bluuebunny/crossref_metadata_2025 huggingface dataset:
Remote sensing of potential lunar resources: 1. Near‐side compositional properties
Authors: Johnson Jeffrey R. , Larson Stephen M. , Singer Robert B.
Published: February 2008

New telescopic CCD multispectral imaging of the lunar near side and 330–870 nm spectroscopy of selected regions are presented as aids in estimating compositional differences relevant to locating potential lunar resources such as ilmenite (FeTiO3) and solar wind‐implanted 3He and H. Conversion of 400/560 nm CCD ratio images to weight percent TiO2 using a version of the Charette et al. (1974) empirical relation allows construction of a new TiO2 abundance map for the lunar maria accurate to ±2 wt % HO2. This map provides a consistent view of TiO2 distribution among mature mare soils and can be used to estimate areas potentially rich in ilmenite. Western Mare Tranquillitatis exhibits the highest TiO2 abundances (>8 wt %), followed by regions near Flamsteed P and in northern Oceanus Procellarum. A 950/560 nm CCD ratio mosaic of the full Moon provides estimates of relative surface maturity on local scales as defined by the degree of agglutinate production due to micrometeorite impacts. Since high 3He concentrations are correlated with mature ilmenite‐rich soils, a combination of relative surface maturity maps and TiO2 abundance maps may be useful for estimating 3He (and possibly H) distribution on local scales. While dark mantle materials are also potential sources of ilmenite, 3He, and H, their compositional differences from mare soils prevent accurate remote mapping of their TiO2 abundance and relative maturity. Reflectance spectra (relative to a more rigorously defined MS‐2 standard region) of dark mantle materials and high‐TiO2 mare areas exhibit previously undocumented near‐UV (<350 nm) changes in spectral slope apparently related to compositional variations. Determination of the primary lunar sites for resource utilization will be dictated by the future goals and priorities of the lunar resource program.
Variations in the Sun's radiative output
Authors: Lean Judith
Published: February 2008

By how much does the Sun's radiation vary? Although the Sun has long been an object of immense fascination, fundamental information about the magnitude and variability of its radiative output, sought for over a century, is only now approaching a level satisfactory for geophysical applications. During the past decade, satellite instruments have measured, simultaneously, both the Sun's spectrally integrated radiative output and its ultraviolet spectrum. These data have been analyzed in terms of their relationships to ground‐based observations that characterize different aspects of the Sun's 11‐year activity cycle, allowing estimates of solar radiative output variations over times scales from days to decades and interpretations of these variations in the broader context of the variable Sun. Uncertainties still remain to be answered by the next generation of solar radiometers, which commenced observations with the launch of the Upper Atmosphere Research Satellite in September 1991, near the maximum of solar cycle 22.
High‐latitude ionospheric phenomena diagnostics by high‐frequency radio wave propagation observations
Authors: Blagoveshchenskij D. V. , Egorova L. V. , Lukashkin V. M.
Published: February 2008

With the help of a system of radio paths in the decameter wave band the problem of diagnostics of high‐latitude ionospheric phenomena is solved experimentally. The latter are understood to be auroral substorms, main ionization trough, and daytime polar cusp. On the term “cusp” we suggest cusp/cleft region. As a source of information on a phenomenon, the use is made of either the statistical parameters of radio signals at radio channel output or the radio wave propagation parameter by the data of the oblique sounding of ionosphere. The first approach is taken in diagnostics of auroral substorms and main ionization trough. The oblique sounding is used in daytime polar cusp diagnostics. The experimental observations were carried out by two systems of paths: one is situated north of Eastern Siberia and the other encompasses the area north of the European part of the USSR. The range of corrected geomagnetic latitudes covered is Φ′ = 55°–75°. The main conclusion of the paper is that this system of radio paths allows us to conduct qualitative short‐time prediction of the said ionospheric phenomena.
Thrust belt development in the central Apennines (Italy): Northward polarity of thrusting and out‐of‐sequence deformations in the Gran Sasso Chain
Authors: Ghisetti Francesca , Vezzani Livio
Published: February 2008

The Lazio‐Abruzzi carbonate platform overrides the outermost sectors of the foreland fold and thrust belt of the central Apennines of Italy along an arcuate thrust front, which swings from E‐W to NNW‐SSE orientation. The E‐W striking, north verging thrust faults of the Gran Sasso cut in their footwall the N‐S oriented, east verging imbricates of the Marche thrust belt and the adjacent Adriatic foredeep. Our field mapping of the Gran Sasso imbricate system shows an array of six major thrust faults crosscutting each other in such a way that oblique propagation of higher thrust faults across the preexisting thrust sheets causes rethrusting of earlier imbricated units, decapitation of previous folds, and superposition of younger on older beds. Deformation in the Gran Sasso thrust belt mainly occurred between Messinian and middle Pliocene times and is partly synchronous with the development of the Marche thrust belt, thus implying that shortening resulted from a complex combination of northward and eastward propagating thrust systems. Increasing west to east shortening along the Gran Sasso thrust front indicates large, differential anticlockwise rotation by decoupling along a N‐S transpressive right‐lateral shear zone. This mechanism could have been induced by the Maiella foreland uplift, acting as a buttress against which the Lazio‐Abruzzi carbonate platform was stacked and forced to rotate anticlockwise, with consequent shortening by out‐of‐sequence thrust propagation.
Intracontinental subduction and hinged unroofing along the Salmon River Suture Zone, west central Idaho
Authors: Selverstone Jane , Wernicke Brian P. , Aliberti Elaine A.
Published: February 2008

