bluuebunny/crossref_metadata_2025 huggingface dataset:
Noble gas solubility in binary CaO‐SiO2 System
Authors: Shibata Tomo , Takahashi Eiichi , Matsuda Jun‐Ichi
Published: February 2004

New noble gas solubility measurements in binary CaO‐SiO2 melts at 1100 bar and 1600 °C are presented. The range of estimated solubilities is He: 8.64–35.8, Ne: 6.54–27.6, Ar: 1.09–8.92, Kr: 0.524–5.67, and Xe: 0.181–2.48 (x 10−5 cm³STP/g‐bar). The solubility is greater for the lighter noble gases and is a strong function of melt composition; the solubility increases with increasing SiO2 and decreasing CaO contents. It is generally known that CaO produces non‐bridging oxygen by breaking the SiO4 network, and thus the correlation between the solubility and SiO2 content suggests that noble gases dissolve in the SiO4 network. It is known that the network is formed by limited anionic structure units. In the case of CaO‐SiO2 melts, most noble gases would be accommodated by two anionic units; chain and three‐dimension structural units. The equilibrium constants of He, Ne, Ar, Kr, and Xe for chain and three‐dimension structure units are 26.9, 19.6, 3.49, 1.71, and 0.613 (× 10−4) and 15.1, 11.3, 4.05, 2.68, and 1.23 (× 10−3), respectively. It is concluded that noble gases dissolve in the three‐dimension structure units more than in the chain units.
Reply [to “Comment of ‘VLF signatures of ionospheric disturbances associated with sprites’ by Inan et al.”]
Authors: Inan U. S. , Bell T. F. , Pasko V. P.
Published: February 2004

The comment by R. L. Dowden does not properly represent the results presented in our recent paper [Inan et al., 1995] and attempts to prematurely classify the VLF events reported in our papers as being produced by elves. There is no experimental evidence that the VLF events reported in our papers are necessarily associated with the optical phenomena of elves. In our recent paper [Inan et al., 1996a] we provide a physically based mechanism which accounts for the forward scatter property of the VLF events observed in our data.
The stability and equation of state of majoritic garnet synthesized from natural basalt at mantle conditions
Authors: Faust J. , Knittle E.
Published: February 2004

The high‐pressure stability and equation of state of majoritic garnet synthesized from natural basalt have been determined using the laser‐heated diamond cell and x‐ray diffraction. Natural mid‐ocean ridge basalt (MORB) and tholeiitic basalt transform from a garnet‐dominated mineral assemblage to a silicate perovskite‐dominated mineralogy near 42 (±3) GPa. Static compression data (at 300 K) for the majoritic garnet synthesized from the natural tholeiitic basalt yields an isothermal bulk modulus, K0T, of 226.2 (±9.3) GPa with dK0T/dP constrained to be 4. An equally acceptable fit to the data is obtained if K0T is constrained to be 180 GPa and dK0T/dP is 7 (±1). Using our new equation of state and phase stability results for basaltic (majorite‐structured) garnet, we calculate density models for the subducting oceanic crust at mantle pressures and temperatures, and find that the basaltic crust is 0.4 g/cm³ (9%) less dense than the lower mantle at 660 km depth. If we assume that the subducted crust can delaminate from the underlying lithosphere, a simple buoyancy model for the crustal portion of subducting slabs indicates that basaltic crust may not sink below 660 km in depth.
Modal depths from shipboard bathymetry: There is a south pacific superswell
Authors: McNutt Marcia K. , Sichoix Lydie , Bonneville Alain
Published: February 2004

Since the first quantification 10 years ago of a large regional depth anomaly in French Polynesia, numerous studies have explored the origin and the geophysical and geochemical consequences of this “South Pacific Superswell.” These efforts would be widely viewed as a waste of time if this superswell were proven not to exist. Recently, Levitt and Sandwell (1996) have proposed just that, based on a modal analysis of multibeam bathymetric data collected on sea floor aged 15 to 35 Ma in eastern French Polynesia. Citing a discrepancy between the ETOPO5 gridded depths and ship data from 4 expeditions in their study area, they suggest that the entire Superswell could be an artifact of poor ETOPO5 sampling and gridding. Here we present a more comprehensive analysis of original ship soundings from 82 oceanographic expeditions with satellite navigation collected since 1967. The soundings span sea floor from less than 30 to more than 110 Ma. We confirm the conclusion of Levitt and Sandwell that depth anomalies calculated from ETOPO5 slightly overestimate the true values from original ship soundings on sea floor aged 30 to 35 million years, but a positive depth anomaly of 250 m exists nevertheless. On older sea floor, we find that ETOPO5 slightly underestimates the magnitude of the depth anomaly based on a modal analysis, but overall the agreement in the mode of the depth/age data between ETOPO5 and the original ship soundings is quite striking, especially given the fact that less than 20% of the ship data used in our analysis had been collected at the time that the global bathymetric grid was prepared. There indeed is a South Pacific Superswell, and the magnitude and age‐dependence of the depth anomaly is as originally calculated from the mode of gridded bathymetry.
Volcanic ash from Icelandic ∼57,300 Yr BP eruption found in GISP2 (Greenland) Ice Core
Authors: Ram Michael , Donarummo John , Sheridan Michael
Published: February 2004

