• Zenith night sky light measurements at College, Alaska

      Wilcox, John B.; Kohls, Fred F.; Cronin, Harold (University of Alaska. Geophysical Institute., 1950-06-30)
      For purposes of studying the character of time fluxuations in arctic night sky brightness, we have erected a photoelectric monitory system at the Ballaine’s Lake Field Station (latitude N64°52', longitude W147°49'). The unit was set in operation September 27, 1949, and dismounted June 6, 1950, when it became evident that further observations would be impossible due to lengthening days. Although no apparatus has been available by which the response curves of phototubes could be calibrated absolutely, a standard by which bright ness recordings of different phototubes can be reduced to approximate absolute values has been evolved. A limited investigation of a possible correlation between fluxuations in the intensity of upper atmospheric emissions and sporadic conditions in the ionosphere has been made.
    • 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.
    • 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.
    • 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.
    • 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.
    • A study on the morphology of magnetic storms

      Sugiura, Masahisa (Geophysical Institute at the University of Alaska, 1955-04-20)
      The morphology of magnetic storms that has been investigated by S. Chapman since 1918 was further extended with more material as regards both the number of storms and the number of observatories, Three hundred and forty-six magnetic storms having sudden commencements were selected for the years 1902 to 19^5- These 3^6 storms were classified by a new method based on the most notable characteristic of the stormtime variation observed in low and middle latitudes, namely, a worldwide diminution in the horizontal force; hence the maximum diminution in the horizontal force averaged over these latitudes was used as a measure to indicate the intensity of magnetic storms. The 3^6 storms here selected were classified into three intensity groups: (l.) weak, (2) active, and {3 ) great storms.. The numbers of storms classed in these categories are 136, 136 and kj, respectively. In the present thesis the investigation on the 136 weak magnetic storms is described. (in the previous study made by Chapman forty storms of moderate intensity were used.) The number of magnetic observatories used in, the present study was also widely extended from eleven (in the previous work) to twentyfive. Seven observatories in the southern hemisphere distributed between geomagnetic latitudes 12° and 48° were included in these twentyfive observatories„ The geomagnetic latitudes of the eighteen northern observatories range from 20° to 80°, Several improvements were also made in the treatment of the magnetic data. One of the improvements is that hour-to-hour differences derived from the hourly values of the three magnetic elements, the horizontal force, declination and the vertical, force, were used, instead of the ordinary hourly values as given in observatory reports. With the 136 weak magnetic storms the storm-time variations of the three elements for the four pre-storm hours and the first seventy-two hours from the storm commencement were determined for eight groups of observatories, whose mean geomagnetic latitudes are 28° S, 21°, 28°, k2°, 52°, 59°, 65° and 80°; the first group being in the southern, the rest in the northern hemisphere. Thus the average features of the storm-time variations at various latitudes were able to be studied more closely. In determining these storm-time changes the daily variations on quiet days uncorrected for the non-cyclic variation were removed from the original data in order to allow for this latter variation. Then the disturbance local-time inequality for the first, second and third storm days was examined for each magnetic element for each of the groups of observatories. The vectograms of these variations were also drawn. Besides confirming, on the whole, the views expressed in Chapman's discussions on the storm-time as well as the disturbance local-time inequality, the present results revealed more detailed features of these variations at various latitudes. The disturbance local-time inequality for each element for each group of observatories was further studied for shorter intervals of storm-time, that is, for four 6-hour intervals in each of the first and second days and for three 8-hour intervals in the third storm day. The results were harmonically analyzed to determine the diurnal (2^-hour) and the semi-diurnal (12-hour) components of these variations. The diurnal component was illustrated by harmonic, dials, by which means the decay of the amplitude of these variations and the change of their phases with storm-time were clearly demonstrated. It was found that the phases of the disturbance diurnal equality in declination and the vertical force have certain definite relations with that in the horizontal force at each latitude, and that if the results for declination and the vertical force are combined -with those for the horizontal force with some appropriate modifications in their amplitudes and phases, and if such averages are further combined among the groups of observatories in low and middle latitudes, the averaged harmonic dial so obtained is much more regular than those for individual elements or for smaller groups. The rates of growth and decay of the storm-time change and the disturbance local-time inequality were compared., The results indicate that these two variations vary at rates that are materially different in their course. Detailed descriptions and discussions on these results, the final objects of the present study and plans for its future extension, are given in the present thesis.
    • Radio wave propagation in the arctic