The Salmon River suture zone in west central Idaho juxtaposes volcanic arc rocks of the Wallowa terrane directly against cratonic North America. Detailed metamorphic studies along a 10 km traverse perpendicular to the suture indicate that the arc and two crystalline fragments thrust upon it each record different pressure‐temperature (P‐T) histories. From lowest to highest structural level: the Wallowa terrane shows only subgreenschist metamorphism, the Rapid River plate (RRP) records unroofing and cooling from ∼8 kbar and 550°C to 6 kbar and 475°–500°C, and the Pollock Mountain plate (PMP) shows evidence for polymetamorphism and records burial and heating paths to final equilibration conditions of 9–11 kbar and 600°–625° C. Ar‐Ar hornblende ages combined with the P‐T data suggest that currently exposed levels of the RRP and PMP were juxtaposed against one another at 15–20 km depth at or prior to 118 Ma, indicating that 10–20 km of uplift, and hence also the onset of collision‐related metamorphism, occurred before ∼118 Ma. Correlation of the metamorphic and age data with geometric constraints from the initial Sr 0.706 line and the dimensions of the RRP and PMP permit construction of large‐scale retrodeformable sections of the west side of the suture from Late Jurassic through Late Cretaceous time. The abrupt nature of the Sr 0.706 line implies that the arc‐continent boundary extends vertically through most of the crust, which requires sharp downwarping of the arc lithosphere in order to account for the PMP metamorphic data. Narrow zoned overgrowths on PMP garnets record this burial event and require initially rapid (≥3 km/m.y.) uplift rates in order to be preserved. We suggest that the onset of rapid uplift resulted from the separation of the negatively buoyant lithospheric root from the downwarped arc, allowing buoyant rise of fragments of thickened crust. Detachment of the root is suggested to change the environment of crustal shortening from one in which footwalls of thrusts or shear zones sink to one in which hanging walls rise. This mechanism represents an alternative to cessation of shortening or onset of tectonic denudation as an explanation for the transition from burial to uplift of high‐pressure metamorphic terrains. Subsequent uplift appears to have been slow and to have occurred in a hinged fashion such that mineral and whole rock ages decrease systematically towards the suture zone. The consumption of lithosphere during ≥40 km of shortening between two crustal blocks implies that the Salmon River suture is the trace of an intracontinental subduction zone. Burial and collision apparently began before about 130 Ma, and thus any precollision strike‐slip faulting or tectonic escape of intervening terranes was likely accomplished in Jurassic and earliest Cretaceous time.
A speculative reconstruction of the Middle Paleozoic Continental Margin of southwestern North America
Authors: Stevens Calvin H. , Stone Paul , Kistler Ronald W.
Published: February 2008

Geologic relations and data from strontium and oxygen isotopic studies are used together to speculate on the paleogeographic positions of various crustal blocks or terranes in southwestern North America with respect to the middle Paleozoic continental margin. The southwestern margin of the middle Paleozoic continent, based on these data, is quite irregular in its present configuration, but most of the irregularities can be accounted for by strike‐slip displacement of continental fragments during several post‐middle Paleozoic tectonic events. We conclude that large‐scale late Paleozoic sinistral displacements and Mesozoic and Cenozoic dextral displacements have been the major events affecting the configuration of this margin. Our preferred model includes the following elements: (1) 500 km of left‐lateral displacement of a large part of the margin during a late Paleozoic truncation, (2) slivering of the margin by right‐lateral faulting during the Mesozoic, amounting to about 275 km of total displacement, and (3) further deformation of the margin during the Cenozoic, primarily by right‐lateral faulting, oroclinal bending, and crustal extension.
K‐spectra of low frequency fluctuations in laboratory plasma simulating conditions of equatorial spread‐F
Authors: Prasad G. , Bora D. , Saxena Y. C.
Published: February 2008

Low frequency electrostatic fluctuations (ω < Ωi) travelling in E×B direction are observed in a laboratory plasma simulating conditions similar to night time equatorial F‐region. The density and potential fluctuations in the region of the plasma where effective g parallel to density gradient ∇n has similar spectral characteristics to that of the results of our earlier experiment of bottom side of equatorial spread F. The k‐spectrum of density in this region of plasma exhibits two marked slopes with indices n= −2.5±0.3 and −4.6± 0.3 where as the potential spectrum exhibits one slope with index −5.2± 0.2. The fluctuations are generated in the region where ∇n is antiparallel to g and appear in the other region due E×B motion. Results are in agreement with in‐situ measurements in F‐region, theoretical predictions and numerical simulation of Rayleigh‐Taylor and drift wave instabilities.
The heterogeneous reaction of HOCl + HCl → Cl2 + H2O on ice and nitric acid trihydrate: Reaction probabilities and stratospheric implications
Authors: Abbatt J. P. D. , Molina M. J.
Published: February 2008

