bluuebunny/crossref_metadata_2025 huggingface dataset:
Interannual to interdecadal variability of sea surface salinity in the Atlantic and its link to the atmosphere in a coupled model
Authors: Mignot J. , Frankignoul C.
Published: April 2004

The interannual to interdecadal variability of sea surface salinity (SSS) in the Atlantic is investigated using 200 years of a control simulation of the Bergen climate model. After verifying that the model behaves realistically, we show that most centers of SSS variability are located near the mouths of the main rivers of the basin. This variability is due primarily to anomalous runoff, except in the St. Lawrence area, and to anomalous Ekman and geostrophic currents, while fluctuations in the freshwater flux play a somewhat lesser role. Away from the coast, SSS variability is strong in the northern tropics, due largely to anomalous advection and freshwater exchanges. Regression analysis and a Lagrangian technique show that the SSS anomalies are advected by the mean oceanic circulation and can be followed along the gyres for several years. The link between SSS anomalies and the dominant modes of variability of the atmosphere is also investigated. The SSS response to the North Atlantic Oscillation (NAO) is dominated by relatively small scales that are forced by anomalous Ekman currents, but the relative influence of the large‐scale freshwater fluxes increases at long timescales. The NAO‐induced SSS anomalies are also strongly advected and distorted by the mean currents, so that their pattern at the interannual timescale only reflects in part that of the atmospheric forcing. The link between SSS anomalies and the East Atlantic pattern is similar.
Implications of “victim pays” infeasibilities for interconnected games with an illustration for aquifer sharing under unequal access costs
Authors: Just Richard E. , Netanyahu Sinaia
Published: April 2004

This paper considers application of interconnected game theory to modeling of bilateral agreements for sharing common pool resources under conditions of unequal access. Linking negotiations to issues with reciprocal benefits through interconnected game theory has been proposed in other settings to achieve international cooperation because it can avoid outcomes that are politically unacceptable due to the “victim pays” principle. Previous studies have not considered adequately the critical nature of this political infeasibility, if it exists, in determining advantages of interconnection. This paper investigates how game structure and benefits suggested by interconnected game theory are altered when victim pays strategies are removed from the feasibility set. Linking games is shown to have greater advantages than when the structural implications of eliminating victim pays strategies are not considered. Conversely, a class of cases exists where the full cooperation benefits of interconnection are attainable without linking through isolated component games when victim pays outcomes are feasible.
Steady two‐dimensional groundwater flow through many elliptical inhomogeneities
Authors: Suribhatla Raghavendra , Bakker Mark , Bandilla Karl , Janković Igor
Published: April 2004

A new analytic element solution has been derived for steady two‐dimensional groundwater flow through an aquifer that contains an arbitrary number of elliptical inhomogeneities. The hydraulic conductivity of each inhomogeneity is homogeneous and differs from the conductivity of the homogeneous background. In addition to elliptical inhomogeneities, other elements (such as wells and line sinks) may be present. The method is based on a separable form of the solution for Laplace's differential equation in elliptical coordinates. The piezometric head and the stream function, expressed as continuous spatial functions (as components of the complex potential), may be obtained up to machine accuracy regardless of the shape, size, orientation, and conductivity of the elliptical inhomogeneities. Components of the discharge vector are expressed in a similar manner, using a complex discharge function. Problems with 10,000 or more inhomogeneities can be solved using parallel computing on distributed memory supercomputer clusters. Two examples are included to demonstrate the precision and capabilities of the method. The second example is used to perform a preliminary study of contaminant transport in a highly heterogeneous formation of lognormal conductivity distribution. The results of the transport study are compared with recent theoretical and numerical results that are based on circular inhomogeneities. The new results with elliptical inhomogeneities confirm the findings based on circular inhomogeneities, including a long dispersion setting time and a zero value of the asymptotic transverse dispersivity.
Analytical solutions for leakage rates through abandoned wells
Authors: Nordbotten Jan Martin , Celia Michael A. , Bachu Stefan
Published: April 2004

Disposal of waste fluids via injection into deep saline aquifers is practiced in a variety of industries. Injection takes place in sedimentary basins that often have a history of oil and gas exploration and production, which means that wells other than those used for waste disposal may exist in the vicinity of the injection site. These existing wells provide possible pathways for leakage of waste fluids toward the shallow subsurface and the land surface. For single‐phase flows of liquids with essentially constant properties, the equations governing the system are linear, and solutions may be written using the superposition principle. Because leakage through existing wells produces a time‐varying flux rate, the solution of the governing equations involves convolution integrals. Previous solutions have addressed the problem of one injection well, one existing (passive) well, and a simple geometry of two aquifers separated by an aquitard by use of Laplace transforms. Even for this simple case, inversion of the transform is difficult. Solutions involving more than one passive well have not been developed. Nor have solutions been developed for more than two aquifers and one aquitard. Realistic injection cases often involve layered systems with multiple aquifers and aquitards, as well as multiple passive wells, sometimes numbering in the hundreds. Solutions for the general case of multiple aquifers and wells may be developed through introduction of approximations to the well function and appropriate simplification of the convolution integral. Such a solution is computationally simple. Comparison to solutions using the full (Laplace transform) solution indicates that the new solution procedure produces excellent results. Application of the new solution to a case of multiple passive wells shows that the cumulative leakage flux in the passive wells is not a simple sum of the single‐well case, owing to leakage‐induced drawdown around the passive wells. In addition, application to the case of multiple aquifers and aquitards demonstrates the importance of leakage into intervening aquifers as a mechanism to mitigate leakage into shallow zones, a process referred to as the “elevator model.” The new analytical solution provides a tool to analyze practical injection problems and forms a foundation on which more complex solutions, such as those involving injection of a nonaqueous fluid into a deep brine formation, may be based.
Tidal flexure at ice shelf margins
Authors: Vaughan David G.
Published: April 2004

