bluuebunny/crossref_metadata_2025 huggingface dataset:
SIMMAX: A modern analog technique to deduce Atlantic sea surface temperatures from planktonic foraminifera in deep‐sea sediments
Authors: Pflaumann Uwe , Duprat Josette , Pujol Claude , Labeyrie Laurent D.
Published: February 2004

We present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern North Atlantic and the South Atlantic between 87°N and 40°S, 35°E and 60°W including published Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) data. These species counts are linked to Levitus's [1982] modern water temperature data for the four caloric seasons, four depth ranges (0, 30, 50, and 75 m), and the combined means of those depth ranges. The relation between planktonic foraminiferal assemblages and sea surface temperature (SST) data is estimated using the newly developed SIMMAX technique, which is an acronym for a modern analog technique (MAT) with a similarity index, based on (1) the scalar product of the normalized faunal percentages and (2) a weighting procedure of the modern analog's SSTs according to the inverse geographical distances of the most similar samples. Compared to the classical CLIMAP transfer technique and conventional MAT techniques, SIMMAX provides a more confident reconstruction of paleo‐SSTs (correlation coefficient is 0.994 for the caloric winter and 0.993 for caloric summer). The standard deviation of the residuals is 0.90°C for caloric winter and 0.96°C for caloric summer at 0‐m water depth. The SST estimates reach optimum stability (standard deviation of the residuals is 0.88°C) at the average 0– to 75‐m water depth. Our extensive database provides SST estimates over a range of −1.4 to 27.2°C for caloric winter and 0.4 to 28.6°C for caloric summer, allowing SST estimates which are especially valuable for the high‐latitude Atlantic during glacial times.

An electronic supplement of this material may be obtained on adiskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN toAGU's FTP account using ANONYMOUS as the username and GUESTas the password. Go to the right directory by typing CD APPEND. TypeLS to see what files are available. Type GET and the name of the file toget it. Finally type EXIT to leave the system.) (Paper 95PA01743,SIMMAX: A modern analog technique to deduce Atlantic sea surfacetemperatures from planktonic foraminifera in deep‐sea sediments, UwePflaumann, Josette Duprat, Claude Pujol, and Laurent D. Labeyrie).Diskette may be ordered from American Geophysical Union, 2000Florida Avenue, N.W., Washington, DC 20009; Payment mustaccompany order.
Suborbital timescale variability of North Atlantic Deep Water during the past 200,000 years
Authors: Oppo Delia W. , Lehman Scott J.
Published: February 2004

We generated ∼200‐kyr‐long proxy records of surface and deepwater variability from a subpolar North Atlantic core (V29–202), enabling us to assess the linkage between surface and deepwater changes on suborbital timescales. In particular, we used a benthic δ13C record to evaluate the deep water response to Dansgaard‐Oeschger temperature oscillations and to Heinrich events, times of massive iceberg delivery to the North Atlantic. We found that the reduction of North Atlantic Deep Water (NADW) production was generally associated with cold or dropping sea surface temperatures (SSTs) as indicated by planktonic foraminiferal assemblages. The NADW contribution to the site did not drop appreciably during Heinrich events H4 through H2, probably because these events followed intervals of prolonged surface cooling already characterized by low rates of NADW production. By contrast NADW reduction appears to have been synchronous with H5. SST rise associated with both Dansgaard‐Oeschger oscillations and Heinrich events was usually accompanied by increasing NADW strength. In a few cases the NADW recovery appeared to lag the SST rise; however, the apparent delay is most likely an artefact of the sedimentary record (low concentrations of benthic foraminifera). As a result of low benthic foraminiferal abundances during stage 6, the stage 6 benthic foraminiferal δ13C record is of lower resolution than the younger part of the record. The stage 6 proxy records for surface hydrography nevertheless reveal millennial‐scale oscillations similar to those seen in stage 3. The available δ13C data suggest that NADW weakened in association with the cold portions of stage 6 SST oscillations. We also sought to confirm a recent study which concluded that there was little NADW variability during the peak of the last interglaciation, marine oxygen isotope substage 5e (Eemian). Isotope stage 5 was marked by a trend of increasing benthic δ13C in V29‐202. Rising δ13C through isotope stage 5 is also seen in tropical surface water records and at some deep Atlantic sites and may reflect the common derivation of these water masses. Variations of ≥ 0.5 ‰ superimposed on this rising δ13C trend within substage 5e in V29‐202 are so far not evident in tropical feed waters and may therefore indicate that NADW production was weaker during the late than mid‐Eemian.

