bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of lateral viscosity variations on postglacial rebound: Implications for recent sea‐level trends
Authors: Gasperini Paolo , Yuen David A. , Sabadini Roberto
Published: February 2008

Global sea‐level changes have been occurring since the last Pleistocene deglaciation. Recently the contribution of current postglacial rebound to local sea‐level variations has been removed by means of a radially stratified earth model in order to assess the amount of sea‐level rise due to recent climatic changes. We have studied the effects of lateral variations in the viscosity structure on the postglacial uplift rates along the continental margins. Finite‐element calculations in cylindrical geometry show that the spread in the cumulative vertical displacement may be affected by 20% in the presence of lateral rheological contrasts. But the vertical rates of deformation can attain differences of up to 50% for the different models. Horizontal deformation rates along continental margins are much more affected by the lateral variations in viscosity and can be used in the future as constraints on mantle rheology.
Structure of interplanetary magnetic field near the Sun
Authors: Washimi Haruichi
Published: February 2008

The interplanetary structures of the magnetic field and the current near the sun are analyzed by MHD computer simulation for the case of the magnetic dipole configuration on the photosphere. It is shown that the solar wind in the closed field region corotates with the sun. The azimuth magnetic field is formed in the open region but remains very weak in the closed region. The poloidal current, which associates with the azimuth magnetic field, is found to come into and go out of the sun in the open and closed regions, respectively.
Transient flux tubes in the terrestrial magnetosphere
Authors: Pontius D. H. , Wolf R. A.
Published: February 2008

We postulate that small, isolated density depletions are introduced into the magnetotail by an uneven plasma loading process in the far tail. Such bubbles would be displaced earthward by an interchange process, and a significant depletion would move faster than either the gradient‐curvature drift speed or the average convection speed. The dissolution of a bubble into the background results in a local reduction in plasma density, thereby violating ideal MHD and the subsequent conservation of plasma content. If a sufficient amount of magnetic flux in the far tail is contained in bubbles, then the net effect may be a reduction of plasma pressure in the near tail sufficient to resolve the pressure balance inconsistency.
Absolute inclination values from deep sea sediments: A reexamination of the Cretaceous Pacific record
Authors: Tarduno John A.
Published: February 2008

New data are used to examine anomalously shallow paleomagnetic inclinations derived from previous analyses of Cretaceous DSDP sediments of the central western Pacific Ocean. While VRMs are shown to produce a similar effect, the bias toward shallow values is still present with thoroughly demagnetized data. Superimposed upon this bias is a trend towards maximum flattening at an expected inclination of ∼55°, with the flattening falling to zero at the equator and pole. Flattening due to sediment compaction, or ‘inclination‐error’, is proposed to explain these observations.
Parsimonious staggered grid finite‐differencing of the wave equation
Authors: Luo Yi , Schuster Gerard
Published: February 2008

A parsimonious staggered grid differencing scheme is presented which requires less storage than the conventional staggered grid method. For three dimensional elastic wave propagation, this scheme only stores displacement components, not stress, and so requires 66% of the memory needed by the standard staggered grid method. The storage requirement is the same as the 2–2 differencing scheme used by Kelly et al. (1976) for the second‐order wave equation. Its advantage is that it is stable and accurate for media with fluid‐elastic contacts and for a wide range of Poisson ratios. A disadvantage is that its computer programming is more involved.
Magnetospheric and Exospheric Imaging in the Extreme Ultraviolet
Authors: Chiu Y. T. , Robinson R. M. , Collin H. L. , Chakrabarti S. , Gladstone G. R.
Published: February 2008

Extreme ultraviolet line emissions by exospheric oxygen ions and neutrals of ionospheric origin can be used to form images of the dynamic magnetospheric regions with sufficient speed to provide a new global means of observing the dynamics of magnetosphere‐ionosphere coupling processes. Computer simulations of such exospheric images based on the latest measurements of ion outflow, on known or estimated solar fluxes, and on known emission and excitation rates are shown. An evaluation of the current and foreseeable EUV imaging technology relevant to magnetospheric imaging is also given.
The nonlinear response of AE to the IMF BS driver: A spectral break at 5 hours
Authors: Tsurutani Bruce T. , Sugiura Masahisa , Iyemori Toshihiko , Goldstein Bruce E. , Gonzalez Walter D. , Akasofu Syun I. , Smith Edward J.
Published: February 2008

We demonstrate the existence of a sharp break in the power spectrum of AE at ∼ 5 hours. At frequencies below the break, AE has a ∼ f−1.0 dependence, and at higher frequencies it has a f−2.2 to f−2.4 dependence. The power spectrum of the IMF Bs for the same time interval has a ∼ f−1.4 dependence with no spectral breaks or peaks. Thus, at frequencies above the break, the power in AE varies as f−0.5 to f−0.8 times the power in Bs and at low frequencies it ranges from being f0 (frequency independent) to a f+0.4 times the power in Bs. Several possible explanations of the nonlinear response of AE to the IMF Bs driver are briefly discussed, including: 1) variable ionospheric conductivity (increasing with Bs) for the high frequency regime, and 2) several AE saturation mechanisms for the low frequency regime.
The dependence of MHD turbulence spectra on the inner solar wind stream structure near solar minimum
Authors: Tu C.‐Y. , Marsch E. , Rosenbauer H.
Published: February 2008