The heterogeneous reaction HOCl + HCl → Cl2(g) + H2O(s) has been observed to proceed readily on cold water‐ice and nitric acid trihydrate (NAT) surfaces. For reactant partial pressures in the 10−7–10−5 torr range, the reaction probability (γ) on water‐ice is found to be 0.16 ± 0.10 at 202 K, and 0.24 +0.5/−0.15 at 195 K, as measured by the decay of HOCl vapor when the HCl partial pressure is above that of HOCl. On NAT, γ is found to have a strong dependence on the H2O vapor pressure of the NAT crystals: at 202 K, reaction probabilities of 0.17 are measured for H2O vapor pressures approaching those of ice (H2O‐rich NAT), whereas γ drops to 0.002 if the H2O pressure is lower by a factor of five (HNO3‐rich NAT). The yield of Cl2(g) relative to HOCl(g) loss is measured to be 0.87 ± 0.20. These results suggest that the heterogeneous process ClONO2 + HCl → Cl2(g) + HNO3(s), which occurs on polar stratospheric cloud surfaces, may be comprised of two steps: ClONO2 + H2O(s) → HOCl + HNO3(s), followed by HOCl + HCl → Cl2(g) + H2O(s). Also, the HOCl + HCl reaction may be directly of importance in the polar stratosphere providing an additional path for chlorine activation.
Identification of the Mount Hudson volcanic cloud over SE Australia
Authors: Barton I. J. , Prata A. J. , Watterson I. G. , Young S. A.
Published: February 2008

On August 20 1991, unusual, hazy clouds were encountered by commercial jet aircraft flying over continental SE Australia. Image data from the AVHRR on board the NOAA satellites have been used to discriminate the clouds from water/ice clouds. The clouds were again observed over Australia by lidar eight days later, presumably after a complete circumnavigation in the zonal winds of the southern mid‐latitudes. The lidar measurements revealed a strong scattered signal from a layer situated near 12 km above the surface. The satellite and lidar data indicate that the clouds were of volcanic origin and we suggest that they originated from the Mt Hudson eruptions in Chile. We have used a numerical model to simulate the transport of the volcanic clouds and find good agreement between the projected position of the clouds and observations.
Transient composite electric field disturbances near dip equator associated with auroral substorms
Authors: Sastri J. Hanumath , Ramesh K. B. , Rao H. N. Ranganath
Published: February 2008

Ionosonde data of Kodaikanal (Geog.Long. 77° 29′E, dip 3.0°N) and Huancayo (Geog.Long. 75°18′W, dip 2.0°N) are used to show the simultaneous occurrence of a transient disturbance in F region height of composite polarity in day and night sectors near the dip equator during the auroral substorm activity on 20 August 1979. At Kodaikanal which is on the nightside at the time of the substorm activity, h′F first underwent an abrupt and rapid decrease (80km in 1 hr) followed by a much larger increase (120km in 1 hr). Perturbation in hpF2 of exactly opposite polarity was simultaneously seen at Huancayo which is on the dayside. The decrease in h′F at Kodaikanal (increase in hpF2 at Huancayo) occurred in association with an increase in polar cap potential drop, ø (estimated from IMF parameters), and the subsequent increase (decrease at Huancayo) with a decrease in polar cap potential. The F‐region height disturbance is interpreted as the manifestation of a global transient composite disturbance in equatorial zonal electric field caused by the prompt penetration of substorm‐related high latitude electric fields into the equatorial ionosphere. The polarity pattern of the electric field disturbance is consistent with the global convection models which predict westward (eastward) electric fields at night (by day) near the geomagnetic equator in response to an increase in polar cap potential drop, and fields of opposite signs for a decrease in polar cap potential.
Slichter modes and Love numbers
Authors: Crossley David. J. , Rochester Michael G. , Peng Z. R.
Published: February 2008

The recent claim by Smylie [1992] to have detected the Slichter modes of the Earth's inner core rests on what appears to be a remarkable agreement between theory and observation. However the theoretical eigenperiods which are used by Smylie conflict significantly with all previously published periods for the Slichter modes, both for non‐rotating and rotating Earth models. A closer examination of the theory used in these calculations reveals the use of static Love numbers to represent the response of the inner core and mantle to dynamics in the liquid core. We here show that the use of dynamic Love numbers restores the eigenperiods to those obtained using standard seismological theory and consequently destroys agreement between these periods and the claimed observations.
Modeling dynamic fracture growth with an elastic network
Authors: Huang Jau‐Inn
Published: February 2008

A conceptually simple model, consisting of a network of particles and springs, is used to model dynamic fracturing processes. In this model, the springs provide the resistance to compression and deformation, and particle masses provide the inertial effect. When such a network is subjected to a dynamic loading, Newton's equations of motion are solved to determine the evolution of the network. If a spring is stretched or compressed beyond prescribed threshold limits at any time‐step, the spring breaks and initiates a fracture. The model results indicate that the fracture pattern depends on the inhomogeneities of the rock, the active crack‐driving force, and the in‐situ stresses.
Relationship between shallow‐ and intermediate‐depth seismicity in the Eastern Aleutian Subduction Zone
Authors: Abers Geoffrey A.
Published: February 2008

