Whistlers and Audio-Frequency Emissions. Monthly Summaries of Whistlers and Emissions for the Period July 1957–December 1958

302 Pages·1965·20.669 MB·English

by  M. G. Morgan (Eds.)

ANNALS OF THE
INTERNATIONAL GEOPHYSICAL YEAR
VOLUME XXXVII
WHISTLERS
AND AUDIO-FREQUENCY
EMISSIONS
Monthly Summaries of whistlers
and emissions for the period
July 1957 - December 1958
Editor
M. G. MORGAN
International Council of Scientific Unions
Comite International de Geophysique
(CIG)
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INTRODUCTION
After the confirmation (Morgan and Allcock 1956) of Storey's hypothesis
(Storey 1953) that whistlers echo back and forth between the hemispheres,
propagating dispersively along the flux of the earth's magnetic field, a
world-wide network of thirty-four observing stations was set up during the
IGY in order to obtain a synoptic description of this phenomenon. The two
largest programs were those of the United States known as "Whistlers-West"
(under Prof. R. A. Helliwell) and "Whistlers-East" (under Prof. M. G.
Morgan). Approximately ten stations were operated in each of these programs
as meridional chains extending into both hemispheres approximately along
the W 110° and the 0° geomagnetic meridians respectively. (Three of the
Whistlers-West stations in the Northern Hemisphere were near W 60°.) Three
stations each were operated by Canada (under Mr. W. E. Thompson) and by
Australia (under Prof. H. C. Webster), and two stations were operated by
Japan (under Prof. A. Kimpara). Other participants operated one station each.
Comprehensive accounts of the results of the synoptic program have
been published for the Whistlers-East network (Laaspere, Morgan, and Johnson
1963 and 1964) and the Australian stations (Crouchley 1961). An extensive
account of the results from the Whistlers-West network is available in
report form (Helliwell and Carpenter 1961). In the following paragraphs
the principal results in the two Whistlers-East publications are summarized.
The principal problem in presenting the results of the synoptic ob
servations, aside from the magnitude of the data reduction problem, has
been to find ways to combine the data so as to smooth out random short-
term variations, but not at the same time to degrade the manifestation of
any of the principal effects.
Although whistlers can be observed at any time of day, it is found
that they occur primarily at night. The local season at the point of
observation (or possibly in the opposite hemisphere) exercises such great
influence on the diurnal variation of occurrence that it is concluded that
the observed occurrence is primarily propagation controlled and not source
controlled. Although the seasonal and geographic dependences of thunder
storm occurrence have noticeable effects, the diurnal dependence of storms
does not seem to.
A basic form of the diurnal curves appears to be one which is sym
metrical about local midnight with a deep minimum at local noon and rela
tively high nighttime activity showing maxima at about 2000, 2400, and 0400
local time. Depending on local season and location of the station, one or
more of these peaks may be absent or enhanced.
Excepting the equatorial station (Huancayo), whistlers were observed
at the lowest latitude station (Toyokawa) and the highest (Godhavn). None
were heard at the equatorial station, confirming a pre-IGY result (Koster
and Storey 1955). The greatest incidence of whistlers during the IGY
period occurred in both hemispheres in the geomagnetic latitude range
50-60°. The day-to-day correlation of whistler activity at geomagnetic-
ally conjugate stations was sometimes very low and sometimes remarkably
high.
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Beginning **ith low values of Kp (the planetary index of geomagnetic
disturbance - see IGY Annals, Vol. IV, part IV), whistler nighttime occur
rence rates increase moderately as Kp increases, but as Kp increases
further a value is reached above which this trend sharply reverses. At
very high values of Kp, whistler rates become strongly depressed. This
reversal occurs at about Kp = 4 at low latitude stations but moves down
to Kp = 2 or less at middle and higher latitudes. The effect of Kp on
daytime rates has been investigated for Dartmouth (Norwich) and it is
found that the rate decreases approximately linearly with increasing Kp,
reaching zero at Kp = 9. There are also seasonal effects in the Kp depend
ence, particularly at lower latitudes.
