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GI Reports
This series consists of Scientific reports, Technical reports and Final reports issued by the Geophysical Institute on all contracts and grants.
Recent Submissions
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Latitudinal and seasonal variations in the night airglowA 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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An interpretation of the auroral breakupA 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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The auroral display of February 13-14, 1958Detailed 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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Types Pc 1-2 and IPDP micropulsations at the auroral zoneA micropulsation recording program was carried out at College and Anchorage, Alaska and at Bar I, Canada, with induction magnetometers. The analysis program centered mainly on synoptic and polarization characteristic for types Pc 1-2, IPDP, and Pi burst micropulsation events. Summaries of the known morphological features for structured Pc 1 and unstructured Pc 1-2 micropulsations are given. The synoptic studies disclosed latitude relationships between unstructured Pc 1-2, IPDP, and Pi burst events. At the onset of a polar substorm, Pi bursts occur near midnight at 65°-70° geomagnetic latitudes. IPDP events follow the Pi burst and are seen in evening hours at 60°-65° latitudes. IPDP events seen in afternoon hours are often preceded by unstructured Pc 1-2 activity which maximizes a few degrees polewards of the IPDP. The IPDP events are seen in the evening “bulge” region of the plasmasphere. The proton plasma requirement for IPDP wave generation suggests that protons which are injected near midnight in the Pi burst event drift westwards into the bulge and generate unstructured Pc 1-2 and IPDPs there. The polarization characteristics of Pc 1 activity indicate that simple structured Pc 1 events originate on a stable tube of force. Unstructured Pc 1 events and events which are superpositions of several events usually display pronounced time-variability in the polarization characteristics.
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Computed HF auroral backscatter traces for various distancesComputed ionospheric backscatter traces in the HF portion of the radio spectrum are illustrated for a number of distances between the auroral belt and the observing radar. The type, frequency range, and observed scattering height of HF auroral backscatter traces are strongly dependent upon the ionospheric propagation conditions existing between the auroral belt and the observer. Backscatter echoes produced in a given region of space by a single backscattering mechanism can have completely different range versus frequency characteristics when observed at sites located at different distances from the scattering region. Even though a given bank of auroral-belt irregularities extends through both the E and F regions, it is possible that only E-scatter is detected at one distance, and F-scatter at another. Trace type, scattering height, and frequency range of the observed backscatter echoes are strongly dependent upon the distance between the auroral belt and the observer.
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The preliminary analysis of IGY magnetic results from Alaskan observatoriesA 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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A note on the DS variation of geomagnetic storms : a critical examination of method of analysis.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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Outline geology of the Aleutian Islands with paleomagnetic data from Shemya and Adak IslandsA brief review of the general geology and tectonic setting of the Aleutian Island Arc is presented, followed by an account of the paleo-magnetism of selected areas. Paleomagnetic results are presented for Tertiary and Quaternary volcanic rocks from Shemya and Adak Islands. The specimens were collected and measured using standard paleomagnetic methods. Alternating field demagnetization techniques were applied to test the stability of the remanence and to remove unwanted secondary components of magnetization. The variation of the intensity of the NRM with the bulk susceptibility is discussed from the standpoint of the magnetic stability of the rocks. Mid-Late Tertiary and Quaternary specimens satisfy several criteria of magnetic stability in igneous rocks, and derived pole positions are thought to reflect the ambient geomagnetic field at the time of the origin of the rocks. By comparison, the remanent magnetization of Early Tertiary rocks investigated is less stable and yields uncertain results in terms of pole positions. The paleomagnetic results from the various sites are discussed with respect to the background geology of each island. Paleomagnetic pole positions derived from the results are compared with pole positions from other Tertiary and Quaternary sites in North Pacific tectonic belts.
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Central Alaska earthquakes during 1972Monthly maps of epicenters determined by the Geophysical Institute, University of Alaska, showing depths and magnitudes for approximately 3,000 events are presented for the year 1972. Many of the earthquakes tend to occur in clusters which correspond to mapped faults and lineaments observable on ERTS-1 imagery. Epicenter location errors are shown to be usually less than 10 km. Calculated magnitudes tend to be high compared to NOAA results but geologic structure appears to have a significant effect on magnitude determinations.
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Nearshore ice characteristics in the eastern Bering SeaA description of Bering Sea nearshore ice conditions is presented based on compilation of fast ice edge satellite data, and observations of specific ice events and results from other studies. Landsat imagery at 1:500,000 scale was used to map Bering Sea ice conditions between 1973 to 1976 in nearshore areas. From these maps, secondary single attribute maps were compiled, giving the edge of fast ice at various epochs during these four years. Maps were then compiled on a seasonal basis representative of 1) midwinter, 2) late winter - early spring, and 3) mid-to-late spring. The seasonal average maps were then compared to determine seasonal trends in fast ice edge location. This information was analyzed together with imagery showing specific ice events and bathymetric charts, wind data, tidal variations and observed ice trajectories. The result is a regional description of average nearshore ice conditions along the Bering Sea coast from Cape Prince of Wales to Cold Bay on the Alaskan Peninsula. Over this distance a north-south transition is found from fast ice conditions similar to those in the Beaufort and Chukchi Seas (fast ice bounded by grounded ridge systems located at 20 meters depth), to conditions generated by large tidal variations, offshore winds and highly mobile ice, with the result that fast ice is found only in highly protected, shallow waters.
