Studies of magnetic micropulsations with special reference to discrete emissions in the vicinity of one cycle per second

STUDIES OF MAGNETIC MICROPULSATIONS

WITH SPECIAL REFERENCE TO

DISCRETE EMISSIONS IN THE VICINITY OF ONE CYCLE PER SECOND

VOLUME I

A Thesis presented for the

degree of Doctor of Philosophy.

University of Canterbury

1965

ABSTI:U\.C'J1

The work on magnetic micropulsations described in this

thesis falls into two parts. The first part considers micropulsations associated with meteoric phenomena, a high-altitude thermo-nuclear explosion, and man-made

el~ctromagnetic interference.

In the study on the association of micropulsations with

meteors, both the effects of hourly meteor rates and individual meteor occurrences on micropulsation activity in the

1.5

cps band recorded at the same site1 are considered. It i.s found that the variation in hourly meteor rates, plotted through a succession of nights, is not significantly related to the

corresponding micropulsation activity. Most individual meteors do not have any associated micropulsation activity, but the number of coincidences is greater than random, and it remains possible that some of the larger meteors do produce magnetic

effects.

Observations of the magnetic disturbance produced by the

July

9,

1962

thermo-nuclear explosion above Johnston Island are

described and the characteristic oscillation periods are

interpreted.

In

the second part of

the

thesis,

the

development

of

recording and data analysis instrumentation, suitable for observing

the

frequency-time properties of signals in the Pc1

band (0.2 -

5

cps), is described and the characteristics of eight months of recorded data are interpreted in order to gain insight into the origin of the discrete Pc1 emissions generally known as pearl-type micropulsations or hydromagnetic emissions .•

Special attention is given to the design of a galvanometer-photocell p.reamplifier and it is shown that the frequency response

of a standard laboratory galvanometer may be extended, by the application of feedback, to cover a considerable portion of the

i i .

The fine structure properties of hydromagnetic emissions are found to be in qualitative agreement with recently suggested theories for emission propagation by hydromagnetic ion cyclotron wave packets in the magnetosphere. Significant diurnal variations in hydromagnetic emission fine structure parameters are established, and it is shown that these are not associated with the daytime

attenuation of hydromagnetic waves in the :ionosphere, but with the emission source in the magnetosphere. The diurnal variations indicate that the emission source is located near the L=4 field

line between 03 - 06 hr

L'r,

and near thEi L::::

6.5

field line between

12 - 15 hr LT.

The diurn~l movement in the emission source position provides a simple explanation fo~ the variation in hydromagnetic emission diurnal occurrence with latitude, and is also consistent with the variation in average emission

frequency with latitude. It is suggested that the diurnal

movement in the source position may result from the magnetospheric convection of low energy trapped particles.

A preliminary analysis of the effects of geomagnetic activity on hydrornagnetic em:L.ssions shows that the average night time location of the emission source is in the vicinity of the L=5 field line on extremely quiet days, and the

L=3.7

field line on moderately

The writer would like to acknowledge the continual advice and suggestions of Professor G.D. Ellyett. He

would also like to thank those who assisted in the

TABLE OF CONTENT'S

ABSTRACT

ACKNOWLEDGEMEJ\f~P.S

LI.ST OF TABLES I. INTRODUCTION

PART JL MAGJ\TETI C EF'FI<:CTS E'ROM ME~PEORS, NU CLEAR DETON A.1_.rION AND MI\J\l-MADE INT'ERF'J:GRENCE.

II. 'l'HE CORRELATION OF METEORS WI'l'H MICROPULSATIONS 2.1 Introduction

2.2 Micropulsation Equipment 2.3 Radar-Meteor Equipment

2.4 Correlation of Diurnal Variations

2 4.1 All-sky Meteor Aerials

2. 4. 2 Yagi Aerials giving Locali:;;:.ed Meteor Rate,s 2.5 Correlation of Magnetic Effects with Individual

Meteors 2.

6

Discus.:;ion

III. MAGNE~1_{IC DISTURBANCE l?ROM 'I'HE ~fULY} 9 ~ _'1962

HIGI-:I-ALTITUDE NUCiiEAR EXP.LOi'HON Introdiic tion

Observations

Discucision

IV. MAN-MADE ELECTROMAGNETIC INTERFEIIJBNCE

iv.

i i i i

ix 1

5

7

9

10 10 1 'I ·12

·15

19

19

20 21

4 1 Introduction 23

4.2 Background Noise at 1.5 cps.

4.3 Interference from a D.C. Electric Train System

4.4 Conclusion

PART B. DISCRETE EMISSIONS IN THE VICINTrY OF ONE CYCLE PER SECOND

v.

THE DESIGN OF RECOIWING IN,SU?Ul'lfEN'rATIOJ\T

5.1

Introduction

5.2

Sensitivity Requirements

5.3

The Detector Coil

5.4 The

Galvanometer-Photocell Amplifier 5.4.1 Transfer Function

5.4.2

PracticaJ Design Considerations

5 5

Slow-Speed Magnetic Tape Recording .5 6 ,c;ummary

24

25

26

26

2'7

') () L .. ~ /

30

30

VI.

nrn

POH'l'ABLE m~COIUJING SYE!TEM 6.'I General

6.2

Calibration

6.3

Operation

VII. THIG DA'l'A ANALYSIS SY.STEM

7.1

Introductiom

7.2 Analysis Method

7.3

Data Channel Specifications

7.3.1.

Sonagraph

7.3.3.

Calibration

7.3.4.

