bluuebunny/crossref_metadata_2025 huggingface dataset:
Crustal structure of the Borderland‐Continent Transition Zone of southern California adjacent to Los Angeles
Authors: Nazareth Julie J. , Clayton Robert W.
Published: August 2003

We use data from the onshore‐offshore component of Los Angeles Region Seismic Experiment (LARSE) to model the broad‐scale features of the midcrust to upper mantle beneath a north‐south transect that spans the continental borderland in the Los Angeles, California, region. We have developed an analysis method for wide‐angle seismic data that consists primarily of refractions, lacks near‐offset recordings, and contains wide gaps in coverage. Although the data restrict the analysis to the modeling of broad‐scale structure, the technique allows one to explore the limits of the data and determine the resolving power of the data set. The resulting composite velocity model constrains the crustal thickness and location and width of the continent‐Borderland transition zone. We find that the mid to lower crust layer velocities of the Inner Borderland are slightly lower than the corresponding layers in the average southern California crust model, while the upper mantle velocity is significantly higher. The data require the Moho to deepen significantly to the north. We constrain the transition zone to initiate between the offshore slope and the southwest Los Angeles Basin. If the Inner Borderland crust is 22 km thick, then the transition zone is constrained to initiate within a 2 km wide region beneath the southwest Los Angeles Basin, and have a width of 20–25 km. The strong, coherent, and continuous Pn phase suggests the Moho is coherent and laterally continuous beneath the Inner Borderland and transition zone. The Inner California Borderland seems to be modified and thickened oceanic crust, with the oceanic upper mantle intact beneath it.
Geodetic determination of relative plate motion and crustal deformation across the Scotia‐South America plate boundary in eastern Tierra del Fuego
Authors: Smalley R. , Kendrick E. , Bevis M. G. , Dalziel I. W. D. , Taylor F. , Lauría E. , Barriga R. , Casassa G. , Olivero E. , Piana E.
Published: August 2003

Global Positioning System (GPS) measurements provide the first direct measurement of plate motion and crustal deformation across the Scotia‐South America transform plate boundary in Tierra del Fuego. This plate boundary accommodates a part of the overall motion between South America and Antarctica. The subaerial section of the plate boundary in Tierra del Fuego, about 160 km in length, is modeled as a two dimensional, strike‐slip plate boundary with east‐west strike. Along the Magallanes‐Fagnano fault system, the principal fault of this portion of the plate boundary, relative plate motion is left‐lateral strike‐slip on a vertical fault at 6.6 ± 1.3 mm/year based on an assumed locking depth of 15 km. The site velocities on the Scotia Plate side are faster than the relative velocity by an additional 1–2 mm/yr, suggesting there may be a wider region of diffuse left‐lateral deformation in southern Patagonia. The north‐south components of the velocities, however, do not support the existence of active, large‐scale transpression or transtension between the South America and Scotia plates along this section of the plate boundary.
Double diffusion in the Mediterranean Sea: Observation and parameterization of salt finger convection
Authors: Onken Reiner , Brambilla Elena
Published: September 2003

For the Mediterranean Sea a large set of historical conductivity‐temperature‐depth casts has been investigated for the occurrence of double‐diffusive vertical mixing due to salt finger convection. All casts were screened in terms of the density ratio Rρ, providing probability distributions of Rρ for the upper 1000‐dbar range of eight geographical areas. Vertical profiles of the salt finger‐driven diffusivities kS and kT of salinity and temperature have been evaluated from the statistics of Rρ and a presumed mixing law, and analytic expressions are provided, which can be used to parameterize the effects of salt finger mixing in ocean circulation models of the Mediterranean. In most areas the diffusivity profiles exhibit an absolute maximum below the core of the Levantine Intermediate Water. Toward the surface the diffusivities decrease rapidly, while the downward decay is less pronounced. A different behavior is found in the Tyrrhenian and Adriatic Seas, where the diffusivities remain high also at greater depth.
A Bayesian coregionalization approach for multivariate pollutant data
Authors: Schmidt Alexandra M. , Gelfand Alan E.
Published: September 2003