The variation of the power spectra (e±) of the fluctuating Elsässer variables δZ± with the solar wind velocity has been examined by either individual case study or statistical analysis with Helios data obtained near solar minimum. It is found, when going from high‐speed to low‐speed wind, that: 1.) The slopes of both energy spectra systematically increase toward the value given by Kolmogorov's law. 2.) The power density of δZ+ in the Alfvénic regime above f ≈ 2 × 10−4 Hz strongly decreases while the power density of δZ− does not change a lot. 3.) A somewhat higher level of e− is found in the leading edges of high‐speed streams near the regions of large velocity shear. We also found that density fluctuations might make some contributions to e− in the low‐frequency domain. The relevance of these findings with respect to the evolution of the solar wind MHD turbulence is discussed.
Source location of the narrowbanded radio bursts at Uranus: Evidence of a cusp source
Authors: Farrell W. M. , Desch M. D. , Kaiser M. L. , Kurth W. S.
Published: February 2008

While Voyager 2 was inbound to Uranus, radio bursts of narrow bandwidth (< 5 kHz) were detected between 17–116 kHz by both the Planetary Radio Astronomy (PRA) and Plasma Wave (PWS) experiments. These R‐X mode bursts, designated n‐bursts, were of short duration (about 250 msec), tended to occur when the north magnetic pole tipped toward the spacecraft, and increased in occurrence with increasing solar wind density. In this report, we present an explicit determination of the burst source location based upon fitting the region of detection at high and low frequencies to field‐aligned, symmetric cones. The region of good fits was located between the north magnetic pole and the rotational pole, corresponding approximately to the northern polar cusp. Based upon the emission power, it is suspected that at certain times large amounts of auroral input power may originate in this cusp.
The stratospheric ozone layer above Spitsbergen in winter 1989
Authors: Neuber R. , Krüger B. C.
Published: February 2008

Ozone soundings are performed from Spitzbergen (79°N, 12°E) by an ozone LIDAR and balloon sondes, the development of the ozone layer from January until the end of March 1989 shows no major depletion, but a significant increase in mid‐February due to the stratospheric warming. In march a secondary concentration maximum occured above the tropopause.
Small‐scale waves encountered during AASE
Authors: Bacmeister Julio T. , Schoeberl Mark R. , Lait Leslie R. , Newman Paul A. , Gary Bruce
Published: February 2008

Variability on scales of 200 km or less in the lower stratosphere is examined using potential temperature data collected during the AASE campaign. Enhanced variability is found over regions containing topography presumably due to gravity waves. The effect of gravity wave critical levels on topographically induced variability is examined. A significant reduction in variability is found when a critical level is present.
Redistribution of reactive odd nitrogen in the lower Arctic stratosphere
Authors: Hübler G. , Fahey D. W. , Kelly K. K. , Montzka D. D. , Carroll M. A. , Tuck A. F. , Heidt L. E. , Pollock W. H. , Gregory G. L. , Vedder J. F.
Published: February 2008

In‐situ measurements of total reactive odd nitrogen (NOy) were made from the NASA DC‐8 aircraft in the lower arctic stratosphere during the 1989 Airborne Arctic Stratospheric Expedition. Throughout January and February, NOy mixing ratios were typically between 0.5 and 3 parts per billion by volume (ppbv) at altitudes between 10 and 12.5 km. During several flights late in the mission, events of unusually high NOy occurred with mixing ratios up to 12 ppbv at these altitudes. Simultaneous measurements of N2O, O3, and H2O during these events suggest that large changes in NOy are not expected. The elevated NOy values are interpreted as a vertical redistribution of NOy in the lower stratosphere resulting from gravitational sedimentation of aerosol particles containing HNO3. No evidence of the redistribution of H2O is noted consistent with observations of denitrification without dehydration higher in the stratosphere.
The sunrise and sunset variation of ClO in the lower stratosphere
Authors: Brune W. H. , Toohey D. W. , Lloyd S. A. , Anderson J. G.
Published: February 2008

The abundances of ClO have been measured, in situ, in the lower stratosphere during sunrise and sunset. Measurements were made with an instrument mounted on the NASA ER‐2 aircraft, which was flown at an altitude of 20 km and latitudes between 35°N and 47°N during a morning and an evening flight. The abundances of ClO were observed over a dynamic range of 20 from a detection threshold of ∼ 1 part per trillion volume (pptv). These data confirm the sunrise variation of the photolysis of chlorine nitrate that is predicted by a zero‐dimensional photochemical model. They also suggest that the absolute photolysis and termolecular formation of chlorine nitrate occur at rates consistent with nominal ClONO2 and NO2 concentrations.
The polar stratospheric cloud event of January 24, 1989, Part 1. Microphysics
Authors: Poole L. R. , Solomon S. , Gandrud B. W. , Powell K. A. , Dye J. E. , Jones R. L. , McKenna D. S.
Published: February 2008

Rapid adiabatic cooling induced by synoptic forcing led to polar stratospheric cloud (PSC) formation on January 24, 1989, at altitudes sampled by the ER‐2 aircraft. Particle characteristics measured by the Forward Scattering Spectrometer Probe (FSSP) on the ER‐2 were compared to those calculated using a theoretical FSC microphysics model. Although calculations were sensitive to local changes in cooling rate, generally favorable agreement was found, that in particle surface area being especially important since this parameter dictates heterogeneous chemical rates. The overall model performance suggests that the current approach for simulating Type 1 (nitric acid trihydrate) PSC formation under rapid cooling conditions is well founded and can be used to study the effects of heterogeneous chemistry on stratospheric composition.
The effect of tracking network configuration on GPS baseline estimates for the CASA UNO Experiment
Authors: Kornreich Wolf S. , Dixon T. H. , Freymueller J. T.
Published: February 2008

