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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An interpretation of the auroral breakup
Daniel W. Swift
A dynamical model of the magnetosphere is presented to account for the main morphological features of the aurora, and the auroral breakup in particular. The aurora is the result of an internal process in the magnetosphere. It is suggested that a fluting instability on the outer boundary of the ring current belt is responsible for auroral breakup. This instability leads to a rapid flow of the ring current plasma into the tail of the magnetosphere. Particular attention is focused on the mechanisms for energizing electrons, the dynamics of the fluting instability in the magnetosphere including the dissipative effects of the ionosphere, and the structure of the ring current belt. It is stressed that the aurora gets its energy from the DR (ring current) belt. It is shown that the asymmetry of the DR belt and the observed asymmetry of the radiation belts can be accounted for by the asymmetric injection of charged particles on the day side of the geomagnetic field.
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Geophysical Institute Annual Report 1964-65
University of Alaska Fairbanks. Geophysical Institute
The 1964–65 Geophysical Institute Annual Report presents an overview of the year’s scientific research achievements across the Institute’s disciplines, alongside operational summaries covering finances, administrative changes, and other key activities.
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A new classification of geomagnetic storms and their source flares
Sekiko Yoshida
Geomagnetic storms which occurred between 1956 and 1963 are classified in terms of different combinations of the three basic storm fields, the DCF, DR and DP fields. For each storm, a new attempt is made to identify the source solar flare, based on several new important findings on characteristics of geomagnetic storms.
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High latitude VLF propagation
Howard F. Bates and Paul R. Albee
This report contains the results of our VLF program which started in 1961. One year’s data obtained in 1963 using a rubidium vapor oscillator as the College frequency standard forms the major part of the data discussed. The VLF variations, primarily perturbations of the phase of the signal, are divided into two categories, 1) those effects known to have been associated with a particular type of event, and 2) those which occur regularly with no apparent connections to geophysical events of a disturbance nature. The first category contains VLF phase anomalies produced by solar flare x-rays, solar flare cosmic rays (these produce the polar cap disturbance, PCD), solar eclipses, and nuclear explosions. Solar flare x-rays produce large amounts of D region ionization. The probability that a given flare produces a VLF sudden phase anomaly (SPA) varies linearly with the optical area of the flare. The SPA magnitude depends upon path length and solar zenith angle, but other factors which have not been determined also enter in strongly. Time differences of a minute or more are observed between SPA onsets on different frequencies over the same path, or over different paths. The SPA decay rate is exponential on long paths, and the lower frequency signal over a given path appears to recover faster. This is consistent with the notion that the lower frequency is reflected lower in the ionosphere. Polar cap disturbances (PCD), produced by low energy cosmic rays, are readily detectable on transpolar VLF signals. Of seven small PCD events since November 1961, we observed four of the five which occurred when our equipment was operating. The polar D region was depressed greatly during this period, even during darkness, and took several days to recover in all the cases noted. The PCD effects were very widespread, undoubtedly covering the entire polar cap. A large scale electron precipitation between the latitudes of 40 and 60 degrees, geomagnetic, on October 1, 1961, produced a markedly abnormal diurnal phase shift on the NBA-College signal. Similar precipitation data is not available for other times so we are not sure that all such abnormal diurnal phase traces can be attributed to widespread particle precipitations. The July 20, 1963, solar eclipse produced a phase retardation that was roughly proportional to the obscured area of the sun as averaged over each VLF path. At first and fourth contact the phase appeared to be decreased. Small phase perturbations were superimposed on the phase anomaly. These appear to be the result of mode interference at the point of totality. Nuclear tests of sufficient yield and altitude produce a definite ‘signature’ on VLF records for paths sufficiently close to the burst. The phase records obtained during the US and USSR high altitude tests of 1962 are shown and discussed briefly. Under the second category we include the regularly-occurring phase anomalies, occurring primarily at night, which are observed at College. Evidence that these variations are the result of phase interference is presented. Using an analysis of the sunrise pattern, we show that second mode energy must normally propagate strongly to 5,000 km and significantly to well over 8,000 km at night. The variations we observed in the VLF phase and amplitude are consistent only with the notion of wave interference. The production mechanism of the phase variations for each propagating mode is still unknown. The phase variations appear to be produced in a relatively small region of the ionosphere; therefore, height changes cannot produce the effects we see. We propose a model in which appreciable mode conversion or coupling between ordinarily independently propagating waves occurs at some sort of D region disturbance. Such coupling appears to be the mechanism for the production of the sunrise-sunset pattern; in that case mode conversion takes place near the sun line in the D region. We suggest that gradients similar to those produced by the sun line might be produced by travelling ionospheric disturbances. The interference between waves produced by coupling at such disturbance lines and those normally propagating could easily produce the large phase changes we observe. This mechanism does not require widespread changes in the D region height, and is therefore in agreement with observations. Some events do produce widespread D region height changes so this mechanism is not being suggested to explain all VLF variations. No significant statistical relationship between geomagnetic disturbances and VLF phase variations was found. A discussion of the present theories about magnetic disturbances shows that none would be expected if no data selection process is used. Our finding is therefore reasonable, in spite of the reports of connections between VLF and geomagnetic effects. Mode interference at great distances greatly complicates the use of VLF signals for ionospheric research purposes. We conclude that the long-distance VLF method is a good detection system for certain events such as cosmic-ray flares, solar-flare-induced ionospheric disturbances, and high altitude nuclear explosions. It cannot presently be used to determine quantitatively the properties of the upper atmosphere or of the various D region disturbance phenomena, so, by itself, it is not a good research tool. In conjunction with other methods it is quite useful.