The transition from shallow interplate thrusting to intermediate‐depth seismicity is often poorly observed, but critical for understanding the fate of the downgoing slab. In order to better examine the transition, 1448 earthquakes are relocated from data recorded by a regional seismic network in the eastern Aleutian arc, using an improved three‐dimensional velocity model and accurate ray tracing. Single‐event first‐motion solutions are determined from these rays for 31 slab events. The interplate thrust zone is a planar fault zone, dipping 10–15° at 25–35 km depth, and is no more than 5–10 km wide. Most intermediate‐depth earthquakes are localized to a plane no wider than 5 km near the top of the descending plate. Fault‐plane solution orientations for these events vary by several tens of degrees in orientation, although 73% show T axes aligned within 45° of the slab dip. A parallel seismic zone, 20–25 km deeper into the slab, also shows down‐dip plunges of T axes for 3 of 5 solutions. The fault‐plane solutions are poorly explained by plate bending or unbending about a neutral fiber. Hypocenters show that intermediate‐depth events are confined near the subducted oceanic crust, supporting compositional rather than pure thermal control of intermediate‐depth seismicity. One explanation is that the upper‐plane events are an indirect consequence of phase changes in subducted crust. Perhaps similar processes are important in producing earthquakes in the lower, parallel zone.
Convection within the inner‐core and thermal implications
Authors: Weber Patrice , Machetel Philippe
Published: February 2008

Estimation of the Rayleigh numbers of the inner‐core leads to the conclusion that, even with low internal heating rates, this region of the Earth is convecting. This work presents an axisymmetrical model able to investigate convection in a sphere and its applications to the Earth's inner‐core. Rayleigh numbers ranging from the critical (onset of the convection) to ten thousand times the critical have been explored. The thermal implications of a convecting inner‐core have been pointed out: in all the cases the temperature profiles are very close to the adiabat, leading to the possibility of a partially molten regions in the inner‐core. Indeed, the most important effects appear in the first tens of kilometers, just below the inner‐core surface and could be at the origin of the low quality factors Qα and Qβ revealed by seismological studies.
Proton aurora and substorm intensifications
Authors: Samson J. C. , Lyons L. R. , Newell P. T. , Creutzberg F. , Xu B.
Published: February 2008

Ground based measurements from the CANOPUS array of meridian scanning photometers and precipitating ion and electron data from the DMSP F9 satellite show that the electron arc which brightens to initiate substorms intensifications is formed within a region of intense proton precipitation that is well equatorward (∼4–6°) of the nightside open‐closed field line boundary. The precipitating protons are from a population that is energized via Earthward convection from the magnetotail into the dipolar region of the magnetosphere and may play an important role in the formation of the electron arcs leading to substorm intensifications on dipolelike field lines.
Microearthquakes on and near the East Pacific Rise, 9°–10°N
Authors: Wilcock William S. D. , Purdy G. M. , Solomon Sean C. , DuBois David L. , Toomey Douglas R.
Published: February 2008

Records from a seismic network deployed as part of an active tomography experiment at 9°30′N on the East Pacific Rise (EPR) provide an opportunity to characterize local microearthquake activity over an 8‐day period. With the exception of the region around the 9°03′ overlapping spreading center (OSC), no events were located on the rise axis. One microearthquake, located from P and S‐wave arrival times, lies adjacent to the network, 18 km to the west of the rise axis. Five more events, located from P‐wave and T‐phase data, are to the south of the network. Three cluster around the western arm of the 9°03′ OSC, while two are located 25–30 km to the east of the OSC. The seismic moments of the microearthquakes range from 5 × 1019 to 4 × 1020 dyn cm, several orders of magnitude larger than those reported in other studies of shallow events along the axis of the EPR. These results suggest that overlapping spreading centers may be the loci of substantial microearthquake activity and that at this location the normal faults that form on the young flanks of the EPR are active off‐axis to distances of at least 20 km.
Theory for low‐frequency modulated Langmuir wave packets
Authors: Cairns Iver H. , Robinson P. A.
Published: February 2008

Langmuir wave packets with low frequency modulations (or beats) have been observed in the Jovian foreshock. Here it is argued that these modulations are direct evidence for the Langmuir wave decay L → L′ + S. In this decay, ‘pump’ Langmuir waves L, driven by an electron beam, produce backscattered product Langmuir waves L′ and ion sound waves S. The L and L′ waves beat at the frequency and wavevector of the S waves, thereby modulating the wave packets. Electron beam speeds are deduced from the observed modulations, thereby providing testable predictions for the theory. Beam speeds calculated using the modulated Jovian wave packets (1) are reasonable, at 4 – 10 times the electron thermal speed, (2) are consistent with theoretical limits on the decay process, and (3) decrease with increasing foreshock depth, as expected theoretically. These results strongly support the theory. The modulation depth of some wave packets suggests saturation by the decay L → L′ + S. Applications to modulated Langmuir packets in the Venusian and terrestrial foreshocks and in a type III radio source are proposed, and future tests are described.
An investigation of the atmospheric sources and sinks of methyl bromide
Authors: Singh Hanwant B. , Kanakidou M.
Published: February 2008