Tape Speed Variations

'?. 4

Timing

VIII .Pc1 GEOMAGNETIC MICJ:IOPULSA'I'IONS

8.1

Introduction

8.2 Uydromagnetic Emissions

8.2.1. Amplitude-Time Characteristics 8.2.2. li'requency-·Tim,3 Characteristic13

39

40 40 42 42

43

44

46

46

48

48

49

49

49

8. 3

Diurnal Variations in Hydromagnetic Emitrnioru3 50

8. 4

Spatia1 Va:ciatio1us in llydromae;net:Lc EmurnJ.oru::3 .'.)'1

8.5

Additional Hydromagnetic EmissJon Pro~~rtie

₅₃

8.5.1.

Ionosp~eric Attenuation

8.5.2

Polarization

8. 6

Hydromagnetic Emic;sion:s and other Geophysical

Phe non1e na

₅₄

8.7

Storm-Time Pc1 Emissions

~55

8. 8

Sur<tmoJ::'y

IX. EXCITA'.rION AND PROPAGArrION Oli' lIYDl?OMAGNE':I'IC EMISSIONS 9.1 Introduction

9.2 Hydromagnetic Wave Propagation in the Magnetosphere 60

9.2.1. General Dispersion Relations

60

9.2.2.

Ion Cyclotron Waves

62

JC ra

9.4

Attenuation Processes

9.4.1 Non-collision Thermal Damping 9.4.2. Ionospheric Attenuation

9.5

Summary

GENERAL PROPERTIES OF

Pc1

EMISSIONS

vi.

68

68

69

69

71

10.1 Introduction 71

10.2 Method of Analysis 71

10.2.'I. Data Reduction 71

10.2.2. Errors

73

10.3 Frequency-Time Characteristics of Hydromagnetic

Emissions

74

10.3.1. Waveform Properties

₇₄

10.3.2. Fine Structure Properties

75

10.4 Relationship between hydromagnetic Emission

Midband Period and Fine Structure Band Spacing

77

10.5 Relationship between Hydromagnetic Emission Fine

Structwne Band Spacing and Band Slope

78

10.6 Hydromagnetic Emission occurrence and Geomagnetic

Activity.

79

10.7 Simultaneous Observations of Hydromagnetic Emi:..1E.ions

at Widely Spaced Stations 80

10.8 Frequency-Time Characteristics of Storm-Time Pc1 Emissions

1

o. 8.1.

Na:r:roW·,,band Emissions

10.8.2. Broad-band Emissions 10.9 Summary

81

81

XI. DIURNAL VARIATIONS IN HYDROMAGNETIC EMISSIONS 11.1 Introduction

82

83

84

84

84

85

85

87

88

11.2 Occurrence Rates

11.

3

Emi,ssion Parameters

11.3.1. Midband Frequency

11.3.2., Fine Structure Ba,:nd Spacing 11.4 Frequency Spectra

11.5 Daytime Hydromagnetic Emissions 11.5.1. Emission Characteristics

11.

5. 2.

Emis,sion. E'requency and Ionospheric

Attenuation 90

XII. GEOMAGNETIC DIS'I'URBANCE AND HYDROMAGNETIC EMISSIONS

92

12.1 Introduction 92

12.2 Selection of Data 92

12.3 Storm-Time Variations in Emission Parameters

93

12.3.1.

Nighttime Emissions

93

12.3.2.

Daytime Emissions 94

12.1 Emission Parameters and Daily Magnetic Activity

97

12.5

Summary

98

XIII .DISCUSSIONS

99

13.1 Fine Structure Properties 100

13.2

Diurnal Variations

102

13.2.1. Emis,:don Parameters

13.2.2. Emission Source Location 13.2.3. EmisGion Occurrence

13.2.4.

Energetic Particle Distributions

13.3 Storm-Time Variations XIV. CONCLUDION,S AND RECOMMENDATIONS APPENDICIES

I. TRANSFER FUNCTION APPROXIMATIONS II. PORTABLE RECORDING ],;QUIPivifmT

2.1 Detector Coil

2.2 Galvanometer-Photocell Amplifier 2.

3

Tape Amplifier

2.4 Bias

Oscillator

2.5 Slow-speed Tape Deck

2.6

Timing System

2.7

Calibration Oscillator

2.8

Power Supply

III. DArrA ANALYSIS EQUIPMENT 3.1 Equalization Amplifier

3.2 Audio Frequency Amplifier

102 104 107 109 110 113 11? 'i 18 118 1 '18

3.3

Pulse Amplifier

3.4 Pulse Counter IV. DATA RECORDING PETUODS

REF'ERENCES

viii.

'!22

123 124

2.1 Correlation of individual meteors with individual micropulsations

2. 2 Number of small and large meteor echoes with accompanying micropulsations

3,'I Characteristic• phases of the J'uly 9, 1962 nuclear

7.1

10.1

10.2

11 1 'i 2. 1

1 ') ") c.. c.

13.1

A:4.1

explosion

Specifications of the data analysis equipment Errors of measurement in frequency and time

from

sonagrams

Fine structure details for the emission event

of April, 4, 1964.

Frequency drifts within hm emission events Storm-time variations in nighttime hm emission para.meters

Storm-time variations in daytime hm emission parameters

Times of diurnal peak occurrence of hm emission activity at fifteen stations

Data recording dates.