Spatial data collection increasingly turns to vector valued measurements at spatial locations. An example is the observation of pollutant measurements. Typically, several different pollutants are observed at the same sampled location, referred to as a monitoring station or gauged site. Usually, interest lies in the modeling of the joint process for the levels of the different pollutants and in the prediction of pollutant levels at ungauged sites. In this case, it is important to take into account not only the spatial correlation but also the correlation among the different variables at each gauged site. Since, conceptually, there is a potentially observable measurement vector at every location in the study region, a multivariate spatial process becomes a natural modeling choice. In using a Gaussian process, the main challenge is the specification of a valid and flexible cross‐covariance function. This paper proposes a rich class of covariance functions developed through the so‐called linear coregionalization model [see, e.g., Wackernagel, 1998] for multivariate spatial observations. Following the ideas in the work of, for example, Royle and Berliner [1999], we can reparameterize a multivariate spatial model using suitable univariate conditional spatial processes, facilitating the computation. We provide explicit details, including the computation of the range associated with the different component processes. As an example, we fit our model to a particular day average of CO, NO, and NO2 for a set of monitoring stations in California, USA.
Mapping and monitoring of the snow cover fraction over North America
Authors: Romanov Peter , Tarpley Dan , Gutman Garik , Carroll Thomas
Published: August 2003

Automated snow maps over North America have been produced at the National Environmental Satellite Data and Information Service (NESDIS) of the National Oceanic and Atmospheric Administration (NOAA) since 1999. The developed snow‐mapping system is based on observations in the visible, middle infrared, infrared, and microwave spectral bands from operational geostationary and polar orbiting meteorological satellites and generates daily maps of snow cover at a spatial resolution of 4 km. Recently, the existing snow‐mapping technique was extended to derive the fractional snow cover. To obtain snow fraction, we use measurements of the Imager instrument on board Geostationary Operational Environmental Satellite (GOES). The algorithm treats every cloud‐clear image pixel as a “mixed scene” consisting of a combination of snow‐covered and snow‐free land surface. To determine the portion of the pixel that is covered with snow, we employ a linear mixture approach, which relies on the Imager measurements in the visible spectral band. The estimated accuracy of subpixel snow fraction retrievals is about 10%. In this paper, we present a description of the snow cover and snow fraction mapping algorithms. Application of the developed algorithms over North America for three winter seasons from 1999–2000 to 2001–2002 has shown that the spatial distribution of the fractional snow cover over areas affected by seasonal snow closely corresponds to the distribution of the forest cover. The fraction of snow in the middle of the winter season generally varied from 100% over croplands, grasslands, and other nonforested areas to 20–30% over dense boreal forests. The snow fraction over dense boreal forests exhibited a slight intraseason variability; however, no obvious correlation of these changes with snowfalls was noticed. Over areas with no or sparse tree vegetation cover (croplands, grasslands), snow fraction showed a noticeable correlation with snow depth for snow depths up to 35–40 cm.
Development and characterization of an airborne‐based instrument used to measure nitric acid during the NASA Transport and Chemical Evolution over the Pacific field experiment
Authors: Zondlo Mark A. , Mauldin R. Leon , Kosciuch Ed , Cantrell Christopher A. , Eisele Fred L.
Published: September 2003

A new inlet and instrument have been developed for the rapid measurement of gas phase nitric acid (HNO3) from an airborne platform. The inlet was kept near ambient temperatures with a very short sampling time (100 ms) to minimize desorption of particle nitrates. In addition, inlet surface adsorption problems were minimized by the use of extruded perfluoroalkoxy as a sampling material. Nitric acid was detected by selected ion chemical ionization mass spectrometry using deprontonated methanesulfonic acid as a reagent ion. Laboratory tests showed no interferences from NO, NO2, NO3, and N2O5 under wet (relative humidity (RH) = 100%) or dry (RH = 0%) conditions at levels exceeding those found in the troposphere. The inlet and instrument were flown on the NASA P‐3B aircraft as part of the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) field campaign off the coast of Asia during February–April 2001. Nitric acid was measured every 5 s for a 3 s integration period with a limit of detection of ∼10 parts per trillion by volume (pptv). The instrument was calibrated by the addition of isotopically labeled H15NO3 near the front of the ion source on a continual basis. Absolute uncertainties including systematic errors are the limit of detection (10 pptv) plus ±20% for HNO3 > 200 pptv, ±25% for HNO3 100–200 pptv, and ±30% for HNO3 < 100 pptv (±2 σ). Rapid changes in ambient HNO3 were resolved, suggesting minimal influences from instrument surfaces. Finally, the measurements compared favorably with the University of New Hampshire’s mist chamber/ion chromatography instrument flown on board the NASA DC‐8 aircraft during two intercomparison flights. The in‐flight performance of the instrument is demonstrated under the wide range of conditions observed in TRACE‐P.
Variability of North Atlantic heat transfer during MIS 2
Authors: Weinelt M. , Vogelsang E. , Kucera M. , Pflaumann U. , Sarnthein M. , Voelker A. , Erlenkeuser H. , Malmgren B. A.
Published: August 2003

