bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimating aggregation between suspended sediments and Frazil ice
Authors: Smedsrud Lars H. 
Published: February 2004

This paper aims to describe the scavenging process, one of the main processes for incorporating sediments (particles) into sea ice. An experiment with suspended sediment and frazil ice in a homogeneous turbulent flow is presented. At the end sediment where incorporated into the surface grease ice. The ice production was constant, and calculated from the salinity measurements, while the turbulent dissipation rate was calculated from high resolution current measurements.A model for aggregation between suspended sediment and frazil is also presented and used to simulate the experiment. The modelled aggregation process depends primarily on concentrations, on the turbulence levels, and on the (constant) radii of the sediments and ice.Efficiency of the aggregation process is estimated from the model and experimental results, and the “aggregation” factor is found to be α ∼ 0.025. This is consistent with theoretical estimates, qualitative observations from laboratory experiments, and field data. Sensitivity analyses suggest that the results does not depend greatly on uncertainty of model parameters.
In situ measurements of Pinatubo aerosol over Kiruna on four days between 18 January and 13 February 1992
Authors: Deshler Terry 
Published: February 2004

Vertical profiles of aerosol were measured on 18 and 27 January and 4 and 13 February, 1992, using balloonborne particle counters released from Esrange (68°N, 21°E) near Kiruna, Sweden. Condensation nuclei (CN) and aerosol with radii ≥ 0.15 µm, in 8 size classes, were measured. In the lower stratosphere concentrations of the larger particles were greater, by factors of 10 to 100, than those measured on flights from Esrange in January and February 1991. CN concentrations in the two years showed no pronounced differences. The bulk of the particles were volcanic aerosol from the eruption of Mt. Pinatubo.On the first three flights, in air polewards of the stratospheric jet stream, there was little volcanic aerosol above 20 km, although a highly structured polar stratospheric cloud (PSC) was detected above the volcanic layer on 27 January. In the main volcanic layer, below about 16 km, the aerosol constituted 10 to 60 ppbm sulfuric acid, with a surface area density of 5 to 10 µm² cm−3, based on lognormal size distributions fit to the concentration measurements. These are respectively 50 and 10 times larger than the mass and surface area densities found in 1991. On the last flight in air equatorward of the jet stream, volcanic aerosol was detected up to 27 km, with peak values, near 20 km, of 100 ppbm sulfuric acid and 20 µm² cm−3 surface area density. These are similar to observations in the mid‐latitudes at that time.
Imaging of subsurface contaminations using dipole EM systems
Authors: Sharma S. P. , Verma S. K. 
Published: February 2004

Major contemporary applications of the dipole EM methods deal with the problems of imaging subsurface contaminated or polluted zones, mapping of saline‐water incursion zones in coastal areas, foundation engineering and waste disposal etc. Because such problems are mostly encountered in populated and/or industrialized areas, inductive electromagnetic (EM) methods employing small dipolar transmit‐receive (T‐R) systems provide efficient tools to tackle them. A number of T‐R orientations, measuring different primary and resultant fields, are currently employed in EM exploration.In most of the above problems the target zone can be simulated by a thin conductive or resistive layer. The present work quantifies the resolving capabilities of various dipole EM systems for such a target layer. The target layer is considered embedded in different types of commonly occuring geoelectrical situations. Comparative study of the resolutions obtained for the target layer by different dipole systems reveals that the perpendicular loop system provides the best resolution due to its unique advantage of being free from primary field interference.
ERS‐1 altimetry on the Greenland Ice Sheet: Preliminary investigations of annual variations
Authors: Andersen Ole Baltazar 
Published: February 2004

