bluuebunny/crossref_metadata_2025 huggingface dataset:
Chromatic assimilation unaffected by perceived depth of inducing
light
Authors: SHEVELL STEVEN K. , CAO DINGCAI
Published: June 2007

Chromatic assimilation is a shift toward the color of nearby light.
Several studies conclude that a neural process contributes to
assimilation but the neural locus remains in question. Some studies
posit a peripheral process, such as retinal receptive-field
organization, while others claim the neural mechanism follows depth
perception, figure/ground segregation, or perceptual grouping. The
experiments here tested whether assimilation depends on a neural
process that follows stereoscopic depth perception. By introducing
binocular disparity, the test field judged in color was made to appear
in a different depth plane than the light that induced assimilation.
The chromaticity and spatial frequency of the inducing light, and the
chromaticity of the test light, were varied. Chromatic assimilation was
found with all inducing-light sizes and chromaticities, but the
magnitude of assimilation did not depend on the perceived relative
depth planes of the test and inducing fields. We found no evidence to
support the view that chromatic assimilation depends on a neural
process that follows binocular combination of the two eyes'
signals.
A single mechanism for both luminance and chromatic grating vernier
tasks: Evidence from temporal summation
Authors: SUN HAO , LEE BARRY B.
Published: June 2007

Vernier thresholds are determined by luminance rather than chromatic
contrast when both are present in vernier targets. The role of
luminance and chromatic mechanisms in vernier performance under
equiluminant conditions remains uncertain. Temporal summation functions
for vernier thresholds with luminance and red–green equiluminant
gratings were compared to those for detection thresholds with similar
stimuli. Vernier thresholds showed similar temporal summation for
luminance and chromatic gratings, which is consistent with a single
mechanism underlying vernier performance in the two conditions.
However, detection thresholds showed a shorter temporal summation
duration for luminance gratings than for chromatic gratings, which
suggests that two different mechanisms underlie detection thresholds.
Analysis of physiological data supports the hypothesis that the
frequency-doubled response of ganglion cells in the magnocellular
pathway can provide accurate spatiotemporal information for vernier
performance at equiluminance.
Molecular genetics of color-vision deficiencies
Authors: DEEB SAMIR S.
Published: June 2007

The normal X-chromosome-linked color-vision gene array is composed of a single long-wave-sensitive (L-) pigment gene followed by one or more middle-wave-sensitive (M-) pigment genes. The expression of these genes to form L- or M-cones is controlled by the proximal promoter and by the locus control region. The high degree of homology between the L- and M-pigment genes predisposed them to unequal recombination, leading to gene deletion or the formation of L/M hybrid genes that explain the majority of the common red–green color-vision deficiencies. Hybrid genes encode a variety of L-like or M-like pigments. Analysis of the gene order in arrays of normal and deutan subjects indicates that only the two most proximal genes of the array contribute to the color-vision phenotype. This is supported by the observation that only the first two genes of the array are expressed in the human retina. The severity of the color-vision defect is roughly related to the difference in absorption maxima (λmax) between the photopigments encoded by the first two genes of the array. A single amino acid polymorphism (Ser180Ala) in the L pigment accounts for the subtle difference in normal color vision and influences the severity of red–green color-vision deficiency.

Blue-cone monochromacy is a rare disorder that involves absence of L- and M-cone function. It is caused either by deletion of a critical region that regulates expression of the L/M gene array, or by mutations that inactivate the L- and M-pigment genes. Total color blindness is another rare disease that involves complete absence of all cone function. A number of mutants in the genes encoding the cone-specific α- and β-subunits of the cGMP-gated cation channel as well as in the α-subunit of transducin have been implicated in this disorder.
Chromatic and contrast selectivity in color contrast adaptation
Authors: MIZOKAMI YOKO , PARAS CARRIE , WEBSTER MICHAEL A.
Published: June 2007

We used color contrast adaptation to examine the chromatic and
contrast selectivity of central color mechanisms. Adaptation to a field
whose color varies along a single axis of color space induces a
selective loss in sensitivity to the adapting axis. The resulting
changes in color appearance are consistent with mechanisms formed by
different linear combinations of the cone signals. We asked whether the
visual system could also adjust to higher-order variations in the
adapting stimulus, by adapting observers to interleaved variations
along both the L versus M and the S versus LM cardinal axes. The
perceived hue of test stimuli was then measured with an asymmetric
matching task. Frequency analysis of the hue shifts revealed weak but
systematic hue rotations away from each cardinal axis and toward the
diagonal intermediate axes. Such shifts could arise if the adapted
channels include mechanisms with narrow chromatic selectivity, as some
physiological recordings suggest, but could also reflect how adaptation
alters the contrast response function. In either case they imply the
presence of more than two mechanisms within the chromatic plane. In a
second set of measurements, we adapted to either the L versus M or the
S versus LM axis alone and tested whether the changes in hue could be
accounted for by changes in relative contrast along the two axes. For
high contrasts the hue biases are larger than the contrast changes
predict. This dissociation implies that the contrast and hue changes
are not carried by a common underlying signal, and could arise if the
contrast along a single color direction is encoded by more than one
mechanism with different contrast sensitivities or if different subsets
of channels encode contrast and hue. Such variations in contrast
sensitivity are also consistent with physiological recordings of
cortical neurons.
Public International Law: Is It Fit For Purpose?
Authors: Triggs Gillian
Published: June 2007

