bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of the 1997–98 El Niño on the surface chlorophyll in the California Current
Authors: Kahru Mati , Mitchell B. Greg
Published: February 2004

Satellite‐derived time series for the California Current System (CCS) showed marked changes in the surface chlorophyll a concentration (Chl, mg m−3) associated with the 1997–98 El Niño. In addition to the previously known decrease in Chl off Southern California (Fiedler, 1984), we also observed a significant increase of Chl off Baja California. Whereas the extent of eutrophic (Chl >1.0) areas decreased throughout the CCS, the extent of mesotrophic areas (0.2 <Chl <1.0) off Baja California approximately doubled. The reduced area of eutrophic waters is attributed to weakened upwelling but the increase in the offshore mesotrophic area off Baja may be caused by blooms of nitrogen‐fixing cyanobacteria. Using revised Coastal Zone Color Scanner data we detected similar changes during the 1982–83 El Niño.
Evidence for high velocity in Koyna seismic zone from P‐wave teleseismic imaging
Authors: Srinagesh D. , Singh Sunil , Reddy K. Srinath , Prakasam K. S. , Rai S. S.
Published: February 2004

Three‐dimensional P‐wave velocity structure of the crust and upper most mantle beneath the Koyna Seismic Zone (KSZ) was determined by inverting 780 P‐wave teleseismic travel times recorded by a 20 station digital network. The velocity image obtained through damped least square was tested for its resolution using checkerboard approach. The results of the inversion show strong lateral velocity variations of 6% to 7% within the study region. A high velocity anomaly (2% to 5%) in the upper and lower crust beneath the KSZ is flanked by lower velocity (−2% to −5%) anomalies on either side. The correlation of high‐velocity with the seismic zone suggests that the earthquakes are occurring in more rigid rocks with increasing ability to store strain energy and release it as brittle failure.
Interannual variability of the air‐sea flux of oxygen in the North Atlantic
Authors: McKinley Galen A. , Follows Michael J. , Marshall John
Published: February 2004

In studies using timeseries observations of atmospheric O2/N2 to infer the fate of fossil fuel CO2, it has been assumed that multi‐year trends in observed O2/N2 are insensitive to interannual variability in air‐sea fluxes of oxygen. We begin to address the validity of this assumption by investigating the magnitude and mechanisms of interannual variability in the flux of oxygen across the sea surface using a North Atlantic biogeochemical model. The model, based on the MIT ocean general circulation model, captures the gross patterns and seasonal cycle of nutrients and oxygen within the basin. The air‐sea oxygen flux exhibits significant interannual variability in the North Atlantic, with a standard deviation (0.36 mol m−2 y−1) that is a large fraction of the mean (0.85 mol m−2 y−1). This is primarily a consequence of variability in winter convection in the subpolar gyre.
Dynamical balance in the Indonesian Seas circulation
Authors: Burnett William H. , Kamenkovich Vladimir M. , Jaffe David A. , Gordon Arnold L. , Mellor George L.
Published: February 2004

A high resolution, four‐open port, non‐linear, barotropic ocean model (2D POM) is used to analyze the Indonesian Seas circulation. Both local and overall momentum balances are studied. It is shown that geostrophy holds over most of the area and that the Pacific‐Indian Ocean pressure difference is essentially balanced by the resultant of pressure forces acting on the bottom.
Relationship between sea‐ice motion and geostrophic wind in the northern hemisphere
Authors: Kimura Noriaki , Wakatsuchi Masaaki
Published: February 2004

This paper presents maps showing the relationship between sea‐ice motion derived from Defense Meteorological Satellite Program (DMSP) Special Sensor Microwave Imager (SSM/I) imagery and the geostrophic wind in the Northern Hemisphere for seven winters (1991/92–1997/98). The sea‐ice motion is highly correlated with the geostrophic wind except for some coastal regions. Overall the direction of the ice motion is nearly parallel to the wind. An obvious contrast between seasonal ice zones and the interior of the Arctic is observed in the speed reduction factor (ratio of ice speed to wind speed), which is probably caused by the spatial variation of internal ice stress. Surface ocean currents are also derived by subtracting the wind effect from the ice motion.
Comparison of spectral direct and diffuse solar irradiance measurements and calculations for cloud‐free conditions
Authors: Mlawer Eli J. , Brown Patrick D. , Clough Shepard A. , Harrison Lee C. , Michalsky Joseph J. , Kiedron Piotr W. , Shippert Tim
Published: February 2004

Ground‐based spectral measurements of direct and diffuse solar irradiance from the Rotating Shadowband Spectroradiometer, taken in cloud‐free conditions in Oklahoma in the fall of 1997, are compared over the spectral range 10000–28500 cm−1 to corresponding calculations by an accurate multiple‐scattering radiative transfer model. For each case analyzed, the aerosol optical depths used in the calculation were determined by fitting an Angstrom relation based on the ratio of the direct‐beam measurements to a direct‐beam calculation with no aerosols present. Also used in the calculation was a spectrally‐independent aerosol single‐scattering albedo chosen to provide agreement with the diffuse measurements. The spectral agreement between the measurements and calculations for the direct and diffuse irradiances is very good, providing strong evidence that in this spectral range there are no unmodeled molecular absorbers of significance to the atmospheric energy balance. Especially notable is the correspondence between the observations and calculations for a case characterized by a large amount of water vapor in the direct‐beam path, directly contradicting the suggestion that water vapor absorbs more shortwave radiation than is represented in radiative transfer models.
Measurement of NMHCs at Oki Island, Japan,: An evidence of long range transport
Authors: Sharma U. K. , Kajii Y. , Akimoto H.
Published: February 2004

