Showing papers in "Journal of Geophysical Research in 1970"

Tectonic stress and the spectra of seismic shear waves from earthquakes

Abstract: An earthquake model is derived by considering the effective stress available to accelerate the sides of the fault. The model describes near- and far-field displacement-time functions and spectra and includes the effect of fractional stress drop. It successfully explains the near- and far-field spectra observed for earthquakes and indicates that effective stresses are of the order of 100 bars. For this stress, the estimated upper limit of near-fault particle velocity is 100 cm/sec, and the estimated upper limit for accelerations is approximately 2g at 10 Hz and proportionally lower for lower frequencies. The near field displacement u is approximately given by u(t) = (σ/μ) βr(1 - e−t/r) where. σ is the effective stress, μ is the rigidity, β is the shear wave velocity, and τ is of the order of the dimension of the fault divided by the shear-wave velocity. The corresponding spectrum is Ω(ω)=σβμ1ω(ω2+τ−2)1/2(1) The rms average far-field spectrum is given by 〈 Ω(ω) 〉=〈 Rθϕ 〉σβμrRF(e)1ω2+α2(2) where 〈Rθϕ〉 is the rms average of the radiation pattern; r is the radius of an equivalent circular dislocation surface; R is the distance; F(e) = {[2 – 2e][1 – cos (1.21 eω/α)] +e2}1/2; e is the fraction of stress drop; and α = 2.21 β/r. The rms spectrum falls off as (ω/α)−2 at very high frequencies. For values of ω/α between 1 and 10 the rms spectrum falls off as (ω/α)−1 for e < ∼0.1. At low frequencies the spectrum reduces to the spectrum for a double-couple point source of appropriate moment. Effective stress, stress drop and source dimensions may be estimated by comparing observed seismic spectra with the theoretical spectra.

Mountain belts and the new global tectonics

Abstract: Analysis of the sedimentary, volcanic, structural, and metamorphic chronology in mountain belts, and consideration of the implications of the new global tectonics (plate tectonics), strongly indicate that mountain belts are a consequence of plate evolution. It is proposed that mountain belts develop by the deformation and metamorphism of the sedimentary and volcanic assemblages of Atlantic-type continental margins. These assemblages result from the events associated with the rupture of continents and the expansion of oceans by lithosphere plate generation at oceanic ridges. The earliest assemblages thus developed are volcanic rocks and coarse clastic sediments deposited in fault-bounded troughs on a distending and segmenting continental crust, subsequently split apart and carried away from the ridge on essentially aseismic continental margins. As the continental margins move away from the ridge, nonvolcanic continental shelf and rise assemblages of orthoquartzite-carbonate, and lutite (shelf), and lutite, slump deposits, and turbidites (rise) accumulate. This kind of continental margin is transformed into an orogenic belt in one of two ways. If a trench develops near, or at, the continenal margin to consume lithosphere from the oceanic side, a mountain belt (cordilleran type) grows by dominantly thermal mechanisms related to the rise of calc-alkaline and basaltic magmas. Cordilleran-type mountain belts are characterized by paired metamorphic belts (blueschist on the oceanic side and high temperature on the continental side) and divergent thrusting and synorogenic sediment transport from the high-temperature volcanic axis. If the continental margin collides with an island arc, or with another continent, a collision-type mountain belt develops by dominantly mechanical processes. Where a continent/island arc collision occurs, the resulting mountains will be small (e.g., the Tertiary fold belt of northern New Guinea), and a new trench will develop on the oceanic side of the arc. Where a continent/continent collision occurs, the mountains will be large (e.g., the Himalayas), and the single trench zone of plate consumption is replaced by a wide zone of deformation. Collision-type mountain belts do not have paired metamorphic belts; they are characterized by a single dominant direction of thrusting and synorogenic sediment transport, away from the site of the trench over the underthrust plate. Stratigraphic sequences of mountain belts (geosynclinal sequences) match those asciated with present-day oceans, island arcs, and continental margins.

