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A SURVEY AND BIBLIOGRAPHY

OF

RECENT RESEARCH

IN THE

PROPAGATION OF VLF RADIO WAVES

BY

JAMES R. WAIT

U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS
THE NATIONAL BUREAU OF STANDARDS

Functions and Activities

The functions of the National Bureau of Standards are set forth in the Act of Congress, March

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properties of materials; the development of methods and instruments for testing materials, devices,

and structures; advisory services to government agencies on scientific and technical problems: in- vention and development of devices to serve special needs of the Government; and the development

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The results of the Bureau's work take the form of either actual equipment and devices or published papers. These papers appear either in the Bureau's own series of publications or in the journals

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of Documents, Government Printing Office, Washington 25, D.C.
NATIONAL BUREAU OF STANDARDS

technical ^nXote,

58

May I960

A SURVEY AND BIBLIOGRAPHY OF RECENT RESEARCH IN THE

PROPAGATION OF VLF RADIO WAVES

by

James R. Wait

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of transient or limited interest. Technical Notes may be

listed or referred to in the open literature. They are for sale by the Office of Technical Services, U. S. Department of Commerce, Washington 25, D. C.

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Price $ »75

-1-

Table of Contents Page

1. Introduction 1 2. Theoretical Studies 3

3. Analyses of Experimental Data 7

4. Recent Applications of VLF Propagation 10

5. Suggestions for Further Work 11 Acknowledgment 13

Contents of Bibliography:

1. Ground Wave Propagation 14

2. Characteristics of the Lower Ionosphere 17

3. General Theories for Propagation in 19

Inhomogeneous Media

4. Calculations of Ionospheric Reflection Coefficients 21

5. Measured Ionospheric Reflection Coefficients (VLF) 23

6. Mode Theory of ELF and VLF Ionospheric Propagation 24

(And related work on waveguides.)

7. Theory of the Propagation of Pulses in ELF and VLF 28

Ionospheric Propagation

8. Characteristics of Lightning Discharges 29

9. Atmospheric Waveforms (VLF) 31

10. Atmospheric Waveforms (ELF) (Including slow-tails) 33

11. Measured Amplitude Characteristics of VLF Fields 35

12. Measured Phase Characteristics of VLF Fields 37

13. Noise (VLF) 38

14. Noise (ELF) 39

15. Radio Signals from Nuclear Detonations 40

16. Whistlers and Magneto-Ionic Duct Propagation 41

17. Exosphere and Dawn Chorus 44

This report has been prepared at the suggestion of

Professor R. A. Helliwell, Chairman of Commission IV of URSI

(International Scientific Radio Union). A paper based, in part,

on the subject matter will be presented at the 13th General

Assembly of URSI to be held in London, England from Aug. 28

to Sept. 15, I960.

A SURVEY AND BIBLIOGRAPHY OF RECENT RESEARCH IN THE

PROPAGATION OF VLF RADIO WAVES

by

James R. Wait

1. Introduction

Although VLF (very low frequency) radio waves were used

extensively in the early part of this century, interest in the subject

waned. This was in spite of the fact that VLF waves propagate to

great distances with extremely small attenuation. Recently, however,

with the pressing need for long range navigational systems, long

distance communication, and world-wide frequency standards the

desirable transmission characteristics are again being utilized.

Since lightning discharges are potent generators of VLF, storm

centers may be located by using DF techniques. Such systems have

been in operation in the United Kingdom and elsewhere for many

years. It has been found that considerable energy at extremely

low frequencies (ELF) is also radiated from lightning. While

frequencies in this range (below 3 kc/s) aave not yet found extensive

application it is believed that they have considerable potential value

in storm location.

It is the purpose of this paper to present a general, but brief,

survey of the field. Attention is confined primarily to terrestrial

propagation, and thus solar and exospheric phenomena are generally

excluded although certain germane references dealing with these

subjects are given in the bibliography.

First a brief description of recent advances of ground wave

propagation is given. This is followed by sections on ray and mode

concepts of ionospheric propagation. The research dealing with the

waveforms of atmospherics is also considered. Finally some recent
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applications of VLF propagation are described. While the emphasis

is on the theoretical approaches used, reference to corroborating

experimental work is included. It is hoped that the shortcomings in a brief article of this kind are partially compensated by the inclusion

of an extensive bibliography on the subject arranged under subject

classification. While attention is confined primarily to the triennium

(1957-1959) a number of basic references prior to 1957 are included.'

The VLF band is here defined as the decade 3 to 30 kc/s whereas

the ELF band covers the range 1.0 c/s to 3 kc/s.

t

After this survey was written, the author's attention was directed to

the review paper "Low and Very Low Frequency Propagation, ft by

H. Poeverlein in Fortschritte der Hochfrequenztechnik, 4, 47,(1959).

Among the topics considered were sferics, whistlers and

-

exospheric

phenomena. Also included were discussions of the lower ionosphere

and noises at extremely low frequencies.
-3-

2, Theoretical Studies

For certain applications at VLF, particularly at short ranges,

it is permissible to neglect the presence of the ionosphere. In fact,

at frequencies of the order of 100 kc/s the ground wave may dominate

the sky wave for ranges as great as 500 km. Furthermore, with the

use of pulse-type transmission, such as used in the Cytac or Loran G

navigation systems, the ground wave may be distinguished from the

sky wave for distances as great as 2000 km [1 - Frantz, et al, 1957].'

With this motivation a number of theoretical papers on ground- wave

propagation have appeared in the literature dealing specifically with:

(i) amplitude and phase vs. distance curves [1 - Johler, et al,

1956; 1 - Wait and Howe, 1956]

(ii) land-sea boundary effects [1 - Wait and Householder, 1957;

1 - Wait, 1958]

(iii) propagation of electromagnetic pulses over the surface of

homogeneous and inhomogeneous ground [1 - Johler, 1957

and 1958; 1 - Johler and Walters, 1959; 1 - Levy and Keller,

1958; 1 - Wait, 1957b, 1957c, 1957d and 1957e]

The penetration of ground-wave fields into the earth or sea has also

been considered in some detail [ 1 - Keilson and Row, 1959; and

1 - Kraichman, I960] and the influence of earth stratification on the

attenuation rate of the ground wave has been given further attention

[1 - Stanley, I960; and 3 - Wait, 1958] . Unfortunately, in cw systems and at distances as small as 100

km from the source, the sky wave may often interfere with the

ground wave. Thus the total field may be considered as the resultant of a ground wave and a number of ionospherically reflected waves

in the VLF band at moderate ranges (i. e. , less than 1000 km or so)

[4 - Johler and Walters, I960; 4- Poeverlein, 1958a and 1958b; and

T

The numeral preceding the cited authors refers to the appropriate

section in the bibliography.
4 - Wait and Perry, 1957] . However, it appears to be more convenient to represent the total field as a sum of wave-guide type

modes for VLF at great distances and, for ELF, at nearly all

distances. In fact, for many applications only one or two modes need

be retained since the higher modes are either "cut-off" or have

severe attenuation. A number of papers on mode theory were

presented at the VL.F Symposium held in Boulder, Colo. , January

1957 [6 - Budden, 1957; 10 - Liebermann, 1956b; 6-Wait, 1957c; and

9 - Wait, 1957] . In these, the ionosphere was represented by a

sharply bounded and homogeneous ionized medium, and the influence

of the earth's magnetic field was neglected. Also, since the

frequency could be assumed to be much less than the effective

collision frequency, the ionosphere was equivalent to an isotropic

conductor. More recent investigations of mode theory have removed some of the earlier restrictions. For example, the influence

of stratification in the D and E regions was accounted for by using

layered and exponential models [ 6 - Shmoys, 1956; 6 - Wait, 1958b

and 1960b; and 6 - Bremmer, 1959] . Alpert [ 6 - 1956] in the USSR has also pursued the mode theory

of VLF propagation. In his work the influence of the earth's magnetic

field is not considered and, in his initial formulation, the ionosphere

is sharply bounded so that Fresnel-type reflection coefficients are

used. He treats the effect of ionospheric stratification by using an

Epstein model which is strictly valid only for horizontal polarization.

By means of a semi-empirical "field-alignment" technique he uses

the computed results of the reflection coefficient for horizontal

polarization to evaluate effective values of the refractive index.

Then, these are substituted into the appropriate (Fresnel) reflection

coefficient for vertical polarization. In common with most other

authors, he neglects the effect of earth curvature for purposes of

computing the attenuation of the modes. Some time earlier Budden

[6 - 1952] had obtained a first-order correction for earth curvature

by Using an earth -flattening type of approximation, and more
-5-

recently Wait [ 6 - 1958a] had used a similar modification in some

published curves of VLF transmission loss. From this work it appears that earth curvature has a negligible effect on the modes

for frequencies less than about 10 kc/s, but for frequencies of the

order of 20 kc/s the inclusion of curvature increases the attenuation

by about a factor of two.

Actually, for frequencies at the upper end of the VLF band

(i.e. , 15 to 30 kc/s), it is necessary to abandon first-order curvature

corrections and to introduce higher-order approximations for the

spherical-wave functions which occur in the rigorous formulation.

