bluuebunny/crossref_metadata_2025 huggingface dataset:
Cloud radar observations of vertical drafts and microphysics in convective rain
Authors: Kollias Pavlos , Albrecht B. A. , Marks F. D.
Published: May 2003

Observations of convective precipitation using a 94‐GHz cloud radar are presented. Due to Mie scattering, the Doppler power spectra collected at vertical incidence contains characteristics of the scatterers (hydrometeors). These characteristics are used for the retrieval of the vertical air motion and the associated raindrop size distribution in an attempt to accurately map the time‐height structure of the vertical air motion and raindrop fields within intense convective precipitation. The data provide strong evidence of the interaction between draft intensity and raindrop size distribution and highlight the variability of convective precipitation at small scales. Horizontal sorting of the raindrops caused by the air motion is documented. Signal attenuation measured at 94 GHz is shown to be well correlated to rainfall rates. The observations demonstrate the capability of 94‐GHz cloud radars for studies of precipitation processes at low altitudes even under intense convective conditions.
Systematic changes of stratospheric temperature: Relationship between the tropics and extratropics
Authors: Salby Murry L. , Callaghan Patrick F.
Published: May 2003

Ozone declined over the extratropics of the Northern Hemisphere during the 1980s and 1990s. The interpretation of those systematic changes rests on the behavior of temperature, which declined simultaneously. New evidence reported here shows that systematic cooling of the wintertime stratosphere at high latitudes was accompanied by systematic warming at low latitudes. Those regions exhibit clear but opposing trends in the wintertime tendency of temperature, which is related directly to adiabatic warming and cooling. Mirrored by ozone, the compensating changes of temperature at high and low latitudes characterize a systematic weakening of the residual mean circulation, which regulates wintertime temperature and spring ozone.
Modeling δ18O in precipitation over the tropical Americas: 2. Simulation of the stable isotope signal in Andean ice cores
Authors: Vuille M. , Bradley R. S. , Healy R. , Werner M. , Hardy D. R. , Thompson L. G. , Keimig F.
Published: May 2003

We use the ECHAM‐4 and the GISS II atmospheric general circulation models (AGCM) with incorporated stable isotopic tracers and forced with observed global sea surface temperatures (SST) between 1979 and 1998, to simulate the δ18O signal in three tropical Andean ice cores, from Huascarán (Peru), Quelccaya (Peru), and Sajama (Bolivia). In both models, the simulated stable isotopic records compare favorably with the observational data, when the seasonality of precipitation and dry season loss due to sublimation and wind scour are taken into account. Our simulations indicate a significant influence of the local climatic conditions (temperature and precipitation amount) on the δ18O signal. Moisture source variability appears to be less of a factor on interannual timescales. Even though the moisture originates over the Amazon basin and the tropical Atlantic, correlation fields with National Centers for Environmental Prediction‐National Center for Atmospheric Research (NCEP‐NCAR) Reanalysis atmospheric variables and SST data indicate a dominant tropical Pacific control on interannual timescales. More enriched (depleted) δ18O values are associated with periods of warm (cold) conditions in the tropical Pacific. This is consistent with modern observational evidence, which shows that climate and atmospheric circulation in the tropical Andes are closely correlated with SST anomalies in the tropical Pacific domain on interannual to interdecadal timescales. The growing number of stable isotope records from tropical Andean ice cores may thus provide an important archive for reconstructing Pacific climate variability.
Chlorine budget and partitioning during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE)
Authors: Schauffler S. M. , Atlas E. L. , Donnelly S. G. , Andrews A. , Montzka S. A. , Elkins J. W. , Hurst D. F. , Romashkin P. A. , Dutton G. S. , Stroud V.
Published: May 2003

The amount of chlorine in the stratosphere has a direct influence on the magnitude of chlorine‐catalyzed ozone loss. A comprehensive suite of organic source gases of chlorine in the stratosphere was measured during the NASA Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) campaign in the arctic winter of 2000. Measurements included chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halon 1211, solvents, methyl chloride, N2O, and CH4. Inorganic chlorine contributions from each compound were calculated using the organic chlorine measurements, mean age of air, tropospheric trends, and a method to account for mixing in the stratosphere. Total organic chlorine measured at tropospheric levels of N2O was on the order of 3500 ppt. Total calculated inorganic chlorine at a N2O mixing ratio of 50 ppb (corresponding to a mean age of 5.5 years) was on the order of 3400 ppt. CFCs were the largest contributors to total organic chlorine (55–70%) over the measured N2O range (50–315 ppb), followed by CH3Cl (15%), solvents (5–20%), and HCFCs (5–25%). CH3Cl contribution was consistently about 15% across the organic chlorine range. Contributions to total calculated inorganic chlorine at 50 ppb N2O were 58% from CFCs, 24% from solvents, 16% from CH3Cl, and 2% from HCFCs. Updates to fractional chlorine release values for each compound relative to CFC 11 were calculated from the SOLVE measurements. An average value of 0.58 was calculated for the fractional chlorine release of CFC 11 over the 3–4 year mean age range, which was lower than the previous value of 0.80. The fractional chlorine release values for HCFCs 141b and 142b relative to CFC 11 were significantly lower than previous calculations.
A revised algorithm for calculating TiO2 from Clementine UVVIS data: A synthesis of rock, soil, and remotely sensed TiO2 concentrations
Authors: Gillis Jeffrey J. , Jolliff Bradley L. , Elphic Rick C.
Published: May 2003