Short‐term changes in sea surface conditions controlling the thermohaline circulation in the northern North Atlantic are expected to be especially efficient in perturbing global climate stability. Here we assess past variability of sea surface temperature (SST) in the northeast Atlantic and Norwegian Sea during Marine Isotope Stage (MIS) 2 and, in particular, during the Last Glacial Maximum (LGM). Five high‐resolution SST records were established on a meridional transect (53°N–72°N) to trace centennial‐scale oscillations in SST and sea‐ice cover. We used three independent computational techniques (SIMMAX modern analogue technique, Artificial Neural Networks (ANN), and Revised Analog Method (RAM)) to reconstruct SST from planktonic foraminifer census counts. SIMMAX and ANN reproduced short‐term SST oscillations of similar magnitude and absolute levels, while RAM, owing to a restrictive analog selection, appears less suitable for reconstructing “cold end” SST. The SIMMAX and ANN SST reconstructions support the existence of a weak paleo‐Norwegian Current during Dansgaard‐Oeschger (DO) interstadials number 4, 3, 2, and 1. During the LGM, two warm incursions of 7°C water to occurred in the northern North Atlantic but ended north of the Iceland Faroe Ridge. A rough numerical estimate shows that the near‐surface poleward heat transfer from 53° across the Iceland‐Faroe Ridge up to to 72° N dropped to less than 60% of the modern value during DO interstadials and to almost zero during DO stadials. Summer sea ice was generally confined to the area north of 70°N and only rarely expanded southward along the margins of continental ice sheets. Internal LGM variability of North Atlantic (>40°N) SST in the GLAMAP 2000 compilation [Sarnthein et al., 2003b; Pflaumann et al., 2003] indicates maximum instability in the glacial subpolar gyre and at the Iberian Margin, while in the Nordic Seas, SST was continuously low.
High‐frequency approximation for mutual coupling calculations between apertures on a perfect electric conductor circular cylinder covered with a dielectric layer: Nonparaxial region
Authors: Persson Patrik , Rojas Roberto G.
Published: August 2003

An asymptotic Green's function technique is presented for the calculation of the surface fields on a perfect electric conductor circular cylinder covered with a dielectric layer. The sources are apertures located on the perfect electric conductor surface. This method is very efficient and valid for large cylinders in terms of wavelengths. The new representation is obtained via Watson's transformation and integral contour deformations. The efficiency of the method results from the circumferentially propagating representation of the Green's function as well as the efficient numerical evaluation of various integrals. Numerical results are presented showing good agreement when compared to other solutions as well as measurements.
Latin hypercube lattice sample selection strategy for correlated random hydraulic conductivity fields
Authors: Zhang Yingqi , Pinder George
Published: August 2003

Given an established probabilistic description of hydraulic conductivity, realizations of the hydraulic conductivity field can be generated using a lattice sampling technique, a special case of Latin hypercube sampling, and subsequently input to a groundwater flow and transport model. Realizations of dependent variables such as contaminant concentration are obtained as the output of the model and their corresponding statistics can be calculated. Compared with the other three alternative methods for generating a random hydraulic conductivity field, the suggested method is more efficient in terms of computational effort because it needs fewer samples to achieve the same statistical accuracy.
Effective hydraulic parameters for steady state vertical flow in heterogeneous soils
Authors: Zhu Jianting , Mohanty Binayak P.
Published: August 2003

