bluuebunny/crossref_metadata_2025 huggingface dataset:
Early transient cooling of Mars
Authors: Choblet Gaël , Sotin Christophe
Published: February 2004

Previous evolution models for one‐plate planets have commonly assumed steady‐state cooling beneath a rigid lid. Recent 3D numerical models indicate however that conductive lid cooling exhibits early transient stages where the quasi‐static assumption is not valid. We apply scaling laws for these transient stages to Mars. A wide range of initial conditions for the Martian mantle reflects the possible consequence of the early differentiation of the planet. Our results display large variations for the timing of early transient cooling from several 100 Ma up to a few Ga indicating that classical quasi‐static models cannot describe a significant part of the planet's evolution. This suggests new scenarios for Mars'‐early history with initial heat fluxes in good agreement with values inferred from both gravity and topography data from the MGS mission.
Disjunct eddy covariance technique for trace gas flux measurements
Authors: Rinne H. J. I. , Guenther A. B. , Warneke C. , de Gouw J. A. , Luxembourg S. L.
Published: February 2004

A new approach for eddy covariance flux measurements is developed and applied for trace gas fluxes in the atmospheric surface layer. In disjunct eddy covariance technique, quick samples with a relatively long time interval between them are taken instead of continuously sampling air. This subset of the time series together with vertical wind velocity data at corresponding sampling times can be correlated to give a flux. The disjunct eddy sampling gives more time to analyze the trace gas concentrations and thus makes eddy covariance measurements possible using slower sensors. In this study a proton‐transfer‐reaction mass spectrometer with response time of about 1 second was used with a disjunct eddy sampler to measure fluxes of volatile organic compounds from an alfalfa field. The measured day‐time maximum methanol fluxes ranged from 1 mg m−2 h−1 from uncut alfalfa to 8 mg m−2 h−1 from freshly cut alfalfa. Night‐time fluxes were around zero.
Summertime moisture divergence over the southwestern US and northwestern Mexico
Authors: Anderson Bruce T. , Roads John O.
Published: February 2004

This paper investigates large‐scale summertime moisture divergence associated with the southwestern branch of the North American monsoon. Diagnostic hydrologic estimates taken from thirty‐three years of seasonal mean reanalysis data indicate that over most of the southwestern United States and northwestern Mexico there is positive vertically‐integrated columnar (i.e. three dimensional) moisture divergence above approximately 700 mbar, implicitly suggesting that mid‐level moisture convergence related to advection from remote source regions cannot support seasonal mean precipitation over the southwestern US. Furthermore, estimates of the horizontal component of this moisture divergence indicate that the southwestern US is actually one of the largest upper‐air (<700 mbar) sources of moisture for the North American continent.
Tracer analysis of transport from the boundary layer to the free troposphere
Authors: Kowol‐Santen J. , Beekmann M. , Schmitgen S. , Dewey K.
Published: February 2004

A mesoscale meteorological model with passive tracers is applied in order to analyze transport from the atmospheric boundary layer to the free troposphere. The validation of the model against aircraft measurements indicates that the model adequately simulates the tracer distributions in the free troposphere as well as in the boundary layer. Budget calculations of passive tracers are performed in order to estimate the amount of transport in the area of a frontal system. The results show a very effective uplift associated in particular with a WCB transporting up to ∼70% of a passive tracer initialized in the boundary layer to the free troposphere within 3 days.
First principles thermoelasticity of MgSiO3‐perovskite: Consequences for the inferred properties of the lower mantle
Authors: Karki Bijaya B. , Wentzcovitch Renata M. , de Gironcoli Stefano , Baroni Stefano
Published: February 2004

Some key thermoelastic properties of MgSiO3‐perovskite (pv) have been determined at lower mantle (LM) pressures and temperatures using the quasi‐harmonic approximation in conjunction with first principles phonon dispersions. The adiabatic bulk moduli (KS) of pv and of an assemblage of 80 vol% pv and 20 vol% MgO were obtained along the thermodynamically inferred adiabat and compared with the seismic counterpart given by the preliminary reference Earth model (KPREM). The discrepancy between calculated KS's and KPREM in the deep LM suggests a super‐adiabatic gradient, or subtle changes of composition, or phase, or all beginning at about 1200 km. The Anderson Grüneisen parameter, δS=(∂lnKS/∂lnρ)P, was predicted to decrease rapidly with depth (from 2.7 to 1.2 across the LM) supporting the thermal origin for the lateral heterogeneities throughout most of the LM.
Impact of Arctic treeline on synoptic climate
Authors: Beringer Jason , Tapper Nigel J. , McHugh Ian , Chapin F. S. , Lynch Amanda H. , Serreze Mark C. , Slater Andrew
Published: February 2004

The position of the Arctic treeline has been associated with the preferred location of Arctic fronts that demarcate the boundary between Arctic and polar air masses. It has been argued that differences in summer energy balance, particularly in sensible heating, across treeline between forest and tundra may help determine the location of these frontal zones. Our observations of the energy balance at treeline show that the daily averaged summer heating contrast between treeline forest and tundra is an order of magnitude less than that previously proposed and that the influence on the atmosphere is confined to a shallow layer. In addition, maximum heating contrasts occurred in spring rather than in summer when the Arctic frontal zone is best expressed. Hence energy‐balance contrasts at treeline are unlikely to be the major determinant of the position of the Arctic front.
Modeling multi‐phase halogen chemistry in the marine boundary layer with size‐segregated aerosol module: Implications for quasi‐size‐dependent approach
Authors: Toyota Kenjiro , Takahashi Masaaki , Akimoto Hajime
Published: February 2004