Methyl Bromide (CH3Br) is a ubiquitous component of the atmosphere and has been implicated as an important player in the depletion of stratospheric ozone. Atmospheric CH3Br abundances, interhemispheric gradients, oceanic concentrations, man‐made emissions, and removal processes have been analyzed and interpreted with the help of a simple box model and a 2‐D global photochemical model. Its calculated atmospheric lifetime (T) of 1.7–1.9 years, based on reaction with OH radicals, is consistent with a global source of 90–110 Gg (109g)/year. Consequences of a much shorter lifetime of 1.2 years, due to possible deposition/hydrolysis losses, are also considered. Available data are used to estimate a CH3Br source that is 35% (20–50%) man‐made and 65% (80–50%) natural. Oceans are substantially supersaturated and provide the most important natural source of ≈60 (40–80) Gg/year. Within the oceans 200–300 Gg/year of CH3Br may be produced. Indirect emissions from automobile exhaust and biomass burning can not be well quantified (1–10 Gg/year). A global trend of 0.1–0.2 ppt/year is predicted. Model results show significant vertical and seasonal variations in the atmospheric abundances and interhemispheric gradients of CH3Br. Substantial uncertainties in calibrations, source estimates, and deposition processes are present.
Effect of sudden solar wind dynamic pressure changes at subauroral latitudes: Time rate of change of magnetic field
Authors: Le G. , Russell C. T.
Published: February 2008

The observations obtained during the IMS from the IGS magnetometer chain extending from Cambridge, England, to Tromso, Norway are used to study the time rate of change of the magnetic field at subauroral latitudes at the time of interplanetary shock passages. The time rate of change of the H component maximizes in the high latitude dayside sector. For these typical interplanetary shocks, the dayside value of time rate of change can be as high as ∼ 3 nT/sec at Tromso and ∼ 1 nT/sec at York. The time rate of change in the dayside roughly depends on the change of square root of solar wind dynamic pressure. The largest of these time rates of change are similar to but slightly smaller than those known to cause disruptive disturbances in power distribution and communication systems. Thus, the daytime effects of sudden impulses may be equal to or greater than the nighttime effects associated with substorms as measured by their impact on terrestrial systems.
Observations of an enhanced convection channel in the cusp ionosphere
Authors: Pinnock M. , Rodger A. S. , Dudeney J. R. , Baker K. B. , Newell P. T. , Greenwald R. A. , Greenspan M. E.
Published: February 2008

Transient or patchy magnetic field line merging on the dayside magnetopause, giving rise to flux transfer events (FTEs), is thought to play a significant role in energizing high‐latitude ionospheric convection during periods of southward interplanetary magnetic field. Several transient velocity patterns in the cusp ionosphere have been presented as candidate FTE signatures. Instrument limitations, combined with uncertainties about the magnetopause processes causing individual velocity transients, mean that definitive observations of the ionospheric signature of FTEs have yet to be presented. This paper describes combined observations by the PACE HF backscatter radar and the DMSP F9 polar‐orbiting satellite of a transient velocity signature in the southern hemisphere ionospheric cusp. The prevailing solar wind conditions suggest that it is the result of enhanced magnetic merging at the magnetopause. The satellite particle precipitation data associated with the transient are typically cusplike in nature. The presence of spatially discrete patches of accelerated ions at the equatorward edge of the cusp is consistent with the ion acceleration that could occur with merging. The combined radar line‐of‐sight velocity data and the satellite transverse plasma drift data are consistent with a channel of enhanced convection superposed on the ambient cusp plasma flow. This channel is at least 900 km in longitudinal extent but only 100 km wide. It is zonally aligned for most of its extent, except at the western limit where it rotates sharply poleward. Weak return flow is observed outside the channel. These observations are compared with and contrasted to similar events seen by the EISCAT radar and by optical instruments.
Akebono (EXOS D) observations of small‐scale electromagnetic signatures relating to polar cap precipitation
Authors: Obara T. , Mukai T. , Hayakawa H. , Nishida A. , Tsuruda K. , Machida S. , Fukunishi H.
Published: February 2008

We have analyzed small‐scale electric and magnetic field variations and electron fluxes which were obtained by the Akebono (EXOS D) satellite in the polar cap region. An electron precipitation most often coincides with a large gradient of flow velocity in which div E is negative (type 1). However, sometimes a steep negative div E is seen only at the edge of a wider region of electron precipitation (type 2). We also observed cases where no particle precipitation occurred in the region of negative div E (type 3). For both type 1 and type 2 cases, a common signature is a spikelike enhancement in the electric field and associated plasma flow in which electron precipitation can be seen on a side where div E is negative. The direction of the spikelike flow is not unique; both sunward flow and antisunward flow are observed. Hence the location of the upward current and the downward current with respect to the noon‐night direction depends on the flow direction in the spike.
A model of solar wind fluctuations with two components: Alfvén waves and convective structures
Authors: Tu C.‐Y. , Marsch E.
Published: February 2008