The analysis of C2–C6 non‐methane hydrocarbons (NMHCs) was conducted at remote site in Oki Island, Japan from July 24–August 10, 1998. Lower molecular weight hydrocarbons, C2–C5 alkanes, ethene, acetylene, propene, and isoprene accounted for more than 90% of the total measured hydrocarbons. The study of trajectory analysis revealed that East Asia Pacific Rim Region is significantly contaminated from the anthropogenic emission transported from Asian continent by rapid convective movement of air masses. Air masses originating from Pacific Ocean and crossing over Japanese Island were rich in C3–C5 hydrocarbon. On the contrary, the air masses arriving directly to the site without any prior continental influence were more aged maritime air masses.
Seasonal changes in pollutant transport to the North Pacific: The relative importance of Asian and European sources
Authors: Newell Reginald E. , Evans Mathew J.
Published: February 2004

The industrialization of south‐east Asia invokes interest in the export path of the associated pollution into the global atmosphere. During the winter the meteorology of this area is dominated by the Siberian anticyclone. Polluted air is typically kept in the planetary boundary layer by the large‐scale subsidence and moved southwards. This contrasts with the summer when it can be lifted to the upper troposphere and transported across the Pacific by the aloft. This seasonal variation is investigated using trajectory calculations. Then the influence of pollution from the European region on south‐east Asia is investigated. During the winter up to 40% of the tropospheric air entering south‐east Asia may have been polluted by Europe. Finally, we propose an extended monitoring program over central Asia to separate south‐east Asian pollution from the general pollution found in the Northern Hemisphere, and, to understand the effects of this industrialization.
Phytoplankton physiology can affect ocean surface temperatures
Authors: Lefèvre Nathalie , Taylor Arnold H. , Geider Richard J.
Published: February 2004

A key biological link between ocean geochemical cycles, ocean color and sea surface temperature (SST) is the nitrogen‐to‐chlorophyll a (N:chl a) ratio of phytoplankton. This is because nitrogen is the limiting factor over approximately 2/3 of the ocean surface and light absorption depends on the concentration of chlorophyll a. Recent work has demonstrated systematic variability in this ratio. Using one‐dimensional models at two locations we show that varying N:Chl a, rather than keeping a fixed mean value (0–150m), leads to lower chlorophyll a in the mixed layer, less light absorption within the mixed layer and cooler sea surface temperatures. At the equator the temperature reduction is 0.15°C throughout the year whereas at 35°N, a temperature difference of about 1°C occurs during the summer. Although demonstrated at only two locations, this effect is likely to occur over large parts of the ocean.
On the origin of elevated surface ozone concentrations at Izana Observatory, Tenerife during late March 1996
Authors: Kentarchos A. S. , Roelofs G. J. , Lelieveld J. , Cuevas E.
Published: February 2004

The origin of relatively high surface ozone concentrations measured at Izana Observatory (Canary Islands) during the end of March 1996 is studied using a coupled chemistry‐GCM (ECHAM4) at T63 resolution (1.875° × 1.875°). Meteorological fields (geopotential height, potential vorticity, specific humidity), and a model‐simulated stratospheric ozone tracer as well as 3‐D back trajectories, show the stratospheric origin of these relatively high surface ozone values caused by cross‐tropopause exchange at the western flank of an upper level trough/cut‐off low (COL) over the extratropical North‐Atlantic Ocean. The good agreement between observations and model results (within 10–15%) indicates that the high resolution chemistry‐GCM is a useful tool towards the understanding of natural sources controlling background surface ozone variability. The results underscore the importance of stratosphere‐troposphere exchange (STE) during late winter/early spring for lower free tropospheric ozone at subtropical latitudes.
Tropical convective outflow and near surface equivalent potential temperatures
Authors: Folkins Ian , Oltmans Samuel J. , Thompson Anne M.
Published: February 2004

We use clear sky heating rates to show that convective outflow in the tropics decreases rapidly with height between the 350 K and 360 K potential temperature surfaces (or between roughly 13 and 15 km). There is also a rapid fall‐off in the pseudoequivalent potential temperature probability distribution of near surface air parcels between 350 K and 360 K. This suggests that the vertical variation of convective outflow in the upper tropical troposphere is to a large degree determined by the distribution of sub cloud layer entropy.
Obtaining single path phase delays from GPS double differences
Authors: Alber Chris , Ware Randolph , Rocken Christian , Braun John
Published: February 2004

We describe a method for obtaining single‐path phase delays from GPS double differences. The resulting “zero differences” (ZDs) can be used for remote sensing of atmospheric water vapor. The method is demonstrated by simulating and observing atmospheric delay gradients, and by comparing ZDs with pointed radiometer observations of integrated water vapor along GPS ray paths. In‐situ GPS antenna phase center and multipath effects are mapped in ZD residuals for a specific site and network. We conclude that ZDs derived from GPS network data show promise for real time sensing of water vapor for use in meteorological modeling and forecasting.
The latitudinal gradient of potential vorticity in the mid‐latitudes of the troposphere
Authors: Satoh Masaki , Neufeld Zoltán
Published: February 2004

