bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic and elastic properties of calcareous sediments across a siliceous diagenetic front on the eastern U.S. continental slope
Authors: Guerin Gilles , Goldberg Dave
Published: February 2004

The Ocean Drilling Program drilled Hole 904A on the upper continental slope offshore New Jersey through 230 m of Eocene chalks and an opal‐A/opal‐CT diagenetic front. In addition to a suite of standard logging tools, a dipole sonic tool was deployed to determine the in situ shear sonic velocity and the elastic properties of these slow, highly porous, sediments. While porosity decreases by 20% across the diagenetic front, the compressional velocity and the density are observed to increase by 30%, the shear sonic velocity and the bulk modulus by about 60%, and the shear modulus by almost 300%. It is shown that shear and compressional velocities are both controlled by porosity and consolidation, and that existing models for the prediction of elastic properties and shear velocity from standard logs are still valid through the diagenetic front. The strong effect of diagenesis on rigidity makes the shear velocity log a highly sensitive indicator of pore shape and pore filling transformations.
A discussion on “The 410‐km‐depth discontinuity: A sharpness estimate from near‐critical reflections” by Vidale et al.
Authors: Krishna V. G. , Ramesh D. S.
Published: February 2004

Vidale et al. [1995] presented a convincing evidence of a fairly sharp ‘410‐km’ seismic discontinuity uncjer the western United States by examining clear noise‐free reflected arrivals from this discontinuity in the near‐critical distance range of 11.5° to 14° (Fig. Ia). They reconstructed the P velocity‐depth model from the arrival times of the 410‐km reflection and initial P waves across the distance range 8°–14°. The prominent features of the upper mantle P velocity model given by them include; a low velocity layer (LVL) in the depth range of about 110–200 km with a broad transitional bottom, a fairly large velocity gradient (0.4 km/s velocity increase from 200 to 410 km depth) above the 410‐km discontinuity which is sharp and associated with a 5.5% velocity increase.

Seismic estimates of sharpness as well as velocity contrast at the ‘410‐km’ and ‘660‐km’ discontinuities in the mantle transition zone provide important constraints to plausible models of composition, temperature and convective processes in the deep earth. The rapid increases of seismic wave velocities inferred in the transition zone, at depths of 410‐Km and 660‐km, are classically associated [Ringwood, 1975] with the pressure‐induced phase transitions in Olivine which is considered to be the predominant mineral in the upper mantle. Recent observations of high quality coherent seismic reflections from the transition zone [Benz and Vidale, 1993; Vidale et al., 1995] conclusively reveal that the 410‐km discontinuity is fairly sharp. Contrastingly the experimental results from mineral physics [Akaogi et al., 1989; Bina and Wood, 1987; Katsura and Ito, 1989] predict a substantially larger transition width, on the order of 6–19 km for the olivine‐beta spinel phase transition at pressures corresponding to 410‐km‐depth discontinuity. Similar inconsistencies in the magnitude of velocity contrast at the 410‐km discontinuity are also found [Duffy et al., 1995; Jeanloz, 1995] by comparison of results from modern seismic measurements and the new experimental models of the olivine‐beta spinel phase transition, the latter revealing a relatively large contrast. In view of these apparently contradicting results it is certainly critical to evaluate the high quality seismic data [Vidale et al., 1995] for reliable estimates of both sharpness and velocity contrast of the 410‐km discontinuity in order to consider its traditional association with the simple phase transition in the olivine dominated compositional model.
A 3D Gravimetric Crustal Model for the northeastern region of the Iberian Peninsula
Authors: Suriñach Emma , Chávez René E.
Published: February 2004

We combine different methodologies normally used separately in exploration geophysics to obtain the topographies of the Moho discontinuity and the boundary between the upper and lower crusts by separating their effects in the Bouguer anomaly map. The SFM method was used to define the average depth of the layers causing the anomalies. The resulting three‐dimensional model which reproduces the observed gravity anomaly was estimated by inverting the corresponding domains of the power spectrum. A good correlation exists between the calculated depths and the upper and lower boundaries of the layered lower crust observed along the reflection seismic lines in the area.
A scan‐angle correction for thermal infrared multispectral data using side lapping images
Authors: Watson Ken
Published: February 2004

Thermal infrared multispectral scanner (TIMS) images, acquired with side lapping flight lines, provide dual angle observations of the same area on the ground and can thus be used to estimate variations in the atmospheric transmission with scan angle. The method was tested using TIMS aircraft data for six flight lines with about 30% sidelap for an area within Joshua Tree National Park, California. Generally the results correspond to predictions for the transmission scan‐angle coefficient based on a standard atmospheric model although some differences were observed at the longer wavelength channels. A change was detected for the last pair of lines that may indicate either spatial or temporal atmospheric variation. The results demonstrate that the method provides information for correcting regional survey data (requiring multiple adjacent flight lines) that can be important in detecting subtle changes in lithology.
Fluxes of mantle and subducted carbon along convergent plate boundaries
Authors: Sano Yuji , Williams Stanley N.
Published: February 2004

