• Air Force Contract No. AF 19(604)-1089

      Geophysical Institute at the University of Alaska, 1954
      This report briefly describes the progress made at the Geophysical Institute of the University of Alaska during the past three months, in the study of arctic radio wave propagation under the Air Force Contract No. AF 19(604)-1089.
    • 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.
    • 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.
    • 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)
    • Auroral zone absorption of radio waves transmitted via the ionosphere

      Owren, Leif; Leinbach, Harold; Nichols, B.; Stark, R.; Smith, Carol (Geophysical Institute at the University of Alaska, 1956)
      TASK A: TRANSMISSION OF HIGH FREQUENCY RADIO WAVES VIA THE ARCTIC IONOSPHERE The experimental data collected from June, 1949, through October, 1955, under "Experiment Aurora" are summarized in tables and diagrams, and the results discussed. The monthly percentage of signal in-time is tabulated for all frequencies and paths» and depicted in diagrams which allow a comparison of the values for East-West and South-North propagation at each frequency. The average monthly percentage of signal in-time for the duration of the 6-year experiment is tabulated for each frequency and path. The seasonal variation in signal in-tim e over short and long paths is shown in diagrams. The relationship found between ionospheric absorption, as measured with a vertical incidence sounder, and signal outtime is summarized. The average diurnal variation in the hourly median signal strength during the different seasons of the year 1954-55 is given for all frequencies on both short and long paths in the East-West as well as the South-North direction. The diurnal variation in signal strength on the 4 me short paths and the 12 me long paths is compared for a year of high solar activity (1949-50) and a year of low solar activity (1954-55). The discussion of the data reveals that a statistically significant difference in signal in-time for the East-West and South-North paths exists only for the 12 me short paths. The larger percentage of signal in-time found in the East-West direction is believed to be due to a preferential orientation of sporadic ionization along parallels to the auroral zone. A study of the critical frequencies observed for the E and F -layers shows that the difference in daytime variation of median signal strength between the years 1949-50 and 1954-55 may be explained in terms of the normal changes in F -layer ionization and D -layer absorption in course of a sunspot cycle. The results indicate that in Alaska there will generally be F2 propagation during daytime of 4 me signals over 350 km paths throughout the solar cycle. Regular daytime F2 propagation of 12 me signals over 1100 km paths may be expected in years of reasonably high solar activity only. TASK B: PULSE TECHNIQUES. BACK-SCATTER AT 12 MC A 12 me radar has been constructed and operated using A -scope and PPI displays. Experimental results obtained during several months of continuous operation are reviewed and discussed. Both direct backscatter and ground back-scatter echoes, as well as possible combinations of these modes, have been observed. The echoes are classified in two groups according to their fading rates, those fading rapidly being associated with aurora. Figures show the diurnal, range and range-azimuth distribution of the observed auroral echoes as well as some special types of echoes recorded. The direct back-scatter echoes at 12 me associated with aurora show characteristics consistent with those observed at YHF when allowance is made for the frequency difference. At 12 me the fading rate is proportionally less than at higher frequencies; and aspect sensitivity, although weaker, still exists. The diurnal variation is similar to that found at VHF. Several types of echoes not observed at VHF are mentioned. TASK B: VISUAL OBSERVATIONS OF THE AURORA Analysis is made of the visual auroral data obtained at five stations in Alaska during the observing period of 1954-55. Graphs giving the percentage occurrence of aurora at each station as a function of latitude and time of day are presented. Graphs showing the variation of auroral occurrence with geomagnetic latitude as a function of magnetic K index are also given. The conclusions drawn from the 1954-55 data are substantially the same as those based on the 1953-54 data discussed in an earlier report.
    • Auroral zone absorption of radio waves transmitted via the ionosphere

      Andersen, Soren; Leonard, Robert S. (Geophysical Institute at the University of Alaska, 1955)
      A discussion of the design for a new antenna system for the transmitter stations is presented together with the measurements and power computation made on the old and new antennas. In the 12 mc back-scatter program at College, the technique used to measure the amplitude of each individual echo and reanalysis of the range distribution previously reported are discussed. Revisions in the techniques of observation of visual auroras and the methods of recording the data for analysis are described in detail.
    • Auroral zone absorption of radio waves transmitted via the ionosphere

      Owren, Leif; Stark, Robert (Geophysical Institute at the University of Alaska, 1955)
      Signal intensity operations have stopped and the preliminary reduction of all field intensity records completed . The 12 me back-scatter equipment is described and operating conditions stated. Tentative interpretations of ob served echoes in terms of possible reflection mechanisms are given.
    • Brief Discriptions of Auroral Displays Over Alaska During 1957-58