Investigating mare basalt compositions, at both the sample and remote‐sensing level for the Apollo and Luna mare sites, reveals the need for a more complex regression procedure than previously proposed in order to extract accurate TiO2 concentrations from Clementine spectral reflectance (CSR) data. The TiO2 algorithm of Lucey and coworkers is modified by using two different sets of regression parameters to relate measured regolith compositions from sampling locations to the CSR properties of these sites. One regression trend fits the majority of Apollo data, and the second regression is a fit to the Apollo 11, Luna 16, and Luna 24 data, which were considered to be anomalous in previous TiO2 calibrations. These three sites have unusually low albedo compared to other mare landing sites, and some 32% of nearside mare regions appear to share this characteristic. Possible reasons for these differences related to proximity of the other sites to mare‐highland boundaries are discussed. Using the dual‐regression method, we find (1) that TiO2 concentrations calculated for the basaltic landing sites faithfully reproduce a bimodal distribution as seen in the sample data, (2) that when coupled with the effects of other thermal neutron absorbers, Ti concentrations are more consistent with observed epithermal‐to‐thermal neutron‐flux ratios than are previous Clementine‐based derivations of TiO2 for basaltic regions, and (3) that basalts of intermediate‐TiO2 concentrations occur most frequently in the Oceanus Procellarum region and that these intermediate concentrations appear to be inherent to the flows underlying the regolith and presumably to the basalt source regions.
Ideal bodies for Mars magnetics
Authors: Parker Robert L.
Published: May 2003

The high‐amplitude magnetic anomalies observed by the Mars Global Surveyor imply the presence of a large intensity of magnetization in the Martian crust. We investigate the mathematical question of determining the distribution of magnetization that has the smallest possible intensity, without any assumptions about the direction of magnetization. The greatest lower bound on intensity found in this way depends on an assumed layer thickness. An analytical expression is discovered for the optimal magnetization, and numerical methods are described for solving the equations that determine the distribution. Some relatively small scale numerical calculations illustrate the theory. These calculations enable us to conclude, for example, that if the magnetization of Mars is confined to a 50‐km thick layer, it must be magnetized with an intensity of at least 4.76 A/m.
Selection of the landing site in Isidis Planitia of Mars probe Beagle 2
Authors: Bridges J. C. , Seabrook A. M. , Rothery D. A. , Kim J. R. , Pillinger C. T. , Sims M. R. , Golombek M. P. , Duxbury T. , Head J. W. , Haldemann A. F. C. , Mitchell K. L. , Muller J.‐P. , Lewis S. R. , Moncrieff C. , Wright I. P. , Grady M. M. , Morley J. G.
Published: May 2003

This paper describes selection and characterization of the landing site for the Mars 2004 Beagle 2 mission. The site is within Isidis Planitia between 10°–12°N, 266°–274°W, centered at 11.6°N, 269.5°W. This is at low elevation (−3600 to −3900 m MOLA), is flat (MOLA RMS slope = 0.57°), radar data suggest a smoother surface at decimeter to meter scales than the Pathfinder site and it has a moderate rock abundance (2–17%, mean 11%). In addition to this, Isidis shows evidence for concentration and remobilization of volatiles. In particular, the basin contains conical landforms. We favor models involving the formation of tuff cones during magma‐ice interaction. Structures identified as dykes in MOC images may be remnants of magma conduits. The pattern of bulk thermal inertia in Isidis (higher values of 500 Jm−2s−0.5K−1 around the SW‐S‐E margin decreasing toward the center and north) suggests that an influx of sediment spread from the Noachian areas around the southern half of the basin over the basin floor. The coarse, higher thermal inertia material was deposited closest to the sediment source. The variable state of erosion of the tuff cones suggests that they formed intermittently over a long period of time during Amazonian and possibly Hesperian epochs. Geologically recent resurfacing of Isidis has also occurred by aeolian processes, and this is shown by a deficit in impact craters <120 m diameter. The proportion of rocky material is predicted to be slightly less than the Viking and Pathfinder sites, but there will probably be more duricrust.
On the mid‐Pleistocene transition to 100‐kyr glacial cycles and the asymmetry between glaciation and deglaciation times
Authors: Tziperman Eli , Gildor Hezi
Published: May 2003