This paper by Professor Gillian Triggs seeks to explore whether the traditional principles of public international law are ‘fit for purpose’ in responding to such contemporary threats to collective security by reference to three issues: the regulation of the use of force; the need to balance the sovereign rights of states with humanitarian concerns; and the relationship between human rights and the orthodox rules applicable to prisoners of war and security detainees.
Sources of Indian Legal Information
Authors: Narayan Uma
Published: June 2007

Abstract: The purpose of this paper by Uma Narayan is to provide an insight into how to use Indian legal materials for research purposes. The following subjects are covered: the evolution of the Indian legal system; systems and procedures in enacting laws in Parliament; Indian legal information sources - both government and private - as well as print and electronic sources and how to understand the method of publication of legislation.
Asian, African and Middle Eastern Legal Materials at SOAS Library
Authors: Spells Sarah
Published: June 2007

Sarah Spells provides information about the SOAS Library, including details of the law collection, services offered, and the challenges faced when dealing with queries about Asian, African and Middle Eastern legal materials.
Too Much Information ... Nor Any Drop To Drink
Authors: Clayton Carl
Published: June 2007

Carl Clayton, Director, SINTO - the information partnership, writes that there is no shortage of legal information, yet for some people it can still be difficult to get access to the legal information they may need as citizens. Libraries in the Sheffield area have a strong history of co-operation but this cannot remove all the barriers.
Sneaky Learning: Has Knowledge Management Had its Day?
Authors: Byrne David
Published: June 2007

David Byrne - Head of Information at BT Legal - explains that within the commercial, legal and regulatory division of BT, their approach to knowledge management is to introduce cultural change whereby knowledge capture and re-use are subordinate to the prime goals of revenue generation and competitiveness. He discusses the innovative methods used for building effective knowledge-sharing relationships including using the “best of the rest”; ensuring that the right technology is in place; measuring value; collaboration and creating the “Sticky Organisation”.
Epistemologische Überzeugungen als kohärente Laientheorien
Authors: Schmid Sebastian , Lutz Alexander
Published: June 2007

Zusammenfassung. Epistemologische Überzeugungen werden in der Pädagogischen Psychologie zumeist als unabhängige Dimensionen konzipiert. Wir nehmen demgegenüber an, dass Überzeugungen zur Sicherheit natur- und sozialwissenschaftlichen Wissens kohärente epistemologische Laientheorien bilden. Unterscheidet man zwischen ontologischen Aspekten (Realismus vs. Antirealismus), epistemologischen Aspekten (Erkenntnisoptimismus vs. -skeptizismus) und wissenschaftskritischen Aspekten (Wissenschaftsoptimismus vs. -pessimismus), können A-priori-Annahmen über die Kohärenz/Inkohärenz der kombinatorisch möglichen Überzeugungskonfigurationen formuliert werden. Die Ergebnisse einer Fragebogen- und einer Online-Untersuchung sprechen dafür, dass inkohärente Konfigurationen seltener sind, als bei Unabhängigkeit der drei Aspekte per Zufall zu erwarten wäre. In der Online-Untersuchung beurteilten die Pbn vorgegebene Überzeugungskonfigurationen hinsichtlich ihrer Kohärenz. Dies gelang ihnen selbst dann, wenn sie die entsprechenden Positionen nicht teilten. Die Ergebnisse sprechen für eine hohe Differenziertheit epistemologischer Überzeugungen und verdeutlichen die Möglichkeit und Notwendigkeit, sie auch entsprechend differenziert zu erfassen.
Die Prävention von Lese-Rechtschreibschwierigkeiten
Authors: Weber Jutta , Marx Peter , Schneider Wolfgang
Published: June 2007

Zusammenfassung. Der Erfolg von vorschulischen Programmen zur Förderung der phonologischen Bewusstheit ist mittlerweile hinlänglich belegt. Unklar ist allerdings, inwieweit auch Kinder mit Migrationshintergrund von solchen Förderprogrammen profitieren. In der vorliegenden Längsschnittstudie nahmen Kinder mit deutscher Muttersprache und Kinder mit Migrationshintergrund an einem vorschulischen Training der phonologischen Bewusstheit und der Buchstabe-Laut-Zuordnung teil. Vor Trainingsbeginn wurde eine umfangreiche Testbatterie zur Erfassung der phonologischen Informationsverarbeitung und der Buchstabenkenntnis eingesetzt. Unmittelbar nach Trainingsende wurden erneut die phonologische Bewusstheit und die Buchstabenkenntnis der Kinder erhoben. Am Ende des ersten Schuljahres wurden dann die Lese-Rechtschreibleistungen bestimmt. Kinder mit Migrationshintergrund zeigten bei den Vortests deutlich niedrigere Leistungen in der phonologischen Informationsverarbeitung als Kinder mit deutscher Muttersprache. Sie profitierten jedoch in vergleichbarem Ausmaß vom Training der phonologischen Bewusstheit hinsichtlich der unmittelbaren Trainingseffekte. In den Lese-Rechtschreibtests schnitten die Migrantenkinder insgesamt etwas schlechter ab als die Kinder mit deutscher Muttersprache.
Entzündung und Alzheimer Krankheit
Authors: Reich Arno , Schulz Jörg B.
Published: June 2007