The greatest incidence of dawn chorus occurred in both hemispheres in
the geomagnetic latitude range 55-65°, that is, about 5° higher than for
whistlers. The incidence falls off slowly towards higher latitudes but
rapidly towards lower latitudes. In marked contrast to whistlers, in the
zone of maximum occurrence the local season exercises virtually no influence
at all on the diurnal variation of occurrence and it is concluded therefore
that the occurrence is primarily source controlled.
Like whistlers, dawn chorus can be heard at anytime of day but, as the
name implies, it is heard most frequently in the early morning hours. The
local time of maximum occurrence is remarkably constant at about 0600 in
the latitude of maximum occurrence and in lower latitudes. It shows no
dependence on Kp or on season although the relative level of chorus activity
is markedly depressed in summer in lower latitudes.
As one approaches the auroral zone, it is found that the local time
of maximum occurrence of chorus becomes later but that this retardation is
inversely dependent upon Kp.
A substantial amount of chorus occurs in the auroral zone at very low
values of Kp and at still higher latitudes (Godhavn) low-Kp chorus is pre
dominant. This chorus has been recognized as a type distinct from that of
lower latitudes and has been called "polar chorus" (Ungstrup and Jackerott
1963; also Martin 1960). This chorus has its maximum occurrence at midday
and in summer. It has been suggested that it us caused by Cerenkov rad
iation from secondary auroral electrons and that the need for a thick
E-layer accounts for the apparent dependence of the emission activity on
the zenith angle of the sun (Ungstrup 1963).
There is one more important fact about the occurrence of chorus. In
low and middle latitudes, the amount of chorus observed increases with
increasing Kp, the amount of the increase increasing with latitude. (Above
Kp = 8, there is a sharp decrease at middle latitudes.)
A plausible picture combining all of these facts concerning the
occurrence of chorus is as follows: In the latitude of maximum occurrence,
say 60°, the amount of chorus production is directly proportional to geo
magnetic disturbance, has no seasonal dependence and is always maximum at
0600 local time. This chorus is observed in lower latitudes subject to
propagation effects, being reduced in strength as one moves away from the
latitude of production, especially in summer. Moving from the latitude of
maximum occurrence towards high latitudes, an admixture of polar chorus
begins to affect the observations. When Kp is low, the polar chorus which
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peaks at midday, has a relatively greater effect, retarding the time of
maximum occurrence. Also, it is noted that chorus activity at auroral zone
stations is somewhat greater in summer and fall than in winter and spring,
again due to the effect of the admixture of polar chorus which has a seasonal
maximum in summer.
The occurrence of hiss is also greatest in about 60° latitude. In this
latitude and above, it has a daily maximum at midday, but the curve of diur
nal variation develops a deep midday depression in local summer and fall at
latitudes slightly lower, and in all seasons in still lower latitudes. The
Kp dependence of hiss is similar to that of chorus.
REFERENCES
J. Crouchley, Aust. Jour, of Phys. , 1961 (vol 14), p 22-39.
R. A. Helliwell and D. L. Carpenter, Whistlers-West IGY-IGC Synoptic
Program, Final Report, 1961 Mar 20. Apply to Prof. Helliwell.
(For address, see infra.)
J. R. Koster and L. R. 0. Storey, Nature, 1955 Jan 1 (vol 175), p 36.
T. Laaspere, M. G. Morgan, and W. C. Johnson, Proc. IEEE, 1963 Apr
(vol 51), p 554-568.
T. Laaspere, M. G. Morgan, and W. C. Johnson, Proc. IEEE, (in press).
L. H. Martin, Nature, 1960 Sep 17 (vol 187), p 1018-1019.
M. G. Morgan and G. M. Allcock, Nature, 1956 Jan 7 (vol 177) p 30-31.
L. R. 0. Storey, Phil. Trans. Roy. Soc. A, 1953 Jul 9 (vol 246)
p 113-141.
E. Ungstrup and I. M. Jackerott, JGR, 1963 Apr 15 (vol 68), p 2141-2146.
E, Ungstrup, Trans. IEEE, PTGAP, 1963 Sep (vol AP 11), p 610 (abstract of
paper presented at 1963 Spring Meetings of USA National Committee of
URSI).
