Space Plasma Physics The Study of Solar-System Plasmas (1978) / Chapter Skim
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Impacts of Ionospheric/Magnetospheric Processes on Terrestrial Science and Technology
Impacts of Ionospheric/Magnetospheric Processes on Terrestrial Science and Technology
Pages 424-515
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From page 424... ...
J Lanzerotti Bell Laboratories Murray Hill, New Jersey 0797^ CONTENTS 1, 2, 3 4, 5, 6, 7 Introduction 10 Scintillation of Communication Satellite Signals at GHz Frequencies Magnetic Storms and Cable Communications Magnetosphere Impacts on GroundBased Power Systems The Space Radiation Environment: Effects on Space Systems Electrostatic Charging on Spacecraft Space Power Systems: Ionosphere Impacts Deep Earth Induction Studies Making Use of Magnetospheric-Ionospheric Current Systems Considerations of Telluric Current Effects on Pipelines 9.1 Pipelines at Middle to Low Latitudes 9.2 The Alaskan Pipeline Problems of Magnetic Fluctuations in Geophysical Exploration R
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From page 425... ...
It has long been known that drastic changes in the ionospheric conductivity produced by particle ejections from solar flares and by large magnetic storms would affect radio communications over a large portion of the globe. As the technical needs of society have begun to require the utilization of larger portions of the space around the
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From page 426... ...
This chapter contains ten brief reports written by engineers and scientists who have been concerned with the implementation of science and technology under the constraints of the terrestrial space environment as it is presently known and understood. The subject areas were selected both because of their present technological and scientific importance as well as for their possible future interest in technological planning, Common themes occur in several of the reports.
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From page 427... ...
A concern since the discovery of the radiation belts has been the radiation damage of semiconductor components and systems by high energy particles of magnetospheric and solar origin. However, the low energy particles also affect spacecraft systems by producing differential electrical charging, with subsequent electrical breakdowns and discharges on satellite surfaces.
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From page 428... ...
The morphology of the satellite -signal characteristics is now reasonably, well mapped out as a result of the observational work. However, there is not yet an adequate theory that can satisfactorily relate ionospheric scintillations at GHz frequencies
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. 2.2 Characteristics of Ionospheric Scintillations 2.2.1 Patterns of Occurrence Scintillations in the GHz frequency range occur principally between ±25° geomagnetic latitude near the years of maximum solar activity (Taur, 1973)
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There is apparently no change in the diurnal pattern as the level of solar activity changes. 2.2.2 Spectral Properties Figure 2.1 contains a typical power spectrum of ionospheric scintillation at 4 GHz.
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. 2.3 Conclusions The effect of ionospheric scintillations on communications satellite signals at GHz frequencies is morphologically defined to a reasonable extent with the exception of a few areas, such as frequency dependence and directional variations, for which more measurements should be made to verify existing postulates.
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1185 In addition, there is little information pertaining to the thickness and spatial distribution of these irregularities. Such information is necessary for the development of a theory to correlate VHP and GHz scintillations (Warnik and Liu, 1974)
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i tc LU -10 -20 -30 0.012S 0.125 FREQUENCY (Hz) 1.25 FIGURE 2.1 Power spectrum of 4 GHz ionospheric scintillation event measured at the Hong Kong earth station in September 1973.
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07920) 3.1 Introduction The correspondence between geomagnetic storms and difficulties on cable communications systems has been observed for many years, both on oceanic systems and land-based systems.
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For example, Lanzerotti and Surkan (1974) , through a statistical analysis of geomagnetic power spectra and Kp, concluded that there "exist no one-to-one relationships between power level
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is given here to demonstrate that for this occurrence, when reasonably good data were available, the induced currents in the earth were produced by magnetospheric disturbances as opposed to solely ionospheric currents.
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. The rate of change of the magnetic field intensity and direction over North America for the one-minute interval 2241 to 2242UT is shown in Figure 3.1.
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, both derived from Figure 3.2, were used together with a threelayer earth conductivity model to calculate the potential difference along the 242 km route. It was found that the calculated surface electric field of 7V/km along the Piano-Cascade cable was more than sufficient to cause a shutdown in the system, which was designed for earth potentials of 6.5 V/km ± 20%.
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From page 439... ...