An electronic supplement of this material may be obtained on a diskette or Anonymous FTP from KOSMOS.AGU.ORG. (LOGIN to AGU's FTP account using ANONYMOUS as the username and GUEST as the password. Go to the right directory by typing CD APEND. Type LS to see what files are available. Type GET and the name of the file to get it. Finally, type QUIT to leave the system.) (Paper 95PA02089, Suborbital timescale variability of North Atlantic Deep Water during the past 200,000 years, by D. W. Oppo and S. J. Lehman) Diskette may be ordered from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, DC 20009; $15.00. Payment must accompany order.
A High‐resolution record of Late Quaternary upwelling along the Oman Margin, Arabian Sea based on planktonic foraminifera
Authors: Naidu Pothuri Divakar , Malmgren Björn A.
Published: February 2004

Planktonic foraminiferal abundances, fluxes, test sizes, and coiling properties are influenced in various ways by the southwest monsoon winds and associated upwelling in the western Arabian Sea. To determine the short‐term changes in the southwest monsoon, we have carried out a high‐resolution time‐series analysis of three upwelling indices (total flux of planktonic foraminiferal tests and flux and relative abundance of the planktonic foraminiferal species Globigerina bulloides) from Ocean Drilling Program (ODP) Site 723A (Oman Margin, western Arabian Sea) spanning the last 19 kyr. In addition, we have determined the relationships between upwelling intensity and the relative abundance, fluxes, and shell concentrations of various planktonic foraminiferal species. Upwelling indices suggest that from 19 to 16 ka (22 to 18.2 cal kyr B.P.) the SW monsoon was relatively strong compared to the period 15.8 to 12.5 ka (17.8 to 13.8 cal kyr B.P.). The intensification of the SW monsoon took place at 12 ka (13.1 cal kyr B.P.) and reached a peak between 10 and 5 ka (10.6 and 4.8 cal kyr B.P.). The high‐resolution data further demonstrate that the SW monsoon has started weakening from 5 ka (4.8 cal kyr B.P.) and the weakest phase was in place at 3.5 ka (3 cal kyr B.P.), which coincides with evidence of an arid climate in western Tibet. Fluxes and shell concentrations of many of the planktonic foraminiferal species increased between 12 and 5 ka in response to the intensification of the SW monsoon winds after the last glacial period. Globigerina bulloides shows a fivefold to tenfold increase in flux during this period of intense upwelling. The other species whose fluxes are influenced by this upwelling change are (in order from strongest to weakest response) Globigerinita glutinata, Globigerinoides ruber, Neogloboquadrina dutertrei, Globigerinella aequilateralis, Globigerina falconensis, and Globigerinoides sacculifer. The relative abundances of G. bulloides and G. ruber increased during intense upwelling, whereas the relative abundances of G. glutinata, N. dutertrei, G. falconensis, and G. sacculifer did not increase during this period, which might be due to differences in the productivity of various species in relation to upwelling change. Therefore the fluxes and shell concentrations provide better and more reliable information about the changes in the monsoon system in the Arabian Sea than relative abundance data.
Reassessment of foraminiferal‐based tropical sea surface δ18O paleotemperatures
Authors: Stott Lowell D. , Tang Carol M.
Published: February 2004

The possibility exists that the magnitude of Glacial/Holocene δ18O change in the tropical oceans was previously under‐estimated due to the dampening effect of bioturbation on bulk foraminiferal δ18O measurements. We have investigated this possibility by isotopically analyzing suites of individual planktonic foraminifera from box core samples from the equatorial Atlantic. We present oxygen isotopic results for individual specimens of two surface‐dwelling planktonic foraminifera Globigerinoides ruber (white) and Globigerinoides sacculifer (no final sac) from glacial‐age box core samples from seven sites located between about 15°N and 15°S in the tropical Atlantic. These data are used to constrain the mimimum glacial temperatures recorded by tropical surface‐dwelling planktonic foraminifera during the last glacial maximum. The individual foraminiferal δ18O temperatures reveal minimum sea surface temperatures (SSTs) that ranged from 1°C colder to as much as 5° to 6°C colder than present‐day summer SSTs after correcting for an “ice volume effect”. However, these minimum temperatures represent less than 10% of the foraminiferal population measured from glacial horizons. Approximately 80% of the glacial specimens record temperatures that were within 2°C of the mean Holocene SST. We conclude that either the tropical Atlantic was not pervasively colder during the Glacial or that there was a systematic negative shift in the isotopic composition of the surface waters that offset a more signficant temperature change.
Reconstructing the stable isotope geochemistry and paleotemperatures of the equatorial Atlantic during the last 150,000 years: Results from individual foraminifera
Authors: Billups Katharina , Spero Howard J.
Published: February 2004