This aspect of the problem is discussed at length in a recent paper

which includes an extensive discussion of related theoretical work

[ 6 - Wait, 1960a] . The influence of the earth's magnetic field on the attenuation

and phase of the modes is a difficult subject. However, if expressions for the plane-wave reflection coefficients for an anisotropic

ionosphere can be derived, it is not too difficult to extend these to

the computation of the modes [ 6 - Budden, 1952 and 6 - Wait 1960a] . Thus the results of Bremmer [6 - 1949] , Yabroff [4 - 1957] , and

others [4 - Johler and Walters, I960 and 4 -Wait and Perry, 1957]

may be adapted for mode propagation between the curved earth and

a doubly refracting ionosphere [ 6 - Wait, 1960a] . Using such an

approach Crombie [ 6 - I960] has adapted the result for plane -wave

reflection with a transverse magnetic field to cover the case of mode

propagation around the magnetic equator. This example, although

based on a flat-earth model, clearly demonstrates non-reciprocity

in VL.F propagation. More recently Wait and Spies [ 6 - I960] have

considered mode propagation for a curved earth and a magnetic

field of arbitrary dip angle. These latter results agree quite well

with the recent experimental data of Taylor [ 9 - I960] which also

show • that attenuation for west-to-east propagation is less than for

east-to-west propagation.
-6-

While the mode theory would seem to be particularly appropriate

at ELF, certain assumptions which are usually made become

questionable. These longer wavelengths penetrate farther into the

ionosphere so that the sharply bounded model must be modified

[4 - Poeverlein, 1958b and 6 - Bremmer, 1959] . Another approach

is to postulate an effective increase in the ionospheric height as the

frequency decreases [ 6 - Pierce, I960] . Even more important at

ELF is the fact that distance from source to observer is usually

comparable with the wavelength. Thus the numerical treatment of

the mode series has been considered by Wait [ 6 - 1960c] for unrestricted distances, and in the same paper the relation of the shape

of the ELF waveforms to the orientation of the lightning stroke is

analyzed.

Again using the concept of modes, the propagation of both VLF

and ELF pulses has also received considerable attention [ 10 - Liebermann, 1956b; 6 - Wait, 1960c and 7 - Wait, 1958] . Of some

importance is the manner in which the quasi-half periods of the

oscillatory waveform of the pulse vary with range and time [ 7 - Wait,

1958 and 9 - Taylor, I960] . At large distances from the source

(i.e. , greater than 3000 km) the VLF portion of the waveform is

usually a damped sinusoid of half-a-dozen or more cycles. The

quasi-half period of a given cycle decreases with range in a

regular manner. On the other hand, for a given range, the quasihalf periods increase in length with increasing time. These consistent and predictable properties of the waveform appear to offer

great promise in range determinations using only a single recording

station. Furthermore, the length of the individual periods and the

particular manner in which they vary with range and time yield

information about the source.
-7-

3. Analyses of Experimental Data

Since the observed characteristics of VLF and ELF propagation

depend on so many factors, one should be careful in placing undue

emphasis on any single experiment. In particular, the validity of a particular theoretical model cannot be established on a basis of

experimental data obtained in a single geographical area and for

restricted intervals of time. Nevertheless, certain experiments are

crucial in the sense that they confirm the concept of the model. For

example, if the measured dependence of VLF field strengths on

distance and frequency are in general accord with theoretical predictions, one can say that, at least for those ionospheric conditions,

the model is perhaps adequate in a phenomenological sense.

A crucial test of the wave -guide mode concept of VLF propagation

was provided by Heritage, Weisbrod and Bickel [ 11 - 1957] in a series

of airborne measurements of field strengths in the Pacific Ocean.

They utilized transmissions in the frequency range of 16 to 20 kc/s

from the United States, Hawaii and Japan. The daytime experimental

data were in good agreement with the mode theory as indicated by

Wait [ 6 - 1957c] ; however, the nightime data were highly variable

and certain non-reciprocal effects were in evidence.

Phase variations of the 16 kc/s carrier signal of station GBR in

England have been measured by Pierce [ 12 - 1955 and 1957] in

Cambridge, Mass., and by Crombie, et al.[12 - 1958] in New Zealand.

The diurnal variation of the change of the phase has been interpreted

by Wait [12 - 1959] in terms of mode theory in a satisfactory manner.

Phase variations of GBR have also been measured by Volland [ 12 -

1959] in Berlin. He indicates that the daytime reflection heights are

between 69 and 76 km for 16 kc/s. During a solar flare it decreases.

Many studies of VLF propagation have been made using lightning

strokes as a source of energy. For example, Watt and Maxwell [ 13 -

1957] showed that the propagation modified the spectral content of

atmospheric radio noise in a manner which again was quite compatible
-8-

with mode theory. In particular, the predicted absorption band

[6 - Wait,. 1957c at frequencies around 3 kc/s was confirmed.

Attenuation rates at VLF have been deduced from the spectral

analyses of atmospheric waveforms observed simultaneously at

widely separated stations [9 - Taylor and Lange, 1959 and 9 - Taylor,

I960] . A similar technique has been developed for deducing phase

characteristics of VLF propagation in a frequency range from 1 to

30 kc/s [ 9 - Jean, et al. ,1960} . Recently Obayashi [ 12 - I960]

indicates that a solar flare shifts the peak of the spectrum of the

atmospheric upwards so that the peak is at frequencies around

25 kc/s.

Experimental studies at ELF have been primarily devoted to the

recording of theELF or "slow tail" portion of the atmospheric waveforms [ 10 - Liebermann, 1956a; 14 - Holzer, et al, 1957; and

9 - Tepley, 1959; 10 - Hepburn and Pierce, 1953; and 10 - Hepburn,

1958] . In many cases it appears that this ELF part of the waveform

is a highly damped pulse with seldom more than two half cycles and

with periods of the order of several milliseconds.

Apparently, Watson-Watt, et al.,[10 - 1937] were the first to

make a study of the ELF portion of atmospheric waveforms. They

observed that the separation between the higher frequency oscillatory

head and the slow tail increased as the distance to the source became

greater. A partial theoretical explanation for this effect was pro L posed by Hales [ 10 - 1948] . Using this theory, Hepburn and Pierce

[10 - 1953] and Hepburn [ 10 - 1957] deduced effective values of the

conductivity of the lower edge of the ionosphere from their own

experimental results. These authors assume that the mean

separation of the oscillatory head and the maximum amplitude of the

slow tail was a linear function of the distance from the source. This

was probably done to facilitate the interpretation in terms of the

theory of Hales [10 - 1948] . It should be pointed out, however, that

the group delay derived by Hales is only valid when the signal contains
-9-

a narrow band of frequencies. Predictions from such a quasimonochromatic theory have only a qualitative value if the signal

contains many spectral components [7 -Wait, 1958] . This fact

is probably sufficient to reconcile certain apparent discrepancies

between the results of Hepburn [ 10 - 1957] and those of Liebermann

[ 10 - 1956a and 1956b] . This latter author treated slow-tail propagation on the assumption that the source could be represented by an

impulse. While not explicitly stated, Liebermann computed the

resulting waveform for the vertical electric field component which

he then compares with his observations of the horizontal electric

field component. Since the ratio of the frequency spectra of these

two components is proportional to the square root of frequency, some

of Liebermann1 s deductions could be questioned. Another disturbing

factor is that Liebermann' s amplifier response is not at all flat. It is just possible, however, that the amplifier response characteristic

could partially compensate for the antenna characteristics. Actually,

full compensation would require an amplifier with an amplitude

response which varied as the inverse square root of frequency.

Despite these questions, it is probable that Liebermann's conclusions

are generally valid. In a recent paper, Wait [ 10 - I960] has shown

that Hepburn's experimental data for the slow-tail separation could

be interpreted in terms of a source whose duration is finite. Values

of effective ionosphere conductivities for day and night deduced from

this analysis were consistent with earlier results for the VLF band.

Extensive experimental studies of ELF propagation have been

carried out at the Institute of Geophysics in the University of

California. Certain aspects of this work have been described by

Holzer and Deal [ 14 - 1956] , Holzer [ 14 - 1958] and Tepley [ 10 - 1959] . An excellent and complete account of the analysis of slow-tail waveforms obtained by this group is included in a recent thesis of Smith

[ 10 - I960] . Employing waveforms records in Hawaii and Los

Angeles an attempt was made to deduce attenuation rates in the

frequency range from 50 - 150 c/s. Difficulty in the analysis occurred
-10-

when it was indicated that the attenuation coefficient varied in a regular manner from one path to another. This geographical dependence

was consistent with the hypothesis that transmission is better for

propagation from south-to-north than from east-to-west. Evidence

based on the observed dispersion of the ELF waveforms also supported

this hypothesis. Unfortunately, as Smith points out, theories dealing

with the influence of the earth's magnetic field, appear to be unable

to account for the effect. In fact, Wait and Carter [6 - I960] have

shown that ELF attenuation is hardly influenced at all by a magnetic

field. It should be mentioned, however, that the direction of propagation may not be the controlling factor; the same results could also

be attributed to a dependence on geographical latitude. In fact, Smith

suggests that if the ELF waves experience increased attenuation in

the vicinity of the equator,his observations could be rather simply

accounted for. For example, if the height of the ionosphere varied

with the zenith angle of the sun, increased absorption would indeed be

observed at equatorial latitudes in the daytime but not at night. This

is just what Smith finds!

4. Recent Applications of VLF Propagation

Research in VLF propagation has been prompted by many

important applications. In particular, the low attenuation and high

phase stability of VLF signals make it feasible to set up a worldwide frequency standard employing only one transmitter. A careful

study of this problem by Watt and colleagues [11 - Watt and Plush,

1959] indicates that a minimum radiated power of 10 to 100 kw for

frequencies of 20 kc/s would be required. Minimum observation

times of 15 to 30 minutes would be needed to obtain a precision of

frequency of 1 part in 10

9

. Another application is to long-range

navigational systems such as the Radux-Omega in which the phase

difference between two widely separated transmitting stations is

measured. Frequencies used in this system are in the range 10 to

18 kc/s with typical phase stabilities on a path of 8000 km of 4 jx sees.
-11-

in day and 5 (J. sees, at night [1Z - Casselman, et al. , 1959] . Within the past few years numerous reports in the press have

been concerning the electromagnetic signal emitted from a nuclear

detonation. This provides the basis of a method of detection. The

phenomenon has been discussed at the "Conference of Experts"

[15 - United Nations, 1958] held in Geneva at various intervals since

the summer of 1958. Kompaneets [15 - 1958] shows that the duration

of the current due to the electronic current produced is of the order

of 1 or Z u. sees. The length of the half-cycles of the electromagnetic

oscillations is approximately ten times as large. On the basis of this

calculation the frequency spectrum of the signal should peak around

30 kc/s.