Zusammenfassung: Die im Gehirn aller Patienten mit Alzheimer Krankheit nachzuweisende Inflammation wird als eine wesentliche Komponente des Neurodegenerationsprozesses diskutiert. Ergebnisse epidemiologischer Studien weisen bei chronischer Einnahme von Antiphlogistika auf ein vermindertes Risiko, eine Alzheimer Demenz zu entwickeln, hin. Diese Befunde legen nahe, dass Entzündungsprozesse entscheidend zur Entstehung und Progression der Alzheimer Erkrankung beitragen. Dennoch blieben bisher mehrere randomisierte, Plazebo-kontrollierte klinische Studien, die die Effekte von Antiphlogistika auf die Progression der Alzheimer Demenz untersuchten, ohne den gewünschten Erfolg. Eine weitere Therapiestrategie besteht in der Modulation des Immunsystems durch Vakzinierung. Nachfolgend geben wir einen Überblick über die Inflammation bei Alzheimer Krankheit, die diesbezüglich bisher durchgeführten Therapiestudien, diskutieren Gründe, warum diese Therapiestudien bisher keinen Erfolg gezeigt haben und geben Aussicht auf zukünftige antientzündliche Therapiestrategien.
Was schützt vor Demenz?
Authors: Laske Christoph
Published: June 2007

Zusammenfassung: Angesichts der in den nächsten Jahrzehnten steigenden Zahl demenzieller Erkrankungen und der bisher begrenzten therapeutischen Möglichkeiten wird die Demenz-Prävention auch aus volkswirtschaftlichen Gründen eine zunehmende Bedeutung für die Medizin der Zukunft bekommen. Diese kann auf medikamentöser und/oder auf nichtmedikamentöser Ebene erfolgen. Doch welche Maßnahmen sind sinnvoll und welche nicht? Der Artikel soll diese Fragestellungen nach derzeitigem Wissensstand beleuchten. Potenzielle Wirkfaktoren der präventiven Maßnahmen werden diskutiert.
Vorhersage von Demenzerkrankungen mit dem Syndrom-Kurztest (SKT)
Authors: Bickel Horst , Mösch Edelgard , Förstl Hans
Published: June 2007

Zusammenfassung: Demenzen kündigen sich zumeist durch leichte kognitive Störungen an. In der vorliegenden Prospektivstudie an 546 nichtdementen Probanden im Alter zwischen 65 und 85 Jahren wurde die Validität des SKT für die Vorhersage von Demenzerkrankungen untersucht. Initial wurde die kognitive Leistung mit dem SKT gemessen und in drei Follow-up-Untersuchungen mit jeweils einjährigem Abstand voneinander wurden die Neuerkrankungen an Demenz diagnostiziert. Eine geringe Leistung im SKT war eng mit dem Demenzrisiko assoziiert. Innerhalb von drei Jahren entwickelten sich in den beiden Teilnehmergruppen mit der geringsten Testleistung bei 35 % bzw. bei 60 % eine Demenz. Die jährlichen Konversionsraten betrugen 16 % bzw. 32 %, während sich die Inzidenz in der Gruppe der Testbesten auf lediglich 0.4 % pro Jahr belief. Der SKT scheint überaus gut für die Identifikation der präklinischen Stadien einer Demenz und für die praktische Anwendung geeignet zu sein.
Indikationen zur Parathyreoidektomie
Authors: Oertli
Published: June 2007

Die chirurgische Entfernung von hyperfunktionellem Nebenschilddrüsengewebe stellt die Standardbehandlung des primären Hyperparathyreoidismus dar. In erfahrenen Händen führt sie in 95 bis 99% der Fälle zum Erfolg mit einer sehr geringen Komplikationsrate. Prinzipiell sollten alle symptomatischen Patienten mit Hyperparathyreoidismus operiert werden. Die Indikation zur Chirurgie ist ebenfalls bei asymptomatischen Individuen gegeben, wenn die Patienten jünger als 50 Jahre sind, eine ausgeprägte Hyperkalzämie, eine eingeschränkte Nierenfunktion oder eine schwere Osteopenie aufweisen (NIH Konsensus Konferenz 2002). Eine präzise präoperative Lokalisationsdiagnostik mit zervikalem Ultraschall und Sestamibi-Szintigraphie erlauben es heute in den meisten Fällen, dass eine gezielte minimal-invasive Parathyreoidektomie durchgeführt werden kann. Die früher routinemässig durchgeführte beidseitige Halsrevision wird nur noch bei unklarer Adenomlokalisation oder bei der Hyperplasie aller vier Nebenschilddrüsen angewendet.
Analysis of Data from a Controlled Repeated Measurements Design with Baseline-Dependent Dropouts
Authors: Overall John E. , Tonidandel Scott
Published: June 2007