The latitudinal gradient of zonally averaged potential vorticity (PV) in the mid‐latitudes of the troposphere is examined in terms of characteristics of isentropic transport. Assuming that the change in PV is given by a relaxation type forcing, the meridional profile of PV is expressed as a weighted integral of the Lagrangian mean of the relaxation values of PV on backward trajectories. The evolution of the Lagrangian mean is studied in a kinematic model flow and in an atmospheric flow generated by a general circulation model. Important differences between the homogeneous chaotic mixing and the atmospheric flow are explained as effects of transport barriers, which are thought to be the tropopause in the atmospheric case. The undulations of the transport barriers have significant effect on the latitudinal gradient of zonally averaged PV.
Meridional flow variability over the Nordic Seas in the Arctic oscillation framework
Authors: Skeie Paul
Published: February 2004

An anomalous recurring atmospheric circulation pattern of high relevance for the climate of the Nordic Seas and Siberia is identified. It is found as the second Empirical Orthogonal Function (EOF) of monthly winter sea level pressure (SLP) anomalies poleward of 30°N where the leading EOF is the Arctic Oscillation (AO). The most prominent centre of action of the circulation pattern is located over the Barents Region. This “Barents Oscillation” (BO) is shown to have a high temporal correlation with the sensible heat loss of the Nordic Seas (r=0.76). The BO also correlates to Eurasian surface air temperature (SAT) anomalies with r=0.72 after the AO related SAT variations are removed by means of a linear regression. Two sets of SLP composites are constructed where one is based on low and high Nordic Seas heat loss months and the other is based on warm and cold Eurasian months. Patterns reminiscent of the BO emerge in the two composites when AO related variability is removed.
Validity of the isotopic thermometer in central Antarctica: Limited impact of glacial precipitation seasonality and moisture origin
Authors: Delaygue Gilles , Jouzel Jean , Masson Valérie , Koster Randal D. , Bard Edouard
Published: February 2004

The classical interpretation of water stable isotopes (deuterium or oxygen 18) retrieved from ice cores into past local temperature relies on the use of the spatial isotope/temperature slope as a surrogate of the temporal slope. Whereas this assumption has been challenged by independent methods in central Greenland, it is still considered as valid in central Antarctica. We use an atmospheric General Circulation Model (GCM) to study two parameters highlighted by previous studies as being among the most important with respect to this assumption. We show that in the GCM, between present‐day and Last Glacial Maximum, the change in precipitation seasonality and the cooling of the moisture sources have limited and opposite effects on the isotopic record of the Antarctic local temperature. This conclusion strengthens the validity of the classical interpretation of isotope records in central Antarctica.
Measurement of OBrO upper limits in the nighttime stratosphere
Authors: Erle Frank , Platt Ulrich , Pfeilsticker Klaus
Published: February 2004

Recent balloon‐borne spectroscopic observations of stratospheric OBrO absorption features [Renard et al., 1998] gave rise to speculations whether OBrO is an important nighttime reservoir for stratospheric bromine. We have analyzed direct moon light spectra collected during 6 Transall flights for OBrO absorption signatures occurring between 470 and 550 nm. OBrO absorptions were not detected by stratospheric measurements at mid‐ or high latitude, both early or late in the night, made in early winter, or spring. Using the recently measured OBrO absorption cross section (σOBrO = (1.8±0.5)×10−17 cm²) by Knight et al. [2000], or the previously assumed OBrO cross section (σOBrO =1.5×10−17 cm²) by Renard et al. [1998] [further on all the results based on the latter cross section are given in () for direct comparison], our measurements imply an upper limit for stratospheric OBrO of < 6.4 (7.7) ppt (typically 2.5 (3) ppt), and as low as 1.5 (1.8) ppt for an assumed Gaussian profile that maximises at 28 km. Although our result is closer in magnitude to the results of Renard et al. [1998], it does not confirm their findings, but it points more to the results of a modeling study that reject sizeable amounts (< 0.01 ppt) of stratospheric OBrO being formed by known gas‐phase reactions even using extreme assumptions in favor of OBrO at night [Chipperfield et al., 1998].
The thermal state of the upper mantle; No role for mantle plumes
Authors: Anderson Don L.
Published: February 2004

A variety of geophysical data indicates that long wavelength temperature variations of the asthenosphere depart from the mean by ±200°C, not the ±20°C adopted by plume theoreticians. The ‘normal’ variation, caused by plate tectonic processes (subduction cooling, continental insulation, small‐scale convection) encompasses the temperature excesses that have been attributed to hot jets and thermal plumes. Geophysical estimates of the average potential temperature of the upper mantle are about 1400°C. Asthenospheric convection at ridges, rifts and fracture zones and at the onset of continental breakup is intrinsically 3D, giving rise to shallow pseudoplume‐like structures without deep thermal instabilities. Deep narrow thermal plumes are unnecessary and are precluded by uplift and subsidence data. The locations and volumes of ‘midplate’ volcanism appear to be controlled by lithospheric architecture, stress and cracks.
A new observation of dynamically triggered regional seismicity: Earthquakes in Greece following the August 1999 Izmit, Turkey earthquake
Authors: Brodsky Emily E. , Karakostas Vassilis , Kanamori Hiroo
Published: February 2004