A photochemical box model with size‐segregated aerosol module, which explicitly accounts for size‐dependent chemical properties of sea‐salt particles, has been developed to simulate multi‐phase chemistry of chlorine and bromine in the marine boundary layer (MBL). Simulated results are compared with those obtained by a model that only implicitly accounts for particle size dependence by applying the quasi‐size‐dependent approach (bulk model). It is found that the bulk model fails to capture the decreased volatilization rates of bromine from the small‐sized sea‐salt particles caused by rapid depletion of bromide. This leads to substantial overestimation of gas phase bromine mixing ratios by the bulk model, affecting the behavior of other species such as ozone and NOx that are sensitive to bromine chemistry. The findings warrant the use of size‐segregated model in simulating MBL halogen chemistry.
The rotation period of Jupiter
Authors: Russell C. T. , Yu Z. J. , Kivelson M. G.
Published: February 2004

The period with which radio bursts recur on Jupiter (the System III period) is defined by the IAU to be 9h 55m 29.71s based on early radio astronomical data, and is generally assumed to represent the period of rotation of the Jovian interior. A recent estimate of the System III period from radio burst data is 0.025s shorter than the IAU value. In apparent contradiction to the radio observations, in situ measurements of the rotation period of Jupiter using the orientation of the dipole moment are consistent with the original rotation period defined by the IAU and inconsistent with the suggested period decrease. Thus, the present IAU period should be retained as the best estimate of the rotation rate of the Jovian interior. Since the radio bursts are generated near the base of the Io field line while the dipole field is measured by Galileo near the equatorial plane, the difference between the two rotation periods could be explained if Jupiter's magnetic field is undergoing perceptible secular variation.
The composition and origin of the lunar crust: Constraints from central peaks and crustal thickness modeling
Authors: Wieczorek Mark A. , Zuber Maria T.
Published: February 2004

Spectral‐reflectance data of lunar central peaks have revealed that the Moon's crust varies both laterally and vertically in composition. We correlate the depths of origin of materials that make up central peaks with a geophysically derived dual‐layered crustal thickness model and find that the peak compositions are consistent with this stratified model. Specifically, peaks composed exclusively of rocks containing more than 85% plagioclase (by volume) come from this model's upper crust, whereas peaks that contain some norite or gabbro‐norite come from the model's lower crust. Extrapolating these data we find that the Moon's upper crust is composed of 88±4% plagioclase, corresponding to 29 to 32 wt.% Al2O3. The most‐mafic lower portion of the crust is composed of 65±8% plagioclase, having an Al2O3 content that lies between 18 and 25 wt.%. We show that the lower portion of the crust is consistent with having formed by cumulate flotation in a lunar magma ocean.
Ionic clusters in the polar winter stratosphere
Authors: D'Auria Raffaella , Turco Richard P.
Published: February 2004

A new hybrid model describing the formation of molecular clusters around naturally occurring ions has been applied to study the conditions found in the lower polar stratosphere in the winter season. The key ion species expected under these conditions include positive hydronium water clusters, and aggregates of water and nitric acid on nitrate anions. Our approach combines basic thermodynamic data with the classical Thomson representation of a charged liquid sphere to derive enthalpies and entropies for cluster formation over the entire mass spectrum from the smallest clusters to nanometer‐size droplets. We find that, at the lowest temperatures achieved in the polar regions, water and nitric acid ions can readily accumulate 10 or more ligands. The size distributions of several ion families are calculated, uncertainties in these distributions are discussed, and the rates of interaction of cluster ions with aerosols and reactive vapors are estimated.
Paleomagnetic pole positions and pole reversals of Mars
Authors: Arkani‐Hamed Jafar
Published: February 2004

The paleomagnetic pole positions of Mars obtained by modeling 10 small‐size, isolated magnetic anomalies show considerable clustering, 7 out of 10 are within a circle of 30 degrees radius centered at (230E, 25N). The directions of the magnetization of some nearby source bodies differ by ∼180 degrees and both north and south poles are found in the cluster, suggesting the magnetic pole reversals of Mars.
Rootless cones on Mars indicating the presence of shallow equatorial ground ice in recent times
Authors: Lanagan Peter D. , McEwen Alfred S. , Keszthelyi Laszlo P. , Thordarson Thorvaldur
Published: February 2004

High resolution Mars Orbiter Camera (MOC) images have revealed the existence of clusters of small cones in the Cerberus plains, Marte Valles, and Amazonis Planitia, Mars. These cones are similar in both morphology and planar dimensions to the larger of Icelandic rootless cones, which form due to explosive interactions between surficial lavas and near‐surface groundwater. Impact crater size‐frequency relationships indicate that surfaces upon which the cones sit are no older than 10 Ma. If martian cones form in the same manner as terrestrial rootless cones, then equatorial ground ice or ground water must have been present near the surface in geologically recent times.
A method for estimating 2D Wrinkle Ridge Strain from application of fault displacement scaling to the Yakima Folds, Washington
Authors: Mège Daniel , Reidel Stephen P.
Published: February 2004