In hydroclimate and land‐atmospheric interaction models, effective hydraulic properties are needed at large grid scales. In this study, the effective soil hydraulic parameters of the areally heterogeneous soil formation are derived by conceptualizing the heterogeneous soil formation as an equivalent homogeneous medium and assuming that the equivalent homogeneous soil will approximately discharge the same total amount of flux and produce same average pressure head profile in the formation. As compared to previous effective hydraulic property studies, a specific feature of this study is that the derived effective hydraulic parameters are mean‐gradient‐dependent (i.e., vary across depth). Although areal soil heterogeneity was formulated as parallel homogeneous stream tubes in this study, our results appear to be consistent with the previous findings of mean‐gradient unsaturated hydraulic conductivity [Yeh et al., 1985a, 1985b]. Three widely used hydraulic conductivity models were employed in this study, i.e., the Gardner model, the Brooks and Corey model, and the van Genuchten model. We examined the impact of parameter correlation, boundary condition (surface pressure head), and elevation above the water table on the effective saturated hydraulic conductivity and shape parameter. The correlation between the saturated hydraulic conductivity Ks and the shape parameter α increases the effective saturated hydraulic conductivity, while it does not affect the effective α. The effective α is usually smaller than the mean value of α, while the effective Ks can be smaller or larger than the mean value depending on no correlation or full correlation between Ks and α fields, respectively. An important observation of this study is that Gardner and van Genuchten functions resulted in effective parameters, whereas it is difficult to define effective parameters for the Brooks Corey model since this model uses a piecewise‐continuous profile for hydraulic conductivity.
Inferred controls on tree/grass composition in a savanna ecosystem: Combining 16‐year normalized difference vegetation index data with a dynamic soil moisture model
Authors: Scanlon Todd M. , Albertson John D.
Published: August 2003

A two‐layer soil moisture model was developed to infer the controls on the tree/grass coexistence in a savanna ecosystem. The model was applied along a mean annual precipitation gradient in southern Africa, known as the Kalahari Transect (KT), which follows a north‐south decline in mean annual rainfall from ∼1600 mm/yr to ∼250 mm/yr between the latitudes 12°–26°S. Satellite‐derived fractional covers for trees, grass, and bare soil were used as input to the model, with the fractional grass cover responsive to interannual variability in rainfall, as defined by observed statistics. Other inputs to the model included satellite‐based radiation budget measurements and interpolated, ground‐based rainfall measurements. The soil moisture model structure allows both trees and grass to have access to the upper zone, while trees alone can extract water from the lower zone. We focus our analysis on the wet season months of November–March, in which 87% of the annual rainfall is received along the KT. Simulations were performed on daily time steps for 16 years, representing a range of interannual rainfall variability, at 196 equally spaced positions along the transect. The results indicate that two distinct areas of the KT exist in terms of vegetation‐rainfall relationships. North of 18°S, the trees and grass are rarely water stressed during the wet season and a large portion of the water balance is accounted for by leakage through the bottom of the root zone in sandy soils. The vegetation cover in the northern end of the transect does not reach its potential in terms of water exploitation and is most likely nutrient limited. In the southern portion of the KT, tree fractional cover is such that trees become water stressed in drier than average wet seasons and suffer no water stress during wetter than average wet seasons. The extent of the fractional grass cover for individual years is controlled by the water demand stress. We find that observed tree/grass fractional cover in the water‐limited region of the transect is best explained by considering, on an individual basis, an allowable range of stress for trees and grass, while minimizing the amount of water that is unexploited by the vegetation and lost as leakage from the root zone.
Propagation of nonlinear reactive contaminants in porous media
Authors: Serrano Sergio E.
Published: August 2003

A study on the effect of nonlinear reactions on the space and time distribution of contaminant plumes governed by the advective‐dispersive equation in porous media was conducted. Several models of nonlinear reactions were considered: the irreversible nonlinear first‐order kinetic sorption model, the nonlinear Freundlich sorption isotherm model, the nonlinear Langmuir sorption isotherm model, and the reversible nonlinear kinetic sorption model. Each of these models was coupled with the advective‐dispersive equation with dimensionless concentration and an approximate analytical series solutions was obtained. Comparison between linear and nonlinear plumes indicated that nonlinear reactions may have a significant effect on the shape and spatial distribution of a contaminant at a given time and in certain cases may explain quantitatively the occurrence of scaled (e.g., concentration change while preserving shape), retarded, and nonsymmetric plumes as well as the presence of back tails and sharp front ends usually observed in the field. By adopting a nonlinear model of contaminant migration a more realistic representation of contaminant propagation is possible than that obtained with a linear model.
First measurements and modeling of Δ17O in atmospheric nitrate
Authors: Michalski Greg , Scott Zack , Kabiling Melanie , Thiemens Mark H.
Published: August 2003

Atmospheric nitrate is anomalously enriched in both the 18O/16O and 17O/16O isotopic ratios, with Δ17O = 20–30.8‰ (Δ17O = δ17O − .52 × δ18O). We have modeled the seasonal variation in Δ17O by utilizing the transfer of Δ17O from ozone to HNO3 during NOx oxidation reactions and by evaluating the relative source strengths of heterogeneous and homogenous HNO3 production. The implications for new insights into the global nitrogen cycle, N2O production and paleoclimate studies are discussed.
Observations of a distinctive infra‐red spectral feature in the atmospheric spectra of polar stratospheric clouds measured by the CRISTA instrument
Authors: Spang Reinhold , Remedios John J.
Published: August 2003