Longshore currents generated by obliquely incident sea waves: 1

Abstract: By using known results on the radiation stress associated with gravity waves, the total lateral thrust exerted by incoming waves on the beach and in the nearshore zone is rigorously shown to equal (E0/4) sin 2θ0 per unit distance parallel to the coastline, where E0 denotes the energy density of the waves in deep water and θ0 denotes the waves' angle of incidence. The local stress exerted on the surf zone in steady conditions is shown to be given by (D/c) sin θ per unit area, where D is the local rate of energy dissipation and c is the phase velocity. These relations are independent of the manner of the energy dissipation, but, because breaker height is related to local depth in shallow water, it is argued that ordinarily most of the dissipation is due to wave breaking, not to bottom friction. Under these conditions the local mean longshore stress in the surf zone will be given by (5/4)ρumax2 s sin θ, where ρ is the density, umax is the maximum orbital velocity in the waves, s is the local beach slope, and θ is the angle of incidence. It is further shown that, if the friction coefficient C on the bottom is assumed constant and if horizontal mixing is neglected, the mean longshore component of velocity is given by (5π/8)(s/C) umax sin θ. This value is proportional to the longshore component of the orbital velocity. When the horizontal mixing is taken into account, the longshore currents observed in field observations and laboratory experiments are consistent with a friction coefficient of about 0.010.

Evolution of the isotopic composition of atmospheric waters in the Mediterranean Sea area

Abstract: The isotopic composition of rain in the Levant is a reflection of the modification of continental air masses by interaction with the warm Mediterranean Sea. The detailed pattern of evolution of Levantine air has been studied by an isotopic survey of rain from twenty coastal and island stations in the eastern Mediterranean Sea area. The changes in tritium, deuterium, and oxygen 18 concentrations as a function of the distance from the coast usually differ from those calculated for a continuous air mass modification model. Rather, the major changes occur in the Aegean Sea and along the Turkish coast, in an area of major cyclogenesis. A model of convergent air masses, based on the synoptic patterns, is more consistent with the observed isotopic composition of atmospheric waters in the area.

Chemical Characteristics and Origin of Oceanic Ridge Volcanic Rocks

Abstract: Oceanic ridge volcanic rocks alkali metal, alkaline earth, rare earth, nickel and major element content, observing partial melting

Longshore sand transport on beaches

Abstract: Simultaneous field measurements of wave and current parameters in the surf zone and the resulting longshore transport of sand have been made on two beaches under a variety of conditions. The direction and flux of wave energy was measured from an array of digital wave sensors placed in and near the surf zone. Quantitative measurements of the longshore sand transport rate were obtained from the time history of the center of gravity of sand tracer. The measurements have been used to test two models for the prediction of the longshore transport rate of sand. The first model gives the immersed weight longshore transport rate of sand, Il, as proportional to the longshore component of wave energy flux (power), Il = K(ECn)b sin αb cos αb, where E is the energy density, Cn is the wave group velocity, and αb is the breaker angle. The second model assumes that the waves provide the power to move and support the sand and that the superimposed longshore current 〈νl〉 provides a longshore component that results in the longshore transport of sand according to the relationship Il = K′ (ECn)b cos αb〈νl〉/um, where um is the magnitude of the maximum horizontal component of orbital velocity near the bottom under the breaking wave, assumed to be proportional to the rate of energy dissipation by friction on the beach bed. The measurements show that both models successfully predict the sand transport rate, with values of the dimensionless coefficients K = 0.77 and K′ = 0.28. The coherence of the models implies that they are interrelated, their common solution giving the relation as 〈νl〉 = K″ um sin αb, where K″ is a dimensionless constant equal to 2.7. This relation can be obtained directly by equating the longshore current and the longshore component of the momentum flux (radiation stress) of the breaking waves. Thus, the coherence of the models appears to be based on the generation of the longshore currents by the longshore radiation stress. The models will not be equivalent if 〈νl〉 owes its origin to some other generating mechanism such as tides or winds.