The Yakima folds on the central Columbia Plateau are a succession of thrusted anticlines thought to be analogs of planetary wrinkle ridges. They provide a unique opportunity to understand wrinkle ridge structure. Field data and length‐displacement scaling are used to demonstrate a method for estimating two‐dimensional horizontal contractional strain at wrinkle ridges. Strain is given as a function of ridge length, and depends on other parameters that can be inferred from the Yakima folds and fault population displacement studies. Because ridge length can be readily obtained from orbital imagery, the method can be applied to any wrinkle ridge population, and helps constrain quantitative tectonic models on other planets.
40Ar/39Ar dating and paleomagnetism of the Miocene volcanic succession of Monte Furru (Western Sardinia): Implications for the rotation history of the Corsica‐Sardinia Microplate
Authors: Deino A. , Gattacceca J. , Rizzo R. , Montanari A.
Published: February 2004

Although it is widely acknowledged that the Corsica‐Sardinia microplate rotated counterclockwise with respect to Europe during Oligocene‐Miocene time, the precise timing of this event has yet to be determined. We have measured the age and degree of rotation of a single ‘tie‐point’ in the rotation history of the microplate. Biotite and sanidine 40Ar/39Ar age determinations of the 200m‐thick Monte Furru volcanic succession indicates that most of the volcanic pile accumulated within less than 200 ky. The paleomagnetic pole obtained for the 12 volcanic flow units comprising this succession indicates that by 18.2 Ma Sardinia remained 13° shy of its final rotation angle. These results demonstrate that the movement of the Corsica‐Sardinia block and the opening of the liguro‐provençal basin terminated later than previously estimated based on paleomagnetic and geochronologic studies of Sardinian volcanic rocks, in agreement with paleomagnetic data from Sardinian sediments.
Heat transport, deep waters, and thermal gradients: Coupled simulation of an Eocene greenhouse climate
Authors: Huber Matthew , Sloan Lisa Cirbus
Published: February 2004

For the first time, a coupled general circulation model with interactive and dynamical atmospheric, oceanic, and sea‐ice components, is used to simulate an Eocene (∼50 Ma) “greenhouse” climate. We introduce efficient ocean spin‐up methods for coupled paleoclimate modeling. Sea surface temperatures (SSTs) and salinities evolve unconstrained, producing the first proxy data‐independent estimates for these Eocene climate parameters. Tropical and extratropical model‐predicted SSTs are warmer than modern values, by 3 and 5°C, respectively. Salinity‐driven deep water formation occurs in the North Atlantic and Tethys. The zonal average overturning circulation is weaker than modern. Eocene ocean heat transport is 0.6 PW less than modern in the Northern Hemisphere and 0.4 PW greater in the Southern Hemisphere. The model‐predicted near‐modern vertical and meridional Eocene temperature gradients imply that the dominant theory for maintaining low gradients—increased ocean heat transport—is incorrect or incomplete and other mechanisms should be explored.
Field‐aligned currents during IMF ∼0
Authors: Papitashvili V. O. , Christiansen F. , Neubert T.
Published: February 2004

We report on field‐aligned currents (FAC) obtained from precise magnetic field measurements made on‐board the Ørsted and Magsat satellites when the interplanetary magnetic field (IMF) was near zero. We found that Region 1/Region 2 currents persist through southward IMF, IMF ∼ 0, and northward IMF; also the central area of both the northern and southern polar caps is always filled with FACs, even during slightly southward IMF. A statistical distribution of the latter currents resembles the dayside NBZ system with the downward/upward currents at post‐noon/pre‐noon hours, discovered earlier from Magsat observations. We hypothesize that the quasi‐viscous interaction of the solar wind with the magnetospheric lobes may cause a sunward convection of the lobes' field lines through the bunch's core, effectively mapping the FACs of NBZ‐type down to the near‐pole area.
Choice of an advection scheme for biogeochemical models
Authors: Lévy Marina , Estublier Audrey , Madec Gurvan
Published: February 2004

Five advection schemes are compared and evaluated in the context of biogeochemical modeling. Using three schemes of comparable quality that have been used in recent biogeochemical models, we found that new production estimates vary by as much as 30%. Test experiments are presented that explain the large discrepancies in terms of the different types of numerical errors inherent to each scheme. One scheme is suggested for eddy‐resolving models and another one for coarse resolution models.
Preferential acceleration of heavy ions in multi‐component plasmas
Authors: Mizuta Takanobu , Hoshino Masahiro
Published: February 2004

We discuss preferential, perpendicular acceleration of α particles in large amplitude magnetohydrodynamic (MHD) waves by using a test particle simulation. In a 3 component plasma that consists of electrons, protons and α particles, one of the wave branches has phase velocity larger than the Alfvén velocity in a long wave length regime. We find that the wave‐particle interaction between this wave and the other Alfvén wave leads to strong anisotropic acceleration in perpendicular direction to the ambient magnetic field. We examine the wave‐particle interaction for a 3 component plasma, and obtain good agreement with the test particle simulation.
Localized failure modes in a compactant porous rock
Authors: Wong Teng‐fong , Baud Patrick , Klein Emmanuelle
Published: February 2004