Geodetic monitoring of subduction of the Nazca and Cocos plates is a goal of the CASA (Central and South America) Global Positioning System (GPS) experiments, and requires measurement of intersite distances (baselines) in excess of 500 km. The major error source in these measurements is the uncertainty in the position of the GPS satellites at the time of observation. A key aspect of the first CASA experiment, CASA Uno, was the initiation of a global network of tracking stations to minimize these errors. We studied the effect of using various subsets of this global tracking network on long (>100 km) baseline estimates in the CASA region. Best results were obtained with a global tracking network consisting of three U.S. fiducial stations, two sites in the southwest Pacific and two sites in Europe. Relative to smaller subsets, this global network improved baseline repeatability, resolution of carrier phase cycle ambiguities, and formal errors of the orbit estimates. Describing baseline repeatability for horizontal components as σ= (a2 + b2L2)1/2 where L is baseline length, we obtained a= 4 and 9 mm and b= 2.8×10−8 and 2.3×10−8 for north and east components, respectively, on CASA baselines up to 1000 km in length with this global network.
Preliminary paleomagnetic results from the Triassic Prida Formation (Lower Star Peak Group), west‐central Nevada, and implications for latitudinal displacement
Authors: Geissman John Wm. , Gillett Stephen L. , Oldow John S.
Published: February 2008

Paleomagnetic data were obtained from two oppositely dipping carbonate sections of the Triassic Prida Formation, lower Star Peak Group, in the Humboldt Range of west‐central Nevada. Progressive demagnetization of the rocks indicated that the remanent magnetization consists of three or fewer vector components. A characteristic component, with the highest unblocking temperatures, was most effectively isolated by low temperature (200–300°C) thermal followed by progressive alternating field demagnetization. The sections yield in situ mean directions that differ significantly, but that have similar inclinations (Star Canyon: D=311, I=+34, α95=5, k=22, N=38 samples; Fossil Hill: D=281, I=+33, α95=2°, k=2814, N=3 section means, 154 samples). The directions diverge upon simple structural correction, from which we infer that at least one and probably both of the sections were remagnetized, probably in latest Middle to Late Jurassic time. These data cannot be used to indicate significant southward translation of Golconda allochthon rocks, as inferred from magnetizations in underlying volcanic rocks. The translation interpretation may require revision if magnetizations in the volcanic rocks are also secondary.
Fractal study and simulation of fracture roughness
Authors: Kumar Sunil , Bodvarsson Gudmundur S.
Published: February 2008

This study examines the roughness profiles of the surfaces of fractures and faults by using concepts from fractal geometry. Relationships between fractal characteristics of profiles and isotropic surfaces are analytically developed and a deterministic representation of the roughness is examined.
Forbush decreases and particle acceleration in the outer heliosphere
Authors: Van Allen J. A. , Mihalov J. D.
Published: February 2008

Major solar flare activity in 1989 has provided examples of the local acceleration of protons at 28 AU (Pioneer 11) and of the propagation of Forbush decreases in galactic cosmic ray intensity to a heliocentric radial distance of 47 AU (Pioneer 10). The combination of these and previous data at lesser distances shows (a) that Forbush decreases propagate with essentially constant magnitude to (at least) 47 AU and with similar magnitude at widely different ecliptic longitudes and (b) that the times for recovery from such decreases become progressively greater as the radial distance increases, being of the order of months in the outer heliosphere. A phenomenological scheme for (b) is proposed and fresh support is given to the hypothesis that the solar cycle modulation of the galactic cosmic ray intensity is attributable primarily to overlapping Forbush decreases which are more frequent and of greater magnitude near times of maximum solar activity than at times of lesser activity.
Magnetic monitoring of pyrrhotite alteration during thermal demagnetization
Authors: Dekkers M. J.
Published: February 2008

Pyirhotite progressively oxidizes via magnetite to hematite during thermal demagnetization of porous artificial samples containing well‐defined natural pyrrhotite. Rockmagnetic and X‐ray diffraction determinations show that the intermediate alteration stages consist of pyrrhotite‐magnetite‐pyrite intergrowths. Alteration is quite differently expressed in two ctaiically virtually identical pyrrhotites.
SEM and magnetic fabric study of a compacting sediment
Authors: Kodama K. P. , Sun W. W.
Published: February 2008

