bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term heat flux variability and winter convection in the Adriatic Sea
Authors: Cardin Vanessa , Gačić Miroslav
Published: September 2003

Calculations of the Adriatic heat fluxes have been carried out. The most appropriate expressions were used assuming that the Adriatic Sea on average loses heat, as shown by some previous studies. Interannual variations of the heat fluxes were analyzed for the period 1989–1999 using the European Centre for Medium‐Range Weather Forecasts ERA‐40 Reanalysis data set. One of the most relevant issues resulting from the climatological analysis is the presence of an interannual signal and a significant intra‐annual variability during the whole period considered. Large year‐to‐year changes were evidenced, including a net heat gain in some years like in 1994. Interannual yearly heat flux variations largely depend on winter heat losses. Winter convection and dense water formation in the southern Adriatic are directly linked to winter heat loss, although the extent of the vertical mixing is also dependent on the characteristics of the preconditioning period, more specifically of December. Because of mild winter climatic conditions, in some years, winter convection was shown to be completely absent. Separate analyses of the southern and northern Adriatic heat fluxes were carried out as well to see whether the two subbasin fluxes change independently on an interannual timescale. This is especially important considering that the ventilation of the Southern Adriatic Bottom Water takes place through the combined influence of the Northern Adriatic Dense Water and a local vertical convection.
Nutrient ratios and fluxes hint at overlooked processes in the Mediterranean Sea
Authors: Ribera d'Alcalà M. , Civitarese G. , Conversano F. , Lavezza R.
Published: September 2003

The Mediterranean is a marginal sea displaying a peculiar biogeochemistry (enhanced deep respiration, non Redfieldian nutrient ratios, etc.). Here we discuss the different processes that may contribute to the observed peculiarities, inferred from the analysis of the nutrient data generated mostly during the last decade. Both nitrate to orthophosphate (N:P) and orthosilicate to nitrate (Si:N) ratios display a decreasing east‐west gradient (N:P > 25 and Si:N > 1.3 in the eastern Mediterranean, and N:P ∼ 20 and Si:N ≤ 1.0 in the western Mediterranean). The analysis of the transports at the two main straits (Gibraltar and Sicily) shows that the eastern Mediterranean is likely the site where the biological pump is non Redfieldian, whereas the Si:N > 1.3 in the eastern nutrient deep pool unexpectedly highlights an important role of the diatoms in the vertical export of matter. A quantitative analysis of the nutrient inputs and distributions suggests that the newly formed dense waters and the turbulent mixing transport a significant load of preformed organic and inorganic nitrogen from the surface, with the Levantine Intermediate Water being by far the most important player because of higher fraction of surface water in its mixture. Nutrient ratios and fluxes also suggests that nitrogen fixation, probably carried out by symbionts hosted by diatoms is taking place. The latter are relatively less important in the western than in the eastern basin. Those features may change in the next future if climate change or anthropogenic forcing alter the elemental fluxes at the boundaries.
Predictability and uncertainty in a regional climate model
Authors: Vidale Pier Luigi , Lüthi Daniel , Frei Christoph , Seneviratne Sonia I. , Schär Christoph
Published: September 2003

The evaluation of the quality and usefulness of climate modeling systems is dependent upon an assessment of both the limited predictability of the climate system and the uncertainties stemming from model formulation. In this study a methodology is presented that is suited to assess the performance of a regional climate model (RCM), based on its ability to represent the natural interannual variability on monthly and seasonal timescales. The methodology involves carrying out multiyear ensemble simulations (to assess the predictability bounds within which the model can be evaluated against observations) and multiyear sensitivity experiments using different model formulations (to assess the model uncertainty). As an example application, experiments driven by assimilated lateral boundary conditions and sea surface temperatures from the ECMWF Reanalysis Project (ERA‐15, 1979–1993) were conducted. While the ensemble experiment demonstrates that the predictability of the regional climate varies strongly between different seasons and regions, being weakest during the summer and over continental regions, important sensitivities of the modeling system to parameterization choices are uncovered. In particular, compensating mechanisms related to the long‐term representation of the water cycle are revealed, in which summer dry and hot conditions at the surface, resulting from insufficient evaporation, can persist despite insufficient net solar radiation (a result of unrealistic cloud‐radiative feedbacks).
Thermal evolution of Tethyan surface waters during the Middle‐Late Jurassic: Evidence from δ18O values of marine fish teeth
Authors: Lécuyer Christophe , Picard Stéphanie , Garcia Jean‐Pierre , Sheppard Simon M. F. , Grandjean Patricia , Dromart Gilles
Published: September 2003