Since dilatancy is generally observed as a precursor to brittle faulting and the development of shear localization, attention has focused on how localized failure develops in a dilatant rock. However, recent geologic observations and reassessment of bifurcation theory have indicated that strain localization may be pervasive in a compactant porous rock. The localized bands can be in shear or in compaction, and oriented at relatively high angles (up to 90°) to the maximum compression direction. Here we report microstructural characterization of the spatial distribution of damage in failed samples which confirms that compaction bands and high‐angle conjugate shears can develop in sandstones with porosities ranging from 13% to 28%. These failure modes are generally associated with stress states in the transitional regime from brittle faulting to cataclastic ductile flow. The laboratory results suggest that these complex localized features can be pervasive in sandstone formations, not just limited to aeolian sandstone in which they were first documented. They may significantly impact the stress field, strain partitioning and fluid transport in sedimentary formations and accretionary prisms. While bifuraction theory provides an useful framework for analyzing the inception of localization, our data rule out a constitutive model that does not account for the activation of multiple damage mechanisms in the transitional regime.
Water level changes in a large Amazon lake measured with spaceborne radar interferometry and altimetry
Authors: Alsdorf Doug , Birkett Charon , Dunne Thomas , Melack John , Hess Laura
Published: February 2004

We demonstrate that interferometric processing of JERS‐1 SAR data over an Amazon lake containing ∼1500 islands yields centimeter‐scale changes in the height of the water surface from February 14 to March 30, 1997. For the method to work, we qualitatively find that inundation of about one or two leafless trees per 25 m² multi‐look SAR pixel is sufficient to return the radar pulse to the side‐looking antenna. Validation is provided by multi‐temporal TOPEX‐POSEIDON altimetry profiles, which directly measure surface heights relative to a fixed datum. Because SAR provides an image, the water height changes (∼12 cm) can be converted to a net volume measurement (280 million m³) over the 44 days separating the JERS‐1 acquisitions. Compared to historical gauge records, removal of this volume from the lake required a ∼50% greater flow.
Attempt to date Pleistocene normal faults of the Corinth‐Patras Rift (Greece) by U/Th Method, and tectonic implications
Authors: Flotté Nicolas , Plagnes Valérie , Sorel Denis , Benedicto Antonio
Published: February 2004

The Rift of Corinth is a major intra‐continental rift controlled by a Pleistocene and still active detachment fault. Its hangingwall contains normal faults which have migrated as evidenced by geomorphologic studies and by the geometrical relations of the sedimentary series that they controlled successively. However, because of the lack of paleontological data in the continental synrift sediments, the timing of this migration is unknown. Therefore, we attempted to date directly the faults using the U/Th method on calcite crystallizations. Preliminary results reveal that this method may be a useful tool in neotectonics. In this first attempt, we studied the Xylokastro‐Loutro fault and the Valimi fault. The age obtained on post‐tectonic calcite of the first fault shows that it locked at least 112.4±0.4ka ago. Syntectonic calcite of the Valimi fault yields an age of 382.0±31.1 ka, showing that the fault was still active at that time. Tectonic implications of these results are discussed.
Control of Jovian radio emission by Callisto
Authors: Menietti J. D. , Gurnett D. A. , Christopher I.
Published: February 2004

Galileo has been in orbit around Jupiter since December 1995 and a large database has been collected. We present the results of a survey of the plasma wave data for the frequency range 2.0 MHz to 5.6 MHz, the low frequency decametric (DAM) emissions. While the control of a portion of the radio emission by the moon Io is well known, and Ganymede control has been more recently indicated, we report that a small but significant portion of DAM emission is seen to be correlated with the orbital phase of Callisto. While the occurrence rate of emission controlled by Ganymede and Callisto is considerably less than for Io, the power levels can be nearly the same. We estimate the power of the Callisto‐dependent emission to be ∼70% of the Io‐dependent radio emission and about the same as the Ganymede‐dependent radio emission. This result indicates an Alfvén current system associated with Callisto, and thus a significant interaction of the magnetosphere of Callisto with that of Jupiter as is believed to exist for both Io and Ganymede.
Use of 17O/16O to trace atmospherically‐deposited sulfate in surface waters: A case study in Alpine watersheds in the Rocky Mountains
Authors: Johnson Craig A. , Mast M. Alisa , Kester Cynthia L.
Published: February 2004

Building on the discovery of excess 17O in atmospheric sulfate by Lee et al. (2001), we have carried out a case study to determine whether 17O might provide a new tool for quantifying the impact of atmospheric deposition on surface‐water sulfate loads. In Rocky Mountain alpine regions, excess 17O was found to be characteristic of atmospheric sulfate deposited in snow. Excess 17O was also evident in stream sulfate in one of two high‐elevation watersheds where analyses were made. Isotope mass balance calculations gave surprizingly low atmospheric contributions to stream sulfate suggesting that (1) despite abundant outcrop and sparse soil in these areas, significant sulfate may be taken up and released by soil microbes before being exported in streams, and (2) surface waters can carry multiple non‐atmospheric sulfate types, some possibly anthropogenic. Measurements of 17O may prove very useful in studies of sulfate behavior in a variety of surficial environments.
Numerical simulation of the December 1997 Debris Avalanche in Montserrat, Lesser Antilles
Authors: Heinrich Ph. , Boudon G. , Komorowski J. C. , Sparks R. S. J. , Herd R. , Voight Barry
Published: February 2004