Scanning electron microscopy (SEM), anisotropy of magnetic susceptibility (AMS) and anisotropy of anhysteretic remanence (AAR) studies were conducted on kaolinite/magnetite samples compacted to pressures between O and 0.2 MPa to determine if clay and magnetic fabric development mimic a change in compaction behavior marked by a break in slope in the compaction curve. This break in slope indicates that the rate of void ratio decrease with increasing pressure abruptly slows down at pressures of about 0.04 MPa. About one‐half of a compaction‐caused inclination decrease occurs at pressures less than 0.04 MPa. SEM photomicrographs show that horizontal clay fabric develops inhomogeneousIy within a sample at pressures below the break in slope. Since pore spaces are larger than magnetite grains at low pressures below the break in slope the observed pattern of inclination decrease during compaction may be due to magnetite grains being attached to clay particles and constrained to follow clay fabric development. This interpretation is supported by the observation that AAR minimum axes become vertical at pressures above the break in slope. This may indicate that magnetic fabric is developing at low pressures and that most of the magnetite particles are constrained to lie subhorizontally. The AMS maximum axes tend to lie 90° from a strong remanence in these samples suggesting single domain magnetic behavior. Measurement of AMS after alternating field demagnetization yields maximum axes which cluster near to the AAR maximum axes suggesting multidomain behavior. This apparent contradiction aay be due to magnetic conditions prior to AMS aeasurement controlling domain wall nucleation.
The role of radium distribution and porosity in radon emanation from solids
Authors: Semkow Thomas M. , Parekh Pravin P.
Published: February 2008

Essential features of the grain emanation and aggregation models are presented. The presence of thin layers containing Ra is shown to enhance the Rn emanation from the grains. A multiple α‐recoil mechanism is suggested to create a nonuniform Ra distribution. It is also shown that the rnesoporosity may increase Rn emanation and the macroporosity may contribute to Rn transport.
Identifying the plane of slip for a fault plane solution from clustering of locations of nearby earthquakes
Authors: Fehler Michael
Published: February 2008

Numerous methods have been proposed recently to analyze the spatial pattern of locations of earthquakes to infer planes along which earthquakes cluster. These planes are considered to be earthquake slip planes. The application of such methods is to find major planes passing through a set of earthquake locations when the fault plane solutions of the events are unusual or when locating planes would contribute to understanding the structural setting in which an earthquake occurred. A modification to one of these methods, the three‐point method, allows one to study anomalous or otherwise interesting events, and to choose which nodal plane in the fault plane solution for the event is the plane of slip. To be successful, the method requires that a sufficient number of other events had the same, or similar, slip plane. The modified three‐point method consists of finding the orientations of planes formed by combinations of the location of the earthquake under study and all other locations in the remainder of the earthquake catalog taken two at a time. A test to determine which orientations occur more often than expected is used to identify statistically significant planes along which earthquakes cluster. Each plane identified passes through the earthquake being studied. If one of these planes is parallel, or nearly parallel, to one of the nodal planes of the fault plane solution, that nodal plane is assumed to be the slip plane. The method is demonstrated by investigating ten earthquakes that occurred during 1983–1984 near Coalinga, California. Using the method, significant alignments of events along planes that are nearly parallel to one of the nodal planes for eight of the ten events were found.
Rupture process and stress‐drop of the Great 1989 MacQuarie Ridge Earthquake
Authors: Tichelaar Bart W. , Ruff Larry J.
Published: February 2008

On May 23, 1989, a great (Mw=8.1) earthquake occurred in the Macquarie Ridge complex, south of New Zealand. The earthquake is one of the largest in the Macquarie Ridge complex this century, and represents the right‐lateral strike‐slip component of the motion between the Pacific plate and the Australian plate. Subduction initiation appears to be presently occurring in the Macquarie Ridge complex, and it has been suggested that plate boundary strike‐slip earthquakes in a transitional tectonic environment have a high stress‐drop. We have investigated the source rupture process of the 1989 earthquake, using teleseismic P and SH waves. The best point source depth is 12 km below the ocean bottom. The deconvolved source time function is dominated by a single pulse with a large moment release (1.8×1021 Nm) and a short duration (20 s). The moment rate increases slowly in the first 10 s of the rapture process, and is suddenly truncated at 20 s. There is no resolvable directivity to this sharp truncation, which given the temporal resolution of the data set, means that the spatial location of the sharp truncation is within approximately 50 km of the epicenter. The stress‐drop and average displacement may be as high as 370 bars and 36 m. These values are unusually high, and strongly support the suggestion that high stress‐drop earthquakes are characteristic for transitional tectonic environments.
Magnetotail acceleration using generalized drift theory: A kinetic merging scenario
Authors: Whipple E. G. , Rosenberg M. , Brittnacher M.
Published: February 2008

It is possible to describe particle behavior in the magnetotail, including particle energization, by means of generalized drift theory. Generalized drift velocities are obtained by using the generalized first invariant which has been shown to be useful in such current sheet configurations. Particles whose generalized invariant is preserved gain energy entirely in the field‐aligned direction. The form of the accelerated particle velocity distribution is obtained and self‐consistency conditions are derived.
VHF remote sensing for mapping river plume circulation
Authors: Forget P. , Devenon J. L. , De Maistre J. C. , Broche P. , Leveau M.
Published: February 2008

The VHF remote sensing radar technique is applied for mapping the current velocities off a river mouth. The river plume and its front are clearly observed in the data. The method appears to provide the convenient time and space resolutions for investigating the kinematics of these highly variable coastal events such as river plumes, even if it cannot at present achieve azimuthal diversity. The radar observations are felt to be particularly relevant for modelling small‐scale coastal circulation.
Feasibility of a synchronized correlation between Hawaiian hot spot volcanism and geomagnetiC polarity
Authors: Marzocchi Warner , Mulargia Francesco
Published: February 2008