The potential impact of increases in atmospheric CO2 is a topic of considerable controversy. Even though volcanic emission of CO2 may be very small as compared to anthropogenic emissions, evaluation of natural degassing of CO2 is important for any model of the geochemical C cycle and evolution of the Earth's atmosphere. We report here the mantle C flux in subduction zones based on He and C isotopes and CO2/³ He ratios of high‐temperature volcanic gases and medium‐ and low‐temperature fumaroles in circum‐Pacific volcanic regions. The calculated volcanic C flux of 3.1 × 1012 mol/a from subduction zones is larger than the flux of 1.5 × 1012 mol/a from mid‐ocean ridges, while contributions from the mantle in subduction zone is only 0.30 × 1012 mol/a, equivalent to about 20% of the C flux in mid‐ocean ridges. Since the estimated mantle C flux in hot spot regions is insignificant, 0.029 × 1012 mol/a, we propose that the global mantle C flux is 1.8 × 1012 mol/a in total. The flux, if accumulated over 4.5 billion year of geological time, amounts to 8.3 × 1021 mol which agrees well with 9 × 1021 mol of the present inventory of C at the Earth's surface. This may support a continuous degassing model of C or the idea that subducted C is recycled into the lower mantle.
Seismic activity triggered by stress changes after the 1978 events in the Asal Rift, Djibouti
Authors: Jacques E. , King G. C. P. , Tapponnier P. , Ruegg J. C. , Manighetti I.
Published: February 2004

Following a sequence of earthquakes in the Asal Rift in November 1978, the deformation resulting from dyke emplacement and associated faulting was measured geodetically and using teleseismic data. Using this information we have computed the resulting Coulomb stress changes, which can explain the features of the distribution of seismicity for the following six weeks. A further major shock then occurred. When this event is included in the modelling, the distribution of all the seismicity within a radius of 40 km in the following 4 years is predicted. The study confirms that increases of Coulomb stress as small as 0.3 bars are sufficient to trigger earthquakes and shows that dykes as well as fault slip can result in stress changes that influence the seismicity distribution over a broad region.
Decametric radiation at the time of the Hyogo‐ken Nanbu Earthquake near Kobe in 1995
Authors: Maeda Koitiro , Tokimasa Noritaka
Published: February 2004

The Hyogo‐ken Nanbu earthquake (JMA Magnitude = 7.2) occurred on January 17, 1995, near Kobe in Hyogo‐ken prefecture, Japan. Unusual pulsed radio emissions at 22.2 MHz (wavelength = 13.5 m) were detected with a radio interferometer at Nishi‐harima Astronomical Observatory, located about 77 km from the epicenter, both before and after this earthquake. These data indicate that one of the most probable source regions was the central part of the Nojima fault, about 25 km from downtown Kobe, and the average pulsed power appeared to be about 0.2 W.
Linearization pseudo‐noise and its effect on the retrieval of atmospheric state from infrared spectral radiances
Authors: Amato U. , De Feis I. , Serio C.
Published: February 2004

Remote sounding of earth's atmosphere from upwelling infrared radiances is highly non‐linear. A linearization step is typically involved in seeking for suitable solutions. This letter discusses possible problems which arise when combining the linearization step with schemes aimed at solving the inverse problem. Possible strategies which could be able to get rid of such problems are discussed, too.
Electromagnetic core‐mantle coupling and paleomagnetic reversal paths
Authors: Aurnou J. M. , Buttles J. L. , Neumann G. A. , Olson P. L.
Published: February 2004

Calculations of electromagnetic torques between the fluid outer core and the heterogeneous lower mantle demonstrate that the geomagnetic field can lock with the mantle during polarity transitions. We show that the Virtual Geomagnetic Pole (VGP) is attracted toward mantle regions with low electrical conductivity and repelled from mantle regions with high conductivity. Using seismically‐determined structure of the lower mantle to infer the pattern of conductivity variations at the base of the mantle, we find two preferred reversal routes for the VGP, one beneath the Americas and another beneath Asia. These paths, particularly the one beneath the Americas, lie close to the VGP paths seen in some sedimentary and lava records of polarity reversals, suggesting that the core and mantle are electromagnetically coupled during reversals.
Application of theoretically derived rock physics relationships for clastic rocks to log data from the Wilmington Field, CA
Authors: Moos D. , Dvorkin J. , Hooks A. J.
Published: February 2004

Relationships between porosity and shear modulus are applied to logs recorded in the Miocene Upper Terminal formation of the Wilmington Field, CA. to predict porosity from shear‐wave velocity data recorded through casing using a dipole sonic logging tool. A relationship based on a modified Hashin‐Shtrikman lower bound, appropriate for the unconsolidated nature of the formation, allows determination of porosity from the shear modulus. The results are similar to those obtained using standard log analysis in sands. Standard logs predict higher porosities in smectite‐bearing wackes because of the inclusion in the standard analysis of bound water or micro‐porosity in the clays which is not included in the porosity value derived from the shear‐wave velocity.
On the presence of aggregates in the basins of Lake Banyoles
Authors: Casamitjana Xavier , Colomer Jordi , Roget Elena , Teresa Serra
Published: February 2004