Hinge zones accommodate the differential tidal movement between floating ice shelves, which move with the sea tide, and grounded ice sheets, which do not. Observations on Rutford Ice Stream and Ronne Ice Shelf, Antarctica, using the kinematic method of Global Positioning System, have yielded the first continuous tidal displacement profiles from an ice sheet hinge zone. The form of these tidal displacement profiles indicates that the flexure can be fit to an elastic beam model using a parameter space optimization technique. The model matches the observed tidal deflection profile to within 5 cm which is similar to the observational uncertainty. The same model and parameter fitting technique is then successfully applied to various other published and unpublished tidal displacement data from Doake Ice Rumples, Bach Ice Shelf, and Ekström Ice Shelf, Antarctica, and Jakobshavns Glacier, Greenland. I conclude that the elastic beam model with a single value of the elastic modulus (0.88±0.35 GPa) adequately describes almost all the data and so can usefully be applied elsewhere. Earlier studies of tidal dissipation in ice shelf hinge zones, based on a viscous or transient creep rheology, showed that perhaps 30% of global tidal energy dissipation could be occurring in ice shelf hinge zones. This study suggests, however, that an elastic rheology may be equally appropriate, in which case this estimation of the tidal energy dissipation is excessively high.
Segregation of tonalitic‐trondhjemitic melts in the continental crust: The mantle connection
Authors: Petford Nick
Published: April 2004

Rates of melt segregation into fractures during fluid‐absent partial melting above a mafic heat source are investigated numerically over a range of viscosities appropriate for tonalitic‐trondhjemitic melts. Static melt segregation is dependent upon large tensile stresses (>10 MPa) set up during fluid‐absent partial melting reactions that promote fracturing and vein formation in the region above the mafic intrusion. Porous flow of partial melt into veins and fractures (regions of reduced pressure) will occur provided the melt is less dense than the surrounding protolith matrix. Where vein size is much less than compaction length, maximum vein filling rates are of the order of 2.5 m/yr. Melt segregation into veins and fractures is likely to be most effective near the intrusion‐protolith interface, where high temperatures result in relatively low melt viscosities (<106 Pa s) and high porosities (melt fractions). For relatively low viscosity tonalitic melts (∼104 Pa s), extraction may occur at values below the critical melt fraction, provided the melt is everywhere interconnected. Larger veins may propagate upward as dikes to feed high level plutons. These conditions for melt extraction are considered likely in tectonic settings where lower (amphibolitic) crust is being partially melted by underplating of mantle derived basalt. The model does not require the existence of large magma chambers in the source region.
2fp radio emission from the vicinity of the Earth's foreshock: WIND observations
Authors: Reiner M. J. , Kaiser M. L. , Fainberg J. , Desch M. D. , Stone R. G.
Published: April 2004

We analyze 2fp radio emission observed during a perigee pass in August 1995 when the WIND spacecraft was between 47 and 72 RE from Earth and upstream of the electron foreshock. The WAVES experiment on WIND measures the direction of arrival and complete polarization state of the 2fp radiation. We found no evidence for significant linear or circular polarization. For one period when we were able to utilize the direction finding capability to determine the actual 2fp source location, using an interplanetary shock as a diagnostic, the radio emitting region was confirmed to lie within the electron foreshock near the contact point. We indicate how such remotely observed 2fp emissions can be used to monitor the response of the electron foreshock to instantaneous changes in the interplanetary magnetic field.
Entropy antidiffusion instability and formation of a thin current sheet during geomagnetic substorms
Authors: Lee L. C. , Zhang L. , Otto A. , Choe G. S. , Cai H. J.
Published: April 2004

In our recent study of the equilibrium configuration of the near‐Earth magnetotail, it is found that a steeper profile of entropy function S leads to the formation of a thinner current sheet. Here S = pVγ, where p is the plasma pressure and V is the volume of a unit magnetic flux tube. In the presence of density gradient at the edges of the current sheet, the lower‐hybrid‐drift instability may lead to pressure diffusion. Since the pressure generally decreases and the entropy function S increases tailward, the diffusion of plasma pressure results in a steepening, or antidiffusion, of the entropy profile. This, in turn, leads to a thinner current sheet, which enhances the pressure diffusion. This positive feedback process is called the entropy antidiffusion instability. On the basis of MHD simulations with a pressure diffusion, we find that the entropy antidiffusion instability leads to a further thinning of the near‐Earth current sheet and the onset of dipolarization of near‐Earth geomagnetic field lines. The growth rate of the instability is linearly proportional to the diffusion coefficient. The growth time at the final stage for the formation of a very thin current sheet is ∼1 min. This instability may explain the observed explosive growth phase of substorms and the onset of dipolarization of geomagnetic field lines.
Results from a gyrotropic two‐ion fluid model for the comet interaction with the solar wind
Authors: Gan‐Baruch Zameret , Wegmann Rudolf , Eviatar Aharon , Schmidt Hermann U.
Published: April 2004