Flexural rigidity, thickness, and viscosity of the lithosphere

Abstract: The earth's lithosphere and asthenosphere are modeled as a thin elastic sheet and a fluid substratum, respectively; the physical principles involved are briefly described. The flexural rigidity of the lithosphere is deduced from observations of the wavelength and amplitude of bending in the vicinity of supercrustal loads. Data from Lake Bonneville given by M. D. Crittenden, Jr., are reinterpreted to give a value for the flexural rigidity of the lithosphere in the Basin and Range province of the western United States of 5×1022 Newton meters. Observations of loading in Canada give values for the flexural rigidity of greater than 3×1020N m for the Caribou Mountains in Northern Alberta; about 4×1023 N m for the topography over the Interior Plains; about 1023 N m for the Boothia uplift in arctic Canada; and about 1025 N m for the bending of the beaches of Pleistocene Lakes Agassiz and Algonquin. The flexure of the lithosphere at Hawaii and the bending of the oceanic lithosphere near island arcs give values of about 2×1023 N m. For short-term loads (103–104 years) the flexural rigidity of the continental lithosphere is almost two orders of magnitude larger than for long-term loads, indicating nonelastic behavior of the lithosphere with a viscous (about 1023 N sec m−2) as well as an elastic response to stress. From the values of the flexural rigidity, the thickness of the continental lithosphere is inferred to be about 110 km and that of the oceanic lithosphere about 75 km or more. The anomalously low flexural rigidity of the lithosphere of the Basin and Range province may be due to a very thin lithosphere, only about 20 km thick, with hot, lower crustal material acting as an asthenosphere.

Turbulent loss of ring-current protons.

Abstract: Ring current protons turbulent diffusion in magnetospheric plasmapause, considering ion cyclotron wave lifetime and geomagnetic storms

Crustal temperature and heat production: Implications of the linear heat‐flow relation

Abstract: The surprising linear relation between surface heat flow and heat production in plutons is easily explained in terms of an exponential decrease of heat production with depth in the crust. If the linear relation is assumed to be true in a mathematical sense, it can be shown that this is the only possible explanation, provided that three other assumptions that seem geologically reasonable are made. The decrement D of the exponential function is determined empirically from surface observations since theory requires that it be equal to the slope parameter of the linear relation. Recently published heat-flow results indicate that D varies little from one province to another, and this suggests a model in which D is a general geochemical property of the crust beneath plutons. The outer layer of variable heat production, suggested by the linear relation, is identified with a zone of partial melting in which the heat-producing elements were redistributed exponentially during the plutonic process. The analysis suggests that this zone typically includes a substantial portion of the crust, and that the upward concentration of crustal heat production and heat flow from much of the continental mantle are both somewhat greater than has generally been supposed. The model leads to simple estimates of crustal temperatures beneath plutons.

Reconstruction of Pangaea: Breakup and dispersion of continents, Permian to Present