Oxygen isotope compositions of phosphate from vertebrate tooth enamel were measured to determine the evolution of tropical sea surface (<∼200 m depth) temperatures in the western Tethys during the Middle‐Late Jurassic. On the basis of a high‐resolution stratigraphic framework with a 1 Myr time resolution, vertebrate teeth were sampled on Aalenian to Portlandian isochrons over the Anglo‐Paris Basin. Asteracanthus sharks and Pycnodontidae teleosteans, identified as sea surface dwellers, have enamel with δ18O values that range from 18.5 to 22.3‰. Thermal variations of tropical surface waters, with amplitudes of a few degrees per few million years, suggest that Middle to Late Jurassic climates were quite variable. Assuming a seawater δ18O value of 0‰ for surface tropical waters in the absence of polar ice caps, temperatures increased from 25 to 29°C from the mid‐Bajocian to mid‐Bathonian. During the middle to late Bathonian, a strong geographic zonation in isotopic compositions is observed between the eastern and western parts of the basin. High δ18O values of fish tooth enamel (up to 22.3‰) could reflect the arrival of a cold water current from the Arctic during the opening of the North Sea rift. An apparent large drop of temperatures from 28 to 21°C is identified at the Callovian‐Oxfordian boundary over no more than ≈2–3 Myr. This cooling is compatible with previous paleobotanical and geochemical studies and can be precisely correlated with the migration of boreal ammonites into the Tethyan domain. Because isotopic sea surface temperatures are probably too low to be compatible with tropical climatic conditions, the δ18O value of seawater could have been >0‰ owing to limited growth of continental ice during the early middle Oxfordian. The resulting sea level fall is estimated to be at least 50 m and is compatible with a global regression stage. The middle Oxfordian thermal minimum is followed by a new warming stage of 3–4°C from the middle to the late Oxfordian.
Tectonic Evolution of the Bristol Bay basin, southeast Bering Sea: Constraints from seismic reflection and potential field data
Authors: Walker Kristoffer T. , McGeary Susan E. , Klemperer Simon L.
Published: September 2003

We interpret the tectonic evolution of the Bristol Bay basin, also known as the North Aleutian basin, on the basis of a deep seismic reflection profile, lithologic data from a well, unreversed seismic refraction profiles, a bathymetry profile, a magnetics profile, forward modeling of a gravity profile, and flexural modeling of a basin‐wide paleosurface. We present evidence that (1) an early or middle Eocene through late Miocene phase of extension led to fault‐controlled subsidence; (2) a late Eocene through early Miocene phase of volcanic‐arc loading led to flexural subsidence, which was amplified by additional factors possibly including lithospheric cooling, tectonic compression, reverse or thrust faulting, or small‐scale intrusions of dense magma; and (3) a late Miocene through Holocene resurgence of arc volcanism and a northward prograding delta continued (or possibly increased) flexural subsidence in the back arc region. Our interpretations imply that the fault‐controlled subsidence in the Bristol Bay basin is genetically linked to that found in the other outer Bering Shelf basins, but the subsequent flexural subsidence of these basins is not related. More fundamentally, our observations suggest that the basin's evolution is unusual and has components typically found in both back arc (extension) and retroarc foreland (flexure) basins.
Flow and transport in highly heterogeneous formations: 1. Conceptual framework and validity of first‐order approximations
Authors: Dagan G. , Fiori A. , Janković I.
Published: September 2003

Flow of uniform mean velocity U takes place in a formation of spatially variable, random conductivity K(x). Advective transport of a plume of an inert solute is investigated by the Lagrangean approach. The aim of the study is to determine the spatial moments of the plume, i.e., of fluid particle trajectories, for highly heterogeneous aquifers, for which σY > 1, where Y = ln K. A multi‐indicator model of the permeability structure, which is different from the common multi‐Gaussian one, is proposed: the formation is modeled as a collection of N blocks of different K(j). The structure is defined by the distribution of K(j), the blocks' shape, and the coordinates of their centroids. The following simplifications are adopted: the blocks are inclusions of a regular shape (circles, spheres for isotropic media investigated here) defined by the radius A, and the inclusions are not overlapping, and their centroids are distributed uniformly and independently in space. At the continuous limit the model is characterized by the joint pdf f(Y, A). The model is shown to be quite general and to comprise binary, bimodal, indicator variograms and unimodal distributions of Y as particular cases. The study is focused on the latter case, with Y normal N [〈Y〉, σY2] and stationary covariance of given integral scale IY; these are the parameters commonly estimated for sedimentary formations. This leaves still freedom in selecting the pdf f(A). The simple model selected for semianalytical and numerical analysis is that of inclusions of radius R and volume fraction n, submerged in a matrix of effective conductivity Kef. The latter represents the effect of inclusions of much smaller radius, which appear as a nugget in the log conductivity two‐point covariance. An approximate analytical solution of the flow is obtained by using a self‐consistent approximation, while a fully numerical one is derived in part 3 [Janković et al., 2003a]. Transport is solved by particle tracking, and the time‐dependent spatial moments (trajectories variance, skewness, kurtosis) are presented in part 2 [Fiori et al., 2003]. In the self‐consistent approximation the asymptotic longitudinal macrodispersivity αL, which is a function of Y, shows strong nonlinear effects: inclusions of large positive Y lead to a finite αL, whereas αL grows unbounded for those of negative Y. This effect is not captured by the common first‐order approximation in σY, which is symmetrical and overestimates αL for Y > 0 and underestimates it for Y < 0. As a result, the second spatial moment is predicted accurately by the first‐order approximation, by cancellation of errors, provided that f(Y) is symmetrical. However, the transient regime and higher‐order moments are not captured by the first‐order approximation.
Contribution of soil respiration in tropical, temperate, and boreal forests to the 18O enrichment of atmospheric O2
Authors: Angert Alon , Barkan Eugeni , Barnett Bruce , Brugnoli Enrico , Davidson Eric A. , Fessenden Julianna , Maneepong Somsak , Panapitukkul Nipa , Randerson James T. , Savage Kathleen , Yakir Dan , Luz Boaz
Published: September 2003