We have found volcanic ash in Wisconsinan ice from the GISP2 ice core retrieved from the Summit location in Central Greenland. The ash consists, predominantly of large rhyolitic glass shards similar to the ones found in Wisconsinan Dye 3 ice from Southern Greenland. We give the results of our analysis of the ash and present evidence that correlates this ash with the Z2 ash layer found in Atlantic sediment cores, with the Dye 3 ash, with ash recently found in the GRIP ice core from Central Greenland and with ash associated with the Icelandic Thorsmörk ignimbrite. The mineralogy of the ash is very similar to that of ash from the Icelandic Tindfjallajökull volcano that is also present in the Thorsmörk ignimbrite and we suggest that this is the source volcano. Tindfjallajökull has also been suggested as the source of the Z2 ash. Based on the excellent dating of the GISP2 ice core, we determined that the eruptions that produced the GISP2 ash occured 57,300±1,700 yr BP which agrees extremely well with the most recent dating of 57,500±1,300 yr BP of the Z2 ash based on the SPECMAP chronology. This provides us with a reliable revision of the Dye 3 ice core dating at a depth of ∼1950 m. This ice was originally dated at ∼70,000 yr BP.
Industrially induced changes in Earth structure at the Geysers Geothermal Area, California
Authors: Foulger G. R. , Grant C. C. , Ross A. , Julian B. R.
Published: February 2004

Industrial exploitation is causing clearly‐measurable changes in Earth structure at The Geysers geothermal area, California. Production at The Geysers peaked in the late 1980s at ∼3.5 × 10³ kg s−1 of steam and 1800 MW of electricity. It subsequently decreased by about 10% per year [Barker et al., 1992] because of declining reservoir pressure. The steam reservoir coincides with a strong negative anomaly (∼0.16, ∼9%) in the compressional‐to‐shear seismic wave speed ratio VP/ VS, consistent with the expected effects of low‐pressure vapor‐phase pore fluid [Julian et al., 1996]. Between 1991 and 1994 this anomaly increased in amplitude by up to about 0.07 (∼4%). This is consistent with the expected effects of continued pressure reduction and conversion of pore water to steam as a result of exploitation. These unique results show that VP/VS tomography can easily detect saturation changes caused by exploitation of reservoirs, and is a potentially valuable technique for monitoring environmental change. They also provide geophysical observational evidence that geothermal energy is not a renewable energy source.
A time domain electromagnetic survey of the TAG Hydrothermal Mound
Authors: Cairns G. W. , Evans R. L. , Edwards R. N.
Published: February 2004

A conductivity survey of the TAG mound was made using innovative transient electric dipole‐dipole instrumentation. The receiver was deployed on the sulfide mound 30 m south of the central black smoker while the submersible ALVIN carried the transmitter on a survey path around the receiver at a radius of approximately 70 m. Conductivity measurements of the seafloor between the transmitter and receiver were made at 5 minute intervals. The survey lasted 4 hours. Measurements made at 12 sites are initially interpreted in terms of an apparent conductivity of a uniform seafloor. A more complex model in which the seafloor has two layers is then used. Apparent conductivities range from 1.4 to 15.9 S/m, generally higher than that of seawater. The results suggest possible focusing of hydrothermal convection in the northern quadrant of the mound, adjacent zones of anhydrite accumulation and fluid convection in the north‐eastern quadrant, heterogeneity and layering in the Kremlin zone, and unexpected spatial variability in the western quadrant. The data from several sites show evidence of distortion attributed to 3‐D anomalies.
Nonlinearity of gravity wave saturated spectra in the middle atmosphere
Authors: Hines Colin O.
Published: February 2004

An argument based on general principles and minimal development is presented to establish the role of nonlinearity in producing the observed saturation of gravity‐wave spectra in the middle atmosphere. The complementary role of instability of the nonlinear spectrum is discussed. Earlier models of nonlinear saturation are reviewed in the context thus provided.
Atmospheric transparency at Flagstaff, Arizona, 1972–1996: Baselines and Volcanic episodes compared
Authors: Thompson Don T. , Wesley Lockwood G.
Published: February 2004

We present a summary of measurements of the atmospheric transparency over Flagstaff, Arizona, USA, made from 1972 to 1996. This period includes two major volcanic eruptions and two periods we believe are free from volcanic influence. The two eruptive periods show general similarity in history, although some differences are noted. Comparison of the two “clear” periods shows some deterioration in the tranparency over Lowell Observatory on a time scale of a decade.
Comparison of wind measurements between Yamagawa MF Radar and the MU Radar
Authors: Igarashi K. , Nishimuta I. , Murayama Y. , Tsuda T. , Nakamura T. , Tsutsumi M.
Published: February 2004