      Little, C.G. (Geophysical Institute at the University of Alaska, 1955-08-15)
      The report is divided into six main sections. The first five deal in turn with the five main Tasks specified in the contract; the sixth describes three other phases of work also concerned with radio wave propagation in the Territory. The progress in these various fields is summarized very briefly below. Task No. 1 Sweep-frequency Ionospheric Back-Scatter No progress was made on this task, owing to lack of equipment. Task No. 2 Auroral Radar Echoes An SCR-270 radar was modified for auroral radar research, and two main investigations were carried out with this equipment. The first one was to determine the mode of propagation of V.H.F. auroral echoes; the results showed conclusively that a strong aspect sensitivity exists, due to the auroral ionization being aligned along the lines of force of the earth's magnetic field. The second investigation was to determine the relationship between the radar echoes and the occurrence of visual aurora; these observations showed that the radar echoes are usually closely associated in range and azimuth with visual aurora, but that the visual brightness of the aurora is not the factor controlling the strengths of the echoes. No echoes were obtained at frequencies greater than 106 mc, owing to lack of suitable equipment. Task No. 3 Investigation of Microwave Link The experimental, observations carried out on this link showed the absence of significant tropospheric refraction effects, and the work has now been terminated. Task No. k Prediction of Auroral and Ionospheric Storms The prediction of aurora and ionospheric storms presumes a thorough understanding of the phenomena. A brief review is given of the source of the disturbances, a stream of ionized particles from the sun, and the several influences which are observed during £nd subsequent to the bombardment of the atmosphere by these particles. Research in several phases of the problem which are in progress at the Institute are mentioned as well as that which is being done on this contract. The principle effort during the past year on this contract was development of some techniques for a better understanding of the aurora. These are the all-sky camera which is being used to study the development of an auroral display and the photoelectric photometer which appears to be useful in supplying data for an index of auroral activity. Some preliminary results from both of these equipments are presented. Task No. 5 Whistlers Observations have shown the fairly frequent occurrence of whistlers at College during the early part of July 1955» Tape recordings of some of these whistlers are now being analysed to determine their frequency dispersion. Additional Work Three main phases of additional work, dealing respectively with the tropospheric propagation of V.H.F. radio waves, the diffraction and scattering of V.H.F. radio waves by mountains, and the absorption of H.F. radio waves of the ionosphere were carried out at the Geophysical Institute. Numbers one and three of these were conducted at the request of the Alaskan Command, U.S. Air Force; the second problem was investigated in view of its possible importance in point-to-point communication in the Territory.
    • Luminous night clouds and low latitude auroras

      Elvey, C.T. (Geophysical Institute at the University of Alaska, 1955-09)
    • 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.
    • 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.
    • Radio wave propagation in the arctic