14

16

19

45

74

79

86

95

96

106

CHAPTER I

IN'l~RODU CTI ON

The existence of rapid variations in the geomagnetic field of the earth was first recognized by Balfour Stewart in the second half of the nineteenth century. However, it is only during the last decade, especially since the begin~ing of the International Geophysical Year, that considerable attention has been devoted to the properties and origin of these fluctuations. Although

the theoretical interpretation of geomagnetic micropulsations is still in a primitive state it is generally believ~that they represent hydromagnetic waves, excited in the magnetosphere, propagated through

the

magnetosphere

at

hydromagnetic velocities, and converted at the lower ionospheric boundary into electromagnetic fluctuations which

then propagate

through the neutral lower

atmosphere.

Geomagnetic micropulsati.on amplitudes range from a fraction of a gamma,to, on rare occasions, as much as a few tens of gammas

(1

gamma o::

10-

9

Wb/m

2

)

while

the

periods of oscillation extend from 0.1sec to 10 min~

At the beginning of the I.G.Y. micropulsations were classified by the International Association of Geomagnetism and Aeronomy into three broad categories; Pc continuous regular pulsations, Pt -damped trains of pulsations of short duration, and Pg - giant long

period pulsations of infrequent occurrence. The results of I.G.Y. and later systematic micropulsation studies revealed the deficiency of this broad classification, and provided the basis of a new

classification system which has recently been adopted by the IAGA

Regular and Continuous Micropulsations (Pc)

Pc1

period range

0.2

- 5 sec

Pc2

5 - 10 sec

Pc3

10 - 45 sec

Pc4

Pc5

Irregular Micropulsations (Pi)

45

-

150 sec

150 -600 sec

Pi1

period range

1 - 40 sec

Pi2

40

-150

sec

This thesis is principally concerned

with

the properties of

micropulsations in the Pc1 band

.

In addition to the generation of micropulsations in the

magnetosphere

,

it has been suggested that minor contributions

to certain classes of micropulsations may result from

magnetic

effects produced in the ionosphere by the influx of meteoric

material.

It is on the premises of this suggestion

,

and the

confusing nature of previous experimental work on the subject,

that micropulsation studies were undertaken in conjunction

with

the radio meteor research programme at the Physics Department's

Radio Research Station at Rolleston.

Apparatus for recording

the time rate of change of the vertical component of the

geomagnetic field was constructed by Eppstein (1960) and an

initial study on the association of meteor occurrence

with

micropulsation activity was conducted by Gillion (1961)

.

The

results of this study (Ellyett and Gillion, 1963) were inconclusi

ve,

and in 1962 the apparatus was modified and a second and more

extensive study was undertaken by the writer

.

The results of

this

work

are presented in Chapter

II.

3.

Following the completion of the meteor-micropulsation study

the decision was made to undertake an experimental study on

geomagnetic micropulsations in the Pc1 band. At this time little

was known about the properties of these

sign

al

s,

and primary

interest lay in the investigation of temporal frequency drifts in

the distinctive class of quasi-sinusoidal oscillations in the Pc1

band generally known as pearls (PP) or hydromagnetic emissions.

This study constitutes Part B of the thesis

.

In order to carry

out an experiment of this type it was necessary to redesign the

recording equipnent.

Also

,

problems with man-made noise during

the daytime precluded continuous observations on Pc1 micropulsations

at the sensitivites required with the available recording

equipment (Chapter IV)

.

These problems were resolved by employing

a completely portable transistorized recording system

,

which,

if

necessary, could operate at an electrically quiet site far from

man-made noise

.

The design criteria and general principles of

operation of this system are considered in Chapters V and VI.

The analysis of Pc1 data in the frequency domain is most conveniently

carried out using spectrographic analysis techniques of the type

pioneered by Duffus et al (1958).

Details of a similar data

analysis system constructed for the present study and

employing

a

Sonagraph Spectrum Analyser are given in Chapter

VII.

ChaptersVIII and IX are of a

review

nature, providing

background information and

establishing

a

framework

into

which

is fitted the analyses described in later chapters.

In Chapter

VIII some of the more important properties of signals occurring in

the Pc1 category are reviewed with particular emphasis being placed

on the characteristics of hydromagnetic emissions.

In Chapter IX

a summary is given of recent theoretical ideas, many as yet

The results of analyses performed on eight months of Pc1

data recorded on the portable micropulsation recording

system

are presented in ChaptersX, XI and XII.

In Chapter X, on the

general properties of Pc1 micropulsations, details of the

reduction of data from spectrograms are presented together

with

observations on the frequency-time characteristics of

hydromagnetic emissions and other types of emissions identified

in the Pc1 Dand.

In Chapter XI the diurnal variations in

hydromagnetic emission occurrence and frequency are considered,

and the emission frequency spectra determined.

In addition,

characteristics of

daytime

hydromagnetic emissions are considered.

Finally, Chapter XII is concerned

with

the effects of magnetic

disturbance on the properties of hydromagnetic emissions.

PART A

MAGNETIC EFFECTS

FROM

METEORS,

NUCLEAR DETONATION

t 'N,v" ,�1�v nF CA��fl,Bl'lt

CH PTER II

THE CORREL TION OF METEORS WITH MICROPULSATIONS

The

work

conducted on the correlation of meteors

with

micropulsations has recently been published (Ellyett and Fraser,

1963 ) and is presented in this chapter in its published form

with

a few minor alterations and additions.

2.1

INTRODUCTION

Meteors entering the lower ionosphere create relatively

intense transient trails of ionization

when

compared

with

the

background electron concentration.

Either the distortion of the

normal ionospheric current system, or the subsequent movement of

the trail

,

will

create associated magnetic field changes

.