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EXPLANATORY NOTES
The data herewith are monthly summaries of whistlers and audio
frequency emissions observed and recorded on magnetic tape at the given
stations during the IGY (1957 Jul - 1958 Dec). The summaries have been
compiled from daily tabulations obtained by aural reduction of the
recordings.
The IGY agreements required only that monthly summaries be sent to
the World Data Centers but for some stations, daily tabulations were sent
instead. Publication of daily tabulations would be much too voluminous to
be practical, and the value of the monthly summaries has been amply demon
strated by the recently published accounts of results from the Whistlers-
East network of the Ujnited States program (Laaspere, Morgan and Johnson,
1963, and 1964, supra;. These accounts have been produced almost entirely
from the monthly summaries. For most stations the daily tabulations and
the magnetic tape recordings themselves have been preserved and are held
by the persons having supervision of each station and the aural reduction
of data therefrom. Following are the names and addresses of these persons:
Prof. N. D. Clarence
Dept. of Physics, University of Natal, Durban, Natal, South Africa.
Durban
Prof. R. A. Helliwell
Electronics Laboratories, Stanford University, California, USA
Anchorage Macquarie Is.
Boulder Seattle
College Stanford
Dunedin Unalaska (under Prof. Morgan to 1958 May)
Kotzebue Wellington
Prof. A. Kimpara
Faculty of Engineering, Nagoya University, Chikusa-ku, Nagoya, Japan
Toyokawa
Wakkanai
Prof. E. A. Lauter
Observatorium fur Ionospha'renforschung
Ktlhlungsborn, Bezirk, Rostock, German Democratic Republic
Kuhlungsborn
Dr. Y. I. Likhter
IZMIRAN, P/0 Vatutenki, Moscow, USSR
Moscow
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Prof. M. G. Morgan
Thayer School of Engineering, Dartmouth College, Hanover,
New Hampshire, USA
Battle Creek Knob Lake
Bermuda Mont Joli
Ellsworth Norwich
Frobisher Bay Port Lockroy
Gainesville Unalaska (under Prof. Helliwell after 1958 Apr.)
Hanover Washington
Huancayo
Prof. R. Rivault
Faculte des Sciences de Poitiers, 16 rue de la Roche,
Poitiers, France
Poitiers
Mr. W. E. Thompson
Telecommunications Establishment, Defense Research Board, Ottawa,
Canada
Halifax
Ottawa
Wetaskiwin
Dr. E. Ungstrup
Ionosphere Laboratory, Technical University, 0ster Voldgade 10G3,
Copenhagen K, Denmark
Godhavn
Prof. H. C. Webster
Faculty of Science, University of Queensland, Brisbane, Queensland,
Australia
Adelaide
Brisbane
Hobart
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STATION LIST
Station Coordinates: Existing Data
Geomagnetic (dates are
(Geographic) inclusive)
Adelaide S44.9 W147.5 1957 Sep-Dec
Australia (S35.0 E138.5) 1958 Jan-Dec
Anchorage N60.9 W101.9 1957 Nov-Dec
Alaska, USA (N61.2 W149.9) 1958 Jan-Dec
Battle Creek N53.2 W 20.3 1957 Aug-Dec
Michigan, USA (N42.3 W 85.2) 1958 Jan-Dec
Bermuda N43.8 E 5.2 1957 Sep-Oct
(N32.4 W 64.7) 1958 Feb-Dec
Boulder N48.9 W 43.6 1957 Jul-Dec
Colorado, USA (N40.0 W105.3) 1958 Jan-Dec
Brisbane S35.8 W133.1 1957 Jul-Dec
Australia (S27.5 E152.9) 1958 Jan-Dec