A two‐and‐a‐half‐dimensional two‐ion fluid model (with gyrotropic pressure tensor) for the interaction of cometary pickup plasma with the solar wind has been developed. Whereas previous models have, in general, assumed a one‐fluid plasma, this generalized model follows the evolution of two fluids: solar wind protons and cometary ions. The two fluids are coupled by the magnetic field and by coupling terms which are the velocity moments of the time relaxation model of Bhatnagar et al. [1954]. Furthermore, a gyrotropic pressure tensor replaces the isotropic pressure assumed in other models. Isotropization terms couple the pressures in the directions perpendicular and parallel to the magnetic field. Among the results received, the standoff distance of the shock increased significantly when the isotropization rate was reduced. The large cometary plasma pressure forces at the shock accelerated the cometary plasma along the shock. As a result, the cometary plasma drifted ahead of the solar wind along the shock flanks parallel to the magnetic field. Close to the nucleus of the comet in the far tail lobes and in the far inner tail the cometary plasma lagged behind the solar wind.
The solar wind velocity determined from Voyager 1 and 2: Low‐Energy Charged Particle measurements in the outer heliosphere
Authors: Kane M. , Decker R. B. , Mauk B. H. , Krimigis S. M.
Published: April 2004

The Voyager 1 and 2 spacecraft are now exploring the outer heliosphere with active field and particle instruments. The primary instrument for the critical plasma bulk flow parameter is the plasma science (PLS) instrument. Unfortunately, on Voyager 1, the spacecraft most likely to first encounter the termination shock and other heliospheric boundaries, the PLS instrument is no longer able to measure plasma flows. In this paper we demonstrate that the Low‐Energy Charged Particle (LECP) detector may, under certain conditions, be used to determine the solar wind plasma flow velocities. We show that higher time resolution radial speeds (daily averages) are obtainable in the downstream regions near interplanetary transient shocks where the ion activity is sufficiently above background levels and where the ion distributions are sufficiently isotropized. Longer‐term (26‐day) averaged speeds are obtainable during lower counting periods, such as during 1980 and 1992, when corotating shocks were prevalent. The Voyager 2 LECP results are in good agreement with known PLS determinations of bulk flow speed from the cold plasma. Using large transient shocks seen during 1989 and 1991 as examples, Voyager 1 calculations indicate slower solar wind speeds near these events despite the higher heliolatitude location of Voyager 1 during this period. During 1992, when Ulysses entered the southern high‐speed stream region, Voyager 1 apparently did not see high‐speed streams at similar northern latitudes. Given the expected activity near the termination shock, our determination of the solar wind speed should serve as an indicator of a Voyager 1 crossing of this shock. The LECP measurements would provide the only determination of bulk flow speed and deviations from the nominal solar wind flow speed at this and other boundaries or shocks encountered by Voyager 1.
Magnetospheric dynamics and mass flow during the November 1993 storm
Authors: Borovsky Joseph E. , Thomsen Michelle F. , McComas David J. , Cayton Thomas E. , Knipp Delores J.
Published: April 2004

The National Space Weather Program (NSWP) Storm that occurred in November 1993 is examined with the use of plasma and energetic‐particle measurements on three satellites in geosynchronous orbit. Geosynchronous orbit affords a powerful perspective on magnetospheric dynamics since both tail and dipole processes can be regularly seen, as well as nightside and dayside processes. The major magnetospheric regions analyzed before, during, and after this storm are the outer plasmasphere, the ion plasma sheet, the electron plasma sheet, and the outer electron radiation belt. Ionospheric outflows into the magnetosphere are also observed, and during the storm the magnetosheath and the low‐latitude boundary layer are both seen briefly. The geosynchronous observations indicate that prior to the storm the magnetosphere was very quiet and the outer plasmasphere was filled out to beyond geosynchronous orbit. Extremely large anisotropies were seen in the ion plasma sheet during a compression phase just prior to storm onset. During the storm's main phase the drainage of the outer plasmasphere to the dayside magnetopause was observed, a super dense ion plasma sheet was tracked moving around the dipole, and a superdense electron plasma sheet was seen. The anomalously large plasma pressure on the nightside led to a β > 1 situation at geosynchronous orbit. The β > 1 region spread around the dipole with the super dense ion plasma sheet. The magnetic‐field tilt angle at geosynchronous orbit indicated that strong cross‐tail currents were present very near the Earth. These currents appear to be associated with plasma diamagnetism. Geosynchronous observations indicate that magnetospheric convection was extremely strong. In the electron plasma sheet, severe spacecraft charging occurred. The density of relativistic electrons was observed to peak very early in the storm, whereas the flux of these relativistic electrons peaked much later in the aftermath of the storm.
Prompt midlatitude electric field effects during severe geomagnetic storms
Authors: Foster J. C. , Rich F. J.
Published: April 2004

