bluuebunny/crossref_metadata_2025 huggingface dataset:
Concept Mapping zum Lernen aus Texten
Authors: Hilbert Tatjana S. , Nückles Matthias , Renkl Alexander , Minarik Carla , Reich Angelika , Ruhe Katharina
Published: August 2008

Concept Mapping ist eine Lernstrategie, die insbesondere das bedeutungsvolle Lernen unterstützt. Ziel dieser Studie war es, den Nutzen von kognitiven und/oder metakognitiven Prompts auf den Lernerfolg beim Lernen durch Concept Mapping zu untersuchen. Die teilnehmenden Schülerinnen und Schüler (N = 112, Durchschnittsalter: 17.20 Jahre) erzielten einen signifikant besseren Lernerfolg, wenn sie durch Prompts beim Anfertigen einer Concept Map unterstützt wurden. Gemischte Prompts waren dabei im Vergleich zu nur kognitiven bzw. nur metakognitiven Prompts nicht effektiver, offensichtlich regte bereits die Verfügbarkeit von Prompts die Lernenden zu systematischerem Lernverhalten an. Als Fazit dieser Studie lässt sich festhalten, dass Prompts als Hilfestellung bei der Anwendung einer neuen Lerntechnik sehr wohl positive Effekte haben. Eine Follow-Up-Messung ohne Prompts zeigte jedoch, dass die einmalige Unterstützung durch Prompts nicht ausreichte, um die Lerntechnik weiterhin selbstständig erfolgreich anzuwenden.
Fragen stellen, um Antworten zu erhalten – oder Fragen generieren, um zu lernen?
Authors: Levin Anne , Arnold Karl-Heinz
Published: August 2008

In der vorliegenden experimentellen Studie wird in einem unvollständigen 2 × 2-Design die differenzielle Wirkung von zwei Formaten der Fragengenerierung (strukturiertes vs. unstrukturiertes Fragenstellen) und zwei Formaten der Fragenbearbeitung (Beantwortung der Fragen vs. Diskussion der Qualität der Fragen) analysiert. Studierende in Seminaren aus den Bereichen Erziehungswissenschaft und Pädagogische Psychologie werden zufällig einer der folgenden drei Lernstrategien zugeordnet: (a) strukturiertes Fragenstellen mit nachfolgender Beantwortung, (b) unstrukturiertes Fragenstellen mit nachfolgender Beantwortung oder (c) strukturiertes Fragenstellen mit anschließender Diskussion der Fragenqualität. Lernleistungsbezogene Effekte der Fragenbearbeitung werden für den Lernstand, der zum Abschluss eines Lernprogramms erreicht wird, untersucht. Strukturiertes Fragenstellen führte zu besseren Lernergebnissen als unstrukturiertes Fragenstellen. Studierende, deren Fragen beantwortet wurden, erzielten keine besseren Lernleistungen als Studierende, deren Fragen nicht beantwortet wurden.
Förderung präexperimenteller epistemischer Aktivitäten im Chemieunterricht
Authors: Neber Heinz , Anton Michael A.
Published: August 2008

In präexperimentellen Phasen der Laborarbeit, die im Chemieunterricht eher vernachlässigt bleiben, werden auf Wissensziele ausgerichtete (epistemische) Fragen gestellt und Versuche geplant. In zwei Studien mit Schülern 10. Jahrgänge wurden diese Aktivitäten auf Basis eines Wissensmodells gefördert. Im Vergleich mit einer Kontrollgruppe wirkte sich die in der zweiten Studie optimierte Intervention positiv auf die Bereitschaft zum Experimentieren sowie auf die Qualität epistemischer Fragen aus. Der Beitrag liefert Anregungen zur Realisierung von Forschungszyklen im Chemieunterricht.
Berufliche Zielorientierungen und wahrgenommener Leistungsmangel bei Lehrkräften
Authors: Tönjes Britt , Dickhäuser Oliver , Kröner Stephan
Published: August 2008

Motivationale Determinanten wie Zielorientierungen zeigten in vielen Studien ihren Einfluss auf Leistungsvariablen von Lernern. In dieser Arbeit soll geprüft werden, ob sich solche Zusammenhänge auch bei Lehrenden zeigen. An zwei Stichproben von n = 84 Lehrkräften und n = 75 Lehramtsstudierenden soll untersucht werden, ob die berufsbezogenen Lern-, Annäherungsleistungs- und Vermeidungsleistungszielorientierungen mit der per Maslach-Burnout-Inventar gemessenen Belastungsdimension wahrgenommener Leistungsmangel zusammenhängen. Da Effekte von Persönlichkeitsfaktoren auf berufliches Belastungserleben bereits in anderen Studien belegt wurden, soll ebenfalls überprüft werden, ob die Zusammenhänge zwischen Zielorientierung und wahrgenommenem Leistungsmangel bei Kontrolle der Persönlichkeitsfaktoren weiter bestehen. Für die Belastungsdimension wahrgenommener Leistungsmangel zeigen Regressionsanalysen erwartungsgemäß negative Effekte der Annäherungs- und positive Effekte der Vermeidungsleistungszielorientierung auch bei Kontrolle von Persönlichkeitsfaktoren. Eine explorative Untersuchung des Zusammenhangs zwischen Zielorientierung und den beiden anderen Dimensionen des MBI zeigt ebenfalls Effekte, die aber bei Kontrolle der Persönlichkeitsfaktoren verschwinden.
Multiple Intelligenzen, multiple Irritationen
Authors: Rost Detlef H.
Published: August 2008