A new MF radar was installed at Yamagawa (31.20°N, 130.62°E), Japan in August, 1994 by the Communications Research Laboratory, and the first comparison of wind measurements taken with the Yamagawa MF radar and meteor wind measurements with the MU radar at Shigaraki (34.85°N, 136.10°E) are carried out. In spite of their spatial separation of approximately 650 km, reasonable agreement between wind velocities by the two radars at 80–92 km in altitude is confirmed, except for small scale perturbations that are probably due to gravity waves enhanced for the period from 17 h LT on September 13 to 7 h LT on September 14, 1994. It is found that the winds of the MF radar above 92 km tend to be smaller than the winds obtained with the MU radar. Receiver saturation and interference are possible causes of the reduced wind velocities observed with the MF radar. The height structures of semidiurnal tides are also compared. The amplitude and phase of zonal components agree at most heights between the two radars. For the meridional component the amplitudes fluctuate above 88 km with a significant difference and the phase from the MU radar leads that of the MF radar by less than several hours at 86 km to 92 km. An enhanced gravity wave seems to pass over the MU radar almost from north to south, resulting in a contamination of the meridional wind component of the semidiurnal variation.
Mechanism of incorporation of trace gases in ice grown from the gas phase
Authors: Dominé Florent , Thibert Emmanuel
Published: February 2004

The equilibrium solubilities and diffusion coefficients of HCl and HNO3 in ice have been measured at −15°C as a function of the trace gas partial pressures, PHCl or PHNO3. The diffusion coefficient of HCl is low: DHCl is about 10−12 cm²s−1 while that of HNO3, DHNO3, is greater, about 10−10 cm²s−1. The solubility values are compared with field measurements performed in central Greenland where HCl in snow was found to be out of equilibrium with the atmosphere, while HNO3 in snow was in equilibrium. A mechanism of incorporation of trace gases in ice growing from the gas phase is proposed from these observations: ice grows by the deposition of layers of a given thickness, whose composition is determined by condensation kinetics. The layers then tends to equilibrate by solid state diffusion until they are covered by the following layer. Implications of these results for ice cloud chemistry and ice core analyses are discussed.
A new airglow layer in the stratosphere
Authors: Evans W. F. J. , Shepherd G. G.
Published: February 2004

A new airglow layer has been observed arising from the 40 to 60 km level in the stratosphere. The upper portion of this layer was first measured by the WINDII instrument when the Upper Atmospheric Research Satellite was rotated in roll angle so the field of view measured down to 60 km in January, 1994. The main hydroxyl airglow layer at 85 km is measured with the WINDII filter channel at 730 nm. After the April roll angle increase, a continuum emission layer was observed below 70 km on numerous images. It is proposed that this emission originates from excited NO2 created from the reaction of O3 with NO. This new airglow layer is peaked around 45 km about 1 hour after sunset. The chemiluminescent glow from this reaction is well known in the laboratory and is used in balloon instruments for the measurement of nitric oxide in the stratosphere and troposphere.
Prediction of iceberg trajectories for the North Atlantic and Arctic oceans
Authors: Bigg Grant R. , Wadley Martin R. , Stevens David P. , Johnson John A.
Published: February 2004

Icebergs are a well‐known hazard for shipping. Their study also provides information about diverse geophysical processes, as varied as ocean circulation, air‐sea fluxes, calving rates of glaciers or the mass balance of ice sheets. As a first step to obtaining this information from iceberg data we have developed a model of iceberg drift driven by ocean and atmospheric forcing derived from general circulation models. We have applied the drift model to a distribution of typical icebergs released from the main tidewater glaciers of the North Atlantic and Arctic Oceans. We demonstrate that the main driving force of iceberg motion is rooted in the unsteady component of oceanic advection. From simulated trajectories we are able to reproduce the observed southwards limit of iceberg penetration and demonstrate sometimes surprising geographical links between iceberg origin and ultimate melting zones.
Clay content, porosity and velocity of Amazon fan sediments determined from ODP Leg 155 cores and wireline logs
Authors: Pirmez Carlos , Flood Roger D. , Baptiste John , Yin Hezhu , Manley Patricia L.
Published: February 2004

We characterize variations in velocity and porosity as a function of clay content for different depositional units of the Amazon Fan (levees, sand‐rich High‐Amplitude Reflection Packets, or HARPs and mass‐transport deposits, or MTDs) using core and log data. Younger fan sediments, including both HARP and levee turbidites, show an increase in porosity and a decrease in velocity with increased clay content, a relationship indicative of a matrix‐supported regime. In contrast, older, more deeply buried overbank turbidites and MTDs, show opposite physical‐property trends, which are indicative of a framework‐supported regime. The changing behavior of physical properties within various fan units results from a combination of the nature of clay distribution within the sediment caused by different depositional processes, and to changes in sediment structure during early burial and diagenesis.
Observations of a sky Lyman α groove related to enhanced solar wind mass flux in the neutral sheet
Authors: Bertaux Jean‐Loup , Quémerais Eric , Lallement Rosine
Published: February 2004

We report several observations of the Lα interplanetary emission recorded by a photometer flown in 1977 on board the soviet spacecraft Prognoz‐5. The Prognoz scans sampled emission in a plane perpendicular to the sun‐spacecraft line and also traversed the Lα maximum emission region (MER), a region centered a few AU from the Sun on the upstream interstellar‐flow axis. These scans reveal the existence of a 10% decrease in intensity centered near the ecliptic plane and about 30° wide. All the dips form a new feature of the interplanetary emission, a “groove” aligned approximately with the ecliptic plane. This groove is present only near the upwind direction, and is interpreted as the result of enhanced ionisation of interstellar H by charge‐exchange with the solar wind in a sheet of approximately 30° width in latitude around the average position of the neutral sheet, at this time of solar minimum.
Simulation of Kelvin Helmholtz Instability in resistive plasmas
Authors: Min K. W. , Lee D. Y.
Published: February 2004