Polar stratospheric cloud particles (PSCs) are known to strongly influence the infra‐red emission spectrum of the lower stratosphere in cold polar winters. The characteristics of these infra‐red features have been examined using limb sounding spectra recorded by the CRISTA experiment in August 1997 when many Antarctic PSCs were observed. A distinctive spectral feature centered at 820 cm−1 has been identified in many of these spectra, the first time that a particular band has been observed in the spectra of PSCs in the atmosphere. The feature can be attributed to the ν2 band of the NO3− ion and strongly suggests a condensed nitric acid component to the particles in the form of solid nitric acid trihydrate (NAT) or liquid ternary solution (STS). The spectral signatures belong to a definite sub‐set of the PSC observations recorded by CRISTA. The particles are observed at temperatures well above 192 K, allowing for temperature errors, and it is suggested that NAT particles are the most likely source of the spectral signature. In addition, it is shown that PSC events in which no spectral signature is present are only observed below 192 K and display a very similar HNO3‐temperature relationship to STS particles.
Tracing the advection of organic carbon into the subsurface Sargasso Sea using a 228Ra/226Ra tracer
Authors: Kim Guebuem , Hussain N. , Church T. M.
Published: August 2003

During a 3‐year record of 228Ra/226Ra ratio profiles (from nine cruises) in the Sargasso Sea, two profiles in the Spring (April 1997 and 1998) show distinct subsurface maxima. Such maxima in the radium isotope ratio record the subsurface advection of surface waters, such as subtropical mode waters. The April 1997 maximum occurred below the euphotic zone (between 300–400 m) and was also coincident with that of POC and dissolved oxygen, supporting the subsurface advection of surface waters. This single event represents a large isopycnal injection (23 g m−2) of organic carbon into the subsurface ocean. Although we cannot quantify carbon export by this process on a basin scale based on these single‐site measurements, it may be an important pathway for short‐term oceanic carbon export.
Favored regions for chorus‐driven electron acceleration to relativistic energies in the Earth's outer radiation belt
Authors: Meredith Nigel P. , Horne Richard B. , Thorne Richard M. , Anderson Roger R.
Published: August 2003

Pitch angle and energy diffusion rates for scattering by whistler‐mode chorus waves are proportional to the wave magnetic field intensity and are strongly dependent on the frequency distribution of the waves and to the ratio between the electron plasma frequency (fpe) and the electron gyrofrequency (fce). Relativistic electrons interact most readily with lower‐band chorus (0.1 < f/fce < 0.5) and energy diffusion leading to local acceleration to relativistic energies is most effective in regions of low fpe/fce. We perform statistical studies of CRRES data and show that, outside of the plasmapause, both fpe/fce and lower‐band chorus activity are dependent on magnetic activity with regions of low fpe/fce and enhanced lower‐band chorus activity occurring over a wide range of geospace during active conditions (AE > 300 nT). Enhanced waves in these regions could play a major role in electron acceleration to relativistic energies during periods of prolonged substorm activity.
Chron C33r paleomagnetic pole for the Pacific plate
Authors: Sager William W.
Published: August 2003

A Pacific plate paleomagnetic pole was calculated for chron C33r (79–83 Ma) using data from Deep Sea Drilling Project (DSDP) and Ocean Drilling Program (ODP) basalt and sediment cores. Six colatitude data were combined with four declination data, one from basalt samples oriented by magnetic overprint direction and three from seamount magnetic anomaly inversions corrected for induced field bias. The resulting pole is located at 72.3°N, 341.7°E (95% confidence ellipse: major semi‐axis, 10.1°; minor semi‐axis, 5.6°; major semi‐axis azimuth, 91°) and is indistinguishable from a published pole calculated using basalt samples from ODP Site 884. The C33r pole implies that prior poles of this age, based on seamount anomaly inversion data, are inaccurate. It changes the shape of the Pacific apparent polar wander path (APWP) and implies rapid polar motion before C33r followed by a polar standstill.
Field‐aligned ion motions in the polar E‐F transition region: Mean characteristics
Authors: Oyama S. , Nozawa S. , Maeda S. , Murayama Y. , Fujii R. , Shinagawa H.
Published: August 2003