A mechanism is proposed for the mid‐Pleistocene transition from a dominant periodicity of 41 kyr to 100 kyr in glacial oscillations. The same mechanism is shown to also explain the asymmetry between the long glaciation and short deglaciation phases of each cycle since that transition versus the symmetry of the 41‐kyr oscillations prior to the transition. These features arise naturally within the framework of the sea‐ice switch glacial cycle mechanism of Gildor and Tziperman [2000] as a result of the gradual cooling of the deep ocean during the Pleistocene. This cooling results in a change of the relation between atmospheric temperature and the rates of accumulation and ablation of continentals ice sheets. It is this latter change that leads to the activation of the sea‐ice switch and therefore to the initiation of the 100‐kyr oscillations. The gradual glaciation and rapid deglaciations during these oscillations occur because the mean value of the ice sheet ablation is not far from the maximum rate of snow accumulation during warm periods. This proximity of mean ablation and maximum accumulation rates is shown to be also a consequence of the mid‐Pleistocene gradual cooling of the deep ocean.
Atlantic Ocean thermohaline circulation changes on orbital to suborbital timescales during the mid‐Pleistocene
Authors: Kleiven H. F. , Jansen E. , Curry W. B. , Hodell D. A. , Venz K.
Published: May 2003

Mid‐Pleistocene benthic δ18O and δ13C time series from the North Atlantic site 983 and Ceara Rise site 928 are compared to an array of existing isotopic records spanning the Atlantic basin and the geographic extremes of the North Atlantic Deep Water/Southern Ocean Water interface during both glacial and interglacial periods. This comparison allows the persistent millennial‐scale intermediate depth North Atlantic ventilation changes recorded at site 983 to be placed within the context of the longer period water mass reorganizations taking place throughout the mid‐Pleistocene. Our benthic δ13C results suggest that the intermediate depth North Atlantic experienced millennial‐scale changes in ventilation throughout the mid‐Pleistocene climate shift. The times of poorest ventilation (low benthic δ13C) persisted for only a few millennia and were associated with rapid decreases in benthic δ18O, suggesting that ice sheet decay and melt water induced salinity changes were effective at throttling deep water production in the North Atlantic throughout the mid‐Pleistocene. Similar but less pronounced decreases in the δ13C of the middepth waters also punctuated interglacials, suggesting that large ice sheet fluctuations do not explain all of the observed thermohaline circulation mode shifts in the North Atlantic. Meanwhile, on orbital timescales, glacial deep to intermediate water δ13C gradients evolved after ∼0.95 Ma. Taken together, these observations provide a number of new constraints for understanding the timing and evolution of deep water circulation changes across the mid‐Pleistocene.
Planktonic foraminiferal depth habitat and δ18O calibrations: Plankton tow results from the Atlantic sector of the Southern Ocean
Authors: Mortyn P. Graham , Charles Christopher D.
Published: May 2003

Plankton tows conducted in the Atlantic sector of the Southern Ocean allow analysis of the influence of water column structure on planktonic foraminiferal abundance and δ18O composition. Foraminiferal abundance varies by several orders of magnitude across a large gradient in sea surface temperature and other hydrographic features, demonstrating high sensitivity of foraminiferal populations to regional differences in water properties. The depth of maximum abundance for key species such as Globigerina bulloides and Neogloboquadrina pachyderma is not constant from station to station. The pattern suggests that their abundance and shell chemistry are tied to density horizons or other conditions (such as food availability) that become more sharply defined with depth in the northern subantarctic. The consistent observation of Globorotalia inflata and Globoratalia truncatulinoides as relatively deep‐dwelling species confirms their utility as indicators of upper thermocline properties. In δ18O all species are observed to be isotopically lighter than predicted from water properties, but the species‐specific offset is fairly uniform at all stations. These observations define the utility of multispecies δ18O for reconstructing temperature and density stratification from past surface oceans.
A Miocene (8–12 Ma) intermediate water benthic stable isotope record from the northeastern Atlantic, ODP Site 982
Authors: Andersson C. , Jansen E.
Published: May 2003

Oxygen and carbon isotope records are presented for the benthic foraminifer Cibicidoides wuellerstorfi from upper middle through lower upper Miocene (11.6–8.2 Ma) sediments recovered at intermediate water depth (1134 m) at Ocean Drilling Program Site 982 on Rockall Plateau. Oxygen isotopic values generally lighter than those for the Holocene indicate significantly warmer intermediate waters and/or less global ice volume during the late middle to early late Miocene than at the present. The most depleted oxygen isotope values occurred at around 10.5 Ma. After this time a long‐term increase in δ18O suggests a gradual increase in global ice volume and/or cooling of intermediate waters during the late Miocene. Comparison of the intermediate depth benthic foraminiferal carbon isotope record from Site 982 and records from various North Atlantic deep sites shows that intermediate waters were generally better ventilated than deep waters between 11.6 and 9.6 Ma. During this time period, increased ventilation of intermediate waters was linked to cooling or the build up of polar ice caps. The Mi events originally proposed by Miller et al. [1991b] and Wright and Miller [1992] are difficult to identify with certainty in sediments sampled at high resolution (<104 year). Comparison of the high‐resolution benthic δ18O records from ODP Site 982 with the low‐resolution benthic δ18O record from Monte Gibliscemi (Mediterranean) show that Mi events, if real, may not be of importance as a stratigraphic tool in upper Miocene sedimentary sequences.
Productivity and organic carbon rain to the California margin seafloor: Modern and paleoceanographic perspectives
Authors: Berelson William M. , Stott Lowell D.
Published: May 2003