Emplacement of a debris avalanche in the White River valley of southern Montserrat (Lesser Antilles), on 26 December 1997, was caused by sector failure of the south flank of the active Soufriere Hills volcano. Pre‐ and post‐emplacement surveys of the region indicate a debris avalanche deposit volume of about 40–50 × 106 m³. This avalanche is modeled as the gravitational flow of a homogeneous continuum governed by a basal friction law. Mass and momentum equations are depth‐averaged over the slide thickness. Numerical results show that the observed distribution of debris and duration of emplacement is simulated well for a Coulomb‐type friction law with a dynamic friction coefficient dependent upon the thickness and the velocity of the flowing mass.
The Antarctic dipole and its predictability
Authors: Yuan Xiaojun , Martinson Douglas G.
Published: February 2004

This study investigates the nature of interannual variability of Antarctic sea ice and its relationship with the tropical climate. We find that the dominant interannual variance structure in the sea ice edge and surface air temperature fields is organized as a quasi‐stationary wave which we call the “Antarctic Dipole” (ADP). It is characterized by an out‐of‐phase relationship between the ice and temperature anomalies in the central/eastern Pacific and Atlantic sectors of the Antarctic. The dipole consists of a strong standing mode and a weaker propagating motion within each basin's ice field. It has the same wavelength as the Antarctic Circumpolar Wave (ACW) and dominates the ACW variance. The dipole is clearly associated with tropical ENSO events; it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead. The prediction performs better in extreme warm/cold years, and best in La Niña years.
The connection between hygroscopic and optical particle properties in the atmospheric aerosol
Authors: Heintzenberg Jost , Maßling Andreas , Birmili Wolfram
Published: February 2004

With the combination of a hygroscopicity tandem differential mobility analyzer (HTDMA) and an optical particle counter the relation between hygroscopic and optical properties has been investigated for 300 nm urban atmospheric particles. Systematic new features of the state of mixture of optically important submicrometer particles were revealed. Besides a high fraction of absorbing (soot) chains, the most hydrophobic 300 nm particles had a high (≈ 30%) number fraction that is classified as “transparent spheres”, which could be anything from glassy spheres to high molecular hydrophobic organic droplets. These optical modes need to be considered when using HTDMA growth factors to convert dry aerosol properties to climatically relevant ambient levels.
AMS‐detection of inverse fabrics without AARM, in ophiolite dikes
Authors: Borradaile Graham J. , Gauthier David
Published: February 2004

“Inverse” fabric contributions from single‐domain (SD) magnetite complicate interpretation of magmatic flow from anisotropy of magnetic susceptibility (AMS) in the S. Troodos ophiolite dike swarm. Flow directions and magma chamber dimensions may only be inferred correctly if magnetic fabrics correspond to the orientation distribution (OD) of minerals. Magnetite shape‐fabrics were isolated by anisotropy of anhysteretic remanence (AARM) but AMS ambiguously merges magnetite and silicate fabrics. However, with the retrospective benefit of AARM, in this area, we recommend avoiding SD complications by excluding magnetite‐rich samples for which the bulk low‐field susceptibility >27,500 µSI. Magma‐flow was steeply upwards to the SW proximal to an axial magma chamber.
Interannual variations of temperature and vertical motion at the tropical tropopause associated with ENSO
Authors: Hatsushika Hiroaki , Yamazaki Koji
Published: February 2004

Interannual variations of tropopause temperature and vertical p‐velocity around the tropical tropopause are investigated. Observations show the tropopause temperature (altitude) is higher (lower) over the east side of maritime continent and lower (higher) over the equatorial eastern Pacific during El Niño compared with La Niña. As for the QBO, the tropopause temperature (altitude) is higher (lower) in all longitudes in the westerly phase. A multiple regression analysis shows the combined effect of ENSO and QBO can explain 25–50 % of the interannual variation. An AGCM simulation agrees with the observation for the ENSO signal. The simulation supports the existence of the stratospheric drain over the maritime continent in the tropopause region and indicates a zonal shift of the upward (downward) motion below (above) the tropopause with ENSO.
Negligible direct radiative forcing of basin‐scale climate by coccolithophore blooms
Authors: Gondwe Mtinkheni , Klaassen Wim , Gieskes Winfried , de Baar Hein
Published: February 2004

The water‐leaving radiance, defined as radiation from the sun reflected off particles in water and exiting the ocean surface back into the atmosphere and space, is often used to derive ocean‐colour information from remotely sensed data. However, it is in itself a measure of the amount of solar irradiance reflected by oceanic constituents and, therefore, not available to the Earth's heat reservoir (changes in which can affect the Earth's energy balance and climate). A strong influence on the water‐leaving radiance is observed from coccolithophore blooms, owing to the highly reflective calcareous platelets or coccoliths covering these marine algae. We analysed remotely sensed water‐leaving radiances (1998–1999) over the N. Atlantic, where the blooms are spatially and temporally most abundant, and found that the direct radiative forcing of climate between 402–565 nm (the major range of optical influence) by coccolithophores in this ocean is negligible (∼0.05 W m−2 mean annually). This is in contrast to what in situ or laboratory measurements on the immense local intensity of coccolithophore visible light scatter in the past two decades have led us to believe.
Coupled oscillations in Antarctic sea ice and atmosphere in the South Pacific Sector
Authors: Venegas Silvia A. , Drinkwater Mark R. , Shaffer Gary
Published: February 2004

