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The preliminary analysis of IGY magnetic results from Alaskan observatories
Joseph C. Cain
A preliminary analysis has been made of the magnetic data from the IGY network stations in Alaska. A few examples of magnetic bays were selected, and the distribution of electric current responsible for them was studied with a simple model for the current system, namely, line, or sheet, currents. The records obtained by the differential magnetometer were analyzed and compared with the gradient of the magnetic elements computed from the regular magnetograms taken at neighboring stations. The differential records were found not in agreement with the latter computed values. The discrepancy is probably due to local electric currents induced in the ground. A suggestion is made for future work on the auroral electrojets.
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An evaluation of auroral all-sky camera observations
T. N. Davis, C. S. Deehr, and H. Leinbach
From photometric, all-sky camera, and visual observations of a moderate auroral display, it is found that the all-sky camera compares favorably with the visual observer in detecting and recording auroral forms. The visual observer can make instantaneous observations and so can detect rapid changes and auroral forms lasting only a few seconds, whereas the poorer time resolution of the all-sky camera prevents it from recording very short-lived phenonema. However, the ability of the all-sky camera to accurately record the shape and intensity of the majority of auroral forms allows it to yield more precise and complete information about these aspects of auroral morphology than is normally obtained through visual observation.
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Incidence of Auroras and Their North-South Motions in the Northern Auroral Zone
T. Neil Davis and Donald S. Kimball
Studies of the incidence of auroral forms and their north and south motions are made by using a close-spaced array of all-sky cameras located in the northern auroral zone at the approximate geomagnetic longitude 250°E. It is found that during the observing season 1957-58 the peak of the average auroral zone occurred at 66-67° geomagnetic latitude. Although the southern extent of auroras retreats northward after local magnetic midnight, the southward motion of the individual forms, observed at the southern edge of the auroral zone, predominates over the northward motion throughout most of the night. The data indicate the existence on any given night of a latitude position near which many auroral forms occur. The first motion of auroras incident north of this position tends to be northward, and the first motion of auroras incident south of this position tends to be southward. A curve showing the occurrence of auroral forms peaks at, and is nearly symmetrical about, local geographic midnight, but the intensity of auroral emissions measured over the celestial hemisphere remains at a high level after midnight.
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Earth Current Activity at College, Alaska, July 1959
V. P. Hessler
This report presents College N-S earth current records for the month of July 1959. The scale of 1 inch per hour permits detailed scaling directly from the reproductions in the report. Scalings of hourly range in amplitude and rapid fluctuation activity are given. The amplitude scalings are also presented as curves together with average curves for a period of several years to show the relative magnitudes of the July 1959 activity. The earth current always displays much more pronounced fine structure than the corresponding geomagnetic activity.
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A Study of the Aurora of 1859
D. S. Kimball
The two great auroral displays of August 28-29 and September 1-2, 1859 are studied from a collection of world-wide descriptive observations. Both auroras reached to unusually low latitudes. Red glows were reported as visible from within 23° of the geomagnetic equator in both north and south hemispheres during the display of September 1-2. It is shown that by using graphic symbols, descriptive reports may be used to indicate the significant features of an auroral display. A series of world-wide maps show the hourly locations and lowest latitude limits of auroral visibility and overhead aurora for the most active hours. They illustrate how the progress of an aurora may be followed throughout the night. Both auroras seen in North America reached their southern limits near local midnight. During the larger display of September 1-2 the aurora moved to lower latitudes and also covered a wide range in latitudes. This indicates that during great displays the auroral activity appears to expand in latitude until local midnight, at the same time moving towards the geomagnetic equator. Over large areas both displays were predominantly red. Magnetic records indicate that there were two distinct disturbances associated with the two displays. A tabulation of all known available auroral observations reported from August 28 to September 5, 1859 illustrates that by using a letter code, significant auroral activity may be recorded for use in auroral catalogues.
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Radio Properties of the Auroral ionosphere, Supplement to Final Report (Phase I)
G. C. Reid and E. Stiltner
The usefulness of the phase-sweep technique in interferometers designed to record radio star signals is discussed. Interferometers of this type have been built for use at frequencies of 223 and 456 Mcs., and their electronic design is explained in some detail. The report also includes a discussion of the automatic data processing system which has been designed to operate in conjunction with the interferometers in the analysis of the amplitude scintillation of radio stars.