We have developed a proxy measurement for the determination of organic carbon (Corg) oxidation rates (Cox) on the seafloor utilizing the δ13C values of two benthic foraminifera: Bolivina argentea, a near‐surface dwelling species, and Buliminella tenuata, an infaunal species. The δ13C isotopic composition of these tests preserve a record of the Σ13CO2 pore water gradient, which is directly related to Cox. On the seafloor of Santa Monica Basin, Cox has fluctuated between 0.6 and 2.5 mmolC m−2 d−1 and generally increased from 1600 to 1980 AD. Between 1920 and 1970, Cox increased from 1 to 2 mmolC m−2 d−1 and then decreased into the 1980s. By adding Cox to a high‐resolution record of Corg burial rate, we have derived the pattern of Corg rain to the seafloor, which fluctuated between 2.9 and 3.8 mmolC m−2 d−1 over the last 80 years. The ratio of Corg rain at 900 m to primary productivity is constant at 10 ± 1% over a 40% change in mean annual primary productivity. Sediments in Santa Monica Basin accumulate ∼50% of the Corg raining to the seafloor; however, there is a trend toward lower burial efficiency with higher productivity and rain rate.
Late Cretaceous and early Paleogene nutrient and paleoproductivity records from Blake Nose, western North Atlantic Ocean
Authors: Faul K. L. , Anderson L. D. , Delaney M. L.
Published: May 2003

We evaluate phosphorus (P) and biogenic barium (bio‐Ba) as nutrient burial and export productivity indicators for the Late Cretaceous and early Paleogene, combining these with calcium carbonate (CaCO3), organic carbon (C), and bulk CaCO3 C isotopes (δ13C). Sample ages span 36–71 Ma (∼1 sample/0.5 m.y.) for a depth transect of sites in the western North Atlantic (Blake Nose, Ocean Drilling Program Leg 171B, Sites 1052, 1051, and 1050). We use a multitracer approach including redox conditions to investigate export productivity surrounding the global Paleocene δ13C maximum (∼57 Ma). Reducing conditions render most of the bio‐Ba record not useful for export productivity interpretations. P and organic C records indicate that regional nutrient and organic C burial were high at ∼61 and ∼69 Ma, and low during the Paleocene δ13C maximum, a time of proposed global high relative organic C burial. Observed organic C burial changes at Blake Nose cannot explain this C isotope excursion.
Seasonal distribution of genetic types of planktonic foraminifer morphospecies in the Santa Barbara Channel and its paleoceanographic implications
Authors: Darling Kate F. , Kucera Michal , Wade Christopher M. , von Langen Peter , Pak Dorothy
Published: May 2003

We present data on the temporal distribution of planktonic foraminifer genotypes (small subunit (SSU) ribosomal (r) RNA gene) and morphospecies (sediment traps) collected during 1999 in the Santa Barbara Channel. The sampling was undertaken with special emphasis on paleoceanographically important morphospecies, predominantly Globigerina bulloides. We found the same genotype of G. bulloides (type IId) in all the changing hydrographic regimes associated with this region throughout the annual cycle with the exception of January, when we recorded the additional presence of the high‐latitude G. bulloides type IIa. We identified three new genotypes: Neogloboquadrina dutertrei type Ic, N. pachyderma dextral type II, and Turborotalita quinqueloba type IId. Our data suggest that G. bulloides type IId and possibly even the new genotypes listed above may be associated specifically with the complex hydrography or other environmental features characteristic of this area. Since G. bulloides type IId occurs throughout the year and its peak fluxes are related to different hydrographic regimes, we argue that the physical properties of the water column are not the major factor influencing the distribution and growth of this genotype. In sediment trap samples we found a skewed coiling ratio for G. bulloides (most likely representing type IId), which is related neither to sea surface temperature nor to genotypic difference. This study illustrates the necessity to map both the spatial and temporal distribution of the genetic types, especially in areas of paleoceanographic interest, where geochemical and paleontological proxies are being calibrated.
Impact of a Tethyan circumglobal passage on ocean heat transport and “equable” climates
Authors: Hotinski R. M. , Toggweiler J. R.
Published: May 2003

The presence of low‐latitude circumglobal passage from the late Jurassic (∼160 Ma) through the Miocene (∼14 Ma) provides a possible mechanism for increased poleward ocean heat transport during periods of warm climate and may help explain low meridional temperature gradients of the past. Experiments using an ocean general circulation model (GCM) with an energy‐balance atmosphere and idealized bathymetry reveal that, like the modern Drake Passage, a circumglobal Tethyan Passage might have induced high rates of wind‐driven upwelling of relatively cold and deep water, but at low latitudes. With no change in radiative forcing, a low‐latitude circumglobal passage increases simulated northern high‐latitude temperatures by 3°–7°C, while tropical temperatures cool by up to 2°C relative to a scenario with solid meridional boundaries. Combining this mechanism of heat transport with increased radiative forcing allows substantial warming of northern high latitudes by 7°–11°C, while tropical temperatures remain within 3°C of present‐day temperatures.
Deep sea records from the southeast Labrador Sea: Ocean circulation changes and ice‐rafting events during the last 160,000 years
Authors: Rasmussen Tine L. , Oppo Delia W. , Thomsen Erik , Lehman Scott J.
Published: May 2003