Abstract. Differences in mean rates of change are of primary interest in many controlled treatment evaluation studies. Generalized linear mixed model (GLMM) procedures are widely conceived to be the preferred method of analysis for repeated measurement designs when there are missing data due to dropouts, but systematic dependence of the dropout probabilities on antecedent or concurrent factors poses a problem for testing the significance of differences in mean rates of change across time in such designs. Controlling for the dependence of dropout probabilities on baseline values poses a special problem because a theoretically correct GLMM random-effects model does not permit including the same baseline score as both covariate and dependent variable. Monte Carlo methods are used herein to evaluate the actual Type 1 error rates and power resulting from two commonly-illustrated GLMM random-effects model formulations for testing the GROUPS × TIMES linear interaction effect in group-randomized repeated measurements designs. The two GLMM model formulations differ by either including or not including baseline scores as a covariate in the attempt to control for imbalance caused by the baseline-dependent dropouts. Results from those analyses are compared with results from a simpler two-stage analysis in which dropout-weighted slope coefficients fitted separately to the available repeated measurements for each subject serve as the dependent variable for an ordinary ANCOVA test for difference in mean rates of change. The Monte Carlo results confirm modestly superior Type 1 error protection but quite superior power for the simpler two-stage analysis of dropout-weighted slope coefficients as compared with those for either of the more mathematically complex GLMM analyses.
Effect of Variable and Subject Sampling on Recovery of Weak Factors In CFA
Authors: Ximénez Carmen
Published: June 2007

Abstract. Two general issues central to the design of a study are subject sampling and variable sampling. Previous research has examined their effects on factor pattern recovery in the context of exploratory factor analysis. The present paper focuses on recovery of weak factors and reports two simulation studies in the context of confirmatory factor analysis. Conditions investigated include the estimation method (ML vs. ULS), sample size (100, 300, and 500), number of variables per factor (3, 4, or 5), loading size in the weak factor (.25 or .35), and factor correlation (null vs. moderate). Results show that both subject and variable sample size affect the recovery of weak factors, particularly if factors are not correlated. A small but consistent pattern of differences between methods occurs, which favors the use of ULS. Additionally, the frequency of nonconvergent and improper solutions is also affected by the same variables.
Strontium isotope tracing of terrigenous sediment dispersal in the Antarctic Circumpolar Current: Implications for constraining frontal positions
Authors: Hemming S. R. , van de Flierdt T. , Goldstein S. L. , Franzese A. M. , Roy M. , Gastineau G. , Landrot G.
Published: June 2007

The vigor of the glacial Antarctic Circumpolar Current (ACC) and the locations of frontal boundaries are important parameters for understanding the role of the Southern Ocean in global climate change. Toward the goal of understanding the locations of currents we present a survey of Sr isotope ratios in terrigenous sediments around the perimeter of Antarctica. The pattern of the variations within the modern ACC is used to suggest that terrigenous sediment from Antarctica is injected into the ACC via the Ross and Weddell gyres in the south. North of the main ACC the Sr isotopes reflect continental contributions from Africa, Australia‐New Zealand, and South America. Along a transect northward from the Ross Sea, Sr isotope ratios show a decrease from higher values in the south (Antarctic provenance) to lower values in the north (provenance from New Zealand). This otherwise monotonic decrease is interrupted within the ACC by a “zigzag” to lower and then higher values, which accompanies minimum terrigenous flux. This zigzag requires contributions from two additional sediment sources beyond the main Antarctic and New Zealand end‐members. The lower Sr isotope ratios are attributable to greater contributions from basaltic sources within the current, a consistent pattern around the ACC. The samples with higher Sr isotope ratios point to an additional contributor, possibly a wind‐transported component from Australia. During the LGM there is a systematic geographical variation in the Sr isotope ratios, similar to that of the Holocene. A small offset of the zigzag to the north (approximately 1°–2°) may indicate a small northward shift of the southern boundary of the ACC. More highly resolved data are required to test whether this northward shift is really significant and whether it applies to other ACC fronts during the LGM.
Simultaneous observations of magnetotail reconnection and bright X‐ray aurora on 2 October 2002
Authors: Borg A. L. , Østgaard N. , Pedersen A. , Øieroset M. , Phan T. D. , Germany G. , Aasnes A. , Lewis W. , Stadsnes J. , Lucek E. A. , Rème H. , Mouikis C.
Published: June 2007

We present simultaneous Cluster and Polar X‐ray and UVI observations on 2 October 2002, when Cluster observed a magnetic reconnection diffusion region at Xgse = −16.6 Re. At the same time a bright auroral feature appeared at the footpoint of the magnetic field line connecting the ionosphere and the diffusion region. However, we found that the electrons measured in the diffusion region by Cluster were not sufficiently accelerated by the reconnection process to produce the aurora X‐ray fluxes measured by Polar. The DMSP F14 passed over the intense X‐ray spot and showed that the X rays (and the fainter UV) were produced by electrons accelerated through a ∼30 kV potential drop. The coincidence in time and the fact that this inverted‐V is very close to the open‐closed field line boundary suggest that the inverted‐V structure are produced by flow shears that could be related to the reconnection process.
Large‐scale traveling ionospheric disturbances observed by GPS total electron content during the magnetic storm of 29–30 October 2003
Authors: Ding F. , Wan W. , Ning B. , Wang M.
Published: June 2007