The existence of an annual signal in the ERS‐1 35‐day repeat altimetry measurements over the Greenland ice sheet is investigated in this paper.Spectral analysis from a collinear set of long tracks indicates, that the timevarying part of the elevation signal is rather constant at a level around 20 cm at frequencies higher than 1 cycle per degree. At lower frequencies the presence of a stationary signal can be seen. This signal can be estimated in a collinear analysis from the entire set of 35‐day altimetry data over the ice sheet spanning one and a half years.Separation of an annual signal revealed a signal highly correlated with topography. The mean amplitude is around 40 cm, with amplitudes between 10–20 cm around the summit of the ice, rising to between 50–80 cm approaching the ablation zone of the ice sheet.
GEOTAIL low energy particle and magnetic field observations of a plasmoid at XGSM = −142 RE
Authors: Machida S. , Mukai T. , Saito Y. , Obara T. , Yamamoto T. , Nishida A. , Hirahara M. , Terasawa T. , Kokubun S. 
Published: February 2004

Data from the GEOTAIL Low Energy Particle (LEP) instrument and magnetometer (MGF) for a plasmoid event on October 8, 1993 when the spacecraft was located at XGMS ∼−142 RE were analyzed. The event started 16 minutes after a substorm onset with a tailward flow of electrons whose characteristic energy was several keV with an apparent energy dispersion. This was followed by the arrival of a beam of high energy ions, which also had a similar energy dispersion, and an enhancement of the magnetic field intensity. There was appreciably high flux of cold ions in the lobe region, and it was further enhanced at the front of the plasmoid. These cold ions were energized at the boundary of the plasmoid where a sharp decrease in the total magnetic field intensity was observed. It was found that the main part of the plasmoid had a significant dusk‐to‐dawn magnetic field, indicating the plasmoid had a flux rope, or a distorted closed‐loop magnetic field structure. After passing the main part of the plasmoid, the spacecraft entered a region characterized by high energy tailward flowing ions and coexisting cold ions. The level of low frequency magnetic field fluctuations was relatively high, and there were some time variations in both high‐energy and cold ion fluxes.Synthesizing these features, we conclude that our observations are consistent with the creation of a plasmoid and surrounding energetic particle layers following a substorm as predicted by the near‐Earth neutral line model of a magnetospheric substorm.
Introduction to the Special Section Northeast Japan: A Case History of Subduction
Authors: Finn Carol , Kimura Gaku , Suyehiro Kiyoshi 
Published: February 2004

Subduction‐related tectonic events such as strike‐slip faulting, uplift of high‐pressure metamorphic rocks in the forearc, back arc spreading, arc magmatism, and continental collisions have shaped northeast Japan, making it a case history for subduction. Much of the record of these events is preserved and can be used to reconstruct the tectonic history of the region.Although many geological, geophysical, and geochemical data have been collected in Japan for the last 30 years, interpretation of these data into a plate tectonic context did not really begin until about 10 years ago. Much of the data and interpretation on northeast Japan have been published in Japanese or as individual local studies. The primary goal of this special section is to present new investigations covering a wide range of topics and scales and place them in a tectonic framework. The papers in this special section focus on three main subjects: Mesozoic aspects of northeast Japan; the relation of Japan Sea opening with the tectonics and geochemistry of northeast Japan in the Tertiary; and the geophysical setting. The purpose of this overview is to link these subjects and provide a tectonic framework for north‐ east Japan and eastern Asia since the Mesozoic.
Introduction: The Alaska Synthetic Aperture Radar Facility special section
Authors: Carsey Frank D. , McNutt Lyn , Rothrock D. Andrew 
Published: February 2004

In 1985 the National Aeronautics and Space Administration (NASA) and the University of Alaska agreed to implement, at the Geophysical Institute of the Fairbanks campus, a facility dedicated to the acquisition, processing, distribution, and archival of synthetic aperture radar (SAR) data to be downlinked from satellites. Since then, the Alaska SAR Facility (ASF) has been an active part of NASA's Mission to Planet Earth. ASF Program goals were outlined by Carsey et al. [1987].Plans were put in place to support three satellites, and the first two, the First European Remote Sensing Satellite (ERS 1) (launched in My 1991) and the Japanese Earth Resources Satellite (JERS 1) (launched in February 1992) are presently in orbit and are being supported by ASF. The third, the Canadian RADARSAT, is scheduled for launch in the spring of 1995. Future satellite missions by U.S. or foreign agencies may well be added in time.
Variation of free tropospheric total nitrate at Mauna Loa Observatory, Hawaii
Authors: Lee Gangwoong , Merrill John T. , Huebert Barry J. 
Published: February 2004