Actually, the electromagnetic signal radiated from nuclear explosions is quite similar to that produced by lightning, thus the

atmospherics act as a source of interference to this method of detection of explosions.

5. Suggestions for Further Work

While the mode theory in its present form appears to explain the

gross features of VLF propagation, additional refinements are still

needed. In particular, the influence of stratification in the D region

requires further study. It would also be worthwhile to extend the

calculations of field strength to heights extending right up to the D

region. In fact, both the analysis and explicit formulas are already

available. A preliminary examination would indicate that just below

the D region the vertical field in the V. L>. F. range should decrease

rather abruptly. It would also be expected that the field strength vs. distance curves at great heights would be very different in form to

those at low heights or on the ground since the higher-order modes

play a more important role. It would also be of great interest to

compute the field within the ionosphere corresponding to a mode in

the earth-ionosphere waveguide. However, some caution should be

exercised in drawing any conclusions from such an analysis since the
-12-

results will be critically dependent on the nature of the profile

assumed at the lower edge of the ionosphere. Nevertheless, such a

study might shed some light on the difficult problem of whistler

generation.

It might also be worthwhile to investigate the influence of the

ionosphere on the impedance of a V. L. F. antenna. For the common

ground-based monopole, it is usually assumed that the radiation resistance is the same as an antenna in the absence of an ionosphere.

Preliminary calculations would indicate that the input impedance of a ground-based antenna could be dependent on ionospheric height changes

such as may occur during a solar flare. In particular, it would be

interesting to estimate the changes of the impedance on a missileborne antenna as it proceeds on its journey from the ground towards

the ionosphere. This might provide a theoretical basis for an experimental method to investigate the D region.

There are many investigations at ELF which should be carried

out. For example, the mode theory could be generalized to include

the effect of heavy ions in the D and lower E region. Since the frequencies are of the same order as the ion gyro frequencies their

influence may be great. Much additional experimental data are also

required in this frequency range. The relatively meagre data which

are available indicate that the attenuation rate and waveform dispersion

depend on the particular path. Further measurements, with an

accurate technique for source location, are urgently needed to show

whether the path dependence is a geomagnetic or a geographical effect.
-13-

Acknowledgment:

I am indebted to Mrs. Eileen Brackett for her assistance in

the preparation of this paper. I would like also to thank A. Glenn

Jean for his comments and for drawing my attention to a number of

references.
-14-

1. Ground Wave Propagation

Bremmer, H. , Applications of operational calculus to ground-wave

propagation, particularly for long waves, IRE Trans. PGAP, AP-6,

267, 1958a. (VLF Symposium paper.

)

Bremmer, H. , Propagation of electromagnetic waves, Handbuch der

Physik , 16, 423, 1958b.

Eckersley, T.JL. , Refraction of electric waves, Radio Review, 1, 421,

1920.

Feinberg,E. , On the propagation of radio waves along an imperfect

surface, Jour, of Phys . , U.S.S.R. , 10, 410, 1946.

a. Frantz, W.P., A precision multi-purpose radio navigation

system, Part I, characteristics and applications;

b. Dean, W. , Part II, Propagation characteristics;

c. Frank, R. L. , Part III, Instrumentation, IRE National Convention

Record, 1957.

Furutsu, K. , Propagation of electromagnetic waves over a flat earth

across a boundary separating different media and coastal refraction,

Jour, of the Radio Res. Labs. , Japan, 2, 1, 1955.

Grunberg, G. , Theory of coastal refraction of electromagnetic waves,

Jour, of Phys., U.S.S.R ., 6, 185, 1942.

Grunberg, G. , Suggestions for a theory of coastal refraction,

Physical Rev. , 63, 185, 1943.

Johler, J.R., Keller, W. J. , and Walters, L.C., Phase of the low

radiofrequency ground wave, NBS Circular No. 573, 1956.

Johler, J. R. , Propagation of the radiofrequency ground-wave

transient over a finitely conducting plane earth, Geof. Pura e Appl.

(Milan), _37, 116, 1957.

Johler, J. R. , Transient radio frequency ground waves over the

surface of a finitely conducting plane earth, J. Research NBS, 60,

281, 1958. —

Johler, J. R. , and Walters, L.C., Propagation of a ground-wave pulse

around a finitely conducting spherical earth from a damped sinusoidal

source current, IRE Trans. PGAP, AP-7, 1, 1959.
-15-

Keilson, J., and Row, R.V., Transfer of transient electromagnetic

waves into a lossy medium, J. Appl. Phys. , 30, 1595, 1959.

Kraichman, Martin B. , Basic experimental studies of the magnetic

field from electromagnetic sources immersed in a semi-infinite

conducting medium, J. Research NBS, 64D, 21, January I960.

(VLF Symposium paper.

)

Levy, B.R., and Keller, J.B., Propagation of electromagnetic pulses

around the earth, IRE Trans. PGAP , AP-6, 56, 1958.

Millington, G. , Ground-wave propagation over an inhomogeneous

smooth earth, Proc. I.E.E. , Paper No. 794R, 96, Part III, 53,

1949.

Norton, K.A. , The calculation of the ground wave field intensity,

Proc. Inst. Radio Engrs ., 29 , 723, 1941.

Norton, K.A. , System loss in radio wave propagation, J. Research

NBS, 63D, 53, 1959.

Pressey, B.G., Ashwell, G.E., and Fowler, C.S., The measurement

of the phase velocity of ground- wave propagation at low frequencies

over a land path, Proc. I.E.E. , Paper No. 1438R, 100, Part III, 73,

1953.

Pressey, B.G., Ashwell, G.E., and Fowler, C.S., Change of phase

with distance of a low-frequency ground wave propagated across a

coast-line, Proc. I.E.E. , Paper No. 2082R, 103B , 527, July 1956.

Pressey, BG., and Ashwell, G.E., The deviation of low-frequency

ground waves at a coast-line, Proc. I.E.E., Paper No. 2083R,

10 3B , 535, July 1956.

Pressey, B.G., Ashwell, G.E., and Roberts, R. , Further studies of

the deviation of low- and medium-frequency ground waves at a coast-line, Proc. I.E.E . , Paper No. 3018E, 10 6B , No. 30, 548,

November 1959.

Senior, T.B.A. , Radio propagation over a discontinuity in the earth's

electrical properties - II, Coastal refraction, Proc. I.E.E., Monograph No. 201R, 10 4C , 139, October 1956.

Smith-Rose, R.L. , A study of radio direction -finding, Radio Research

Board Special Report No. 5, (H.M. Stationery Office, 1927.
-16-

Sommerfeld, A.N. , Uber die ausbreitung der wellen in der

drachtlosen telegraphic Ann, Physik, 81, 1135, 1926.

Stanley, G. M. , Layered-earth propagation in the vicinity of Point

Barrow, Alaska, J. Research NBS , 64D , 95, I960. (VLF Symposium

paper.

)

Wait, J.R., and Howe, H.H., Amplitude and phase curves for groundwave propagation in the band 200 cycles per second to 500 kilocycles,

NBS Circular 574, 1956.

Wait, J.R. , Low frequency radiation from a horizontal antenna over a

spherical earth, Can. Jour. Phys. , 34, 586, 1956a.

Wait, J. R. , Mixed path ground wave propagation: 1. Short distances,

J. Research NBS, 57, 1, 1956b.

Wait, J.R. , Amplitude and phase of the low-frequency ground wave

near a coastline, J. Research NBS, 58, 237, 1957a.

Wait, J.R., The transient behaviour of the electromagnetic ground

wave over a spherical earth, IRE Trans. PGAP , AP-5 , 198, 1957b.

Wait, J.R. , Propagation of a pulse across a coastline, Proc. IRE,

45, 1550, 1957c.

Wait, J.R. , Transient fields of a vertical dipole over homogeneous

curved ground, Can. J. Research, 34, 116, 1957d.

Wait, J. R. , A note on the propagation of the transient ground wave,

Can. J. Phys . , 35 , 1146, 1957e.

Wait, J. R. , and Householder, James, Mixed-path ground-wave

propagation: 2 larger distances, J. Research NBS, 59, 19, 1957.

(A similar solution has been given recently by Y . K. I^alinin and

E. L. Feinberg, Radiotechnika i Electronika, 3, September 1958.

Wait, J.R. , On the theory of propagation of electromagnetic waves

along a curved surface, Can. Jour. Phys., 36, 9, 1958.
-17-

2 . Characteristics of the Lower Ionosphere

Bailey, D.K., Bateman, R. , und Kirby, R. C. , Radio transmission

at VHF by scattering and other processes in the lower ionosphere,

Proc. Inst. Radio Engrs . , 4_3, 1181, 1955.

Ehmert, A., und Revellio, K. , Solare ultrastrahling und ionospharische D-schicht, Z. Geophys. , 23, 113, 1957.

Evans, J.V. , The electron content of the ionosphere, J. Atmos.

Terrest. Phys . , 11, 259, 1957.

Houston, R. E. , The effect of certain solar radiations on the lower

ionosphere, J. Atmos. Terrest. Phys., 12, 225, 1958.

Jones, R. E. , The development of an E-region model consistent with

long wave phase path measurements, J. Atmos. Terrest. Phys. , 6, 1, 1955.

Lauter, E. A. , und Sprenger, K. , Nachtliche ionisationsstorungen

der tiefen ionosphare, K. Meteorol. , 6, 151, 1952.