      Little, C.G.; Dyce, R.B.; Hessler, V. P.; Leonard, R. S.; Owren, L.; Roof, R. B.; Sugiura, M.; Swenson, G. W. Jr (Geophysical Institute at the University of Alaska, 1956)
      The main body of this report is divided into eight sections, corresponding to the eight aspects of Arctic radio wave propagation listed in Section I, Purposes of the Contract, In cases where the work has already been fully described in Interim Scientific Report No. 1 (AFCRC-TN- 55-579, here in after referred to as R(l)), brief summaries only are given. The progress in these eight fields is summarized as follows: Task No. 1 Sweep-Frequency Ionospheric Backscatter Because of lack of equipment, no progress was made on this task. Task No. 2 Auroral and Meteor Echoes Three frequencies were used in this work: (a) At 50 me A low“power9 50 me radar equipments specially designed and built for auroral radar research, was operated with a steerable antenna to monitor both auroral and meteor activity,, The results showed that the diurnal distribution of meteor activity is similar at College to that observed elsewhere, and that the meteor echo rates observed on this equipment are not affected by the presence of aurora. (b) At 106 me The 106 me SCR 270 DA radar was used for two main experiments, as described in R(l). First, the aspect sensitivity of the auroral echoes was investigated. The results showed clearly that the auroral ionization giving rise to VHF auroral radar echoes is aligned along the earth's magnetic lines of force3 in that the auroral radar echoes are strongest when the radio waves are traveling perpendicularly to the magnetic lines of force through the aurora. Second, the relationship between visual and radar aurora was investigated; this work showed that the auroral radar echoes are often closely associated in range and azimuth with visual aurora, although the strength of the echoes is not proportional to the visual brightness of the auroral forms„ (c) At 210 me The 210 me SA-2 radar was installed in a trailer and tested without modification, It was then modified by the building of a steerable 16-Yagi array, by increasing the pulse length, and by reducing the receiver bandwidth„ Simultaneous operation of the 50 me and the improved 210 me equipment resulted in the detection of many auroral echoes at the lower frequency; no auroral (or meteor) echoes were obtained on the 210 me equipment during the contract period although good mountain * echoes were obtained at ranges up to 250 km„ Task No„ 3 Investigation of Microwave Link As explained in R(l), the experimental observations carried out on this link showed the absence of significant tropospheric refraction effects, and the work was terminated at the end of the first year of the contract. Task No. 4 Prediction of Auroral and Ionospheric Storms Several types of work were undertaken in order to improve our understanding of auroral and ionospheric storms; these storms are two aspects of the bombardment of the upper atmosphere by particles from the sun, In particular, a solar radio interferometer was set up to monitor the solar radio emissions at 65 me As described in R(l), an all sky camera and a photoelectric photometer were developed for the monitoring of the visual auroral activity. An investigation of earth potentials has shown that they provide a simple method of monitoring magnetic activity; some tests were also made using a rapid-response electronic magnetometer. Some of the results obtained with these equipments are discussed in the report. A study of the form of the front surface of a neutral corpuscular stream advancing into a magnetic field similar to the earth's magnetic field is presented. This study shows the presence of equatorial and polar forbidden zones and the fact that only the particles arriving near the border between these forbidden zones can reach the earth's upper atmosphere. An equatorial motion of the zone of bombardment could be produced by an increase either in particle density or in particle velocity. Task No. 5 Whistlers A new type of whistler has been discovered that has simultaneous rising and descending components. Analysis of data obtained during the contract period indicates a diurnal variation in the rate of occurrence of whistlers that appears to be correlated with ionospheric heights. A correlation between the day-to- day occurrence of the dawn chorus and the daily K-index sums is also found. Task No. 6 Diffraction and Scatter of Radio Waves by Mountains (a) Diffraction The diffraction of VHF radio waves by mountains has been investigated over three diffraction paths. The results show that the experimentally observed signal strengths are in fair agreement with the values calculated theoretically using knife-edge approximations. One important observation, which has not been reported previously, is the variability of the diffracted signal strength from point to point across the ground. Also, although diffracted signals are normally described as being very constant in amplitude, slow fades lasting some hours and occurring over a relatively narrow frequency band were observed over one 200- mile path. (b) Mountain scatter Observations of mountain scatter were made using the SCR-270 DA radar and a mobile receiving equipment. The results imply that detectable scattered signals can be obtained over a very wide range of azimuths (greater than + 135°) relative to the line joining the transmitter and the mountain. It was found that the scattered signals were considerably broadened in pulse length.Task No. 7 Ionospheric Absorption The work done in connection with ionospheric absorption under this contract has been described previously in R(l). Undertaken at the request of the 58th Weather Reconnaissance Squadron, USAF, this study demonstrated convincingly that their communication failures were caused by ionospheric absorption phenomena, rather than by equipment or personnel failures. Task No. 8 Assistance to the Alaska Air Command on Problems of Radio Propagation As described in R(l), an investigation of a VHF radio link was made at the request of the Alaska Air Command. Continuous records of received signal strength at each end of the link revealed that the communication failures were caused by tropospheric refraction effects. A low-noise preamplifier, built and operated in parallel with a normal equipment, was found to reduce the number of fade-outs. A one-day symposium on Arctic radio wave propagation was held at the Geophysical Institute on January 26, 1956, for the benefit of communications personnel in the territory,, Approximately fifty visitors attended these meetings. The Geophysical Institute has also assisted the Alaska Air Command by the loan of electronic equipment and pen recorders as well as by supplying specialists who have acted in an advisory capacity on problems of radio wave propagation.
    • Papers read at the Conference on Arctic Radio Wave Propagation