We measured total nitrate (TN) concentrations (defined as nitric acid vapor plus nitrate aerosol) nightly at the Mauna Loa Observatory (MLO) from September 1988 to September 1991. Using three meteorological criteria, (condensation nuclei, wind direction, and dew point) we selected samples that represented the free troposphere. The 3‐year mean and median of TN mixing ratios were 113 parts per trillion by volume (pptv) and 93 pptv, respectively. Each year the TN concentrations at MLO during the spring and summer were larger by more than a factor of 2 than those during the fall and winter. The springtime peak TN corresponded to incidents of increased Asian dust over the northern Pacific Ocean. Isentropic back trajectories confirmed that spring air masses with high TN originated over the Asian continent. Back trajectories also indicated that the North American continent was often the source of high TN during the summer. Air mass source regions and flow patterns to MLO were classified into five distinct groups of trajectories by cluster analysis.Despite the different source regions for each of the clusters the distributions of TN were very similar. This suggests that the source region may be less important for determining TN at MLO than such factors as the degree of vertical mixing over source regions, stratospheric injection, and wet removal rates.
The latitudinal distribution (50°N–50°S) of NO2 and O3 in October/November 1990
Authors: Kreher K. , Fiedler M. , Gomer T. , Stutz J. , Platt U. 
Published: February 2004

The present paper reports on shipboard DOAS (Differential Optical Absorption Spectroscopy) measurements of stratospheric NO2 and O3 vertical column abundances. The data were obtained between 50°N and 50°S during October and November 1990, before the eruption of Mt. Pinatubo. The daily measurements were made during morning and evening twilight. The retrieved column abundances were averaged over a solar zenith angle (SZA) range of 87° to 91°, for both NO2 measured in the visible wavelength region and for O3 measured in the UV. The instrumentation and the data evaluation technique are briefly discussed.In the Northern Hemisphere (autumn) the NO2 vertical column abundances show a steady decrease from 50°N to the equator, while in the Southern Hemisphere (spring) the corresponding increase with latitude is both more pronounced and more variable. Depending on latitude, the measured mean am/pm ratios are between 0.55 and 0.63, generally consistent with the pre‐Pinatubo overnight conversion of NO2 to N2O5.Within the estimated error of our DOAS measurements, the retrieved O3 vertical column amounts are in good agreement with the TOMS data. Both data sets show a slightly different longitudinal distribution than expected from the O3 climatology.
Implications of spatial and temporal development of the aftershock sequence for the Mw 8.3 June 9, 1994 Deep Bolivian Earthquake
Authors: Myers Stephen C. , Wallace Terry C. , Beck Susan L. , Silver Paul G. , Zandt George , Vandecar John , Minaya Estela 
Published: February 2004

On June 9, 1994 the Mw 8.3 Bolivia earthquake (636 km depth) occurred in a region which had not experienced significant, deep seismicity for at least 30 years. The mainshock and aftershocks were recorded in Bolivia on the BANJO and SEDA broadband seismic arrays and on the San Calixto Network. We used the joint hypocenter determination method to determine the relative location of the aftershocks. We have identified no foreshocks and 89 aftershocks (m > 2.2) for the 20‐day period following the mainshock. The frequency of aftershock occurrence decreased rapidly, with only one or two aftershocks per day occuring after day two. The temporal decay of aftershock activity is similar to shallow aftershock sequences, but the number of aftershocks is two orders of magnitude less. Additionally, a mb ∼6, apparently triggered earthquake occurred just 10 minutes after the mainshock about 330 km east‐southeast of the mainshock at a depth of 671 km.The aftershock sequence occurred north and east of the mainshock and extends to a depth of 665 km. The aftershocks define a slab striking N68°W and dipping 45°NE. The strike, dip, and location of the aftershock zone are consistent with this seismicity being confined within the downward extension of the subducted Nazca plate. The location and orientation of the aftershock sequence indicate that the subducted Nazca plate bends between the NNW striking zone of deep seismicity in western Brazil and the N‐S striking zone of seismicity in central Bolivia. A tear in the deep slab is not necessitated by the data. A subset of the aftershock hypocenters cluster along a subhorizontal plane near the depth of the mainshock, favoring a horizontal fault plane. The horizontal dimensions of the mainshock [Beck et al., this issue; Silver et al., 1995] and slab defined by the aftershocks are approximately equal, indicating that the mainshock ruptured through the slab.
A very broadband study of the 1994 Deep Bolivia Earthquake Sequence
Authors: Wu Jun , Wallace Terry , Beck Susan 
Published: February 2004