A two‐component incompressible fluctuation model is presented to explain the radial evolution of the solar wind fluctuations. The basic idea is to consider the small‐scale fluctuations in the solar wind as being composed of Alfvén waves and convective structures. The major Alfvén waves are believed to be created near the coronal base and to propagate outward along the magnetic field lines. The convective structures are defined as the small‐scale variations perpendicular to the local magnetic field direction. They are either quasi‐static or turbulent and slowly evolving in the plasma frame of reference. The small‐scale perpendicular variations are connected, in the parallel direction, with large‐scale magnetic field variations, which are convected by the solar wind as quasi‐static structures during the wind expansion time. The decomposition of the original fluctuations can be done by using special space and time averages, which are defined by space averaging along the directions parallel and perpendicular to the local magnetic field vector and by time averaging in the plasma frame of reference. The equations of motion of the fluctuations and of the correlation functions for both Alfvén waves and convective structures have been derived from the one‐fluid MHD equations. A combination of the correlation functions of these two components is then used for a comparison with observational results. The influence of the angle between the sampling direction and the magnetic field vector on the final results has also been considered. As a first step to apply these equations, a simple model has been suggested that is based on the assumption that the fluctuations are only composed of outward propagating Alfvén waves and static magnetic structures. For comparison with the observations, new statistical results from data obtained by Helios 1 during days 1–95, 1975, and Helios 2 during days 19–109, 1976, are presented. The numerical solutions are shown to describe well the basic evolution trend of the fluctuation energy, the normalized cross helicity, and the Alfvén ratio. It is also shown that the basic physical process of the evolution of the convective structures is the convection of the fluctuating velocity vortex lines and the magnetic field lines by the expanding solar wind.
Effects of electrical coupling on equatorial ionospheric plasma motions: When is the F region a dominant driver in the low‐latitude dynamo?
Authors: Crain D. J. , Heelis R. A. , Bailey G. J.
Published: February 2008

Previous studies of the low‐latitude atmospheric dynamo have concluded that the E region dynamo is the principal source of electric fields during the day, with the F region dynamo being of significant importance in the postsunset period. By computing field line integrals of the Hall and Pedersen conductivities and wind‐driven currents from a sophisticated F region model, we find that the F region may provide a significant contribution to the dynamo electric field at all local times in a limited altitude and latitude region. Though the peak value of the Pedersen conductivity in the E region is larger than the peak value of the F region Pedersen conductivity, the field line integrated Pedersen conductivity of the F region can be significantly larger than the integrated Pedersen conductivity of the E region. This effect is most pronounced for low‐latitude flux tubes with apex altitudes slightly above the F peak. This is due to the unique geometry of the equatorial geomagnetic field in which the field line path length through the F region is much greater than the field line path length through the E region. This effect decreases with increasing latitude as the field lines become more vertical and the path lengths through the appropriate parts of E and F regions become more comparable. We examine the consequences of this effect upon the low‐latitude drifts derived from three dynamo circuit assumptions and compare the results to average drifts observed at Jicamarca, Peru.
Coronal mass ejections and long risetimes of solar energetic particle events
Authors: Kahler S. W.
Published: February 2008

We have surveyed the risetimes of all E > 15 MeV solar energetic proton (SEP) events observed on the NOAA GOES spacecraft between 1984 and 1989 and associated with well‐connected (W20‐W70) solar flares. Twelve events occurred during the times of observations by the coronagraph on the SMM spacecraft, and each event was associated with a coronal mass ejection (CME) observed above the west limb. In each of the three SEP events with the longest flux risetimes a second CME was observed before the time of peak flux. While all the initial CMEs were associated with prominent solar flares, the subsequent CMEs were not accompanied by obvious X ray or radio bursts. We interpret the long risetimes of two of the three SEP events in terms of a second SEP injection due to the second CME.
Semirelativistic maser cyclotron instabilities in multicomponent plasmas
Authors: Mourenas D. , Krasnosel'skikh V. V. , Beghin C.
Published: February 2008

Maser cyclotron instability is studied in the case of interaction between a weakly relativistic hot loss‐cone‐like component and a cold‐cool plasma, for a wide range of parameters applying to natural or artificial beam‐plasma phenomena. We focus on the relativistic mode lying just below the electron gyrofrequency, which appears to couple to ordinary and Z modes. The semirelativistic dispersion relation is numerically solved in a number of cases, showing that the relativistic mode is much more easily excited than the usual upper X mode (fnof; > fnof;ce), and that it generally retains the highest extraordinary mode growth rate, dominating over the O mode for very small (< 0.15) or high (> 1) values of fnof;pe/fnof;ce. This mode is therefore expected to prevail, at least locally, in the source region. The width of the instability range is found to be mostly determined by the ratio nhot/ncold, which must typically lie between 1 and 100. When nhot/ncold < 10, Tcold needs in addition to be smaller than 0.2 Thot. Specific signatures of modes and implications for auroral kilometric radiation are derived.
Fine structure of Langmuir waves produced by a solar electron event
Authors: Gurnett D. A. , Hospodarsky G. B. , Kurth W. S. , Williams D. J. , Bolton S. J.
Published: February 2008

Highly structured bursts of Langmuir waves produced by energetic electrons ejected from a solar flare have been observed using wideband plasma wave measurements on the Galileo spacecraft. The wideband sampling system on Galileo provides digital electric field waveforms at sampling rates up to 201,600 samples s−1, much higher than any previous instrument of this type. The solar flare of interest occurred on December 10, 1990, while the spacecraft was at a radial distance of 0.98 AU from the Sun. This flare emitted a stream of energetic electrons and an associated type III radio event, both of which were detected by Galileo. Starting about 1 hour after the onset of the flare, a large number of intense Langmuir wave bursts were detected near the local electron plasma frequency, which was about 25 kHz. The Langmuir wave bursts, which lasted about 1.5 hours, coincided with the arrival of the solar electrons. The bursts are highly structured and consist mainly of isolated wave packets with durations as short as 1 ms and beat‐type waveforms with beat frequencies ranging from 200 to 500 Hz. The peak electric field strengths are about 1.7 mV m−1. The highly structured envelopes of these waves are strongly suggestive of nonlinear parametric decay processes such as those predicted by various theories dealing with the saturation of beam‐driven electrostatic instabilities. However, the intensities are too low for strong turbulence effects to be important.
Ion depletion zones in the polar wind: EXOS D suprathermal ion mass spectrometer observations in the polar cap
Authors: Horita R. E. , Yau A. W. , Whalen B. A. , Abe T. , Watanabe S.
Published: February 2008

