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Radio-star visibility fades observed in the auroral zone
Edward Joseph Fremouw
The operation of a phase-switch interferometer is analyzed to show that reductions in output may be interpreted as reductions in correlation between signals arriving at the two antennas. Such reductions, therefore, constitute decreases in the visibility of the source under observation. Visibility fades of the radio stars Cygnus A and Cassiopeia A, observed on 223 megacycles in the auroral zone during one year of maximum sunspot activity, are analyzed empirically. Fade-occurrence distributions in time and space are presented and comparisons with certain other geophysical phenomena are discussed. Fades observed on 456 megacycles during one month are compared with those observed on 223 megacycles. The visibility fades appear to be caused by scattering irregularities whose geographical distribution peaks near the maximum of the visual auroral zone. There is evidence of contributions from both the E-layer and F-layer. Primary occurrence maxima appear in autumn and at magnetic midnight.
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Electron content variations in the auroral ionosphere determined from satellite radio observations
Jerry L. Hook
The Geophysical Institute of the University of Alaska and the Lockheed Missiles and Space Company conducted a joint experiment to study the relationship between (1) spatial distribution of ionization using 20 and 40 mc/s transmissions from a satellite, (2) the location and luminosity profiles of auroras as measured from ground stations in Alaska, and (3) the flux and energy spectrum of particles penetrating to auroral height as measured by satellite instruments. The experiment was carried out in March, 1962 using a polar orbiting satellite which made twelve passes over Alaska during its operational lifetime. The emphasis of this work is on the determination by radio techniques of the variation of electron content in the ionosphere connected with incident particle fluxes. Methods of determining the electron content from differential Doppler measurements are discussed in detail. The experimental results show that increases in electron content are morphologically correlated with regions of auroral luminosity and incident particle fluxes. The results of the experiment also point out the value of conducting coordinated experiments in the study of auroral phenomena.
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Catalogue of Huet auroral spectra 1957-1963
Gerald J. Romick
The zenith auroral spectra at College, Alaska, obtained during the six observing seasons from the fall of 1957 through the spring of 1963 have been assembled into 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. From the general appearance of the spectra and other factors a table of daily activity index number (1-9) is given for each observing period. The monthly averages of these index numbers have been plotted for this entire period and compared with various indices of solar and geomagnetic activity. An anomalous increase in the auroral activity index in the fall of 1962 destroys an otherwise perfect trend in the relation of the auroral activity to the decline in the sunspot cycle. It is suggested that a more detailed investigation of both solar and geomagnetic variations is warranted in order to assess the relative contribution of natural and man-made events in producing this anomalous effect.
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Hydromagnetic interpretation of sudden commencements of geomagnetic storms
Charles Roland Wilson
A new hydromagnetic model for the sudden commencement (SC) of a magnetic storm is presented. The model is based on a new morphology of the SC field that was derived from an analysis of the characteristics of vector diagrams for the first few minutes of the SC field variation. The vector diagrams representing the locus of the end point of the total horizontal disturbance vector of the SC field were constructed from rapid-run magnetograms from stations all over the world for SC’s that occurred during a four year period beginning with the I.G.Y. The most characteristic feature of the SC field is the polarization of the field that is due to a combination of circularly and linearly polarized components. The variation of the SC field over the earth is described in terms of the variations with local time and latitude of the direction of polarization (i.e. clockwise or counterclockwise) and initial phase of the circularly polarized component and the ration of the amplitudes of the two components. The two polarized components of the SC field are identified as circularly polarized transverse and linearly polarized longitudinal hydromagnetic waves. The longitudinal wave is the immediate consequence of the impact of a solar plasma cloud on the magnetosphere; whereas the transverse wave is produced by a coupling with the longitudinal shock wave in the magnetosphere. The triply refracting nature of the plasma in the magnetosphere results in the production of three hydromagnetic modes by the SC disturbance; namely, ordinary and extraordinary transverse waves with opposite directions of circular polarization which propagate to high latitudes in the morning and evening hemispheres respectively, and longitudinal waves which propagate to the earth in low latitudes.
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Radiowave absorption coefficients based on Sen-Wyller magneto-ionic formula
Jean Chorbajian, Masahisa Sugiura, and R. Parthasarathy
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The auroral display of February 13-14, 1958
T. Neil Davis and D. S. Kimball
Detailed synoptic maps of the auroral display of February 13-14, 1958 are presented. These maps depict both the auroral configurations and the magnitude and direction of magnetic disturbance at intervals of five minutes as determined from several observing stations in Alaska. The maps demonstrate pronounced but imperfect relationships of the position, magnitude, and orientation of magnetic disturbance with the position, intensity, and configuration of auroral forms.