The Mw = 7.4 Izmit, Turkey earthquake triggered widespread regional seismicity in Greece over a study region extending from 400 km to nearly 1000 km away from the epicenter. Small events began immediately after the passage of the mainshock surface waves suggesting that the transient stresses of the seismic waves were the trigger. The increase in cataloged earthquakes in ordinary continental crust is a new observation and is statistically significant at the 95% level. Unlike the previous example of distant triggering during the Landers earthquake, the activated seismicity occurred entirely in non‐volcanic areas. The Greek sites were triggered by waves with amplitudes at least a factor of 3 lower than the observed triggering threshold for Imperial Valley. We speculate that dynamic triggering on a regional‐scale results in countrywide episodes of increased seismicity, or “superswarms”, in regions with low triggering thresholds such as Greece.
Seismic anisotropy of the shallow crust at the Juan de Fuca Ridge
Authors: Almendros Javier , Barclay Andrew H. , Wilcock William S. D. , Purdy G. M.
Published: February 2004

Microearthquake data recorded on four ocean bottom seismometers are used to study shear‐wave splitting on the Endeavour Segment of the Juan de Fuca Ridge. The covariance matrix decomposition method is used to determine the sensor orientation from explosive shot data and to estimate the anisotropy parameters for 238 earthquake records. At three of the four sites, the results show a remarkably consistent fast direction parallel to the ridge axis. The time delays between the fast and the slow waves range from 40 to 200 ms, with an average of 90 ms. They are not clearly related to earthquake range, focal depth or source‐receiver azimuth. The splitting of the shear waves is interpreted as an effect of structural anisotropy due to the presence of ridge‐parallel cracks in the shallow crust. If we assume that anisotropy is concentrated in the upper 1–2 km, the splitting times require a high crack density of ∼0.1.
In situ stresses in the Southern Bonaparte Basin, Australia: Implications for first‐ and second‐order controls on stress orientation
Authors: Mildren Scott D. , Hillis Richard R.
Published: February 2004

Four‐arm dipmeter logs from six wells and a Formation MicroScanner (FMS) image log from one well in the southern Bonaparte Basin were interpreted for in situ stress indicators. Results of the analysis reveal a consistent NE‐SW in situ maximum horizontal stress (σHmax) orientation (055°N). This orientation is parallel to the average σHmax determined in the northern Bonaparte Basin, the onshore Canning Basin, and in New Guinea. The data support the interpretation that the NE‐SW σHmax orientation in the area reflects a first‐order stress pattern controlled by plate boundary forces along the northeastern margin of the Indo‐Australian Plate (IAP) and contradict the suggestion that NE‐SW σHmax in the northern Bonaparte Basin is a second‐order effect associated with boundary induced flexural stresses. Numerical modeling suggests that the divergence of σHmax from an orientation parallel to plate motion can be explained by the heterogeneous nature of the northeastern boundary of the IAP.
Measurements of air‐sea gas transfer during an open ocean algal bloom
Authors: Nightingale Philip D. , Liss Peter S. , Schlosser Peter
Published: February 2004

Measurements of air‐sea gas transfer were made during the development of a large algal bloom that immediately followed in‐situ iron enrichment in the equatorial Pacific Ocean. Gas transfer rates were determined from changes in the ratio of the deliberately released tracers sulphur hexafluoride and helium‐3. This first application of the dual tracer technique in the open ocean produced estimates of the gas transfer rate that were similar in magnitude to those obtained previously from measurements in shelf seas. We found no evidence that gas transfer rates declined during the development of the algal bloom. Incorporation of the new open ocean measurements with other published dual tracer data gives a relationship between transfer velocity and wind speed that explains 82% of the total variance in the dataset.
Atmospheric manifestation of tropical instability wave observed by QuikSCAT and tropical rain measuring mission
Authors: Liu Timothy W. , Xie Xiaosu , Polito Paulo S. , Xie Shang‐Ping , Hashizume Hiroshi
Published: February 2004

Observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the Pacific equatorial cold tongue. A unique zonal‐temporal band‐pass filter enables the isolation of the propagating signals and the determination of their phase differences. The phase differences between the propagation of wind and sea surface temperature (SST) signals observed from space and the vertical wind profiles measured from a research ship are consistent with the hypothesis that the coupling between wind and SST is caused by buoyancy instability and mixing, which reduces the wind shear in the atmospheric boundary layer. The coupling causes higher evaporative cooling over the warm phase and infers a negative thermal feedback.
On the relationship between microstructure and electrical and hydraulic properties of sand‐clay mixtures
Authors: Wildenschild Dorthe , Roberts Jeffery J. , Carlberg Eric D.
Published: February 2004