Efforts in the Bell System have now produced power regulation systems that can withstand earth potential variations up to 7.5 V/km without any noticeable transmission impairments. However, further work needs to be done on investigating the scale sizes of large geomagnetic disturbances and how these are related to the powering systems of transcontinental and transoceanic cables.
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G MacLennan, Outage of the L-4 System and the Geomagnetic Disturbances of August 4, 1972, Bell System Technical Journal, 53^ 1817, 1974.
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. 4.1 Introduction One of the most dramatic manifestations of large scale magnetospheric plasma dynamics is the geomagnetic storm - a phenomenon identified as an intense worldwide decrease of the earth's surface magnetic field intensity produced by the sudden inward motion, and subsequent electric and magnetic field-produced drift, of the high altitude magnetospheric plasma.
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was held responsible for the failure of a 230 KV power transformer at the British Columbia Hydro and Power Authority. 4.2 Cause of Problem The cause of these disruptions of power-distribution systems is the induction of earth currents and resultant earth surface potentials during a geomagnetic storm.
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The final understanding that geomagnetic activity is the cause of these relay perturbations has led to a reasonable operational procedure to significantly reduce potential hazards. Given prior knowledge of geomagnetic disturbances, operators now do not remove transformers from the supply network in the case of a relay trip during a geomagnetic storm.
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From page 446... ...
The rectangles placed above the magnetogram trace show the time periods of induced currents in transformer windings and the magnitudes of the currents. Actual recordings of the induced currents are shown on an expanded scale in the upper right-hand corner of Figure 4.1 for the interval 2100 UT 15 May through 0200 UT 16 May for three power stations.
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From page 447... ...
Thus, the problems posed to ground-based power distribution systems by geomagnetic storms are quite real. While these problems can best be solved by power systems engineers, our continuing and advancing understanding of magnetospheric processes and how they effect geomagnetic storm development should be made available to operators of these systems in order that they may understand in a much more comprehensive way the input conditions defining their problems.
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From page 448... ...
J., Terrestrial effects of solar activity, Proceedings of Minnesota Power Systems Conference, October, 1966. McKinnon, J., The August 1972 solar activity and related geophysical effects, NOAA Space Environment Laboratory Report, December 1972.
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1202 i cw Xi -- 3J Si o B o a g "*
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Clarke proposed the concept of synchronous-orbiting communications satellites, he could not have anticipated that energetic particle radiation, trapped in the earth's magnetic field, would be one of the factors that designers of synchronous-orbiting spacecraft would have to face. Similarly,designers of early concepts of space stations envisioned these stations to orbit the earth at an altitude of about 1000 miles - an orbit which we now know passes through the heart of the inner Van Allen radiation belt.
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Accordingly, this section presents a description of the radiation environment at synchronous orbit (altitude ^5.6 earth radii above the surface) and the effects of this radiation environment on the cost and capabilities of present and future space systems.
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The study of the dynamics and interactions of the various plasmas with vastly different temperatures and densities and the development of an understanding of the processes which generate and transport energetic electrons and energetic protons is an area of research vital to economic utilization of synchronous-orbiting spacecraft. The trapped radiation environment at the synchronous orbit consists of electrons and protons (and higher atomic number particles)
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From page 453... ...
. The useful lifetime of radiation sensitive devices such as computer memories, although these may be deeply buried in the interior of a spacecraft, are totally determined by their accumulated radiation dose from trapped energetic electrons during periods of low solar activity, and by the sum of the dosage from trapped electrons and solar cosmic ray protons (and alpha particles)
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(The problem is magnified because mass market pressures, rather than considerations of radiation hardness, drive the semiconductor manufacturers.) Quantitative predictions of the space radiation environment at the accuracy desired by spacecraft designers elude space scientists.
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It may thus be advantageous for some purposes to place a spacecraft into a slightly inclined synchronous orbit, purchasing in the process an improvement in the radiation environment at the expense of additional operational complexity. Solar activity, affecting the magnetosphere via the solar wind and the interplanetary magnetic field, causes both long term (II years)
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From page 456... ...