Lauter, E. A. , Variationen der D-schichtdampfung aug 245 kHz,

Z. Meteorol . , 7, 321, 1953.

Lauter, E.A. , Bartels, G., Sprenger, K. , und Skeib, K. , Der

intensitatsantieg der kosmischen strahlung am 23. 2 1956 und

gleichzetige effekte in der tiefen ionosphare, Z. Meteorol. , 10, 1956.

Nertney, R. J. , The lower E and D region of the ionosphere as deduced from long radio wave measurements, J. Atmos. Terrest.

Phys. , 3, 92, 1953.

Nicolet, M, The collision frequency of electrons in the ionosphere,

J. Atmos. Terrest. Phys . , 3, 200, 1953.

Parkinson, R. W. , The night-time lower ionosphere as deduced from

a theoretical and experimental investigation of coupling phenomena

at 150 kc/sec. , J. Atmos. Terrest. Phys., 7, 203, 1955.

Pfister, W. , Effect of theD-ionospheric layer on very low frequency

radio waves, J. Geophys. , Res. , 54, 315, 1949.

Scott, J. C. W. , The gyro-frequency in the arctic E layer, J. Geophys.

Res. , 56, 1, 1951.

Sprenger, K. , und Lauter, E. A. , Beobachtungen der tiefen

ionosphare wahrend der sonnenfinsternis am 30.6 1954, Gerlands

Beitrage zue Geophysik, 64, 284, 1955.
-18-

Waynick, A.H. , The present state of knowledge concerning the lower

ionosphere, proc. Inst. Radio Engrs. , 45, 741, 1957. (VLF Symposium paperT)

See also

:

Moler, W. F. , VLF Propagation effects of a D-region layer produced

by cosmic rays, Jour. Geophys. Res. , 65, 1459, I960.
-19-

3. General Theories for Propagation in Inhomogeneous Media

Bailey, V. A. , Reflection of waves by an inhomogeneous medium,

Phys. , Rec . , 96, 865, 1954.

Bremmer, H. , Terrestrial radio waves, Elsevier Pub. Co.,

Amsterdam, Netherlands, 1949.

Bremmer, H. , Propagation of electromagnetic waves, Handbuch der

Physik , 16, 423, 1958.

Budden, K.G. , The numerical solution of differential equations

governing reflexion of long radio waves from the ionosphere, I, Proc. Roy. Soc, 227, 516, 1955a.

Budden, K.G. , The numerical solution of the differential equations

governing the reflexion of long radio waves from the ionosphere, II, Philos. Trans. Math, and Phys. , Sci. , 248, 45, 1955b.

Davids, N. , Theoretical group heights of reflection of 150 kc/s radio

waves vertically incident on the ionosphere. J. Atmos. Terrest.

Phys . , 2, 324, 1952.

'

Epstein, P.S. , Reflection of waves in an inhomogeneous absorbing

medium, Proc. Nat. Acad. Sci., U.S.A ., 16, 627, 1930.

Friedman, B. F. , Propagation in a non-homogeneous atmosphere,

in Theory of Electromagnetic Waves, ( Academic Press, 1951).

Gans, R. , Fortpflanzung des lichts durch ein inhomogenes medium,

Ann. Phys. (Lpz), 47, 709, 1915.

Gibbons, J.J. , Methods of solving the coupled equations of plane wave

propagation in the ionosphere. Report of the Phys. Soc. Conference

on Physics of the Ionosphere (Cambridge) S. 351; Physical Society,

London, 1955.

Namba, S. , General theory of the propagation in the upper atmosphere, Proc. Inst. Radio Engrs. , 21, 238, 1933.

Poeverlein, H. , Low-frequency reflection in the ionosphere, I. , J. Atmos. Terrest. Phys r , 12, 126, 1958.

Rawer, K. , Elektrische wellen in einem geschichteten medium. Zur

frage der partiellen reflexion und zur berechnung der scheinbaren

hohe von ionospharenschichten, Ann. Phys. (Lpz.), 35, 385, 1939.
-20-

Suchy, K. , Gekoppelte wellengleichungen fur inhomogene anistrope

mediem, Z. Naturforsch, 9a, 630, 1954.

Wait, J. R. , Transmission and reflection of electromagnetic waves in

the presence of stratified media, J. Research NBS , 61, 205, 1958.
-21-

4. Calculations of Ionosph eric Reflection Coefficients

Barber, N. F. , andCrombie, D.D. , V.L.F. reflec tions from the

ionosphere in the presence of a transverse magnetic field, Jour.

Atmos. Terrest. Phys ., 16, 37, 1959.

Bracewell, R. N. , and Bain, W. C. , An explanation of radio propagation at 16 kc/sec in terms of two layers below E layer, J. Atmos.

Terrest. Phys . , Z, 216, 1952.

Bremmer, H. , Terrestrial radio waves, Elsevier Pub. Co. , Amsterdam, Netherlands, 1949.

Budden, K.G. , The reflection of very low frequency radio waves at

the surface of a sharply bounded ionosphere with superimposed

magnetic field, Phil. Mag . , 42 , 833, 1951.

Budden, K.G. , A reciprocity theorem on the propagation of radio

waves via the ionosphere, Cavendish Lab. , Cambridge, 604, 1953

and 1954.

Budden, K.G., and Clemmow, P. C, Coupled forms of the

differential equations governing radio propagation in the ionosphere,

II, Proc. Cambridge Phil. Soc. , 53_, 669, 1957.

Butler. S. R. , Gibbons, J. J. , Levy, G.S., and May, J. J. , Solutions

of the coupled wave equations for vertical ionospheric propagation

at 75 and 150 kc/s. Ionospheric Ressearch Scientific Report No. 84,

Pennsylvania State Univ. , State College, Penn. , 1956.

Davids, N. , and Parkinson, R.W., Wave solutions for critical and

nearcritical coupling conditions in the ionosphere, J. Atmos. Terrest.

Phys . , 1_, 173, 1955.

Epstein, P.S. , Reflection of waves of an inhomogeneous absorbing

medium, Proc. Nat. Acad. Sci. U.S.A. , 16, 627, 1930.

Gardner, F.F., and Pawsey, J. L. , Study of the ionospheric -Dregion using partial reflections, J. Atmos. Terrest. Phys., 3, 321,

1953. -

Heading, J., and Whipple, R. T.P., The oblique reflexion of long

wireless waves from the ionosphere at places where the earth's

magnetic field is regarded as vertical, Phil. Trans. Roy. Soc, A,

244,469, 1952.

Heading, J. , The reflexion of vertically-incident long radio waves

from the ionosphere when the earth's magnetic field is oblique,

Proc. Roy. Soc, A, 321, 414, 1955.
-22-

Johler, J.R. , and Walters, L. C. , On the theory of reflection of lowand very low-radiofrequency waves from the ionosphere, J. Research

NB5, 64D , May, I960.

Mallinckrodt, A. J. , The boundary problem in ionospheric wave

propagation, Radio Propagation Lab. , Stanford Univ. , Stanford,

Calif., 1954.

Poeverlein, H. , Low-frequency reflection in the ionosphere, I. , J. Atmos. Terrest. Phys. , 12, 126, 1958a.

Poeverlein, H. , Low-frequency reflection in the ionosphere, II. , J. Atmos. Terrest. Phys ., 12, 236, 1958b.

Ratcliffe, J. A. , Magneto-ionic theory, Cambridge Univ. Press,

1959.

Stanley, J. P. , The absorption of long and very-long waves in the

ionosphere, J. Atmos. Terrest. Phys., 1, 65, 1950.

Wait, J.R. , Oblique reflection of radio waves from an inhomogeneous

region, Jour. Appl. Phys. , 23 , 1403, 1952.

Wait, J.R. , and Murphy, A. , Multiple reflections between the earth

and the ionosphere in VLF propagation, Geof. Pura e Appl. , 35,

61, 1956. ~~

Wait, J. R. , and Perry, L. B., Calculations of ionospheric reflection

coefficients at very low radio frequencies, J. Geophys. Research

62, 43, 1957.

Wait, J\R. , and Murphy, A. , The geometrical optics of VLF skywave propagation, Proc. IRE , 45, 754, 1957. (VLF Symposium

paper.)

Wait, J.R. , Diffraction corrections to the geometrical optics of low

frequency propagation, Proc. Symposium on Propagation of Radio

Waves, Liege, Belgium, 1958. Published by Academic Press,

London, 1959.

Wilkes, M. V. , The theory of reflection of very -long wireless waves

from the ionosphere, Proc. Roy. Soc . , A175, 143, 1940.

Wilkes, M.V. , The oblique reflection of very long wireless waves

from the ionosphere, Proc. Roy. Soc , A189, 130, 1947.

Yabroff, I. W. , Reflection at a sharply bounded ionosphere, Proc.

IRE, 45, 750, 1957. (VLF Symposium paper.

)
-23-

5. Measured Ionospheric Reflection Coefficients (VLF)

Bracewell, R.N., Budden, K.G., Ratcliffe, J. A. , Straker, T.W.,

and Weekes, K. , The ionospheric propagation of low and very low

frequency radio waves over distances less than 1000 km, Proc. Inst.

Elect. Engrs. , 98_, 221, 1951.

Bracewell, R.N. , and Bain, W. C. An explanation of radio propagation at 16 kc/sec in terms of two layers below E layer, J. Atmos.

Terrest. Phys. , 2, 216, 1952.

Bracewell, R.N. , Harwood, J., and Straker, T.W. , The ionospheric

propagation of radio waves of frequency 30-65 kc/s over short distance s , Pr^c^^Jn^^El^c^Ejigj^s^ 154, 1954.