A series of laboratory experiments, including measurements of electrical properties, permeability, and porosity, were performed on saturated sand‐clay mixtures. Different mixtures and packing geometries of quartz sand and 0 to 10% Na‐montmorillonite clay were investigated using solutions of CaCl2 and deionized water. Two main regions of electrical conduction exist: a region dominated by surface conduction and a region where the ionic strength of the saturating fluid controlled conduction. For low fluid conductivities, the sample geometry was found to greatly affect the magnitude of the surface conductance. The influence of the microstructural properties on the electrical properties was quantified by estimating formation factors, Λ‐parameters, and surface conductances. The surface conductances estimated using the theory of Johnson et al. [1986] agreed well with measured values. We suggest that high and low bounds on the expected surface and bulk conductances in a natural system can be derived from the measurements on these artificial geometries.
Displacement‐length relations of thrust faults associated with lobate scarps on Mercury and Mars: Comparison with terrestrial faults
Authors: Watters Thomas R. , Schultz Richard A. , Robinson Mark S.
Published: February 2004

The displacement Dand length Lof thrust faults associated with lobate scarps on Mercury and Mars are estimated from topographic and planimetric measurements. Dranges from 0.29 to 3.58 km for mercurian thrust faults (n=10) and from 0.27 km to 2.90 km for martian thrust faults (n=13). The D‐Lrelationship between thrust fault populations analyzed on Mercury and Mars is very similar (γMercury= 6.5 ± 3.2 ×10−3, γMars= 5.9 ± 2.0 × 10−3), and about an order of magnitude lower than terrestrial thrust faults. The difference is probably dominated by the contrast in tectonic setting between terrestrial thrust faults and those on Mercury and Mars. The similarity in morphology and the D‐Lrelationship of the mercurian and martian thrust faults may be due to the similarity in mechanical properties of the deformed materials and the acceleration due to gravity of the two planets.
Selectivity of spontaneous rupture propagation on a branched fault
Authors: Aochi H. , Fukuyama E. , Matsu'ura M.
Published: February 2004

We simulated spontaneous dynamic rupture propagation on a branched fault system using the boundary integral equation method (BIEM) in 3D homogeneous, unbounded elastic medium. From the numerical experiments, we found that slightly heterogeneous preload stress field on the branches caused selective rupture propagation. Dynamic rupture propagation spontaneously on both branches requires very delicate conditions for the initial stress field as well as for the fracture criterion on them.
Interhemispheric oscillations in the surface air pressure field
Authors: Guan Zhaoyong , Yamagata Toshio
Published: February 2004

The low frequency variability in the surface air pressure (SAP) field is investigated using the NCEP/NCAR 40‐year reanalysis data. The EOF1 (EOF2), which accounts for 36% (21%) of total variance of the zonal mean anomalous SAP, corresponds to the air mass oscillation in the middle and high latitudes of the Southern (Northern) Hemisphere. While the total air mass is conserved globally, EOF3 (14.5%) represents the air mass redistribution between the two hemispheres on time‐scales ranging from several months to a decade. This is referred to as the interhemispheric oscillation (IHO). An index is defined to describe the IHO variability. The EOF3 explains 65% of the total variance of the IHO index. Moreover 14.5% of the total variance of the zonal mean SAP anomalies represents the variability of the IHO.
Mechanical relationship between catastrophic volcanic landslides and caldera collapses
Authors: Hürlimann Marcel , Martí Joan , Ledesma Alberto
Published: February 2004

Large‐scale sector collapses of volcanic edifices and collapse calderas represent some of the most catastrophic geological events taking place at the earth's surface. Examples of these two processes occurring simultaneously suggest that a mechanical relationship between landslides and collapse calderas may exist. We demonstrate that a caldera collapse can trigger large‐scale landslides in volcanic terrains. Moderate seismic shocks caused by seismogenic slip on the ring fault on which the caldera subsidence takes place act as the driving force necessary to destabilize the volcano flank. This process is favored on steep volcanoes and where flank strength is reduced by agents such as hydrothermal alteration, pore fluid pressure increase or the presence of weak soils.
Thermodynamic Stability of Fe/O Solid Solution at Inner‐Core Conditions
Authors: Alfè D. , Price G. D. , Gillan M. J.
Published: February 2004

We present a new technique which allows the fully ab initio calculation of the chemical potential of a substitutional impurity in a high‐temperature crystal, including harmonic and anharmonic lattice vibrations. The technique uses the combination of thermodynamic integration and reference models developed recently for the ab initio calculation of the free energy of liquids and anharmonic solids. We apply the technique to the case of the substitutional oxygen impurity in h.c.p. iron under Earth's core conditions, which earlier static ab initio calculations indicated to be thermodynamically very unstable. Our results show that entropic effects arising from the large vibrational amplitude of the oxygen impurity give a major reduction of the oxygen chemical potential, so that oxygen dissolved in h.c.p. iron may be stabilised at concentrations up a few mol % under core conditions.
Mid mantle scatterers near the Mariana Slab detected with a double array method
Authors: Krüger Frank , Baumann Marlyse , Scherbaum Frank , Weber Michael
Published: February 2004

We use a cluster of deep earthquakes, the fore‐ and aftershocks of the 23‐AUG‐1995 Mw=7.1 (18.8N, 145.3E, h=595 km) event in the Mariana subduction zone as source array to locate where waves scatter near the deep slab. In order to obtain the high‐precision location needed in this context, we first relocate the events with a modified master event technique. Using the double beam method on the relocated events and data from the Warramunga array in Australia, we identified two non‐standard S‐to‐P conversions arriving about 20.5 and 24 s after the P‐wave. The corresponding scatterers are approximately located at a depth of 790 km (720 km) and a distance of 0.9° to the southeast (2.3° to the southwest) of the main shock. The scatterers positions correspond to the location of lithosphere subducted below the 660 km discontinuity.
Compensation of atmospheric CO2 buildup through engineered chemical sinkage
Authors: Elliott S. , Lackner K. S. , Ziock H. J. , Dubey M. K. , Hanson H. P. , Barr S. , Ciszkowski N. A. , Blake D. R.
Published: February 2004