The 18O content of atmospheric O2 is an important tracer for past changes in the biosphere. Its quantitative use depends on knowledge of the discrimination against 18O associated with the various O2 consumption processes. Here we evaluated, for the first time, the in situ 18O discrimination associated with soil respiration in natural ecosystems. The discrimination was estimated from the measured [O2] and δ18O of O2 in the soil‐air. The discriminations that were found are 10.1 ± 1.5‰, 17.8 ± 1.0‰, and 22.5 ± 3.6‰, for tropical, temperate, and boreal forests, respectively, 17.9 ± 2.5‰ for Mediterranean woodland, and 15.4 ± 1.6‰ for tropical shrub land. Current understanding of the isotopic composition of atmospheric O2 is based on the assumption that the magnitude of the fractionation in soil respiration is identical to that of dark respiration through the cytochrome pathway alone (∼18‰). The discrimination we found in the tropical sites is significantly lower, and is explained by slow diffusion in soil aggregates and root tissues that limits the O2 concentration in the consumption sites. The high discrimination in the boreal sites may be the result of high engagement of the alternative oxidase pathway (AOX), which has high discrimination associated with it (∼27‰). The intermediate discrimination (∼18‰) in the temperate and Mediterranean sites can be explained by the opposing effects of AOX and diffusion limitation that cancel out. Since soil respiration is a major component of the global oxygen uptake, the contribution of large variations in the discrimination, observed here, to the global Dole Effect should be considered in global scale studies.
Extension along the Australian‐Pacific transpressional transform plate boundary near Macquarie Island
Authors: Daczko Nathan R. , Wertz Karah L. , Mosher Sharon , Coffin Millard F. , Meckel Tip A.
Published: September 2003

The Australian‐Pacific transform plate boundary fault zone along the Macquarie and McDougall segments of the Macquarie Ridge Complex (MRC), south of New Zealand, is characterized by dominantly normal faults and pull‐apart basins, in apparent conflict with the regional transpressional tectonic setting. We propose that present‐day curvature of the transform is inherited from a preexisting divergent plate boundary and that the overall extensional kinematics shown by faults along the main plate boundary trace and exposed on Macquarie Island result from local stresses related to right‐lateral, right stepping, en echelon plate boundary faults and not to the current transpressional setting. Transpression along the Australian‐Pacific transform plate boundary has resulted in uplift along the ∼1500 km long Macquarie Ridge Complex. Macquarie Island, the only subaerial exposure of the complex, sits atop a ∼5 km high, ∼50 km wide submarine ridge of oceanic crust and lies ∼4.5 km east of the major active plate boundary fault zone. Thus Macquarie Island and the surrounding seafloor provide a unique opportunity to study an active oceanic transform fault using complementary marine geophysical and land‐based geological data. Mapping of recent faults affecting the topography of Macquarie Island shows that the island is extensively cut by high‐angle normal faults forming pull‐apart basins. Furthermore, evidence for reverse motion is rare. Using marine geophysical data, including swath bathymetry, reflectivity, and seismic reflection data, collected along the Australian‐Pacific plate boundary north and south of the island, we have defined a 5–15 km wide plate boundary zone. A series of right stepping en echelon faults, within this zone, lies along the main plate boundary trace. At the right stepping fault terminations, elongate depressions (≤10 km wide and 1.2 km deep) parallel the plate boundary, which we interpret as extensional relay zones or pull‐apart basins. We propose that transpression is partitioned into en echelon strike‐slip faults at the plate boundary and a convergent component that flexes the crust, causing the anomalous bathymetric ridge and trough morphology of the McDougall and Macquarie segments of the MRC.
Genovesa Submarine Ridge: A manifestation of plume‐ridge interaction in the northern Galápagos Islands
Authors: Harpp Karen S. , Fornari Daniel J. , Geist Dennis J. , Kurz Mark D.
Published: September 2003

Despite its circular coastline and calderas, Genovesa Island, located between the central Galapagos Platform and the Galapagos Spreading Center, is crosscut by both eruptive and noneruptive fissures trending NE‐SW. The 075° bearing of the fissures parallels that of Genovesa Ridge, a 55 km long volcanic rift zone that is the most prominent submarine rift in the Galapagos and constitutes the majority of the volume of the Genovesa magmatic complex. Genovesa Ridge was the focus of detailed multibeam and side‐scan sonar surveys during the Revelle/Drift04 cruise in 2001. The ridge consists of three left stepping en echelon segments; the abundances of lava flows, volcanic terraces, and eruptive cones are all consistent with constructive volcanic processes. The nonlinear arrangement of eruptive vents and the ridge's en echelon structure indicate that it did not form over a single dike. Major and trace element compositions of Genovesa Ridge glasses are modeled by fractional crystallization along the same liquid line of descent as the island lavas, but some of the glasses exhibit higher Mg # than material sampled from the island. Most of the submarine and the subaerial lavas have accumulated plagioclase. Incompatible trace element abundances of dredged Genovesa Ridge rocks are lower than the island's lavas, but ratios of the elements are similar in the two settings, which suggests that the island and ridge lavas are derived from nearly identical mantle sources. Glass inclusions in plagioclase phenocrysts from the ridge are compositionally diverse, with both higher and lower MgO than the matrix glass, indicative of homogenization at shallow levels. The structural and geochemical observations are best reconciled if Genovesa Ridge did not form in response to injection of magma laterally from a hot spot‐supplied central volcano, like Kilauea's Puna Ridge. Instead, Genovesa Ridge and its western extension are the result of passive upwelling directed by far‐field tectonic stresses that are generated by tension across the 91°W transform. The proximity of the plume causes magmatism in the extensional zones where it would not ordinarily occur.
Propagation of energetic particles in the high‐latitude high‐speed solar wind
Authors: Sanderson T. R. , Marsden R. G. , Tranquille C. , Dalla S. , Forsyth R. J. , Gosling J. T. , McKibben R. B.
Published: September 2003