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Experiment Luxembourg, Scientific Report No. 4
G. C. Rumi and R. F. Benson
Experiment Luxembourg was designed to measure the electron density and electron collision-frequency as a function of height in the D region over College, Alaska using the technique of radio-wave interaction. A block diagram, which includes all the equipment necessary for the actual operation of the experiment, is described and illustrated in detail. The major parts of the system are: the disturbing transmitter operating on 17.5 Mc/s and using a 4x4 array of Yagi antennas, the wanted transmitter operating on ~ 5 Mc/s and using a circular polarization unit with 4 dipoles arranged in a quadrangle, a similar circular polarization unit and antenna for 5 Mc/s at the receiving site, and the delicate receiving system which detects a cross-modulation of 1x10 -4 for a one volt input signal. Some values of electron density and collision-frequency have been obtained and will be discussed in following publications.
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A Note on Harmonic Analysis of Geophysical Data with Special Reference to the Analysis of Geomagnetic Storms
Masahisa Sugiura
Some geophysical characteristics tend to have a fixed distribution relative to the sun. An example is the distribution of air temperature on an ideal earth that is perfectly symmetrical (e.g., in its pattern of land and water) about its axis of rotation. In such a case the geophysical characteristic at any fixed station on the earth undergoes a daily variation that depends only on local time (and latitude and season). This simple pattern of daily change may be modified by intrinsic changes in the solar influences on the earth. The harmonic components of the daily variation at any station may in this case undergo phase changes, in some respects corresponding to Doppler shifts of frequency in optical or sonic phenomena. Care is then needed if the results of harmonic analysis are to be properly interpreted. Such interpretation is discussed with reference to the parts Dst and DS of the magnetic storm variations. Like caution must be observed in cases where the amplitude of a harmonic variation changes,with fixed phase.
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The Height of F-Layer Irregularities in the Arctic Ionosphere
Howard F. Bates
Results and interpretations of oblique incidence soundings of the arctic ionosphere are presented. Anomalous echoes are found to be prevalent in high latitudes in contrast to lower latitudes where 2F groundscatter predominates. One of the echoes seen regularly at College, Alaska has been identified as direct F-layer (IF) backscatter. The observations of the IF echo provide direct evidence of the presence of irregularities in the F-layer between heights of 350 and 600 km. The IF echoes are recorded regularly at night and occasionally during the day in disturbed periods. They appear to be associated with auroral ionization. Simultaneous reception of 2F echoes from the north and the south indicates that at times the reflecting layer is tilted. Tilt-angles in the vicinity of 2 to 3 degrees are found. The 2F echoes from the north usually connect to the extraordinary branch of the vertical incidence trace while the 2F echoes from the south appear to connect to the ordinary branch. The analysis of groundscattered (2F) echoes is extended from a plane to a spherical geometry, and it is shown that a geometrical extension of the plane earth theory is adequate. The observed range-frequency dependence differs only slightly from that predicted by the latter theory.
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Rapid Fluctuations in Earth-Currents at College
V. P. Hessler and E. M. Wescott
An unusual type of earth-current variation is regularly observed in the College records. The phenomena consist of more or less regular fluctuations with range from a few mv/km to more than 1000 mv/km, and periods ranging upwards from 6 seconds. The fluctuations may continue from a few minutes to several hours. They have a strong diurnal variation at College with a broad maximum at 0600 local time. The fluctuations also occur at a site about 100 km southeast of College, but are not observed at Barrow« Thus these rapid fluctuations display characteristics quite different from the previously classified magnetic and earth-current continuous pulsations, pc's, and train pulsations, pt's. Special equipment was devised to count and record the period of the fluctuations on a continuous basis. Typical rapid, fluctuation, traces.and charts showing their activity patterns are presented.