The contributions that solar cosmic ray protons make to the total radiation dose accumulated by a synchronous orbiting spacecraft were mentioned earlier and illustrated in Fig.5.2. It turns out that solar protons have surprisingly efficient access to this region of space and the radiation damage associated with a single major solar proton event may be comparable to the damage caused in several years of exposure to the trapped energetic electron population (Figure 5.2)
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Simultaneously, the development of an understanding of the physical processes governing the evolution of the space environment is necessary if we are ever to approach the predictive capability which we seek. 5.4 Summary As noted in the scientific discussions, there are strong similarities and analogies between the work magnetospheric physicists must do in order to carry out analyses of the plasmas encountered in space and the research going on in other branches of plasma physics.
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Using detailed waveparticle interaction calculations, space scientists have obtained quite satisfactory agreement between the theoretically calculated and the experimentally observed structure of portions of the earth's radiation belts (Coroniti and Thorne, 1973)
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The premium on a precise, quantitative understanding of the space environment and the impact of the environment on space systems is enormous. Even savings of fractions of a percent, derived as a result of better information regarding the energetic radiation (for example, extending the life of a spacecraft and thus decreasing the replenishment rate)
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AUGUST 1972 SOLAR PROTON FLARE 20 30 40 50 60 MONTHS IN SYNCHRONOUS ORBIT FIGURE 5.2 Performance of a solar cell array as a function of time after launch. The long-term decrease in performance is attributable to damage by energetic electrons; the step function decrease is the effect of one large solar proton event (from Goldhammer and Gelb, 1976)
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correlated with the direction of the interplanetary magnetic field and two geomagnetic disturbance indices (from Paulikas and Blake, 1976)
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From page 462... ...
All uncontrolled spacecraft charging compromises or ruins the measurement of low energy particles of all species. When the complication of photoelectrons and other locally-produced secondary particles are considered, a spacecraft can assume a slightly positive potential, but the plasma sheath surrounding the vehicle has a potential minimum (Whipple, 1975, Grard, 1972)
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For spacecraft at the important synchronous orbit, (see Section 5 above) this means that locally-produced electric fields of magnitude few volts per meter can distort both particle and field measurements.
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In at least one case, total loss of an Air Force spacecraft most probably occurred because of extreme differential charging prolonged by an intense geomagnetic substorm. 6.2 Understanding and Controlling Spacecraft Charging 6.2.1 Understanding Theoretical and experimental studies are currently under way (McPherson, 1976)
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This requirement also implies a knowledge of local electric and magnetic fields. For example, McIlwain (1976)
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However, design problems with the outer surfaces of spacecraft optics may still exist. Scientific spacecraft which have as a prime mission the measurement of low energy particles will most probably have to carry some means of active control of the spacecraft potential.
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6.4 Other Spinoffs Cosmological Studies As mentioned above, spacecraft charging has cosmological implications. Many investigators are interested in the electrostatic charging of bodies in space by particles because of the implications for planet formation.
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For a scientific payload, great care must be taken to avoid spurious noise in the measured particle fluxes and the electric and magnetic field data. However, for many operational spacecraft the question becomes one of probability and economics.
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From page 469... ...
A., Spacecraft Charging Modeling Status, prepared for SAMSO, Los Angeles Air Force Station, Los Angeles, Ca., 1976. Rosen, A., Spacecraft Charging Environment Induced Anomolies, AIAA paper 75-91, presented at Pasadena, Ca., January 1975.
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7.1 Introduction Among the prospects for meeting our country's energy needs in the 21st century, perhaps the boldest, and certainly the most exciting, are the space power systems. As currently envisioned, huge power stations, each capable of serving a large city, would orbit at geosynchronous altitude and transmit space-generated microwave power to earth.
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From page 471... ...
The microwave photons are much less energetic than the solar radiation and are unable to produce ionization or dissociation. In fact, the solar EUV photons interact initially with the atmospheric molecules and atoms, whereas the microwave radiation reacts with the ambient electrons.
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From page 472... ...
It is found that the energy absorbed from the heater beam by the ionospheric electrons raises the electron temperature. This electron heating results in a spatial redistribution of the electron density due to thermal expansion along the earth's magnetic field lines.
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Of course, any modification of the ionosphere by the microwave beam of the space power system will likely be localized in extent and thus will probably not have an impact on a global-scale. The absorption of energy is initially confined to the beam width (roughly 7 km)
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The possible effects of microwave transmission in the thermosphere and ionosphere are summarized in Table 7.1. Whether any or all of these phenomena would occur as a result of space power systems is a question yet to be answered.
