• 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.
    • 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.
    • A Note on Harmonic Analysis of Geophysical Data with Special Reference to the Analysis of Geomagnetic Storms

      Sugiura, Masahisa (Geophysical Institute at the University of Alaska, 1960-04-18)
      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.
    • 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.
    • 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.
    • 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.
    • 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.
    • Radiation Information from 1958 δ2

      Basler, R. P.; DeWitt, R. N.; Reid, G. C. (Geophysical Institute at the University of Alaska, 1960-01)
      The telemetered radiation information from the satellite 1958 δ2 (Sputnik III) has been analyzed for sixty-two separate passes recorded in College, Alaska. The data indicate a dependence of radiation intensity on altitude in the range 250-500 km. Both the high and low energy components apparently contribute to the overall increase of intensity with altitude, but the presence of a continuous afterglow in the scintillating crystal prevented detailed interpretation of the results.
    • 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.
    • 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.
    • Radio Properties of the Auroral ionosphere, Supplement to Final Report (Phase I)

      Reid, G. C.; Stiltner, E. (Geophysical Institute at the University of Alaska, 1960-02-01)
      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.
    • 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)
    • 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.
    • 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.
    • 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.
    • Results of a Survey of IGY Patrol Spectra at College, Alaska

      Herman, L.; Belon, A. E. (Geophysical Institute at the University of Alaska, 1961-03)
      The behavior of prominent auroral emissions has been studied statistically using the IGY patrol spectrograms obtained at College, Alaska during the International Geophysical Year. Results are presented in the form of mean diurnal intensity variations and in the form of correlation tables. Both presentations suggest the occurrence of two types of auroras. One is relatively weak, has a broad intensity maximum around magnetic midnight, and contains the hydrogen Balmer emissions. The other gradually increases in intensity until magnetic midnight and thereafter maintains a high intensity level until dawn. Its spectrum is usually characterized by the presence of the first positive bands of N2. The mean diurnal intensity variation of the sodium emission suggests that the twilight enhancement of the sodium D-lines persists to much greater solar depression angles than those previously reported. Some evidence is found for a small auroral contribution to the sodium emission. This contribution is however erratic and does not correlate well with any specific auroral emission. The (OI) 6364A emission shows, as expected, a strong twilight enhancement persisting to large solar depression angles. No enhancement is observed for the (OI) 5577A emission. A weak correlation is found between the intensity of the hydrogen Balmer emissions and the occurrence of red auroras.
    • 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.
    • 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.
    • A study of magnetic storms and auroras

      Akasofu, Syun-Ichi; Chapman, Sydney (Geophysical Institute of the University of Alaska, 1961-03)
      New notations for magnetic disturbance fields are proposed, based on the theoretical consideration of the electric current systems by which they are produced. A typical magnetic storm begins suddenly when the onrush of the front of the solar gas is halted by the earth's magnetic field. This effect (DCF field) is most markedly observed as a sudden increase of the horizontal component of the earth's field (the storm sudden commencement, abbreviated to ssc)— like a step function. In many cases, however, the change of the field during the ssc is more complicated, and different at different places. Such a complexity superposed on the simple increase (DCF) is ascribed to a complicated current system generated in the polar ionosphere (DP current). It is found that the changes of electromagnetic conditions in the polar regions are communicated, without delay, to lower latitudes, even down to the equatorial regions. It is inferred that the equatorial jet is affected by such a change and produces the abnormal enhancement of ssc along the magnetic dip equator. From the extensive analysis of several magnetic storms that occurred during the IGY and IGC, it is suggested that the capture of the solar particles in the outer geomagnetic field occurs when irregularities (containing tangled magnetic fields and high energy protons) embedded in the solar stream, impinge on the earth.. Thus the development of a magnetic storm depends on the distribution of such irregularities in the stream. The motions and resulting currents and magnetic fields of such "trapped" solar particles are studied in detail for a special model. It is inferred that a large decrease (DR field) must follow the initial increase; it is ascribed to the ring current produced by such motion of solar protons oi energy of order 500 Kev. It is proposed that during the storm there appears a transient 'storm-time1 belt well outside the outer radiation belt. It is predicted that the earth's magnetic field is reversed in limited regions when the ring current is appreciably enhanced. This involves the formation of neutral lines there. These may be of two kinds, called X lines or 0 lines according as they are crossed or encircled by magnetic lines of force. These may be entirely separated or may be joined to form a loop, called an OX loop. It is shown that one of them, the X line, which is connected with the auroral ionosphere by the lines of force, could be the proximate source of th<e particles that produce the aurora polaris. By postulating the existence of such X-type neutral lines at about 6 earth radii, an explanation is obtained of the detailed morphology of the aurora. This includes the auroral zones and their changes, the nighttime peak occurrence of auroras, their thin ribbon-like structure and their multiplicity, their diffuse and active forms and the transition between them (break-up) the required electron and proton flux, and the ray and wavy structures. Among the most important phenomena associated with the sudden change of the aurora from the diffuse to the active form are the simultaneous appearance of the auroral electrojet and the resulting polar magnetic disturbances (DP sub-storms). Several typical DP sub-storms are studied in detail. It is concluded that a westward auroral jet is produced by a southward electric field. It is shown that an instability of the sheetbeam issuing from along the X-type neutral line can produce a southward electric field of the required intensity. The southward electric field produces an eastward motion of the electrons in the ionosphere. This may be identified with the eastward motion of an active aurora and with the westward auroral electrojet. Besides such large changes- of the field, there often appear various quasi-sinusoidal changes of the field, much less intense. They are supposed to be hydromagnetic waves, some of which are generated in the outer atmosphere and propagated through the ionosphere, where a certain amount of their energy is dissipated. It is concluded however that Such a dissipation is not sufficient to produce any appreciable heating of the ionosphere.
    • A Study of the Aurora of 1859

      Kimball, D. S. (Geophysical Institute at the University of Alaska, 1960-04)
      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.