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College oblique ionograms
Howard F. Bates and Arthur Goddard
This report illustrates some of the typical backscatter echoes observed at College, Alaska. Backscatter soundings are being made in five directions—015, 105, 210, 270 and 325 degrees true bearing. The majority of the echoes seen were not groundscatter as usually defined. Many echoes from the northern directions were, in fact, direct scatter echoes from the ionosphere. Groundscatter echoes were regularly observed from the south during this past winter, but only rarely from the north. Sample forward oblique ionograms recorded over the Andöya, Norway, to College, Alaska, path are shown. Preliminary results indicate that the signals were primarily propagated via E or Es layers. Signals with delays of 3 to 10 milliseconds over the great-circle path delay were quite common on all the paths monitored at College. The sample records shown contain signals with delays of 4 to 5 milliseconds.
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Latitudinal and seasonal variations in the night airglow
T. Neil Davis and L. L. Smith
A four-color turret photometer has been used for shipboard observations of the night airglow and the aurora. Zenith observations have been obtained during 1962 close to the 70° W meridian from the northern auroral zone to the Antarctic pack ice. Most of the observations were taken during the Southern Hemisphere Winter. Maximums in the [0I] 5577 Å intensity were found near 30-40° N and 40° S, with the Southern Hemisphere level being generally lower than that in the Northern Hemisphere. The [0I] 6300Å latitudinal variation was similar to that of 0Iλ 5577Å except that maximums in the latitudinal distribution were found near 15° geomagnetic north and south latitudes. In contrast with the [0I] emissions, the sodium group (NaD doublet and OH bands near 5893Å) generally increased to the south with maximums near 20-30° N and 40-50° S geographic latitude. The total 5340Å background increased from north to south. When the integrated starlight and zodiacal light components were subtracted from the total background, the resultant terrestrial component showed a pronounced minimum at low latitudes and apparent symmetry about the geomagnetic equator.
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A report of activities concerned with the eclipse of 20 July 1963
C. T. Elvey, C. S. Deehr, R. D. Hunsucker, H. F. Bates, and Yoshio Kato
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Geophysical Institute Annual Report 1963-64
University of Alaska Fairbanks. Geophysical Institute
The 1963–64 Geophysical Institute Annual Report presents an overview of the year’s scientific research achievements across the Institute’s disciplines, alongside operational summaries covering finances, administrative changes, and other key activities.
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An investigation of solar induced phenomena at magnetically conjugate points
Eugene M. Wescott and Keith Benson Mather
The results of a comprehensive study of solar induced geophysical phenomena at pairs of stations linked by a magnetic field line are presented. Studies have established that magnetic variations (except Sq), telluric currents, ionospheric absorption, visual auroras, VLF and ELF emissions and auroral X-rays occur in similar manner in conjugate areas—in time, form and amplitude. The variations of the magnetic field were the most thoroughly studied phenomena. It was found that auroral zone electrojets occur in conjugate patterns, and that a conjugate area, elongated in geomagnetic latitude, can be defined by comparisons of magnetic records. This conjugate area appears to move in time, as the electrojets depart somewhat from conjugate patterns. The magnetic variations at mid and low latitude due to the return current paths of the electrojets are conjugate to approximately the same degree as the ‘primary’ auroral zone activity. At very high latitudes there is a diurnal variation in the degree of correlation at conjugate points—probably due to the distortion of the magnetic field by the solar wind. Some evidence is presented for two kinds of very high latitude magnetic disturbance. One occurring on the night side is probably due to the poleward expansion of auroral electrojet systems. The other occurs on the day side, even on very quiet days, and is possibly due to hydromagnetic waves, produced by the interaction of the magnetosphere surface and the solar wind. This dayside agitation shows inferior correlation. The Sq variation was investigated and found to be a non-conjugate phenomenon. The theoretical effects of field line linkage are found to skew rather than to equalize the variations from a conjugate pattern. The close relationship of telluric currents to magnetic variations, and the effects of local conductivity are considered. Comparison of records from paired stations confirm that telluric currents are conjugate. The mechanism of short period (~ 1 minute) oscillations may be found in modes of oscillation of the magnetosphere, as apart from ionospheric current systems. A pronounced diurnal variation was found in the power spectra and the polarization of short period oscillations at a mid-latitude pair. Comparisons of all-sky camera data from several conjugate pairs confirm that auroras occur in similar, simultaneous displays in conjugate areas. Occasional differences between the northern and southern displays were observed, similar to the anomalies in the magnetic variations. An attempt was made to study the conjugacy of radio auroras at 50-55 Mc/s but the results were inconclusive. Ionospheric absorption of cosmic radio noise—a phenomenon closely related to influx of charged particles and X-rays—has been shown in several studies to occur as a conjugate phenomenon. A conjugate area, similar in shape to that defined by correlation of magnetic variations was found for absorption events. Although no new work was carried out, the published results of conjugate studies of VLF (whistlers, etc.), ELF (micropulsations) and auroral zone balloon flights (auroral zone X-rays) are presented and discussed.