Retrieval of background carbon dioxide into regional chemical extractors would counter anthropogenic inputs in a manner friendly to established industries. We demonstrate via atmospheric transport/scaling calculations that for idealized flat removal units, global coverage could be less than two hundred thousand square kilometers. The disrupted area drops to a small fraction of this with engineering into the vertical to bypass laminarity. Fence structures and artificial roughness elements can both be conceived. Sink thermodynamics are analyzed by taking calcium hydroxide as a sample reactant. Energy costs could be minimized at near the endothermicity of binding reversal. In the calcium case the value is 25 kcal mole−1, as against a fuel carbon content of 150 in the same units. Aqueous kinetics are less than favorable for the hydroxide, but misting could counteract slow liquid phase transfer. Properties of superior scrubbers are outlined.
Sensitivity of surface fluxes to the number of layers in the soil model used in GCMs
Authors: de Rosnay P. , Bruen M. , Polcher J.
Published: February 2004

Many GCM land surface schemes were recently developed in order to take into account the physical processes of soil water flow by resolving Darcy equation. But numerical resolution of the Darcy equation requires care because of its high degree of non‐linearity. This paper presents a sensitivity experiment of the numerically computed surface fluxes to the vertical soil resolution. It is shown that too coarse resolutions drastically affects the ability of the scheme to give physically based representations of moisture and energy fluxes.
Lightning activity within a tornadic thunderstorm observed by the optical transient detector (OTD)
Authors: Buechler D. E. , Driscoll K. T. , Goodman S. J. , Christian H. J.
Published: February 2004

The first storm‐scale, total lightning observations from space during tornadogenesis are presented. During the overpass of an Oklahoma supercell, just minutes prior to tornado touchdown on 17 April 1995, the NASA (National Aeronautics and Space Administration) OTD (Optical Transient Detector) detected a total of 143 flashes during approximately 3 minutes of observation time. The estimated total flash rate ranges from 45 (raw counts) to 78 (corrected for detection efficiency) flashes min−1. This total flash rate was at least 17 times greater than the cloud‐to‐ground lightning rate detected by the National Lightning Detection Network (NLDN), indicating most of the lightning was intracloud. Cloud‐to‐ground lightning at this time was also dominated by positive polarity flashes. In addition, total lightning rates were decreasing rapidly prior to touchdown. These OTD observations are consistent with the limited results from recent ground based measurements of total lightning activity in tornadic storms and corroborate that such storms have unusually high total flash rates, are dominated by intracloud lightning, and that the total flash rates are observed to decrease rapidly in the minutes prior to touchdown.
The lognormal distribution as a reference for reporting aerosol optical depth statistics; Empirical tests using multi‐year, multi‐site AERONET Sunphotometer data
Authors: N. T. O'Neill , Ignatov A. , Holben B. N. , Eck T. F.
Published: February 2004

Aerosol optical depth data representative of various types of aerosols was employed to empirically demonstrate that the lognormal probability distribution is a better reference for reporting optical depth statistics than a normal probability distribution.
The effect of two decades of ozone change on stratospheric temperature as indicated by a general circulation model
Authors: Rosier Suzanne M. , Shine Keith P.
Published: February 2004

The effect on stratospheric temperatures of ozone change since 1979 is investigated using a general circulation model employing observations of the vertical profile of ozone change. The stratopause region is generally cooler in 1997 than in 1979 by about 2 K. Results from a ‘Seasonally Evolving Fixed Dynamical Heating’ simulation indicate that this cooling is mostly radiative in origin. In Antarctica the model indicates statistically significant cooling of the lower stratosphere between 1979 and 1997, peaking at 13 K in November; this agrees quite well with observations. In the Arctic no significant cooling is seen in winter or early spring, in contrast with observations, indicating that ozone loss is not the main cause of the observed temperature change here. The peak Antarctic cooling is accompanied by a warming of the upper stratosphere; dynamics are responsible for this warming and for making the lower stratospheric cooling less severe than it would otherwise be.
The Assessment of Marine Gas Hydrates Through Electrical Remote Sounding: Hydrate Without a BSR?
Authors: Yuan J. , Edwards R. N.
Published: February 2004

Marine gas hydrates, prevalent in offshore sediments in Canada and Japan, are a possible hydrocarbon resource, a hazard to drilling and a source of a major greenhouse gas. Quantitative estimates of hydrate concentrations in deep sea sediment are difficult to obtain by conventional methods. We have sought novel techniques specifically designed for assessment such as transient electric dipole‐dipole electromagnetics. The latter method is based on the assumption of a reduced electrical conductivity in hydrate rich zones. Field trails of new apparatus on the Cascadia margin have proven successful. Excellent data were collected and analysed using a differential phase method to reduce systematic error. Apparent resistivities collected on three lines demonstrate that the resistivity of the seafloor is remarkably uniform over the whole survey area. The average hydrate concentration, deduced with the aid of a reference model based on the electrical logs of ODP holes 888 and 889, is about 17–26% of pore space (9–13% of sediment volume) in the 100 m interval above the BSR. The values are consistent with those obtained by other analyses. Further, the presence of hydrate is predicted in a region to the east of 889B where there is no visible BSR.
GRIM5‐C1: Combination solution of the global gravity field to degree and order 120
Authors: Gruber Thomas , Bode Albert , Reigber Christoph , Schwintzer Peter , Balmino Georges , Biancale Richard , Lemoine Jean‐Michel
Published: February 2004