Ferraro, A.J. , Gibbons, J. J. , Houston, R.E., Ross, W.J. , and

Schmerling, E. R. , 75 kc/sec pulsed normal incidence ionospheric

sounding - submitted to J. Research NBS, Section D. (VLF Symposium paper.

)

Gardner, F.F. , and Lawsey, J. L. , Study of the ionospheric Dregion using partial reflections, J. Atmos. Terrest. Phys. , 3, 321,

1953.

Gnanalingam, S. , and Weekes, K. , D-region echoes observed with

a radio wave of frequency 1.4 Mc/s. Report of the Phys. Soc. Conference on Physics of the Ionosphere (Cambridge) S. 63, Physical

Society, London, 1955.

Gregory, J. B. , Ionospheric reflections from heights below the E

region, Austral. J. Phys. , 9, 324, 1956.

Jean, A. G. , Lange, L. J., and Wait, J.R., Ionospheric reflection

coefficients at VLF from sferics measurements, Geof. Pura e Appl . , 38 , 147, 1957. (VLF Symposium paper.

)

Straker, T. W. , The ionospheric propagation of radio waves of

frequency 16 kc/s over short distances, Proc. Inst. Elect. Engrs.,

B102 , 396 and CIO

2

, 122, 1955.

Watts, J. M. , and Brown, J. N. , Some results of sweep -frequency

investigation in the low frequency band, J. Geophys. Res. 59, 71,

1954.

Watts, J. M. , Complete night of vertical incidence ionospheric

soundings covering frequency range from 50 kc/s to 25 Mc/s.

J. Geophys. Res., 62, 484, 1957.
-24-

6. Mode Theory of ELF and VLF Ionospheric Propagation

(and Related Work on Waveguides)

Al'pert, Ya. L, , Low frequency electromagnetic wave propagation

over the surface of the earth, Monograph published by Academy of

Science, USSR, 1955.

Al'pert, Ya. L. , Computation of the field of LF and VLF radio waves

over the earth's surface under natural conditions, Radiotechnika i Electronika, 1, 281, 1956.

Barron, D. W. , The "wave -guide" mode theory of radio wave propagation when the ionosphere is not sharply bounded, Phil. Mag. , 50,

1068, 1959.

Bremmer, H. , Terrestrial radio waves, Elsevier Publishing Co. , Amsterdam, Netherlands, 1949.

Bremmer, H. , Propagation of electromagnetic waves, Handbuch der

Physik , 16 , 423, 1958.

Bremmer, H. , Mode expansion in the low-frequency range for propagation through a curved stratified atmosphere, J. Research NBS,

63D , 75, 1959.

Budden, K.G. , The calculation of the wave-guide mode characteristics

for a curved earth, Informal Communication.

Budden, K.G., The propagation of a radio-atmospheric , Phil. Mag.,

42, 1, 1951.

Budden, K.G., The propagation of a radio-atmospheric - II, Phil.

Mag. , 43, 1179, 1952.

Budden, K.G. , The propagation of very low frequency radio waves to

great distances, Phil. Mag . , 44, 504, 1953.

Budden, K.G. , The "waveguide mode" theory of the propagation of

very-low-frequency radio waves, Proc. IRE, 45, 772, 1957. (VLF

Symposium paper.

)

Crombie, D. D. , On the mode theory of VLF propagation in the

presence of a transverse magnetic field, J. Research NBS, 64D,

265-268, May I960.

Eckersley, T. L. , Studies in radio transmission, Jour. Inst. Elec.

Engs . , 71_, 405, 1932.

Friedman, B. , Low frequency propagation in the ionosphere, Proc. of

Symposium on the Propagation of Radio Waves, Liege, Belgium;

1958. "
-25-

Hales, A.L., A possible mode of propagation of the 'slow' or tail

component in atmospherics, Proc. Roy. Soc. , A , 193, 60, 1948.

Howe, H.H., and Wait, J. R. , Mode calculations for VLF ionospheric

propagation, VLF Symposium paper No. 36, Boulder, Colorado,

1957.

Kaden, H. , Die reflexions und schirmwirkung metallischer hullen in

einer ebenen elektromagnetischen welle, Sonderdruck aus Archiv

Elektrischen Uberstragung, 403, 1957.

Karbowiak, A.E. , Guided wave propagation in submillimetric

region, Proc. Inst. Rad. Engs. , 46, 1706, 1958.

Karbowiak, A.E. , Radiation and guided waves, Trans. IRE, AP-7,

191, 1959.

Kendrick, G.W., Radio transmission formulae, Physical Review,

3L 1040, 1928.

Koo, B. Y. -C and Katzin, M. , An exact earth -flattening procedure in

propagation around a sphere, J. Research NBS, 64D, 61, I960.

Lamont, H.R.L., Waveguides, Methuen and Co. , 1942.

Motz, H. , Electromagnetic problems of microwave theory, Methuen

and Co. , 1951.

Norton, K.A. , Low and medium frequency radio propagation, Proc.

of Symposium on the Propagation of Radio Waves, Liege, Belgium,

W5ZT.

Pekeris, C.L. , Accuracy of the earth -flattening approximation in the

theory of microwave propagation, Phys. Rev., 70, 518, 1946.

Pierce, E.T. , The propagation of radio waves at frequencies less

than 1 kc/s, Proc. IRE , 48, 329-331, March I960.

Poeverlein, H. , Lang und langstwellausbreitung, Sonderdruck aus,

Fortschr.. der Hochfrequenztech . , 4, 47-101, 1951T

Rosner, O. , Die ausbreitung elektromagnetischer TE-(H) -wellen,

erzeugt durch eine horizontal strom durchflossene leiterscheife,

Zeits, fur angew. Physik, 9, 448, 1957.

Rydbeck, O.E.H. , On the propagation of radio waves, Trans.

Chalmers Univ. , 34, 1944.
-26-

Schmelovsky, K.H. , Problem der ausbreitung in tropospherischen

und ionosphischen wellen-leiter , Abhanglungen der Meteorologischen

und Hydrologischen Dienstes der Deutschen Demokratischen Re

publik , 7, 19b».

Schumann, W.O. , Uber die oberfelder bei der ausbreitung langer,

elektrischer wellen im system erde-luft-ionosphare und 2

anwendungen (horizontaler and senkrechter dipol), Zeits. fur

angew. Phys. , 6, 34, 1954a.

Schumann, W. O. , Uber die strahlung langer wellen des horizontalen

dipols in dem luftohlraum zwischen erde und ionosphare, Zeits. fur

angew. Phys. , 6, 225, 1954b.

Schumann, W. O. , Uber die ausbreitung langer elektrischer wellen

um die erde and einige anwendungen auf senderinterferenzen und

blitzsignale, Zeits. angew. Phys., 6, 346, 1954c.

Schumann, W. O. , Der einflub des erdmagnetfeldes auf die

ausbreitung elektrischer langstwellen, Zeits. fur angew. Phys. , 7, 284, 1955.

Schumann, W. O. , Der einflub des horizontalen erdmagnetfeldes

auf elektrische wellen zwischen erde und ionosphare, die schrag

zum magnetischen meridian verlaufen, Zeits. fur angew. Phys. , 8, 126, 1956a.

Schumann, W.O. , Uber wellenausbreitung im plasma zwischen zwei

unendlich gut leitenden ebenen in richtung eines aufgepragten

auberen magnetfelds, Zeits. fur angew. Phys. , 8, 482,1956b.

Schumann, W.O., Uber die ausbreitung langer elektrischer wellen

in magnetisierten plasmer und ihr durchgang durch plasmaschichten,

Zeits. fur angew. Phys ., 10, 428, 1958.

Shmoys, J. , Long-range propagation of low-frequency radio waves

between the earth and the ionosphere, Proc. IRE, 44, 163, 1956.

Wait, J.R. , Note on the theory of radio propagation over an ice

covered sea, Def. Res. Tele., Est., Radio Physics Lab. , Project

Report 18-0-7, 1954. (Gives solution for dielectric slab over a conductive base.)

Wait, J.R. , On the mode theory of VLF ionospheric propagation,

Rev. Geofis. Pura e Appl .

, _37, 103, 1957a. (Paper presented at

International URSI Conference of Radio Wave Propagation, Paris,

Sept. 1956.
-27-

Wait, J.R. , and Howe, HH. , The waveguide mode theory of VLF

ionospheric propagation, Proc. IRE, 45, 1957b.

Wait, J.R. , The mode theory of VLF ionospheric propagation for

finite ground conductivity, Proc. IRE , 45 , 760, 1957c. (VLF

Symposium paper.)

Wait* J. R. , Transmission loss curves for propagation at very low

radio frequencies, IRE Trans., CS-6, 58, 1958a.

Wait, J.R. , An extension to the mode theory of VLF ionospheric

propagation, J. Geophys. Research, 63, 125, 1958b.

Wait, J.R. , Terrestrial propagation of VLF radio waves, J. Research NBS, 64D, 153, 1960a. -

Wait, J.R. , On the propagation of ELF radio waves and the influence

of a non-homogeneous ionosphere, J. Geophys. Research, 65, 597,

Feb. 1960b.

Wait, J.R. , Mode theory of the propagation of ELF radio waves,

J. Research NBS, 64D 1960c (July/A ug. issue).

Wait, J.R. , and Carter, N. F. , Field strength calculations for ELF

radio waves, NBS Tech. Note No. 52, I960.

Wait, J.R. , and Spies, K. , Influence of earth curvature on the

terrestrial megnetic field on VLF propagation (to be submitted to

Jour. Geophys. Research, I960.)

Watson, G.N. , The transmission of electric waves round the earth,

Proc. Roy. Soc . , 95, 546, 1919.