Geomagnetic field‐aligned (FA) ion motions in the transition region between E and F regions (from 150 to 250 km; hereafter termed the E‐F transition region) in the polar ionosphere are analyzed statistically using data from European Incoherent Scatter (EISCAT) radar from 1987 to 1999. We use all available EISCAT data sets that satisfy the definition of data selection criteria (i.e., 24‐hour observation periods beginning at 1200 UT); therefore it has not been feasible to investigate seasonal, solar, and geomagnetical activity dependences. FA ion motions above and below the E‐F transition region (250–300 km and 100–150 km, respectively) are also analyzed to compare with lower‐altitude ion motions in the E‐F transition region. The FA ion velocity that is observed with the EISCAT radar can be written as the sum of the FA ion diffusion velocity and FA component of the thermospheric wind using the ion momentum equation. The main purpose of this paper is to understand quantitatively the relative contributions of ion diffusion and neutral wind on FA ion motions in the E‐F transition region. We derive the amplitude and phase of the first three daily harmonics, i.e., the 24‐, 12‐, and 8‐hour periodic oscillations in observed FA ion velocities and estimated FA ion diffusion velocities. The spectral characteristics are determined with a Fast Fourier Transfer (FFT) method after averaging velocity data in 1‐hour bins. The amplitude of the 24‐hour periodic oscillation is the largest of the three harmonic components for the FA ion velocity as well as FA ion diffusion velocity. While the amplitude of the 24‐hour periodic oscillation in FA ion diffusion velocity below 230 km is considerably smaller than the values of the observed FA ion velocities, the amplitude from 230 to 300 km is comparable to that in observed FA ion velocities. From 230 to 300 km the phase of the 24‐hour periodic oscillation in FA ion diffusion velocity has about 180° difference from that in the observed FA ion velocity. This spectral analysis results suggest that, in the E‐F transition region, FA ion diffusion velocity is not the major contributor to the three harmonic oscillations in the observed FA ion velocities; thus FA component of thermospheric winds or tides prove to be the primary contributor.
Numerical modeling of localized electromagnetic waves in the nightside subauroral zone
Authors: Streltsov A. V. , Mishin E. V.
Published: August 2003

Results from a numerical study of localized, intense electromagnetic structures observed by the Defense Meteorological Satellite Program (DMSP) satellite F15 in the nightside subauroral zone during the magnetic storm of 6 November 2001 are presented. It is shown that these structures can be interpreted as standing and propagating Alfvén waves generated in the process of ionosphere‐magnetosphere coupling mitigated by the storm and substorm activities. In particular, computations show that when the Pedersen conductivity is low (<1 mho) and a large‐scale electric field in the ionosphere exists, small‐scale irregularities in the E‐layer plasma density can generate Alfvén waves with substantial amplitudes. Initially, perpendicular components of the electric and magnetic fields in those waves are in antiphase and the corresponding Poynting vector is directed along the ambient magnetic field from the ionosphere. As time proceeds, the standing pattern of the resonant Alfvén waves has been developing between the conjugate ionospheres and π/2 phase shift between E⟂ and B⟂ appears. At this time the Poynting vector can change direction along the ambient magnetic field several times within one structure. Both types of behaviors of the Poynting vector were observed within localized subauroral electromagnetic structures.
Estimation of the all‐wave urban surface radiation balance by use of ASTER multispectral imagery and in situ spatial data
Authors: Chrysoulakis Nektarios
Published: September 2003

In this study, Terra/Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery was analyzed together with in situ spatial data to examine the potential of high spatial resolution multispectral remote sensing to support the definition of energy exchanges in urban environment. The spatial distributions of physical parameters with relation to the urban energy budget were determined, and finally, taking into account the effects of different types of built‐up areas and different land uses, the spatial distribution of all‐wave surface net radiation balance for the center of the metropolitan city of Athens was estimated within about ±44.5 Wm−2. The atmospheric downward longwave flux was estimated with the use of radiosonde measurements. The Santa Barbara DISORT atmospheric radiative transfer model was used for the simulation of the radiative transfer in the atmosphere. The results indicate that ASTER multispectral imagery enables a better understanding of energy aspects and their causes and effects, providing an important addition to conventional methods of monitoring the urban environment.
Geostationary satellite retrievals of aerosol optical thickness during ACE‐Asia
Authors: Wang Jun , Christopher Sundar A. , Brechtel Fred , Kim Jiyoung , Schmid Beat , Redemann Jens , Russell Philip B. , Quinn Patricia , Holben Brent N.
Published: August 2003

