This series consists of Scientific reports, Technical reports and Final reports issued by the Geophysical Institute on all contracts and grants.
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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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The preliminary analysis of IGY magnetic results from Alaskan observatories
Joseph C. Cain
A preliminary analysis has been made of the magnetic data from the IGY network stations in Alaska. A few examples of magnetic bays were selected, and the distribution of electric current responsible for them was studied with a simple model for the current system, namely, line, or sheet, currents. The records obtained by the differential magnetometer were analyzed and compared with the gradient of the magnetic elements computed from the regular magnetograms taken at neighboring stations. The differential records were found not in agreement with the latter computed values. The discrepancy is probably due to local electric currents induced in the ground. A suggestion is made for future work on the auroral electrojets.
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An evaluation of auroral all-sky camera observations
T. N. Davis, C. S. Deehr, and H. Leinbach
From photometric, all-sky camera, and visual observations of a moderate auroral display, it is found that the all-sky camera compares favorably with the visual observer in detecting and recording auroral forms. The visual observer can make instantaneous observations and so can detect rapid changes and auroral forms lasting only a few seconds, whereas the poorer time resolution of the all-sky camera prevents it from recording very short-lived phenonema. However, the ability of the all-sky camera to accurately record the shape and intensity of the majority of auroral forms allows it to yield more precise and complete information about these aspects of auroral morphology than is normally obtained through visual observation.
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Incidence of Auroras and Their North-South Motions in the Northern Auroral Zone
T. Neil Davis and Donald S. Kimball
Studies of the incidence of auroral forms and their north and south motions are made by using a close-spaced array of all-sky cameras located in the northern auroral zone at the approximate geomagnetic longitude 250°E. It is found that during the observing season 1957-58 the peak of the average auroral zone occurred at 66-67° geomagnetic latitude. Although the southern extent of auroras retreats northward after local magnetic midnight, the southward motion of the individual forms, observed at the southern edge of the auroral zone, predominates over the northward motion throughout most of the night. The data indicate the existence on any given night of a latitude position near which many auroral forms occur. The first motion of auroras incident north of this position tends to be northward, and the first motion of auroras incident south of this position tends to be southward. A curve showing the occurrence of auroral forms peaks at, and is nearly symmetrical about, local geographic midnight, but the intensity of auroral emissions measured over the celestial hemisphere remains at a high level after midnight.
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Earth Current Activity at College, Alaska, July 1959
V. P. Hessler
This report presents College N-S earth current records for the month of July 1959. The scale of 1 inch per hour permits detailed scaling directly from the reproductions in the report. Scalings of hourly range in amplitude and rapid fluctuation activity are given. The amplitude scalings are also presented as curves together with average curves for a period of several years to show the relative magnitudes of the July 1959 activity. The earth current always displays much more pronounced fine structure than the corresponding geomagnetic activity.
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A Study of the Aurora of 1859
D. S. Kimball
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.
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Radio Properties of the Auroral ionosphere, Supplement to Final Report (Phase I)
G. C. Reid and E. Stiltner
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.
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Experiment Luxembourg, Scientific Report No. 4
G. C. Rumi and R. F. Benson
Experiment Luxembourg was designed to measure the electron density and electron collision-frequency as a function of height in the D region over College, Alaska using the technique of radio-wave interaction. A block diagram, which includes all the equipment necessary for the actual operation of the experiment, is described and illustrated in detail. The major parts of the system are: the disturbing transmitter operating on 17.5 Mc/s and using a 4x4 array of Yagi antennas, the wanted transmitter operating on ~ 5 Mc/s and using a circular polarization unit with 4 dipoles arranged in a quadrangle, a similar circular polarization unit and antenna for 5 Mc/s at the receiving site, and the delicate receiving system which detects a cross-modulation of 1x10 -4 for a one volt input signal. Some values of electron density and collision-frequency have been obtained and will be discussed in following publications.
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A Note on Harmonic Analysis of Geophysical Data with Special Reference to the Analysis of Geomagnetic Storms
Masahisa Sugiura
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.