In this paper, the effects of magnetic reconnection induced by the Kelvin‐Helmholtz (KH) instability are examined in resistive plasmas. It is found from the magnetohydrodynamic (MHD) simulations that highly distorted magnetic field lines deformed from the initial parallel configuration by the KH instability become reconnected and flattened when the magnetic field intensity is not strong. Energy conversion and the momentum transport are most effective in the small range of magnetic field intensity. A strong magnetic field stabilizes vortex growing early on and a weak magnetic field does not grow much before it diffuses, while the electromagnetic stress plays an important role in transferring momentum and energy across the velocity shear boundary.
Evidence for continuing current in sprite‐producing cloud‐to‐ground lightning
Authors: Reising Steven C. , Inan Umran S. , Bell Timothy F. , Lyons Walter A.
Published: February 2004

Radio atmospherics launched by sprite‐producing positive cloud‐to‐ground lightning flashes and observed at Palmer Station, Antarctica, exhibit large ELF slow tails following the initial VLF portion, indicating the presence of continuing currents in the source lightning flashes. One‐to‐one correlation of sferics with NLDN lightning data in both time and arrival azimuth, measured with an accuracy of ±1° at ∼12,000 km range, allows unambiguous identification of lightning flashes originating in the storm of interest. Slow‐tail measurements at Palmer can potentially be used to measure continuing currents in lightning flashes over nearly half of the Earth's surface.
The sensitivity of post‐glacial sea level to viscosity structure and ice‐load history for realistically parameterized viscosity profiles
Authors: Fang Ming , Hager Bradford H.
Published: February 2004

The continuous variation of viscosity with depth expected from microphysical theories of silicate creep differs significantly from the layered structures typically used to model post‐glacial relative sea level variations and to refine models of ice load histories. Here we predict relative sea level (RSL) curves for a set of realistically parameterized continuous viscosity profiles with different amounts of depth dependence. We demonstrate by forward modeling that different classes of realistically parameterized mantle viscosity structures are resolvable by RSL at the edge sites, but the predicted RSL there is very sensitive to the assumed ice load history. Furthermore, the sensitivity of RSL variations at these sites to the viscosity structure depends strongly upon the ice model. At sites less sensitive to the ice model, the resolving power for viscosity structure is also less. When ICE‐1A, an ice model derived without assumption of mantle viscosity structure, is used to compute RSL variations, some models with realistic continuous viscosity increases with depth fit the observations better than the “standard model” used to derive more recent ice models.
Accuracy of total ozone column amounts observed with solar infrared spectroscopy
Authors: Murata I. , Kondo Y. , Nakajima H. , Koike M. , Zhao Y. , Matthews W. A. , Suzuki K.
Published: February 2004

Total ozone column amounts were observed at Rikubetsu (43.5°N, 143.8°E), Japan on 90 days between May 18, 1995 and April 26, 1996 with a high‐resolution infrared (IR) Fourier transform spectrometer and compared with Dobson spectrometer measurements. The sensitivities of the analysis for IR solar absorption spectra to initial profiles were examined using two kinds of initial profiles for ozone and temperature, namely monthly and yearly averages. IR/Dobson mean column ratios in the two cases were 1.02 and 1.03 and the standard deviation of the ratios were 3.7 and 4.1%, which correspond to 14 and 16 Dobson Units. The standard deviations are smaller than or comparable to the amplitudes of the day‐to‐day total ozone column variations indicating that day‐to‐day variations can be detected using monthly or yearly averaged profiles. However, significant solar zenith angle (SZA) dependences were observed in the columns derived using yearly averaged profiles. The SZA dependence was most significant in January and February when the ozone amount in the lower stratosphere was largest. The SZA dependence is considered to be caused by the difference between initial and actual ozone profiles.
Carbon‐13 variations in the dissolved inorganic carbon in estuarine waters
Authors: Sackett William M. , Netratanawong Toedsit , Holmes M. Elizabeth
Published: February 2004

The stable carbon isotope composition of dissolved inorganic carbon [DIC] was measured in Tampa Bay and Florida Bay. The dependence of isotopic composition was evaluated in terms of atmospheric CO2 exchange, carbon exchange between fresh water and seawater (i.e. salinity) and DIC derived from the reaction between calcium carbonate and organically derived CO2.

The extent of organic carbon oxidation and the magnitude of organic carbon loading [pollution] in an estuary have implications for variations in the δ13C of DIC and its use as an indicator of the relative amounts of land and marine derived organic and inorganic carbon in paleogeographic studies.
Can the Topex/Poseidon altimetry data be used to estimate air‐sea heat flux in the North Atlantic?
Authors: Wang Liping , Koblinsky Chester
Published: February 2004

We propose a novel approach to directly invert large‐scale anomalous annual net air‐sea heat flux from the Topex/Poseidon altimetry data in the North Atlantic. The major advantage of this new approach over the conventional bulk formula approach is that it does not need those climate parameters used in the conventional bulk formula calculation in estimating the large‐scale anomalous annual net air‐sea heat flux. Comparison with expendable bathythermograph data demonstrates that it is a feasible approach.
Wave activity near Pluto
Authors: Shevchenko V. I. , Ride S. K. , Baine M.
Published: February 2004