This study represents an attempt to extract paleoclimatic data from the deep‐sea record by analyzing foraminiferal shells individually. Using the oxygen (δ18O) and carbon (δ13C) isotopic composition of individual Orbulina universa and Neogloboquadrina dutertrei, we present an approach to reconstruct the δ18O of seawater (δ18Ow), the δ13C of ΣCO2, and seasonal maximum sea surface temperatures (SST) in the western and eastern equatorial Atlantic. We examine the glacial and interglacial extremes of the last 150,000 years (isotope stages 1, 2, 5e, and 6). Comparison of recent water column hydrography with reconstructions from core top assemblages shows that O. universa and N. dutertrei δ18O and δ13C values accurately record hydrographic conditions in the mixed layer and upper thermocline at both sites. By analyzing shells individually, we can evaluate the effect of bioturbation on the range of δ18O and δ13C values in each interval and take it into consideration in our data interpretations. Downcore results show that N. dutertrei δ18O values in the western equatorial Atlantic reflect glacial to interglacial changes in δ18Ow due to continental ice formation (Δδ18O=1.30 ‰). We use changes in N. dutertrei δ18O values between core intervals to estimate the ice‐volume effect in paleotemperature calculations for the mixed layer. To validate the use of O. universa for mixed layer reconstructions, we have added individual Globigerinoides sacculifer data for stages 1 and 2 at both sites. Paleotemperature reconstructions from O. universa δ18O values indicate that maximum seasonal mixed layer temperatures in the equatorial Atlantic decreased by at most 2.6°C between isotope stages 1 and 2 and by no more than 3.4°C between stages 1 and 6. Individual shell data from G. sacculifer yield similar results indicating that maximum O. universa δ18O values reflect the mixed layer environment. In agreement with Climate: Long‐Range Investigation, Mapping, and Prediction (CLIMAP) [1981] SST reconstructions for stage 2, these data indicate little change between glacial and interglacial paleotemperatures in the equatorial Atlantic.

An electronic supplement of this material may be obtainedon a diskette or Anonymous FTP from KOSMOS.AGU.ORG.(LOGIN to AGU's FTP account using ANONYMOUS as theusername and GUEST as the password. Go to the rightdirectory by typing CD APEND. Type LS to see what files areavailable. Type GET and the name of the file to get it.Finally, type EXIT to leave the system.) (Paper 95PA03773,Reconstructing the stable isotope geochemistry andpaleotemperatures of the equatorial Atlantic during the last150,000 years: Results from individual foraminifera,Katharina Billups and Howard J. Spero). Diskette may beordered from American Geophysical union, 2000 FloridaAvenue, N. W., Washington, DC 20009; $15.00. Paymentmust accompany order.
Neogene growth of the sedimentary organic carbon reservoir
Authors: Derry Louis A. , France‐Lanord Christian
Published: February 2004

We develop a recycling model using 13C/12C mass balance for net growth/loss of the sedimentary organic carbon (Corg) reservoir, and apply it to the Neogene bulk marine carbonate δ13C record. The model allows for variations in photosynthetic fractionation factors, carbon cycling rates, and the isotopic composition of riverine carbon inputs to the oceans. The sign of the net flux term is controlled by the difference between fractional Corg burial and fractional Corg weathering, independent of any variations in carbon cycling rate. These terms are in turn estimated from the carbon isotope mass balance of newly deposited and weathered sediments, respectively. The magnitude of the net flux is sensitive to the global carbon cycling (erosion/deposition) rate, which may be estimated by the use of the records of radiogenic isotopic variations (Nd, Sr) in paleoseawater. A key observation and input to the model is that photosynthetic carbon isotope fractionation by both marine algae and terrestrial plants has decreased during the Cenozoic. Incorporating time‐dependent carbon isotope fractionation into the model shows that the sedimentary Corg reservoir has grown throughout most of the Neogene, even as marine δ13C values fell after 14 Ma. A similar result is obtained if the variation in the marine δ13C record is largely caused by changes in the carbon isotopic composition of river fluxes to the oceans, rather than changes in the organic/inorganic ratio of output to the burial sink. The growth of the sedimentary organic carbon reservoir requires that the Neogene sedimentary carbon cycle was a net source of O2 and a net sink of CO2 to the atmosphere, at least until the Plio‐Pleistocene. As a consequence, Neogene CO2 consumption by silicate weathering cannot be balanced by oxidation of sedimentary Corg, placing a significant constraint on global carbon balance models. A related prediction of our model is that atmospheric O2 levels rose during the Neogene.
Earth rotation and global change
Authors: Wilson Clark R.
Published: February 2004

Variations in the rotation of the Earth include changes in the rate of rotation (altering the Length of the Day, LOD), in orientation of the rotation axis relative to a terrestrial frame (Polar Motion, PM) and in orientation relative to a celestial frame due to external torques (Nutation and Precession). Variations occur over a wide range of time scales, from hours to the age of the Earth. Scientific interest in and understanding of Earth rotation variations have proceeded rapidly over the last several decades due, in large part, to enormous improvements in observations by space geodetic means, including satellite laser ranging (SLR), very long baseline interferometry (VLBI), lunar laser ranging (LLR), and satellite positioning methods, especially the global positioning system (GPS). The study of the Earth's rotation is a mature interdisciplinary field, and extensive reviews of many aspects of the field are contained in the AGU monographs ‘Contributions of Space Geodesy to Geodynamics’ (Smith and Turcotte, 1993). Articles by Eubanks (1993), Dickey (1993), Hide and Dickey (1991), and monographs by Lambeck (1988,1980) and Munk and Mac Donald (1960) provide excellent background material on these problems, as well. The reader may also wish to review other IUGG Report articles in this series on related subjects, specifically those on the global gravity field, VLBI technology, satellite orbit dynamics, and GPS.
How the bow shock does it
Authors: Omidi N.
Published: February 2004