We present observations of energetic particles in the energy range ∼1 MeV to ∼100 MeV made by the COSPIN instrument on board the Ulysses spacecraft during the recent second northern polar pass. For a short time during this pass the Ulysses spacecraft was at high heliographic latitude, above the current sheet, and immersed in high‐speed solar‐wind flow coming from the northern polar coronal hole. Four large solar energetic particle events were observed. For the first two or three days of each event, the spacecraft was in a homogeneous region devoid of any structures. We discuss the rise to maximum of these events. We examine the onset time and the anisotropy of the energetic particles. We find that during these events the particle angular distributions were almost isotropic, but with a net outward flow along the magnetic field lines. We conclude that particles reached these high latitudes traveling along the magnetic field lines. We do not find any evidence for cross field diffusion at Ulysses.
Venus: Estimation of age of impact craters on the basis of degree of preservation of associated radar‐dark deposits
Authors: Basilevsky A. T. , Head J. W. , Setyaeva I. V.
Published: September 2003

Venus impact craters larger than 5 km in diameter (∼90% of all craters) have been classified based on the presence and prominence of associated radar‐dark deposits. Approximate estimates of the absolute age of craters of different morphologic classes are made. Analysis of age relations of dated craters and volcanic and tectonic structures permits the estimation of the age and duration of different volcanic and tectonic events.
On the termination of the 2002–03 El Niño event
Authors: Vecchi Gabriel A. , Harrison D. E.
Published: September 2003

Every new El Niño presents an opportunity to revisit our understanding of El Niño characteristics and processes. We examine the extent to which the termination of the 2002–03 El Niño followed the scenario of Harrison and Vecchi [1999], in which (1) there is a late‐year southward shift of near‐equatorial westerly wind anomalies, and (2) subsequent eastern equatorial Pacific cold tongue thermocline shallowing is driven by the wind shift. There was a prominent late‐year southward shift in the low‐frequency west Pacific zonal wind anomalies in 2002–03. Ocean general circulation model experiments establish the shift as the primary cause of cold tongue thermocline shallowing. Reflected equatorial waves and local wind anomaly changes are much less important. Successful theories and models of El Niño should address the processes that cause the year‐end southward wind shift. Interactions between anomalous El Niño conditions and the seasonal cycle of solar insolation may provide such a process.
Comparison of a large‐scale inertia‐gravity wave as seen in the ECMWF analyses and from radiosondes
Authors: Plougonven R. , Teitelbaum H.
Published: September 2003

The location, characteristics and evolution of a large‐scale inertia‐gravity wave that occurred in the lower stratosphere over the North of the British Isles on February 6, 1997, are studied. Numerous high‐resolution radiosondes were available at that time and in that region as part of the FASTEX database. They reveal an intense, large‐scale inertia‐gravity wave (IGW), propagating upwards above the tropopause. Maps of the divergence of the horizontal wind, on isentropic surfaces, were obtained from the ECMWF analyses, and showed a clear pattern of alternating bands of convergence and divergence, at the lower stratospheric heights, in the same geographical region and starting at the same time. The comparison of the characteristics of this IGW in the analyses and in the observations suggests that the ECMWF analyses can be used for qualitative indications regarding the locations most favorable to large‐scale IGW generation and the corresponding orientation of the waves.
The asymmetric reflectivity effect on the LAGEOS satellites and the germanium retroreflectors
Authors: Lucchesi David M.
Published: September 2003

We propose a new mechanism to explain the physical cause of the empirical asymmetric reflectivity effect observed for the LAGEOS satellites. To reach this result we have modelled the reflection of the Sun's visible light from the four Germanium Cube Corner Retroreflectors of these laser‐ranged satellites. The position of the cubes play a crucial role in defining the characteristics of the effect and its impact in the satellites orbit. We analyzed the long‐term effects of the perturbation in the satellites eccentricity vector excitations and in their perigee rate. With the new model we have been able to reproduce the time evolution of LAGEOS eccentricity vector excitations and perigee rate as due to the empirical effect. In the case of LAGEOS II, the asymmetric reflectivity effect needs to be modelled with an analytical expression different from that for LAGEOS.
Aircraft icing at low temperatures in Tropical Storm Chantal (2001)
Authors: Herman Robert L. , Heymsfield Andrew J.
Published: September 2003