Howard Gardners «Multiple Intelligenzen» («MI») sind – insbesondere im pädagogischen Bereich – sehr populär. Gardner behauptet, die «MI» seien theoretisch gut fundiert, unabhängig voneinander und würden nicht mit der allgemeinen Intelligenz g korrelieren. Für die pädagogisch-psychologische Praxis und für prädiktive Zwecke sei die «MI»-Theorie deutlich valider als die «klassische» IQ-Konzeption. Es wird gezeigt, dass diese Behauptungen bei näherer Betrachtung nicht aufrechterhalten werden können. Die Kritik an der «MI»-Theorie weist auf folgende Schwachstellen hin: geringer Neuigkeitswert und Selektivität der Kriterien, theoriewidrige nichttriviale Korreliertheit der «MI», einseitige Literatursichtung, vorschnelle pädagogische Popularisierung, mangelhafte Diagnostik, ungeprüfte Praxis sowie anekdotische Fundierung bzw. inferiore empirische Bewährung.
Long‐term development of phosphorus and nitrogen loads through the subsurface and surface water systems of drainage basins
Authors: Darracq Amélie , Lindgren Georg , Destouni Georgia
Published: August 2008

We analyze and compare simulations and controlling processes of the past 60 years and possible future short‐ and long‐term development of phosphorus and nitrogen loading from the Swedish Norrström drainage basin to the Baltic Sea under different inland source management scenarios. Results indicate that both point and agricultural source inputs may need to be decreased by at least 40% in order to reach a long‐term sustainable 30% reduction of anthropogenic coastal nitrogen loading, as required by national environmental goals. A corresponding 20% anthropogenic phosphorus load reduction goal may be reached in the short term by analogous combined 40% source input reduction, but appears impossible to maintain as a long‐term achievement by inland source abatement only. In general, realistic quantification of the slow subsurface nutrient transport and accumulation‐release dynamics may be essential for accurately predicting and managing nutrient loading to surface and coastal waters.
Ionospheric ions in the near‐Earth magnetotail
Authors: Chen Sheng‐Hsien , Moore Thomas E.
Published: August 2008

We report studies of the relationship between geomagnetic storms and the spatial distribution of cold ions, mostly of ionospheric origin, in the near‐Earth magnetotail using in situ particle and field measurements from the Polar spacecraft, solar wind measurements from the ACE spacecraft, and ground geomagnetic indices, during the years from 2000 to 2005. We find local time and latitude‐dependent distributions of the plasma moments of cold ions at various levels of geomagnetic storms characterized by the Sym‐H and Dst indices. (1) Denser cold ions were observed at the duskside (N > 10 cm−3 compared with 1 cm−3 on average): consistent with the formation of plasma plumes and enhanced bulge region formed as the cold ions wrapped under corotation. (2) Higher temperatures were observed in the auroral oval regions, and a larger temperature anisotropy was observed at the dawnside. (3) Heating processes were strongest near midnight and in the auroral oval regions, which map to PSBL or CPS, except during extremely high geomagnetic activity levels, when heating occurred at high latitudes toward the dawnside, which map to the plasma mantle or distant magnetotail. We interpret these variations as results of ionospheric outflows and plasmaspheric expansion interacting with enhancements of near‐Earth magnetospheric convection and geomagnetic‐storm‐related heating processes in the magnetotail.
Inversion of needle‐probe data for sediment thermal properties of the eastern flank of the Juan de Fuca Ridge
Authors: Goto Shusaku , Matsubayashi Osamu
Published: August 2008

An estimation method is introduced for measuring thermal conductivity, thermal diffusivity, and heat capacity of sediment from temperatures using a needle probe. This method is based on the continuous cylindrical heat‐source model. Thermal conductivity is estimated from needle‐probe temperature data using asymptotic approximation of the model. Heat capacity is then inverted from early time temperature data using a complete form of the model. Finally, thermal diffusivity is calculated from the estimated thermal conductivity and heat capacity. Numerical experiments with synthetic temperature data indicate that the estimation error of the sediment's heat capacity is ∼12%. The error of thermal diffusivity is thought to be greater than that of heat capacity. We apply the method to needle‐probe temperature data obtained during Integrated Ocean Drilling Program Expedition 301 carried out on the eastern flank of the Juan de Fuca Ridge and estimate the sediments' thermal properties. The results indicate that thermal properties of sediments are strongly dependent on lithology and porosity. Examination results of the relations of heat capacity and thermal diffusivity to thermal conductivity show that these relations depend on the amount of quartz. The empirical formulas for these relations are provided, and they differ from those which are commonly used in thermal conductivity reduction schemes.
Attenuation of radiated ground motion and stresses from three‐dimensional supershear ruptures
Authors: Dunham Eric M. , Bhat Harsha S.
Published: August 2008