In the high‐altitude polar cap, the suprathermal ion mass spectrometer (SMS) on the EXOS D (Akebono) satellite frequently “observed” ion depletion zones (IDZ) in which the thermal‐energy ion flux was below the detection limit of SMS, corresponding to thermal‐energy ion densities less than 10−2 cm−3. These IDZ are located primarily in the nightside region of the magnetosphere at invariant latitudes above 70° and at altitudes preferentially near apogee and between 8000 and 10,000 km (EXOS D apogee) but extending down to 3000 km. In contrast, outside the IDZ, the SMS regularly observed 3/16/2009 2:01:59 PMoutflowing H+, He+, O+, and O++ polar wind ions with energies typically less than 10 eV in the polar cap. Also, at sufficiently low altitudes below the IDZ the SMS instrument always observed H+, He+, O+, and O++ ions that were stationary in the Earth's corotating frame, i.e., ions observed in the spacecraft ram direction.
Evidence for the generation of juvenile granitic crust during continental extension, Mineral Mountains Batholith, Utah
Authors: Coleman Drew S. , Walker J. Douglas
Published: February 2008

Field, chemical and isotopic data from the Miocene Mineral Mountains batholith in southwest Utah are consistent with the batholith being derived through differentiation of material recently separated from the lithospheric mantle, with little involvement of pre‐Oligocene crust. The batholith ranges in composition and texture from diabase and gabbro to high‐silica rhyolite and granite and is distinctly calcalkaline in nature. Field evidence for anatexis of intermediate‐composition Oligocene crust and magma mixing suggest that fractional melting and mixing were important processes during the evolution of the batholith. Major oxide and rare earth element data for the batholith are consistent with chemical evolution of the magma system being controlled by fractionation of hornblende, plagioclase and sphene (all of which occur in restitic portions of Miocene migmatites exposed in the field area) during partial melting, and mixing between gabbro and granite. Isotopic data indicate a lithospheric mantle source for mafic rocks in the study area and, on the basis of field data and their similarity in isotopic composition, granitic rocks are interpreted to be derived indirectly from the same source during Basin and Range extension. Evolution of the granites is hypothesized to involve a series of partial melting steps, one of which is exposed in the batholith, which refine mantle‐derived gabbros into high‐silica rocks. Thus the Mineral Mountains batholith represents juvenile granitic material added to the crust during extension. This raises the possibility that extension may be an important granitic crust‐forming event. Furthermore, this suggests that pure‐shear igneous inflation of the crust by the mantle can be an important mechanism during extensional deformation. Data presented here indicate that fractional melting of young mafic crust may be an important process in the evolution of isotopically homogeneous intrusive suites which span a broad compositional range. Furthermore, the data support the idea that lithospheric mantle in the Great Basin region may be Proterozoic in age.
Chemical trends in abyssal peridotites: Refertilization of depleted suboceanic mantle
Authors: Elthon Don
Published: February 2008

It is suggested that the chemical trends in abyssal peridotites result dominantly from two processes. The first process is fractional melting of the suboceanic mantle (Johnson et al., 1990) to the point at which clinopyroxene (CPX) is essentially eliminated from the residual mantle. The residue at this stage is depleted harzburgite with either no CPX or <2% CPX that has very low abundances of Na2O (0.01 wt %), Ti (300 ppm), Zr (0.1 ppm) and Ce (0.02 × chondrites). The composite liquids produced during melting are comparable to primitive mid‐ocean ridge basalt glasses (1.5–2.6% Na2O, 5500–7500 ppm Ti, 50–80 ppm Zr). The second process is low‐pressure (<5 kbar) refertilization of the depleted harzburgite with the addition of up to 10% depleted basaltic liquids; following recrystallization, mantle peridotites at this stage are CPX‐bearing harzburgites and Iherzolites. The chemical trends in abyssal peridotites are suggested to result dominantly from these refertilization processes rather than from partial melting. The rejection of fractional melting as the dominant process controlling the chemical trends in abyssal peridotites is based principally on the Na2O versus MgO variations in abyssal peridotites; the Na2O abundances in abyssal peridotites at 42% MgO (0.055 wt %) are 30 times higher than the Na2O abundances (0.002 wt %) in residual mantle formed by fractional melting of primitive upper mantle.
A differential semblance criterion for inversion of multioffset seismic reflection data
Authors: Symes W. W.
Published: February 2008