Abstract: We present a new continental drift reconstruction of the universal continent of Pangaea in the Permian plus a series of five world maps to depict the breakup and dispersion of continents with each subsequent geologic period, Triassic to Recent. Plate tectonics and sea-floor spreading are accepted as the guiding rationale. Also utilized are the morphologic fitting of continental margins and paleomagnetic pole positions. Rigor is imposed by the geometric requirements involved in presenting continental drift dispersion on maps in orderly time sequence and by following certain assumed rules of plate tectonics. The reconstructions were first made on a globe and then transferred to an Aitoff world projection. In the Permian, the Atlantic and Indian oceans were closed so that all the continents were configured into the universal landmass of Pangaea. The reconstruction is based largely on the morphologic best fit of continental margins to the 1000-fathom isobath, except for India, the east coast of which is placed against Antarctica, as dictated by plate tectonics. In the Triassic the breakup of Pangaea commenced. The southwest Indian Ocean rift was created, which split West Gondwana (South America and Africa) away from East Gondwana while a Y junction lifted India off Antarctica. An independent North Atlantic–Caribbean rift also formed, which lifted Laurasia (North America and Eurasia) off of South America and the bulge of Africa. In the Jurassic, northward and westward sea-floor spreading further opened the central North Atlantic and the Indian oceans. At the end of the period, a new rift incipiently split South America away from Africa. The Walvis mantle thermal center or ‘hot spot’ formed, which would subsequently provide an absolute geographic reference point for subsequent continental drift. In the Cretaceous, the motions already established continued. The North Atlantic rift grew northward, blocking out the Grand Banks and the western margin of Greenland. Spain rotated sinistrally, forming the Bay of Biscay. An offshoot rift split Madagascar from Africa, dropping off this subcontinent from Africa, which continued its northern flight. The northward trek of India continued, and Australia incipiently split away from Antarctica. During the Cenozoic, Antarctica rotated further westward. Australia experienced a remarkable flight northward, and New Zealand was split away from its east coast. The North and South Atlantic oceans continued to open; the rift that formerly passed west of Greenland now switched to the east and split Greenland away from northern Europe and extended through the Arctic Ocean. Africa moved slightly northward, continuing sinistral rotation. The Tethyan megashear became dextral for the first time, India collided with and underran Asia.

Ridges and Basins of the Tonga‐Kermadec Island Arc System

Abstract: West of the Tonga-Kermadec trench is a series of ridges and basins including, from east to west, the Tonga-Kermadec ridge (frontal arc), the Lau-Havre trough (interarc basin) and the Lau-Colville ridge (third arc). The frontal and third arcs have asymmetric cross sections with scarps on the flanks facing the interarc basin and substantial accumulations of sediment on the outer ridge flanks. Geology of exposed islands indicates that the Tonga-Kermadec ridge has been a frontal arc since the early Tertiary; the third arc is probably at least as old. A thin cover of rapidly deposited sediment suggests that the morphology of the interarc basin, which consists of linear ridges and troughs with approximate relief of 1000 meters, is no older than latest Tertiary. The interarc basin is underlain by a crust of oceanic character and is the locus of high heat flow. The regional morphology and distribution of sediment must be ascribed to tectonic activity, involving either creation of new oceanic crust or modification of older oceanic crust. An origin of the interarc basin by extensional rifting within an older frontal arc best satisfies the available data and suggests that the extension is related to intensification of island arc tectonism at the close of the Tertiary. Additional studies indicate that the South Fiji basin and at least several other marginal basins on the concave sides of western Pacific trenches have had a similar mode of origin at an earlier time. The result of such activity would be the migration of the trench-frontal arc complexes away from the Asian continent, with creation of new basins with oceanic crust on the convex sides of the frontal arcs.

Vertical drift velocities and east‐west electric fields at the magnetic equator

Abstract: Incoherent scatter observations of vertical drifts taken at Jicamarca (2° dip) are presented. Vertical drifts are found to be nearly constant as a function of height. These vertical drifts can also be taken as a direct measurement of the east-west electric fields at the magnetic equator. Their daily and seasonal behavior is presented. The effect of geomagnetic activity is discussed.

Growth phase of magnetospheric substorms

Abstract: Magnetospheric substorms model modification for growth phase inclusion prior to explosive expansion phase

The compensated linear-vector dipole: A possible mechanism for deep earthquakes

Abstract: Models of earthquake sources that have no volume change, no net force, and no net torque as criteria for the radiation of first motions, have five degrees of freedom in their spatial orientation. The usual double-couple model has only three degrees of freedom. The most general source of high-frequency seismic motions must be a linear combination of a double couple and another source called the compensated linear-vector dipole. A radiation pattern of amplitudes of first motions on the focal sphere cannot be uniquely decomposed into the radiation patterns due to the two sources.