Radiating shear and Rayleigh waves from supershear ruptures form Mach waves that transmit large‐amplitude ground motion and stresses to locations far from the fault. We simulate bilateral ruptures on a finite‐width vertical strike‐slip fault (of width W and half‐length L with L ≫ W) breaking the surface of an elastic half‐space, and focus on the wavefield out to distances comparable to L. At distances much smaller than W, two‐dimensional plane‐strain slip‐pulse models (i.e., models in which the lateral extent of the slip zone is unbounded) accurately predict the subsurface wavefield. Amplitudes in the shear Mach wedge of those models are undiminished with distance from the fault. When viewed from distances far greater than W, rupture is accurately modeled as a moving point source that produces a shear Mach cone and, on the free surface, Rayleigh‐wave Mach fronts. Geometrical spreading of the shear Mach cone occurs radially and amplitudes there decrease with the inverse square‐root of distance. The transition between these two asymptotic limits occurs at distances comparable to W. Similar considerations suggest that Rayleigh Mach waves suffer no attenuation in the ideally elastic medium studied here. The rate at which fault strength weakens at the rupture front exerts a strong influence on the off‐fault fields only in the immediate vicinity of the fault (for both sub‐Rayleigh and supershear ruptures) and at the Mach fronts of supershear ruptures. More rapid weakening generates larger amplitudes at the Mach fronts.
Crustal structure of the Caribbean–northeastern South America arc‐continent collision zone
Authors: Christeson Gail L. , Mann Paul , Escalona Alejandro , Aitken Trevor J.
Published: August 2008

We present the results of a 568‐km‐long regional wide‐angle seismic profile conducted in the southeastern Caribbean that crosses an active island arc, a remnant arc, two basins possibly floored by oceanic crust, an allochthonous terrane of forearc affinity, and the passive margin of northern South America. The velocity structures of the Late Cretaceous Aves Ridge remnant arc and Miocene and younger Lesser Antilles arc are remarkably similar, which implies that magmatic processes have remained moderately steady over time. Crustal thickness is ∼26 km at the Aves Ridge and ∼24 km at the Lesser Antilles arc. In comparison to the Izu‐Bonin and Aleutian arcs, the Lesser Antilles arc is thinner and has no evidence for a lower crustal cumulate layer, which is consistent with the estimated low magma production rates of the Lesser Antilles arc. Crustal thickness beneath the Grenada and Tobago basins is 4–10 km, and the velocity structure suggests that these basins could be floored by oceanic crust. A decrease of ∼1 km/s in average seismic velocity of the upper crust is observed from NW to SE across the North Coast fault zone; we argue that this marks the suture between the far‐traveled Caribbean arc and the passive margin of the South American continent. Current strike‐slip motion between the Caribbean and South American plates is located ∼30 km to the south, and thus material originally deposited on the South American passive margin has now been transferred to the Caribbean plate.
Submarine back‐arc lava with arc signature: Fonualei Spreading Center, northeast Lau Basin, Tonga
Authors: Keller Nicole S. , Arculus Richard J. , Hermann Jörg , Richards Simon
Published: August 2008

We present major, volatile, and trace elements for quenched glasses from the Fonualei Spreading Center, a nascent spreading system situated very close to the Tofua Volcanic Arc (20 km at the closest), in the northeast Lau Basin. The glasses are basalts and basaltic andesites and are inferred to have originated from a relatively hot and depleted mantle wedge. The Fonualei Spreading Center shows island arc basalt (IAB) affinities, indistinguishable from the Tofua Arc. Within the Fonualei Spreading Center no geochemical trends can be seen with depth to the slab and/or distance to the arc, despite a difference in depth to the slab of >50 km. Therefore we infer that all the subduction‐related magmatism is captured by the back arc as the adjacent arc is shut off. There is a sharp contrast between the main spreading area of the Fonualei Spreading Center (FSC) and its northernmost termination, the Mangatolu Triple Junction (MTJ). The MTJ samples are characteristic back‐arc basin basalts (BABB). We propose that the MTJ and FSC have different mantle sources, reflecting different mantle origins and/or different melting processes. We also document a decrease in mantle depletion from the south of the FSC to the MTJ, which is the opposite to what has been documented for the rest of the Lau Basin where depletion generally increases from south to north. We attribute this reverse trend to the influx of less depleted mantle through the tear between the Australian and the Pacific plates, at the northern boundary of the Lau Basin.
Structure and petrology of newly discovered volcanic centers in the northern Kermadec–southern Tofua arc, South Pacific Ocean
Authors: Graham Ian J. , Reyes Agnes G. , Wright Ian C. , Peckett Kimberley M. , Smith Ian E. M. , Arculus Richard J.
Published: August 2008