Mean square error leading to least squares inversion of multioffset reflection seismograms is insensitive to velocity trend information except in the immediate vicinity of a kinematically correct model. In contrast, differential semblance retains sensitivity to velocity trend changes over a wide range of models. The differential semblance criterion combines mean square error with the mean square differences of inverted models from data sets at neighboring shot positions (or offsets, or slownesses, …). Differential semblance compares model estimates at nearby acquisition parameters which are similar even when the model velocity trends are incorrect. Because the method inverts the data, so that the estimated model amplitudes are meaningful, simple differences between the (unstacked) model estimates give a reliable measure of velocity error. A mathematical investigation indicates that the differential semblance criterion is smooth and convex over a large range of velocity models. Numerical simulation using synthetic data sets verifies this contention.
Microtopographic evolution of lava flows at Cima Volcanic Field, Mojave Desert, California
Authors: Farr Tom G.
Published: February 2008

Microtopographic profiles were measured and power spectra calculated for dated lava flow surfaces at Cima volcanic field in the eastern Mojave Desert of California in order to quantify changes in centimeter‐to meter‐scale roughness as a function of age. For lava flows younger than about 0.8 m.y., roughness over all spatial scales decreases with age, with meter‐scale roughness decreasing slightly more than centimeter scales. Flows older than about 0.8 m.y. show a reversal of this trend, becoming as rough as young flows at these scales. Modeling indicates that eolian deposition can explain most of the change observed in the offset, or roughness amplitude, of power spectra of flow surface profiles up to 0.8 m.y. Other processes, such as rubbling and stone pavement development, appear to have a minor effect in this age range. Changes in power spectra of surfaces older than about 0.8 m.y. are consistent with roughening due to fluvial dissection. These results agree qualitatively with a process‐response model that attributes systematic changes in flow surface morphology to cyclic changes in the rates of eolian, soil formation, and fluvial processes. Identification of active surficial processes and estimation of the extent of their effects, or stage of surficial evolution, through measurement of surface roughness will help put the correlation of surficial units on a quantitative basis. This may form the basis for the use of radar remote sensing data to help in regional correlations of surficial units.
Application of the global positioning system to crustal deformation measurements: 3. Result from the southern California borderlands
Authors: Larson Kristine M.
Published: February 2008

Five years of measurements from the Global Positioning System (GPS) satellites collected between 1986 and 1991 are used to investigate deformation in the offshore regions of southern California. GPS provides the first practical technique to make precise geodetic measurements in the region. The geodetic network is situated along the California coastline from Vandenberg (120.6°W, 34.6°N) to San Diego, with additional sites on Santa Cruz, San Nicolas, Santa Catalina, Santa Rosa, and San Clemente Islands. The precision of horizontal interstation vectors is subcentimeter, and the interstation vector rate between OVRO and Vandenberg agrees with the very long baseline interferometry derived rate to within one standard deviation. No significant motion is observed in the western Santa Barbara Channel between Vandenberg and Santa Rosa Island, 0.5 ± 1.6 mm/yr, where the quoted uncertainties are one standard deviation. Motions in the eastern Santa Barbara Channel are consistent with compressional deformation of 6 ± 1 mm/yr at N16 ± 3°E. This motion is in agreement with seismicity and an independent geodetic analysis for the period 1971–1987 (Larsen, 1991). San Clemente Island is moving relative to San Diego at the rate of 5.9 ± 1.8 mm/yr at a direction of N38 ± 20°W. The motion between San Nicolas Island and San Clemente Island, 0.8 ± 1.5 mm/yr, is insignificant.
Electrical resistivities of crustal fluids
Authors: Nesbitt Bruce E.
Published: February 2008

Results of calculations on the electrical resistivities of crustal fluids as a function of temperature, pressure and fluid composition indicate that crustal fluids can range in resistivity from approximately <0.01 to >1 Ω m. The dominant contribution to decreasing the resistivities of crustal fluids comes from increased concentrations of chloride and bicarbonate salts and increased temperature and density of the fluids. Calculations indicate that the sharpest decrease in fluid resistivity occurs at shallow depths < 8 km and low temperatures < 200°C. Consequently, the observed decrease in resistivity of the mid‐crust at depths generally > 10 km and temperatures > 300°C can not be readily explained as a product of variations in resistivities of crustal fluids. These results indicate that a transition in mineralogy or pore shape geometry is more likely responsible for the observed decrease in electrical resistivity of the middle crust than a major change in fluid resistivity.
The Jan Mayen Current of the Greenland Sea
Authors: Bourke Robert H. , Paquette Robert G. , Blythe Robert F.
Published: February 2008

Oceanographic measurements acquired by the USNS Bartlett during September 1989 in and north of the area of the Jan Mayen Current (JMC) show that, in terms of upper layer baroclinic flow, about half of the JMC is a wide meander in the East Greenland Current (EGC) and about half continues eastward to close the Greenland Gyre (GG) on the south. This phenomenon has been charted in the past but has elicited no comment. Surface drifters and a numerical model corroborate this behavior. At deeper depths (>100 m) the meander dissipates with the flow becoming more easterly. A drifting float at 500 m depth confirms that the flow is relatively undeviated toward the east ultimately merging with the northward flowing Norwegian Atlantic Current. Near the GG the fresh water content of the water column is low in the upper layers but high in the middepths. Where there is a substantial content of EGC water (e.g., in the JMC), the converse is usually true. The FWC of the GG computed for the period 1953–1966 was smaller by a factor of 2 in both layers than in 1989, indicating that 1989 is in another period of low salinity comparable to that of 1968, the period of the Great Salinity Anomaly described by Dickson et al. (1988).