If a correlation existed between the volcanic eruptive activity of the Hawaiian–Emperor chain and the Earth's magnetic field it would be a very important evidence of a link between outer core convection to Earth surface phenomena. In the quantitative definition of the problem, the main difficulty is the scarcity of reliable data. A careful scrutiny of the available data shows that a statistical study is possible only for the last 7.2 million years. In order to obtain a meaningful answer we apply two independent statistical tests related to the validity of the following hypotheses: a) the probability of occurrence of volcanic events is independent of polarity; b) the volume of the erupted material is independent of polarity. We find no evidence supporting the existence of a correlation between eruptive activity and geomagnetic polarity and hence there is no evidence for a direct link between the core and surface phenomena.
Underplating of the crust and xenolith geotherms in Australia
Authors: Cull James Phillip
Published: February 2008

Xenolith data indicate extreme geothermal gradients at shallow depth in eastern Australia contrary to results obtained from models based on thermal conduction. Consequently mechanisms involving partial melting accompanied by underplating must be assumed to supply additional heat unrelated to radiogenic profiles. A mid‐crustal heat‐source is required to satisfy the xenolith data suggesting a layered structure consistent with episodic underplating at maximum rates approaching 900m/Myr in eastern Australia.
Static compression of Ca(OH)2 at room temperature: Observations of amorphization and equation of state measurements to 10.7 GPa
Authors: Meade Charles , Jeanloz Raymond
Published: February 2008

We report x‐ray diffraction measurements on Ca(OH)2‐portlandite as it is compressed to 37.6 gigapascals (GPa) in the diamond cell at room temperature. Between 10.7 and 15.4 GPa crystalline Ca(OH)2 transforms to a glass, and on decompression the glass recrystallizes between 3.6 and 5.1 GPa. Below pressures of 10.7 GPa we measure the elastic compression of crystalline Ca(OH)2. A finite strain analysis of these data shows that the isothermal bulk modulus and its pressure derivative are K0 = 37.8 (±1.8) GPa and K0'= 5.2 (±0.7) at zero pressure. From the change in the unit cell dimensions, we find that the linear incompressibilities of Ca(OH)2 differ by a factor of three. These data show that hydrogen bonding can produce large anisotropies in the elastic properties of hydroxides. We infer from the amorphization that dense, high‐pressure phases of Ca(OH)2 exist at pressures of 11 GPa and above.
Broadband study of the 1989 Loma Prieta Earthquake
Authors: Kanamori Hiroo , Satake Kenji
Published: February 2008

We determined the source characteristics of the Oct. 18, 1989 Loma Prieta, California, earthquake using teleseismic data. The solution from body waves gives a mechanism with dip=70°, rake=138°, and strike=128°, and a seismic moment of 3×1026dyne‐cm (Mw=6.9). This solution is similar to those obtained from long‐period Rayleigh and Love waves, PnLwaves, and first‐motion data. The body wave form suggests a depth of about 15 km. The effective duration of the source is 6 sec, which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting, respectively. Considering the extent of the aftershock area, we used 35 km as an estimate of the total rupture length. The strike‐slip and the thrust components of the coseismic slip are 177 and 159 cm, respectively. The large thrust component raises an important question regarding the recurrence pattern. If the Loma Prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years, the 159 cm displacement implies a long term uplift rate of about 1 cm/year, which appears too large for this region. Three hypotheses for reconciling this apparent conflict are: (1) the geometry of plate motion along the Santa Cruz Mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief; (2) the coseismic sHp direction varies from event to event; (3) the slip plane of the 1989 Loma Prieta earthquake is different from the major boundary between the Pacific and the North American plates; if this is the case, the Loma Prieta earthquake is a rather rare non‐characteristic event. The surface slip of about l m for the 1906 San Francisco earthquake is one of the key data in long‐term forecasting. No surface slip was observed for the 1989 Loma Prieta earthquake, even if the horizontal slip at depth is as large as 1.8 m. This points to a risk of relying too heavily on surface observations for long‐term seismic risk analysis.
Temperature and density anti‐correlations in solar wind fluctuations
Authors: Zank G. P. , Matthaeus W. H. , Klein L. W.
Published: February 2008

We summarize recent theoretical investigations of low Mach number flows, that describe two distinct approaches by fluids to the incompressible regime. The first includes the effects of relatively strong density and temperature fluctuations (Type I), while the second places fluctuations in mechanical pressure, density and temperature on an equal footing (Type II). In the latter case, the pseudosound relations between density and pressure, in slightly generalized form, are recovered, whereas the former case yields entirely different small departures from incompressible behavior in that density and temperature fluctuations are predicted to be anti‐correlated. It is suggested that nearly incompressible fluids be classified as either Type I or II and it is shown that the well‐known pressure‐balanced structures represent a sub‐class of static solutions within this classification. Two examples from Voyager data illustrate the potential for observing these distinct nearly incompressible dynamical orderings in the solar wind.
Balloon observations of nitric acid aerosol formation in the Arctic stratosphere: II. Aerosol
Authors: Hofmann D. J. , Deshler T. , Arnold F. , Schlager H.
Published: February 2008