The NZAPLUME III expedition of September–October 2004 to the northern Kermadec–southern Tofua (NKST) arc, between 28°52′S and 25°07′S, resulted in the discovery of at least seven new submarine volcanic centers and a substantial caldera complex adjacent to the previously known Monowai Seamount. The volcanic centers form a sublinear chain that coincides with the Kermadec Ridge crest in the south (Hinetapeka) and diverges ∼45 km westward of the ridge crest in the north (“V”) just to the south of where the Louisville Ridge intersects with the arc. All of the centers contain calderas or caldera‐like structures, as well as multiple cones, domes, fissure ridges, and vent fields. All show signs of recent eruptive and current hydrothermal activity. There are strong structural controls on edifice location, with cones and fissure ridges typically associated with faulting parallel to the regional ∼12° strike of the arc front. Several of the calderas are ellipsoidal, orientated northwest–southeast in the general direction of least compressive stress. Sampled volcanic rocks, representing the most recently erupted lavas, are all low‐K tholeiites. Two of the centers, Gamble and Rakahore, yielded only high‐silica dacite to rhyolite (69–74 wt% silica), whereas two others, Monowai and “V,” yielded only basalt to andesite (48–63 wt% silica). Mineral assemblages are plagioclase‐pyroxene dominated, with accessory Fe‐Ti oxides, apatite, olivine, and quartz/tridymite/cristobalite, typical of dry volcanic arc systems. Hornblende occurs only in a felsitic rhyolite from Hinepuia volcanic center, and zircon is absent. Glass contents range to 57% in basalts–andesites (mean 20%), and 97% in andesites–rhyolites (mean 59%) and other quench textures, including swallow‐tailed, plumose, or dendritic crystal forms and crystallites, are common. Most lavas are highly vesicular (≤63%; mean 28%) and have low volatile contents (mostly <2 wt%) which, together with the occurrence of tridymite or cristobalite, indicates explosive eruption and rapid cooling. Exceptions are rocks from “U” volcanic center, which have low vesicularity and low glass contents across a wide compositional range, indicating effusive eruption. Disequilibrium mineral textures, the frequent occurrence of xenoliths and xenocrysts, and macroscopic evidence for magma mingling indicate that many of the lavas are hybrids, having resided only a short time in upper crustal reservoirs prior to eruption. Silicic magmas are major components of NKST arc volcanism and caldera formation is the dominant eruptive style. The scale of silicic magmatism is in marked contrast to the dominant basaltic–andesitic magmatism in the southern Kermadec arc. With evidence from other arcs, silicic magmatism is now recognized as a major feature of intraoceanic arcs globally.
Observations of hydrography and downflow of brine‐enriched shelf water in the Storfjorden polynya, Svalbard
Authors: Skogseth R. , Smedsrud L. H. , Nilsen F. , Fer I.
Published: August 2008

Observations of hydrography and currents in the active Storfjorden polynya during fieldwork in April 2004 and 2006 are presented. The polynya adds salt from its efficient ice production, usually increasing the density ∼0.15 kg m−3. Downflow of dense water from the coastal polynya to the deeper basin enclosed by the Storfjorden sill was captured in both years. April 2006 had a period of strong heat loss and intense frazil ice growth in the polynya. This created downflow of brine‐enriched shelf water (BSW) with a maximum salinity of 35.25, i.e., an increased density ∼0.4 kg m−3 above that of the source water. In April 2004, the salinity remained lower than BSW (S > 34.8), reflecting the fresh source water in fall 2003 due to the heavy ice conditions in the western Barents Sea that year. A portion (0.05 Sv) of such source water probably enters Storfjorden through Freemansundet where the mean current transports less saline and warmer water from the northwestern Barents Sea. Freemansundet has additionally a strong tidal current peaking at 53 cm s−1, dominated by the M2 component. The tidal wave propagates through the narrow sound producing shallow water components and a locally well‐mixed water column. The estimated ice production in winter 2004, twice as large as that of winter 2006, could not overcome this less saline well‐mixed source water. BSW downflow within Storfjorden was both observed and modeled to occur in areas with steep bathymetry. Our observations show that high‐resolution hydrographical data, spacing less than 0.5 km, are necessary to resolve such downflow. Consistent with the observed polynya water salinity, current data at the sill showed weaker overflow in 2004 than in 2006. Overflow of BSW was observed on the eastern part of the Storfjorden sill in April 2006, indicating that overflow occurs across the entire sill width during the freezing period. Current, temperature, and salinity data from the overflow indicate a time lag of 12–18 days between the BSW production and the sill. This downflow–overflow link is confirmed by a numerical experiment and analytical scaling, making results applicable to other polynyas.
Inner shelf circulation patterns and nearshore flow reversal under downwelling and stratified conditions off a curved coastline
Authors: Sanay Rosario , Yankovsky Alexander , Voulgaris George
Published: August 2008

The role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments. Different scenarios include constant versus variable wind‐forcing and variations in bottom friction. The three‐dimensional response of the shelf within the domain (embayment enclosed by capes) is associated with the generation of a velocity/pycnocline disturbance at the upstream cape and its subsequent downstream advection. This disturbance is more pronounced under variable wind conditions. Its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape. When inertia dominates, the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore. The separation occurs at a low Rossby number (Ro ∼ 0.15), which is attributed to the positive curvature of the coastline forming the cape. When friction dominates, the advection path is constrained along the coastline, resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast/isobaths. Simulations with spatially variable bottom friction, with higher friction toward the coast, result in the generation of eddy‐like features. The numerical results are in agreement with both observations and surface temperature imagery from Long Bay, South Carolina, an embayment enclosed by two capes, and emphasize the role that coastline and associated shelf morphology can play in enhancing cross‐shelf transport and exchange.
A five‐year study of coastal recirculation and its effect on air pollutants over the East Mediterranean region
Authors: Levy Ilan , Dayan Uri , Mahrer Yitzhak
Published: August 2008