Meridian‐plane elevation scans with the Millstone Hill incoherent scatter radar provide evidence of a strong perturbation of the coupled mid‐latitude magnetosphere‐ionosphere system during the early phases of the November 4, 1993 magnetic storm. A narrow ionospheric trough formed at L=3.5 in the pre‐midnight sector, immediately poleward of the Millstone Hill site. The most pronounced radar signature of the developing activity was a brief (20 min) uplifting of the F region plasma equatorward of the trough, such that the peak altitude increased with distance away from the trough. A similar signature had been observed during storm onset on March 20, 1990, and in that event a pronounced topside ionospheric depletion developed in the region far equatorward of the mid‐latitude trough and was observed by the radar and the DMSP F9 satellite. During the November 4, 1993 event, the DMSP F10 satellite observed narrow, magnetically conjugate regions of plasma density depletion and strong horizontal and upward plasma velocity (> 1500 m/s) at L=1.5 at the time of the uplifting of the mid‐latitude F region observed by the radar. These observations were confined to longitudes near the South Atlantic magnetic anomaly and, in the Nov 1993 case, the perturbation was coincident with the peak of the precipitating particle fluxes associated with innerbelt losses at the anomaly. Both the uplifting of the ionospheric F layer and the triggering of topside density perturbations can be explained in terms of an eastward electric field imposed on the mid and low‐latitude ionosphere during the initial stages of the geomagnetic storm. The low‐latitude ionospheric perturbations in these events were similar to supersonic equatorial bubbles, triggered by the destabilizing effects of the upward E×B drift associated with the eastward electric field.
Energetic electrons at geostationary orbit during the November 3–4, 1993 storm: Spatial/temporal morphology, characterization by a power law spectrum and, representation by an artificial neural network
Authors: Freeman J. W. , O'Brien T. P. , Chan A. A. , Wolf R. A.
Published: April 2004

Electrons of energy several MeV or greater have been implicated in the failure and malfunction of geostationary spacecraft. It is therefore important to be able to specify and even forecast the fluxes of these particles during and following geomagnetic storms. A first step is the understanding of their relationship to lower‐energy electrons that can already be well modeled. It is therefore the goal of this paper to examine the relative time, spatial, and spectral relationships between 1.5 MeV electrons and intermediate energy electrons down to about 100 keV. For the November 1993 geomagnetic storm we find that electrons from about 100 keV to 1.5 MeV at GEO can be conveniently characterized by a power law spectrum and that the slope and intercept of this spectrum vary in systematic ways during the storm. This suggests the possibility of developing prediction filters or artificial neural networks, driven by a storm activity indicator (such as Dst), local time and a lower‐energy electron flux, to specify the energetic electron spectral characteristics. We further find that local time diurnal effects are an important contributor to the apparent time delay of the recovery of energetic electrons and when these effects are considered the recovery phase enhancement is nearly uniform across the spectrum. This paper will report the spatial and temporal morphology of these intermediate to energetic electrons, their characterization by a power law and the variations of the power law slope and intercept throughout the November 1993 storm. These temporal, spatial, and spectral properties suggest that the recovery phase enhancement is due to the entry of the intermediate energy electrons from the geomagnetic tail as part of the storm injection process. We also discuss our success at building an Artificial Neural Network system to specify the storm time energetic electron flux spectra.
Global analysis of three traveling vortex events during the November 1993 storm using the assimilative mapping of ionospheric electrodynamics technique
Authors: Ridley A. J. , Moretto T. , Ernström P. , Clauer C. R.
Published: April 2004

We have studied three traveling vortex events during the November 3–11, 1993, storm period using the assimilative mapping of ionospheric electrodynamics technique to help interpret the ground magnetic response from a global set of stations. When the AMIE potential patterns are high‐pass filtered, clear vortex structures are observed. The AMIE output compares reasonably well with the ground magnetic data, although AMIE has a tendency to smooth out the structures. Single vortices are observed to form near 1000 MLT and propagate to 1400 MLT, over the Greenland magnetometers and across noon. The velocity of the vortices is approximately 4–8 km/s (0.2° – 0.3° s−1 between 70° and 75°) eastward along a line of invariant latitude. The number of vortices, as well as the motion of the vortices, differs from the classical picture of a traveling convection vortex. We therefore suggest that these vortex events might have a different generation mechanism or occur under a different state of the magnetosphere, and thus that they should be considered a separate class of events. The AMIE technique offers the possibility to relate the vortices to the large‐scale convection patterns. We note how the vortices can be interpreted as small scale, rapid changes in the large‐scale convection pattern, although these changes show many differences to previous studies of changing large‐scale convection patterns. We speculate that this particular class of traveling vortex event may be generated by a perturbation in the separatric on the dayside magnetopause, caused by an enhancement or depreciation of the magnetic merging.
Substorm modeling based on observations of an intense high‐latitude absorption surge event
Authors: Stauning Peter
Published: April 2004