Equatorial spread F: Implications of VHF radar observations

Abstract: VHF radar measurements of scattering by field aligned irregularities associated with equatorial spread F

Surface motion of a layered medium having an irregular interface due to incident plane SH waves

Abstract: A practical method is devised to calculate the elastic wave field in a layer-over-half-space medium with an irregular interface, when plane waves are incident from below. This method may be used for studying the interface shape of the M discontinuity, for example, using the observed spectral amplitude and phase-delay anomalies due to teleseismic body waves. The method is also useful for the engineering-seismological study of earthquake motions of soft superficial layers of various cross sections. The scattered field is described as a superposition of plane waves, and application of the continuity conditions at the interface yields coupled integral equations in the spectral coefficients. The equations are satisfied in the wave-number domain when the interface shape is made periodic and the equations are Fourier transformed and truncated. Frequency smoothing by using complex frequencies reduces lateral interferences associated with the periodic interface shape and permits comparison of computed results with those obtained from finite bandwidth observations. Analyses of the residuals in the interface stress and displacement, performed for each computed solution, provided estimates of the errors. The relative root-mean-square residual errors were generally less than 5% and often less than 1% for problems in which the amplitude of the interface irregularity and the shortest wavelength were comparable. The method is applied to several models of ‘soft basins’ ‘dented M discontinuity’ and ‘stepped M discontinuity’ The results are compared with those derived from the flat-layer theory and from the ray theory. In addition to vertical interference effects familiar in the flat-layer theory, we observe the effects of lateral interference as well as those of ray geometry on the motion at the surface.

Photoelectron fluxes in the ionosphere

Abstract: Photoelectron fluxes and energy spectra in ionosphere for predawn and sunlit atmospheres, taking into account elastic and inelastic collisions

Longshore currents generated by obliquely incident sea waves: 2

Abstract: The profile of the longshore current, as a function of distance from the swash line, is calculated by using the concept of radiation stress (introduced in an earlier paper) together with a horizontal eddy viscosity μe of the form μe = ρNx(gh)1/2, where ρ is the density, x is the distance offshore, g is gravity, h is the local mean depth, and N is a numerical constant. This assumption gives rise to a family of current profiles whose form depends only on the nondimensional parameter P = (Π/2)(sN/αC), where s denotes the bottom slope, α is a constant characteristic of breaking waves (α ≑ 0.41), and C is the drag coefficient on the bottom. The current profiles are of simple analytic form, having a maximum in the surf zone and tending to zero at the swash line. Comparison with the laboratory experiments of Galvin and Eagleson (1965) shows remarkably good agreement if the drag coefficient C is taken as 0.010. The theoretical profiles are insensitive to the exact value of P, but the experimental results suggest that P never exceeds a critical value of 2/5.

VLF electric field observations in the magnetosphere

Abstract: Magnetospheric VLF electric field emissions above electron cyclotron frequency from OGO 5 observation at magnetic equator

Tectonic contact between the Franciscan Mélange and the Great Valley Sequence—Crustal expression of a Late Mesozoic Benioff Zone