Balloonborne aerosol measurements over the size range r = 0.01 to 10 μm on 31 January 1990 are used to determine the HNO3 vapor mass deposited in Arctic nitric acid trihydrate (NAT) clouds in the 21–24 km region. The clouds consisted mainly of small (r≈ 0.2 μm) particles and appeared to have been formed during recent cooling because the r ≥ 0.15 μm aerosol concentration in the coldest part of the cloud was nearly equal to the condensation nuclei concentration, suggesting a large vapor supersaturation. The maximum inferred HNO3 vapor mixing ratio which condensed in the cloud was about 4 ppbv, in good agreement with the observed depletion of HNO3 vapor in the same altitude region under similar temperature conditions 23 hours earlier.
Small domes on Venus: Probable analogs of Icelandic lava shields
Authors: Garvin James B. , Williams Richard S.
Published: February 2008

On the basis of observed shapes and volumetric estimates, we interpret small, dome‐like features on radar images of Venus to be analogs of Icelandic lava‐shield volcanoes. Using morphometric data for venusian domes in Aubele and Slyuta (in press), as well as our own measurements of representative dome volumes and areas from Tethus Regio, we demonstrate that the characteristic aspect ratios and flank slopes of these features are consistent with a subclass of low Icelandic lava‐shield volcanoes (LILS ). LILS are slightly convex in cross‐section with typical flank slopes of ∼3°. Plausible lava‐shield‐production rates for the venusian plains suggest formation of ∼53 million shields over the past 0.25 Ga. The cumulative global volume of lava that would be associated with this predicted number of lava shields is only a factor of 3–4 times that of a single oceanic composite shield volcano such as Mauna Loa. The global volume of all venusian lava shields in the 0.5–20‐km size range would only contribute a meter of resurfacing over geologically significant time scales. Thus, venusian analogs to LILS may represent the most abundant landform on the globally dominant plains of Venus, but would be insignificant with regard to the global volume of lava extruded. As in Iceland, associated lavas from fissure eruptions probably dominate plains volcanism and should be evident on the higher resolution Magellan radar images.
Three‐dimensional convection under drifting plates
Authors: Cserepes László , Christensen Ulrich
Published: February 2008

Three‐dimensional numerical models are used to study the planform of thermal convection in rectangular boxes, imposing uniform velocity at the surface. This problem is relevant to the structure of mantle convection under moving tectonic plates. Different planforms can be obtained depending on the Rayleigh number, viscosity structure and length of the plate. If there is a thin low viscosity layer in the uppermost part of the model, the solution consists of narrow ascending plumes below the divergent edge of neighboring plates as well as descending sheets below lines of plate convergence. If the experimental box is long, well developed drifting columnar blobs arise from the unstable lower boundary layer, giving the solution an oscillatory character.
Energetic charged particle angular distributions near (r ≤ 2 RN) and over the pole of Neptune
Authors: Mauk B. H. , Kane M. , Keath E. P. , Cheng A. F. , Krimigis S. M. , Armstrong T. P. , Ness N. F.
Published: February 2008

Energetic ion ( > 28 keV) and electron ( > 22 keV) pitch angle distributions very close to (r ≤ 2RN) and over the north planetary pole of Neptune are presented using data from the Low Energy Charged Particle (LECP) and magnetometer (MAG) Experiments on the Voyager 2 spacecraft. The particle data are temporally structured and spectrally soft; a similarity with Earth‐like auroral signatures has previously been noted. However, the pitch angle distributions (showing trapped distributions at high magnetic latitudes) do not support an Earth‐like auroral interpretation, and alternative explanations for the temporal dynamics must be sought. Between r ∼ 1.6 and 2.0 RN and in the vicinity of the magnetic equator, the higher energy ion and electron pitch angle distributions (E ≥ 80 keV) display dramatic “bite‐outs” at ∼90°. This bite‐out feature could be caused by interactions with the newly discovered ring 1989N3R.
Short‐term variability of solar wind number density, speed and dynamic pressure as a function of the interplanetary magnetic field components: A survey over two solar cycles
Authors: Bowe G. A. , Hapgood M. A. , Lockwood M. , Willis D. M.
Published: February 2008

The variability of hourly values of solar wind number density, number density variation, speed, speed variation and dynamic pressure with IMF Bz and magnitude |B| has been examined for the period 1965–1986. We wish to draw attention to a strong correlation in number density and number density fluctuation with IMF Bz characterised by a symmetric increasing trend in these quantities away from Bz = 0 nT. The fluctuation level in solar wind speed is found to be relatively independent of Bz. We infer that number density and number density variability dominate in controlling solar wind dynamic pressure and dynamic pressure variability. It is also found that dynamic pressure is correlated with each component of IMF and that there is evidence of morphological differences between the variation with each component. Finally, we examine the variation of number density, speed, dynamic pressure and fluctuation level in number density and speed with IMF magnitude |B|. Again we find that number density variation dominates over solar wind speed in controlling dynamic pressure.
The magnetopause and boundary layer for small magnetic shear: Convection electric fields and reconnection
Authors: Paschmann G. , Sonnerup B. , Papamastorakis I. , Baumjohann W. , Sckopke N. , Lühr H.
Published: February 2008

Convection electric fields, Ec = −Vp×B, measured during a magnetopause/boundary layer encounter at low latitude by the AMPTE/IRM spacecraft, are shown to yield an accurate determination of the magnetopause normal vector, N, even though the magnetic shear across the magnetopause was small. The average plasma velocity along N is used to deduce a boundary layer thickness of about 1.3 RE. Analysis of Ec in the magnetopause itself reveals the existence of a deHoffmann‐Teller frame in which the flow is nearly field aligned and approximately Alfvénic, indicating that the magnetopause was a rotational discontinuity; this is interpreted as a signature that magnetic‐field reconnection was occurring somewhere on the magnetopause.
Longwavelength gravity anomalies and the deep thermal structure of the baikal rift
Authors: Diament Michel , Kogan Mikhail G.
Published: February 2008