Recent in situ measurements of water vapor, meteorological properties, and cloud particles provide evidence for large slushy ice particles at −40°C in an intense tropical updraft. During a flight through Tropical Storm Chantal (20 Aug. 2001), the NASA DC‐8 aircraft encountered strong convection, high humidities, high particle concentrations, and plugged probe inlets. This paper addresses the question of whether these observations can be explained with our current understanding of cloud microphysical processes. The microphysical evolution of particles in the updraft is simulated with a model to demonstrate that millimeter‐sized slushy ice particles can exist at environmental temperatures below the ice homogeneous nucleation temperature. Supercooled liquid droplets are inferred to exist at higher temperatures in the updraft, below the DC‐8 altitude.
Late Summer chlorophyll blooms in the oligotrophic North Pacific Subtropical Gyre
Authors: Wilson Cara
Published: September 2003

In the late summer of 1997, 1999, and 2000 satellite observations of surface chlorophyll from SeaWiFS recorded large blooms in the oligotrophic North Pacific Subtropical Gyre (NPSG) near 30°N and between 130–160°W. The largest blooms covered more than 350,000 km2 and lasted as long as 4 months. They are distinct from the surface seasonal cycle of chlorophyll in both timing and amplitude. The blooms are not associated with either SSH or SST anomalies indicative of changes in subsurface structure, nor do they appear to be forced by nutrient fertilization from dust deposition or rainfall. These blooms are compared with summer blooms that have been previously observed in this region by in situ studies, and some potential causes for them are discussed.
Ionospheric remote sensing of the Denali Earthquake Rayleigh surface waves
Authors: Ducic Vesna , Artru Juliette , Lognonné Philippe
Published: September 2003

Using the Global Positioning System, we have detected ionospheric disturbances associated with the long‐period Rayleigh waves from the 2002 Denali earthquake (Ms = 7.9). The dense California GPS networks allowed us to map the ionospheric perturbations and to compute the group velocity with a high spatial resolution above the Pacific coasts. Due to a low sampling rate, a large error in the velocity determination remains. Nonetheless, it demonstrates that bi‐static remote sensing measurements of seismic waves with GPS networks can be performed. Monostatic measurements with a dedicated satellite could possibly be used to record in the ionosphere surface waves originating from large earthquakes. Such a space‐based remote sensing of the local group velocity of Rayleigh surface waves would effectively complement the seismic networks for high‐resolution global tomography of the Earth's lithosphere.
The 30–60 day intraseasonal oscillation over the western North Pacific Ocean and its impacts on summer flooding in China during 1998
Authors: Zhu Congwen , Nakazawa Tetsuo , Li Jianping , Chen Longxun
Published: September 2003

Eastern China experienced a series of severe floods during the summer of 1998. These floods are shown to be consistent with the propagation and activity of the 30–60 day intraseasonal oscillation (ISO) over the western North Pacific (WNP), where the monsoon trough and the subtropical anti‐cyclone appear as an anti‐clockwise propagation with the enhanced and suppressed convective anomalies in a 30–60 day period. The Meiyu circulation pattern in the lower atmosphere successively dominates the WNP, which results in southern China and the Yangtze River valley suffering much more rainfall and floods than normal. There are remarkable signals of 30–60‐day ISO in convective anomalies over the Bay of Bengal and east of Philippine Sea. During the cycle of the 30–60 day ISO, these convective anomalies move towards the South China Sea (SCS), where they affect the convective activity of the SCS summer monsoon, therefore maintaining the cycle of 30–60 day ISO over the WNP.
A fresh perspective of the substorm current system and its dynamo
Authors: Lui A. T. Y. , Kamide Y.
Published: September 2003

The common view for the substorm current system is a current wedge involving principally an azimuthal current system. We first evaluate briefly previous studies that provide strong evidence for the dominance of a meridional current system (MCS) in substorms. Based on these clues, we propose the dynamo for the MCS to be a kinetic current disruption process such that dipolarization is achieved by magnetic field line slippage, thus producing the dynamo action of a tailward directed current with an earthward directed electric field. The total current strength is estimated to be ∼10 MA for an average substorm size, consistent with that obtained from the KRM algorithm.
An evaluation of cloud affected UV radiation from polar orbiting and geostationary satellites at high latitudes
Authors: Meerkötter Ralf , Verdebout Jean , Bugliaro Luca , Edvardsen Kare , Hansen Georg
Published: September 2003

For the first time two satellite‐derived decadal scale climatologies of UV daily doses that are based on independently developed methods have been intercompared and compared to surface measurements. The methods mainly differ in the use of data from different instruments for probing the cloud fields (i.e. the AVHRR instrument aboard the polar orbiting NOAA satellites and the MVIRI instrument aboard the geostationary Meteosat satellite). This study focuses at the high latitudes close to 70°N (Northern Norway), a region initially expected as particularly problematic for geostationary satellites. However, an intercomparison of satellite derived UV‐A, UV‐B, and CIE daily doses for March, April, May, and July in the period from 1990 to 2001 gives correlation coefficients ranging from 0.91 to 0.97 depending on the area of averaging. A comparison of satellite derived CIE daily doses to surface measurements provides correlation coefficients in the order of 0.93.
Variability in geyser eruptive timing and its causes: Yellowstone National Park
Authors: Rojstaczer Stuart , Galloway D. L. , Ingebritsen S. E. , Rubin D. M.
Published: September 2003