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Environmental studies for radar operations in the auroral zone
Warren L. Flock
The relations between VHF and UHF radio aurora and geomagnetic activity, as indicated by telluric current records, have been investigated. (VHF and UHF radio aurora are considered in Parts I and II, respectively, of this report.) VHF radio aurora, observed over Barrow, Alaska by a 41 Mc/s radar at Kotzebue, Alaska, and telluric current activity at Barrow show a high correlation, particularly with respect to onsets of major activity. Slight or moderate activity usually gives some forewarning of intense activity, but some disturbances have extremely abrupt onsets of intense activity. The correlation is clearly highest for overhead and nearly overhead radio aurora and drops off for separations of 300 km and more. Incoherent scatter from ionosphere has been recorded by the BMEWS UHF radar at Clear, Alaska by use of two different techniques. A generally applicable procedure is to record radar return for a period of time in analog form on magnetic tape for subsequent processing by a digital computer. The BMEWS radar is also capable of detecting incoherent scatter by the use of “DTO” reports accumulated over a period of time. Conventional ionospheric electron density profiles showing E, F1, and F2 layers, with the highest electron densities in the F2 layer, have been obtained at times. On other occasions the peak in electron density occurs at F1 layer heights. The technique is capable of providing profiles under conditions causing “blackout” of conventional ionosonde recorders.
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Solar activity and polar cap absorption events
Anne B. Kahle
The known facts about visible characteristics of solar flares and flare associated solar radio emission, solar ultraviolet and x-rays, solar cosmic rays and polar cap absorption, and solar corpuscular streams are briefly reviewed. Tables of data of the occurrence of these phenomena in conjunction with polar cap absorption (PCA) events are given. It is shown that all large PCA events, which are caused by solar cosmic rays, are associated with large solar flares. The cosmic rays created by flares on the eastern part of the sun’s disk are found to take up to 65 hours to reach the earth, while flares from the western part generally reach the earth in one or two hours. Type II and Type IV solar radio emissions apparently occur more frequently during the flares which create PCA than with all class 3 flares. Types I and III occur with almost every PCA event. All the flares which create PCA also cause strong sudden short wave fadeout, and often cause sudden cosmic noise absorption and sudden enhancement of atmospherics. It was found that the more intense the PCA event the shorter the time was between the flare and the onset of a sudden commencement magnetic storm. The more intense PCA also appeared to be associated with a more intense Forbush decrease. The theories of origin of the various types of solar emission are discussed, as are the theories of interplanetary magnetic fields and their plausibility from the standpoint of the observed PCA events.
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A study of magnetic storms and auroras
Syun-Ichi Akasofu and Sydney Chapman
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
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The aurorally associated ionospheric absorption of cosmic radio noise
Roy P. Basler
The riometer records of 27.6 Mc/s cosmic noise from the Alaskan IGY stations are used to study the phenomenon of aurorally associated absorption. The emphasis of the work is on the comparison of the auroral absorption recorded at different latitudes, and the primary result is the definition of an auroral absorption zone. This zone is compared to the analogous visual auroral zone, and the geomagnetic latitude of maximum intensity of the absorption zone is found to be near College (64.65°) whereas the latitude of the peak of the visual zone is near Ft. Yukon (66.69°). The auroral absorption zone is more pronounced during magnetically disturbed periods, but daily and seasonal variations are generally the most effective secondary factors determining its character. Absorption is found to exhibit a daytime maximum at all stations, and a winter maximum in auroral absorption is observed at College. Possible interpretations of the discrepancy between the absorption and visual zones are suggested in terms of the relation of these zones to the primary auroral particles.