Suspension of sediment by subterranean springs is a very common phenomena in the karstic, multibasin Lake Banyoles. The flow of groundwater into the lake introduces a suspension of marly and argilaceous materials. The temperature of this slurry is nearly constant throughout the year, around 19°C. The lake is formed by 6 basins and at the bottom of these basins there are 12 sources where the presence of suspended material signifies entering groundwater (Figure 1). Suspension of bottom lake sediment by groundwater is a feature of Lake Banyoles that has not been described elsewhere. Here we present experimental results which show that the maximum height that the sediment can rise to is affected by the formation of aggregates.
The temporal evolution of 3–9 MeV/nucleon He flux trapped in the magnetosphere
Authors: Pugacheva G. I. , Gusev A. A. , Martin I. M. , Spjeldvik W. N. , Kohno T.
Published: February 2004

Results of measurements of the absolute values and long term temporal evolution of the spatial distribution of trapped He ion fluxes of 3.2–9.2 MeV/nucleon energy at L <4 obtained by the OHZORA satellite are reported. The annually averaged radial profile exhibits one persistently present peak at L=1.3–1.5 as well as very significant transient trapped fluxes at L=1.4–4.0 during the period 1984–1986. Together the absolute values of the fluxes measured by OHZORA and S72‐1, SAMPEX, and CRRES spacecrafts may approximately be described by a power spectrum with index of −8.0±1.0 at L=1.9–2.3 within the energy range of 3–100 MeV/nucleon.
A simple transport model for the Io plasma torus “ribbon”
Authors: Herbert Floyd
Published: February 2004

A model for the generation of the Io plasma torus “ribbon” density feature is proposed. In this model a self‐regulation mechanism for plasma pressure is hypothesized, operating through ring current inhibition of flux‐tube interchange transport. Torus plasma outflow drives hot plasma from the middle magnetosphere inwards, raising its confining pressure and impeding further outflow of torus plasma. As the hot plasma cools by collisions with torus ribbon electrons its pressure diminishes, allowing more torus outflow. This negative feedback modulates torus ion flux‐tube content NL² in such a way as to hold it relatively constant. In order to simulate this process, we have constructed numerical models which approximate plasma transport by a non‐linear diffusion process, with the feedback mechanisms built into the diffusivity. For certain reasonable parameter values, these models produce a density enhancement near L = 5.6 to 5.8 which somewhat resembles the “ribbon” feature that is actually observed near that position.
High pressure constraints on percolative core formation
Authors: Shannon M. C. , Agee C. B.
Published: February 2004

The effect of pressure on the wetting behavior of liquid Fe‐Ni‐S alloy in a solid silicate matrix was investigated. Experiments were performed on a chondritic starting material in piston‐cylinder and multi‐anvil apparatuses over a pressure range of 2 to 20 GPa, at temperatures below the silicate solidus. The dihedral angle of the quenched liquid iron alloy in contact with the silicate matrix exhibited no change over the pressure interval. The average value of 108° for the dihedral angle is well above the 60° critical value for efficient percolation of iron alloy through a solid matrix, therefore core formation by percolation at upper mantle pressures is not feasible. We conclude that melting of the silicate mantle may be required for efficient planetary core formation.
Magnetic properties of synthetic milled and annealed titanomagnetite (Fe2.3Ti0.7O4) particles 1–125 µm in diameter and analysis of their microcrystalline structure
Authors: Zitzelsberger A. , Schmidbauer E.
Published: February 2004

Magnetic hysteresis properties were measured on dispersed synthetic milled titanomagnetite (Fe2.3Ti0.7O4) particles in the range 1–125 µm and after annealing. Milling is thought to introduce internal stresses in the particles by increasing the dislocation density that is reduced again by annealing. Thus, it was intended to investigate the stress‐dependence of magnetic parameters. The particles were examined by mineralogical and crystallographic methods in the milled state and after annealing. Small particles (1–2 µm) were very inhomogeneous after milling with anisotropic strains and a crystallite size of ≈ 50 nm as found from X‐ray line broadening; annealing led to increased crystallite size but hardly reduced strains. For larger grains, an outer ≈1 µm thick ‘damaged’ shell was detected that could be removed by etching or recrystallized by annealing. After these procedures, particles showed reduced coercive force and reduced relative saturation remanent magnetization. The two‐shell behaviour of milled 10–15 µm particles could be seen from wasp‐waisted hysteresis curves that disappeared after etching or annealing. For larger particles these effects were reduced.
Statistical acceleration of interstellar pick‐up ions in co‐rotating interaction regions
Authors: Schwadron N. A. , Fisk L. A. , Gloeckler G.
Published: February 2004

Observations from the SWICS instrument on Ulysses reveal that there is little evidence for the acceleration of interstellar pick‐up ions at the forward and reverse shocks which surround Co‐rotating Interactions Regions (CIR's) in the solar wind. Rather, the pick‐up ions exhibit strong acceleration in regions within the CIR where there are increased variations in the magnitude of the magnetic field. A simple model is presented in which the pick‐up ions are statistically accelerated by transit‐time damping the magnitude variations. The model yields the observed distribution functions for the accelerated pick‐up ions.
Late Quaternary variations in relative sea level due to glacial cycle polar wander
Authors: Bills Bruce G. , James Thomas S.
Published: February 2004