We have examined the source process of the June 9, 1994 Bolivia earthquake in the period range of body waves to free oscillations. A series of moment tensor inversions were performed on various teleseismic wave types and frequency bands to infer the source parameters and to map the temporal character of the source process. Time independent moment tensor inversion of the body waves (P and SH) yields a source time function of 46 seconds duration with four major “pulses” of moment release, with moment release dominated by the third pulse. The focal mechanism is dominantly dip‐slip on the sub‐horizontal nodal plane (strike 287°, dip 8° and slip −74°). The best bodywave fit requires a non‐double‐couple component of approximately 7%; although this could be due to an isotropic component of the source, it is at the margin of resolution. Time dependent moment tensor inversion of the body waves, which yields independent time histories for each moment tensor element, shows that the source orientations (fault plane and slip direction) change very little throughout the rupture duration. Analysis at several frequencies shows that the seismic moment is very stable (3.0 × 1021 Nm ± 6%) at periods greater than 150 seconds and that the isotropic moment is negligible given the resolution.We also modeled the P‐waves for the January 10, 1994 event, the strong aftershock of June 9, 1994 and the August 8, 1994 earthquake. Rotation of the P axes for events after the mainshock may suggest a possible stress adjustment.
Tracer‐based inferences of new and export primary productivity in the ocean
Authors: Jenkins W.J. 
Published: February 2004

Obtaining regional estimates of seasonal to decadal average new productivity in the ocean is an important goal. Tracer studies have proven useful in making such determinations, although the nature of the estimates made are colored by the character and space/time scales of the tracer systems used. These differences provide important clues as to mechanisms and processes. Knowledge of new, export and particulate export fluxes are powerful constraints for biogeochemical models. We have made significant advances over the past four years, with different tracer systems yielding more or less consistent results in, for example, the subtropical North Atlantic. The general agreement between essentially independent approaches does much to build our confidence in the veracity of their results. Further, exciting new insights are provided by new information regarding the relative magnitude of particulate export flux.Some nagging concerns remain, however, both due to the mismatch between these measurements and other more traditional approaches (e.g., sediment traps), and some unresolved implications of some of the observations. With improved measurement techniques, more sophisticated interpretive tools, and the large field programs in progress, we have high hopes that the future will bring a clearer view.
The ionosphere's wild ride in outer space
Authors: Horwitz J. L. 
Published: February 2004

Plasma of terrestrial origin is produced chiefly by either solar photo‐ionization or electron bombardment ionization of the Earth's upper atmosphere, forming the ionosphere. Under many conditions, components of the higher‐altitude ionosphere acquire sufficient energy to escape the Earth's gravitational attraction and flow out along geomagnetic field lines into various regions of the magnetosphere, and perhaps beyond, into the solar wind. Over the past two decades, intense observational and modeling efforts by numerous researchers have sought to understand the processes driving these ionospheric outflows and the resulting presence and consequences of these ionospheric plasmas populating the major regions of the magnetosphere.The matter of ionospheric outflows directly influences two significant thrusts of current magnetospheric research. First, the exciting concept of imaging magnetospheric plasmas is now believed to be feasible and is planned for future NASA missions. Some of the envisioned imaging approaches are based on detection of solar EUV radiation resonantly‐scattered from ionospheric‐origin He+ and O+ ions. Second, there is the major unresolved issue of whether the ionospheric outflows supply much of the plasma content of such regions as the ring current and the plasma sheet, and exactly what the geophysical consequences of the significant presence of heavy ionospheric He+ and O+ ions might be on general wave‐particle processes and substorm triggering and amplification in the tail plasma sheet.
Low grade metamorphism of mafic rocks
Authors: Schiffman Peter 
Published: February 2004