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An HF sweep frequency study of the arctic ionosphere
Howard F. Bates
Observations made during 1958 and 1959 using a sweep frequency, HF, oblique sounder located at College, Alaska, are discussed, and selected groups of echoes are illustrated. Groundscatter is the predominant echo type observed on mid-latitude backscatter records, but this is not true in the high latitudes. The majority of the scatter echoes from soundings toward geomagnetic north were direct F region scatter of two main types - IF and constant range echoes. These same echo types were observed from the E region during magnetic disturbances (the slant Es echo corresponds to the IF echo). These echoes were centered about geomagnetic north on swept azimuth soundings and were produced by scatter near the oblique reflection point in the ionosphere. Thus, we conclude that the echoes were caused by scatter from irregularities aligned along the geomagnetic field. The IF echo branches off the first order vertical incidence F region trace and increases linearly in range with frequency. It is produced by scattered energy which is least-time focused. The scatterers are essentially randomly distributed within large regions called clouds in the F region. The height of the irregularities producing the IF echo can be computed if the vertical incidence traces are clear; heights between 200 and 350 km have been found by this technique, indicating that electron density irregularities are not confined only to the lower ionosphere. From the regularity of occurrence of the IF echo, it is highly probable that the irregularities extend throughout much of the F region. The constant range echo is produced by energy scattered from the field-aligned surface of a cloud of irregularities. The soundings were made to the north so the clouds producing the observed constant range echo extended east and west. The IF and the constant range echoes are useful research tools because they indicate the amount of cloudiness present in the F region. During the summer day, the F region is relatively free of clouds, while during the winter night, it is quite overcast. The cloud size and distribution depend primarily upon the zenith angle of the sun, the smaller the zenith angle, the smaller and fewer the clouds. Geomagnetic effects do not appear to influence the behavior or the F region clouds, although this point is somewhat uncertain. The E region clouds which produced the slant Es echo were definitely correlated with geomagnetic activity but not to solar radiation, there appeared to be no connection between the causes of the E and the F region direct scatter echoes even though they were propagated by the same general mechanisms. This study raised several new problems whose explanations might contribute greatly to ionospheric research. The sweep frequency sounding technique is a good method, but the system sensitivity must be raised greatly over that of the present equipment if meaningful results are to be obtained.
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Experiment Luxembourg
W. L. Flock and R. F. Benson
The radio-wave interaction technique has been applied to the study of the lower ionosphere at College, Alaska. The system employs a pulsed wanted transmitter operating at a frequency of 4.86 Mc/s and a pulsed disturbing transmitter operating at 17.5 Mc/s with an output power of 100 kw. Radio-wave interaction has been recorded over the elevation range from 30 to 70 km. The system is best adapted to observations under somewhat disturbed ionospheric conditions. The observed interaction normally shows significant variation within time intervals of the order of minutes. Some collision frequency and electron density values have been derived. The disturbing transmitter, the 4x4 array of 3-element Yagi antennas, and the receiving circuitry have been adapted to allow the reception of backscatter signals at the disturbing frequency or cosmic noise on an adjacent frequency. Analysis of system performance in the various modes of operation is continuing.
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Results of a Survey of IGY Patrol Spectra at College, Alaska
L. Herman and A. E. Belon
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.
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Distribution of Radar Auroras Over Alaska
Robert S. Leonard
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.
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Catalogue of Huet auroral spectra 1957-1959
Gerald J. Romick
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.
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A note on the DS variation of geomagnetic storms : a critical examination of method of analysis.
Masahisa Sugiura
The determination of DS variation of magnetic storms as a function of storm time is critically examined. The regular changes in the phase angles of harmonics for DS, found by Yokouchi (1958), are attributed to irregular features that are not adequately averaged out. This apparently paradoxical circumstance is explained with an illustrative example.
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A study of the morphology of geomagnetic storms
Masahisa Sugiura
The average morphology of magnetic storms with sudden commencement was studied with 346 magnetic storms that occurred in the years 1902 to 1945. Magnetic records from 26 observatories were used. The 346 magnetic storms were classed into three intensity groups of great, moderate and weak storms, and their morphology was investigated separately. The storm variation was analyzed into two parts, Dst and DS. DS was analyzed harmonically, and its changes with storm time were studied in great detail. The author’s present views on storm sudden commencements and on the abnormal nature of the storm variations at the geomagnetic equator are briefly reviewed in this report.
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Asymmetry of Dst variations of geomagnetic storms with respect to the geomagnetic equator
Masahisa Sugiura
The seasonal variations in the Dst part of magnetic storms are determined for three pairs of stations, each pair consisting of two stations at nearly equal geomagnetic latitudes in the northern and southern hemispheres. The results show that in solstitial seasons the Dst field is not symmetrical with respect to the geomagnetic equator. The asymmetry is small in low latitudes and increases toward the auroral zones. Dm has a similar asymmetry with respect to the equator. These characteristics of Dst and Dm are interpreted as due to the asymmetry of auroral electrojets with respect to the geomagnetic equator in solstitial seasons.
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Radiation Information from 1958 δ2
R. P. Basler, R. N. DeWitt, and G. C. Reid
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.
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