Various

authors

,

particularly in the last decade, have endeavoured to find

magnetic micropulsation effects at the earth's surface associated

with meteor input to the upper atmosphere

.

There is still a

wide

divergence of opinion as to the reality of the effect.

In

some reports the gross effect only of a shOllllet' of meteors has

been looked for.

In most other studies,

meteor data used have

been obtained by different workers at earlier times and other

places,

and these make poor starting material for correlation

studies

with

currently obtained magnetic fluctuations. The

present work overcomes this defect by observing the two effects

simultaneously

.

b.

Bumba (1955) considered that the magnetic K index increased

significantly with the passage of large meteor showers and then

decreased below normal three days later

.

Attempting to verify Kalashnikov's results, Hawkins (1959 )

used three mutually perpendicular coils connected to amplifiers

with a frequency response of 0.5 to 10 cps and a maximum

sensitivity of 3 m�.

No correlations of individual meteors

with

magnetic pulses

were

found other than those that might be

expected

randomly.

His work, however, included frequencies

that could be attributed to thunderstorm activity, and Campbell

(1960) criticized it on these grounds

.

showers was not examined.

Correlation

with

meteor

Jenkins et al. (1960) ,

with

a somewhat increased maximum

sensitivity of 0. 3 mt, claimed an enhancement of nighttime

micropulsation activity in the 1.5 cps band on several nights

of meteor shower activity.

More recently, Campbell reported

increased micropulsation activity in the

0.03

to

0.2

cps range

,

with flux density increases lying between 20 and 320 m

₀

during

the� Aquarid, � Aquarid

,

and Perseid meteor showers of 1958

.

Again only nighttime data were used.

The first preliminary result with the present equipment,

but with only 1/6 the subsequent sensitivity

,

was obtained by

Ellyett and Gillion (1963) during a single 24-hour period on

July 29

,

1961, when the� Aquarid shower was active, giving

2750 radar echoes.

No correlation was obtained, either

with

selected latge amplitude meteors or on a i-minute

time

basis.

Experimental work already carried out thus gives no evidence

of a magnetic effect due to a single meteor,

with

the possible

exception of the first worker, Kalashnikov.

The correlation to date with showers also lacks conviction,

both on the data actually put forward, and on the fact that both

Jenkins et al. and Campbell compare micropulsation activity

with

7.

If there is such a co

rre

la

t

ion

,

one implication might be that

showers cause a large total rate increase over the background.

Observations at high

r

a

te

s

,

however,

show that showers cause a

relatively insignificant increase in the general rate (Ellyett

and K

e

ay

,

1956; Whipple and Hawkins

,

1959)

.

Also the hourly

meteor rate measurements usually apply at the observing station

only

,

and, to be

meantagful

1

must be converted to incident meteor

flux on the eart

h

'

s atmosphere

(Keay

and Ellyett, 196

1

)

.

Moreover, if any correlation does exist,

it should also be

found between micropulsations and the diurnal meteor var

i

ation,

where rate changes are as large as those produced by a meteor

shower.

After a brief description of the apparatus involved, a

comparison is given between radar-meteor rates at the Rolleston

field sta

t

ion

,

fifteen miles from Christchurch (geographic

coordinates 43

°

_37'S,

₁₇₂

°

₂₄

_'

_E

_;

_{geomagnetic coordinates 48}

_.

₂

°

_s,

0

253

.

5 E) and micropulsations in the

1.

5 cps band at the same sit

e.

Both all-sky meteor rates and meteor rates observed in the

vicinity of the magnetic field line of the earth which is

incident on the micropulsation loop are considered.

This is

followed by an investigation of the magnetic effect of single

meteors.

2

.

2 MICROPULS TION EQUIPMENT

A block diagram of the recording equipment is

shown

in

Figure 2.1.

Micropulsations of the vertical component of the

earth's magnetic field induced a voltage in a two-turn horizontal

loop 100 meters in diameter,

with

an effective area of 1

.

59 x 10

4

m

2

•

This loop was buried in the ground and fed to a galvanometer

8.

bandwidth from 1. 0 to 5. 0 cps and a semi•logarithmic amplitude

response was used to eliminate the

lower

m.icropulsation frequencies

and provide an extended amplitude response over a range of 34db.

This also presented a limited output to a following 1. 5 cps filter

amplifier, removing the possibility of oscillation in the filter

caused by large-amplitude lower-frequency micropulsations.

The filter amplifier had a bandwidth of 0.3 cps centred on

1. 5 cps, and hence had a

rise

time of about 3 sec.

This

frequency was chosen to agree

with

that used by Jen.kins et al.

when they found a correlation

with

night meteor showers.

For

studying the magnetic effects of individual meteors, a sharper

rise time of about 1 sec was desired, and so the bandwidth was

increased to 1 cps.

The frequency response curves of the various

components of the apparatus are shown in Figure

2.

2

.

Maximum sensitivity was aimed for, as any detectable effect

would almost certainly be small.

Full-scale deflection on the

chart of the pen recorder, which moved at 0.

75

mm/sec, was only

2 my; the

mimimum

detectable signal was

0

.

05 m(.

Because of

the very high sensitivity of the present apparatus, the readings

often reached full scale, but this was of no consequence as only

the time occurrence or absence of micropulsations was under

consideration.

Time marks were recorded o� the chart at

1-minute intervals, and once daily a constant amplitude calibration

signal,

sweeping

from 0. 5 to 3 cps, was applied.

This signal

checked both the frequency response and the amplitude calibration

of the filter amplifier.