Growth and decay of continental ice sheets can excite significant motion of the Earth's rotation pole and cause a complex spatio‐temporal pattern of changes in relative sea level. These two effects have generally been considered separately, but may interact in important ways. In particular, a simple model of the melting of the Laurentide ice sheet causes a uniform eustatic sea level rise of 55 m, and also induces a motion of the rotation pole by 0.1 to 1 degree, depending on viscosity structure in the mantle. This motion produces a secular pole tide, which is a spherical harmonic degree 2, order 1 component of the relative sea level pattern, with peak‐to‐peak amplitude of 20 to 40 m. The maximum effect is along the great circle passing through the path of the pole and at latitudes of ±45°. This secular pole tide has been ignored in most previous attempts to estimate ice sheet loading history and mantle viscosity from global patterns of relative sea level change. It has a large influence along the East coast of North America and the West coast of South America, and significantly contributes to present day rates of relative sea level change.
Seismic anisotropy in ocean basins: Resistive drag of the sublithospheric mantle?
Authors: Tommasi Andréa , Vauchez Alain , Russo Raymond
Published: February 2004

We use finite‐element models to evaluate the effect of asthenospheric strain associated with the motion of an oceanic plate over a presumed stationary mantle on shear wave splitting observations. Modeled velocity profiles display a clear strain localization within a horizontal shear zone several tens of kilometers wide developed between an almost rigid mechanical lithosphere and a mildly deformed upper mantle. For young oceanic lithosphere, cooling results in migration of the maximum shear strain rate towards deeper levels and progressive widening of the shear zone. Shear strain accumulates with plate displacement. The deformed layer thickness depends on plate age and velocity. Seismic anisotropy depends on the preferred orientations of olivine developed, and thus on the strain field. For a ray propagating vertically (e.g., SKS) the fast wave will be polarized parallel to the flow direction, i.e., the APM. The delay time will depend on the thickness of the sheared layer and on its intrinsic anisotropy. It will therefore increase away from the ridge at a progressively decreasing rate and depend on the absolute plate velocity. The estimated anisotropies agree with seismic anisotropy measurements in old domains of ocean basins, suggesting that, away from mid‐ocean ridges, this simple model may provide a first approximation of the mechanism responsible for the observed seismic anisotropy.
Fastest known spreading on the Miocene Cocos‐Pacific Plate Boundary
Authors: Wilson Douglas S.
Published: February 2004

New magnetic anomaly identifications for the central part of the Cocos plate and the corresponding part of the Pacific plate indicate a pulse of extremely rapid seafloor spreading in the middle Miocene, about 11–18 Ma, possibly beginning as early as 25 Ma. The spacing of anomalies 5A–5D indicates a full spreading rate for the southern Cocos‐Pacific boundary of 180–210 mm/yr, depending on the choice of time scale. Relative to the maximum 0–3 Ma spreading rate of 152 mm/yr, this result significantly expands the upper limit of well documented rates.
A new tool for determining ionospheric currents from magnetic satellite data
Authors: Olsen Nils
Published: February 2004

An algorithm for determining ionospheric currents at high latitudes from magnetic measurements made by low altitude satellites is presented and illustrated using MAGSAT data. The ionospheric currents are assumed to flow in a height of 115 km perpendicular to the orbit plane of the satellite, which corresponds to East‐West direction in the case of the dawn/dusk MAGSAT orbit. The method allows for studying the time development of both the strength and the location of the auroral electrojets. Application to 13 days of MAGSAT data in winter 1979 yields a correlation coefficient of r=0.88 between the AE‐index and the strength of the auroral electrojets; their latitudinal location moves southward with increasing magnetospheric ring current as measured by the Dst‐index.
Crustal thickness variations beneath the peninsular ranges, southern California
Authors: Ichinose Gene , Day Steven , Magistrale Harold , Prush Ted , Vernon Frank , Edelman Adam
Published: February 2004

We investigate the crustal thickness under the Peninsular Ranges using P‐to‐S converted phases of teleseismic body waves recorded on a temporary broadband seismometer array and isolated by the receiver function method. Ps minus P times at sites west of a compositional boundary that separates the Peninsular Ranges batholith into east and west zones indicate a relatively flat, deep Moho. Ps minus P times at sites east of the compositional boundary decrease eastward, Moho depth estimates (made from the Ps delays and crustal velocities from seismic tomography) indicate a relatively constant 36 to 41 km thick crust in the western zone. In the eastern zone the crust thins rapidly from 35 km thick at the compositional boundary to 25 km at the edge of the Salton trough, a lateral distance of 30 km. The lack of correlation between topography and Moho depths suggests compensation via lateral density variations in the lower crust or upper mantle. We propose that the compositional boundary decouples the eastern and western portions of the batholith, and that the eastern portion has thinned in response to regional Miocene extension, or Salton trough rifting, or both.
The influence of non‐regularly decaying coda wave envelopes upon the estimation of coda Q
Authors: Doherty John T. , Bean Christopher J.
Published: February 2004

The single isotropic scattering model proposed for the origin of seismic coda predicts a regularly decaying coda wave envelope. In real data however, this regular decay is often interrupted by non‐random arrivals (e.g. reflections) coming later in the coda. This additional energy may be due to clustered scatterers and represents a departure from the inherent assumption in the theory that the scatterers are uniformly randomly distributed. We have simulated the effect of clustered scatterers in synthetic seismograms in order to investigate their influence upon the measured coda Q (Qc). We show that the position and amplitude of such arrivals within the otherwise regularly decaying coda give rise to elevated Qc estimates. Often this additional energy in the coda is difficult to detect on a single isolated seismogram as evidenced by an example from the 1994 Northridge California earthquake. We therefore recommended that where possible, the use of seismic arrays (commonly reserved for P‐wave coda studies) be extended to S‐wave coda studies to aid in the detection of clustered scatterers, prior to the calculation of Qc.
Reply [to “Comment on ‘Mars as the parent body of the CI carbonaceous chondrites’ by J.E. Brandenburg”]
Authors: Brandenburg John E.
Published: February 2004