Field data from Upper Geyser Basin, Yellowstone, indicate that geyser frequency is less sensitive to elastic deformation than might be surmised from a review of the literature. Earth‐tide influences are not identifiable in any of the geysers we monitored. Though atmospheric‐pressure influences are observed, only long‐period variations on the order of 5 mBars or greater seem to influence geyser frequency. Long‐distance interconnections between geysers are common and add to the difficulty of identifying strain influences. Additional variations in geyser periodicity may be governed by the internal dynamics of the geysers rather than external influences.
Hybrid simulations of the magnetosheath compression: Marginal stability path
Authors: Hellinger Petr , Trávníček Pavel , Mangeney André , Grappin Roland
Published: September 2003

This paper reports a two‐dimensional hybrid simulation study which utilizes an expanding box model to represent the slow compression of the plasma as it flows through the magnetosheath. In the code we model the compression as an external force: The physical sizes of the simulation box decrease with time. We present results of a simulation which starts in a parameter region of low beta where the plasma is stable with respect to both the Alfvén ion cyclotron (AIC) and mirror instabilities. In this stable region the plasma behaves double‐adiabatically and an important proton temperature anisotropy appears. When the plasma becomes unstable to AIC instability, the adiabatic behavior is broken and the AIC waves keep the system close to marginal stability, the theoretical growth rate being about constant, small and positive. The AIC waves are continuously generated and the proton parallel beta increases with time. This marginal stability behavior is slightly disrupted for high proton parallel beta, where the mirror mode becomes unstable. The mirror waves rapidly grow and coexist with AIC wave, in later times the growth of AIC waves is inhibited and mirror waves become dominant. During the stages dominated by AIC and mirror waves, anticorrelation between anisotropy and proton parallel beta is observed. The hybrid expanding box simulation directly verifies the marginal stability evolution of the magnetosheath plasma.
Impact of microorganisms on unsaturated flow at fracture intersections
Authors: Stoner Daphne L. , Stedtfeld Robert D. , Tyler Tina L. , White Fred J. , McJunkin Timothy R. , LaViolette Randall A.
Published: September 2003

An experiment is described in which a groundwater bacterium, Sphingomonas sp., influenced the dynamics of unsaturated flow at a fracture intersection. A washed cell suspension increased by three‐fold the length of time that water pooled at the fracture intersection. On the other hand, the addition of growth substrates resulted in cell growth and the conversion from intermittent to continuous flow behavior at the fracture intersection. The results suggest that microbial properties and processes need to be included with other important variables for understanding unsaturated flow in fractured geomatrices.
Hydraulic transience and the role of bedding fractures in a bedrock aquitard, southeastern Wisconsin, USA
Authors: Eaton Timothy T. , Bradbury Kenneth R.
Published: September 2003

Hydraulic heads in a dolomitic shale bedrock aquitard in Wisconsin, USA, are apparently not in equilibrium with drawdown in the underlying aquifer system caused by pumping for municipal supply over the last century. Measurements of head with depth, downhole geophysical logs, and estimates of hydraulic conductivity indicate very low vertical hydraulic diffusivity, and show that high horizontal permeability within the aquitard due to bedding‐plane fracture zones can allow lateral groundwater flow. Unlike the hydrogeological conceptual models used in many investigations, flow in aquitards cannot always be inferred to be primarily one‐dimensional and vertical. Failure to account for transient conditions and lateral flow in similar settings of intensive groundwater pumping could lead to error in estimates of aquitard leakage and underlying aquifer properties.
Cambrian explosion triggered by geosphere‐biosphere feedbacks
Authors: von Bloh Werner , Bounama Christine , Franck Siegfried
Published: September 2003

A new hypothesis for the cause of the Cambrian explosion is presented. For that the evolution of the planet Earth is described by the co‐evolution of the geosphere‐biosphere system. Here we specify our previously published Earth system model for the long‐term carbon cycle by introducing three different types of biosphere: procaryotes, eucaryotes, and complex multicellular life. They are characterized by different global temperature tolerance windows. The biotic enhancement of silicate weathering by complex multicellular life adds an additional feedback to the system and triggers the Cambrian explosion. The Cambrian explosion is characterized by a sudden increase of biomass and a rapid cooling, which amplified the spread of complex multicellular life. Cooling events in the Neoproterozoic, however, could force a premature appearance of complex multicellular life.
Simulation study of mid‐latitude ionosphere fluctuations observed at Millstone Hill
Authors: Huba J. D. , Joyce G. , Fedder J. A.
Published: September 2003

Quasi‐periodic variations in ionospheric F‐region parameters associated with interplanetary magnetic field fluctuations have been reported by Huang et al. [2002]. Two mechanisms that could generate these ionospheric fluctuations are a time‐varying electric field or neutral wind. We present simulation results of the response of the mid‐latitude F‐region ionosphere to these drivers using the NRL ionosphere model SAMI2. We obtain good agreement with Millstone Hill density and velocity observations for a zonal F‐region electric field E ≃ ±2.4 mV/m. We also obtain good agreement with density observations if the neutral wind fluctuates ∼±40 m/s along the geomagnetic field. However, this neutral wind variation corresponds to ∼±140 m/s in the meridional component of the horizontal neutral wind, and the fluctuating ion velocity is ∼30% larger than those observed. This suggests that a fluctuating penetration electric field is probably responsible for the Millstone Hill observations.
Geostatistical evaluation of permeability in an active fault zone
Authors: Fairley Jerry , Heffner James , Hinds Jennifer
Published: September 2003