Between the world of living organisms and inanimate objects exists a zone inhabited by animate, but nonliving, physical entities. These fascinating, and often nonlinear systems exhibit characteristics which in many ways mimic that of simple biological organisms. They seem to have an instinctive desire to accomplish certain tasks, and devise many creative strategies to achieve their goal. The bow shock, the topic of this paper, is one of the inhabitants of this zone and it forms due to solar wind interaction with the Earth's magnetic field. As one would expect, its goal is to decelerate and divert the supersonic solar wind flow around the magnetosphere. But unlike the usual shock waves, it has to accomplish the task without the use of collisions; quite a challenge indeed. A bigger challenge, however, has been for us to use space age technology and supercomputers to find out how the bow shock does it! We have made much progress; many of the pixels are in place but the picture is not complete. What we have found is a truly fascinating and complex story which is a testament to the creativeness of the bow shock. Depending on the upstream Mach number (ratio of the solar wind speed to the sound speed) and location on the paraboloid surface of the shock, a different strategy for dissipation of the flow energy into heat is utilized. In some regimes, the transition from upstream to downstream takes place on short ( ∼100 km) length scales, while in others, the shock transition is masked with an extended region of electromagnetic waves and turbulence. As part of the dissipation process, electrons and ions are reflected off the shock. The interaction between the solar wind and the reflected particles forms the foreshock, a region extending many Earth radii upstream of the shock. The foreshock is populated by a variety of electrostatic and electromagnetic waves, making it a great natural laboratory for studies of nonlinear wave‐particle interactions. Among these are the fast magnetosonic waves which steepen to form spatially localized shock waves, named shocklets! Creation of shocklets by the bow shock is not quite reproduction, but is close enough to stir the imagination and make one marvel at its parallelism to live organisms. There are many motivations for the study of the bow shock. One set deals with the inherent interest in collisionless shocks,and how it can be used to enhance our knowledge of nonlinear plasma physics, collisionless dissipation, particle acceleration, and their extension to astrophysical settings. The other concerns the influence of the bow shock on magnetospheric phenomena. Before reaching the magnetopause, the solar wind is greatly modified by the bow shock through heating, deceleration, and considerable enhancement of its field fluctuations.
Atmospheric planetary boundary‐layer research in the U.S.: 1991–1994
Authors: Moeng Chin‐Hoh , LeMone Margaret A.
Published: February 2004

With the increasing emphasis on coupled climate systems, planetary‐boundary‐layer (PBL) research has also gained increasing attention. Atmospheric and oceanic PBLs serve as the interface between all of the system components: atmosphere, ocean, land, and biosphere. Boundary‐layer clouds also play important roles in climate, e.g., trade‐wind cumulus in the hydrological cycle and subtropical marine stratus in the Earth's radiation budget. Therefore, proper PBL parameterization schemes are needed to accurately link all of the climate system components and to represent cloud formation and dissipation.
Magellan: A new view of Venus' geology and geophysics
Authors: Bindschadler D. L.
Published: February 2004

Within the past fifteen years, the surface of Venus has gone from being the least well understood of all the terrestrial planets to the most thoroughly mapped surface of any terrestrial planet, including the Earth. This is primarily due to the Magellan mission, which has collected a variety of data on the surface morphology, physical properties, and interior density structure of Venus amounting to more than 1 Terabit (1012 bits) of data. Synthetic aperture radar images have been obtained for over 95% of the surface; their high resolution reveals most surface features larger than 100–200 meters across. Using its radar altimeter, Magellan has collected data on surface elevations, sub‐meter scale roughness, and radar reflectivity at a resolution of approximately 10 km. Further information on the physical properties of the surface was gathered by measuring the passive microwave emissivity of the surface [Pettengill et al, 1992]. Two‐way Doppler tracking of the spacecraft has yielded line‐of‐sight (LOS) gravity data and a spherical harmonic model of gravity and geoid out to degree 75. Collection of high‐resolution gravity data has been aided by an innovative aerobraking maneuver, which used Venus' atmosphere to brake the spacecraft and lower it from a highly elliptical orbit to a near‐circular orbit.
Magnetic reconnection at the magnetopause: A fundamental process and manifold properties
Authors: Otto A.
Published: February 2004

The solar wind ‐ magnetosphere plasma system provides a unique opportunity to study the interaction of plasmas of different origin. One of the major challenges for our understanding of both basic plasma dynamics and the dynamics of the magnetosphere is the coupling of the solar wind plasma and the magnetosphere ‐ ionosphere system. Being the interface between the solar wind and the magnetosphere, the magnetopause controls the interaction between these plasmas. Although the plasma in the vicinity of the magnetopause is highly collisionless, a multitude of observations implies the transport of plasma, momentum and energy from the solar wind into the magnetosphere. The dynamics of the magnetosphere cannot be understood without processes which facilitate this transport.
Recent advances in simulation‐optimization groundwater management modeling
Authors: Wagner Brian J.
Published: February 2004

In recent years, the aquifer simulation model has been combined with techniques of optimization to address important groundwater management problems. The combined simulation and optimization model accounts for the complex behavior of the groundwater system and identifies the best management strategy under consideration of the management objectives and constraints. Simulation‐optimization groundwater management models have been developed for a variety of applications, such as restoration of contaminated groundwater, control of aquifer hydraulics, allocation of ground and surface water resources, and evaluation of groundwater policies [see reviews by Gorelick, 1983, 1990; Yeh, 1992; Ahlfeld and Heidari, 1994; Bredehoeft et al, 1994].