The analysis of the gravity field over the Baikal rift area has been carried out in order: (1) to detect the amount of the deep hot material, and (2) to constrain the flexural rigidity of the lithosphere. We removed a few first harmonics of the global field and the gravity effects due to the crust from the observed field and found a residual anomaly which is aligned with the rift. This residual, which we attribute to the mantle, shows a minimum of about 15 mgal in amplitude and 900 km in width, which is superimposed over a wider minimum with smaller amplitude. A model involving a simple stretching of the lithosphere with diffusion of heat predicts right order of magnitude for both the amplitude and the wavelength of the “900‐km” anomaly. Our results confirm that the stretching factor is of the order of 1.2 to 1.5. Interpretation of the coherence function computed between gravity and topography shows that the lithosphere in the area has a significant equivalent elastic thickness of about 30 km (i.e. flexural rigidity about 2.3 1023N.m).
A search for long‐term periodicities in large earthquakes of southern and coastal central California
Authors: Stothers Richard B.
Published: February 2008

It has been occasionally suggested that large earthquakes may follow the 8.85‐year and 18.6‐year lunar‐solar tidal cycles and possibly the ∼ 11‐year solar activity cycle. From a new study of earthquakes with magnitudes ≥ 5.5 in southern and coastal central California during the years 1855–1983, it is concluded that, at least in this selected area of the world, no statistically significant long‐term periodicities in earthquake frequency occur. The sample size used is about twice that used in comparable earlier studies of this region which concentrated on large earthquakes.
Elasticity of a majorite‐pyrope solid solution
Authors: Bass Jay D. , Kanzaki Masami
Published: February 2008

The elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 percent Mg4Si4O12‐majorite (a high‐pressure form of pyroxene), have been measured by Brillouin spectroscopy under ambient conditions. Values of the adiabatic bulk modulus, Ks=164±15 GPa, and shear modulus, G = 89.4±3.7 GPa, are similar to those for low‐pressure aluminosilicate garnets. The enstatite‐majorite reaction is characterized by a large (49%) increase in Ks and a much smaller (13%) increase in G. The properties of low‐pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in Ca‐rich systems. Taken at face value, the STP properties of these phases imply that large quantities of Ca‐rich clinopyroxene are needed in order to satisfy seismiologically determined shear modulus gradients in the transition zone. This suggestion is, however, subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals, and the velocity structure of the transition zone.
Attenuation spectra of olivine/basalt partial melts: Transformation of Newtonian creep response
Authors: Green Douglas H. , Cooper Reid F. , Zhang Shanyong
Published: February 2008

The flexural creep responses of a Co‐Mg olivine‐plus‐basalt aggregate at temperatures near 1100°C have been transformed to give attenuation spectra (QE−1 vs. ω) as functions of temperature. The experimental creep response of this mantle‐analog material is well‐modeled as a Burgers solid, displaying a steady‐state creep that is preceded by a transient deceleration. Calculated attenuation spectra are based on the Burgers solid viscosities and elastic constants obtained from the creep experiments. The attenuation becomes total and zero in the low‐ and high‐frequency limits, respectively, as is appropriate for polycrystalline olivine having a diffusional creep rheology. At intermediate frequencies (10−4Hz to 10−2Hz), QE−1 experiences a local maximum. Both the magnitude (QE−1≈15) and central frequency of this loss maximum increase with temperature. The attenuation peak is an anelastic loss compatible with the transient creep response; it is inferred to represent a melt flow mechanism that adjusts the size of melt‐bearing triple‐grain junctions in response to changes in the stress state.
Unique chemistry of the hydrothermal solution in the mid‐Okinawa Trough Backarc Basin
Authors: Sakai H. , Gamo T. , Kim E‐S. , Shitashima K. , Yanagisawa F. , Tsutsumi M. , Ishibashi J. , Sano Y. , Wakita H. , Tanaka T. , Matsumoto T. , Naganuma T. , Mitsuzawa K.
Published: February 2008

Submarine hydrothermal fluids from JADE and CLAM sites in the mid‐Okinawa Trough Backarc Basin are highly enriched in CO2, K, Li, NH4, CH4 and titration alkalinity compared to MOR fluids so far studied, while their H2S and 3He contents are similar. The He and C isotopic ratios as well as these chemical features indicate that the hydrothermal systems are controlled by reaction between seawater and CO2‐rich intermediate to acid volcanic rocks of island‐arc type, with strong influence of organic matter and are consistent with its initial stage of rifting on a continental plate margin. While the endmember JADE fluid is nearly devoid of Mg and SO4, the CLAM fluid has definite concentrations of Mg (upper limit 22 ± 5 nM) and, most interestingly, of 34S‐enriched SO4 (upper limit 10 ± 2 mM, δ34S= 27 to 39‰).
Flow trajectories in the Bering Sea: Evidence for chaos
Authors: Reed R. K. , Stabeno P. J.
Published: February 2008