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. Advanced heavy lift launch vehicles will probably expel only water vapor when at ionospheric altitudes (Beichel, 19710- However, the expulsion of large quantities of water molecules can produce significant changes in the local ionospheric structure, as was strikingly demonstrated during the launch of Skylab 1 (Mendillo et al., 1975)
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Preliminary studies have not indicated serious pollution problems in the ionsphere or magnetosphere; however, further investigation using realistic traffic models is necessary. 7.4 Conclusions Considerations of ionospheric effects will no doubt influence decisions related to transmission power levels of space power systems as well as the propellants and propulsion systems necessary for placing the systems in orbit.
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R., Geosynchronous Satellite Solar Power, Astron. and Aeron., 13, 46, Nov.
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1231 Table 7.1 Possible Effects of Microwave Propagation IONOSPHERE Electron temperature increase Electron density decrease in D-region, increase in P-region Modification of electron energy distribution Anomalous absorption and heating, leading to field-aligned irregularities and radio scattering phenomena THERMOSPHERE Neutral temperature increase Modification of relative composition Modification of airglow characteristics Excitation of atmospheric gravity waves MUTUAL COUPLING EFFECTS Neutral composition affects the electron-ion recombination rate Ion density affects the neutral wind system Neutral winds and gravity wave structure affect the ion distribution
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1232 100 10 11 10 POWER ABSORBED, J-m FIGURE 7.1 Daily average absorption of solar radiation at middle latitudes compared with the energy that would be absorbed from a microwave beam of uniform flux 100 W/m2 at a frequency of 2.5 GHz.
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in magnetic storms. S u An important parameter in induction studies is the skin depth, the depth at which a field of period T falls to 1/e of its incident amplitude.
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In low and middle latitudes substorms provide transient magnetic fields of order 20 nT in the period range 15 < T < 150 minutes. The geometry of the currents is complicated and is still undergoing active exploration CRostoker, 1972, Kisabeth and Rostoker, 1977)
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The spectrum of the D _ field, associated with ST/ the decay of the ring-current in the late stages of magnetic storms, contains useful energy at periods up to 3 days and has been used in induction studies to depths of order 700 km (Lahiri and Price, 1939; Matsushita, 1975)
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From page 483... ...
. In the magnetotelluric method, sources such as magnetic pulsations and magnetospheric substorms provide -1 4 input in the period range 10 to 10 seconds or more, to a single station at which two orthogonal horizontal components of magnetic field, H (T)
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. In magnetometer array studies, an array of threecomponent magnetometers records magnetic fields in the period range 10-1440 minutes, at a number of points on the earth's surface.
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1238 each station, as a transfer function from the horizontal components (in which the external source field is largest) to the vertical component (in which the fields of internal, induced currents often predominate)
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In the top 100 km the resistivity varies through four orders of magnitude, from 0.25 ohm-m for 4 sea-water to 10 ohm-m for dry crystalline crustal rock. Local anomalies in geomagnetic variation fields represent currents induced in conductive structures within 300 km of the earth's surface.
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From page 487... ...
1240 ascribed to induced electric currents in the sea-water. There may also be a contribution due to a step in the conductive structure of the upper mantle below the continental edge, but existing information is indecisive on this point.
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1241 Local anomalies associated with induced currents in the upper mantle and crust have been discovered beneath the eastern Rift Valley of Kenya and have been studied by a magnetometer array and by the magnetotelluric method. High conductivities rise to crustal depths in Iceland and it is highly probable that an array study across a mid-ocean ridge would contribute to identifying the location of molten material.
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From page 489... ...
Further references to the literature of induction studies using the current systems of the magnetosphere and ionosphere can be found in recent reviews by Frazer (197M and Gough (1973b, 197*
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and G Rostoker, Modeling of the three dimensional current system associated with magnetospheric substorms, Geophys, J
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Polar magnetic substorms, Rev. Geophys.
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1245 50454035 FIGURE 8.1 Distribution of anomalously high conductivity in the upper mantle of western North America as mapped by three large magnetometer arrays. The density of stippling indicates variations of the thicknessconductivity product in an upper mantle layer.
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1246 28 August I972 T-68.3min IB.
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From page 494... ...
These pipelines were, in effect, long insulated electrical conductors subject to inductive effects from variable magnetic fields (see, for example, Gideon et al., 1970)
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From page 495... ...