Using 30 days of hourly geostationary satellite (GMS5 imager) data and discrete ordinate radiative transfer (DISORT) calculations, aerosol optical thickness (AOT) at 0.67 μm was retrieved over the west Pacific Ocean (20°N–45°N, 110°E–150°E) during the Aerosol Characterization Experiment (ACE‐Asia) intensive observation period in April 2001. Different from previous one‐channel retrieval algorithms, we have developed a strategy that utilizes in situ and ground measurements to characterize aerosol properties that vary both in space and time. Using Mie calculations and bilognormal size distribution parameters inferred from measurements, the relationship between Ångström exponent (α) and the ratio of two volume lognormal modes (γ) was obtained. On the basis of spectral AOT values inferred from the Aerosol Robotic Network (AERONET) sites, NASA Ames Airborne Sun photometers (AATS6 and AATS14) and a Sun photometer on board a ship, a successive correction method (SCM) was used to infer the spatial distribution of α in the study area. Comparisons between the satellite‐retrieved AOT and AERONET values over four sites show good agreement with linear coefficients (R) of 0.86, 0.85, 0.86, and 0.87. The satellite‐derived AOTs are also in good agreement with aircraft (R = 0.87) and ship measurements (R = 0.98). The average uncertainty in our AOT retrievals is about 0.08 with a maximum value of 0.15 mainly due to the assumptions in calibration (±0.05), surface reflectance (±0.01–±0.03), imaginary part of refractive index (±0.05), and SCM‐derived α values (±0.02). The monthly mean AOT spatial distribution from GMS5 retrievals in April 2001 clearly shows the transport pattern of aerosols with high AOT near the coast of east Asia and low AOT over the open ocean. Using high temporal resolution satellite data, this paper demonstrates that the diurnal variation in AOT can be retrieved by current generations of geostationary satellites. The next generation of geostationary satellites with better spectral, spatial and radiometric resolution will significantly improve our ability to monitor aerosols and quantify their effects on regional climate.
Isotopic fractionation of water during evaporation
Authors: Cappa Christopher D. , Hendricks Melissa B. , DePaolo Donald J. , Cohen Ronald C.
Published: August 2003

Variations in the isotopic content (18O/16O and D/H ratios) of water in the natural environment provide a valuable tracer of the present‐day global hydrologic cycle and a record of the climate over at least 400,000 years that is preserved in glacial ice. The interpretation of observed isotopic ratios in water vapor, rain, snow, and ice depends on our understanding of the processes (mainly phase changes) that produce isotopic fractionation. Whereas equilibrium isotopic fractionation is well understood, kinetic effects, or diffusion‐controlled fractionation, has a limited experimental foundation. Kinetic effects are significant during evaporation into unsaturated air and during condensation to form ice from vapor. Kinetic effects are also thought to control the deuterium excess (d = δD − 8δ18O) of precipitation. We describe experiments to observe kinetic effects associated with evaporation. Analysis of our own and previous experiments shows that surface cooling of the liquid is a crucial variable affecting fractionation from evaporating water that has not been properly considered before. Including the effects of evaporative surface cooling reconciles observed D/H fractionation with kinetic theory and removes the need to invoke an unusual size for the HDO molecule. Thus the isotopic molecular diffusivity ratios are D(H218O)/D(H216O) = 0.9691 and D(HD16O)/D(H216O) = 0.9839. Implications of this work for representation of kinetic fractionation in global circulation models and cloud physics models are briefly discussed.
Mass‐independent sulfur isotopic compositions in present‐day sulfate aerosols
Authors: Romero Alvaro B. , Thiemens Mark H.
Published: August 2003

Mass‐independent (MI) sulfur isotopic anomalies recently observed in Precambrian rock samples have been attributed to photochemistry and used to establish oxygen levels in Earth's early atmosphere [Farquhar et al., 2000b, 2000a]. Here we report the first MI sulfur isotopic compositions in the present atmosphere from samples of Northern Hemispheric aerosol sulfate. The MI sulfur isotopic compositions do not correlate with MI oxygen signatures previously observed in the same samples [Lee and Thiemens, 2001; Lee, 2000; Bao et al., 2001]. Antarctic dry valley soil sulfate, which is atmospheric in origin and has a MI oxygen signature [Bao et al., 2000], is mass‐dependent (MD) with respect to sulfur. A different process than that proposed to explain the MI oxygen signature in sulfate [Savarino et al., 2000] is therefore required. Possible sources of the anomaly are discussed, as well as potential applications to global climate and implications for Archean geology and the Earth's early atmosphere.
A Laplace transform power series solution for solute transport in a convergent flow field with scale‐dependent dispersion
Authors: Chen Jui‐Sheng , Liu Chen‐Wuing , Hsu Hui‐Tsung , Liao Chung‐Min
Published: August 2003