Results from two deep sea cores from northeast of Newfoundland at 1251 and 2527 m water depth, respectively, indicate that during the time period from 160,000 to 10,000 years BP, ice rafting events in the Labrador Sea were accompanied by rapid variations in deep and surface water circulation. Twelve ice‐rafting events occurred, each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters. Eleven of these can be correlated with the North Atlantic Heinrich events H1–H11. The remaining very conspicuous ice‐rafting event took place early in MIS substage 5e, at a time when the planktic faunal assemblage suggests marked warming of the sea surface. In the shallower core, benthic δ13C values rise from a minimum during the deglaciation to peak substage 5e values following the last ice‐rafting event, indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e. The benthic foraminifera suggest that this well‐ventilated water mass was comparable to the modern Labrador Sea Water (LSW). The benthic faunas suggest that a relatively warm intermediate water mass entered the SE Labrador Sea during Heinrich events. Generally low benthic δ13C values indicate that this water mass was poorly ventilated and rich in inorganic nutrients. Isotope data and benthic faunal distributions indicate that North Atlantic Deep Water (NADW) formed in the Norwegian‐Greenland Sea reached the SE Labrador Sea between the Heinrich events.
Planktonic foraminifera, sea surface temperatures, and mechanisms of oceanic change in the Peru and south equatorial currents, 0–150 ka BP
Authors: Feldberg Melissa J. , Mix Alan C.
Published: May 2003

Planktonic foraminiferal faunas of the southeast Pacific indicate that sea surface temperatures (SST) have varied by as much as 8–10°C in the Peru Current, and by ∼5–7°C along the equator, over the past 150,000 years. Changes in SST at times such as the Last Glacial Maximum reflect incursion of high‐latitude species Globorotalia inflata and Neogloboquadrina pachyderma into the eastern boundary current and as far north as the equator. A simple heat budget model of the equatorial Pacific shows that observed changes in Peru Current advection can account for about half of the total variability in equatorial SSTs. The remaining changes in equatorial SST, which are likely related to local changes in upwelling or pycnocline depth, precede changes in polar climates as recorded by δ18O. This partitioning of processes in eastern equatorial Pacific SST reveals that net ice‐age cooling here reflects first a rapid response of equatorial upwelling to insolation, followed by a later response to changes in the eastern boundary current associated with high‐latitude climate (which closely resembles variations in atmospheric CO2 as recorded in the Vostok ice core). Although precise mechanisms responsible for the equatorial upwelling component of climate change remain uncertain, one likely candidate that may operate independently of the ice sheets is insolation‐driven changes in El Niño/Southern Oscillation (ENSO) frequency. Early responses of equatorial SST detected both here and elsewhere highlight the sensitivity of tropical systems to small changes in seasonal insolation. The scale of tropical changes we have observed are substantially greater than model predictions, suggesting a need for further quantitative assessment of processes associated with long‐term climate change.
Climatically influenced interactions between the Mediterranean and the Paratethys during the Tortonian
Authors: Sprovieri Mario , Sacchi Marco , Rohling Eelco J.
Published: May 2003

The Paratethys was a separate branch of the Tethys Ocean that developed as a series of inland seaways, brackish lakes, and wetlands within the interiors of central‐eastern Europe and western Asia during the Oligocene‐Neogene. A short‐lived connection between the Mediterranean Sea and the Paratethys continental realm toward the very end of the Messinian salinity crisis is documented on the basis of the Paratethyan affinity of the brackish shallow water faunas in several Mediterranean localities. Nevertheless, there are at present only a few comparative studies on stratigraphy paleobiogeography and paleoceanography of these two contiguous Neogene provinces [e.g., Benson, 2000]. In this study we compare and integrate different stratigraphic data sets from middle‐upper Miocene sequences of the central Mediterranean and the western Pannonian basins (central Paratethys) that are seen as parts of a complex paleoclimatic and paleoceanographic system. On the basis of this comparison we propose that the Paratethys had a long‐lived influence on the large‐scale oceanographic circulation of the eastern Mediterranean, at least since the Tortonian (between 9.7 and 7.5 Ma); that is, well before the onset of the Messinian Lagomare event (∼5.5 Ma). The integrated stratigraphy of coeval marine (Tortonian) and continental (Transdanubian) strata presented here suggests that mutual interaction and interdependence of climate subsystems ostensibly developed over the Mediterranean area and central‐eastern Europe continent and were orbitally forced. Long‐eccentricity insolation forcing is hypothesized to have exerted a broad control on the freshwater budget of the brackish Pannonian Basin and the consequent oceanographic setting of the Mediterranean region.
Stable isotopes in benthic foraminiferal calcite from a river‐influenced Arctic marine environment, Kara and Pechora Seas
Authors: Polyak Leonid , Stanovoy Vladimir , Lubinski David J.
Published: May 2003