We have investigated the propagation of large‐scale traveling ionospheric disturbances (LSTIDs) during the super magnetic storm of 29–30 October 2003. Two‐dimensional total electron content (TEC) perturbation maps over North America were built using TEC data provided by the American GPS network and the International GNSS Service. Three LSTID events were observed in the range of 30°N–50°N, 60°W–110°W during this period. The first two LSTIDs occurred consecutively during 0620–0800 UT on 29 October at the local time of midnight, right after the onset of the big substorm; the third one was found at noon during the expansion phase of another substorm on 30 October. The phase fronts of these LSTIDs passed over the United States and traveled southwestward to the distance of ∼2000 km with the maximum front width of ∼4000 km and the duration of less than 2 hours. The maximum amplitude of TEC perturbations attained 3 total electron content units (TECUs). The results differ from the former observation of Afraimovich and Voeykov (2004) and Afraimovich et al. (2006), who reported a solitary LSTID propagating southwestward over the United States with the amplitudes of up to 14 TECU on 30 October 2003. We have checked the magnetic H component observed at the geomagnetic observatories in North America and found it is most likely that the auroral westward electrojet was the cause of the LSTIDs on 29 October. The source region for these TIDs was likely to be located several hundred kilometers north of 50°N. Cross‐spectral analysis was conducted to obtain the global propagation characteristics of LSTIDs during this superstorm. Equatorward LSTIDs were found in all the three sectors of North America, Europe, and Asia, showing high correlation with the occurrence of auroral substorms.
Cosmogenic 10Be and 36Cl geochronology of offset alluvial fans along the northern Death Valley fault zone: Implications for transient strain in the eastern California shear zone
Authors: Frankel Kurt L. , Brantley Katherine S. , Dolan James F. , Finkel Robert C. , Klinger Ralph E. , Knott Jeffrey R. , Machette Michael N. , Owen Lewis A. , Phillips Fred M. , Slate Janet L. , Wernicke Brian P.
Published: June 2007

The northern Death Valley fault zone (NDVFZ) has long been recognized as a major right‐lateral strike‐slip fault in the eastern California shear zone (ECSZ). However, its geologic slip rate has been difficult to determine. Using high‐resolution digital topographic imagery and terrestrial cosmogenic nuclide dating, we present the first geochronologically determined slip rate for the NDVFZ. Our study focuses on the Red Wall Canyon alluvial fan, which exposes clean dextral offsets of seven channels. Analysis of airborne laser swath mapping data indicates ∼297 ± 9 m of right‐lateral displacement on the fault system since the late Pleistocene. In situ terrestrial cosmogenic 10Be and 36Cl geochronology was used to date the Red Wall Canyon fan and a second, correlative fan also cut by the fault. Beryllium 10 dates from large cobbles and boulders provide a maximum age of 70 +22/−20 ka for the offset landforms. The minimum age of the alluvial fan deposits based on 36Cl depth profiles is 63 ± 8 ka. Combining the offset measurement with the cosmogenic 10Be date yields a geologic fault slip rate of 4.2 +1.9/−1.1 mm yr−1, whereas the 36Cl data indicate 4.7 +0.9/−0.6 mm yr−1 of slip. Summing these slip rates with known rates on the Owens Valley, Hunter Mountain, and Stateline faults at similar latitudes suggests a total geologic slip rate across the northern ECSZ of ∼8.5 to 10 mm yr−1. This rate is commensurate with the overall geodetic rate and implies that the apparent discrepancy between geologic and geodetic data observed in the Mojave section of the ECSZ does not extend north of the Garlock fault. Although the overall geodetic rates are similar, the best estimates based on geology predict higher strain rates in the eastern part of the ECSZ than to the west, whereas the observed geodetic strain is relatively constant.
Frontal accretion: An internal clock for bivergent wedge deformation and surface uplift
Authors: Hoth S. , Hoffmann‐Rothe A. , Kukowski N.
Published: June 2007

We propose a conceptual model of frontal accretion within bivergent wedges, which is based on two‐dimensional sandbox simulations and the analysis of particle displacement fields. Each frontal accretion cycle consists of a thrust initiation, an underthrusting phase, and a reactivation phase. The location and magnitude of deformation within a bivergent wedge and its associated surface uplift vary systematically with the phase of the frontal accretion cycle and are thus predictable. Therefore the frontal accretion cycle can be considered as an internal clock for wedge‐scaled deformation and surface uplift. We further demonstrate that the geometry of the deformation front and the spatial distribution of surface uplift can be used to infer the currently active phase within a frontal accretion cycle. Surface uplift of the axial zone and the retrowedge may reach up to half of the thickness of the incoming sedimentary layer during a frontal accretion cycle. We estimate cycle duration to range between 104 and 105 years, which is thus similar to the time frame of climatic cycles. The proposed conceptual model provides an explanation for the commonly observed transience of deformation and surface uplift and for the discrepancy between geodetic, paleoseismologic, and geologic estimates of fault slip.
Compressible thermochemical convection and application to lower mantle structures
Authors: Tan Eh , Gurnis Michael
Published: June 2007

A new finite element code for compressible thermochemical convection is developed to study the stability of a chemical layer at the base of the mantle. Using composition‐dependent compressibility and a density difference between compositions at a reference pressure, a composition‐dependent density profile is derived. Together with depth‐dependent thermal expansion, this combination of parameters yields a wide range of dynamic evolutions for the chemical layer. The chemical structures are classified into five major categories (classical plumes, mushroom‐shaped plume, domes, ridges, and continuous layers) and a few abnormal cases, such as hourglass‐shaped plumes and columnar plumes. Several models have a chemical structure morphologically similar to the African low VS structure in the lower mantle, at least at a single time. Guided by our models, several dynamic scenarios are proposed for the dynamic nature of the lower mantle low‐velocity structures (a.k.a. superplumes), including plumes at an early stage, plume clusters, ridges, passive piles, sluggish domes, and high‐bulk‐modulus domes. We predict seismic velocity anomalies from these dynamic models. The thermoelastic parameters used in the conversion are additional constraints. We compare the density structure with normal mode inversion, the predicted seismic signature observations, and the required thermoelastic parameters with mineral physics data. Among the proposed scenarios, only the scenario of high‐bulk‐modulus domes satisfies all constraints simultaneously. The implication on the geochemistry and mineralogy of lower mantle chemical structures is discussed.
Effects of lateral inhomogeneity in a spherical Earth on gravity Earth tides
Authors: Fu Guangyu , Sun Wenke
Published: June 2007