College N64.7 W103.5 1957
Alaska, USA (N64.9 W147.8) 1958 Jan-Dec
Dunedin S50.8 W108.5 1957
New Zealand (S45.9 E170.6) 1958 Feb-Dec
Durban S31.1 E 93.3 1957 Sep-Dec
South Africa (S29.9 E 31.1) 1958 Jan-Dec
Ellsworth S66.9 E 14.7 1957 Jul-Dec
Antarctica (S77.7 W 41.1) 1958 Jan-Dec
Frobisher Bay N75.3 E 1.0 1957 Aug-Sep, Nov-Dec
NWT, Canada (N63.8 W 68.6) 1958 Jan-Mar, Sep-Oct
Gainesville N40.8 W 15.3 1957 Jul-Dec
Florida, USA (N29.6 W 82.3) 1958 Jan-Dec
Godhavn N79.8 E 32.5 1957 Jul-Dec
Greenland (N69.3 W 53.5) 1958 Jan-Dec
Halifax N56.0 E 6.9 1957 Jul-Dec
Canada (N44.6 W 63.6) 1958 Jan-Dec
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STATION LIST - continued
Station Coordinates: Existing Data
Geomagnetic (dates are
(Geographic) inclusive)
Hanover N55.2 W 4.2 1957 Jul-Dec
New Hampshire, USA (N43.7 W 72.3) 1958 Jan-Oct
Hobart S51.7 W135.4 1957 Jul-Dec
Australia (S42.9 E147.3) 1958 Jan-Dec
o
Huancayo S 0.6 W 6.2 1957 Dec
Peru (S12.1 W 75.3) 1958 Jan-Dec
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N66.2 E 4.7 1957
Knob Lake (N54.8 W 66.8) 1958 May-Dec
Quebec, Canada
Kotzebue N63.6 W117.8 1957 Dec
Alaska, USA (N66.9 W162.6) 1958 Jan-Dec
Kuhlungsborn N54.4 E 96.8 1957 Jul-Dec
East Germany (N54.1 E 11.8) 1958 Jan-Dec
Macquarie Island S61.1 W116.9 1957
Australia (S54.4 E159.0) 1958 Feb-Dec
Mont Joli N60.1 E 1.8 1957
Quebec, Canada (N48.6 W 68.2) 1958 Jan-Dec
Moscow N50.8 E120.5 1957
USSR (N55.5 E 37.3) 1958 Jun-Dec
Norwich N55.2 W 4.2 1957 Sep-Dec
Vermont, USA (N43.7 w 72.3) 1958 Jan-Dec
Ottawa N56.9 w 8.7 1957 Jul-Dec
Ontario, Canada (N45.4 w 75.7) 1958 Jan-Dec
Poitiers N49.5 E 81.8 1957 Jul-Dec
France (N46.6 E 0.3) 1958 Jan-Dec
Port Lockroy S53.4 E 3.9 1957 Jul-Dec
Antarctica (S64.8 W 63.5) 1958 Jan-Dec
Seattle N53.6 W 65.6 1957 Jul-Dec
USA (N47.8 W122.4) 1958 Jan-Dec
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STATION LIST - continued
Station Coordinates: Exis"t ing Data
Geomagnetic (da-tes are
(Geographic) inc^l usive)
Stanford N43.7 W 61.6 1957 Jul-Dec
California, USA (N37.4 W122.2) 1958 Jan-Dec
Toyokawa N24.5 W156.5 1957 Jul-Dec
Japan (N34.8 E137.4) 1958 Jan-Dec
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Unalaska N50.9 W112.1 1957 Nov-Dec
Alaska, USA (N53.9 W166.5) 1958 Jan-Dec
Wakkanai N35.3 W154.0 1957 Jul-Dec
Japan (N45.4 E141.7) 1958 Jan-Dec
Washington N50.3 W 9.9 1957 Oct-Dec
USA (N38.9 W 77.1) 1958 Jan-Dec
Wellington S45.5 W105.9 1957 Aug-Dec
New Zealca nd (S41.2 E175.0) 1958 Jan-Dec
Wetaskiwin N60.4 W 56.7 1957 Oct-Dec
Alberta, Canada (N53.0 W113.4) 1958 Jan-Dec
Notes
1. Recordings were made twice per hour.
2. Aural reduction at the station. No whistlers, chorus,
hiss or emissions reported.
3. Otherwise known as Schefferville, Quebec.
4. Data also exist for 1957 Jul-Oct but these were recorded
on a three-hourly schedule. Aural reduction of these
recordings was made but only a rough measure of whistler
rate was tabulated rather than an actual count. The
presence of emissions was tabulated. No monthly summaries
were prepared. For daily tabulations, apply to. Prof.
Morgan.
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