      Davis, T. Neil (Geophysical Institute at the University of Alaska, 1960-01)
    • Catalogue of Huet auroral spectra 1957-1959

      Romick, Gerald J. (Geophysical Institute of the University of Alaska, 1961-03)
      The zenith auroral spectra at College, Alaska, obtained during the 1957-1959 observing seasons, has been assembled in catalogue form. The prime purpose of this catalogue is to present the auroral activity in a manner which can be used by others in the interpretation of aurorally associated phenomena. Prom the general appearance of the spectra and other factors, a table of daily index numbers (1 -9) is given for two observing periods. Although these numbers should not be used in themselves as correlation data they are valuable as representative indices. This point is indicated by the clear appearance of the spring maximum in activity and a general yearly decline in activity towards the minimum of the sunspot cycle.
    • 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.
    • Construction of an all-sky camera

      Davis, T.N.; Elvey, C.T. (Geophysical Institute at the University of Alaska, 1955-10)
      The "All-Sky" camera herein described is an outgrowth of camera* operated in Alaska by the staff of the Geophysical Institute. The principle has been of use in cloud studies and was first used by C. W. Gar tie in for auroral photography. In its p resent form the camera is capable of recording stable or slowly moving auroral forms and is useful for synoptic "mapping of auroras and detail studies. By proper scaling methods the camera gives fa irly well defined mapping of aurora occurring within a circle of 500 km radius and along the lengths of arcs, i.e . geomagnetic East and West, to distances of about 1200 km. These radii are based on an estimated lower border height of 100 km with curved earth consideration. Since the main use of the camera will be in high latitudes where severe weather conditions occur, special effort has been made to design a rugged instrument capable of withstanding high winds and low temperatures. Ease of operation under adverse weather conditions has also been a consideration. Whenever possible, use has been made of commercially available parts to reduce construction costs. An attempt has been made to simplify the construction of those parts not commercially available. The camera is designed to be built in a shop having a d rill press, lathe, milling machine, welding equipment, and carpentry tools. The recording element is a 16 mm movie camera with a 50 mm f/l. 5 lens and equipped for lapse-time photography. The camera views the entire sky in a convex mirror. A number of cameras have been considered, two of which, the Bolex H-16 Leader and the Kodak K-100, appear best suited with respect to cost and adaptability. The Bolex H-16 is equipped for lapse-time photography and requires no modification. The Bolex has the disadvantage of only sixteen feet of film run per spring winding, hence, requires attention each ten hours if one picture per minute is to be taken. The Kodak K-100 must be modified for lapse photography but has forty feet of useful film run and will operate without attention for twenty-four hours at one frame per minute. Both these cameras may be solenoid driven which allows variation of exposure times with minimum effort. An overall view of the camera is shown in Fig. 1. Fig. 2 shows t the optical arrangement. Calculations made on the basis of Fig. 2 and the graph of height, angle, and distance, Fig. 3, allows the location with respect to the earth's surface of any point on the photographic image.
    • Description of the All-Sky camera, its Method of Operation; An Instrument (Ascagraph) for Measuring the Film

      Elvey, C. T.; Belon, Albert (Geophysical Institute at the University of Alaska, 1957)
      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.
    • The determination of the luni-solar variations in the magnetic elements at Sitka, Alaska

      Cain, Joseph C. (Geophysical Institute at the University of Alaska, 1953-11-30)
      The Chapman-Miller method of calculating harmonic coefficients for luni-solar daily variations is here applied to the hourly values of the magnetic elements at Sitka, Alaska for the period 1902-1952. The formation of the group sum sequences for groupings of the data according to solar activity, magnetic activity, lunar phase and lunar distance using punched card methods is described.
    • Distribution of Radar Auroras Over Alaska

      Leonard, Robert S. (Geophysical Institute at the University of Alaska, 1961-04)
      Analysis of data collected by five auroral radars located in Alaska shows the distribution of ionospheric disturbances as a function of time and location. The radars were operated during the IGY and were located in a nearly straight line running magnetically north-south across Alaska; these locations made it possible to observe disturbances continuously in the range, from 60 to 80 degrees geomagnetic latitude, which includes the visual auroral zone. An apparent radar auroral zone with a maximum at 67 degrees geomagnetic latitude is indicated by this study. The decrease in occurrence to the south of this maximum is verified, but the decrease to the north can not be accurately defined as the roll of aspect sensitivity is not fully understood. The radar auroral zone spreads to the south during increased magnetic disturbance, and some indication is found of a lessening of activity well north of the visual auroral zone. A conclusion is also reached that the layer causing radio wave absorption during aurora is not uniform but contains "holes" or regions of low absorption. The diurnal occurrence curves indicate two principal maxima. One is observed at all stations at times near local midnight. The time of the other maximum depends on the latitude of observation; it is later in the morning at the more northern locations. These two echoes exhibit differing degrees of aspect sensitivity, the morning echoes having a narrower scattering polar diagram.
    • Drift Motions of Auroral Ionization