Abstract: Late Mesozoic Franciscan rocks of the California Coast Ranges, chaotically deformed and consisting of graywacke, micrograywacke, shale, chert, and mafic pillow lava, are considered to have been deposited in and adjacent to a northwest-trending oceanic trench. Principally on the east, contemporaneous, well-bedded conglomerate, lithic sandstone, siltstone, and shale of the Great Valley sequence evidently were laid down on a continental shelf, slope, and sea floor environment. The junction between these two sequences, one the ensimatic eugeosynclinal melange of Franciscan rocks, the other the more orderly Great Valley miogeosynclinal strata overlying chiefly sialic-type basement, is marked by the South Fork Mountain-Stoney Creek-Ortigalita (–Sur-Nacimiento) fault system. This structural break is interpreted as the crustal expression of a Late Mesozoic Benioff zone. Episodic or relatively continuous underthrusting of the trench melange beneath this former seismic shear zone is held responsible for the contrasting characteristics of the Franciscan rocks and the simultaneously deposited Great Valley sequence, as well as for their ubiquitous tectonic juxaposition. A speculative four-state tectonic model is proposed that involves: (1) rapid Late Jurassic relative northeastward or eastward spreading of the Pacific Ocean floor, coupled with westward or southwestward encroachment by the continental lithospheric plate; (2) mid-Cretaceous buoyant uplift of portions of the eugeosynclinal prism during a period of less intense spreading; (3) accelerated post-Cretaceous convergence between oceanic and continental lithospheric plates; and (4) Miocene-Pleistocene diapiric uplift of the Franciscan melange related to northwestward seafloor spreading.

A study of the influence of magnetic activity on the location of the plasmapause as measured by OGO 5

Abstract: Magnetic activity effect on magnetospheric plasmapause position, measuring ion concentrations as function of local time from OGO 5 observations

Inward motion of the magnetopause before a substorm

Abstract: Magnetopause inward motion before substorm, showing association with interplanetary field vertical component reversal

Thermal regime of a downgoing slab and new global tectonics

Abstract: The new global tectonics and sea-floor spreading hypotheses imply downwarping and descent of the lithosphere in island-arc regions. These downgoing slabs of crust and upper-mantle material will affect the local temperature regime. Geophysically observable variables of surface-heat flux and gravity and seismic travel times will be influenced by the temperature. Using a quasi-dynamic computational scheme and a finite difference solution of the conservation of energy equation we have determined the effects of spreading rate, adiabatic compression, radioactivity, phase changes, and strain heating on the temperature regime of a downgoing slab. Effects of these parameters on surface heat flux, gravity anomalies, and local seismic travel time are also estimated. Predicted travel-time anomalies show good agreement with observed anomalies in Japan and Tonga-Kermadec. Several implications on the localized mechanical behavior of the upper mantle and the evolution of a downwarping slab are made on the basis of our computational results.

Effects of ionospheric conductivity on convective flow of plasma in the magnetosphere

Abstract: Convective flow of plasma in the magnetosphere is apparently driven by the interaction between the solar wind and the magnetosphere, but the flow pattern is regulated by the ionosphere and by pressure gradients in the magnetospheric plasma. The equations for conservation of ionospheric currents are used here to deduce theoretical flow patterns. The currents caused by the pressure of magnetospheric plasma are neglected. When all merging and friction processes are assumed to take place in the tail, and the dayside magnetopause is assumed to be an equipotential, computed trajectories of plasmasphere particles generally exhibit bulges in the dusk-to-midnight sector; if the conductivity model includes a sharp drop in conductivity at sunset, the computed bulge has a sharp onset near local sunset. When convection is assumed to be caused by merging or some other friction process operating near the nose of the magnetosphere, the outer-plasmasphere trajectories have pronounced bulges in the dusk-to-midnight sector, with sharp onset near local sunset, if the conductivity model includes a sharp drop in conductivity at local sunset and a band of substantially enhanced Pedersen and Hall conductivities in the auroral zone. Vasyliunas' observations indicate that the plasma sheet is generally well defined throughout the evening and afternoon sectors of the magnetosphere, to about 1300 LT. Comparing the observed plasma-sheet region with the regions of the computed flow patterns that are accessible to kilovolt electrons from the tail, we find agreement only in cases where the day-night asymmetry is included in the conductivity model, and only when a potential drop ≳35 kv is assumed to exist across the nose region of the magnetosphere. Throughout most of the afternoon and evening sectors, the computed shape of the inner edge of the plasma sheet is insensitive to the assumption about the rate of precipitation. The computed ionospheric current patterns resemble observed currents only if the auroral-zone Pedersen and Hall conductivities are assumed to be enhanced by an order of magnitude or more over the midlatitude nightside conductivities. When peak auroral-zone enhancements of the Pedersen and Hall conductivities are taken to be 3.3 and 10 mhos, respectively, current patterns computed assuming a large voltage drop across the nose of the magnetosphere are roughly consistent with observed DP2 fluctuations; currents computed assuming that all merging activity takes place in the tail then generally resemble DS currents.