Oxygen and carbon stable‐isotope compositions of modern benthic foraminifera in the Kara and Pechora estuarine regions of the Arctic continental shelf were compared with water δ18O, δ13CDIC, temperature, and salinity. The foraminiferal δ18O distribution is mostly similar to that of equilibrium calcite, primarily controlled by mixing of runoff and seawater in near‐estuarine areas (depth < 15–20 m), with additional temperature control seaward. The δ13C composition is controlled by remineralization of organic matter, mostly imported by rivers, and by water mixing. Most analyses used the common Arctic foraminifer Elphidium excavatum forma clavata, which yields depleted δ13C, as expected for an infaunal species. Isotope records for sediment cores off the Pechora and Yenisey rivers show a decelerating rise in isotope values, of up to 10‰ in δ18O, over the last 10 kyr in a pattern similar to that of rising sea level and concomitant retreat of river mouths, with local complexities probably resulting from glacio‐isostatic rebound and changes in sedimentation.
Dyes as tracers for vadose zone hydrology
Authors: Flury Markus , Wai Nu Nu
Published: May 2003

Dyes are important tracers to investigate subsurface water movement. For more than a century, dye tracers have provided clues about the hydrological cycle as well as flow and transport processes in the subsurface. Groundwater contamination often originates in the vadose zone. Agrochemicals applied to the soil surface, toxic compounds accidentally spilled by human activities, and contaminants released from waste repositories leach through the vadose zone and can ultimately pollute groundwater resources. Dyes are an important tool to assess flow pathways of such contaminants. This review compiles information on dyes used as hydrological tracers, with particular emphasis on vadose zone hydrology. We summarize briefly different human‐applied tracers, including nondye tracers. We then provide a historical sketch of the use of dyes as tracers and describe newer developments in visualization and quantification of tracer experiments. Relevant chemical properties of dyes used as tracers are discussed and illustrated with dye intermediates and selected dye tracers. The types of dyes used as tracers in subsurface hydrology are summarized, and recommendations are made regarding the use of dye tracers. The review concludes with a toxicological assessment of dyes used as hydrological tracers. Many different dyes have been proposed as tracers for water movement in the subsurface. All of these compounds, however, are to some degree retarded by the subsurface medium. Nevertheless, dyes are useful tracers to visualize flow pathways.
Thirty‐five‐gigahertz measurements of CO2 crystals
Authors: Foster J. L. , Chang A. T. C. , Tsang L. , Chen C.‐T. , Hall D. K. , Tait A. B. , Barton J. S.
Published: May 2003

In order to learn more about the Martian polar caps, it is important to compare and contrast the behavior of both frozen H2O and CO2 in different parts of the electromagnetic spectrum. Because relatively little attention has been given, thus far, to observing the seasonal Martian polar caps in the thermal microwave part of the spectrum, in this experiment, a 35‐GHz handheld radiometer was used to measure the microwave emission and scattering from layers of manufactured CO2 (dry ice). Compared to natural snow crystals, results for the dry ice layers exhibit lower microwave brightness temperatures for similar thicknesses, regardless of the incidence angle of the radiometer. For example, at 50° H (horizontal polarization) and with a covering 18 cm of dry ice, the brightness temperature was 76 K. When the total thickness of the dry ice was 27 cm, the brightness temperature was 86 K. The lower brightness temperatures are due to a combination of the lower physical temperature and the larger crystal sizes of the commercial CO2 crystals compared to the snow crystals. While little is known about the CO2 and water snowpacks on Mars, it is likely that the particles are in close contact with one another as is the case for ice sheets on Earth – the grains are interconnected. This would qualify as a dense media. In densely packed media, the particles do not scatter independently; rather, they interact with other particles. Dense media calculations compare very favorably with the observed values from the handheld radiometer. The calculated versus observed TBs are within 10% for each case with the exception of the 26 cm layer thickness and the 0.8 mm particle size (15%) and for the 14 cm layer thickness and the 2.0 mm particle size (16%). Thus, it appears that dense media transfer modeling (DMRT) will be useful for modeling the flow of energy emerging from frozen CO2 deposits. Because the dry ice used in this experiment was manufactured in the shape of cylindrical pellets, an effort was made to see what effect, if any, the shape of the crystal, for different particle sizes, has on microwave scattering. Results from a discrete dipole scattering (DDSCAT) model show that differently shaped crystals, having the same effective radius of a sphere, give very similar cross section/efficiencies.
Cometary surface layer properties: Possible approaches to radio sounding retrieval during the CONSERT experiment—Numerical simulation and discussion
Authors: Ilyushin Y. A. , Hagfors T. , Kunitsyn V. E.
Published: May 2003

The instrumentation to be carried to the comet Wirtanen in the Rosetta mission includes a radio experiment, Comet Nucleus Sounding Experiment by Radio Wave Transmission (CONSERT), designed to reveal the average dielectric properties of the nucleus, and the structure of the interior. The analysis of the data to retrieve information about the internal structure has the character of rudimentary radio tomography. We investigate mathematically the behavior of the surface field under the transition from direct propagation to geometrical shadow to determine possible effects of the electrical properties in the close vicinity of the lander. In particular we investigate the effects of a surface layer of composition different from that of the nucleus to determine whether such a layer can influence the wave propagating into the geometrical shadow zone. It is shown that the behavior of the field in the shadow zone is determined chiefly by the topmost layer properties.
Study on ground clutter prevention fences for boundary layer radars
Authors: Rao Qinjiang , Hashiguchi Hiroyuki , Fukao Shoichiro
Published: May 2003