During the early November 1993 study interval selected for the international Space Weather Initiative a remarkably intense early evening substorm event was observed at around 2200 UT on November 4, 1993, in high‐latitude magnetometer and riometer recordings. The event, the most intense absorption event recorded by the imaging riometer in Sdr. Strømfjord (STF), Greenland, during 1993, occurred at the center of strong upward region 1 field‐aligned currents during a major reconfiguration of the polar ionospheric plasma convection system. The event was preceded by some substorm activity at lower latitudes. At STF, however, it appeared with nicely isolated and exceptionally clear signatures in the geophysical observations, primarily in the imaging riometer measurements of ionospheric radio wave absorption at 38 MHz. The event was characterized by multiple intense and sudden absorption pulsations with increasing amplitudes of up to 11 dB separated by about 20–30 s and with duration of around 10–15 s superimposed on a general level of a few decibels of absorption. The event was selected for a modeling study to investigate the possible generation mechanisms for the ionized layers causing the absorption. We conclude that the event was most probably caused by precipitation of magnetospheric electrons accelerated repeatedly through transient field‐aligned potential structures of 10–30 kV associated with the intense upward currents. We find that these structures were located at a few Earth radii's distance and that the field‐aligned potential structures have positive feed‐back to the ionospheric potentials affected by the conductivity changes caused by accelerated electrons. We suggest that such coupled potential systems may provide a general mechanism for acceleration of electrons of a thermal magnetospheric plasma to the much higher energies found in auroral precipitation and in the radiation belts.
Volcanic margin formation and Mesozoic rift propagators in the Cuvier Abyssal Plain off Western Australia
Authors: Mihut Dona , Müller R. Dietmar
Published: April 2004

The western margin of Australia is characterized by synrift and postrift magmatism which is not well understood. A joint interpretation of magnetic anomaly, satellite gravity anomaly and seismic data from the Cuvier Abyssal Plain and margin shows that the breakup between India and Australia started circa 136 Ma (M14) and was followed by two rift propagation events which transferred portions of the Indian Plate to the Australian Plate. Post breakup magmatism continued with the emplacement of the Wallaby and Zenith plateaus (∼17–18 km thick at their centers) along a transform margin. Two narrow magmatic edifices adjacent to the Wallaby Plateau (Sonne and Sonja ridges) represent an extinct ridge and a pseudofault, respectively. They formed by excess volcanism, probably by lateral migration of buoyant melt along upside‐down crustal drainage channels from the melt source underneath the Wallaby Plateau. In a mantle plume scenario a small plume (∼400 km diameter) located underneath the rift could have locally uplifted the Bernier Platform and Exmouth Sub‐basin in the Early Cretaceous and left a track consistent with the azimuth of the Wallaby and Zenith plateaus. In this case, ridge‐plume interaction would have caused two consecutive ridge propagation events towards the plume while the ridge moved away from the hotspot. The abrupt end of the hotspot track west of the Zenith Plateau would be a consequence of the accelerating south‐eastward motion of the spreading ridge relative to the mantle after 120 Ma, leaving the mantle plume underneath the Indian Plate. An alternative nonmantle‐plume scenario is based on the observation that between breakup and chron M0 (∼120 Ma) the ocean crust in the southern Cuvier Abyssal Plain was formed while the spreading ridge abutted Indian continental crust. Small‐scale convection may have been initiated during rifting in the Early Cretaceous and maintained until the Wallaby‐Zenith ridge‐transform intersection passed by the eastern edge of Indian continental crust at chron M0.
Flow and convective cooling in lava tubes
Authors: Sakimoto S. E. H. , Zuber M. T.
Published: April 2004

Tube‐fed basaltic lava flows with lengths ranging from 10 to 200 km are inferred to exhibit similar amounts of cooling. To explain the wide range of implied cooling rates, we consider forced convection as a dominant cooling process in lava tubes and present solutions that express mean temperature versus distance down the tube as a function of flow rate and flow cross section. Our models treat forced convective thermal losses in steady laminar flow through a lava tube with constant temperature walls and constant material properties. We explore the effects of different wall temperature and heat flux rate boundary conditions for circular tube and parallel plate flows over a range of tube sizes, plate spacings, eruption temperatures, and volume flow rates. Results show that nonlinear cooling rates over distance are characteristic of constant wall temperature for a piecewise parallel plate/circular tube model. This provides the best fit to temperature observations for Hawaiian tubes. Such a model may also provide an explanation for the very low (∼10°C) cooling observed in ∼10 km long Hawaii tube flows and inferred in longer ∼50 to 150 km tube‐fed flows in Queensland. The forced convective cooling model may also explain similar flow morphologies for long tube‐fed basaltic lava flows in a wide variety of locations, since small variations in eruption temperature or flow rate can accommodate the entire range of flow lengths and cooling rates considered. Our results are consistent with previous suggestions that long basaltic flows may be a reflection of low slopes, a particularly steady moderate eruption rate, and well‐insulated flow, rather than of high discharge rates.
Emplacement and erosion by Archean komatiite lava flows at Kambalda: Revisited
Authors: Williams David A. , Kerr Ross C. , Lesher C. Michael
Published: April 2004