The simplest interpretation of present data remains that Mars is the parent body of the CIs.
Intense local toroidal motion generated by variable viscosity compressible convection in 3‐D spherical‐shell
Authors: Zhang S. , Yuen D. A.
Published: February 2004

Strong dynamical effects arising from lateral viscosity variations are found near the heads of fast‐upwelling plumes approaching the top boundary for unsteady 3‐D compressible convection in a spherical geometry at an average Rayleigh number of O(106). The temperatures at the center of fast‐upwelling plume are very hot due to the positive feedback interaction between viscous dissipation and temperature‐dependence of the viscosity. Although the laterally averaged ratio of toroidal to poloidal energy varies only around 10%, the local toroidal velocities can reach about 40% of the poloidal velocities. The strongest toroidal motions always take place right above or close to the fast upwelling plume heads and behave as vortical flows with time. This finding may explain the origins of microplate rotation in regions with hotspot activity (e.g. Easter Island), which shows no direct relation to the transform‐faulting system near the mid‐ocean ridge.
Problems with imaging cellular hydrothermal convection in oceanic crust
Authors: Davis Earl E. , Chapman David S.
Published: February 2004

Heat‐flow variations are commonly used to infer the existence of hydrothermal convection in young oceanic crust and, in special cases, the geometry and vigor of convection. In a small area on the eastern flank of the Juan de Fuca Ridge where the sea floor and seismic basement relief are only about 10 m, a coherent pattern of heat‐flow variation having 40 mW m−2 peak‐to‐peak amplitude and half‐wavelength of about 600 m has been previously observed and interpreted to be caused by cellular convection within the extrusive layer 2a of the oceanic crust. In August, 1995, new seismic reflection and heat‐flow data were collected to define better the structure of basement in this area, and to determine the planform of the heat‐flow variations revealed along the single transect of the earlier observational study. The new, higher resolution seismic results show considerable intra‐crustal structure; in particular, the uppermost crust is reverberant beneath areas of lower heat flow, and a diffractive character extends close to the basement surface beneath areas of higher heat flow. This relationship suggests that the heat‐flow variations may be caused by variations in depth to the top of a high‐permeability intracrustal zone that is not coincident with acoustic basement, where relatively uniform temperatures are maintained by vigorous hydrothermal circulation of unresolved planform. If this is the case, the search that began in the 1970's for heat‐flow variations that might reveal the scale of cellular convection, and hence by inference the penetration depth of hydrothermal circulation in the oceanic crust, may have been frustrated once again.
Diffusion creep of fine‐grained polycrystalline anorthite at high temperature
Authors: Wang Z. , Dresen G. , Wirth R.
Published: February 2004

We performed creep experiments on synthetic fine‐grained polycrystalline anorthite (d < 30 µm) at temperatures from T = 1000°C to 1300°C, oxygen fugacities of fO2 = 10−19–10−4 MPa, and stresses of σ = 5–80 MPa at room pressure. Experimental results show creep with high strain‐rate sensitivity for stresses below σ < 30 MPa. We found the empirical flow law: Transmission electron microscopy shows that the material is free of melt. The dislocation density is less than 1×108 cm−2. We suggest that the samples deformed in diffusion‐controlled grain size sensitive creep.
Depth of the upper mantle discontinuities beneath the East Pacific Rise
Authors: Lee Duk‐Kee , Grand Stephen P.
Published: February 2004

We observe discontinuities at depths of 415 and 655 km beneath the northern East Pacific Rise (EPR). The data consist of precursors to SS waves from 71 tangential component seismograms ranging in epicentral distance from 107° to 167°. The mid‐points of the paths are beneath the northern EPR region with about half the data bouncing beneath ocean younger than 9 Ma. The SS phases were aligned and then time shifted to account for the ocean age at the bounce point. The data were then stacked to remove theoretical moveout for underside reflections from the transition zone. The stacked results show clear underside reflections. These values are slightly more shallow than recently derived average values for oceans but the depth difference between the discontinuities is almost identical to the average for all oceans (Shearer, 1996). Although the absolute depths are dependent on the velocity model used in the estimate, the depth difference in the discontinuities is not sensitive to velocity structure. Our results suggest there are not unusually hot temperatures within the transition zone beneath the EPR relative to average ocean. This implies that deep upwelling beneath the ridge, if it exists, is passive.
Recent apparent changes in relationships between the El Niño‐Southern Oscillation and Australian rainfall and temperature
Authors: Nicholls Neville , Lavery Beth , Frederiksen Carsten , Drosdowsky Wasyl , Torok Simon
Published: February 2004

