch-angle

distributions throughout the equa-

torial regions of the outer magneto-

sphere, with special insight into

magnetopause-shadowing drift-shell

effects, field-configuration-change

drift-shell-splitting effects, and

substorm effects. These data pro-

vide a good view of the azimuthal

drift motions of electrons in the

distorted-field regions of the outer

magnetosphere. .

• Detailed motions of the plasma

sheet in the tail were observed dur-

ing a substorm, using the proton

east-west effect. These data show

the almost complete collapse of the

tail field prior to substorm

expansion for the case studied.

• The transport of solar electrons to

the polar caps was studied via cor-

relative data from both the OGO-5

and OV1-19 satellites. These data

provide insight into magnetospheric

structure.

There is still considerable work to be

done with our OGO-5 data that we believe

to be significant:

• The detailed organization of the slot

and the outer-belt data needs to be

completed so that theoreticians can

study the transport problem in the

trapping regions following storm-

time injection (our inner belt data

already are organized adequately).

• Electron pitch-angle distributions

need to be studied more thoroughly

in light of the recent theoretical

advances in our understanding of

pitch-angle diffusion in the

plasmasphere.

• Electron and proton distributions

need to be studied near the noon

magnetopause to assess their azi-

muthal drift motions through

minimum-B regions in the earth's

magnetic field.

• Electron pitch angles need to be

studied more thoroughly in the pre-

midnight magnetosphere to permit

better understanding of the pitch-

angle signature in the study of mag-

netic field topology,, especially with

regard to substorms.

• A complete survey of proton pitch-

angle distributions needs to be con-

ducted at all local times in the

equatorial regions.

• The proton east-west effect needs

to be exploited more fully in the

study of plasma-sheet dynamics,

especially during substorms. This

seems to be the most effective way

of studying boundary motions on a

single satellite.

• The manner in which electrons

drift azimuthally through the region

-60-

of the midnight cusp so as to main-

tain some semblance of the butter-

fly pitch-angle distribution needs to

be understood. This will provide\

additional insight into field topology

for dynamic and static periods.

• Well-defined plasma sheet oscilla-

tions, observed past midnight in

terms of particles and B-fields,

need to be understood. Are these

effects associated with the solar

wind?

• The appearance of energetic elec-

trons and protons in the magneto-sheath near the high latitude mag-

netopause needs to be understood.

There may be a tie-in to reconnec-

tion.

• The highly directed solar protons

observed interplanetary need to be4

investigated. Do these low energy

particles follow the convective

flow of the solar wind?

• The scatter-free propagation of

solar electrons from the sun to the

earth needs to be investigated fur-

ther in order to enhance our under-

standing of particle transport.

• The April 1969 solar particle event

needs to be understood more thor-

oughly in terms of particle trans-

port. As a follow up on this work,

there are several other events that

should be studied.

• The manner in which solar protons

gain access to the near-earth trap-

ping regions (~3 RE> needs to be

understood.

The above list is by no means com-

plete. This experiment has provided a

veritable goldmine of information. It is

hoped that a significant portion will reach

the printed page.

Acknowledgments

Many people contributed to the suc-

cess of this experiment. Those assist-

ing in the construction phase are cited

in the instrument report. In the data

reduction and analysis phase, we acknowl-

edge the continued support of E.

Mercanti (Program Manager), K. Meese

(Program Coordinator), J. Meenen

(Operations), and H. Lindner (Data

Processing) of GSPC. We thank P. J.

Coleman and C. T. Russell of UCLA for

the ready availability of their OGO-5

vector magnetometer data. In addition,

we thank C. T. Russell, R. L. McPherron,

Margaret G. Kivelson, and T. A. Farley,

all of UCLA, for many stimulating dis-

cussions during the course of data

analysis.

The people directly assisting the auth-

ors at Lawrence Livermore Laboratory

were M. M. Zeligman and Bettie Myers.

They were responsible for handling the

large amounts of data produced by the

experiment. R. G. D'Arcy, Jr., who was

responsible for the proton spectrometer

while at Livermore, has continued with

the data reduction of these data at the

Bartol Foundation.

The work covered in this report was

performed under the auspices of the U. S.

Atomic Energy Commission, funded in

part by NASA under P. O. S-70014-G.

-61-

References

Buck, R.M., H.I. West, Jr., and R. G. D'Arcy, Jr., "Evidence for thinning of the

plasma sheet during the August 15, 1968 substorm," EOS Trans. Amer.

Geophys. Union 51, 810, 1970.

Buck, R. M., H.I. West, Jr., and R. G. D'Arcy, Jr., "Energetic protons as probes of

magnetospheric particle gradients," EOS Trans. Amer. Geophys. Union 53,

486, 1972.

Buck, R.M., H.I. West, Jr., and R. G. D'Arcy, Jr., "Satellite studies of magneto-

spheric substorms on August 15, 1968: 7. OGO-5 energetic proton observa-

tions —Spatial boundaries," J._GejDp_h^s,._JRe_s_. 78, 3103, 1973.

Fairfield, D. H., "Average magnetic field configuration of the outer magnetosphere,"

J. Geophys. Res. 73, 7329, 1968.

Haskell, G. P., "Anisotropic fluxes of energetic particles in the outer magnetosphere,1

J. Geophys. Res. 74, 1740, 1969.

Lyons, L. R., R. M. Thorne, andC.S. Kennel, "Pitch angle diffusion of radiation belt

electrons within the plasmasphere," J. Geophys. Res. 77, 3455, 1972

McPherron, R. L.( M. P. Aubry, C.T. Russell, and R. J. Coleman, "Satellite studies

of magnetospheric substorms on August 15, 1968: 9. Phenomenological models

for substorms," J. Geophys. Res. 78, 3131, 1973.