We have developed a mathematical model to evaluate the flow and erosional potential of submarine, channelized komatiite lavas at Kambalda, Western Australia. Field data from Kambalda were used to constrain the choice of important input parameters, and model results were compared with data from field studies and geochemical analyses. Our results suggest that thermal erosion is strongly dependent upon the nature and behavior of the substrate. If the substrate is treated as an unconsolidated, hydrous sediment that can be fluidized by vaporized seawater, then our model predicts that an initially 10‐m‐thick basal Kambalda komatiite lava could have produced very high thermo‐mechanical erosion rates (∼23–10 m/day), crustal thicknesses of ∼5–20 cm at distances of ∼5–35 km from the source, and a high degree of lava contamination (∼3–12%). In contrast, if the substrate is treated as a more consolidated, anhydrous sediment that could not be fluidized, then our model predicts that a Kambalda komatiite flow would have had much lower thermal erosion rates (∼1.2–0.4 m/day) and degrees of contamination (∼1–3%), and would have had crustal thicknesses of ∼5–20 cm at longer flow distances of ∼30–165 km. Field constraints are generally consistent with our predictions for a non‐fluidized substrate. The reentrant embayments at Kambalda are thought to form from either erosion of deep channels in a flat basaltic seafioor [Huppert et al., 1984], or erosion of a thin (<5 m) sediment with minor undercutting of basalt in pre‐existing topography [Lesher et al., 1984]. Our modeling indicates that the former was possible for long eruption durations (months), whereas the latter was possible for short eruption durations (<2 weeks). As the latter hypothesis is more consistent with the existing field evidence for thermal erosion at Kambalda, we believe it is the preferred interpretation.
Erosion by flowing lava: Field evidence
Authors: Greeley Ronald , Fagents Sarah A. , Harris Robert Scott , Kadel Steven D. , Williams David A. , Guest John E.
Published: April 2004

Erosion of substrate materials by melting or mechanical means has been suggested in active lava flows on Earth and other planets. Although there are many references to lava erosion on Earth, unambiguous evidence is rare; geological relationships commonly cited as evidence of downcutting by lava can be explained without recourse to erosion. In order to assess possible erosion by flowing lava we carried out field studies of tube‐fed basalt flows, sheet flows of the Columbia River Basalt Province (CRB), and Precambrian komatiites. Unequivocal evidence for thermal erosion (melted dacite substrate) was found at the Cave Basalt lava tube, Mount St. Helens, for which fluid dynamic analysis indicates laminar flow, although erosion was enhanced in areas of locally steep slopes, possibly as a result of localized turbulence. Other lava tubes in our study display strong, but inconclusive, evidence for erosion. Komatiite flows display good evidence for erosion of their substrate, possibly in a turbulent regime, but assessment of the extent of erosion is hampered by limited and disrupted exposures. No evidence for thermal erosion was found in the CRB. Our findings suggest that an erosional origin for planetary sinuous rules and canali would be favored by high Reynolds number flows (high mass flux, low‐viscosity lava, steep slopes) and substrates having a lower melting temperature than the lava or low mechanical strength (e.g., regolith).
Emplacement of Columbia River flood basalt
Authors: Reidel Stephen P.
Published: April 2004

Evidence is examined for the emplacement of the Umatilla, Wilbur Creek, and the Asotin Members of Columbia River Basalt Group. These flows erupted in the eastern part of the Columbia Plateau during the waning phases of volcanism. The Umatilla Member consists of two flows in the Lewiston basin area and southwestern Columbia Plateau. These flows mixed to form one flow in the central Columbia Plateau. The composition of the younger flow is preserved in the center and the composition of the older flow is at the top and bottom. There is a complete gradation between the two. Flows of the Wilbur Creek and Asotin Members erupted individually in the eastern Columbia Plateau and also mixed together in the central Columbia Plateau. Comparison of the emplacement patterns to intraflow structures and textures of the flows suggests that very little time elapsed between eruptions. In addition, the amount of crust that formed on the earlier flows prior to mixing also suggests rapid emplacement. Calculations of volumetric flow rates through constrictions in channels suggest emplacement times of weeks to months under fast laminar flow for all three members. A new model for the emplacement of Columbia River Basalt Group flows is proposed that suggests rapid eruption and emplacement for the main part of the flow and slower emplacement along the margins as the of the flow margin expands.
Meddy trajectories in the Canary Basin measured during the SEMAPHORE experiment, 1993–1995
Authors: Richardson Philip L. , Tychensky Aude
Published: April 2004

As part of the Structures des Echanges Mer‐Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Experimentale (SEMAPHORE) experiment, four Mediterranean water eddies (Meddies) were identified in the Canary Basin and tracked with freely drifting RAFOS floats. One large and energetic Meddy, discovered 1700 km west of Cape Saint Vincent, Portugal, set a distance and speed record as it translated another 1700 km southwestward at 3.9 cm/s during 1.5 years. This Meddy traveled 57% of the distance from Cape Saint Vincent toward the spot McDowell and Rossby [1978] found a possible Meddy north of the Dominican Republic. Two Meddies were observed to interact with the Azores Current as they passed underneath or through it. Three Meddies collided with tall seamounts, which seemed to disrupt the normal swirl velocity, perhaps fatally in two cases. One Meddy appeared to bifurcate when it collided with seamounts.
Hydrological and dynamical characterization of Meddies in the Azores region: A paradigm for baroclinic vortex dynamics
Authors: Tychensky A. , Carton X.
Published: April 2004