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The spatial and temporal variations in high latitude cosmic noise absorption and their relation to luminous aurora
Ziauddin Ahmad Ansari
The spatial and temporal variations in cosmic radio noise absorption were investigated at College, Alaska, during 1962-1963 by means of riometers using one narrow beam antenna and two relatively broad beam antennas which were pointed at different direction along the magnetic meridian. The narrow beam antenna had a 12° beamwidth and was periodically swung in the magnetic meridian from 12° north of zenith to 12° south of zenith. Each of the broad beam antennas had a 26° beamwidth and was directed to 40° from zenith, one to the south and the other to the north. In order to explore the relation of the spatial variations in absorption with the differences in auroral luminosity existing in different directions at a given time, two λ 5577A photometers were operated in the two switching directions of the narrow bean antenna i.e. 12°N and 12°S. The information about the auroral coverage of the various antenna beams was obtained from all-sky photographs. A simultaneous study of radio-wave absorption in relation to luminous aurora resulted in the conclusion that the nighttime radio-wave absorption observed at College, Alaska falls into the following two main categories. The absorption belonging to Category I is observed at any time between 2000-0200 hrs., correlates well with the intensity fluctuations of λ 5577A, and is limited to luminous regions of the sky only. Included in the above category is the absorption associated with the quiet as well as bright and active phases of the display. The absorption belonging to Category II is observed only in the post-midnight hours, does not correlate with the intensity fluctuations of λ 5577A and, most probably, is not limited to luminous regions of sky only. With the absorption making a transition from Category I to Category II, a 10-100 fold increase takes place in the ration of absorption to λ 5577A intensity. In order to explore the contribution of bremsstrahlung X-rays to the observed absorption of both categories, the X-ray intensity is calculated on top of the D-region assuming reasonable flux values of the primary electrons. Using the results of the generalized magnetoionic theory, it is shown that the contribution of X-rays to the observed absorption is at the most 2¹/₂% and therefore may be safely neglected. The close association between radio-wave absorption and luminous aurora during absorption events of Category I suggests that the primary particles responsible for the absorption are approximately in the energy range 10-20 kev. It is shown that the absorption associated with the quiet phase of the auroral display is easily explained by a flux of 107-108 electrons cm⁻² sec⁻¹ in the above energy range. It is also shown that the transition from the quiet phase to the bright and active phase is the result of a momentary 10-100 fold increase in the flux of low energy electrons. The lack of correlation between absorption and λ 5577A intensity fluctuations and the pronounced increase in the ratio of absorption to λ 5577A intensity observed during absorption events of Category II are indicative of a hardening of the primary particle energy spectrum, possibly due to the injection of a large number of electrons in the energy range 30-100 kev. It is estimated that a flux of 106-107 electron cm⁻² sec⁻¹ in the above energy range can adequately account for the observed absorption. In the light of the above observations, the apparent discrepancy between the results of two rocket flights at Fort Churchill, one by McIlwain and the other by McDiarmid et al, is easily resolved. This work was supported by National Science Foundation, Grants 14133 and 947.
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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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Geophysical Institute Annual Report 1962-63
University of Alaska Fairbanks. Geophysical Institute
The 1962-63 Geophysical Institute Annual Report, the inaugural issue of this series, presents an overview of the year’s scientific research achievements across the Institute’s disciplines, alongside operational summaries covering finances, administrative changes, and other key activities.
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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.