Many studies have shown that air pollutants concentrations in coastal cities may be gravely affected by coastal recirculation. In this study an attempt is made to examine the properties of coastal recirculation over a long period (5 yrs) at multiple sites along the East Mediterranean Sea (EMS). For this purpose, a single station quantitative measure of horizontal recirculation is used based on wind field measurements over periods of 1–96 hrs. The horizontal recirculation is examined with respect to the integration time period, synoptic flow, seasonality, coastline variations, elevation, and air pollutants concentrations. The interaction between synoptic and mesoscales is shown to be a governing factor by allowing or overruling the land sea breeze winds. Favorite conditions for coastal recirculation are shown to be light or variable winds such as under a Cole or a High‐Pressure system. The monthly distribution of the recirculation potential has a bimodal behavior with two peaks during the transitional seasons and October in particular. This is as a result of the annual cycle of night‐time land‐sea temperature difference driving the land breeze and the more frequent passage of synoptic scale flows with an easterly wind component at the EMS. Two factors leading to variations along the coastline are the urban heat island, weakening the breeze winds and reducing recirculation potential, and the concaved shape of the southern shoreline that causes a convergence and strengthening of the land breeze, thus supporting recirculation. The primary pollutants NOx and SO2 have the highest concentrations during weak daily mean wind speeds. O3 levels depict an almost opposite image of NOx, with higher values for both high and low recirculation, possibly resulting from either long range transport or coastal recirculation.
A height resolved global view of dust aerosols from the first year CALIPSO lidar measurements
Authors: Liu Dong , Wang Zhien , Liu Zhaoyan , Winker Dave , Trepte Charles
Published: August 2008

Based on the first year of CALIPSO lidar measurements under cloud‐free conditions, a height‐resolved global distribution of dust aerosols is presented for the first time. Results indicate that spring is the most active dust season, during which ∼20% and ∼12% of areas between 0 and 60°N are influenced by dust at least 10% and 50% of the time, respectively. In summer within 3–6 km, ∼8.3% of area between 0 and 60°N is impacted by dust at least 50% of the time. Strong seasonal cycles of dust layer vertical extent are observed in major source regions, which are similar to the seasonal variation of the thermally driven boundary layer depth. The arid and semiarid areas in North Africa and the Arabian Peninsula are the most persistent and prolific dust sources. African dust is transported across the Atlantic all yearlong with strong seasonal variation in the transport pathways mainly in the free troposphere in summer and at the low altitudes in winter. However, the trans‐Atlantic dust is transported at the low altitudes is important for all seasons, especially transported further cross the ocean. The crossing Atlantic dusty zones are shifted southward from summer to winter, which is accompanied by a similar southward shift of dust‐generating areas over North Africa. The Taklimakan and Gobi deserts are two major dust sources in East Asia with long‐range transport mainly occurring in spring. The large horizontal and vertical coverage of dust aerosols indicate their importance in the climate system through both direct and indirect aerosol effects.
Stable isotope chronology and climate signal calibration in neotropical montane cloud forest trees
Authors: Anchukaitis K. J. , Evans M. N. , Wheelwright N. T. , Schrag D. P.
Published: August 2008

Tropical montane cloud forests are ecosystems intrinsically linked to a narrow range of geographic and meteorological conditions, making them potentially sensitive to small changes in precipitation or temperature. We investigate the potential application of stable isotope analysis to cloud forest dendroclimatology at Monteverde in Costa Rica in order to be able to extract both chronological and paleoclimate information from trees without annual growth rings. High‐resolution δ18O measurements are used to identify regular cycles in wood of up to 9‰, which are associated with seasonal changes in precipitation and moisture sources. The calculated annual growth rates derived from the isotope time series match those observed from long‐term basal growth measurements. Interannual variability in the oxygen isotope ratio of lower forest trees is primarily related to interannual changes in wet season precipitation. Forward modeling independently supports our detection of both annual chronology and a climate signal. The confirmation of annual chronology and sensitivity to interannual climate anomalies suggests that tropical cloud forest dendroclimatology can be used to investigate local and regional hydroclimatic variability and change.
Spatial and seasonal dynamics of riverine carbon fluxes of the Brantas catchment in East Java
Authors: Aldrian Edvin , Chen Chen‐Tung Arthur , Adi Seno , Prihartanto  , Sudiana Nana , Nugroho Sutopo Purwo
Published: August 2008

Dissolved and particulate organic and inorganic carbon concentrations and flux were measured from July 2005 to June 2006 in the Brantas River basin, a midsized tropical mountainous river and the second largest in Java. There were large seasonal differences in carbon fluxes. Dissolved inorganic carbon (DIC) fluxes were 9.3 times greater and dissolved organic carbon (DOC) fluxes were 532 times greater in the wet season (October to April) than in the dry season. These large contrasts in concentration lead to large differences in load between dry and wet months. In the wet season between January and April, DIC and DOC fluxes are 66% and 87%, respectively, of the total annual fluxes. Most of the annual fluxes of total suspended solids (2.7 × 106 t a−1), total dissolved solids (2.3 × 106 t a−1), DIC (0.26 × 106 t a−1), and DOC (0.2 × 106 t a−1) are transported into the Madura Strait. Accordingly, the Brantas River ranks number 17 among the top 20 rivers that originate at elevations above 3000 m. The concentration of DIC is consistently high all yearlong due to carbonate weathering in the river basin, except in the middle part of the basin, whereas the concentration of DOC is highly seasonal because of variations in biological activities. The total inorganic carbon concentration substantially exceeded the total organic carbon concentration, but the differences decreased from January to April when DOC increased sharply. The carbon budget indicates that the upstream river is a carbon source, and the middle sections of the river are a carbon sink. No carbon trapping was observed by the several impoundments over the basin while sediment trapping was obvious.
Reflector antenna distortion determination: An iterative‐field‐matrix solution
Authors: Martinez‐Lorenzo Jose A. , Rappaport Carey M. , Pino Antonio G.
Published: August 2008