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Carbon monoxide emissions from moving vehicles in Fairbanks, Alaska : vol. 3 reportThis report is the third and final volume in a series constituting the final report on a research project which has investigated carbon monoxide (CO) emissions from motor vehicle in Fairbanks, Alaska. This volume (Vol. 3) presents the findings of that part of the study dealing with vehicles operating in the moving mode. Two investigations were performed: 1. Driving cycles were developed which are representative of actual driving conditions in the urban area of Fairbanks. Development of two cycles was necessary to demonstrate the effect of traffic control strategies implemented during the summer of 1975. Therefore, the cycles presented here describe traffic conditions both before and after implementation of the new controls, with accompanying qualitative discussion of the effect on CO emissions. In an effort to retain consistency and ease comparison, the cycles developed here were modeled after the CVS-3 cycle used in the Federal Test Procedure. 2. CO emissions from in-use vehicles operating in the moving mode were measured in order to provide quantitative modal emission data for use in conjunction with the driving cycles. Quantitative emissions data for the steady-state mode of operation are presented; however, limitation in the response time of the CO analyzer used in testing precluded acquisition of reliable data for the transient (Acceleration and Deceleration) mode of operation.
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Crustal deformation propagationDuring the contract period the main emphasis was on the observation of crustal tilts associated with earthquakes, their directions, amplitudes and propagation velocities. Data from the seismology laboratory’s three borehole installations at GLM, PAX, MCK, the COL World Wide Standard Station and the ALPA (Alaska Long Period Array) have been analyzed for tilt steps associated with local earthquakes. Tilt steps from distant earthquakes observed at GLM, PAX and MCK and data presented in the literature are discussed. Observed tilt steps cover a distance range from 8 to 12600 km and a magnitude range from 2 to 8. Tilt step propagation velocities have been observed from 1.2 to 4.0 km/sec, and those corresponding to arrival times of teleseismic S waves. Tilt directions, amplitudes and velocities observed at several stations simultaneously for the same earthquake are internally consistent and are likely to depend on the tectonic environment of the observing station in addition to the focal mechanism. The low velocity of 1.2 km/sec is consistent with a plastic wave propagation. Other velocities are close to the Rayleigh wave short-period group velocity. The tilt amplitude for fixed epicenter distance, focal depth and stress system depends logarithmically on the magnitude, with a possible cut-off, but are too large when compared to existing theoretical dislocation models for a single layered homogeneous isotropic elastic crust. Alternative solutions in terms of more realistic crustal layering and including plastic deformation under preexisting tectonic stress probably could account for a number of observations. The operation of a number of short-period telemetry stations has been discontinued, new ones installed and one was relocated. A seismicity map was published for the period 1968-1971, based on recordings from the telemetry net and the results related to the geology of Alaska. The map and its geology related discussion proved very useful to a number of state agencies (such as the Highways Department) and aroused much interest from private sources as well.
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High latitude VLF propagationThis 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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Telluric, geomagnetic, and auroral activity on Arctic drifting stations and at Pt. BarrowThis report presents results of scaling and analysis of telluric, magnetic and auroral data taken at Point Barrow, and on Arctic drifting stations Charlie, Arlis I and Arlis III. Scalings of hourly range in telluric current activity for Point Barrow are presented for the epoch August 1961 through December 1965. Similar scalings are presented for the 2 to 4 month data recording periods for each of the three drifting stations. Studies of the diurnal variation of telluric current activity with respect to the auroral oval show relatively good correlation. However, the differences suggest the need for more study in relating the telluric activity to the auroral activity and, perhaps, in the delineation of Akasofu’s “approximate” auroral ovals. The relative amplitude of telluric activity at College, Barrow and Charlie is in the order of 13 to 5 to 1. Normal run magnetograms are presented for about one month at each of stations Charlie and Arlis I. At Arlis I several measurements of declination were made as well as a number of measurements of total field, F. The total field measurements were made with a Rubidium vapor magnetometer. At Arlis III the Askamia variograph was equipped with a 6 in/hr chart recorder for comparison with telluric records. Simultaneous N-S, E-W, H and D traces are presented for several polar substorms. An all sky aurora camera was operated on Arlis III to provide data for the analysis of auroral arc drift and orientation with respect to the electric and magnetic disturbance vectors at the surface of the sea. Analysis of the E and H disturbance vectors generally shows the orthogonality required by the plane wave inducing field theory. However, there are marked discrepancies as predicted by Price when the scale values of the inducing field are taken into account. The telluric current in the sea is generally aligned with “systems” of auroral arcs but major differences occur. A study of the northward surge of auroral arcs in relation to the E and H vector activity was made. The E and H disturbance at the surface of the sea begins when the auroral arc arrives at the zenith, but maximum amplitude does not occur until the auroral arc reaches its most northernmost limit of travel. The arcs analyzed did not disappear over the northern horizon.