Interannual oscillations with period of about 3–6 years have dominated the winter atmospheric and ice variability in the Ross, Amundsen, and Bellingshausen Seas, Antarctica, during 1979–1998. Anomalies in sea ice concentration and drift propagate eastward in the winter ice pack, coupled to sea level pressure anomalies. This signal accounts for the ice and atmospheric components of the Antarctic Circumpolar Wave during its eastward passage through the Pacific sector of Antarctica. Sea ice concentration anomalies at the ice margin seem to result from air‐ice‐sea interactions which involve both the dynamic effect of the anomalous, wind‐driven ice motion, and the thermodynamic ice growth and melting due to surface air and ocean temperature anomalies.
Impact induced damage beneath craters
Authors: Xia Kaiwen , Ahrens Thomas J.
Published: February 2004

Ackermann et al. (1975) described the subsurface structure of Meteor Crater and identified a fractured rock zone extending to about 1 km deep. The depth of the fractured/damage zone can be used to extract information about the impact cratering process. We impacted rock samples (San Marcos gabbro) in the laboratory and imaged the damage structure using both dicing and tomography methods. We propose a simple model to describe the damage zone depth based on the laboratory measurements. The model agrees well with other methods for the estimation of the projectile size of Meteor Crater and it may be used for estimates of damage around craters of other planets and moons.
Seasonal variations of the terdiurnal tide in the mesosphere and lower thermosphere: A model study
Authors: Akmaev R. A.
Published: February 2004

Observations of the terdiurnal (8‐hour) tidal wind oscillations in the mesosphere and lower thermosphere (MLT) reveal strong seasonal and latitudinal variations. The tidal amplitudes reach a maximum of about 15–20 m s−1 at midlatitudes in winter. The vertical phase progression corresponds to very long vertical wavelengths. During summer the amplitudes are typically weaker and the phases are less regular. First simulations of the terdiurnal tide with the Spectral Mesosphere/Lower Thermosphere Model are presented. The model explicitly accounts for the solar thermal excitation in the middle and upper atmosphere and reproduces the salient features of the terdiurnal wind oscillations well. The preferential solar excitation of antisymmetric terdiurnal modes capable of propagating into the MLT combined with an asymmetric atmospheric response appears to be primarily responsible for the observed seasonal variations. Nonlinear interactions of the diurnal and semidiurnal tides are demonstrated to make a noticeable in situ contribution to the excitation of the terdiurnal tide at 95–100 km, especially during equinox.
Migration of large earthquakes along the San Jacinto Fault; Stress diffusion from the 1857 Fort Tejon Earthquake
Authors: Rydelek Paul A. , Sacks I. Selwyn
Published: February 2004

Historic and modern catalogs of seismicity in California suggest a migration of earthquakes (M ≥ 5.6) along the San Jacinto Fault; these events appear to travel down the fault with a migration speed of 1.7 km/year (Sanders [1993]). This migration is explained by postseismic strain diffusion due to viscoelastic relaxation from the great Fort Tejon earthquake in 1857. We model this postseismic effect and find that significant stress diffuses down the San Jacinto fault for distances in excess of 200 km and the corresponding migration may be a result of Coulomb triggering from this stress perturbation. The level of postseismic stress that seems to be the trigger level for most of the events is of order 1 bar. Since the temporal evolution of the postseismic strain field is mainly dependent on the inelastic properties of the lower crust and uppermost mantle, the observed migration enables a viscosity estimate of ∼4 × 1018 Pas for this region of California.
Particle transformations and export flux during an in situ iron‐stimulated algal bloom in the Southern Ocean
Authors: Nodder Scott D. , Charette Matthew A. , Waite Anya M. , Trull Tom W. , Boyd Philip W. , Zeldis John , Buesseler Ken O.
Published: February 2004

During the first Southern Ocean Iron RElease Experiment (SOIREE), a suite of biogeochemical measurements (water column 234Th and δ13Corg inventories, particle fluxes from sediment traps, phytoplankton sinking rates) were undertaken to test the hypothesis that the vertical export of particulate organic carbon (POC) is enhanced due to iron‐induced increases in phytoplankton production. During the 13‐days that the SOIREE bloom was monitored, export fluxes within the iron‐fertilised patch were not substantially different to those in waters outside the bloom. On days 11–13, iron enrichment may have caused particle transformations that could lead to elevated future export via particle aggregation and/or diatom chain formation. The unknown time‐lag between increased production and export, the longevity of the SOIREE bloom, and the absence of nutrient limitation over days 1–13, however, prohibit prediction of any iron‐induced export. This conclusion highlights the difficulties of fully testing the “Iron Hypothesis” and for evaluating the implications for global climate change.
The isotopic composition of oxygen in the fast solar wind: ACE/SWIMS
Authors: Wimmer‐Schweingruber Robert F. , Bochsler Peter , Gloeckler George
Published: February 2004