The idealized shapes of satellite reflector antennas are often distorted once they are placed in orbit. The performance of such antennas can be improved by identifying the locations and amount of their surface distortions and then by correcting them using active surface distortion or array feeding. This work presents a method to determine the required discrete surface distortions to correct errors. The algorithm starts by discretizing the entire reflector surface into triangular patches, then by determining the linear relationship between the local distortion and the difference between distorted and undistorted far‐fields patterns. A linear system of equations with discrete distortions as unknowns results when this scattered field is sampled at specific observation points. Singular Value Decomposition combined with Tikhonov regularization, is used to solve for the set of distortions, which are translated into a physically realizable continuous surface by projecting onto a Polynomial‐Fourier‐Series basis. The later scheme is iteratively repeated in order to minimize the residual error. The method has been applied successfully to determine thermal/gravitational distortions on a reflector antenna, with up to 97% accuracy in tenth iteration.
Tilted refractive‐index layers possibly caused by Kelvin–Helmholtz instability and their effects on the mean vertical wind observed with multiple‐receiver and multiple‐frequency imaging techniques
Authors: Chen J.‐S. , Hassenpflug G. , Yamamoto M.
Published: August 2008

Clear‐air VHF/UHF radars worldwide have observed that long‐term mean vertical winds are downward in the middle troposphere and usually slightly upward above the jet‐stream wind maximum. Kelvin–Helmholtz instability (KHI), which can tilt quasi‐specular layers in opposite orientations above and below the jet‐stream wind maximum, has been postulated to be one important contributing factor to the radar‐measured mean vertical wind (r). This factor is examined here using simultaneous radar interferometric observations of echo centers and layer structures. The altitude of layer structure and the incident angle of echo center were estimated, respectively, with multiple‐frequency and multiple‐receiver techniques. Radar data were collected with the Japanese MU radar, between 3 km and 22.2 km and over 33 h. The observations of r showed downward tendency in the middle troposphere, with a maximum of ∼10 cm/s at the height of ∼8 km. However the reversal height of r was at ∼15 km, which is higher than the jet‐stream wind maximum observed (∼12 km). Positive correlations between the vertical velocities (wr) and the incident angles of echo centers were found in the region of downward r, and moreover, the mean vertical velocities derived from the incident angles of echo centers below ∼10 km were close to r. Statistical distributions of layer slopes, incident angles of echo centers, and echo power imbalance between two symmetrically oblique radar beams provide evidence of asymmetrically tilted layer structures in the region of downward r, suggesting that wind‐shear tilted/KHI layers contributed a significant part of r in the middle troposphere.
Analysis and implementation of different topologies of transversal filters in planar technology
Authors: Cañete Rebenaque D. , Martínez‐Mendoza M. , Gómez‐Tornero J. L. , Pascual‐García J. , Álvarez‐Melcón A.
Published: August 2008

This paper uses a simple configuration to implement microwave transversal filters based on microstrip technology. The structure is of second order and implements two transmission zeros and two reflection zeros in the frequency response of the filter. The basic configuration consists of input and output ports coupled in a shunt configuration to two printed resonators of different lengths. A modification of the original structure is introduced to allow an additional direct coupling between the source and the load. Depending on the value and the sign of the coupling terms, different frequency responses can be obtained. In this way, small modifications in the basic structure allow to obtain band‐pass or band‐stop responses. Following this circuit topology, the paper discusses the possibilities to have transmission zeros in the real or in the complex plane and their effects on the frequency response and on the group delay of the filter. Also, two practical implementations in microstrip technology are proposed, and a third filter implementing group delay equalization is demonstrated. Measured results confirm theoretical predictions and validate the structures for practical applications.
What controls the width function shape, and can it be used for channel network comparison and regionalization?
Authors: Moussa Roger
Published: August 2008

The width function captures the essential features of the catchment's GIUH's response. This paper aims to identify the morphometric properties which control the shape of the width function, and assess whether these properties can be used as similarity indices for catchment comparison. A new deterministic iterative model of the width function is proposed on the basis of a conceptualization of the topology of the channel network, and exploiting the morphometric characteristics of internal and external nodes. Tests are carried out on eleven French catchments and compared to the reference Peano catchment. Results show that the morphometric properties of three main internal and external nodes such as the drained area, the distance to the outlet, and the position on the channel network are useful descriptors for modeling the width function and for representing the scaling properties of a channel network. While the GIUHs based on Horton‐Strahler ratios are strongly related to the method used to extract the channel network from the DEM, the new indices are independent of the method used. They are sufficient descriptors to reproduce the main shape of the width function, the peak, the time to peak, and the main properties such as non‐negativity, non‐stationarity, and power law decay of the spectrum. They may be used to establish catchment typology, to compare catchments, and to classify the width function peaks for catchment regionalization.
Probability density functions of hydraulic head and velocity in three‐dimensional heterogeneous porous media
Authors: Nowak Wolfgang , Schwede Ronnie L. , Cirpka Olaf A. , Neuweiler Insa
Published: August 2008