Gorelick [1983] divides groundwater management models into three categories: groundwater hydraulic management, groundwater quality management, and groundwater policy evaluation and allocation. This review focuses in detail on the recent advances made in groundwater hydraulic and groundwater quality management modeling, which encompasses most of the aquifer management work done in the past four years. For a review of recent research in groundwater policy evaluation and allocation, see Bredehoeft et al. [1994].
A critical review of stratospheric chemistry research in the U.S.: 1991–1994
Authors: Toohey Darin W.
Published: February 2004

After the previous review [Brune, 1991] of the breadth of scientific activity following reports of an ozone hole over Antarctica and of similar photochemistry over the Arctic, it is surprising to find as rich a literature base for this review. Admittedly, some of the recent publications are new, but belated, reports of studies carried out before 1991, while some are results of ongoing studies. However, there have also been important new developments in stratospheric chemistry, many of which were initiated by the long‐awaited launch of the Upper Atmosphere Research Satellite (UARS) [Reber, 1993], the Second Airborne Arctic Stratospheric Expedition (AASE II) [Anderson and Toon, 1993], the European Arctic Stratospheric Ozone Expedition (EASOE) [Pyle et al, 1994], the NASA High‐Speed Research Program (HSRP) [Albritton et al, 1993], the eruption of Mount Pinatubo [McCormick, 1992], and the Stratospheric Photochemistry, Aerosols, and Dynamics Expedition (SPADE) [Wofsy et al, 1994]. The review period was also highlighted by observations of the lowest global ozone abundances on record [Gleason et al, 1993], detection of enhanced ultraviolet radiation at the earth's surface [Frederick and Alberts, 1991], examinations of possible strategies for mitigating ozone losses [Cicerone et al, 1991], and direct confirmation of the effectiveness of international agreements limiting the production of ozone‐destroying substances [Elkins et al, 1993].
Soil vapor extraction and bioventing: Applications, limitations, and future research directions
Authors: Rathfelder K. , Lang J.R. , Abriola L.M.
Published: February 2004

Soil vapor extraction (SVE) has evolved over the past decade as an attractive in situ remediation method for unsaturated soils contaminated with volatile organic compounds (VOCs). SVE involves the generation of air flow through the pores of the contaminated soil to induce transfer of VOCs to the air stream. Air flow is established by pumping from vadose zone wells through which contaminant vapors are collected and transported above ground where they are treated, if required, and discharged to the atmosphere. The popularity of SVE technologies stems from their proven effectiveness for removing large quantities of VOCs from the soil, their cost competitiveness, and their relatively simple non‐intrusive implementation. Widespread field application of SVE has occurred following the success of early laboratory and field scale feasibility studies [Texas Research Institute, 1980, 1984; Thornton and Wootan, 1982; Marley and Hoag, 1984; Crow et al., 1985, 1987]. As many as 18% of Superfund sites employ SVE remediation technologies [Travis and Macinnis, 1992] and numerous articles and reports have documented the application of SVE [e.g. Hutzler et al., 1989; Downey and Elliott, 1990; U.S. EPA, 1991; Sanderson et al, 1993; Gerbasi and Menoli, 1994; McCann et al., 1994;].
Crustal deformation
Authors: Larson Kristine M.
Published: February 2004

Geodetic measurements of crustal deformation provide direct tests of geophysical models which are used to describe the dynamics of the Earth. Although geodetic observations have been made throughout history, only in the last several hundred years have they been sufficiently precise for geophysical studies. In the 19th century, these techniques included leveling and triangulation. Approximately 25 years ago, trilateration measurements were initiated by the USGS (United States Geological Survey) to monitor active faults in the United States. Several years later, NASA (National Aeronautics and Space Administration) begin an effort to measure plate tectonic motions on a global scale, using space geodetic techniques, VLBI (Very Long Baseline Interferometry) and SLR (Satellite Laser Ranging). The period covered by this report to the IUGG, 1991–1994, was a transition period in the field of crustal deformation. Trilateration measurements (previously the backbone of measurements across plate boundaries in the western United States and Alaska) have been abandoned. This system was labor‐intensive, involved highly trained crews to carry out the observations, and only measured the length between sites. In addition, NASA drastically cut the budgets for VLBI and SLR during this period. Fixed site VLBI systems are still operational, but mobile VLBI measurements in North America have ceased. SLR measurements continue on a global scale, but the remaining crustal deformation measurements are now being made with the Global Positioning System (GPS). Nonetheless, because of the time scales involved, older geodetic data (including leveling, triangulation, and trilateration) continue to be important for many geophysical studies.
Crustal magnetic anomalies
Authors: Raymond Carol A. , Blakely Richard J.
Published: February 2004

This Quadrennial Report departs in format from its predecessors. Earlier reports provided brief descriptions of the entire range of topics on “crustal magnetic anomalies.” Following guidelines established by the AGU, we instead focus our discussion on only a few selected topics. Our abbreviated list of references reflects this restricted focus. A more comprehensive bibliography can be obtained from the authors as noted subsequently.