In addition,

the output of the

Pulses of 81 -kw pe ak power and

26-

µ

s pulse width were

radiated at 69.

5

Mc/s

with

a pulse repetition rate of 150/sec .

Separated

,

crossed , folde d dipole s for the transmitter and

re ceiver , giving all-sky

viewing ,

were used in the first part of

the work. Echoes were recorded from an intensity-modulated

cathode ray tube on a continuously moving 35-mm film. A

detaile d de scription of the meteor equipment and operation is

given by Ellyett and Ke ay ( 1 963 )

.

Meteors were re corded down

to a zenithal magnitude of +8

.

2 (Keay

,

1 963 ) .

In the second part of the work the all -sky

viewing

aerials

were replaced by five-element Yagi aerials pointing in the dire ction

o f magnetic nor th at an elevation angle o f 65

°

.

This is the

elevation angle of a point at a ve rtic al height of 95 km lying

on the magnetic line of force passing through Christ church .

The measured horizontal beamwidth betwee n half-power points

0

was 55 .

The ve rtical beamwidth

w

i

ll be slightly greater

(Fishenden and Wiblin , 1 949)

.

With these aerials the minimum

de tectable zenithal meteor magnitude was incre ase d to

+10

.

8

.

The meteor detection equip�ent operated at the main field

station and the mic ropulsation equipment was situated at an

electrically quie t site 1 mile beyond the main stat

i

on

.

In the

final part o f the work, whe n the magnetic effect of individual

meteors was being considered

,

timing requirements demanded that

the meteor echo pulse s be placed on the same chart as the 1

.

5

cps

mic

ropu

l

sations

.

The meteor re cei

ver

,

with its Yagi aerial , was

1

0.

eliminating both slowly varying background noise (McLauchlan,

1960) and pulse-type interference (

Ellyett

and Keay,

1963).

It

was hoped that these features,

combined with the low noise

site,

would lead to a reasonably true count rate.

The paper chart recording system was tested by operating

it at the meteor site alongside the normal film recording system

for one night

.

In the period shown in Figure

2

.

3

,

1 784 meteors

were recorded on the film

,

and 1 704 on the ch

ar

t,

with

a correlation

coefficient of 0

.

95

.

(A period of noise caused the chart to

give some false meteors.

)

When the receiver was operated at the micropulsation site

,

tuning difficulties caused the recorded meteor rate to decrease

by a factor of about 2

.

This was not serious

,

however

,

as all

large-amplitude or long-duration meteors were still being recorded.

2

.

4 CORRELATION 0

2

.

4.

1

Most meteors in the magnitude range being observed move in

short-period orbits of low inclination to the plane of the

ecliptic.

Consequently , orbit interception by the earth will

show helion and antihelion maxima at around 10 hr and 02 hr

L T

,

respectively

.

A third

,

often smaller maximum arises at 06 hr

L

T

,

when the part of the earth containing the observing station is

moving toward the apex of the earth 's way and hence intercepting

meteors.

A diurnal minimum occurs 1 2 hours later,

at 18 hr LT,

when meteors, to be recorded, must catch up with the earth as it

moves alo�g its orbit (Ellyett and Keay,

1

963).

The mean hourly all-sky meteor rates for the period March

5 - 16

,

1962

,

are shown in Figure

2.

4

.

This is a typical

omnidirectional rate curve at Christchurch

,

showing the helion

At this stage

,

owing

to the possible occurrence of man-made

micropulsations in the daytime

,

it was decided to restrict

correlation studies to the night hours , between 19 hr and 07 hr LT.

Micropulsation activity at 1. 5 cps was recorded as either being

present or absent in the level about 0

.

05

mt

in each � min.

Figure 2

.

5 shows the antihelion peak in averaged meteor activity

and the corresponding averaged micropulsation occurrence

.

Clearly

there is no positive corr

e

liion

,

as is shown by a negative

correlation coefficient of -0. 64.

On no single night in the

interval was any increase observed corresponding to the constantly

present antihelion rate peak.

The minor peak in the micropulsation curve at 01 hr is due

to a magnetic disturbance (local K

=

4) which occurred on March 6.

This was the only occasion during the whole period when the local

K index rose above 3.

The meteor rate for each hour

was

plotted through the

succession of nights March 10 - 15 and in general showed a steady

and consistent decrease at all hours.

No similar trend appeared

in the corresponding curves of micropulsation activity.

2

.

4

.

2

Yagi erials giving Localized Meteor Rates :

A meteor producing a plasma of ions and electrons in its

wake does not constitute an electric current.

Any gross current

effects are likely to be produced only by the subsequent movement

of the trail as a whole

,

or by the disturbance of normal

12

.

possible

r

ange

,

and at the same time covering those meteors that

have any likelihood of sho

w

ing a fiel

d-

al

i

gn

e

d magnetic change due

to partial subsequent motion of the trail electrons around the

earth

'

s field line .

The mean ob served diurnal meteor rate curve for the period

March 23 through April 6

,

1962

,

is given in Figure

2

.

6

;

as

e

xpected

,

it has a markedly different di stribution from that of

the omnidirectional

arr

ay

,

the helion and antihelion peaks being

displaced later in time

owing

to the north-directed aerial

.

The night period only is again compared with micropulsation

occurrence in Figure 2

.

7

.

The meteor activity decreases to a

minimum at 04 hr and i s not followed by the micropulsation

curve,

which has an earlier minimum near 01 hr.

The correlation

coefficient is

0

.

39

.