The new satellite Earth gravity field model GRIM5‐S1 was recently prepared in a joint GFZ and GRGS effort. Based on this satellite solution and terrestrial and altimetric gravity anomalies from NIMA, a combined model GRIM5‐C1, with full variance‐covariance matrix up to degree and order 120, was computed. Surface gravity and altimetric gravity data are corrected for several systematic effects, such as ellipsoidal corrections and aliasing. A weighting scheme for gravity anomalies, according to their given standard deviations was developed. From each data set full normal equations were set up and finally combined with the GRIM5‐S1 normals. To take into account good information from the satellite‐only model a procedure was developed to identify such coefficients and appropriately weighed them in the final normal equation system. Internal error propagation and comparisons to external data sets show, that the GRIM5‐C1 model represents the best state of long wavelength gravity field models.
Assimilation of coastal acoustic tomography data into a barotropic ocean model
Authors: Park Jae‐Hun , Kaneko Arata
Published: February 2004

A data assimilation technique was applied to analyze the first coastal acoustic tomography data, obtained in the Neko‐Seto Channel of the Seto Inland Sea, Japan on March 2–3, 1999. The ensemble Kaiman filter technique accompanied by the forecast of error covariances by means of the Monte Carlo method is found to be best fitted to the present problem because currents in the tomography region are dominated by the strongly nonlinear tidal vortices. Furthermore, the analyzed results are in better agreement with the shipboard ADCP results than those obtained by the inverse analysis of the travel time difference data for the pairs of acoustic stations.
Are observed decadal changes in intermediate water masses a signature of anthropogenic climate change?
Authors: Banks Helene T. , Wood Richard A. , Gregory Jonathan M. , Johns Timothy C. , Jones Gareth S.
Published: February 2004

Recent observations have shown relatively large changes in the temperature and salinity of intermediate water masses in the ocean on decadal timescales. We compare the observed changes with simulations of the coupled climate model HadCM3. In simulations driven by anthropogenic forcing, we see significant changes in intermediate waters in the Southern Ocean which are similar in both pattern and magnitude to the observations. Our results suggest that the observed changes are most likely to be a signal of anthropogenic climate change. The strong signal in the Southern Ocean, which is detectable in the model from the 1980s, is in marked contrast with the intermediate waters of the Northern hemisphere oceans, where internal climate variability is large and a signal of anthropogenic climate change is not detectable in the model until 2020 at the earliest. Our results suggest that intermediate waters, particularly those of the Southern hemisphere, are a potentially sensitive indicator of anthropogenic climate change, and could be an important part of a climate monitoring network.
Absence of Short‐Period ULVZ Precursors to PcP and ScP from two Regions of the CMB
Authors: Persh Steven E. , Vidale John E. , Earle Paul S.
Published: February 2004

We present results from a study of the core‐mantle boundary (CMB) underneath Mexico, Central America, and the northeast Pacific using core‐reflected phases PcP and ScP, which provide a direct means of sampling the deep mantle. Precursor arrivals to these phases produced by reflection from the top of an ultra‐low velocity layer (ULVZ) at the base of the mantle would contain information about the thickness of such a layer and the velocity reductions within it. Stacks of these phases from 17 earthquakes recorded by the Northern and Southern California Seismographic Networks do not exhibit coherent or incoherent precursor arrivals from a ULVZ. In precursor time windows, ratios of stack amplitudes to those of the CMB‐reflected phases fall below predicted values from published ULVZ models. We conclude that ULVZs, if present in these regions, have VP and VS reductions less than 10%, are less than five km thick, or have transitions greater than five km wide at their upper boundaries.
Modifications of the local environment by natural marine hydrocarbon seeps
Authors: Leifer Ira , Clark Jordan F. , Chen Robert F.
Published: February 2004

The bubble gas partial pressures, dissolved gas and oil, and fluid motions within the rising bubble streams of three shallow (<70 m) natural hydrocarbon seeps in the Santa Barbara Channel were measured. Aqueous methane concentrations near the surface in the bubble plumes were substantially greater (>108times) than atmospheric equilibrium values; at two of the seeps it was slightly supersaturated with respect to the bubble's partial pressure. This indicates that the rate limiting step for methane, CH4, transfer into the water column was not bubble gas transfer, but rather turbulence transfer of water out of the saturated bubble stream to the bulk ocean. Strong upwelling flows were observed, as well as elevated fluorescence indicative of dissolved oils. At the bottom, bubbles are circa 90% CH4, but at the surface they were circa 60% CH4, 30% air, and 10% higher hydrocarbons.
Intraplate earthquakes and a seismically defined lateral transition in the upper mantle
Authors: Thybo H. , Perchuć E. , Zhou S.
Published: February 2004