In this paper, we analyze wave activity near Pluto. The situation is somewhat analogous to that near comets: molecules (in this case methane) escape from the atmosphere; some are phono‐ionized, and a comet‐like mass‐loading of the solar wind plasma takes place. But the wave activity due to planetary ion interaction with the solar wind is quite different from that near comets. In the weak interplanetary magnetic field near Pluto, there is no MHD wave excitation; instead, we show that ion acoustic waves are excited. We construct a nonlinear theory of ion‐acoustic wave excitation. These waves are excited due to a dissipative instability. The frequency, characteristic growth rate, and spatial scale of the instability are calculated. The main physical mechanism for wave amplitude saturation is the smearing of the velocity distribution function of the beam ions. We use a quasilinear approach to determine the characteristic scale for the electric wave amplitude.
Polar temperature sensitivity to lunar forcing?
Authors: Shaffer John A. , Cerveny Randall S. , Balling Robert C.
Published: February 2004

Climate models and paleoclimatic evidence suggest that the earth's polar regions are particularly responsive to global scale climatic forcing. Empirical climatological evidence of the last century has thus far failed to confirm conclusively this regional sensitivity. We conduct an empirical study of polar sensitivity to climate forcing by comparing a high‐quality, 17‐year satellite‐derived dataset of daily temperatures for 2.5° latitudinal bands to a known external forcing mechanism, the lunar phase cycle. The earth's polar regions display a temperature range of greater than 0.55°C over the course of a synodic (29.53 day) month. This lunar‐influenced range in temperature is 25 times larger than a similarly computed range in aggregated global temperatures over a synodic month. Temperature variations between the polar and non‐polar regions also produce a pronounced temporal shift in sensible heat transfer. Strong poleward transfer of heat dominates near the full moon but the transfer substantially weakens near the new moon. It is unlikely that this sensitivity can be explained by the type of polar forcing previously identified in GCM simulations and paleoclimatic reconstructions, because of the short duration of the lunar cycle. However, it does demonstrate a new and potentially important external influence on the polar regions' climates.
Evidence of non‐LTE in the CO2 15 µm weak bands from ISAMS and WINDII observations
Authors: López‐Puertas M. , Dudhia A. , Shepherd M. G. , Edwards D. P.
Published: February 2004

An analysis of the measurements of the CO2 15 µm radiance emission by the UARS/ISAMS 30W channel and the kinetic temperature from UARS/WINDII taken on July 21, 1992 at northern latitudes around the mesopause is presented. The modeling of the measurements clearly show evidence of non‐LTE emissions in the CO2(ν2=1) levels of the minor isotopes 636, 628, and 627 in the 70–90 km region. A comparison with non‐LTE model predictions by López‐Puertas et al. [1992a] shows a good agreement within the errors in the measured quantities. This constitutes the first experimental evidence of non‐LTE emissions in these CO2 15 µm weak bands. The measurements also represent indirect evidence of the net radiative heating produced by these bands around the summer mesopause.
Infra‐red rocket glow: A mechanistic analysis
Authors: Murtagh D. P. , Llewellyn E. J. , Espy P. J.
Published: February 2004

A two channel infra‐red radiometer observed a contaminating glow at 1.53 µm on the up and down legs of a rocket flight between 90 and 105 km. No contamination was detectable at 1.27 µm nor by broadband uv/visible photodiode photometers. The structures in the glow showed a remarkable similarity with the structures on the simultaneously measured atomic oxygen profile. We have been able to show that the glow can be successfully modelled by I ∞ [O]² v², where v is the rocket speed. This implies that two oxygen atoms arriving on the surface are involved in the production of the emitting species. It is suggested that the oxygen atoms form a molecule which is either radiatively stabilized or undergoes an association/dissociation with a surface adsorbed oxygen molecule.
Georadar anisotropy in the Gotthard Gneiss, Switzerland
Authors: Cook Frederick A. , Vasudevan Kris
Published: February 2004

Georadar data recorded in a crystalline gneiss of southern Switzerland exhibit two effects that are related to anistropic metamorphic fabric. In the first, signal coherence appears to be better for waves propagating parallel to the direction of foliation and, in the second, rms velocities of waves propagating along the foliation are higher than for waves propagating at a high angle to foliation.
Comet Hyakutake x‐ray source: Charge transfer of solar wind heavy ions
Authors: Cravens T. E.
Published: February 2004

Recently, Lisse et al. (1996) reported on exciting observations by the Röntgen X‐ray satellite (ROSAT) of x‐ray and extreme ultraviolet emissions from comet C/Hyakutake 1996 B2. The spatial distribution of the emissions was displaced sunward of the nucleus and the spatial extent was about 105 km. Lisse et al. (1996) suggested that the emission could be explained by thermal bremsstrahlung associated with hot electrons, possibly due to solar wind interaction effects. In the present paper, an alternate emission mechanism is proposed. The solar wind contains a large number of minor/heavy ion species with a range of charge states, such as O6+, C5+, N5+, and Si10+. These ions will readily charge transfer with cometary neutrals, producing ions which can be highly excited and consequently emit photons in the extreme ultraviolet and x‐ray part of the spectrum. The photon emission rate is proportional to the solar wind heavy ion flux and hence to the solar wind flux and, with some assumptions concerning the solar wind velocity, to the solar wind number density. The emission rate should be greatest downstream of the bow shock along the sun‐comet axis in agreement with the observed spatial distribution. The x‐ray images are really images of the line of sight integration of the solar wind density convoluted with the cometary neutral density. A total EUV/x‐ray luminosity for comet Hyakutake from this charge transfer mechanism agrees with the observed luminosity of 4 × 1015 ergs s−1 within a factor of two.
A limited‐area‐model case study of the effects of sub‐grid scale Variations in relative humidity and cloud upon the direct radiative forcing of sulfate aerosol
Authors: Haywood J. M. , Ramaswamy V. , Donner L. J.
Published: February 2004