Weidner, Julius, Uber eine verfeinerung der theorie der ausbreitung

langer elektrischer wellen um die erde, Zeits. fur angew. phys. , 7, Part 2, 77-82, 1955.
-28-

7. Theory of the Propagation of Pulses in ELF and VLF Ionospheric

Propagation

Budden, K.G., The propagation of a radio -atmospheric, Phil. Mag.,

42, 1, 1951.

Budden, K.G. , The propagation of a radio-atmospheric - II, Phil.

Mag., 43, 1179, 1952.

Norton, K. A. , System loss in radio wave propagation, J. Research

NBS, 63D, 53, 1959.

Schumann, WO., Uber die ausbreitung sehr langer elektrischer

wellen um die erde und die signale des blitzes, Nuovo Cimento, 9»

1116, 1952.

Schumann, W. O. , Uber die zeitliche form und das spektrum

ausgesendeter dipolsignale in einer dielectrischen hohl kugel mit

leitenden wanden, Verlag Bayerischen Akad. Wiss. , Munich, 1956a.

Schumann, W. O. , Zur deutung der von blitzen ausgesendeten

impulsreihen, Zeits. angew. Phys., 8, 24, 1956b.

Schumann, W. O. , Uber elektrische eigenschwingungen des hohlraumes

erde-luft-ionosphare arregt durch blitzentladungen, Zeits. fur angew.

Phys . , 9, 373, 1957.

Stablein, H. G. , Bemerkungen zur ausbreitung langwelliger blitz - signale um die erde, Zeits. fur angew. , Phys. , 7, 290, 1954.

Wait, J.R. , The propagation of VLF pulses to great distances, J.

Research NBS, 61, 187, 1958.
-29-

8. Characteristics of Lightning Discharges

Atlas, D. , Radar lightning echoes and atmospherics in vertical crosssection, R.A.A.E., 441 (Pergamon Press, 1958).t

Bays, C.V., Progressive lightning, Nature, 118, 749, 1926.

Brook, M. , Thunderstorm electricity, New Mexico Institute of

Mining and Technology, Res. and Dev. Div. , Socorro, New Mexico, October, 1957.

Bruce, C.E.R., and Golde, R.N., The lightning discharge, J. Inst.

Elect. Engrs. , 88 , (II), 487, 1941.

Delloue, J., Electricite atmospherique , C.R.Acad. Sci. , Paris,

244 , 797, 1957.

Hay, D.R., and Hartz, T.R. , Thunderstorm signals at very-high

frequency and ultra-high frequency, Nature, 175, 949, May, 1955.

Hill, E. L. , Very low-frequency radiation from lightning strokes,

Proc. IRE , 45, No. 6, 775, June, 1957. (VLF Symposium paper.

)

Horner, F. , The relationship between atmospheric radio noise and

lightning, J. Atmos. Terrest. Phys. , 13, 140, 1958.

Ishikawa, N. , and Kimpara, A. , Lightning mechanism and atmospheric radiation, R.A.A.E., 583 (Pergamon Press, 1958).

Jones, N. L. , The identification of lightning discharges by sferic

characteristics, R.A.A.E., 543 (Pergamon Press, 1958).

Kitagawa, N. , and Kobayashi, M. , Field-changes and variations of

luminosity due to lightning flashes, R.A.A.E. , 485 (Pergamon

Press, 1959),

Large, M. I. , Some investigations in atmospheric electricity,

Dissertation (Cambridge Univ. , 1957.)

Malan, D. J. , and Schonland, B. F. J. , Charge distribution and

electrical processes deduced from lightning measurements,

Thunderstorm Electricity , 238, (Univ. of Chicago Press, 1953.)

Malan, D. J. , Radiation from lightning discharges and its relation

to the discharge process, R.A.A.E., 557 (Pergamon Press, 1958).

7

R.A.A.E. = Recent Advances in Atmospheric Electricity.
-30-

Norinder, N. , On the measurement of atmospheric s produced by

electric discharges in snow-squalls and from other sources, Tellus,

1, No. 2, 1, 1949.

Norinder, N. , Variations of the electric field in the vicinity of

lightning discharge, Arkiv for Geofysik, 1, 543, 1952.

Norinder, N. , and Knudsen, E. , Combined analysis of daylight

photographs of lightning paths and simultaneous oscillographic

records, R.A.A.E., 503 (Pergamon Press, 1958).

Norinder, N. , Knudsen, E. , and Vollmer, B., Multiple strokes in

lightning channels, R.A.A.E., 525 (Pergamon Press, 1958).

Ollendorf, F. , Radiation field of lightning, Elektrische NechritenTechaik , 7, 108, 1930.

Pierce, E.T. , Electrostatic field-changes due to lightning discharges,

Quart. Jour. Roy. Met. Soc, 81, 211, 1955a.

Pierce, E.T., The development of lightning discharges, Quart. Jour.

Roy. Met. Soc . , 81_, 229, 1955b.

Pierce, E.T. , The frequency spectra of the radiation fields from

lightning discharges, Symposium uber Langstwellen und Atmospherics; Elektrophysikalisches Institut der Technischen Hochschule,

Munchen, 1955c.

Pierce, E.T., Meteorology, Science Progress, 177, 70, Jan. 1957.

Pierce, E. T. , Some topics in atmospheric electricity, R.A.A.E.,

5 (Pergamon Press, 1958).

Schonland, B. F. J. , The pilot streamer in lightning and the long

spark, Proc, Roy. Soc. of London, Series A, 220, 25, Oct. 1953.

Schonland, B. F.J. , The lightning discharge, Handbuch der Physik,

22 , Springe r-Verlag, Berlin, S. 576, 1956.

Taylor, W. L. , and Jean, A.G. , VLF radiation spectra of returnstroke lightning discharges, J. Research NBS , 63D, 199, 1959.

Wait, J. R. , On the waveform of a radio atmospheric at short ranges,

Proc. IRE, 44, 1052, August, 1956.
-31-

9. Atmospheric Waveforms (VLF)

Al'pert, Ya. L. , Investigation of the propagation of long and very long

radio waves by the method of analyzing the shape of atmospherics,

Radiotechnika i Electronika, 1, 293, 1956.

Appleton, E.V., und Chapman, F. W. , On the nature of atmospheric sIV, Proc, Roy. Soc , A 158, 1, 1937.

Bowe, P.W.A. , The waveforms of atmospherics and the propagation

of very low frequency radio waves, Phil. Mag. , 42, 121, 1951.

Budden, K.G., The propagation of a radio-atmospheric , Phil. Mag.,

42, 1, 1951.

Budden, K.G., The propagation of a radio -atmospheric - II, Phil.

Mag. , 43_, 1179, 1952.

Chapman and Edwards, Proc. UR5I , 8, Pt. 2, 35, 1950.

Chapman, F. W. , and Matthews, W.D. , Audio-frequency spectrum of

atmospherics, Nature, 172, 495, 1953.

Chapman, F. W. , and Macario, R.C.V. , Propagation of audio frequency

radio waves to great distances, Nature, 177, 930, 1956.

Chapman, J. , The waveforms of atmospherics and the propagation

of very low frequency radio waves, J. Atmos. Terrest. Phys. , 11,

223, 1957.

Chapman, J. , und Pierce, E.T. , Relations between the character of

atmospherics and their place of origin, Proc. Inst. Radio Engrs. , 45 , 804, 1957. (VLF Symposium paper.")

Gardner, F. F. , The use of atmospherics to study the propagation of

very long radio waves, Phil. Mag. , 41, 1259, 1950.

Hepburn, F. , Wave -guide interpretation of atmospheric waveforms,

J. Atmos. Terrest. Phys . , 10, 121, 1957.

Hepburn, F. , Interpretation of smooth-type atmospheric waveforms,

J. Atmos. Terrest. Phys ., 14, 262, 1959.

Humphrey, L. C. , Waveforms of short atmospheric transients,

Symposium on the Propagation of VLF Radio Waves, 40, NBS,

Boulder, Colorado, 1957.

Jean, A.G., Lange, L. J. , and Wait, J.R., Ionospheric reflection

coefficients at VLF from sferics measurements, Geof. Pura e Appl. , 38, 147, 1957. (VLF Symposium paper.

)
-32-

Jean, A.G., Taylor, W.L. , and Wait, J. R. , VLF phase

characteristics deduced from atmospheric waveforms, J. Geophys.

Res . , 65_, March, I960.

Jones, N. L. , The identification of lightning discharges by sferic

characteristics, R.A.A.E., 543 (Pergamon Press, 1959).

Kimpara, A. , Atmospherics in the Far East, R. A. A. E . , 565 , (Pergamon Press, 1959).

Laby, T.H., McNeill, J. J. , Nichols, F.G., und Nickson, A.F.B.,

Waveform , energy and reflexion by the ionosphere, of atmospherics, Proc, Roy. Soc , A174 , 145, 1940.

Norinder, N. , Variations of the electric field in the vicinity of

lightning discharge, Arkiv. for Geofysik, 1, 543, 1952.

Norinder, N. , The waveforms of the electric field in atmospherics

recorded simultaneously by two different stations, Arkiv. for

Geofysik, 2, No. 9, 161, Nov. 1954.

Pierce, E. T. , The frequency spectra of the radiation fields from

lightning discharges. Symposium uber Langstwellen und Atmospherics; Elektrophysikalisches Institut der Technischen Hochschule,

Munchen, 1955.

Potter, R.K. , Analysis of audio-frequency atmospherics, Proc. Inst.

Radio Engrs r, 39, 1067, 1951.

Schonland, B.F. J. , Elder, J. S. , Hodges, D.B., Phillips, W.E.,

and Van Wyck, J. W. , The wave form of atmospherics at night, Proc.

Roy. Soc . , A176 , 180, 1940.

Taylor, W. L. , and Lange, J. , Some characteristics of VLF propagation using atmospheric waveforms, Recent Advances in Atmospheric

Electricity, p. 609 (Pergamon Press, 1959).