      Elvey, C.T. (Geophysical Institute at the University of Alaska, 1956-01-26)
      On February 18, 1954, we held a conference attended by representatives of military organizations in Alaska to discuss general problems of radio communications in the Arctic. Since that conference was so successful, we have decided to hold a second conference broadening its scope in attendance and subject matter with the idea of making the conference an annual event. At this conference, and we hope future ones, we had the active participation of the North Pacific Radio Warning Service of the National Bureau of Standards. Included in the discussions at this conference were some of the new equipments and techniques being used at the Geophysical Institute in its research work. In particular, I refer to the employment of radio astronomy as a tool for ionospheric research.
    • 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 measurement of ionospheric absorption using extraterrestrial radio waves

      Little, C. G. (Geophysical Institute at the University of Alaska, 1957-01-28)
      Introduction: The discovery by Jansky in 1932 of the presence of radio waves incident upon the earth from outer space has led to several new methods of studying the earth's upper atmosphere. This report describes the manner in which these extraterrestrial radio waves may be used to measure the radio absorption characteristics of the ionosphere. It opens with a brief discussion of the theory of ionospheric absorption; this is followed by a description of the basic principles involved in this new technique. Two different types of equipment which may be used for this type of absorption measurement are then discussed. The report concludes with a brief summary of three types of ionospheric absorption phenomena which have been studied at various latitudes with such equipments.
    • Equilibrium and Transport in a Fully Ionized Gas

      Brittin, Wesley Emil (Geophysical Institute at the University of Alaska, 1957-04)
    • A Study of the Morphology of Magnetic Storms: Moderate Magnetic Storms

      Sugiura, Masahisa; Chapman, Sydney (Geophysical Institute at the University of Alaska, 1957-06-30)
      Some average characteristics are determined for 136 moderate magnetic storms with sudden commencements that occurred during the interval 1902-1945. The average storm field is resolved for different epochs of storm time st into Dst, independent of local time, that is, of longitude X , relative to the sun, and into DS, that depends on X , Part DS is expressed in terms of harmonic components with respect to X , and like Dst, the amplitudes and phases of these components, are functions of st and of geomagnetic latitude. They are determined, for each of the three magnetic elements, declination, horizontal force, and vertical force, at eight geomagnetic latitudes ranging from 80*N to 1°S. In the first, and main harmonic component of DS, its variations with respect to storm time differs notably from that of Dst: its maximum is attained earlier and its decay is more rapid. The storm -time changes of the smaller harmonic components of DS have been less fully determined. The average characteristics of moderate storms are compared with those of weak storms.
    • 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 Potential Electrodes in Permafrost and Tundra

      Hessler, V. P.; Franzke, A. R. (Geophysical Institute at the University of Alaska, 1957-11)
    • Optical Earth Satellite Observations

      Abbott, W. N. (Geophysical Institute at the University of Alaska, 1958-02-14)
      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.