Through most of this past century, metamorphic petrologists in the United States have paid their greatest attention to high grade rocks, especially those which constitute the core zones of exhumed, mountain belts. The pioneering studies of the 50's through the 80's, those which applied the principles of thermodynamics to metamorphic rocks, focused almost exclusively on high temperature systems, for which equilibrium processes could be demonstrated. By the 1980's, metamorphic petrologists had developed the methodologies for deciphering the thermal and baric histories of mountain belts through the study of high grade rocks.Of course, low grade metamorphic rocks ‐ here defined as those which form at pressures and temperatures up to and including the greenschist facies ‐ had been well known and described as well, initially through the efforts of Alpine and Circum‐Pacific geologists who recognized that they constituted an integral and contiguous portion of mountain belts, and that they underlay large portions of accreted terranes, many of oceanic origins. But until the mid 80's, much of the effort in studying low grade rocks ‐ for a comprehensive review of the literature to that point see Frey (1987) ‐ had been concentrated on mudstones, volcanoclastic rocks, and associated lithologies common to continental mountain belts and arcs. In the mid 80's, results of the Deep Sea Drilling Project (DSDP) rather dramatically mitigated a shift in the study of low grade metamorphic rocks.
Demarcating the magnetopause boundary
Authors: Sibeck David G. 
Published: February 2004

Determining the shape of the magnetopause is one of the oldest problems in space physics and one of its earliest success stories. Chapman and Ferraro [1931] were the first to recognize that the Earth's magnetic field carves out a cavity in the oncoming solar wind. Theoretical studies based on gas dynamics which predicted the shape of the magnetopause bounding this cavity [e.g., Ferraro, 1960; Spreiter and Hyett, 1963] were followed by studies demonstrating that magnetopause crossings generally occur in the expected locations [Ness, 1965]. Some years passed before it was realized that the orientation of the interplanetary magnetic field (IMF) also has an important effect on the size and shape of the magnetosphere [Aubry et al, 1970].Determining the location and shape of the magnetopause is useful for both practical and theoretical reasons. The magnetic field rotates from magnetosheath to magnetospheric orientations at the magnetopause. Since some satellites in geosynchronous orbit make attitude adjustments by applying magnetic torques using the ambient field, it is important to know whether the magnetopause is Earthward or Sunward of the satellite. An accurate knowledge of the magnetopause location may help in planning data acquisition during forthcoming missions which lack the resources to take continuous observations. Analytical modellers of the magnetospheric magnetic field wish to confine‐that field within a well‐determined magnetopause boundary. Finally, changes in the magnetopause location and shape reveal important information about solar wind and magnetospheric conditions.
Modeling of multiphase multicontaminant transport in the subsurface
Authors: Russell Thomas F. 
Published: February 2004

This review addresses modeling of subsurface hydrological systems in which contaminants are transported in more than one fluid phase. The primary focus is on problems involving nonaqueous‐phase liquids (NAPLs), a dynamic gas phase, or both, so that the unsaturated and saturated zones are both discussed. Basic research in simpler settings is included if it develops concepts that could be applied in modeling of such problems.Recent developments in practical models are reviewed, along with experimental work and theoretical issues related to the formulation of mathematical models. It will be seen that the extent of validity of the local equilibrium assumption (LEA) for component partitioning among phases is a major question influencing the direction of these formulations. Also emphasized are upscaling to macroscopic and grid lengths, and the choice and coupling of primary variables in multicomponent systems. Relations to and possible use of developments in petroleum reservoir simulation are discussed.