These holes develop from damage during the laying of the pipe. A short-term study of the peak values of induced currents on pipelines in several states made by Gideon et al.
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9.1 that for telluric currents with periods in the range of 5 mins. to several hours (typical of geomagnetic variations)
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9.1.2 Telluric Currents and Pipeline Corrosion Control When making field measurements to ascertain the level of cathodic protection on a pipeline, the cognizant corrosion engineer must make observations of pipeline-toearth potential and direct current flew measurements accurate to at least ±5 millivolts and ±100 milliamps, respectively. The inability to make observations to such levels of accuracy could result in misleading or completely meaningless data.
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From page 498... ...
It is obvious that without advance warning of possible telluric current activity, pipeline corrosion survey work could be scheduled and performed at a time when the results obtained are meaningless insofar as interpretation of normal conditions are concerned. Recognizing this, the NOAA Space Environment Services Center in Boulder, Colorado, initiated regular publication of predictions for pipe-induced current activity (Campbell and Doeker, 19710.
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From page 499... ...
1252 corrosion survey engineering work. This problem is a sufficient nuisance to have caused the implementation of a regular service for predicting pipe-induced current activity.
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9.2.1 Introduction Associated with every occasion that society finds reason to build long lines of conducting material there is a reawakened interest in the induced currents in these lines associated with geomagnetic disturbances (Burbank, 1905)
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. The ducted induced electric fields that are of concern are those parallel to this pipeline route.
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The electric field values are deduced from analyses of magnetic field variations measured at several places along the pipeline route and then using a three-layer model of the earth to compute the induced electric field. The magnetic variation studies are carried out for different levels of geomagnetic disturbance as represented by the geomagnetic disturbance index Ap.
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From page 503... ...
Similar calculations for small and large magnetic disturbance conditions (Ap ^ 52 and Ap > 150, values that can statistically occur approximately once every two months and every two years; see Campbell, 1977) give current surges -- 95 and £ 280 amps, respectively.
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From page 504... ...
H., Spectral composition of geomagnetic field variations in the period range of 5 min.
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Geomagnetic latitudes along this route are indicated by line segments every degree from 60° to 70°. Location of geomagnetic observatories at Barrow, College, and Sitka are appropriately marked.
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of high latitude geomagnetic disturbances. Separate curves represent values for geomagnetic activity level indices, Ap, shown at the right.
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10.1 Introduction In exploration geophysics, magnetic surveys are conducted to obtain information about subsurface rocks. Most of the surveys involve measurements of the total intensity of the earth's magnetic field across the survey area.
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The contour interval is one gamma, with half-gamma contours in places, and the survey was flown with east-west lines one mile apart and north-south tie lines three miles apart. Magnetic surveys such as this are interpreted in geological terms, both from contour maps, and from profiles along the survey lines.
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From page 509... ...
Thus, gradiometer surveys represent a very small proportion of the total volume of magnetic survey work presently being done, and have only partially replaced total intensity surveys, even in petroleum exploration. A second approach is to use a fixed, ground-based magnetometer to record time fluctuations, and to accept survey data only when these fluctuations fall within specified limits.
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From page 510... ...
Forecasting of magentic fluctuaions is no more certain than forecasting weather, and an unpredicted period of several weeks excessive magnetic activity is simply one of the hazards of working near the auroral zone.
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First, the fixed ground magnetometer measurements may be subtracted from the airborne magnetometer measurements. For success, this pre-supposes certain conditions.
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Hence, the method is applied usually on a limited and empirical basis, and not in areas such as the auroral zones, where it is likely to introduce more problems than it solves. As a rule of thumb in middle latitudes, ground stations may be located so that the mobile magnetometer is not taken more than 200 kms away.
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Study of the adjustments can show any lines of data which might be badly affected by erratic time fluctuations. The distance between tie lines is partly set with regard to errors that could arise from unrecognized time fluctuations (Reford and Summer, 1964)
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1267 O •e « _ O t/5 e -a 2 ra O O
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1268 i AIR MAG WITH ALTITUDE CORRECTION ®GROUND MAG 20 SECS AIR MAG WITH ALTITUDE CORRECTION MINUS GROUND MAG FIGURE 10.2 Aeromagnetic survey over the Gulf of Mexico and ground "base" station data taken to help eliminate the magnetic fluctuations.
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