This study presents a description of permeability in an active fault zone located in the Great Basin extensional province. The fault hydraulic structure is inferred from geostatistical analysis of temperatures in 143 geothermal springs, located along a fault trace in the Alvord Basin of southeast Oregon. Based on this analysis, we conclude that the fault zone is predominately low permeability, interspersed with relatively few, spatially‐discrete, high‐permeability channels. The conceptual model presented is in agreement with the findings of other investigators, but extends their work by offering a representation of fault properties at the tens to hundreds of meters scale.
Seasonal discharge of estuarine freshwater to the western Chukchi Sea shelf identified in stable isotope profiles of mollusk shells
Authors: Khim Boo‐Keun , Krantz David E. , Cooper Lee W. , Grebmeier Jacqueline M.
Published: September 2003

Oxygen and carbon isotope profiles of bivalve mollusks (Serripes groenlandicus and Macoma calcarea) record distinct changes of water mass properties in the Bering Strait region associated with the seasonal discharge of estuarine freshwater from Kolyuchin Bay into the western Chukchi Sea. Cycles in the δ18O profiles are correlated with shell growth bands and interpreted as annual; maximum δ18O values corresponding to coldest water temperatures coincide with dark internal bands in the shell that mark slower growth during winter. A 0.5 ‰ offset between the baseline winter δ18O values of two specimens (HX68 and HX65), at different distances from the estuarine discharge, is attributed to a difference in seawater δ18O between the two sites and indicates that the influence of the estuarine water persists through much of the year. The isotope profiles of specimen AK55, collected north of Bering Strait in the Chukchi Sea, reflect the Bering Shelf‐Anadyr Water flowing from south of Bering Strait. Comparison of the δ13C profiles shows that HX68, collected closer to Kolyuchin Bay, has high‐amplitude negative δ13C excursions associated with incorporation of dissolved inorganic carbon that is isotopically depleted in 13C, probably from terrestrial runoff. The significant positive correlation between δ18O and δ13C values in these specimens suggests that the properties of the ambient water masses are reflected in the stable isotope profiles. These results show that the stable isotope profiles of mollusk shells can serve as proxy indicators of water mass properties, particularly during runoff events in Arctic coastal regions that are logistically difficult to sample directly.
The Ka‘ storm (November 2000): Imaging precipitable water using GPS
Authors: Foster James , Bevis Michael , Chen Yi‐Leng , Businger Steven , Zhang Yongxin
Published: September 2003

We use a network of GPS receivers on the Big Island of Hawaii to examine in detail the precipitable water field of the Ka‘ storm, which generated record rainfall and flash floods over much of the southern and eastern portions of the island. With GPS stations distributed from sea level to the highest points on the island, the spatial and temporal variations in precipitable water as the storm passed over the network are investigated. The results highlight the role of the topography in controlling the location of convection, revealing relatively static zones of high precipitable water where onshore winds and terrain anchor the storm. Using the observed correlation between the precipitable water and rainfall, estimates of rainfall based on the GPS data are generated. These estimates compare well with most of the high‐rainfall sites but tend to overestimate rainfall for the low‐rainfall areas. Rainfall predictions from a mesoscale spectral model of the storm consistently underestimate the observed heavy values. Comparison with the GPS, however, suggests that this underestimate is probably due to a correlated underestimate of precipitable water, indicating that significant improvements in predictions could be expected if the precipitable water field can be better constrained.
Number size distributions and concentrations of the continental summer aerosols in Queen Maud Land, Antarctica
Authors: Koponen Ismo K. , Virkkula Aki , Hillamo Risto , Kerminen Veli‐Matti , Kulmala Markku
Published: September 2003

Total particle number concentrations and particle size distributions in the diameter range 3–800 nm were measured in continental Antarctica during the austral summers 2000 and 2001. Observed total particle number concentrations varied between about 200 and 2000 cm−3, with on average higher concentrations in marine/coastal air masses than in continental air masses. Concentrations in excess of about 300–400 cm−3 were attributable to the presence of small (<20 nm) nucleation mode particles. Measured size distributions were fitted with two to four lognormal modes. All the spectra displayed an accumulation mode peaking at about 70–150 nm and an Aitken mode peaking at about 30–50 nm. The average mean diameter of the accumulation mode was much lower in continental air masses, whereas that of the Aitken mode was almost the same for the two air mass types. A nucleation mode was present in more than a half of the measured spectra, and occasionally two nucleation modes could be identified. Evidence on recent new particle formation with subsequent particle growth up to about 40 nm was observed in marine/coastal air masses only. Our measurements indicate that these recently formed particles contribute significantly to the overall particle budget of the Antarctic boundary layer, and they can be also a source of climatically important Aitken and accumulation mode particles.
Frequency of HLA class 1 and 2 alleles in Brazilian patients with AIDS and cytomegalovirus retinitis
Authors: De Lourdes Veronese Rodrigues Maria , De Castro Figueiredo José Fernando , Deghaide Neifi Hassan Saloum , Romão Erasmo , De Souza Nivaldo Vieira , Donadi Eduardo Antonio
Published: September 2003

Purpose:  To evaluate the human leucocyte antigen (HLA) class 1 (HLA‐A and HLA‐B) and HLA class 2 (HLA‐DRB1 and HLA‐DQB1) allele profiles in the susceptibility to cytomegalovirus retinitis (CMV‐R) in patients with AIDS.