The individual nightly curves again showed

the independence of the two phenomena

,

as seen in the three

selected hours given in Figure

2

.

8

.

Because of the tilt of the earth

'

s axi

s

,

a north-directed

aerial

will show

a marked seasonal change in the diurnal

distribution of meteors

.

If there i s any connection

with

micropulsations,

these should also show a seasonal change in

act

i

vity

.

Further micropulsation results were therefore obtained

in the periods September 1 4 through October 6 and October 9

through November 6 (Figure

2

.

9

)

.

The curves show a pattern similar

to that in Figure 2

.

7 obtained six months

e

arlier

.

2

.

5

CORREL TION 0

Correlation was recorded as positive if a micropulsation

occurred within !2 sec of the occurrence of a meteo

r

.

This

criterion for the simultaneity of meteor echo and micropulsation

occurrence automatically double s the coincidence probability since

the causality requirement that the meteor precedes the

phenomena presented side by side on the same paper chart, as shown

in Figure 2.

10

.

A micropulsation peak was counted as a discrete

event if its amplitude exceeded 0. 05 mt •

Observations were taken

continuously between 1900 hr and 0659 hr LT each night during a

week

in May.

The results are set out in the first four columns of Table

2

.

1.

The event occurrence rate for the two phenomena,

within the

limits chosen, was of equal order, micropulsations

being

somewhat

the higher.

Clearly most of the recorded meteors produce no

corresponding micropulsations.

If a = the total number of meteors in any

given

night, b =

the total number of micropulsations in the same night, and n =

the total number of 4-sec time intervals, then, if both meteors

and micropulsations are distributed randomly among the n time

intervals, the probability P that x meteors occur in the b

time

intervals is given by

p =

(1 - -)

b a -

_n

X

This distribution gives a calculated mean = ab/n ; the resulting

values are given in the fifth column of Table

1

.

The sixth

column gives the standard deviation S about the calculated mean ,

obtained from

s

= a b _n ( 1 - - ) b

_n

1/2

The final column shows to what extent the excess of observed

coincidences over calculated exceeds the standard deviation. Two

nights

show

no excess.

Including these, the average excess is

three

times the standard deviation.

The significance of this

Date,

No

.

of'

May 1 962

Mete ors ,

a

21 -22

371

22-23

401

23

-

24

41 6

24-25

328

25-26

331

26-27

309

27

-

28

300

Algebraic average

TABLE 1 :

Calculated

No

.

of'

Mete ors

with

No

.

of'

Observed No

.

of'

C orresponding

Ob served to

Micro-

Met eors

with

Micropulsati on

Calculated

pulsati on

Corresponding

If' Both Are

Standard

Standard

Peaks

,

b

Mi cropulsati on

Random , ab/n

Deviati on ,

s

Deviati on

240

23

8

.

2

±2

.

8

5

.

3

488

31

1 8 .1

+

-4

.

0

3

.

2

695

36

26

.

8

+

-

5

-

4

1

•

7

376

37

1 1

.

4

+

-

3

.

6

7

.

1

848

25

26

.

0

+

-

5

.

2

-0

.

2

620

40

1

7

-

7

!4

.

4

5 .1

2

6

.

4

+

-1

.

4

951

1 9

-5

-

3

s. o

1957 )

,

and no such correlation has been found.

If this result

be accepted

,

then correlation among the lengths of time intervals

between micropulsation peaks does not affect the argument.

In

any case, there is no evidence to suggest that such peaks possess

any time relationship.

The sum of the local 3-hourly K indices of magnetic activity

was zero throughout the whole of the first six

nig

hts

,

indicating

no appreciable magnetic ac

t

i

v

ity

.

The 12-hour period on the final

night gave an integrated K value of 1 1

.

This was the only

night on which appreciably fewer meteors were observed than would

be expected on chance coincidence

.

Magnetic disturbance does not

therefore appear to be a factor causing an increase in correlation.

As Table 2.

1 shows some slight evidence of a relationship

between the two phenomena, it was decided to separate the meteors

into those with echoes saturating the amplitude scale and those

lying between half and full scale ( smaller echoes were not counted)

.

The results (Table 2.2 ) show quite generally that large meteors

are accompanied almost

twic e

as often as small meteors by a

simultaneous magnetic micropulsation.

2

.

6 DISCU SI0N

From the evidence given above, correlation between meteors

and micropulsation activity in the 1

.

5

cps band is clearly

infrequent.

If some meteors do produce an effect at the earth's

surface

,

the vertical component of the magnetic effect, as seen

from a typical section of record in Figure

2

.

10

is seldom larger

than

0

.

1

m t·

No

.

of

Date,

Mic ropulsati on No

.

of Large

May 1 962

Peaks

Meteors

21

-

22

240

243

22

-

23

488

294

23-24

695

299

24-25

376

223

25-26

848

21 6

26

-27

620

1 97

27

-

28

951

1 91

Average

Observed No

.

of Large Meteors

with C orresponding

N

o

.

of Small

Micropulsati on

Meteors

20

=

₈

_.

_2%

_{1 28}

24

=

₈

_.

_2%

_{1 07}

32

=

_{1 o}

_.

7%

_{1 1 7}

28

=

_{1 2}

_.

_6%

_{1 05}

1 8

=

₈

_.

_3%

_{1 1 5}

34

=

_{1 7}

_-

_3%

_{1 1 2}

1 8

=

₉

_-

_4%

_{1 09}

1 o

.

7%

Observed No

.

of Small Meteors

with C orresponding

Micropulsation

3

=

₂

_.