Molodenskiy (1977, 1980) presented the disturbance method to deal with the effect of a lateral inhomogeneous structure on tidal gravimetric factors. Those studies introduced expressions to calculate the effects caused by seismic waves, but ignored the contribution of lateral density changes. The present study develops the theory by reformulating the expressions with new notation and calculation. We present novel expressions for computing the effects of lateral density inhomogeneity and introduce a new three‐dimensional lateral inhomogeneous Earth model (Zhao, 2001) to compute these effects. Our numerical results show that the effects of density are of the same level as those of seismic waves: they are not negligible. The effects of the lateral inhomogeneous structure calculated for the real three‐dimensional inhomogeneous model are much less, by a factor of about 0.2, than those of the simple Ocean‐Land model presented in Molodenskiy and Kramer (1980). Collecting contributions from the seismic wave and density models, we obtain the completed total effect of the real three‐dimensional inhomogeneous Earth structure on semidiurnal gravimetric factors, with a magnitude of about −0.16 to 0.1%. This result is less than, but almost of the same order as that of Earth’s elliptical effect (ca. 0.7%; Dehant, 1995). Finally, we calculate the corresponding effects on tidal gravity for all three kinds of Earth tide: semidiurnal, diurnal, and long period ones. Compared to the tidal gravity changes, the gravity variations caused by the increments are about 0.15% for the semidiurnal tide and 0.1% for the diurnal and long period tides.
Tide‐surge interaction off the east coast of Canada and northeastern United States
Authors: Bernier N. B. , Thompson K. R.
Published: June 2007

Sea level observations and a dynamical model are used to investigate tide‐surge interaction in the coastal waters off the east coast of Canada and northern USA. The study is motivated in part by the need to improve operational forecasts of total water level and coastal flooding. Two statistical methods are used to search for evidence of tide‐surge interaction in hourly sea level records from 23 coastal locations. The methods are based on comparison of the statistical properties of the sea level residuals (observed sea level minus tide) occurring at different stages of the tidal cycle. While recognizing the limitations of such an approach, it is concluded that tide‐surge interaction does occur in the Northumberland Strait which is located in the southern Gulf of St. Lawrence. Results for the Gulf of Maine and Bay of Fundy are less conclusive. A dynamical model is also used to quantify tide‐surge interaction in the study region and to identify its physical causes. Tide‐surge interaction in the model is strongest in the Northumberland Strait where the amplitude of the effect can reach 20 cm during and following strong storm surge events. This is large enough to be of practical significance in terms of flood forecasting. A series of sensitivity experiments with the model shows that the nonlinear parameterization of bottom stress is the principal contributor to tide‐surge interaction.
An investigation into the aerosol dispersion effect through the activation process in marine stratus clouds
Authors: Peng Yiran , Lohmann Ulrike , Leaitch Richard , Kulmala Markku
Published: June 2007

The aerosol dispersion effect (the influence of an increasing number of aerosol particles on the width of the cloud droplet size distribution) has been observed in maritime clouds [e.g., Liu and Daum, 2002]. Climate model simulations show that the dispersion effect at least partially compensates the first indirect aerosol effect. The application of observational data from maritime stratus/stratocumulus clouds into an adiabatic parcel model allows to analyze the role of the aerosol activation process for the dispersion effect in order to better understand the microphysical mechanism of the dispersion effect in the early stage of cloud formation. When the total aerosol number concentration is increased, the parcel model simulations show that the higher number of aerosol particles at cloud base reduces the supersaturation, which results in a slower particle growth rate, and thus more cloud droplets remain small. This extends the droplet spectra toward the smaller size end and increases the spectral width. The broadening effect partially offsets the reduction of droplet radius because of an enhanced number of aerosol particles, leading to a positive aerosol dispersion effect. Sensitivity studies show that the dispersion effect decreases for increasing updraft velocities. When the updraft velocity approaches 55 m s−1, the dispersion effect almost vanishes for maritime stratus clouds. Aerosols composed of sulfate or of less soluble organics increase the dispersion effect as compared to sea‐salt aerosols, whereas condensation of gaseous nitric acid on aerosols decreases the dispersion effect in marine stratus clouds.
Surface temperature patterns in complex terrain: Daily variations and long‐term change in the central Sierra Nevada, California
Authors: Lundquist Jessica D. , Cayan Daniel R.
Published: June 2007

