• Arctic Radio Wave Propagation

      Owren, Leif; Little, C. Gordon (Geophysical Institute at the University of Alaska, 1958-03)
      The object of this investigation is to obtain additional information concerning the effects of aurora on high frequency radio signals which is essential to a complete understanding of new modes of propagation that have tactical and strategic applications.
    • Radio Properties of the Auroral Ionosphere

      Little, C. Gordon; Merritt, Robert P.; Rumi, G. C.; Stiltner, Ernest; Cognard, Rene (Geophysical Institute at the University of Alaska, 1958-05-31)
      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.
    • An Optics Field Site for Auroral Studies

      Clark, K. C.; Romick, G. J. (Geophysical Institute at the University of Alaska, 1958-07)
      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.
    • Radio Properties of the Auroral Ionosphere, Supplementary Progress Report

      Jalbert, Roland A.; Stiltner, Ernest; Reid, George C. (Geophysical Institute at the University of Alaska, 1958-08)
    • A Study of the Morphology of Magnetic Storms Great Magnetic Storms

      Sugiura, Masahisa; Chapman, Sydney (Geophysical Institute at the University of Alaska, 1958-08-31)
      Average characteristics are determined for 74 great magnetic storms with sudden commencements that occurred in 1902-1945. The storm field is resolved for different epochs of storm time into tv;o parts: (i) Dst, which is independent of local time, that is, of longitude A, relative to the sun, and (ii) DS, which depends on A . They are obtained, for each of the three magnetic elements, declination, horizontal force, and vertical force, at eight geomagnetic latitudes ranging from 80°N to 1°S. DS is harmonically analyzed; the first harmonic component is shown to be the main component of DS. The storm-time course of this component is compared with that of Dst; DS attains its maximum earlier and decays more rapidly. The results of the analysis of great storms are compared with those for weak and moderate storms that were reported previously. Some characteristics of Dst change with intensity. Except in magnitude, main characteristics of DS are independent of intensity.
    • Photometric Studies of Auroral Luminosity and its Connection with Some Atmosphere Ionization Phenomena

      Murcray, W. B. (Geophysical Institute at the University of Alaska, 1958-09)
      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.
    • Studies of Ground Conductivity in the Territory of Alaska

      Stanley, Glenn M. (Geophysical Institute at the University of Alaska, 1958-10-31)
      The effective ground conductivity of Alaska has been determined by a comparison of experimental and theoretical field strengths. The experimental field strengths have been obtained by use of an airborne receiver, flown along radial paths from a large number of CAA radio ranges and beacons. The surface wave attenuation factor was computed for both a plane and a curved, homogeneous earth by methods presented by Norton. The experimentally determined relative field strengths were plotted as a function of distance and were compared with a family of curves for assumed values of conductivity and dielectric constant. From this comparison, that value of conductivity that best fits the experimental data is taken as the effective conductivity over the path. An investigation of the effect at dielectric constant on the transmitted signal shows that, within the frequency range used, a change of dielectric constant from 1 to 20 has but little effect on the attenuation of the transmitted signal for values of conductivity between 1 and 5 mmho/m. The experimental results indicate that for most sections of Alaska, the effective conductivity falls within this range. In some cases the earth was not homogeneous over the entire flight path as evidenced by changes in the slope of the field strength vs distance curves. In such cases, the data were replotted with an initial point at the discontinuity and new theoretical curves were drawn for each section of the field strength vs distance curves. Investigation of the variation of effective conductivity with change of frequency and at different seasons was made. In addition, wave tilt methods of determining the conductivity were used. A 'Ground Constants Measuring Set' was obtained from the Signal Corps and measurements were made in selected areas in Alaska. Attempts were made to use 1height-gain' and 'mutual coupling of loops' techniques but these were not successful. An investigation of anomolous propagation in the vicinity of Point Barrow was made. It was determined that this anomolous propagation appears to be the result of a layered earth. In addition to the anomolous propagation in the vicinity of Point Barrow, there appears to be similar anomolies in the vicinity of Kotzebue, Galena, Bethel and Port Heiden. From the above investigations a map showing the effective conductivity of Alaska as determined by the attenuation method is presented.
    • Indices of Upper Atmospheric Disturbance Phenomena in Auroral Zone

      Elvey, C. T.; Sugiura, M. (Geophysical Institute at the University of Alaska, 1958-12)
      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.
    • A Magneto-Ionic Theory of the Aurora

      Reid, G. C. (Geophysical Institute at the University of Alaska, 1958-12)
      A qualitative description of the development of a typical auroral display as the result of an electrical discharge in the ionosphere is presented. The prime cause of the discharge is taken as the potential difference existing between points in the interplanetary medium as a result of an interaction between charged particles of solar origin and the earth's magnetic field. The characteristics of the occasional very intense aurorae visible over large areas of the earth are discussed, as well as the normal diurnal and seasonal variation of auroral occurrence. The origin of the electric field is discussed, and a possible explanation in terms of particles trapped in the earth’s magnetic field, is presented.
    • Some Notes on the Interpretation of Rapid Fluctuations in Earth-Currents Observed in High Latitudes

      Sugiura, Masahisa (Geophysical Institute at the University of Alaska, 1958-12)
      This paper shows that a periodically varying infinite linear current, or a periodically varying turbulent circular current of small radius (here approximated by a magnetic dipole with a changing dipole moment), in the ionosphere, which will give rise to magnetic variations of observed order of magnitude, is adequate for producing voltage differences in the ground of order 0 .1 to 1 volt per kilometer that are frequently observed in high latitudes during disturbed periods. It appears difficult to interpret the earth-current record in terms of its primary origin, unless the distribution of the perturbing magnetic field and that of electric conductivity of the earth are both adequately known. However, the earth-current record is a good indicator of the upper atmospheric disturbance in the polar regions.
    • Experiment Luxembourg

      Rumi, G. C.; Little, C. G. (Geophysical Institute at the University of Alaska, 1958-12)
      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.
    • Rapid Fluctuations in Earth-Currents at College

      Hessler, V. P.; Wescott, E. M. (Geophysical Institute at the University of Alaska, 1959-01)
      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.
    • Radio Properties of the Auroral Ionosphere, Final Report (Phase I)

      Reid, C. G.; Stiltner, E.; Cognard, R. (Geophysical Institute at the University of Alaska, 1959-02)
      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.
    • The Height of F-Layer Irregularities in the Arctic Ionosphere

      Bates, Howard F. (Geophysical Institute at the University of Alaska, 1959-03)
      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.
    • An Investigation of Whistlers and Chorus at High Latitudes

      Pope, J. H. (Geophysical Institute at the University of Alaska, 1959-04)
      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.
    • Experiment Luxembourg, Scientific Report No. 2

      Rumi, G. C. (Geophysical Institute at the University of Alaska, 1959-05)
    • Catalogue of IGY All-Sky Camera Data for Alaskan Stations

      Young, M. J. (Geophysical Institute at the University of Alaska, 1959-07-31)
      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.
    • Low Energy Cosmic Ray Events Associated With Solar Flares

      Reid, George C.; Leinbach, Harold (Geophysical Institute at the University of Alaska, 1959-09)
    • Arctic Propagation Studies at Tropospheric and Ionospheric Modes of Propagation: Final Report

      Owren, Leif; Bates, H. F.; Hunsucker, R. D.; Pope, J. H.; Stark, R. A. (Geophysical Institute at the University of Alaska, 1959-10)
      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.
    • Auroral Index for College, Alaska Derived from All-Sky camera Photographs, September 1957- December 1958

      Tryon, Helen M. (Geophysical Institute at the University of Alaska, 1959-11)