A set of trajectories from drifting buoys in the Bering Sea is analyzed for evidence of chaos. The separation distance between drifters was found, in most cases, to have regions of exponential increase, which strongly suggests Lagrangian chaos. Analysis of the Kolmogorov entropy indicated a fractal dimension of 1.2 and a time scale of (22 d)−1.
Measuring precise sea level from a buoy using the global positioning system
Authors: Rocken Christian , Kelecy Thomas M. , Born George H. , Young Larry E. , Purcell George H. , Wolf Susan Kornreich
Published: February 2008

High‐accuracy sea surface positioning is required for sea floor geodesy, satellite altimeter verification, and the study of sea level. An experiment to study the feasibility of using the Global Positioning System (GPS) for accurate sea surface positioning was conducted. A GPS‐equipped buoy (floater) was deployed off the Scripps pier at La Jolla, California during December 13–15, 1989. Two reference GPS receivers were placed on land, one within ∼100 m of the floater, and the other about 80 km inland at the laser ranging site on Monument Peak. The position of the floater was determined relative to the land‐fixed receivers using: (a) kinematic GPS processing software developed at the National Geodetic Survey (NGS), and (b) the Jet Propulsion Laboratory's GIPSY (GPS Inferred Positioning SYstem) software. Sea level and ocean wave spectra were calculated from GPS measurements. These results were compared to measurements made with a NOAA tide gauge and a ParosTMpressure transducer (PPT). GPS sea level for the short 100‐m baseline agrees with the PPT sea level at the 1‐cm level and has an rms variation of 5 mm over a period of 4 hours. Agreement between results with the two independent GPS analyses is on the order of a few millimeters. Processing of the longer Monument Peak ‐ floater baseline is in progress and will require orbit adjustments and tropospheric modeling to obtain results comparable to the short baseline.
Laboratory measurements of NO2 line parameters near 1600 cm−1 for the interpretation of stratospheric spectra
Authors: May R. D. , Webster C. R.
Published: February 2008

Tunable diode laser laboratory measurements of infrared spectral parameters of selected NO2 lines near 1600 cm−1 have been made to assess the contribution of uncertainties in these parameters to stratospheric measurements of NO2 made using the Balloon‐borne Laser In‐Situ Sensor (BLISS) tunable diode laser spectrometer. Relative line intensities are measured to accuracies of better than 2%, with a root‐sum‐squared uncertainty in the absolute linestrengths of 4.5%. Air‐broadening coefficients have been determined from measurements at total pressures in the range 20–100 Torr, at températures of 293 K and 214 K. These results are also discussed in the light of the discrepancies between infrared instruments flown in the 1982 and 1983 Balloon Intercomparison Campaigns.
Airborne and vapor phase hydrocarbons over the Mediterranean Sea
Authors: Marie‐Alexandrine Sicre , Jean‐Claude Marty , Anne Lorre , Alain Saliot
Published: February 2008

n‐Alkane distributions and concentrations have been determined in the atmospheric particulate and gas phases for samples collected over the Mediterranean Sea. Distributions of airborne alkanes exhibited a strong odd to even predominance in the C22‐C38 range associated with the presence of unresolved compounds indicating a mixture of terrigenous and anthropogenic inputs. Variations in their concentration levels could be related to the origin of air masses. Solvent extractable gas phase n‐alkanes dominated in the C15‐C22 range with a slight predominance of n‐C17 except in one sample were C18 and C20 were dominant. A hump of unresolved compounds shifted toward low molecular weight was observed in all the samples. The origin of vapor phase hydrocarbons is discussed with respect to the composition of seawater samples collected during the same cruise. From lifetime and transport time considerations as well as distribution features, both marine and continental origins, likely anthropogenic, are suggested. The strong terrigenous signal of the suspended particles in the microlayer and underlying waters is attributed to aerosol deposition. The dissolved alkane compositional feature suggested both marine and anthropogenic sources.
Balloonborne measurements of polar stratospheric clouds and ozone at‐93° C in the Arctic in February 1990
Authors: Hofmann D. J. , Deshler T.
Published: February 2008

Balloonborne measurements of ozone and particle size distributions at Kiruna, Sweden indicate that on 6 February 1990 a major cooling event occurred over northern Scandinavia, reaching temperatures as low as −93° C at 22 km. Both nitric acid trihydrate and water ice clouds formed in the 19 to 23 km region. The temperature of the appearance of the water ice clouds is consistent with about 5 ppmv of water vapor at 22 km, The particle size distributions suggest that a sizeable degree of denitrification had occurred in the 19 to 23 km region in this air mass. Although ozone levels may have been reduced by a small degree of chemical depletion, the ozone “minihole” of 165 DU observed by TOMS was probably an artifact caused by ice clouds at 22 km since two ozonesonde measurements on that day indicated total ozone values of about 285 DU.
temporal evolution of HF‐enhanced plasma lines
Authors: Kuo S. P. , Ho A. Y. , Lee M. C.
Published: February 2008

The temporal evolution of HF‐enhanced plasma lines (HFPLs) is investigated theoretically. The HFPLs refer to the radar echoes at frequencies near the sum and difference of the radar frequency and the HF heater wave frequency. These enhanced spectral lines are caused by backscatter of radar signals from plasma waves having a wavenumber of 18 m−1. A nonlinear theory has been developed to explain both the intensity overshoot and altitude expansion of HFPLs observed at Arecibo, Puerto Rico [Djuth and Sulzer, 1989] with good agreement.