Electron precipitation pulsations

Abstract: Electron precipitation modulation exponential dependence on micropulsation amplitude derived from idealized model

Equation of State of Polycrystalline and Single‐Crystal MgO to 8 Kilobars and 800°K

Abstract: MgO has been measured again. Most measurements of the elastic properties of materials, interesting to geophysics, have been made as a function of pressure at room temperature or as a function of temperature at atmospheric pressure. A lapped seal between a buffer rod and sample has made it possible to use ultrasonic interferometry to 1000°K and 10 kb. The elastic constants of poly crystalline and single-crystal MgO were measured in a gas high-pressure system over a temperature range from 300°K to the Debye temperature of MgO. Data from the polycrystalline specimen indicated large effects of temperature on the pressure derivatives. These data did not agree with the results obtained from single-crystal measurements. Upon remeasuring the ceramic sample it becomes apparent that the data are not reproducible after the sample has been cycled to high temperature and pressure. Additional sintering, deformation of the individual grains, and recrystallization take place, which change the properties of the sample. These problems and the problems of sintering isotropic aggregates of theoretical density limit the usefulness of this widely used procedure. Order from the American Geophysical Union, Suite 435, 2100 Pennsylvania Ave., N.W., Washington D.C 20037. Document J70-001; $1.00.

Oxygen and carbon isotope ratios of fresh-water carbonates as climatic indicators

Abstract: Carbonates and molluscs from sediments of four lakes in Maine, New York, Indiana, and South Dakota show increased 18O content during the hypsithermal interval. This increase suggests higher mean annual temperatures for this interval than found at present. The changes in 18O content not correlative with temperature changes are small, indicating stable atmospheric circulation patterns for the regions studied. The influence of seasonal variations in 18O content of atmospheric precipitation on the 18O content of carbonates is discussed for a small lake in Connecticut. The 13C content of fresh-water carbonates appears a less useful climatic indicator than 18O content.

OGO 3 observations of ELF noise in the magnetosphere: 2. The nature of the equatorial noise

Abstract: An examination of the noise present between 1 and 1000 Hz at the magnetic equator with the OGO 3 search coil magnetometer has revealed a previously unobserved class of signals existing only in the outer plasmasphere. These waves are propagating nearly perpendicular to the magnetic field, probably within less than 1° of perpendicular to it; they exist only between about twice the proton gyrofrequency and half the lower hybrid resonant frequency. The waves are confined to a region within about 2° of the equator and therefore have a large amplitude gradient along the magnetic field lines. They are resonant with harmonics of the electron bounce frequency and have sufficient amplitude (∼10 mγ rms) to cause the observed pitch-angle diffusion of electrons mirroring near the equator.

Configuration of the geomagnetic tail during substorms

Abstract: Geomagnetic tail configuration during substorms from Imp 4 magnetic field and auroral index measurements

Instabilities associated with heat conduction in the solar wind and their consequences

Abstract: Associated with the large heat conduction in the solar wind is a skewing of the ion and electron distribution functions. It is shown that this collisional skewing of the electron distribution function can linearly excite collisionless ion-acoustic, electrostatic ion cyclotron, magnetoacoustic, and ion cyclotron waves in the steady-state solar wind even though the net equilibrium current parallel to B is zero. The initial growth rates for these unstable waves are derived, and the effectiveness of the wave-particle interactions in heating the ions and in altering the thermal and electrical conductivities is discussed.