      Nichols, B. (Geophysical Institute at the University of Alaska, 1957-07)
      The primary subject of this report is the drift motions of auroral ionization. The existence of rapid motions of the ionization has been demonstrated in previous radar studies of the aurora, but neither the nature of the motions nor their explanation has been established until now. The purpose of our experimental observations was to determine the direction and speeds of the motions. In doing so, we obtained additional information concerning the general nature of the auroral ionization. Measurements were taken at College, Alaska, during the winter and spring of 1956-57* using CW transmitters. By locating the transmitters at Sielson Air Force Base, it was possible to separate the transmitters and the receivers by bZ kilometers along a ge©magnetically east-west line. The basic technique used was to examine the frequency spectra of radio echoes from the aurora at 106 Mc/s and tyl.l5 Mc/s. A comparison of the results obtained at 106 Mc/s and WL.15 Mc/s showed that the frequency shifts are proportional to the transmitted frequency, as would be expected of Doppler shifts. By measuring the spectra of the echoes received from east and west of geomagnetic north at the same time, it was possible to determine the following: (i) That the motions are generally horizontal and in the geomagnetic east-west plane; and (ii) That the speeds of the motions vary from 350 meters per second to 2,000 meters per second. On the basis of our experimental results and the published literature, we show that the electron drift motions in the aurora are of the same order of magnitude and direction as the motions of the electrons in the ionospheric current system required to explain magnetic disturbances. These electron motions produce the Doppler shifts that are responsible for the well known rapid fading of auroral radio echoes. The fading of radar auroral echoes is therefore associated with the increased electric fields which drive the currents in auroral regions. Following a review of the available information concerning general motions in the ionosphere, motions of the visible aurora, and motions inferred from magnetic storms, we show that the drift motions of auroral ionization do not constitute a separate and distinct group. Instead, they are found at the upper end of a continuous curve of increasing speed of motions with increasing magnetic disturbance. The intense ionospheric currents that produce the magnetic disturbances are found to be associated with both increased electron density and increased speed of motion. In our examination of the amplitude of VHF radio auroral echoes, the basic premises of the theory of scattering by non-isotroplc irregularities produced by turbulence [Booker, 1956] are found to be satisfactory. However, the numerical values of the parameters suggested by Booker require revision. In particular, our results indicate that the mean square fractional deviation of electron density is much greater than Booker conjectured on the basis of the then available evidence; in fact, it is greater by two to three orders of ten.
    • Earth Current Activity at College, Alaska, July 1959

      Hessler, V. P. (Geophysical Institute at the University of Alaska, 1960-06-15)
      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.
    • Earth Potential Electrodes in Permafrost and Tundra

      Hessler, V. P.; Franzke, A. R. (Geophysical Institute at the University of Alaska, 1957-11)
    • Equilibrium and Transport in a Fully Ionized Gas

      Brittin, Wesley Emil (Geophysical Institute at the University of Alaska, 1957-04)
    • An evaluation of auroral all-sky camera observations

      Davis, T. N.; Deehr, C. S.; Leinbach, H. (Geophysical Institute of the University of Alaska, 1960-03)
      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.
    • Evaluation of chemical methods for the determination of atmospheric ozone

      Mukherjee, Nalin R. (Geophysical Institute at the University of Alaska, 1952-11-15)
      Since the concentration of the ozone in the atmosphere near the earth's surface is of the order of 10 gm. per gm. of air, the quantitative determination of this ozone by chemical methods is rather difficult. Therefore, the different methods have been evaluated to determine the best, all conceivable precautions being taken into account. The chemical methods may be classified into two groups --Titer Methods and Spectro-chemical Methods. Among the former, two; namely, the Thiosulphate and Arsenite Methods, have been proposed and used. For the low concentration of ozone in the atmosphere near the earth 's surface, the Thiosulphate Method is found to give unreliable results due to the instability of the thiosulphate solution as well as to various side reactions which could not be controlled. The arsenite solution, however, is much more stable than the thiosulphate solution. Side reactions are very few and can largely be controlled. Reliable results can be obtained by the Arsenite Method when employing proper precautions. The oxidants and other interfering substances in the atmosphere present serious problems. Some oxidants behave like ozone as far as the reactions with the chemical reagents are concerned. Their occurrence in the atmosphere and their effects on the chemical reagents used for the quantitative determination of the atmospheric ozone are discussed in detail. Suggestions are made for their elimination from the atmosphere without affecting the ozone concentration.