A low elevation sidelobe suppression algorithm based on the uniform physical theory of diffraction (PTD) is developed to simulate ground clutter prevention fences for boundary layer radars (BLRs). As applications to the algorithm, the most suitable fence is achieved for the lower troposphere radar (LTR) and the L‐28 boundary layer radar, respectively. The developed algorithm can also be applied to other radar systems where reducing low elevation sidelobes is desired.
Determining riometer quiet day curves 1. The matrix method
Authors: Drevin G. R. , Stoker P. H.
Published: May 2003

A number of methods have been proposed for the determination of quiet day curves of riometer recordings of cosmic radio noise in polar regions. Most of these methods are based on the distribution of the recorded intensities, in a given siderial time period, over a number of consecutive days. The method proposed in this paper is based on the filtering, using a low‐pass filter in the Fourier domain, of a discrete two‐dimensional function or matrix. The two dimensions of the matrix are siderial time and day number, with each row of the matrix representing one siderial day. With a low‐pass filter the low frequency Fourier coefficients are retained while the high frequency Fourier coefficients are discarded. The highest Fourier coefficient that is retained is the cutoff frequency of the filter. The proposed method was compared to two existing methods using data obtained from a single broad beam antenna. It was found that the proposed method is less sensitive to noise than the existing methods.
On aspects of the physical realizability of perfectly matched absorbers for electromagnetic waves
Authors: Teixeira F. L.
Published: May 2003

A discussion on the physical realizability of electromagnetic wave absorbers with perfectly matched impedances over arbitrary (i.e., doubly) curved, smooth surfaces is presented. The focus is on the analysis of the spectral characteristics (and their impact on the absorptive properties) of hypothetical material blueprints derived from the zero‐reflection condition over such geometries.
A modal impedance‐angle formalism: Schemes for accurate graded‐index bent‐slab calculations and optical fiber mode counting
Authors: de Hon Bastiaan P. , Bingle Marianne
Published: May 2003

The propagation coefficients of guided modes along bent slabs and optical fibers may be calculated with the aid of a complex‐power‐flow, variational scheme. This scheme can be cast in the form of a Newton iterative scheme for a characteristic equation in terms of impedances rather than fields. Singularities of the associated Riccati equations for the impedances are circumvented via a generalized coordinate transformation, involving an angle for bent slabs, or a matrix of angles for optical fibers. Adopting the resulting impedance‐angle formalism for bent slabs, numerical difficulties disappear, and accuracy ensues. The analysis of the vectorial optical‐fiber problem benefits from its scalar bent‐slab counterpart. In particular, the connection between the power flow and the impedance‐angle formalism forms the physical underpinning for understanding that beyond a certain distance from the fiber core the derivative of the impedance matrix with respect to the propagation coefficient is positive definite. In turn, this provides the basis for the full‐wave generalization for optical fibers of the mode‐counting scheme developed in 1975 by Kuester and Chang for scalar wave propagation along a straight slab. With these key results, root‐finding can be rendered more robust and efficient. A companion paper contains the necessary proofs for the complex‐power‐flow variational scheme and the mode‐counting and mode‐bracketing theorems.
A modal impedance‐angle formalism: Rigorous proofs for optical fiber mode counting and bracketing
Authors: de Hon Bastiaan P.
Published: May 2003

In a companion paper, a complex‐power‐flow variational scheme is applied to analyze mode propagation along open circularly cylindrical graded‐index waveguides. It leads to a characteristic equation in terms of impedances rather than fields. The resulting impedance‐angle formalism provides the basis for the full‐wave generalization for optical fibers of the mode‐counting scheme previously developed for a scalar wave propagation problem. The complex‐power‐flow variational scheme for bent waveguides is based on energy considerations. Hence, in its derivation, it is natural to consider a waveguide section (a volume) rather than a cross section (a surface). In the proof of the mode‐counting and mode‐bracketing theorems, the key issue is to show that the characteristic roots and the roots of the so‐called separation function alternate. For general circularly cylindrical open waveguides, the required proofs are intricate. However, the special limiting cases in which the optical fiber is surrounded by electrically or magnetically perfectly conducting walls are tractable. To account for the general case, it appears to be necessary to regard a class of optical waveguide problems with a continuous transition from perfect electric conductor to perfect magnetic conductor boundary conditions via the situation pertaining to the actual exterior medium. Thus, a half‐strip is constructed on which the so‐called characteristic and separation graphs are seen to alternate. As spin‐off, such a “sweep” might prove useful in the design of a fiber cladding.
Integral equation formulation and solution for extended vertical current sheets in multilayered planar structures
Authors: Vrancken M. , Vandenbosch G. A. E.
Published: May 2003