High quality historical temperature and rainfall data sets have been used to produce time series of annual rainfall and temperature, averaged over Australia. The relationships between these series, and with the Southern Oscillation Index, have been examined. A change in the relationships between the variables appeared in the early 1970s. Since then, for any value of the SOI or rainfall, maximum temperature has tended to be higher than previously. Likewise, rainfall, for any value of the SOI, has tended to be greater than would have been expected for such an SOI value in previous years. Artificial changes, such as changes in instrumentation, seem unlikely to account for these observed changes in relationships. Model experiments have duplicated some of the changes in the relationships. Increased Indian Ocean temperatures may be the causal factor underlying these changes.
Ozone and aerosol observed by lidar in the Canadian Arctic during the winter of 1995/96
Authors: Donovan D. P. , Bird J. C. , Whiteway J. A. , Duck T. J. , Pal S. R. , Carswell A. I. , Sandilands J. W. , Kaminski J. W.
Published: February 2004

Lidar observations of stratospheric ozone made at Eureka (80.0°N, 86.42°W) during the 95/96 winter show substantial declines in ozone mixing ratios. Reductions in ozone levels of up to 40% between the 410 K and 580 K isentropic levels were observed between mid‐January and mid‐March. The correlation of the ozone data with potential vorticity and concurrent lidar observations of stratospheric aerosol is consistent with the claim that significant chemical depletion did occur.
Relationships of inter‐american rainfall to tropical Atlantic and Pacific SST variability
Authors: Enfield David B.
Published: February 2004

Area‐averaged anomalies of sea surface temperature (SSTA) and rainfall, developed from large scale data sets, have been used to explore the relative importance of Pacific versus Atlantic SST variability for inter‐American (50°S–50°N) climate variability at interannual time scales. SSTA in the tropical Pacific and tropical North Atlantic are comparably related to rainfall north of 15°S, with clear associations distributed between the southeastern United States (US) in the north and northern South America in the south. Although NINO3 explains 25% of the variance of the North Atlantic SSTA index, the rainfall correlations with North Atlantic SSTA are for the most part opposite in sign to those with NINO3. Hence, a significant part of the Atlantic SSTA probably has a direct association with rainfall, rather than being merely an indirect proxy for Pacific ENSO linkages. In contrast to the North Atlantic, South Atlantic SSTA appear to be only related to rainfall in northeast (NE) Brazil. The entire region between Venezuela and NE Brazil appears to be sensitive to both the ITCZ and to antisymmetric configurations of SSTA across the ITCZ, in a manner consistent with the relationships between SST, surface wind and surface wind divergence fields, and with previous studies.
Characteristics of mid‐latitude whistler ducts as deduced from ground‐based measurements
Authors: Ohta K. , Kitagawa T. , Shima N. , Hayakawa M. , Dowden R. L.
Published: February 2004

Propagation characteristics of mid‐latitude whistlers, especially whistler duct characteristics, have been investigated based on measurements in August, 1994 at Dunedin, New Zealand(L=2.78) and in August, 1989 at Ceduna, Australia(L=1.93), both during local midnight. Polarization analyses have enabled us to locate whistlers which exited the ionosphere just above the observing station (LDF is defined in this way). The nose extension method was also applied to these whistlers (their Ln is estimated by this method). The following findings have emerged from the analyses; LDF ≃ Ln (at Dunedin) and LDF ≃ Ln‐0.43(at Ceduna). Our analysis suggests that mid‐latitude ducts are likely to extend down to the ionosphere at L ≈ 2.8. Ray tracing studies for realistic density profiles indicates that a whistler duct terminates at an altitude of about 3,500 ∼ 5,500 km at an L value of ∼1.9 with its enhancement factor being a few percent at least. These results may imply a strong variability of the latitudinal or temporal variations of mid‐latitude whistler ducts.
Heat flow highs on the Norwegian‐Barents‐Svalbard continental slope: Deep crustal fractures, dewatering, or “memory in the mud”?
Authors: Vogt Peter R. , Sundvor Eirik
Published: February 2004

Heat flow transects across the Norwegian‐Barents‐Svalbard continental margin (Sundvor and Eldholm, 1992) reveal anomalously high (by about 60 mK/m) sub‐seafloor thermal gradients on the upper continental slope, at water depths about 600m–800m. Of several hypotheses which might explain these enhanced gradients, deep crustal fractures or igneous activity along the ocean continental crustal boundary (COB) is rejected by the lack of associated seismicity, extrusive/intrusive activity, or systematic correlation of gradient anomaly with the COB, which does not correspond to any specific water depth. A “Memory in the Mud” explanation is possible if the base of the Norwegian‐Atlantic (warm) current rose by ca. 150–200 m ca. 50–300 years ago. However, high local spatial variability in observed gradients renders this mechanism suspect. Alternatively the thermal gradients were locally steepened by enhanced rise of pore fluids, mud and/or methane gas. This is most likely on the upper continental slope because post‐opening sediment accumulations (i.e., dewatering) tend to be maximal there.
Phase transformations in sulfuric acid aerosols: Implications for stratospheric ozone depletion
Authors: Imre Dan G. , Xu Jun , Tridico Anthony C.
Published: February 2004

