• 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.
    • A Study of the Morphology of Magnetic Storms Great Magnetic Storms

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