In this study, we assess probability density functions of hydraulic heads and specific discharges in three‐dimensional bounded heterogeneous porous media by Monte Carlo (MC) simulation. We discuss their empirical shapes and demonstrate that the intuitive use of obvious information on boundedness leads to parametric distribution functions, which fit surprisingly well. On the basis of statistical moments of hydraulic heads and velocities up to fourth order, we discuss the spatial dependence of the empirical distributions and their dependence on the variance of log conductivity. Comparison of the first and second central moment to the results from classical numerical first‐order second‐moment (FOSM) analysis reveals that FOSM predicts these moments surprisingly close for hydraulic heads. On the basis of this fact, we demonstrate that fitting the chosen parametric distributions for hydraulic heads to FOSM moments is promising for the sake of estimating exceedance probabilities. Our MC scenarios vary in variance of log conductivity (0.125 to 5.0), in the type of multivariate dependence, in correlation scale and types of boundary conditions. Our study illustrates that in contrast to the common assumption, FOSM is a reasonable choice for evaluating multivariate and univariate moments for heads, if used in conjunction with additional information on distribution shapes. In the absence of utilizable additional information, we demonstrate that second‐moment methods are mostly inadequate for assessing distributions accurately. Significant deviations from Gaussian distributions occurred for discharge components even at a variance of log conductivity as low as 0.125, and we found that the distributions of transverse discharge components are extremely fat‐tailed. The observed non‐Gaussianity questions the results of approximate approaches in solute flux and dispersion studies where velocity fields are assumed to be multi‐Gaussian and then directly represented by or generated from their covariances. The main implication is to apply more accurate schemes such as exact non‐local methods, extensive MC or higher‐order stochastic Galerkin approaches, and to include higher‐order moments, at least if no additional assumptions on the shape of distributions are available or justifiable.
Protracted construction of gabbroic crust at a slow spreading ridge: Constraints from 206Pb/238U zircon ages from Atlantis Massif and IODP Hole U1309D (30°N, MAR)
Authors: Grimes Craig B. , John Barbara E. , Cheadle Michael J. , Wooden Joseph L.
Published: August 2008

Sensitive high‐resolution ion microprobe (SHRIMP) U‐Pb zircon ages of 24 samples from oceanic crust recovered in Integrated Ocean Drilling Program (IODP) Hole U1309D and from the surface of Atlantis Massif, Mid‐Atlantic Ridge (MAR) (30°N) document a protracted history of accretion in the footwall to an oceanic detachment fault. Ages for 18 samples of evolved Fe‐Ti oxide gabbro and felsic dikes collected 40–1415 m below seafloor in U1309D yield a weighted mean of 1.20 ± 0.03 Ma (mean square of weighted deviates = 7.1). However, the ages range from 1.08 ± 0.07 Ma and 1.28 ± 0.05 Ma indicating crustal construction occurred over a minimum of 100–200 ka. The zircon ages, along with petrologic observations, indicate at least 2 major periods of intrusive activity with age peaks separated by 70 ka. The oldest ages are observed below 600 mbsf, an observation inconsistent with models requiring constant depth melt intrusion beneath a detachment fault. The data are most consistent with a “multiple sill” model whereby sills intrude at random depths below the ridge axis over a length scale greater than 1.4 km. Zircon ages from broadly spaced samples collected along the southern ridge of Atlantis Massif yield a detachment fault slip rate of 28.7 ± 6.7 mm/a and imply significant asymmetric plate spreading (up to 100% on the North American plate) for at least 200 ka during core complex formation.
A document‐based 318‐year record of tropical cyclones in the Lesser Antilles, 1690–2007
Authors: Chenoweth Michael , Divine Dmitry
Published: August 2008

The most comprehensive and longest document‐based time series of tropical cyclone activity for any area of the world is presented for the Atlantic and Caribbean region of the Lesser Antilles for the years 1690–2007. Newspaper accounts, ships' logbooks, meteorological journals, and other document sources were used to create this new data set, and a new methodology was applied for classifying historical tropical cyclone intensity. This compilation estimates the position and intensity of each tropical cyclone that passes through the 61.5°W meridian from the coast of South America northward through 25.0°N. The additional resources used here fills in gaps in the HURDAT record, which undercounts tropical storms and hurricanes by 28% (7%) in the years 1851–1898 (1899–1930) over populated islands from 12 to 18°N. The numbers of tropical cyclones show no trends that were significant at the 5% level. The time span 1968–1977 was probably the most inactive period since the islands were settled in the 1620s and 1630s.
Stratification of very deep, thermally stratified lakes
Authors: Boehrer Bertram , Fukuyama Ryuji , Chikita Kazuhisa
Published: August 2008

In very deep freshwater lakes, deep recirculation presents itself with remarkable differences to shallower lakes. We consider the stratification where density gradients are exclusively due to temperature differences. The annual circulation patterns are discussed for various climatic conditions. Very deep lakes do not necessarily produce full overturns during Tmd transition in autumn and spring. Peculiarities of the stratification are derived for cases, in which surface temperatures cross 4°C during the annual cycle: Firstly, the asymmetry between autumn and spring circulation, secondly, the proximity of temperature to the Tmd profile, and thirdly, the isothermal deep water. We compare conceptual model results of horizontally homogeneous lakes with measurements in very deep caldera lakes in Japan (Lakes Ikeda, Tazawa, Toya, Kuttara and Shikotsu). Between oligomictic lakes and thermobarically stratified lakes, we have found lakes circulating reliably despite their enormous depth. We discuss susceptibility to climate variability supported by comparisons with single point measurements from the 1920s and 1930s.
Sea salt aerosol production and bromine release: Role of snow on sea ice
Authors: Yang Xin , Pyle John A. , Cox Richard A.
Published: August 2008