Activation reactions of benign chlorine species (HCl, ClONO2) on aerosols in the winter polar stratosphere set the stage for the spring‐time catalytic destruction of ozone leading to the Antarctic ozone hole. Field observations have demonstrated the existence of both solid and liquid particles consisting of H2SO4, HNO3, and H2O. The exact freezing conditions and final composition of the solid aerosols remain the subject of investigations. We present laboratory observations of isolated individual sulfuric acid/water particles under stratospheric temperatures and water vapor pressures. Our experiments demonstrate that this binary system would not freeze unless temperatures were below the water‐ice frost point. Upon freezing, we observe H2SO4·8H2O, not the generally invoked H2SO4·4H2O. We suggest that the water‐rich octahydrate phase is likely to be one of the high relative humidity forms which is efficient in chlorine activation.
The warm oceanic surface layer: Implications for CO2 fluxes and surface gas measurements
Authors: McNeil Craig L. , Merlivat Liliane
Published: February 2004

The ocean and air‐sea interface are important for the exchange of heat, momentum, water vapour and carbon‐dioxide. The details of the exchange mechanisms, which are often coupled and complex, have to be understood in order to assess the future role of the global oceans in climate change. Recently, much attention has focused on the ‘thermal skin effect’, cooling or warming of the uppermost millimeters of the sea surface, and its global implications for enhancing CO2 uptake [Robertson and Watson, 1992; Van Scoy et al., 1995]. Routinely, air‐sea flux estimates derived from oceanic pCO2 measurements are corrected for the usually cooler thermal skin by applying a correction factor [Sarmiento and Sundquist, 1992; Wong et al., 1995]. Here we describe how near surface warming of the upper few meters of the ocean by solar radiation, routinely observed but not fully appreciated in this context, can significantly affect the net daily exchange of CO2 over and above the skin effect, and can even lead to a reversal of the direction of the air‐sea flux calculated from pCO2 measurements and wind speed alone. The warming and cooling cycle produces a net asymmetry between CO2 invasion and evasion, having the effect of decreasing CO2 invasion and increasing CO2 evasion.
Evidence for the reversal of magnetic field polarity in coronal streamers
Authors: Woo Richard
Published: February 2004

Faraday rotation observations are unique amongst radio occultation measurements in that they respond to magnetic field in addition to electron density, making it possible to probe the coronal magnetic field. Signatures interpreted as transients in Faraday rotation measurements made by Pioneer 6 in 1968 in the heliocentric distance range of 6–11 Ro are shown to be caused by coronal streamer stalks of angular size 1–2° observed in white‐light measurements rather than the magnetic bottles interpreted earlier. This identification makes available the first magnetic field observations of coronal streamers. The detection of the reversal of magnetic field polarity high in the corona provides observational evidence confirming what has previously only been inferred from modeling — that streamers observed in white‐light measurements are the manifestation of the heliospheric current sheet. These results reinforce the apparent connection between the coronal streamer stalk observed in white‐light coronagraphs and the heliospheric plasma sheet identified by in situ fields and particles measurements beyond 0.3 AU.
Very high frequency tides observed in the airglow over Eureka (80°)
Authors: Walterscheid R. L. , Sivjee G. G.
Published: February 2004

The absolute brightness and spectral distributions of OH airglow Meinel band near infrared emissions (1.0µ–1.7µ) were obtained from a Michelson Interferometer operating at Eureka (80° 0′N, 85° 56′W), Canada, during polar night. A cross‐spectral analysis of brightness and rotational temperature data from December 1, 1993, to December 20, 1993, shows spectral features with periods near 12, 8, 6, 4, and 3 hours. The periods (tidal harmonics) and persistence (days to weeks) of these features argue for a tidal interpretation. Tidal Hough functions indicate that the dominant spectral features are most likely the manifestation of zonally symmetric tides. The tides at Eureka exhibit a high degree of transience. There is a suggestion of an oscillation with a period close to 5 hours.
A mechanism for decade fluctuations in the length of day
Authors: Buffett Bruce A.
Published: February 2004

Strong gravitational coupling between the solid inner core and the mantle provides a means of exchanging angular momentum between the fluid outer core and the mantle. The proposed mechanism involves oscillations in the fluid core which exert a large electromagnetic torque on the inner core by virtue of its high electrical conductivity. The inner core does not freely respond to this torque because it is constrained by gravitational forces to remain nearly aligned with the mantle. Angular momentum is transferred to the mantle by the gravitational torques that result from small misalignments with the inner core. A calculation of the normal modes of this coupled system predicts observable fluctuations of the mantle with periods of several decades. Damping of the oscillations due to ohmic losses produces a quality factor Q of about 20. An excitation mechanism to sustain the oscillations is proposed on the basis of recent dynamo calculations.
Climatology and trends of tropospheric ozone over the eastern Pacific Ocean: The influences of biomass burning and tropospheric dynamics
Authors: Kim Jae H. , Newchurch M. J.
Published: February 2004