The Structure des Echanges Mer‐Atmosphere, Proprietes des Heterogeneites Oceaniques: Recherche Expérimentale (SEMAPHORE) oceanographic experiment surveyed a 500 × 500 km2 domain south of the Azores from June to November 1993 and collected hydrological data, float trajectories, and current meter recordings. This data exhibited three intrathermocline eddies of Mediterranean water (Meddies), two of them being repeatedly sampled. Their hydrological and dynamical properties are quantified here by an isopycnic analysis. For the three Meddies, intense temperature and salinity anomalies (up to 4°C and 1.1 practical salinity units (psu)) are observed extending vertically over up to 1000 m and centered around 1000 m. Horizontally, these anomalies spread out to radii of 50–60 km, while the maximum azimuthal velocities (30 cm s−1, as computed by geostrophy) lie only at 35–40 km from the central axis. These Meddies followed curved trajectories, with drift velocities up to 7.5 cm s−1, under the influence of the neighboring mesoscale features (cyclonic vortices or Azores Current meanders). The three‐dimensional structure of potential vorticity in and around these features evidences their complex interactions. Northwest of the domain, a Meddy was coupled to a subsurface anticyclone, forming an “aligned” vortex. It later interacted with the Azores Current, creating a large‐amplitude northward meander by vertical alignment of vorticity. In the southeastern part of the domain, another Meddy was vertically aligned with an anticyclonic meander of the Azores Current and horizontally coupled with a cyclone of large vertical extent. These two features, as well as a small warm and salty fragment in their vicinity, seem to result from the southward crossing of the Meddy under the Azores Current. These observations illustrate previous theoretical studies of baroclinic vortex dynamics.
Comparison of sea surface flux measured by instrumented aircraft and ship during SOFIA and SEMAPHORE experiments
Authors: Durand Pierre , Dupuis Hélène , Lambert Dominique , Bénech Bruno , Druilhet Aimé , Katsaros Kristina , Taylor Peter K. , Weill Alain
Published: April 2004

Two major campaigns (Surface of the Oceans, Fluxes and Interactions with the Atmosphere (SOFIA) and Structure des Echanges Mer‐Atmosphère, Propriétés des Hétérogénéités Océaniques: Recherche Expérimentale (SEMAPHORE)) devoted to the study of ocean‐atmosphere interaction were conducted in 1992 and 1993, respectively, in the Azores region. Among the various platforms deployed, instrumented aircraft and ship allowed the measurement of the turbulent flux of sensible heat, latent heat, and momentum. From coordinated missions we can evaluate the sea surface fluxes from (1) bulk relations and mean measurements performed aboard the ship in the atmospheric surface layer and (2) turbulence measurements aboard aircraft, which allowed the flux profiles to be estimated through the whole atmospheric boundary layer and therefore to be extrapolated toward the sea surface level. Continuous ship fluxes were calculated with bulk coefficients deduced from inertial‐dissipation measurements in the same experiments, whereas aircraft fluxes were calculated with eddy‐correlation technique. We present a comparison between these two estimations. Although momentum flux agrees quite well, aircraft estimations of sensible and latent heat flux are lower than those of the ship. This result is surprising, since aircraft momentum flux estimates are often considered as much less accurate than scalar flux estimates. The various sources of errors on the aircraft and ship flux estimates are discussed. For sensible and latent heat flux, random errors on aircraft estimates, as well as variability of ship flux estimates, are lower than the discrepancy between the two platforms, whereas the momentum flux estimates cannot be considered as significantly different. Furthermore, the consequence of the high‐pass filtering of the aircraft signals on the flux values is analyzed; it is weak at the lowest altitudes flown and cannot therefore explain the discrepancies between the two platforms but becomes considerable at upper levels in the boundary layer. From arguments linked to the imbalance of the surface energy budget, established during previous campaigns performed over land surfaces with aircraft, we conclude that aircraft heat fluxes are probably also underestimated over the sea.
The Great African Plume from biomass burning: Generalizations from a three‐dimensional study of TRACE A carbon monoxide
Authors: Chatfield R. B. , Vastano J. A. , Li L. , Sachse G. W. , Connors V. S.
Published: April 2004

The “Great African Plume” flows westward from a wind divergence line over Central Africa to pollute the Equatorial Atlantic Ocean. The plume arises from agricultural burning fumes which mix in a 3–4 km deep boundary layer over Africa, then override cooler rainforest air, and finally swerve westward, where their progress into the Atlantic is “gated” by southern storm systems. Another prominent elevated “Global Burning Plume” from Tropical South America flows past South Africa above 8 km altitude. Joining elevated African plumes, it influences the South Indian and Southern Oceans. These are results from our GRACES (Global Regional Atmospheric Chemistry Event Simulator), which was used to study carbon monoxide during an intensive experimental period, September‐October 1992. Traces of the plumes are also evident in observations of CO in the Measurement of Air Pollution from Satellites (MAPS) samples of October, 1994, suggesting a general phenomena. To arrive at these conclusions, we used the detailed weather reconstructions afforded by MM5 meteorological model dynamics to drive GRACES. Both statistical and detailed (event) comparisons of CO and observed aboard the NASA DC‐8 are good, especially <6 km altitude. The following model adaptations that we required may inform global analysis and global models: (1) Parameterized vertical transport like planetary boundary layer convection and deep cumulonimbus convection strongly control CO, allowing far more precision than trajectory studies and models using only large‐scale motions. (2) CO sources during this period were consistent with the Hao and Liu [1994] report‐based carbon‐burn rates; (3) deep convection is even more active than as parameterized by MM5's Grell‐scheme: on the large scale: mass fluxes effective for CO redistribution may be over twice core‐updraft values diagnosed strengths.
CH4 oxidation by tundra wetlands as measured by a selective inhibitor technique
Authors: Moosavi Sadredin C. , Crill Patrick M.
Published: April 2004