Snow lying on sea ice could be a potentially important source of sea salt aerosol, as small snow particles, rich in salts, can be easily lifted into the air though blowing‐snow events. Using a measured distribution of snow salinity on Antarctic sea ice and a blowing snow sublimation parameterization, we derive a method for estimating sea salt aerosol production, and bromine release, during blowing‐snow events. Compared with sea salt aerosol production rates from the open ocean, we find that the aerosol production rate from snow can be more than an order of magnitude larger per unit area under typical weather conditions. The large sea ice cover may thus enhance the supply of sea salt to the polar lower atmosphere. This is consistent with observations of sea salt aerosol seasonality and with the ice‐core record. This large emission of sea salt from snow also implies an additional tropospheric bromine source in these regions.
Rheological stratification of the lithosphere: A direct inference based upon the geodetically observed pattern of the glacial isostatic adjustment of the North American continent
Authors: Peltier W. R. , Drummond Rosemarie
Published: August 2008

A sequence of new analyses of the process of glacial isostatic adjustment (GIA) is described. The focus is upon the resolution of a recognized flaw in the currently prevalent model of this process, that denoted ICE‐5G(VM2). The flaw concerns a previously noted inability of the model to simultaneously reconcile the VLBI and GPS measured rates of vertical and horizontal motion in the region of the North American continent that lay outboard and to the south of the Laurentide Ice‐Sheet (LIS) at Last Glacial Maximum. This characteristic misfit of the model to the data has been suggested to be reconcilable only by recourse to models that explicitly incorporate the influence of lateral viscosity heterogeneity. It is demonstrated herein that, on the contrary, this flaw is entirely and unambiguously attributable to the rheological stratification of the lithosphere, an influence not previously accounted for in global models of the GIA process but which must exist on a priori grounds.
Dual‐probe heat pulse method for snow density and thermal properties measurement
Authors: Liu G. , Si B. C.
Published: August 2008

Measuring the density (ρ), thermal conductivity (k) and thermal diffusivity (α) of snow is important for modeling the energy and water balance of the earth's surface. The objective of this letter is to determine if the dual‐probe heat pulse (DPHP) method can be used to measure snow density as well as thermal properties k and α. DPHP experiments with 60‐s heat pulse duration and variable strength of q′ < 15 W m−1 were carried out on ice and various kinds of snow to avoid melting. There was a linear relationship between the DPHP measured snow density and that of gravimetrically measured density. With calibration, the DPHP method may be accurate for determining snow density.
Climate change hotspots in the United States
Authors: Diffenbaugh Noah S. , Giorgi Filippo , Pal Jeremy S.
Published: August 2008

We use a multi‐model, multi‐scenario climate model ensemble to identify climate change hotspots in the continental United States. Our ensemble consists of the CMIP3 atmosphere‐ocean general circulation models, along with a high‐resolution nested climate modeling system. We test both high (A2) and low (B1) greenhouse gas emissions trajectories, as well as two different statistical metrics for identifying regional climate change hotspots. We find that the pattern of peak responsiveness in the CMIP3 ensemble is persistent across variations in GHG concentration, GHG trajectory, and identification method. Areas of the southwestern United States and northern Mexico are the most persistent hotspots. The high‐resolution climate modeling system produces highly localized hotspots within the basic GCM structure, but with a higher sensitivity to the identification method. Across the ensemble, the pattern of relative climate change hotspots is shaped primarily by changes in interannual variability of the contributing variables rather than by changes in the long‐term means.
Measured and modeled backscatter of ionospheric photoelectron fluxes
Authors: Richards Phil G. , Peterson W. K.
Published: August 2008

This paper examines the backscatter of ionospheric photoelectrons from the thermosphere using photoelectron measurements made on closed field lines in the magnetosphere from 1997 to 2004. The satellite made simultaneous measurements of both the precipitating photoelectrons from the sunlit conjugate hemisphere and the backscattered electrons from the dark thermosphere. The backscatter ratios of the observed fluxes are in very good agreement with photoelectron model calculations for energies ranging from a few eV to several hundred eV and for different levels of solar activity. The backscattered electron flux consists of a direct elastic backscatter component that is a weak function of energy and a much stronger cascade component that greatly increases with decreasing electron energy so that the backscatter ratio ranges from 0.2 at high energies to greater than one at low energies. Although the photoelectron fluxes can vary by up to an order of magnitude over the solar cycle, the backscatter ratios show only a small variation above 20 eV. There can be a factor of 2 or more variability in the backscatter ratios for energies below 20 eV due to thermal electron Coulomb interactions. The calculations show that 55–60% of the precipitating flux energy is backscattered from the thermosphere back along the field line to the conjugate hemisphere. The model–data comparisons show that photoelectrons are able to travel the long journey from the sunlit hemisphere to the satellite without significant degradation indicating that pitch angle scattering and trapping of photoelectrons in the magnetosphere may be small.