A realistic description of how temperatures vary with elevation is crucial for ecosystem studies and for models of basin‐scale snowmelt and spring streamflow. This paper explores surface temperature variability using temperature data from an array of 37 sensors, called the Yosemite network, which traverses both slopes of the Sierra Nevada in the vicinity of Yosemite National Park, California. These data indicate that a simple lapse rate is often a poor description of the spatial temperature structure. Rather, the spatial pattern of temperature over the Yosemite network varies considerably with synoptic conditions. Empirical orthogonal functions (EOFs) were used to identify the dominant spatial temperature patterns and how they vary in time. Temporal variations of these surface temperature patterns were correlated with large‐scale weather conditions, as described by National Centers for Environmental Prediction‐National Center for Atmospheric Research Reanalysis data. Regression equations were used to downscale larger‐scale weather parameters, such as Reanalysis winds and pressure, to the surface temperature structure over the Yosemite network. These relationships demonstrate that strong westerly winds are associated with relatively warmer temperatures on the east slope and cooler temperatures on the west slope of the Sierra, and weaker westerly winds are associated with the opposite pattern. Reanalysis data from 1948 to 2005 indicate weakening westerlies over this time period, a trend leading to relatively cooler temperatures on the east slope over decadal timescales. This trend also appears in long‐term observations and demonstrates the need to consider topographic effects when examining long‐term changes in mountain regions.
ULF electromagnetic noise due to random variations of background atmospheric current and conductivity
Authors: Surkov V. V. , Hayakawa M.
Published: June 2007

A mechanism of ULF electromagnetic noise generation due to random fluctuations of the atmospheric conductivity and background currents was examined. Current fluctuations similar to 1/f noise, or flicker noise, are assumed to develop inside large‐scale atmospheric inhomogeneities such as thunderstorms, hurricanes, mesoscale convective systems, etc. The random current fields are assumed to be steady, uniform, and isotropic inside the inhomogeneity, which, in turn, implies that the spectral density of the process is delta correlated. A correlation radius of the random process is supposed to be dependent on gas transfer and on the acoustic wave propagation due to pressure and temperature gradients in the atmosphere. To relate the electromagnetic spectra with current fields, a transfer matrix was found, and then the correlation matrix and power spectra of the random electromagnetic field were calculated. It was shown that the large‐scale random fluctuations of the atmospheric background current are capable of sustaining generation of the ULF magnetic noise that can be detected on the ground. The spectral index of magnetic noise was found to be 1.5, which is consistent with observation in the 10−2 to 10−4 Hz frequency range.
Local time influence in single‐satellite radio occultation climatologies from Sun‐synchronous and non‐Sun‐synchronous satellites
Authors: Pirscher B. , Foelsche U. , Lackner B. C. , Kirchengast G.
Published: June 2007

The sampling error of Global Positioning System (GPS) radio occultation (RO) derived temperature climatologies is computed over a representative time span of 2 years and compared for Sun‐synchronous and non‐Sun‐synchronous Low Earth Orbit (LEO) satellites. The main focus lies on the sampling error's local time component, which is caused by incomplete sampling of the diurnal cycle and which depends on the geometry of the satellite orbits. The Sun‐synchronous satellite MetOp (Meteorological Operational European weather satellite) and the non‐Sun‐synchronous satellite CHAMP (Challenging Minisatellite Payload), both carrying GPS RO instruments on board, serve as representative cases. For the Sun‐synchronous satellite MetOp the local time component remains constant during the whole observation period such that the magnitude of the local time errors in monthly mean or longer‐term mean RO climatologies is generally lower than ±0.1 K. Except for potential long‐term effects of global warming on the diurnal cycle, which might require calibration, this small local time component is stable on decadal timescales and is mainly positive in the Northern Hemisphere and at low latitudes, whereas it is mainly negative in the Southern Hemisphere. These features are attributable to a slight orbit‐determined asymmetry in local time sampling. The typical (temporally stable) local time error of an annual mean MetOp climatology resolved into 18 zonal bands amounts to ∼0.04 K. For the non‐Sun‐synchronous satellite CHAMP the local time error component in monthly mean RO climatologies is also small (up to about ±0.15 K) but more variable (about zero mean) at middle and high latitudes. At low latitudes it results in sinusoidally varying positive and negative deviations with a several‐months period, resulting from the local time drift of the satellite. The magnitude of local time errors is slightly larger compared to MetOp since the monthly averaging period is too short for CHAMP to entirely sample a diurnal cycle; a longer averaging period further decreases CHAMP's local time component. An annual mean climatology resolved into 18 zonal bands shows for CHAMP a typical local time residual error component of ∼0.03 K. The overall evidence is that even with single RO satellites, monthly climatologies of high accuracy (sampling error <0.3 K) with the local time component being a minor part (<0.1 K to 0.15 K) can be obtained.
Quantification of the factors controlling tropical tropospheric ozone and the South Atlantic maximum
Authors: Sauvage B. , Martin Randall V. , van Donkelaar A. , Ziemke J. R.
Published: June 2007

We quantify the processes controlling the tropical tropospheric ozone burden with particular attention to the tropical Atlantic, using a global chemical transport model (GEOS‐Chem) constrained by satellite and in situ observations of O3, NO2, and HCHO. Lightning is the dominant contributor to tropical tropospheric O3, accounting for more than 37% of the O3 burden over the Atlantic on annual average. The contributions from biomass burning, soils, and fossil fuels are 4 to 6 times smaller, despite comparable source strengths. This discrepancy can be explained by the tropical ozone production efficiency of lightning (32 mol/mol), soils (14 mol/mol), biomass burning (10 mol/mol), and fossil fuel (13 mol/mol) sources, as calculated using sensitivity simulations with a 1% perturbation. The role of volatile organic compound emissions on the tropical Atlantic ozone burden is negligible (<2.5%). Stratosphere‐troposphere exchange accounts for less than 5% of the regional O3 burden. The tropical Atlantic O3 burden is more strongly influenced by nitrogen oxides from Africa (>30%) than from South America (>18%) or the eastern tropics (>11%). Lightning is responsible for more than 39% of the atmospheric oxidation capacity, higher than other sources. The dominant sources of uncertainty in the tropical oxidation rate are the lightning magnitude and the cloud convective parameterization.
Aerosol retrieval over land using a multiband polarimeter and comparison with path radiance method
Authors: Waquet F. , Goloub P. , Deuzé J.‐L. , Léon J.‐F. , Auriol F. , Verwaerde C. , Balois J.‐Y. , François P.
Published: June 2007