The integral analysis of multilayered planar structures owes its high efficiency to the excellent matching of the Spectral Domain Approach (SDA) to the planar nature of the problem. This highly efficient approach is strongly encroached upon when arbitrary three‐dimensional (3‐D) surfaces in a multilayered environment have to be analyzed. However, for 3‐D structures that consist of horizontal and strictly vertical conducting surfaces, the analytical possibilities of the SDA can be exploited further. The integral equation formulation is adapted to the geometry by expressing it in a hybrid dyadic‐mixed potential form. The solution is improved with a combined spectral‐spatial domain approach, where part of the reaction integrals are done in closed form in the spectral domain. This modified method avoids most theoretical and numerical problems, while the majority of practical 3‐D problems in stratified media can still be handled.
Homogenization of the Maxwell equations in an anisotropic material
Authors: Kristensson Gerhard
Published: May 2003

This paper contains an overview of the homogenization of anisotropic materials at fixed frequency using the concept of two‐scaled convergence. The homogenized electric and magnetic parameters, the relative permittivity, and the relative permeability are found by suitable averages of the solution of a local problem in the unit cell. A comparison between the exact homogenization method presented in this paper and the traditional mixture formulae, which are based on physical arguments, is made.
Nonlinear waveguides
Authors: Sjöberg Daniel
Published: May 2003

We investigate the propagation of electromagnetic waves in a cylindrical waveguide with an arbitrary cross section filled with a nonlinear material. The electromagnetic field is expanded in the usual eigenmodes of the waveguide, and the coupling between the modes is quantified. We derive the wave equations governing each mode with special emphasis on the situation with a dominant TE mode. The result is a strictly hyperbolic system of nonlinear partial differential equations for the dominating mode, whereas the minor modes satisfy hyperbolic systems of linear, nonstationary, and partial differential equations. A growth estimate is given for the minor modes.
Short‐pulse radiation by a sequentially excited semi‐infinite periodic planar array of dipoles
Authors: Capolino Filippo , Felsen Leopold B.
Published: May 2003

This paper deals with the fourth in a sequence of canonical problems aimed toward an understanding of the time domain (TD) behavior of wideband‐excited sequentially pulsed planar periodic finite arrays of dipoles, which play an important role in a variety of practical applications. The present investigation of sequentially pulsed semi‐infinite planar dipole arrays extends our previous studies of sequentially pulsed infinite and semi‐infinite line dipole arrays and of infinite planar dipole arrays. The discrete element‐by‐element radiations are converted collectively to radiations from a series of Floquet wave (FW)‐modulated truncated smooth equivalent aperture distributions, and to corresponding FW‐modulated edge diffraction. After a summary of necessary results from the earlier studies, emphasis is placed on the new truncation‐induced TD results and interpretations, which are extracted via phenomenology‐matched high‐frequency asymptotics from rigorous frequency and time domain formulations parameterized in terms of the dispersive FW instantaneous frequencies and wave numbers. As in our previous studies, the outcome is a numerically efficient, physically incisive algorithm whose accuracy is verified preliminarily by application to a pulsed planar strip array of dipoles.
Decomposable bianisotropic media: Factorization, equivalent media, Green dyadics, and Hertz potentials
Authors: Olyslager Frank , Lindell I. V.
Published: May 2003

The aim of this paper is to provide the reader with a rigorous, well‐structured, and complete study of the most general decomposable bianisotropic media. These media were introduced elsewhere. We will give full expressions for the factorization of the Helmholtz determinant operator, for the equivalent media, for the Green dyadics of these equivalent media, and for the generalized Hertz potentials. This will be done efficiently using a six‐vector formalism. Finally, we will treat, as an example, an anisotropic medium that has not been treated before.
Frame‐based Gaussian beam summation method: Theory and applications
Authors: Lugara Delphine , Letrou Christine , Shlivinski Amir , Heyman Ehud , Boag Amir
Published: May 2003

A discrete phase‐space Gaussian beam summation representation for electromagnetic radiation from a planar source is presented. The formulation is based on the theory of frames and removes the inherent difficulties of the Gabor representation for both monochromatic and ultra wideband (UWB) fields. For monochromatic fields the frame‐based representation leads to an efficient and flexible discrete Gaussian beam representation with local and stable expansion coefficients. For UWB fields a novel scaling of the frame overcompleteness parameter is introduced, leading to a new expansion that utilizes a discrete frequency‐independent set of beams over the entire relevant spectrum. It is demonstrated that the isodiffracting Gaussian beams provide the snuggest frame representation over the entire spectrum. The rules for choosing the “optimal” frame and beam parameters for a given problem are discussed and demonstrated on application examples.
FDTD‐SUPML‐ADE simulation for Ground‐Penetrating Radar modeling
Authors: Rejiba Fayçal , Camerlynck Christian , Mechler Pierre
Published: May 2003

GPR data simulations require above all an efficient forward modeling algorithm. A Finite Difference Time Domain code is presented with Simplified Unsplit Perfect Matched Layer that leads to insignificant reflections on border with few modifications of the core algorithm. In addition, the Auxiliary Differential Equation method allows GPR simulations including dispersive phenomena that could not be neglected at radar frequencies. The numerical validation is done in a classic way for amplitude/time wave propagation and SUPML, and using the nonconventional Dispersion Analysis technique for physical dispersion behavior. Full 3‐D and 2‐D forward modeling results are finally presented for lossy, dispersive and random media in GPR conditions.