Taylor, W. L. , Attenuation characteristics of VLF propagation deduced from sferics, J. Research NFS, 64D, July, I960.

Tepley, L.R. , A comparison of sferics as observed in the VLF and

ELF bands, Jour. Geophys. Res ., 64, 2315, 1959.

Wait, J. R. , The attenuation vs. frequency characteristics of VLF

radio waves, Proc. IRE, 45 , 768, 1957. (VLF Symposium paper.

)

Watson -Watt, R.A., Herd, J.F., and Lutkin, F.E., On the nature of

atmospherics, Proc. Roy. Soc. , A162, 267, 1937.
-33-

10. Atmospheric Waveforms (ELF)

(Including Slow-Tails)

Chapman, F. W. , and Matthews, W. D. , Audio-frequency spectrum

of atmospherics, Nature, 172, 495, 1953.

Chapman, F. W. , and Macario, R.C.V., Propagation of audiofrequency radio waves to great distances, Nature, 177, 930, 1956.

Chapman, J. , The waveforms of atmospherics and the propagation of

very low frequency radio waves, J. Atmos. Terrest. Phys. , 11,

223, 1957.

Deal, O.E. , The observation of very low frequency electromagnetic

signals of natural origin, unpublished Ph. D. Thesis, The University of California, Los Angeles, 1956.

Hales, A.L. , A possible mode of propagation of the 'slow* or tail

component in atmospherics, Proc. Roy. Soc, A 193, 60, 1948

Hepburn, F. , and Pierce, E.T., Atmospherics with very low

frequency components, Nature, 172, 837, 1953.

Hepburn, F. , Atmospheric waveforms with very low frequency components below 1 kc/s known as slow tails, J. Atmos. Terrest. Phys. , 10_, 266, 1957.

Hepburn, F. , Classification of atmospheric waveforms, J. Atmos.

Terrest. Phys . , 12, 1, 1958.

Liebermann, L. , Extremely low-frequency electromagnetic waves, I. Reception from lightning, J. Appl. Phys. , 27, 1473, 1956a. (VLF

Symposium paper.

)

Liebermann, L. , Extremely low-frequency electromagnetic waves,

II. Propagation properties, J. Appl. Phys. , 27, 1477, 1956b.

(VLF Symposium paper.

)

Liebermanti, L. , Anomalous propagation below 500 c/s, Proc. Sym.

of VLF Radio Waves , 3, paper No. 25, Boulder, ColoracTo, 1957.

Pierce, E.T., The frequency spectra of the radiation fields from

lightning discharges, Symposium uber Langstwellen und Atmospherics; Elektrophysikalisches Institut der Technischen Hochschule,

Munchen, 1955.

Pierce, E. T. , The propagation of radiowaves at frequencies less than

lkc/s, Proc. IRE, 48, 329, March, I960.
-34-

Schumann, W.O., and Konig, H. , Uber die beobachtung von

"atmospherics" bei geringsten frequenzen, Die Naturwissehschaften,

41_, 183, 1954.

Smith, E.J. , The propagation of low-audio frequency electromagnetic

waves, Ph.D. Thesis, Inst, of Geophysics, Univ. of Calif. , Feb.

I960.

Tepley, L..R. , A comparison of sferics as observed in the VLF and

ELF bands, Jour. Geophys. Res., 64, 2315, 1959.

Wait, J.R. , On the theory of the slow-tail portion of atmospheric

waveforms, Jour. Geophys. Res., 65, I960 (July issue).

Watson-Watt, R.A., Herd, J.F., and Lutkin, F.E., On the nature

of atmospherics, Proc. Roy. Soc. , A, 162, 267, 1937.
-35-

11. Measured Amplitude Characteristics of VLF Fields

Anderson, C.N. , Correlation of long wave transatlantic radio with

other factors affected by solar activity, Proc. Inst. Radio Engrs . , 16, 207, 1928.

Anderson, C.N. , Notes on radio transmission, Proc. Inst. Radio

Engr_s, , 19, 1150, 1931.

Austin, L.W. , Preliminary note on proposed changes in the constants

of the Austin-Cohen transmission formula, Proc. Inst. Radio Engrs. , 14_, 377, 1926.

Austin, L.W. , A series of reports on "Long-distance receiving

measurements at Washington," Proc. Inst. Radio Engrs., 12, 19,

1931.

Brown, J. N. , Round-the-world signals at very low frequency,

Jour. Geo. Res . , 54, 367, 1949.

Budden, K.G. , The propagation of very low frequency radio waves to

great distances, Phil. Mag. , 44, 504, 1953.

Crombie, D. D. , Differences between east-west and west-east propagation of VLF signals over long distance, Jour. Atmos. Terrest.

Phys . , 12, 110, 1958.

Heritage, J.L., Weisbrod, S. , and Bickel, J E. , A study of signal

versus distance data at VLF, Symposium on the Propagation of

VLF radio waves, Prepublication Record, 4, 29, NBS, Boulder,

Colo. , 1957.

Hollingsworth, J. , The propagation of radio waves, Jour. Inst.

Elect. Engrs. , 64, 579, 1926.

Kitchen, F.A., Pressey, B.G., and Tremellen, K. W. , A review of

present knowledge on the ionospheric propagation of very-low, lowand medium-frequency waves, Proc. Inst. Elect. Engrs, 100, 100,

1953.

Pierce, J. A. , Sky wave field intensity 1; Low and very-low radio

frequencies, Cruft Lab. Tech. Rept. 158, Harvard Univ. , 1952.

Round, H.J. , Eckersley, T.L., Tremmelen, K. , and Lunnon, F.C,

Report on measurements made on signal strength at great distances

during 1922 and 1923 by an expedition sent to Australia, Jour. Inst.

Elect. Engrs. , 63, 933, 1925.
-36-

Tremellen, K. , A study of ionospheric ray field intensities in the

10-30 and 500-1100 kc/s bands, Marconi Review, 13, 153, 1950.

Watt, A.D. , and Plush, R. W. , Power requirements and choice of

an optimum frequency for a world-wide broadcasting station,

J. Research NBS, 63D , 35, 1959.

Weekes, K. , The ground interference pattern of very-low frequency

radio waves, Proc, Inst. Elect. Engrs. , III, 97, 100, 1950.

Yokoyama, E. , and Nakai, T. , East-west and north-south attenuations of long radio waves in the Pacific, Proc. Inst. Radio Engrs. , 17, 1240, 1929.

Yokoyama, E. , and Nakai, T. , Effect of sunspots and magnetism

on long distance reception on VLF waves, Proc. Inst. Radio Engrs.,

19, 882, .1931.

Yokoyama, E. , and Tanimua, I. , Some long distance transmission

phenomena of low frequency waves, Proc. Inst. Radio Engrs. , 21,

263, 1933.
-37-

12. Measured Phase Characteristics of VLF Fields

Allan, A.H., Crombie, D.D., and Penton, W.A., Frequency variations in New Zealand of 16 kc/s, Transmission from GBR Rugby,

Nature , 177, 178, 1956.

Al'pert, Ya. L. , On the speed of propagation of electromagnetic

waves at audio frequencies, J. Exptl. Theoret. Phys. (USSR), 33,

1305, 1957.

Al'pert, Ya. L. , and Bordina, S.V., On the velocity of propagation

of audio frequency electromagnetic waves, Radiotechnika i Elektronika , 4, 195, 1959.

Brown, J.N. , Round-the-world signals at very low frequency, Jour.

Geo. Res . , 54, 367, 1949.

Casselman, C. J. , Heritage, D.P., and Tibbals, M.L. , VLF propagation measurements for the Radux-Omega navigation system, Proc . IRE, 47, 829, 1959.

Crombie, D.D., Allan, A.H., and Newman, M. , Phase variations of

16 kc/s transmissions from Rugby as received in New Zealand, Proc,

Inst. Elect. Engrs. , B 21, 301, 1958.

Essen, L. , Standard frequency transmissions, Proc. Inst. Elect . Engrs. , (HI) , 101, 249, 1954.

Jean, A.G., Taylor, W.L., and Wait, J.R. , VLF phase characteristics deduced from atmospheric waveforms, J. Geophys. Res . , 65 , March, I960.

Obayashi, T. , Measured frequency spectra of VLF atmospherics,

J. Research NBS, 64D , 41, I960.

Pierce, J. A. , The diurnal carrier-phase variation of a 16-kilocycle

transatlantic signal, Proc. IRE, 43, 584, 1955.

Pierce, J. A. , Intercontinental frequency comparison by very-lowfrequency radio transmission, Proc. IRE, 45, 794, 1957. (VLF

Symposium paper.)

Volland, H. , Die frequenzabhangigkeit der sonneneruptionseffekte im

langstwellengebiet, Archiv der Elektrischen Ubertragung, 13, 443

1959.

Wait, J.R. , Diurnal change of ionospheric heights deduced from

phase velocity measurements at VLF, Proc. IRE, 47, 998, 1959.
-38-

13. Noise (VLF)

Crichlow, William Q. , Noise investigation at VLF by the National

Bureau of Standards, Proc. IRE, 45 , 778, June, 1957. (VLF

Symposium paper.

)

Fulton, Forrest F. , Jr. , The effect of receiver bandwidth on the

amplitude distribution of VLF atmospheric noise. (To be submitted

to J. Research NBS, Section D. ) (VLF Symposium paper.

)

Horner, F. , The relationship between atmospheric radio noise and

lightning, J. Atmos. Terrest . Phys. , 13, 140, 1958.

McKerrow, C.A., Some recent measurements of atmospheric noise

in Canada, Proc. IRE, 45, 782, June, 1957. (VLF Symposium

paper.