Oxygen is the most abundant element in the solar system after H and He, and the lightest element with three stable isotopes. Oxygen is a volatile element; it was not retained completely in meteorites or in their predecessors during their formation in the early solar system. The solar oxygen isotopic composition is important because the Sun is by far the largest reservoir of oxygen in the solar system. Oxygen occurs in highly volatile phases of the solar system, such as water, as well as in refractory phases, for example in silicates. Because of this, the differences between the isotopic composition of oxygen in solar‐system bodies and the Sun are a sensitive measure of the gas to dust ratio in the early solar system. We report the first measurements of the oxygen isotopic composition in the fast solar wind with the Solar Wind Isotope Mass Spectrometer (SWIMS) on the Advanced Composition Explorer (ACE). The fast solar wind is the least fractionated type of solar wind. We obtain an isotopic abundance ratio 16O/18O of 446±90 which is (within the quoted uncertainties) consistent with the terrestrial value of 498. However, in combination with previously published values for the photosphere (16O/18O=440±50 [Harris et al., 1987]) and the isotopically more fractionated slow solar wind (16O/18O=450±130[Collier et al., 1998]), this new determination may suggest that the Sun is isotopically heavier than terrestrial.
Periodicity of strain accumulation detected by permanent GPS Array: Possible relationship to seasonality of major earthquakes' occurrence
Authors: Murakami Makoto , Miyazaki Shin'ichi
Published: February 2004

Continuous GPS measurements at about 500 sites in Japan reveal a time periodic component of crustal strain accumulation within the island arc. The magnitude of this variability is about 20–30 % of the steady annual component of deformation driven by coupling across the subduction zone. The amplitude of temporal variability is strongly organized in space, and its correlation with the secular velocity field suggests a geodynamic origin for the phenomenon. The observed periodicity may help to explain the seasonality of occurrence of the major earthquakes (Magnitude >7.5) associated with the Japanase subduction zone.
Seismic scattering attenuation estimates for the German KTB Area derived from well‐log statistics
Authors: Müller Tobias M. , Shapiro Serge A.
Published: February 2004

We applied a recently developed scattering attenuation theory to model Q‐values measured at the German KTB site and found that scattering attenuation plays an important role in the upper crust in this area. This does not conform with previous studies that suggest absorption mechanisms as the main reason for the attenuation. The scattering attenuation model used is based on the wave propagation theory in random media and allows quantification of scattering attenuation in complex geological regions using simple statistical estimates from well‐log data. For our estimates of scattering Q we used statistical models of heterogeneities obtained from KTB logs. A good agreement between the magnitude of scattering attenuation and the measured Q‐values shows the necessity of evaluating the role of scattering in seismic attenuation phenomena.
Retention of dissolved iron and FeII in an iron induced Southern Ocean phytoplankton bloom
Authors: Croot Peter L. , Bowie Andrew R. , Frew Russell D. , Maldonado Maria T. , Hall Julie A. , Safi Karl A. , La Roche Julie , Boyd Philip W. , Law Cliff S.
Published: February 2004

During the 13 day Southern Ocean Iron RE‐lease Experiment (SOIREE), dissolved iron concentrations decreased rapidly following each of three iron‐enrichments, but remained high (>1 nM, up to 80% as FeII) after the fourth and final enrichment on day 8. The former trend was mainly due to dilution (spreading of iron‐fertilized waters) and particle scavenging. The latter may only be explained by a joint production‐maintenance mechanism; photoreduction is the only candidate process able to produce sufficiently high FeII, but as such levels persisted overnight (8 hr dark period) —ten times the half—life for this species—a maintenance mechanism (complexation of FeII) is required, and is supported by evidence of increased ligand concentrations on day 12. The source of these ligands and their affinity for FeII is not known. This retention of iron probably permitted the longevity of this bloom raising fundamental questions about iron cycling in HNLC (High Nitrate Low Chlorophyll) Polar waters.
The dependence of acoustic properties of a crack on the resonance mode and geometry
Authors: Kumagai Hiroyuki , Chouet Bernard A.
Published: February 2004

We examine the dependence of the acoustic properties of a crack containing magmatic or hydrothermal fluids on the resonance mode and geometry to quantify the source properties of long‐period (LP) events observed in volcanic areas. Our results, based on spectral analyses of synthetic waveforms generated with a fluid‐driven crack model, indicate that the basic features of the dimensionless frequency (ν) and quality factor (Qr) for a crack containing various types of fluids are not strongly affected by the choice of mode, although the actual ranges of Qr and ν both depend on the mode. The dimensionless complex frequency systematically varies with changes in the crack geometry, showing increases in both Qr and ν as the crack length to aperture ratio decreases. The present results may be useful for the interpretation of spatial and temporal variations in the observed complex frequencies of LP events.
Indications for a wave dependent charnock parameter from measurements during ASGAMAGE
Authors: Oost Wiebe A. , Komen Gerbrand J. , Jacobs Cor M. J. , van Oort Cor , Bonekamp Hans
Published: February 2004

Eddy‐correlation measurements of the wind stress and wave measurements were made during ASGAMAGE, an experiment carried out in 1996 at research platform Meetpost Noordwijk (MPN) in the southern North Sea. An analysis of the results confirms the predicted wave dependence of the Charnock parameter. As in HEXOS, an earlier experiment at the same platform, the corresponding values of the drag are higher than those found in the open ocean. We show that this is consistent with the existence of a waveage dependent Charnock parameter and the fact that, for given wind speed, on average, wave ages are lower at MPN than in the open ocean.
Observations of high speed deep currents in the northern Gulf of Mexico
Authors: Hamilton Peter , Lugo‐Fernandez Alexis
Published: February 2004