We show that the lateral transition in the upper mantle between the cratonic central/eastern and the tectonically active western regions of North America is narrow and deep‐reaching by travel time analysis of Early Rise explosion seismic data. A concentration of enigmatic intraplate earthquakes coincides with the transition. Differential potential energy from density changes across the transition may generate a high compressional stress level which, locally, exceeds the shear strength of the lithosphere. The resultant deformation is ductile in most parts of the lithosphere, but in the brittle upper crust it explains the enigmatic intraplate earthquakes around the lateral transition in the upper mantle.
Broadband seismology in the oceans: Lessons from the Ocean Seismic Network Pilot Experiment
Authors: Collins J. A. , Vernon F. L. , Orcutt J. A. , Stephen R. A. , Peal K. R. , Wooding F. B. , Spiess F. N. , Hildebrand J. A.
Published: February 2004

The fundamental objective of the Ocean Seismic Network Pilot Experiment (OSNPE)—which was carried out over a period of about 4 months at a site 225 km southwest of Oahu, Hawaii—was to learn how to make high‐quality, broadband seismic measurements in the deep oceans. The OSNPE results demonstrate that broadband data of quality similar to that of quiet land stations can be acquired with seafloor seismographs, but that the location of the seismometer—whether it be on the seafloor, surficially buried within the seabed, or in a deep borehole—has a profound effect on data quality. At long‐periods (< 0.1 Hz), data quality was highest for a seismometer buried just beneath the seafloor, while at short‐periods (> 0.1 Hz), data quality was best for a seismometer deployed 242 m below the seafloor in a borehole.
Can long‐term variability in the Gulf Stream Transport be inferred from sea level?
Authors: Ezer Tal
Published: February 2004

Recent studies by Sturges and collaborators suggest a simple, but powerful, technique to estimate climatic changes in the transport of the Gulf Stream from the difference between the oceanic sea level calculated with a simple wind‐driven Rossby wave model and the observed coastal sea level. The hypothesis behind this technique is tested, using 40 years of data (1950 to 1989) obtained from a three‐dimensional Atlantic Ocean model forced by observed surface data. The analysis shows that variations in sea level difference between the ocean and the coast are indeed coherent with variations of the Gulf Stream transport for periods shorter than 1 year or longer than 4–5 years. The results obtained from the three‐dimensional model confirm the findings of the simple Rossby wave model that decadal climatic changes in the Gulf Stream transport vary considerably with latitude.
Snow grain size retrieved from near‐infrared radiances at multiple wavelengths
Authors: Li Wei , Stamnes Knut , Chen Bingquan , Xiong Xiaozhen
Published: February 2004

A comprehensive forward radiative transfer model is used to construct a snow grain size retrieval algorithm that relies on the use of NIR radiances. Data collected by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) at the wavelengths 0.86, 1.05, 1.24 and 1.73 µm are used to retrieve snow grain size. Based on a single‐layer (homogeneous) snow model, the retrieved snow grain size appears to depend on wavelength. The photon penetration depth defined as the e‐folding flux attenuation depth has be computed for different snow grain sizes and different wavelengths. It reveals that this apparent wavelength dependence occurs because (i) the snow grain size generally increases with depth, and (ii) the photon penetration depth decreases with increasing wavelength. The results show that the wavelength dependence of the photon penetration depth can be used to retrieve the depth dependence of the snow grain size.
An off‐line 3D model of anthropogenic CO2 uptake by the oceans
Authors: Thomas Helmuth , England Matthew H. , Ittekkot Venugopalan
Published: February 2004

A key unanswered question in global climate research is the extent to which the oceans absorb and redistribute anthropogenic CO2 (ΔDICant). We apply an offline ocean carbon cycle model, one that uses atmospheric CO2 concentrations and simplified ocean ventilation estimates. We estimate ocean ventilation by introducing the full age distributions of water masses obtained from a global ocean circulation model. The two model cases we use are known to respectively underestimate and overestimate observed ventilation rates, thereby providing upper and lower bounds on CO2 uptake. The error in determining ΔDICant is reduced significantly by minimising the number of tunable parameters. The development of the oceanic ΔDICant inventory is resolved from the beginning of industrialisation to the present time. According to the model, 177Gt anthropogenic carbon have been locked up in the oceans by 1999, corresponding to an annual uptake rate of 3.9GtC*a−1 during 1999. Uncertainties in our estimated oceanic CO2 uptake are discussed.
QuikSCAT's sea winds facilitates early identification of tropical depressions in 1999 hurricane season
Authors: Katsaros Kristina B. , Forde Evan B. , Chang Paul , Liu W. Timothy
Published: February 2004

Far from land and surface ship observations, most tropical depressions are identified by examining images from geostationary satellites for the presence of rotation of the convective cloud masses. During the 1999 hurricane season, surface wind vectors obtained by the SeaWinds scatterometer on the QuikSCAT satellite for the tropical Atlantic and Caribbean Sea were examined to test the hypothesis that developing tropical depressions (TDs) could be observed with this satellite sensor, before identification by the traditional means. QuikSCAT was able to detect the presence of closed circulation in the surface winds before the systems were designated as depressions. The satellite's unprecedented large swath width of 1800 km allows twice a day observation of most of the tropical oceans. SeaWinds data can, therefore, provide valuable guidance that are an important addition to the tools available to the tropical cyclone forecasting community.