To study the latitudinal variation of tropospheric ozone over the eastern Pacific Ocean, we derive ozone in the lower troposphere by subtracting TOMS column ozone over the Andes from the ozone column over the eastern Pacific Ocean. The analysis of tropospheric ozone climatology in conjunction with meteorological and biomass‐burning data suggests three latitude bands with different characteristics for tropospheric ozone. (1) Air in the latitude range 3°N–7°N experiences persistent upward motion in the middle troposphere over the eastern equatorial Pacific Ocean. This condition results in relatively low ozone amounts in this region. (2) Tropospheric ozone between latitudes 2°N–22°S shows strong seasonal variation that is well correlated with the biomass burning season over southern tropical South America. Persistent subsidence in the middle troposphere and prevailing easterlies over this region provide favorable conditions for enhancing ozone amounts in the lower troposphere. (3) Tropospheric ozone over 23°S–36°S does not appear to be influenced by biomass burning. Regression analysis of deseasonalized tropospheric ozone shows positive trends from 12°S to 23°S and from 2°N to 5°N with essentially zero trends elsewhere. Trends north of the equator are generally smaller and less consistently positive than trends from 12°S–23°S. With tropospheric ozone seasonally in phase in the presence of enabling horizontal and vertical winds, the average increasing trend of +0.9±0.3(2σ)[%/yr] or +0.14±0.04(2σ)[DU/yr] between 12°S and 23°S over the 14 years analyzed here is consistent with an increasing biomass‐burning source.
New regional gravity and magnetic maps of the Levant
Authors: Rybakov M. , Goldshmidt V. , Rotstein Y.
Published: February 2004

A new compilation of regional gravity and magnetic maps of the Levant, based on detailed local maps and data bases for various parts of the region, is presented. The most apparent feature of the Levant gravity map is the regional high associated with the Mediterranean basin. High values extend eastward on land to the Dead Sea rift (DSR), suggesting a relatively thin basic crust under northern Israel and Lebanon. The magnetic pattern offers additional evidence on the transform nature of the DSR; it also suggests that the Gulf of Suez is associated with an arcuate lineament which extends in a NNE direction, deep into the Mediterranean Sea, possibly up to the Cyprean Arc. This apparent lineament may indicate an ancient shear zone.
Split‐window retrieval of particle size and optical depth in contrails located above horizontally inhomogeneous ice clouds
Authors: Duda David P. , Spinhirne James D.
Published: February 2004

Multichannel radiometer measurements of a newly formed contrail taken from a NASA ER‐2 aircraft over northern Oklahoma during the FIRE Cirrus‐II experiment are used in a split‐window retrieval of the contrail's particle size and optical depth. The effect of horizontal inhomogeneity in an underlying cirrus layer on the contrail retrieval is studied through the use of multi‐dimensional radiative transfer model simulations. Estimates of the contrail's effective radius are significantly smaller (5–7 µm) than those in the underlying cirrus (21 µm). The effect of horizontal inhomogeneity in the underlying cirrus on contrail particle size and optical depth retrievals is generally smaller than the corresponding effects of particle shape or spectral variations in surface emissivity on the retrievals. The differences in particle size retrievals are 10 percent or less as a result of the inhomogeneity, while they are from 10 to 40 percent for ice cylinders, and range from 1 to 40 percent for ice spheroids. Horizontal inhomogeneity affected the optical depth retrievals by only one or two percent, while surface emissivity variations affected the retrievals by 12 to 24 percent, and particle shape produced differences as large as 9 percent.
Stratospheric thermal damping times
Authors: Newman Paul A. , Rosenfield Joan E.
Published: February 2004

Radiative damping of stratospheric temperature waves has wide implications for stratospheric physical processes. Damping is linearly parameterized as proportional to the local temperature. Thermal damping is calculated using the Goddard radiative transfer model and 17 years observations. Damping times of stratospheric temperatures are calculated for each month at all latitudes. These damping times are consistent with previous stratospheric estimates, but show shorter tropical time scales. Damping times range from an annual global average of 28 days (100 hPa) to 4 days (1 hPa). A considerable annual cycle is seen over much of the stratosphere, which is directly related to the annual cycle of temperatures, with longer damping times associated with colder temperatures.
Thermoelastic equation of state of jadeite NaAlSi2O6: An energy‐dispersive Reitveld Refinement Study of low symmetry and multiple phases diffraction
Authors: Zhao Yusheng , Von Dreele Robert B. , Shankland Thomas J. , Weidner Donald J. , Zhang Jianzhong , Wang Yanbin , Gasparik Tibor
Published: February 2004

We report the first measurement of a complete set of thermoelastic equation of state of a clinopyroxene mineral. We have conducted an in situ synchrotron x‐ray diffraction study of jadeite at simultaneous high pressures and high temperatures. A modified Rietveld profile refinement program has been applied to refine the diffraction spectra of low symmetry and multiple phases observed in energy dispersive mode. Unit cell volumes, measured up to 8.2 GPa and 1280 K, are fitted to a modified high‐temperature Birch‐Murnaghan equation of state. The derived thermoelastic parameters of the jadeite are: bulk modulus K=125 GPa with assumed pressure derivative of bulk modulus K′ = ∂K/∂P = 5.0, temperature derivative of bulk modulus
, and volumetric thermal expansivity α = a + bT with values of a=2.56×10−5K−1 and b=0.26x10−8 K−2. We also derived thermal Grüneisen parameter γth=1.06 for ambient conditions; Anderson‐Grüneisen parameter δTo=5.02, and pressure derivative of thermal expansion ∂α/∂P = −1.06×10−6 K−1 GPa−1. From the P‐V‐T data and the thermoelastic equation of state, thermal expansions at five constant pressures of 1.0, 2.5, 4.0, 5.5, and 7.5 GPa are calculated. The derived pressure dependence of thermal expansion is: Δα/ΔP = −0.97×10−6K−1GPa−1, in good agreement with the thermodynamic relations.