Recent measurements in water depths of 2000 m in the vicinity of the Sigsbee Escarpment, south of New Orleans, show the presence of recurring high speed current episodes, some of which had velocities greater than 85 cm/s only 10 m above the local bottom. In the Gulf of Mexico, currents above about 1000 m are not locally coupled with the relatively depth‐independent currents in the deeper layers. Topographic Rossby waves, with periods of approximately 10 to 14 days, appear to control the dynamics of the lower water‐column.
Explanation for the simultaneous occurrence of bipolar structures and waves near ion‐cyclotron harmonics in the auroral ionosphere
Authors: Crary F. J. , Goldman M. V. , Ergun R. E. , Newman D. L.
Published: February 2004

In the downward current region of the auroral ionosphere, the FAST spacecraft has observed bipolar electrostatic structures on Debye length scales and waves at frequencies between the H+ ion cyclotron harmonics. Such bipolar structures have been previously identified with the nonlinearly evolved state of a two‐stream electron instability. In this paper, we present the results of long‐duration and large‐scale particle‐in‐cell (PIC) simulations which produce, from one set of initial conditions, both bipolar electrostatic structures and, at later times, ion Bernstein waves with peak intensities between multiples of the ion cyclotron frequency. The ion Bernstein waves are driven by a weaker beam instability caused by a residual positive slope in the nonlinearly evolved (nonthermal) electron distribution. Although there are a variety of processes which can produce ion Bernstein modes, we show that a common source (an electron beam) can produce both of these observed phenomena in the downward current region.
Crustal deformation caused by magma migration in the northern Izu Islands, Japan
Authors: Nishimura Takuya , Ozawa Shinzaburo , Murakami Makoto , Sagiya Takeshi , Tada Takashi , Kaidzu Masaru , Ukawa Motoo
Published: February 2004

Intense crustal activity including earthquake swarms, eruptions, and a caldera formation in the northern Izu Islands started on June 26, 2000, accompanied with large crustal deformation. Permanent GPS data reveals the spatial pattern and time evolution of ground deformation. The observations reveal shrinking and subsidence of Miyakejima and extension between Kouzushima and Niijima. We constructed a source model to explain the observed displacements during the period between June 26 and the end of August. The model consists of a deflation source (0.12km³) beneath Miyakejima, tensile faults (1.04km³) located between Miyakejima and Kouzushima, and several shear faults. Mass balance considerations suggest that a large amount of magma migrated 30km from Miyakejima toward Kouzushima.
Gravity waves and ionospheric irregularities over tropical convection zones observed by GPS/MET Radio Occultation
Authors: Hocke Klemens , Tsuda Toshitaka
Published: February 2004

GPS/MET observations of the tropical atmosphere of the southern hemisphere (5°S to 25°S) during February 1997 are analysed, when a high amount of convective tropospheric water vapor is at these latitudes. Enhanced gravity wave activity of the lower stratosphere at h=22–28 km is associated to areas of increased tropospheric water vapor pressure at h=4–6 km, regarded as a measure of tropical convection. Sporadic E and other ionospheric irregularities (vertical scales less than 7 km) of the mesosphere/lower thermosphere are observed to be highly correlated to gravity wave activity in the lower stratosphere and to tropical convection zones. We find 4 areas of enhanced ionospheric irregularities and stratospheric wave activity over Pacific (around 140°W), Brazil (50°W), Africa (40°E), and Indonesia/Australia (110°E).
Mechanism and duration of banding in Mississippi Valley‐type sphalerite
Authors: Katsev Sergei , L'Heureux Ivan , Fowler Anthony D.
Published: February 2004

We present a new quantitative model of mm‐scale Fe‐Zn banding in sphalerite Mississippi‐Valley type ore deposits. The banded sphalerite is typically intergrown with dendritic galena in cm‐scale clusters. We show that this pattern may arise due to a combined effect of geochemical reactions, crystal growth, dissolution, and ripening in far‐from‐equilibrium conditions. The simulated patterns are due to a self‐propagating sequence of growth and dissolution events (so called coarsening wave). One of the surprising results is the geologically short time scale of the pattern formation.
Present day kinematics of the Eastern California Shear Zone from a geodetically constrained block model
Authors: McClusky S. C. , Bjornstad S. C. , Hager B. H. , King R. W. , Meade B. J. , Miller M. M. , Monastero F. C. , Souter B. J.
Published: February 2004

We use Global Positioning System (GPS) data from 1993–2000 to determine horizontal velocities of 65 stations in eastern California and western Nevada between 35° and 37° N. We relate the geodetic velocities to fault slip rates using a block model that enforces path integral constraints over geologic and geodetic time scales and that includes the effects of elastic strain accumulation on faults locked to a depth of 15 km. The velocity of the Sierra Nevada block with respect to Nevada is 11.1±0.3 mm/yr, with slip partitioned across the Death Valley, (2.8±0.5 mm/yr), Panamint Valley (2.5±0.8 mm/yr), and Airport Lake/Owens Valley (5.3±0.7/4.6±0.5 mm/yr) faults. The western Mojave block rotates at 2.1±0.8°/My clockwise, with 3.7±0.7 mm/yr of left lateral motion across the western Garlock Fault. We infer 11±2 mm/yr of right lateral motion across the Mojave region of the Eastern California Shear Zone.