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Arctic Propagation Studies at Tropospheric and Ionospheric Modes of Propagation: Final Report
Leif Owren, H. F. Bates, R. D. Hunsucker, J. H. Pope, and R. A. Stark
Two types of direct scatter from the F region are identified on the records from the oblique incidence sweep-frequency sounder located at College, Alaska. One type of echo appears to come from randomly distributed, field-aligned irregularities in the ionosphere and the other from discrete patches of irregularities. The former is essentially a nighttime phenomenon, while the latter occurs mostly during the day. From these direct scatter modes we can obtain an estimate on the horizontal and the vertical extents of the irregularities. Analysis of the data for the past year has shown that the randomly distributed irregularities commonly occur in regions having horizontal extents of more than 1000 km. The discrete irregularities appear to extend throughout most of the lower half of the F layer. The sequence of events near sunrise and sunset on a magnetically quiet winter day indicates that solar radiation eliminates the random irregularities and accentuates the discrete irregularities. Certain phenomena frequently recorded on high latitude ionograms such as Spread F and triple splitting are probably manifestations of backscatter from ionospheric irregularities. The occurrence of Z-traces in College ionograms is studied statistically and it is concluded that the majority, if not all, of the Z-traces are produced by backscatter of the radiation obliquely incident in the direction of the magnetic zenith. Fixed frequency oblique incidence soundings on frequencies of 12, 18 and 30 mc/s made at College, Alaska show both direct backscatter from the E and F layers and F layer propagated backscatter from the ground. The 12 mc/s soundings made during 1956 have been re-scaled under this contract to extract the available information concerning direct backscatter echoes at ranges below 1000 km. The direct backscatter echo from the F layer (IF echo) has a large diurnal maximum at approximately 1800 AST and a smaller maximum at 0400 AST. IF echoes are observed at ranges from 500 to 1000 km, usually occurring at approximately one-half the range of the 2F echo. The azimuth distribution of the IF echo has a maximum centered on magnetic north. Direct backscatter from the E layer (IE echo) occurs in the range interval of 200 to 800 km with a maximum between 300 and 500 km. The azimuth distribution maximum is centered on magnetic north and the diurnal distribution shows maxima from 0000 to 0200 AST and 0300 to 0400 AST. F layer propagated backscatter from the ground (2F echo) is investigated using both the 12 mc/s 1956 soundings and soundings on 12, 18 and 30 mc/s obtained during 1958. Histograms showing the diurnal distribution of 2F echo occurrence on 12 mc/s for 1956 and 1958 are essentially the same, and illustrate solar effects on the F layer. The behaviour of the regular 2F echo on 12, 18 and 30 mc/s for a typical day in December 1958 is illustrated by a series of PPI photographs. The results obtained during an experimental investigation of the drift motions of auroral ionization are summarized, and certain properties of the luminous aurora established by photo-electric measurements reviewed. Some preliminary observations of solar radio emission at 65 mc/s are reported. A technique of estimating the electron densities of the outer ionosphere by the use of nose whistlers is described. The method involves the numerical integration of the whistler dispersion equation after first assuming a model for the distribution in density. This technique is applied to several whistlers which occurred on 19 March 1959 resulting in estimates of electron densities between four and five earth's radii. The temporal variations in the occurrence of chorus during the IGY at College and Kotzebue, Alaska are studied. The results of an investigation of the effect of latitude on the diurnal maximum of chorus indicate that it is desirable to use a latitude based on the location of the eccentric dipole rather than the usual geomagnetic latitude for the study of chorus. The mathematical theory of longitudinally propagated whistlers in a magnetic dipole field is developed. The usual method for deriving electron density distributions in the exosphere from nose whistler observations by means of assumed distribution functions is criticized and shown to be ambiguous and subjective. A systematic method which avoids subjective assumptions is described. The whistler propagation problem is reduced to an integral equation and a first order principal value solution is obtained by using an approximate form of the equation. Higher order solutions may then be derived by an indicated iterative procedure. Five short-term transpolar transmission tests conducted jointly by the Geophysical Institute and the Norwegian Defence Research Establishment during 1956-59 are described briefly. Some preliminary results of a transarctic propagation study on 12, 18 and 30 mc/s made by the Geophysical Institute in cooperation with the Kiruna Geophysical Observatory, Sweden, are reported. Simultaneous backscatter soundings of the polar region from College, Alaska and recordings c£ the forward propagated signal at Kiruna, Sweden are used to deduce the propagation conditions and modes. The 12 mc/s and 18 mc/s pulse transmissions from College were received at Kiruna over 80% of the time during the month of December 1958. Groundscatter echoes from the polar regions indicated that a three-hop mode occurred 52% of the time on 12 mc/s and 49% of the time on 18 mc/s. Similarly, a two-hop mode occurred 9% of the time on 12 mc/s and 127. of the time on 18 mc/s. A signal was recorded at Kiruna 197. of the time without any corresponding groundscatter being observed from College. This could indicate propagation by a one-hop high ray (Pedersen) mode or by a lateral mode.