_3%

7

=

6

.

5%

4

=

₃

_.

_8%

9

=

₈

_.

_6%

7

=

6 .

1 %

6

=

₅

_-4%

1

=

₀

_.

_9%

4

.

8%

pulses of this magnitude do occasionally showan associated me

t

eo

r

,

but any basic theory cannot as yet be regarded as established by

this result

.

Work carried out by Jenkins et

al

.

( 1960) showed that the

enhanced micropulsation activity in the 1

.

5

cps band at the peak

of the Geminid

,

Draconid

,

0rionid , and Ursid showers predominated

on the N-S

c

omponent

.

In the first place

,

this result is

sur-prising as the last two showers have very low rates.

There was

a lesser effect on the E-W component and only a slight increase in

the vertical component

.

As the present observations were made

on the vertical component , there could be some doubt as to

whether the meteor effects would be observed on this component

.

Jenkins ' results might be further questioned, however

,

as the six

meteor showers they consider occur ,

with

the exception of the

Draconids

,

in the early morning hours , which is also the time of

maximum occurrence of pearl-type Pc1 micropulsations at middle

latitude stations

( Be

nioff

,

1

9

6

0

)

.

Furthermore

,

additional

details of this work (Mason et al

. ,

1961) indicate that the 1

.

5 cps

micropulsation signals consisted of quasi-sinusoidal wavetr

ains

.

This again is a characteristic property of pearls and it is not clear

whether these have been excluded

.

Pearls can last up to an hour

or more (Jacobs and Jolley

,

1962)

,

can correlate with polar-cap

absorption ( Tepley

,

1961)

,

can be a worldwide effect

,

and are

clearly in no way connected with

meteors

.

Such pearls were observed

during the current observations on March 13 between 01 hr and 04 hr LT

,

and again on March 15 - 16 between 23 hr and 06 hr

LT

.

During these

Roura the meteor rates were normal

.

Such pearls were excluded

from the present

analysi

s.

The low percentage correlation between micropulsation spikes

and individual meteors as compared

with

up to a 35 per cent

18

.

which would include a much higher time occurrence of micropulsations,

and also possibly the lower-frequency edge of lightning effects.

The final result of the present work cannot be entirely

conolusive.

It is found that most meteors do not produce

detectable micropulsations, even with a higher limit to the

sensitivity in the present instance than has been used by o

thers

.

However, more correlations do occur than would be expected on a

random basis

,

and the correlation is higher for meteor trails

giving

a larger echo amplitude.

If the matter is to be pursued further,

it

will

be desirable to investigate the characteristics of the

individual meteor echo and the frequency coverage of the accompanying

micropulsation to see if there is any particular characteristic

that can be associated with a correlation.

The frequency of 1.5 cps

was chosen for the present work to make the results strictly

CH PTER I I

MAGNETIC DISTURB NCE FROM THE JULY 9

,

1 962

.

HI H

-

ALTITUDE NUCLE

R

EXPLOSION

3

,

1 INTRODUCTION

On July 9 , 1 962 , at 0900 hr OOmin 09sec , the United States

Atomic Energy Commission detonated a high altitude thermonuclear

device above Johnston Island (geomagnetic coordinates 1 4

.

3

°

N

,

2

56

.

5

°

_E)

_.

_{The height of the explosion was 400 km and the yield}

approximately 1

.

4

me

gatons

.

At this time the micropulsation recording equipment described

in section 2

.

2

was in operation to detect any magnetic effects

resulting from the explosion.

Data recorded on the broad-band

channel

wi th

a bandwidth of 0

.

008

-

1

.

6 cps were of primary

importance.

Full-scale pe ak-to-peak deflection on the chart

corresponded to a change in magnetic flux density of 0.5 r/sec

and the minimum detectable signal was 0

.

0

_{15 0}

/

sec

.

A chart

speed of 0. 75 mm/sec was used and the resulting time re

s

olut

i

on

,

limited by the thickness of the pen trace

,

was

0

.

3 sec

.

No great effects from the explosion were expected at

Christchurch

,

since the magnetic disturbances associated with the

1958 Teak and Orange explosions were not detected in New Zealand

20

.

3

.2

A preliminary description of the observed magnetic disturbance

has been

given

by Fraser (1962). More recently the data have

been reanalysed (March, 1963) and it is the results of this

reanalysis that are included

here .

The original chart record is shown in Figure

3

.

1.

In order

to interpret this record the response of the galvanometer amplifier

to large impulsive signals must be considered. For signals with

amplitudes greater than 0

.

_{95 t/sec . the galvanometer light spot}

moved completely off the photocells and the chart indicated a

zero

reading.

Each time the polarity of the input signal

reversed, and the light spot deflected across the photocells

,

a

pair of positive and negative spikes appeared on the record. From

the sequence of these spikes it was possible to reconstruct the

record shown in Figure 3.2 •

Off-scale peak-to-peak signal

amplitudes between 0.5

t

_{/sec and 0.95 0 /sec and greater than}

0

.

_{95 t/sec are also indicated}

.

Beaause of slight uncertainties

in timing,

it is possible to state only that the first effects of

the explosion were recorded at 0900 ·hr 00 min 09!5 sec.

First indication on the record was a small negative impulse

with an extremely fast rise time and an amplitude of 0.05 0 /sec.

It should be noted that the small irregular fluctuations commencing

6 sec prior to the bomb disturhance were caused by local man-made

interference. The initial impulse was followed

0

.

5!0

.

