Numerical solutions to the problem of charged particel flow around an ionospheric spacecraft

The interaction of a conducting body moving through the ionosphere with the surrounding plasma is treated numerically. The Poisson and Vlasov equations are solved using computer techniques to give information about the redistribution of charged particles in the wake behind the body and the perturbation of the electric potential sheaths around the body. Three cases of interest are studied: body size less than, equal to, and greater than the Debye length in the surrounding plasma. A range of body potentials and ion Mach numbers are considered which are typical of conditions found in the ionosphere. Wake features, such as ion-free wake lengths and angles of propagation of disturbances in the wakes, are investigated for these conditions. Physical pictures of the mechanisms of wake formation behind a plate and a disc are built up for the three classes of body size, and differences due to geometry or size are explained. The smaller bodies are comparable in size to instrument booms, diagnostic probes, antennae, etc. and the larger bodies approach the dimensions of ionospheric satellites and space probes.     

Redefinition of system III longitude

There is a current need for a redefinition of the Jovian System III longitude measure. We report on a proposed new definition which has been widely circulated among users and has met with general acceptance. Some errors in current calculations of System III [1957.0] are not noted so that these errors can be avoided in future calculations.     

Quantitative modeling of compaction in the Holyoke flood basalt flow,Hartford Basin,Connecticut

Compaction in the Holyoke flood-basalt flow is modeled using a quantitative phase equilibrium routine based on the MELTS algorithm that is coupled with compaction-driven heat and mass transport equations. For a crystal-liquid mush that is cooling from both the top and the bottom, the compaction is qualitatively different in the upper and lower parts of the flow. The solid fraction in the lower part increases as a result of concurrent compaction and solidification. In contrast, cooling from the upper boundary results in an increase in viscosity and a decrease in permeability toward the top. This causes the velocity of the solid matrix to increase downward and the upper part to undergo dilation of the solid matrix. The result is an "S"-shaped profile for compatible elements, and an inverse profile for incompatible elements. The region of modeled maximum dilation matches the location of segregation sheets in the Holyoke flow. Discrepancy between observed deformation, as calculated from textural deformation of plagioclase chain networks versus compositional profiles, suggest some crystal accumulation and/or compaction prior to the formation of the plagioclase chains.     

Between beds and sequences: stratigraphic organization at intermediate scales in the Quaternary of the Virginia coast, USA

ABSTRACT Stratigraphy presupposes a hierarchy of scales of spatial organization supplemented at the small‐scale end by sedimentological concepts (beds, bed sets and bed cosets) and, at larger spatial scales, by sequence‐stratigraphic concepts (systems tracts, parasequences, sequences). Between these two end‐members are intermediate‐scale bodies described as ‘lithofacies’, or simply ‘facies’. A more restricted concept, granulometric facies, can be described in terms of horizontal grain‐size gradients (‘facies change’) and cyclic vertical grain‐size gradients (‘stratification’). Assemblages of facies so defined (also called depositional systems) are not random, but occur in a limited suite of patterns. Such assemblages may be linked to two classes of bounding surfaces, a source diastem (the immediate source of the sediment) and a surface of closure (if preserved), between which is sandwiched a transgressive or regressive, basinward‐fining facies succession. Systems‐bounding surfaces are notably more continuous than internal (gradational) facies boundaries. By thus restricting the definition of a facies assemblage (depositional system), it is possible to describe the Quaternary of the Virginia coast with as few as 12 systems. Depositional systems in the Quaternary of the Virginia coast are allometric, in that any system can be derived from any other by plastic expansion of one or more facies relative to another, or by simple symmetry operations. Self‐similarity prevails across this intermediate scale of stratigraphic organization. Facies assemblages (depositional systems) consist of event beds, which themselves have erosional basal boundaries and internal successions of microfacies. At larger spatial scales, depositional systems are repeated, either autocyclic repetitions forced by processes within the basin of deposition or allocyclic repetitions, as ‘parasequences’ and high‐frequency sequences. In the Virginia Quaternary, systems architecture is compatible with sequence architecture and nests conformably within its framework, but analysis of systems architecture reveals rules beyond those governing sequence architecture.     

Potassium Doppler-resonance lidar for the study of the mesosphere and lower thermosphere at the Arecibo Observatory

We have developed a lidar to study the temperature structure of the nighttime mesopause region over the Arecibo Observatory (18.35°N, 66.75°W) by measuring the lineshape of the fluorescence spectrum of atomic potassium that is deposited in the mesosphere and lower thermosphere (MLT) by meteors. To demonstrate how the potassium lidar can enhance MLT studies at Arecibo, we show recent results for: (1) comparisons with airglow temperature measurements; (2) simultaneous operations with stratospheric and mesospheric temperature profiling by Rayleigh lidar; (3) simultaneous observations of K, Ca⁺, and E-region electron density profiles; and (4) occurrences of sporadic K layers, and relationships to sporadic E layers.     

Pore water evolution in oilfield sandstones: constraints from oxygen isotope microanalyses of quartz cement

Oxygen isotope microanalyses of authigenic quartz, in combination with temperatures of quartz precipitation constrained by fluid inclusion microthermometry and burial history modelling, are employed to trace the origin and evolution of pore waters in three distinct reservoirs of the Brae Formation in the Miller and Kingfisher Fields (North Sea). Oxygen isotope ratios of quartz cements were measured in situ in nine sandstone thin sections with a Cameca ims-4f ion microprobe. In conjunction with quartz cement paragenesis in the reservoirs, constrained from textural and cathodoluminescence (CL) microscopy studies, pore water evolution was reconstructed from the time of deposition of the sandstones in the Upper Jurassic until the present.CL photomicrographs of quartz overgrowths in the Brae Formation sandstones show three cement zones (A, B and C) which can be related to different oxygen isotope compositions: (1) the earliest, and thinnest, zone A (homogeneous CL pattern with probable δ¹⁸O values between +23‰ and +26‰—direct measurements were not possible) precipitated in the sandstones at temperatures <60 °C; (2) the second zone B (complex CL pattern and directly measured δ¹⁸O values between +15‰ and +18‰) precipitated in the sandstones most likely between 70 and 90 °C; (3) the third zone C (homogeneous CL pattern and directly measured δ¹⁸O values between +16‰ and +22‰) precipitated in the sandstones most likely at temperatures >90 °C. Calculated oxygen isotope compositions of pore waters show that zone A quartz cements, and enclosing concretionary calcite, precipitated from a meteoric-type fluid (∼−7‰) during shallow burial (<1.5 km). Zone B quartz cements precipitated from fluids which evolved in composition from a meteoric-type fluid (δ¹⁸O −7‰) to a more ¹⁸O-enriched fluid (δ¹⁸O −4‰) as burial continued to ∼3.0 km. Data from zone C quartz cements are consistent with further fluid evolution from δ¹⁸O −4‰ to basinal-type fluids with δ¹⁸O similar to the present-day formation water oxygen isotope composition (+0.6‰ at 4.0 km burial). A similar pore water evolution can be derived for all three reservoirs studied, indicating that hydrogeologic evolution was similar across sandstones of the whole Brae Formation.The quartz cement zones observed in the Brae Formation sandstones, and the pore water history derived for the area studied, is analogous to published petrographic and pore water evolution data from the nearby Brent Group reservoirs and from reservoirs located in the Haltenbanken area on the Atlantic margin offshore Norway. Considering quartz cement is a major porosity-occluding phase in many reservoir sandstones, and because pore waters both dissolve quartz and carry the dissolved silica to cementation sites, the data presented are valuable for improving the understanding and prediction of reservoir quality development in sandstones globally.