The past quadrennium was distinguished by a significant change in the scale and scope of crustal magnetic anomaly research. Advances in instrumentation, navigation, and data processing techniques resulted in increasing use of two‐dimensional anomaly maps rather than profile data. Although maps are commonly used in aeromagnetic studies of continental areas, their use in the ocean basins has been limited until recently. The other important change has been a trend towards increased integration of magnetic anomaly data with gravity, seismic, geochemical, remote sensing, and geologic data to enhance the interpretation and reduce the ambiguity of magnetic field data.
Serendipitous science from flybys of secondary targets: Galileo at Venus, Earth, and asteroids; Ulysses at Jupiter
Authors: Galland Kivelson Margaret
Published: February 2004

During this quadrennium, while the Voyager and Pioneer spacecraft moved through the outer heliosphere, ever further from the sun, the Ulysses and Galileo spacecraft were traversing the inner heliosphere. Sophisticated navigation [see for example, D'Amario et al., 1992] directed them from one planet to another, directing them into orbits tailored to match the primary scientific requirements of the missions. In both cases the trajectories were indirect; the desired orbits required flybys of one or more planets to obtain gravitational assists. It is those flybys, visits to secondary targets as it were, on which this review focuses. The flybys provided rich mines of data that are being exploited with great benefit to space plasma physics. The intriguing results obtained more than justify the effort made to grasp opportunities that were in a sense accidental.
GPS data, acquisition, environmental effects
Authors: Yunck Thomas P.
Published: February 2004

Precise geodesy with the Global Positioning System (GPS) emerged in the early 1990s from a decade‐long incubation to find vigorous application worldwide. Today we enjoy a full 24‐satellite constellation, a new generation of high‐precision receivers at about one‐third the 1991 cost, a growing permanent global network, and a vital International GPS Service to support GPS geodesy worldwide. In addition, dedicated regional GPS networks are springing up on every continent. The period has been marked less by conceptual advance than by disciplined application and refinement. Here we review the key developments in receivers and networks, and in understanding the environmental factors that limit GPS geodetic performance.
Introduction to dynamics of the solid Earth and other planets
Authors: Schubert Gerald
Published: February 2004

In this section of the U.S. National Report (USNR) to the IUGG for the period 1991–1994 are 44 papers on seismology, geodesy, tectonophysics, and planetology. With limitations on both the total number of pages in this section and on the number of pages per paper, it is impossible to review in detail all the work done in the U.S. on such a broad range of subjects. Instead, and in agreement with the overall philosophy of this Report, choices of topics were based on several criteria including scientific impact and societal relevance. If important science has gone unmentioned, then responsibility must lie with this editor and the authors of relevant papers, although in a few instances planned papers went uncompleted. Compared to previous similar collections, the papers in this section will therefore generally not provide a comprehensive review of the literature. On the plus side, however, the papers in this section may be more readable and accessible to the nonspecialist than were previous USNR papers.
Applications of mineral surface chemistry to environmental problems
Authors: White Art F.
Published: February 2004

Environmental surface chemistry involves processes that occur at the interface between the regolith, hydrosphere and atmosphere. The more limited scope of the present review addresses natural and anthropogenically‐induced inorganic geochemical reactions between solutes in surface and ground waters and soil and aquifer substrates. Important surficial reactions include sorption, ion exchange, dissolution, precipitation and heterogeneous oxidation/reduction processes occurring at the solid/aqueous interface. Recent research advances in this field have addressed, both directly and indirectly, societal issues related to water quality, pollution, biogeochemical cycling, nutrient budgets and chemical weathering related to long term global climate change. This review will include recent advances in the fundamental and theoretical understanding of these surficial processes, breakthroughs in experimental and instrumental surface characterization, and development of methodologies for field applications.
Nature and composition of the continental crust: A lower crustal perspective
Authors: Rudnick Roberta L. , Fountain David M.
Published: February 2004