3

sec later

by five cycles of off-scale fluctuations having periods between

2 and 5 sec , and lasting until 30 sec after onset.

The amplitude s

of fluctuations within this time interval were greater than

0

.

95

1(

/sec

between

O. 5 and 19 sec and in the range O

.

5

-

O

.

95

₀

sec

between 19 and 30 sec. For the next three minutes fluctuations

with periods of 20

-

40 sec and amplitudes greater than O

.

95

t

/sec

were evident.

After 3.5 min three cycles of long period

back to normal 10 min after detonation

.

The features of the

disturbance described above are summarized in Table 3. 1.

Phase

Time Interval

Period

Amplitude

(A)

( secs . )

(secs. )

_{c 0 /sec.)}

1

0

-

0

.

5-0

+

.

3

Impulse

0

.

05

19

2

-

5

>

0

.

95

2

{ 0 . 5 -

₁₉

_-

₃₀

_2-5

_{. 5< A <}

₀

_.

₉₅

3

30

-

210

20

-40

>

•

95

4

210

- 600

100-140

0

.

3

T BLE

3.

1

Characteristic phases of the July 9 nuclear explosion.

Time is taken from initial onset

.

3

.

3 DISCUSSION

From consideration of the predominant oscillation periods

given in Table 3.1

,

it is convenient to divide the disturbance into

four phases and consider possible physical mechanisms which may

explain the characteristic oscillation periods within each phase

.

Before any mechanism can be suggested for the first two

phases

,

it is necessary to establish a more exact onset time for

the disturbance .

This can be achieved by considering other

micropulsation and earth current data recorded in New Ze

al

and

.

Christoffel (1962) estimates the arrival time of the main magnetic

+

disturbance at H

+

0. 6-

0

.

2

sec, while Poletti and Gadsden (1965 )

timed it at H +

0

.

5

sec.

These times correspond to the commencement

+

of phase

2 of the present data, which began 0

.

5

-

0

.

3 sec. after

the initial impulse. It is therefore possible that this impulse

is produced by the low frequency components of the instantaneous

VLF atmospheric recorded in New Zealand

(

Hanley,

1962 ; Allcock et al.,

1963

)

.

Instantaneous small amplitude micropulsation signals of

22

.

Christo ffel bas shown that a hydromagne tic wave me chanism

canno t be invoke d to explain the commencement of phase 2 sinc e

the travel time of such a wave in an e xospheric duct of the type

sugge sted by Bomke e t al . ( 1 960 ) is far in excess of the me asured

disturbance propagation

t ime

of approximately

0

.

5

sec .

A more at tractive me chanism i s that o f neutron decay proposed

by Crain and Tamarkin ( 1 961 )

.

Here it is postulated that prompt

neutrons radiate isotropically from the detonation point and decay

into protons and ele ctrons

which

are ultimately trappe d in the

geomagnetic fie ld .

If the pit ch angle is sufficiently small then

the particle s

will

be dumpe d into the lower ionosphere . The

peaks in the energy distributions of these particle s occur at

approximate ly 250 kev for ele ctrons and 1 Mev for protons .

The minimum travel time to Christchur ch for a disturbance produced

by a 1 Mev neuton and a 250 kev e lectron is approximately 0 . 3 sec .

Hence the me chanism suggested by Crain and Tamarkin

will

explain

the disturbance arriving at H +

0

.

5

se c .

The mirror period of

0

.

3

sec asso ciated wi th 250 kev ele ctrons doe s not , however , agree

with the observed period (2-5 se c ) . Although ne utron decay

protons require longer than 0 . 5 se c to re ach a mirror point above

C

hri st chur ch

,

the ir mirror pe riods are approximately 4 seconds

and agree well with the ob served periods

.

It is there fore possible

that this me chanism could contribute to later disturbance in thi s

phase .

CH

PTER

I

M N-MADE K EvTROMAGNETIC INTERFEREI CE

. 1

INTRODUCTION

The detection o f mi

c

ro pulsa

t

i

ons o f the geomagnetic field

in the milligamma range is greatly influenced by the inherent

background noise which

,

providing recording equipment noise is

sufficiently low

,

may l-

0

attributed to external electromagnetic

noise of atmospheric and man-made or

i

g

i

ns

.

In the course of the meteor-micropulsation study it became

apparent that many of the impulsive signals observed were of

either thunderstorm o r man-made origins. In tnis chapt

e

r

,

which

has been adapted from Fraser and Ellyett (1964)

,

analyses o f

man-made noise in the Pc1 and lower frequency bands are briefly

reported.

4

.

2

BACKGROUND NOISE AT

1

.

5

CPS .

The presence or absence of 1

.

5 cps micropulsations in the

amplitude

range 0

.

05

-

2

.

0 m

(

,·.as

recorded

every minute for

selected days in September - November 1962

.

The equ; pment noise

level was

0

.

02

m

'I .

Results fron selected groups o f days are

shown in Figure 4. 1.

Mondays are typical of all days through

to Friday in

showing

at sharp rise at 08 hr LT

.

This rise is

invariant throughout the year

,

as it would not be for activity of

true geophysical origin.

There

is

a dip at 1 2

-

13 Jr and a

very pronounced falloff at 17 hr

LT

.

These times agree with the

times of local industrial activity.

The minor evening peak at

19 - 20 hr LT is produced by naturally occurring Pi1 activity

associated with the geomagnetic storm of October 8,

1962.

Saturdays show some morning activity only,

again agreeing with a

lowered amount of industrial activity,

and Sundays are practically