A limited‐area non‐hydrostatic model with a horizontal spatial resolution of 2km by 2km is used to assess the importance of sub‐grid scale variations in relative humidity and cloud upon the direct radiative forcing (DRF) by tropospheric sulfate aerosols. The DRF from the limited‐area model for both clear and cloudy regions is analyzed and the results compared against those obtained using general circulation model (GCM) parameterizations that perform the computations over coarse horizontal grids. In this idealized model study, the GCM calculations underestimate the clear sky DRF by approximately 73% and the cloudy sky DRF by approximately 60%. These results indicate that, for areas where the relative humidity is high and where there is substantial spatial variability in relative humidity and cloud, GCM calculations may considerably underestimate the DRF.
Inter‐decadal signals during the last millennium (AD 1117–1992) in the Varve record of Santa Barbara Basin, California
Authors: Biondi Franco , Lange C. B. , Hughes M. K. , Berger W. H.
Published: February 2004

Annual varve thickness (AD 1117–1992) from Santa Barbara basin has been decomposed into orthogonal components using singular spectrum analysis (SSA) to identify and retrieve inter‐decadal oscillations. After removing all variability with periods greater than 150 years, leading SSA eigenfunctions (EOFs) identify four oscillatory pairs with periods of ∼100, ∼58, ∼25, and ∼12 years respectively. Based on 2500 simulated series and on two‐sided confidence intervals, EOFs 1–7 are significant at the 99% level and EOFs 8–9 are significant at the 90% level. Oscillatory signals retrieved from the marine varves show an abrupt change in frequency and amplitude near AD 1600. The largest contribution to this environmental shift is given by the interdecadal components, especially the ∼25 and the ∼12‐year oscillation. The near‐AD 1600 change may be related to multi‐annual events reported in the stratigraphy of the nearby Santa Monica Basin and in dendrochronological records of the American Southwest.
Dynamical consequences of mid‐mantle viscosity stratification on mantle flows with an endothermic phase transition
Authors: Cserepes László , Yuen David A.
Published: February 2004

Recent geophysical evidences from seismology and geoid inversions have pointed out the existence of some layering between 900 and 1000 km depth and the possibilities of a low viscosity zone between 660 and 1000 km depth. Using a finite‐difference and spectral code, we have conducted 3‐D calculations of thermal convection with the endothermic phase transition at 670 km depth and a family of viscosity profiles with emphasis on the presence of two low viscosity zones, one in the upper mantle between 100 and 250 km depth and the second one between 670 and 1000 km depth. Below 1000 km the viscosity increases with depth. The surface Rayleigh number used was in the range of 107. The dominating effect is that due to the second low viscosity zone below the phase change. Layered convection is induced by the presence of this second asthenosphere, which causes horizontal flow to develop in there. Alternatively, a viscosity increase at 670 km depth would shift convection to the single‐layer regime. The potential sharp variations of the viscosity structure between 670 and 1000 km depth can greatly influence the global flow dynamics of the mantle.
The response to deforestation and desertification in a model of West African monsoons
Authors: Zheng Xinyu , Eltahir Elfatih A. B.
Published: February 2004

Since Charney proposed his theory on the dynamics of deserts and droughts in the Sahel [Charney, 1975], there has been significant scientific interest in the interaction between vegetation and climate in this region. The essence of this interaction is that the atmospheric circulation, and therefore rainfall, over this region may be sensitive to changes in vegetation cover near the desert border. Here we describe simulations of the West African monsoons with a simple zonally‐symmetric model. The results suggest that the potential impact of human induced change of land cover on regional climate depends critically on the location of the change in vegetation cover. That is, desertification along the border with the Sahara (e.g., in Chad, Niger, Mali and Mauritania) leaves a relatively minor impact on monsoon circulation and regional rainfall; deforestation along the southern coast of West Africa (e.g., in Nigeria, Ghana and Ivory Coast) may result in complete collapse of monsoon circulation, and a significant reduction of regional rainfall.
Undersaturation of CH3Br in the Southern Ocean
Authors: Lobert Jürgen M. , Yvon‐Lewis Shari A. , Butler James H. , Montzka Stephen A. , Myers Richard C.
Published: February 2004

Dry mole fractions of methyl bromide (CH3Br) in marine boundary layer air and in air equilibrated with surface water were measured in the Southern Ocean. Saturation anomalies were consistently negative at −36±7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH3Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at −21 (−11 to −32) Gg y−1.
Radiogenic heat production in the upper third of continental crust from KTB
Authors: Pribnow Dan F. C. , Winter Helmuth R.
Published: February 2004