This study focuses on the development of a new approach to retrieve aerosol properties over land, based on the use of multispectral polarized measurements (0.67–2.2 μm). We use the measurements of the airborne MICROPOL polarimeter during regional aircraft field experiments located in France and dedicated to the study of aerosol (pollutant and mineral dust particles) and surface properties. We have developed a multiband polarization algorithm (MBP) and compared the retrievals with both a path radiance algorithm and Sun photometer data. It is shown that surface polarized reflectance exhibits only a small spectral variation for forward scattering geometries (3% on average, 15–20% for a single view and scattering angle < 110°). The atmospheric contribution at 2.2 μm is small for aerosol optical thicknesses (AOTs) up to 0.15 at 0.67 μm and can be accounted for in the retrieval of surface properties. The 2.2 μm channel therefore enables us to accurately derive the surface polarization in the shorter MICROPOL bands. For the observations we have made, the surface model developed for the analysis of the Polarization and Directionality of the Earth Reflectance (POLDER) measurements overestimates surface polarization from a few to fifty percents. This leads to AOT underestimation by a factor two. For the pollutant aerosol cases (0.065 < AOT < 0.20), the MBP approach retrieves AOT with an accuracy of 0.03, over both natural and urban surfaces. However, this method remains only weakly sensitive to coarse mode particles and fails when dust particles associated with large AOTs (0.5) are considered.
Spatial and temporal variability of surface mass balance near Talos Dome, East Antarctica
Authors: Frezzotti Massimo , Urbini Stefano , Proposito Marco , Scarchilli Claudio , Gandolfi Stefano
Published: June 2007

Predictions concerning Antarctica's contribution to sea level change have been hampered by poor knowledge of surface mass balance. Snow accumulation is the most direct climate indicator and has important implications for paleoclimatic reconstruction from ice cores. Snow accumulation measurements (stake, core, snow radar) taken along a 500‐km transect crossing Talos Dome (East Antarctica) have been used to assess accumulation signals and the representativeness of ice core records. Stake readings show that accumulation hiatuses can occur at sites with accumulation rates below 120 kg m−2 yr−1. Differences between cores and stakes can lead to statistical misidentification of annual layers determined from seasonal signals at sites with accumulation rates below 200 kg m−2 yr−1 because of nondetection of higher and lower values. Achieving ±10% accuracy in the reconstruction of snow accumulation from single cores requires high accumulation (750 kg m−2 yr−1). Low‐accumulation sites are representative if cumulative rates computed over several years are used to reach the 750 kg m−2 yr−1 threshold. Temporal variability of accumulation over the last two centuries shows no significant increase in accumulation. Wind‐driven processes are a fundamental component of surface mass balance. Spatial variations in accumulation are well correlated with surface slope changes along the wind direction and may exceed 200 kg m−2 yr−1 within 1 km. Wind‐driven sublimation rates are less than 50 kg m−2 yr−1 in plateau areas and up to 260 kg m−2 yr−1 in slope areas and account for 20–75% of precipitation, whereas depositional features are negligible in surface mass balance.
Sun‐to‐thermosphere simulation of the 28–30 October 2003 storm with the Space Weather Modeling Framework
Authors: Tóth Gábor , De Zeeuw Darren L. , Gombosi Tamas I. , Manchester Ward B. , Ridley Aaron J. , Sokolov Igor V. , Roussev Ilia I.
Published: June 2007

In late October and early November 2003 a series of some of the most powerful solar eruptions ever registered shook the heliosphere. These “Halloween storms” damaged 28 satellites, knocking two out of commission, diverted airplane routes, and caused power failures in Sweden, among other problems. This paper presents a 4‐day end‐to‐end simulation of one of the major events (following the X17 flare) that produced the most geoeffective interval of the Halloween storm. The simulation was carried out with the newly developed Space Weather Modeling Framework (SWMF, see http://csem.engin.umich.edu/SWMF) that self‐consistently couples physical domain models spanning from the solar corona to the upper atmosphere. The various attempts and iterations leading to the final simulation are also described. We briefly discuss the technological advances enabling the faster than real‐time operation of the SWMF with the required high resolution. We compare the simulation results with observations from space‐ and ground‐based measurements. We have also performed a reference magnetospheric simulation driven by ACE and Geotail observations and compared its results with the Sun‐to‐thermosphere simulation and the magnetospheric observations. The magnetic structure of the coronal mass ejection (CME) observed at the L1 point on the ACE spacecraft is not correctly reproduced because of the insufficient observations and theoretical understanding of the CME initiation mechanism. On the other hand, we find that the SWMF reasonably well reproduced both the hydrodynamic characteristics of the coronal mass ejection and some of the major indexes characterizing the strength of the geomagnetic storms.