McQuaid, J. H., "An electron and proton spectrometer detector system for an OGO-E

satellite experiment," IEEE Trans. Nucl. Sci. NS-13 No. 1. 515, 1966.Pfitzer, K., "The spectra and intensity of electrons in the radiation belts," Space Rej^.

6_, 702, 1966. .

Pfitzer, K. A., and J. R. Winkler, "Experimental observation of a large addition to the

electron inner radiation belt after a solar flare event," J. Geophys. Res. 5792,

1968.

Roederer, J. G., "On the adiabatic motion of energetic particles in a model magneto-

sphere," J. Geophys. Res. 72, 981, 1967.

Roederer, J. G., "Quantitative models of the magnetosphere," Rev. Geophys. 77, 77,

1969. .

Serlimitsos, P., "Low energy electrons in the dark magnetosphere," J. Geophys. Res.

7J_, 61, 1966.

Shabansky, V. P., "Some processes in the magnetosphere," Space Sci. Rev. 12, 299,

1971.

Speiser, T. W., "Particle trajectories in model current sheets: (Part 1). Analytical

solutions," J. Geophys. Res. 70, 4219, 1965.

Speiser, T. W., "Particle trajectories in model current sheets: (Part 2). Aplications

to auroras using a geomagnetic tail model," J. Geophys. Res. 72, 3919, 1967.

Speiser, T. W., "The Dungey model of the magnetosphere, and astro-geophysical

current sheets," Radio Sci. 6, 315, 1971.

-62-

Sugiura, M., B. G. Ledley, T. L. Skillman, and J. P. Heppner, "Magnetospheric-field

distortions observed by OGO-3 and 5," J. Geophys. Res. 76, 7553, 1971.

West, H. I., Jr., L. G. Mann, and S. D. Bloom, "Some electron spectra in the radiation

belts in the Fall of 1962," Space Res. 5, 423, 1965.

West, H. I., Jr., "Some observations of the trapped electrons produced by the Russian

high altitude nuclear detonation of October 28, 1962," in Radiation Trapped in the

Earth's Magnetic Field (B. M. McCormac, ed.), Dordrecht, Holland: D. Reidel

Publishing Company, 634, 1965.

West, H. I., Jr., J. H. Wujeck, J. H. McQuaid, N. C. Jenson, R. G. D'Arcy, Jr., R.W.

Hill, and R. M. Bogdanowicz, "The LRL electron and proton spectrometer on

NASA's Orbiting Geophysical Observatory V(E) (instrumentation and calibra-

tion)," Lawrence Livermore Laboratory, Rept. UCRL-50572, June 1969.

West, H. I., Jr., R.W. Hill. J. R. Walton, R. M. Buck, and R. G. D'Arcy, Jr.,

"Electron and proton pitch-angle distributions in the outer magnetosphere,"

EOS Trans. Amer. Geophys. Union 50, 659, 1969.

West, H. I., Jr., R. M. Buck, and J. R. Walton, "Electron spectra in the slot and the

outer radiation belt," EOS Trans. Amer. Geophys. Union 51, 806, 1970.

West, H. I., Jr., R. M. Buck, and J. R. Walton, "The butterfly pitch-angle distribution

of electrons in the postnoon to midnight region of the outer magnetosphere as

observed on OGO-5," EOS Trans. Amer. Geophys. Union 53, 486, 1972a.

West, H. I., Jr., R. M. Buck, and J. R. Walton, "Shadowing of electron azimuthal-drift

motions near the noon magnetopause," Nature Phys. Sci. 240, 6, 1972b.

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throughout the magnetosphere as observed on OGO-5," J. Geophys. Res. 78

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substorms on August 15, 1968: 6. OGO-5 energetic electron observations —

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78, 3093, 1973b.

-63-

Distribution

LLL Internal Distribution

Roger E. Batzel

J. S. Kane

W. E. Nervik

H. L. Reynolds

J. E. Carothers

J. N. Shearer

R. D. Neifert

H.I. West, Jr.

R. M. Buck

J. R. Walton

LBL Library

TID File

External Distribution

100

30

K. MeeseE. MercantiOffice of DirectorOffice of Assistant Director, Projects 3Office of Assistant Director, T&DS 3

Office of Assistant Director, SSOffice of Technical ServicesLibraryNegotiatorTechnical Information DivisionNational Space Science Data CenterTechnical DirectorGoddard Space Flight CenterGreenbelt, Maryland

M. PomerantzThe Bartol Research Foundation

of the Franklin InstituteSwarthmore, Pennsylvania

R. G. D'Arcy, Jr.Cambridge, Massachusetts

A. SchardtE. SchmerlingL. KavanaughCode SGNASA HeadquartersWashington, D. C.

Technical Information CenterOak Ridge, Tennessee

332

57

NOTICE

"This report was prepared as an account of work sponsored bythe United States Government. Neither the United Stales northe United States Atomic Energy Commission, nor any of theiremployees, nor any of their contractors, subcontractors, or theiremployees, makes any warranty, express or implied, or assumesany legal liability or responsibility for the accuracy, completenessor usefulness of any information, apparatus, product or processdisclosed, or represents that its use would not infringe privately-owned rights."

CSM/rt/edas

-64-