The heat production rate of continental crystalline rocks was determined from cores and drill cuttings recovered from depths up to 9.1 km in boreholes drilled by the Continental Deep Drilling Program of Germany (KTB). The drilled rocks are mainly gneisses and metabasites. Based on a large amount of data, the comparison of laboratory and in situ determinations by logging shows good agreement. The loss of radioactive elements in drill cutting samples at the shaker tables was minimized by using a broad range of available fragment sizes. The data reveal a clear lithological dependence of the heat production rate of the metamorphic rocks at KTB. The lithologically caused variations of the heat production rate have a wavelength in the order of the drilled depth and therefore, they cover up any decreasing trend if there is one. Below 6 km, tectonic elements such as fault zones play also an important role in the observed vertical distribution. Despite the availability of data for the upper third of the crust, models to predict temperatures for greater depths still contain uncertainties.
Finding the isentropic density of perovskite: Implications for iron concentration in the lower mantle
Authors: Anderson Orson L.
Published: February 2004

The definition of the adiabatic modulus, KS, is used as the basis of an isentropic P(V) equation of state (EoS) to find the density isentrope at lower mantle conditions. The adiabatic constraint makes temperature depend on pressure in the EoS. Thus one can calculate the density isentrope corresponding to the lower mantle values of P at every depth, and this is done for perovskite. A silicate perovskite with iron concentration fp=0.12 and without the addition of magnesiowüstite produces a density distribution exactly matching that of PREM (the chondritic case), the same result as presented by Stixrude et al. However, this apparent agreement results from ignoring higher‐order terms of the EoS; when such terms are included, the agreement between the calculated density of perovskite and the density of the lower mantle is not good. A smaller amount of iron in perovskite lowers the isentropic density and suggests the addition of magnesiowüstite in order to match the PREM density distribution (the pyrolitic case). Recent results of Stacey and of Kesson and Fitzgerald strongly suggest that fp=0.05–0.06, requiring that the remaining iron be in magnesiowüstite (pyrolite).
CO2 amount on Venus constrained by a criterion of topographic‐greenhouse instability
Authors: Hashimoto George L. , Abe Yutaka , Sasaki Sho
Published: February 2004

Which mechanism determines the planetary atmospheric inventories of various gases is an important problem. It has been suggested that Venus' atmospheric CO2 abundance is controlled or buffered by carbonation reaction on the surface (carbonate buffer). According to this hypothesis, the formation or decomposition of carbonate stabilizes atmospheric CO2 concentration. However, the amount of carbonate existing on the Venus' surface is not established yet. Using a stability analysis that combines the greenhouse effect, carbonation reaction, and topography, we place an upper limit to carbonate on Venus. This upper limit of carbonate is only about 4 bar of CO2 and is much smaller than the amount of CO2 in the atmosphere. This suggests that the present CO2 concentration in Venus' atmosphere is not controlled by the carbonation reaction but by the total abundance of CO2 in near surface layers.
Springtime Antarctic total ozone measurements in the early 1970s from the BUV instrument on Nimbus 4
Authors: Stolarski R. S. , Labow G. J. , McPeters R. D.
Published: February 2004

Data from the BUV instrument on the Nimbus 4 satellite have been used to construct maps of the measured total ozone field over the Antarctic region during the Austral springs of 1970 through 1973. These maps show an October mean ozone distribution similar to that measured in 1979 by the Nimbus 7 TOMS instrument. These ozone maps during the 1970s are very different from those measured during the late 1980s and early 1990s. The ozone distribution for each of the years during the early 1970s is characterized by a circumpolar, crescent‐shaped maximum surrounding a shallow minimum centered near the pole. The total ozone amounts in the polar minimum region in the early 1970s average about 300 Dobson units, comparable to the amounts measured at that time over Halley Bay and Syowa by ground‐based Dobson Spectrophotometers.
Solar wind control of density and temperature in the near‐Earth plasma sheet: WIND/GEOTAIL collaboration
Authors: Terasawa T. , Fujimoto M. , Mukai T. , Shinohara I. , Saito Y. , Yamamoto T. , Machida S. , Kokubun S. , Lazarus A. J. , Steinberg J. T. , Lepping R. P.
Published: February 2004

A statistical survey of GEOTAIL observations reveals the following properties of the near‐Earth plasma sheet (−15 < XGSM′ < −50 Re): During the periods when the northward IMF dominates, (1) the plasma sheet becomes significantly cold and dense, (2) the best correlations between the plasma sheet and the IMF parameters occur when the latter quantities are averaged over 9−4+3 hours prior to the plasma sheet observations, and (3) temperatures diminish and densities increase near the dawn and dusk flanks of the plasma sheet. We suggest that during prolonged northward IMF periods (∼ several hours) there is a slow diffusive transport of the plasma from the solar wind into the plasma sheet through the the magnetotail flanks.
Pressure dependence of velocity and attenuation and its relationship to crack closure in crystalline rocks
Authors: Meglis I. L. , Greenfield R. J. , Engelder T. , Graham E. K.
Published: February 2004