)

Watt, A. D. and Maxwell, E. L. , Characteristics of atmospheric

noise from 1 to 100 kc, Proc. IRE, 45, 787, 1957. (VLF Symposium

paper.

)
-39-

14, Noise (ELF)

Aarons, J. , and Henissart, M. , Low frequency noise in the range

0. 5 to 20 c/s, Nature , 172, 682, 1953.

Aarons, J. , Low frequency electromagnetic radiation 10 to 900 c/s,

J. Geophys. Res . , 6L, 647, 1956.

Benoit, R. , Low frequency radio wave noise of the earth's magnetic

field, C.R. Acad. Sci. , 242, 2534, 1956.

Campbell, W.H. , A study of micropulsations in the earth's magnetic

field, Sci. Rep. No. 1,233, (47), Univ. of Calif. , Inst, of Geophys.,

Los Angeles, April, 1959.

Deal, O.E. , The observation of very low frequency electromagnetic

signals of natural origin, Unpublished Ph. D. Thesis, The Univ. of

California, Los Angeles, 1956.

Duffus, H.J. , Nasmyth, P.W., Shand, J. A., and Wright, C.S. , Sub-audible geomagnetic fluctuations, Nature, 181, 1258, 1958.

Duffus, H. J. , and Shand, J. A. , Some observations of geomagnetic

micropulsations, Can. J. Phys. , 36, 1958. (VLF Symposium paper.

)

Ellis, G.R., Low-frequency radio emission from aurorae, J. Atmos.

Terrest. Phys . , 10, 302, 1957.

Goldberg, P. A. , Electromagnetic phenomena of natural origin in the

1.0 - 150 c/s band, Nature , 177 , 1219, 1956.

Holzer, R.E., and Deal, O.E., Low audio -frequency electromagnetic

signals of natural origin, Nature, 177, 536, 1956.

Holzer, R.E., Deal, O.E., and Ruttenberg, S. , Low audio-frequency

natural electromagnetic signals, Symposium on the Propagation of

VLF Radio Waves , Prepublication Record, 3, 45, NBS, Boulder,

Colorado, 1957. See also R.E. Holzer, World thunderstorm

activity and ELF sferics, in Recent Advances in Atmospheric

Electricity, p. 559 (Pergamon Press, 1958.)

Large, M.I., and Wormell, T-W. , Fluctuations in the vertical

electric field, Recent Advances in Atmospheric Electricity, p. 603,

(Pergamon Press, 1959JT

Willis, H.F., Audio frequency magnetic fluctuations, Nature, 161,

887, 1948.
-40-

15. Radio Signals from Nuclear Detonations

Fusca, J. A., U.S. explores global monitoring methods, Aviation

Week, p. 26, May 12, 1958.

Kompaneets, A.S. , Radio emission from an atomic explosion,

J. Expl. Theoret. Phys. , (USSR), 35_, 1538, 1958.

United Nations, Report of the conference of experts to study the

possibility of detecting violations of a possible agreement on the

suspension of nuclear tests, United Nations Doc. 5/4091, 28 Aug,

1958.
-41-

16. Whistlers and Magneto-Ionic Duct Propagation

Bell, T.F-, and Helliwell, R.A., Traveling -wave amplification

in the ionosphere, Stanford Electronic s Laboratories, Tech.

Rpt. No. 2, September 15, 1959.

Carpenter, D. L. , Identification of whistler sources on visual

records and a method of routine whistler analysis, Stanford

Electronics Laboratories, Tech. Rpt. No. 5, March 15, I960.

Crary, J.H. , Helliwell, R.A., and Chase, R.E., Stanford-Seattle

whistler observations, J. Geophys. Res., 61, 35, 1956.

Ellis, G.R. , On the propagation of whistling atmospherics, J. Atmos. Terrest. Phys . , 8, 338, 1956.

~~

Gallet, R. M. , and Helliwell, R.A., Origin of 'very-low frequency

emissions', J. Research NBS , Vol. 63D, No. 1, 21, July-August

1959.

Grierson, J. Kenneth, A technique for the rapid analysis of whistlers,

Proc. IRE, 45, 806, June 1957. (VLF Symposium paper.

)

Helliwell, R.A. , Low frequency propagation studies; Part I, whistlers and related phenomena, Radio Propagation Laboratory,

Stanford Univ. , Stanford, California, i95b.

Helliwell, R.A. , Whistlers and very low frequency emissions,

Geophys. and the IGY , Geophys. Mono. No. 2, AGU, 35, July 1958.

Helliwell, R.A., Hybrid whistlers, (Abstr.) Program of the Joint

Meeting of URSI and IRE, Washington, D-C, p. 28, May 1959.

Helliwell, R.A. Crary, J.H. , Pope, J. H. , and Smith, R. L. , The

"nose" whistler - a new high-latitude phenomenon, J. Geophys. Res. , 61, 139, 1956.

Helliwell, R.A., and Gehrels, E. , Observations of magneto -ionic

duct propagation using man-made signals of very low frequency,

Proc. Inst. Radio Engrs . , 46, 785, 1958.

Helliwell, R.A., Jean, A.G., and Taylor, W.L. , Some properties of

lightning impulses which produce whistlers, Proc. IRE, 46, No. 10,

1760, October 1958.

Helliwell, R.A. , and Morgan, M.G., Atmospheric whistlers, Proc.

IRE, 47, 200, February 1959.
-42-

Helliwell, R.A. , and Bell, T.F. , A new mechanism for accelerating

electrons in the outer ionosphere, Stanford Electronics Labs. , Tech. Rpt. No. 4, February 23, I9b0.

Hines, CO. , Heavy-ion effects in audio-frequency radio propagation,

Jour. Atmos. Terrest. Phys . , 11, 36, 1957. (Shows that whistler

ray directions can diiier markedly from the direction of the earth's

magnetic field when heavy ions are considered.) (VLF Symposium

paper.

)

Martin, L.H., and Helliwell, R.A. , Association between aurorae

and VLF hiss observed at Byrd Station, Antarctica - (Submitted to

Nature , April I960.)

Morgan, M.G. , and Johnson, W.C. , Whistlers and dawn chorus at

Univ. of Alaska and their correlation with simultaneous data at the

geomagnetic conjugate whistlers and dawn chorus at Knob Hill,

Quebec - to be submitted to J. Research NBS, Section D. (VLF

Symposium paper.)

Morgan, M.G., and Allcock, G. McK. , Observations of whistling

atmospherics at geomagnetically conjugate points, Nature, 177,

30, 1956.

Morgan, M.G. , Whistlers and dawn chorus, Annals I.G. Y. , Pergamon

Press , London, Vol. 3 , Part 4, 315, 1957.

Smith, R. L. , The guiding of whistlers in a homogeneous medium

(To be submitted to J. Research NBS, Section D. (VLF Symposium

paper.

)

Smith, R. L. , and Helliwell, R.A., Calculation of the electron density

of the outer ionosphere using whistlers (To be submitted to J. Research NBS , Section D. (VLF Symposium paper.)

Smith, R.L., Crary, J.H., and Kreiss, W.T., IGY instruction

manual for automatic whistler recorders, Stanford Electronics

Labs. , NSF Grant Y-6. 10/20, January 195ST"

Smith, R.L., Helliwell, R.A. , and Yabroff, I. W. , A theory of

trapping of whistlers in field-aligned columns of enhanced ioniization,

J. Geophys. Res . , 64, No. 3, 815, March i960.

Storey, L.R-O., An investigation of whistling •atmospherics, Phil.

Trans. Roy. Soc, 246, 113, 1953.
-43-

Storey, L.R.O. , A method for interpreting the dispersion curves of

whistlers, Can. J. Phys. , 35, 1107, 1957. (VLF Symposium paper.

)

Yabroff, I. W. , Computation of whistler ray paths, Final Letter

Report- -Part II. , AFOSR-TN-60-71, Stanford Research Institute,

Prepared for Stanford University Electrical Engineering Department,

SRI Project 2241, December 1959.
-44-

17. Exosphere and Dawn Chorus

Allcock, G. McK. , A study of the audio-frequency radio phenomenon

known as "dawn chorus, " Austral. J. Phys . , 10_, 286, 1957.

Ellis, G.R., Low-frequency radio emission from aurorae, J.Atmos.

Terrest. Phys . , H)_, 302, 1957.

Gallet, R. M. , and Pfelliwell, R. A. , A theory of the production of

VLF noise (so-called dawn chorus) by traveling wave amplification

in the exosphere of the earth. Symposium on the Propagation of

VLF Radio Waves, Prepublication, Bd. 2, 20, NBS, Boulder,

Colorado, 1957.

Gallet, R. M. , A very low frequency emission generated in the

earth's exosphere, Proc. IRE, 47, 211, 1959.

Hines, C. O. , Heavy-ion effects in audio-frequency radio propagation, Jour. Atmos. Terrest. Phys. , 11, 36, 1957. (Shows that

whistler ray directions can differ markedly from the direction of the

earth's magnetic field when heavy ions are considered.) (VLF

Symposium paper.

)

Morgan, M. G. , Whistlers and dawn chorus, Annals I.G. Y. , (Pergamon Press, London.) Vol. 3, Part 4, 315, 1957.

Storey, L.R.O. , A method to detect the presence of ionized hydrogen

in the outer atmosphere, Can. Jour. Phys., 34, 1153, 1956. (Discusses the effect of protons on the propagation of whistlers in the

exosphere, collisions are neglected.)

Watts, J. M. , Audio -frequency electromagnetic hiss recorded at

Boulder in 1956, Geof. Pura e Appl . , 37, 169, 1957a. (VLF Symposium

paper.

)

Watts. J. M. , An observation of audio-frequency electromagnetic

noise during a period of solar disturbance, J. Geophys. Res. , 62,

199, 1957b. —
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