Geophysical, petrological, and geochemical data provide important clues about the composition of the deep continental crust. On the basis of seismic refraction data, we divide the crust into type sections associated with different tectonic provinces. Each shows a three‐layer crust consisting of upper, middle, and lower crust, in which P wave velocities increase progressively with depth. There is large variation in average P wave velocity of the lower crust between different type sections, but in general, lower crustal velocities are high (>6.9 km s−1) and average middle crustal velocities range between 6.3 and 6.7 km s−1. Heat‐producing elements decrease with depth in the crust owing to their depletion in felsic rocks caused by granulite facies metamorphism and an increase in the proportion of mafic rocks with depth. Studies of crustal cross sections show that in Archean regions, 50–85% of the heat flowing from the surface of the Earth is generated within the crust. Granulite terrains that experienced isobaric cooling are representative of middle or lower crust and have higher proportions of mafic rocks than do granulite terrains that experienced isothermal decompression. The latter are probably not representative of the deep crust but are merely upper crustal rocks that have been through an orogenic cycle. Granulite xenoliths provide some of the deepest samples of the continental crust and are composed largely of mafic rock types. Ultrasonic velocity measurements for a wide variety of deep crustal rocks provide a link between crustal velocity and lithology. Meta‐igneous felsic, intermediate and mafic granulite, and amphibolite facies rocks are distinguishable on the basis of P and S wave velocities, but metamorphosed shales (metapelites) have velocities that overlap the complete velocity range displayed by the meta‐igneous lithologies. The high heat production of metapelites, coupled with their generally limited volumetric extent in granulite terrains and xenoliths, suggests they constitute only a small proportion of the lower crust. Using average P wave velocities derived from the crustal type sections, the estimated areal extent of each type of crust, and the average compositions of different types of granulites, we estimate the average lower and middle crust composition. The lower crust is composed of rocks in the granulite facies and is lithologically heterogeneous. Its average composition is mafic, approaching that of a primitive mantle‐derived basalt, but it may range to intermediate bulk compositions in some regions. The middle crust is composed of rocks in the amphibolite facies and is intermediate in bulk composition, containing significant K, Th, and U contents. Average continental crust is intermediate in composition and contains a significant proportion of the bulk silicate Earth's incompatible trace element budget (35–55% of Rb, Ba, K, Pb, Th, and U).
Geomagnetic activity forecasting: The state of the art
Authors: Joselyn Jo Ann
Published: February 2004

Short‐term (days to weeks) geomagnetic forecasts are valuable for a variety of public and private sector endeavors. However, forecast skill, as measured by the success of predicting geomagnetic indices, is disappointing, especially for disturbed conditions. Possible reasons for this lack of proficiency include an incomplete understanding of the solar origins of interplanetary disturbances, insufficient observations of solar phenomena and interplanetary disturbances, and an underestimation of magnetospheric‐ionospheric control of observed geomagnetic activity. Until more progress can be made on each of these problems, desirable forecasting precision is likely to remain elusive. The best opportunity for improved service to those agencies requiring advance notice of geomagnetic disturbances is “nowcasting” using real‐time, near‐Earth observations of the approaching solar wind.
Tropical precipitation studies using a 915‐MHz wind profiler
Authors: Ecklund Warner L. , Gage Kenneth S. , Williams Christopher R.
Published: February 2004

Precipitation echoes obtained with 915‐MHz wind profilers operated in the tropics provide useful information on the structure of precipitating cloud systems. This paper examines the sensitivity of the 915‐MHz profiler to precipitation. Observations of precipitation echoes at Manus Island, Papua New Guinea, illustrate profiler performance capabilities for observing several types of tropical convective systems. Special attention is given to the occurrence of deep precipitating clouds which are often present without rain at the surface. Analyses of profiler data from Manus Island show that over a 10‐month period, deep precipitating clouds were present more than 25% of the time. The importance of the deep precipitating clouds to the heat budget of the tropical atmosphere is briefly discussed.
Wavelet analysis on transient behavior of wind fluctuations observed by MST radar
Authors: Chen K. Y. , Fu I. J. , Su S. Y. , Liu C. H.
Published: February 2004

Wind fluctuations observed by the MST radar technique often show complicated temporal behavior. Waves with different periods may occur at different times. Conventional fast Fourier transform (FFT) analysis will not be able to follow the temporal evolution of the wave spectrum. Multiscale, multiresolution wavelet analysis proposed in this paper is quite useful to study this transient behavior of the waves. A complex Gabor wavelet with a few cycles of monochromatic waves is chosen as the wavelet base, and this choice leads to successful results for gravity‐wave like wind disturbances observed by MST radar in the troposphere. Possible interpretations in terms of nonlinear wave‐wave or wave‐mean flow interactions are proposed.
The frequency‐agile radar: A multifunctional approach to remote sensing of the ionosphere
Authors: Tsunoda R. T. , Livingston R. C. , Buonocore J. J. , McKinley A. V.
Published: February 2004

We introduce a new kind of diagnostic sensor that combines multifunctional measurement capabilities for ionospheric research. Multifunctionality is realized through agility in frequency selection over an extended band (1.5 to 50 MHz), system modularity, complete system control by software written in C, and a user‐friendly computer interface. This sensor, which we call the frequency‐agile radar (FAR), incorporates dual radar channels and an arbitrary waveform synthesizer that allows creative design of sophisticated waveforms as a means of increasing its sensitivity to weak signals while minimizing loss in radar resolution. The sensitivity of the FAR is determined by two sets of power amplifier modules: four 4‐kW solid‐state broadband amplifiers, and four 30‐kW vacuum tube amplifiers. FAR control is by an AT‐bus personal computer with on‐line processing by a programmable array processor. The FAR does not simply house the separate functions of most radio sensors in use today, it provides convenient and flexible access to those functions as elements to be used in any combination. Some of the first new results obtained with the FAR during recent field campaigns are presented to illustrate its versatility. These include (1) the first detection of anomalous high‐frequency (HF) reflections from a barium ion cloud, (2) the first evidence of unexpectedly large drifts and a shear north of the equatorial electrojet, (3) the first HF radar signature of a developing equatorial plasma bubble, and (4) the first measurements by a portable radar of altitude‐extended, quasi‐periodic backscatter from midlatitude sporadic E. We also mention the potential of the FAR for atmospheric remote sensing.
Measurement of rainfall path attenuation near nadir: A comparison of radar and radiometer methods at 13.8 GHz
Authors: Durden S. L. , Haddad Z. S. , Im E. , Kitiyakara A. , Li F. K. , Tanner A. B. , Wilson W. J.
Published: February 2004