Measurements of linear strain, ultrasonic velocity, and attenuation (Q−1) were made simultaneously as functions of confining pressure on core and outcrop samples from the Moodus, Connecticut, area. Strain measurements indicate the core samples contain cracks which formed in part by stress relief during recovery (Meglis et al., 1991). The outcrop samples have a small crack porosity compared with the cores. Closure of cracks with increasing confining pressure causes an increase in velocity and a decrease in attenuation. We present a form for the pressure dependence of the crack density parameter ε (the number of cracks of unit radius per unit volume), which was used to incorporate the influence of crack closure with pressure into models of wave velocity and attenuation in cracked solids. The crack density parameter is represented as an exponentially decreasing function of confining pressure. The pressure dependence of ε was determined from the strain measurements using the non‐self‐consistent effective modulus approach of O'Connell and Budiansky (1974), from the velocity data using the solutions of Garbin and Knopoff (1973) and Hudson (1981), and from the attenuation measurements using the frictional attenuation model of Walsh (1966). All of the models fit the data reasonably well using an exponentially decaying ε described by one decay constant τ. However, some of the data are better fit by a crack density parameter with two decay constants, reflecting a rapid decrease of ε at low pressure and a slower decrease at higher pressure. There is considerable variation among the predicted decay constants for a given sample from the different data sets. Several factors contribute to this variation. For example, the two velocity models predict a different dependence of velocity on ε, which results in a different dependence of ε on pressure. For the Q−1 data, approximating dε/dP by a function with a single decay constant results in lower τ values for Q−1 than for strain or velocity. Finally, a large anisotropy in attenuation measured in the deepest core samples indicates that scattering is a significant source of wave energy loss in these samples, and therefore a frictional attenuation mechanism alone cannot account for all the observed attenuation.
Incorporating “sinuous connectivity” into stochastic models of crustal heterogeneity: Examples from the Lewisian gneiss complex, Scotland, the Franciscan formation, California, and the Hafafit Gneiss Complex, Egypt
Authors: Goff John A. , Levander Alan
Published: February 2004

Stochastic models are valuable and sometimes essential tools for investigating the behavior of complex phenomena. In seismology, stochastic models can be used to describe velocity heterogeneities that are too small or too numerous to be described deterministically. Where analytic approaches are often infeasible, synthetic realizations of such models can be used in conjunction with finite difference algorithms to systematically investigate the response of the seismic wave field to complex heterogeneity. This paper represents a continuing effort at formulating a complete and robust stochastic model of lithologic heterogeneity within the crust, and the means of generating synthetic realizations; “complete” implies that the model is flexible enough to describe all types of random heterogeneity within the crust, while “robust” implies sufficiently constrained parameterization that an inversion problem may be well‐posed. As a basis for investigation we use geologic maps of crustal exposures and petrophysically inferred velocities. Earlier efforts at stochastic modeling have focused on characterization of the univariate probability density function, which is typically modal (i.e., binary, ternary, etc.), and the covariance function, which is typically fit with a von Kármán function. Here we provide a means of characterizing the property of “sinuous connectivity” and for generating realizations that possess this property. Sinuous connectivity is the tendency for individual lithologic units to be continuous over long and highly contorted paths; there is no means in the earlier modeling of either characterizing or synthesizing this property. We generate sinuously connective realizations by mapping regions encompassed by two contours in a Gaussian‐distributed surface into the two values of the binary field. This operation is nonunique, as one can choose, in many ways, the values for the contours.
Chemical and isotopic evidence for sources of fluids in a mud volcano field seaward of the Barbados accretionary wedge
Authors: Martin Jonathan B. , Kastner Miriam , Henry Pierre , Le Pichon Xavier , Lallement Seigfried
Published: February 2004

Chemical, isotopic, and heat budgets are controlled by fluid flow and venting at convergent margins. Fluids vent from accretionary complex sediments via numerous pathways including mud volcanoes, which are common at the Barbados convergent margin. Chemical and isotopic compositions of fluids collected from four mud volcanoes, located east of the Barbados deformation front at 13°50′N, indicate venting is sufficiently rapid to prevent diffusion from seawater. In sediments surrounding the mud volcanoes, the rate of nonfocused fluid flow is ∼0.26 cm/yr. Although this rate is ∼3 orders of magnitude slower than the flow from the mud volcanoes, significantly more fluid vents from the sediments surrounding the mud volcanoes than from the restricted areas of rapid flow from the volcanoes. Chloride concentrations are depleted to a minimum of 211 mM (∼45% of seawater value) primarily by mixing diagenetically altered pore fluids with an 18O‐enriched fresh water released from the dissociation of methane hydrate. This reaction is accompanied by the release of sufficient methane to form a free gas phase and initiate eruption of the mud volcanoes. The geochemical compositions of the diagenetically altered pore fluids reflect the interplay between five major reactions: (1) clay mineral dehydration, which releases H2O and influences a range of chemical and isotopic compositions; (2) organic matter regeneration, which increases alkalinity, NH4+, and Br− and decreases SO42− concentrations; (3) cation exchange with clay minerals, which increases Na+ and decreases NH4+ concentrations; (4) carbonate recrystallization and precipitation, which decrease Ca2+ but increase Sr2+ concentrations; and (5) conversion of volcanic ash to clay minerals, which utilizes H2O and decreases Mg2+ concentrations. The geochemistry of the pore fluids suggests that these reactions occurred at temperatures ranging from ∼75° to 115°C. Thus at the regional geothermal gradients of ∼27 to 40°C/km, these temperatures indicate that the source regions are at ∼2 to 4.5 km depth.