Rates of methane (CH4) oxidation were measured in three wet sedge communities on Alaska's North Slope in 1993 and 1995 using the selective inhibitor methyl fluoride (CH3F). Comparison of CH4 flux prior to inhibition (net flux) with flux after inhibition (gross flux) enables one to infer CH4 oxidation rates by difference. Oxidation rates from Franklin Bluffs, Sagavanirktok River floodplain, Toolik Lake Inlet, and Toolik Lake Outlet averaged 24.9, 14.7 (1.6), (17.6), and 25.2 (49.8) mg CH4/m2/d in 1995 (1993), respectively. Plot level data suggest that oxidation rates vary greatly spatially and temporally down to the meter scale. As a percentage of flux, however, mean CH4 oxidation rates of 13.4, 21.7 (2.0), (16.5), and 19.4 (38.0)% at Franklin Bluffs, Sagavanirktok River, Toolik Lake Inlet, and Toolik Lake Outlet in 1995 (1993), respectively, were seen to be rather uniform over the region. The effects of temperature on CH4 production appear to be the dominant control on CH4 oxidation rates in wet sedge environments as opposed to soil moisture dependency in upland soils. Nutrient fertilization was not found to influence the fraction of CH4 lost to oxidation. This suggests that CH4 oxidation, while significant in tundra wetlands, may consume a near‐constant fraction of available CH4.
Failure of inactivated influenza A vaccine to protect healthy children aged 6−24 months
Authors: Maeda Taro , Shintani Yukihiro , Nakano Kanako , Terashima Kazuhiro , Yamada Yoshiyasu
Published: April 2004

Abstract
Background
: The efficacy of inactivated influenza vaccine in healthy infants and children younger than 24 months has not been confirmed. The aim of the present study was to determine the prophylactic effect of inactivated influenza vaccine against influenza A in healthy children aged 6−24 months.

Methods
: Healthy infants and young children (6−24 months old) were immunized by subcutaneous injection of inactivated influenza vaccine before influenza seasons. Age matched children were randomly assigned as the control. These children were followed up from January to April in each year (2000, 2001 and 2002). The attack rates of influenza A infection was compared and statistically assessed.

Results
: The attack rate of influenza A virus infection in the vaccine group and the control group were 14.8% (n = 27) vs 12.5% (n = 32) in 2000 (P = 0.526); 2.8% (n = 72) vs 7.2% (n = 69) in 2001 (P = 0.203); and 3.4% (n = 52) vs 8.9% (n = 56) in 2002 (P = 0.205). The attack rates of influenza A between the two groups were not significantly different.

Conclusion
: Inactivated influenza vaccine did not reduce the attack rate of influenza A infection in 6−24 month old children.
Molecular epidemiology of enterovirus 71 infection in the Western Pacific Region
Authors: Shimizu Hiroyuki , Utama Andi , Onnimala Napa , Li Chen , Li‐Bi Zhang , Yu‐Jie Ma , Pongsuwanna Yaowapa , Miyamura Tatsuo
Published: April 2004

Abstract
Background
: Recently, there have been large outbreaks of hand, foot and mouth disease (HFMD) mainly caused by enterovirus 71 (EV71) associated with severe neurological diseases in the Western Pacific Region (WPR). To monitor the realtime trend of EV71 transmission throughout the WPR, the authors conducted a molecular epidemiological analysis of EV71 infection.

Methods
: Viruses were isolated from clinical samples from patients with HFMD or those with neurological complications. The EV71 isolates were identified by microneutralization assay. The VP4 and/or VP1 regions of recent EV71 isolates were sequenced and subjected to phylogenetic analysis using reference EV71 strains.

Results
: The phylogenetic analysis of EV71 isolates from the WPR revealed two major genogroups, B and C, based on the nucleotide sequence alignment of the VP1 or VP4 region. These two major genogroups were further divided into subgenogroups, B1, B2, B3, and B4 and C1, C2, C3 and C4, respectively.

Conclusion
: The molecular epidemiological analyses of recent and previous EV71 isolates in the WPR indicated that two major genogroups of EV71 are co‐circulating in Australia, Malaysia, Singapore, Taiwan and Japan. Recent EV71 isolates in Mainland China constitute a new distinct genetic cluster, subgenogroup C4. Two major lineages of EV71 are the major causative agents of the present HFMD epidemics in the WPR and both are considered to be neurovirulent.