Rain profile retrieval from spaceborne radar is difficult because of the presence of attenuation at the higher frequencies planned for these systems. One way to reduce the ambiguity in the retrieved rainfall profile is to use the path‐integrated attenuation as a constraint. Two techniques for measuring the path‐integrated attenuation have been proposed: the radar surface reference technique and microwave radiometry. We compare these two techniques using data acquired by the Airborne Rain Mapping Radar (ARMAR) 13.8‐GHz airborne radar and radiometer during the Tropical Ocean‐Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE) in the western Pacific Ocean in early 1993. The two techniques have a mean difference close to zero for both nadir and 10° incidence. The RMS difference is 1.4 dB and is reduced to 1 dB or less if points where the radiometer was likely saturated are excluded. Part of the RMS difference can be attributed to variability in the ocean surface cross section due to wind effects and possibly rain effects. The results presented here are relevant for the Tropical Rainfall Measuring Mission, which will include a 13.8‐GHz precipitation radar.
Experimental study of double resonance parametric excitations in the ionosphere
Authors: Song B. , Wong A. Y. , Villaseñor J. , Rosenthal G. , McCarrick M. , Pau J. , Sentman D.
Published: February 2004

We report the double resonance excitation of two pump waves with frequencies separated from 5 to several hundred Hz. The cyclotron frequencies of NO+ and O2+, abundant at the bottom of the F layer (∼ 150 km), are within this range. The nonlinear mode coupling takes place at ∼ 150 km where the pump frequency matches the plasma frequency. The experiments show that when the beat frequency is close to the NO+ cyclotron frequency at ∼ 30 Hz, the energy transfer from the higher frequency to the lower frequency wave is enhanced through parametric coupling. When the two pump waves have equal power, discrete sidebands are symmetrically distributed around the pump frequencies. However, a burst of lower‐frequency sidebands, lasting for several seconds, frequently breaks the symmetry. We attribute this asymmetry to the cascade parametric process. The asymmetric spectra only occur only during O mode experiments.
Nonlinear inversion in induction logging using the modified gradient method
Authors: van den Berg P. M. , van der Horst M.
Published: February 2004

A method for reconstructing the electrical conductivity profile of a contrasting object in an embedding medium is applied to the problem of induction logging as it is known in the oil industry. The conductivity of the formation and the unknown electromagnetic fields are simultaneously reconstructed in an iterative way using a conjugate gradient type of algorithm. In the algorithm it is assumed that the conductivity is a positive quantity. This fact, together with the knowledge that the contrasting domain is constrained in some test domain, constitutes the only a priori information about the configuration that is needed. Results of a number of numerical examples are presented which demonstrate the robustness of the present inversion scheme and show that an artificial regularization technique is not needed.
Communication with reentry space vehicles via short pulses
Authors: Nazarenko Sergey V. , Newell Alan C. , Rubenchik Alexander M.
Published: February 2004

The resonant absorption of a short pulse of electromagnetic radiation in a plasma slab is considered in order to examine the effectiveness of using short pulses for information transfer through the plasma sheaths surrounding reentry vehicles. The amplitudes of the Raman scattering (RS) on the Langmuir oscillations associated with resonant absorption and the amplitude of the Brillouin scattering (BS) on the nonlinear modifications of the plasma profile are calculated. On‐board detection of the RS and BS signals are proposed as parallel and independent channels for reading the message encoded on the electromagnetic pulse sequence. The information transfer capacity of two other nonlinear effects, the generation of the fast electrons in the wave breaking process, and the excitation of the ion‐sound waves by the radiative pressure of the Langmuir oscillations are also considered.
Cross correlations and cross spectra for spaced antenna wind profilers: 1. Theoretical analysis
Authors: Doviak Richard J. , Lataitis Richard J. , Holloway Christopher L.
Published: February 2004

The presented theory ties the properties of a turbulently advected scattering medium to the cross correlation and cross spectrum of signals in a general configuration of receiving and transmitting antennas. The correlation length of Bragg scatterers and antenna diameter are the significant parameters determining the diffraction pattern's correlation length. We examine how vertical anisotropy of the scattering medium affects the diffraction pattern's correlation length. We demonstrate that the cross spectrum can be formulated in terms of a pair of spectral sampling functions (a one‐dimensional Doppler and a three‐dimensional wavenumber function), and closed form solutions are obtained. We give the conditions under which the scattering medium's statistical properties can be represented by a Gaussian correlation or spectral model, and the distance over which the diffraction pattern simply advects without significant change. We show that the diffraction pattern of a pair of scatterers can translate at the speed of the scatterers, not twice their speed as is commonly thought.