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An Investigation of Whistlers and Chorus at High Latitudes
J. H. Pope
The whistlers and chorus received at College, Alaska during the period from December 1955 through March 1958 are studied particularly with respect to temporal variations. The diurnal curves for whistler activity show maxima after midnight local time while the seasonal variation peaks during the winter. It appears that these variations in whistler activity are in part explainable in terms of very low frequency propagation conditions. The diurnal variation of chorus shows a maximum at about 1400 hours local time. By the use of data from lower latitude stations a dependence of this time of diurnal maximum on the geomagnetic latitude of the station is shown. The coefficients of correlation for chorus activity versus magnetic activity were determined on a monthly basis. A seasonal variation in these correlations is indicated which appears to be unique for the geomagnetic latitude of College. A preliminary statistical study of one of the more easily measured characteristics of chorus is discussed. The characteristic chosen is the mid-frequency in an element of chorus. A diurnal variation in this parameter is indicated.
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Radio Properties of the Auroral Ionosphere, Final Report (Phase I)
C. G. Reid, E. Stiltner, and R. Cognard
It has been found in recent years that a study of the fluctuations in the signals received from radio stars affords a powerful means of investigating the irregular structure of the ionosphere. In 1955 studies of this type, using frequencies of 223 Me and 456 Me, were initiated at the Geophysical Institute, with a view to investigating the smallscale structure of the highly disturbed auroral ionosphere. The purpose of this report is to present a complete description of the initial experimental arrangement. Further developments of the equipment and some results of analysis of the data have been presented in Quarterly Progress Reports covering the period since 1 June 1956, The report is divided into three sections. Section I contains a description of the basic philosophy of the experiment with an elementary discussion of the various parameters involved. Section II contains a brief description of the actual field installation, and Section III is devoted to the electronic design features. The diagrams pertaining to each section are located at the end of the section.
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Catalogue of IGY All-Sky Camera Data for Alaskan Stations
M. J. Young
The earlier orbits and ephemerides for the Soviet satellites were not sufficiently accurate to be very useful in making observations in Alaska. Extrapolations from our own observations gave better predictions. This merely pointed out the fact that rough observations of meridian transits at high latitudes will give better values of the inclination of the orbit than precision observations at low latitudes. Hence, it was decided to observe visually the meridian transits estimating the altitude by noting the position with respect to the stars or using crude alidade measurements. The times of the earlier observations were observed on a watch or clock and the clock correction obtained from WWV. Later the times were determined with the aid of stop watches, taking time intervals from WWV signals. This rather meager program of optical observations of the Soviet satellites was undertaken to give supplementary data for use of the radio observations, and particularly to assist in the prediction of position of the satellite so that the 61-foot radar of Stanford Research Institute could be set accurately enough to observe it (the beam width at the half-power points is about 3°). This report contains primarily the visual observations made at the Geophysical Institute by various members of the staff, and a series of observations by Olaf Halverson at Nome, Alaska. In addition there is a short discussion of the geometry of the trajectory, the illumination of a circumpolar satellite, and a note on the evaluation of Brouwer's moment factors.
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Optical Earth Satellite Observations
W. N. Abbott
I. INTRODUCTION The earlier orbits and ephemerides for the Soviet satellites were not sufficiently accurate to be very useful in making observations in Alaska. Extrapolations from our own observations gave better predictions. This merely pointed out the fact that rough observations of meridian transits at high latitudes will give better values of the inclination of the orbit than precision observations at low latitudes. Hence, it was decided to observe visually the meridian transits estimating the altitude by noting the position with respect to the stars or using crude alidade measurements. The times of the earlier observations were observed on a watch or clock and the clock correction obtained from WWV. Later the times were determined with the aid of stop watches, taking time intervals from WWV signals. This rather meager program of optical observations of the Soviet satellites was undertaken to give supplementary data for use of the radio observations, and particularly to assist in the prediction of position of the satellite so that the 61-foot radar of Stanford Research Institute could be set accurately enough to observe it (the beam width at the half-power points is about 3°). This report contains primarily the visual observations made at the Geophysical Institute by various members of the staff, and a series of observations by Olaf Halverson at Nome, Alaska. In addition there is a short discussion of the geometry of the trajectory, the illumination of a circumpolar satellite, and a note on the evaluation of Brouwer's moment factors.