Methods:  Cytomegalovirus retinitis was clinically diagnosed by indirect binocular ophthalmoscopy. Human leucocyte antigens class 1 were typed using a complement‐dependent microlymphocytotoxicity assay, and HLA class 2 alleles were identified using amplified DNA hybridized to sequence‐specific oligonucleotide primers.

Results:  The frequencies of HLA class 1 antigens and HLA class 2 alleles observed in patients and controls were similar; however, HLA‐A31 antigen was over‐represented in patients with AIDS, independent of the presence of CMV‐R.

Conclusion:  There was no association between HLA molecules/alleles and CMV‐R in Brazilian patients with AIDS. However, the results support the role of the HLA system in the susceptibility to developing AIDS.
Regulation of bovine corneal endothelial cell cycle by transforming growth factor‐β
Authors: Motegi Yutaka , Usui Tomohiro , Ishida Kouichi , Kato Satoshi , Yamashita Hidetoshi
Published: September 2003

Purpose:  The transforming growth factor‐β (TGF‐β) family includes three multifunctional proteins, TGF‐β1, TGF‐β2 and TGF‐β3, expressed in ocular tissue, which are involved in regulating cell differentiation, cell proliferation and other cell functions. TGF‐β is present in aqueous humour and regulates corneal endothelial cells. This study explores the mechanism by which TGF‐β regulates the cell cycle in cultured corneal endothelial cells.

Methods:  The expression of specific receptors for the TGF‐β family was investigated at the protein level by affinity cross‐linking with radio‐iodinated TGF‐β1 and immunoprecipitation with specific antibodies to TGF‐β receptors. Regulation of entry into the S‐phase of the cell cycle was determined by 5‐bromo‐2′ deoxyuridine (BrdU) incorporation into the cells. The signal transduction pathways were investigated using various blocking agents for protein kinase transducers involved in intracytoplasmic signal transduction.

Results:  Cultured bovine corneal endothelial cells were confirmed to express TGF‐β type 1 and type 2 receptors and endoglin. In the confluent state, TGF‐β1 and TGF‐β2 stimulated the cells to progress to the S‐phase of the cell cycle through platelet‐derived growth factor‐B (PDGF‐B) chain production and protein kinase C.

Conclusions:  TGF‐β accelerated cell cycle progression from the G0/G1 phase to the S‐phase in cultured corneal endothelial cells, under our experimental conditions, through pathways involving protein kinase C. These pathways are related to the cross‐talk between TGF‐β and other cytokines. The conditions employed in the present experiments may be useful for investigating the complex cross‐talk between various cytokines and growth factors.
Chronic angle closure glaucoma secondary to frail zonular fibres and spherophakia
Authors: Asaoka Ryo , Kato Masaru , Suami Masahiro , Usami Yoshimasa , Hotta Yoshihiro , Sato Miho
Published: September 2003

Purpose:  We describe a 39‐year‐old Japanese woman with chronic angle closure glaucoma secondary to spherophakia and frail zonular fibres. The patient was 143 cm in height with short fingers and had no family history of eye problems. High intraocular pressure, total optic disc cupping and severe visual field constriction were found in the right eye.

Methods:  The patient was treated successfully with trabeculectomy in the right eye and laser iridotomy in the left eye.

Conclusion:  The clinical findings imply that this was a borderline case of Weil–Marchesani syndrome.
Contact versus peribulbar anaesthesia in trabeculectomy: a prospective randomized clinical study
Authors: Pablo Luis E. , Pérez‐Oliván Susana , Ferreras Antonio , Polo Vicente , Gómez Maria Luisa , Honrubia Francisco M.
Published: September 2003

Purpose:  To compare the pre‐, intra‐ and postoperative pain scores and complication rates in trabeculectomy under contact‐topical anaesthesia versus peribulbar injection anaesthesia.

Methods:  A total of 100 patients selected to undergo primary trabeculectomy were randomly allocated to receive either contact or peribulbar anaesthesia. Patients were asked to rate their pain levels on a 5‐point scale for four periods: during the administration of the anaesthetic agent, during surgery, immediately after surgery and 24 hours postoperatively. At the same time, the surgeon was asked to record his subjective assessment of the stress he himself had suffered during the course of the intervention. Surgical parameters, intra‐ and early postoperative complications were also evaluated.

Results:  The difference between groups was statistically significant during anaesthetic administration. Six patients who received contact‐topical anaesthesia reported mild discomfort during delivery of the anaesthetic agent, while 43 patients complained of mild to severe pain during the injection of bupivacaine (p < 0.001). Thirty‐two patients in the contact anaesthesia group and 26 in the injected anaesthesia group reported no pain during surgery (p = 0.127). Only one patient in each group reported mild pain 30 min postoperatively. We found no differences between pain rates after surgery. Complications included prolonged chemosis and we also noted that conjunctival haemorrhage occurred more frequently in the peribulbar group than in the contact anaesthesia group (p = 0.012).

Conclusion:  Both anaesthetic methods provided high levels of pain control without additional sedation during surgery. The use of contact‐topical anaesthesia reduces both pain and the possibility of complications during the administration of anaesthetics.