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An Optics Field Site for Auroral Studies
K. C. Clark and G. J. Romick
The earlier orbits and ephemerides for the Soviet satellites were not sufficiently accurate to be very useful in making observations in Alaska. Extrapolations from our own observations gave better predictions. This merely pointed out the fact that rough observations of meridian transits at high latitudes will give better values of the inclination of the orbit than precision observations at low latitudes. Hence, it was decided to observe visually the meridian transits estimating the altitude by noting the position with respect to the stars or using crude alidade measurements. The times of the earlier observations were observed on a watch or clock and the clock correction obtained from WWV. Later the times were determined with the aid of stop watches, taking time intervals from WWV signals. This rather meager program of optical observations of the Soviet satellites was undertaken to give supplementary data for use of the radio observations, and particularly to assist in the prediction of position of the satellite so that the 61-foot radar of Stanford Research Institute could be set accurately enough to observe it (the beam width at the half-power points is about 3°). This report contains primarily the visual observations made at the Geophysical Institute by various members of the staff, and a series of observations by Olaf Halverson at Nome, Alaska. In addition there is a short discussion of the geometry of the trajectory, the illumination of a circumpolar satellite, and a note on the evaluation of Brouwer's moment factors.
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Indices of Upper Atmospheric Disturbance Phenomena in Auroral Zone
C. T. Elvey and M. Sugiura
The earlier orbits and ephemerides for the Soviet satellites were not sufficiently accurate to be very useful in making observations in Alaska. Extrapolations from our own observations gave better predictions. This merely pointed out the fact that rough observations of meridian transits at high latitudes will give better values of the inclination of the orbit than precision observations at low latitudes. Hence, it was decided to observe visually the meridian transits estimating the altitude by noting the position with respect to the stars or using crude alidade measurements. The times of the earlier observations were observed on a watch or clock and the clock correction obtained from WWV. Later the times were determined with the aid of stop watches, taking time intervals from WWV signals. This rather meager program of optical observations of the Soviet satellites was undertaken to give supplementary data for use of the radio observations, and particularly to assist in the prediction of position of the satellite so that the 61-foot radar of Stanford Research Institute could be set accurately enough to observe it (the beam width at the half-power points is about 3°). This report contains primarily the visual observations made at the Geophysical Institute by various members of the staff, and a series of observations by Olaf Halverson at Nome, Alaska. In addition there is a short discussion of the geometry of the trajectory, the illumination of a circumpolar satellite, and a note on the evaluation of Brouwer's moment factors.
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Radio Properties of the Auroral Ionosphere, Supplementary Progress Report
Roland A. Jalbert, Ernest Stiltner, and George C. Reid
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Radio Properties of the Auroral Ionosphere
C. Gordon Little, Robert P. Merritt, G. C. Rumi, Ernest Stiltner, and Rene Cognard
This report, prepared during May 1958, summarizes the analysis of over twelve months of amplitude and angular scintillation data obtained using phase-switch interferometers at 223 Mc and 456 Mc on the Cygnus and Cassiopeia radio sources. The main parameters of the equipment used are first discussed. The method of scaling the records, involving the arbitrary division of the records into four (456 Mc) or six (223 Mc) levels of activity is then described. The probability distributions of the amplitude variations, as derived using a phase-sweep interferometer, are given for the main levels of scintillation activity at 223 Mc. Values of mean fractional deviation of power, -A.P. } for the main levels of activity at 223 Mc are also given. Preliminary probability distributions of angular deviation, and values of mean angular deviation, are also given for the different levels of activity at 223 Mc. The solar-time dependence and sidereal-time (elevation angle) dependence of the scintillation activity are presented arid c6mpared with similar data from temperate latitudes. The report concludes with a section in which a recent theory of radio star scintillations^ is modified to include the effect of an elongation of the irregularities along the earth's magnetic lines of force.
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Photometric Studies of Auroral Luminosity and its Connection with Some Atmosphere Ionization Phenomena
W. B. Murcray
The auroral radiation, 3914 AO, received from the entire sky on a horizontal diffusing plate was monitored continuously during the nights of 1955-56 and 1956-57. The 1955-56 data and part of the 1956-57 data were used to obtain a diurnal curve for the sky luminosity in this wavelength. The auroral light increases to a broad maximum which lasts from magnetic midnight till dawn. The luminosity was found to correlate fairly well with absorption as inferred from F-min values and with (F Eg)2 and very well with the magnetic K indices.
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