This study presents a novel mathematical model to describe solute transport in a radially convergent flow field with scale‐dependent dispersion. The scale‐dependent advection‐dispersion equation in cylindrical coordinates derived based on the dispersivity is assumed to increase linearly with the distance of the solute transported from its input source. The Laplace transformed power series technique is applied to solve the radially scale‐dependent advection‐dispersion equation with variable coefficients. Breakthrough curves obtained using the scale‐dependent dispersivity model are compared with those from the constant dispersivity model to illustrate the features of scale‐dependent dispersion in a radially convergent flow field. The comparison results reveal that the constant dispersivity model can produce a type curve with the same shape as that from the proposed scale‐dependent dispersivity model. This correspondence in type curves between the two models occurs when the product of the Peclet number used in the constant dispersivity model and the dispersivity/distance ratio used in the scale‐dependent dispersivity model equals 4. Finally, the scale‐dependent dispersivity model is applied to a set of previously reported field data to investigate the linearly scale‐dependent dispersion effect. The analytical results reveal that the linearly scale‐dependent dispersion model is applicable to this test site.
Bilaminar techniques for the treatment of recession‐type defects. A comparative clinical study
Authors: Zucchelli G. , Amore C. , Sforza N. M. , Montebugnoli L. , De Sanctis M.
Published: September 2003

Objectives: Complete root coverage is the primary objective to be accomplished when treating gingival recessions in patients with aesthetic demands. Furthermore, in order to satisfy patient demands fully, root coverage should be accomplished by soft tissue, the thickness and colour of which should not be distinguishable from those of adjacent soft tissue. The aim of the present split‐mouth study was to compare the treatment outcome of two surgical approaches of the bilaminar procedure in terms of (i) root coverage and (ii) aesthetic appearance of the surgically treated sites.

Material and Methods: Fifteen young systemically and periodontally healthy subjects with two recession‐type defects of similar depth affecting contralateral teeth in the aesthetic zone of the maxilla were enrolled in the study. All recessions fall into Miller class I or II. Randomization for test and control treatment was performed by coin toss immediately prior to surgery. All defects were treated with a bilaminar surgical technique: differences between test and control sites resided in the size, thickness and positioning of the connective tissue graft. The clinical re‐evaluation was made 1 year after surgery.

Results: The two bilaminar techniques resulted in a high percentage of root coverage (97.3% in the test and 94.7% in the control group) and complete root coverage (gingival margin at the cemento‐enamel junction (CEJ)) (86.7% in the test and 80% in the control teeth), with no statistically significant difference between them. Conversely, better aesthetic outcome and post‐operative course were indicated by the patients for test compared to control sites.

Conclusions: The proposed modification of the bilaminar technique improved the aesthetic outcome. The reduced size and minimal thickness of connective tissue graft, together with its positioning apical to the CEJ, facilitated graft coverage by means of the coronally advanced flap.
Metamorphic T3‐response genes have specific co‐regulator requirements
Authors: Havis Emmanuelle , Sachs Laurent M , Demeneix Barbara A
Published: August 2003

Thyroid hormone receptors (TRs) have several regulatory functions in vertebrates. In the absence of thyroid hormone (T3; triiodothyronine), apo‐TRs associate with co‐repressors to repress transcription, whereas in the presence of T3, holo‐TRs engage transcriptional coactivators. Although many studies have addressed the molecular mechanisms of T3 action, it is not known how specific physiological responses arise. We used T3‐dependent amphibian metamorphosis to analyse how TRs interact with particular co‐regulators to differentially regulate gene expression during development. Using chromatin immunoprecipitation to study tissue from pre‐metamorphic tad‐poles, we found that TRs are physically associated with T3‐responsive promoters, whether or not T3 is present. Addition of T3 results in histone H4 acetylation specifically on T3‐response genes. Most importantly, we show that individual T3‐response genes have distinct co‐regulator requirements, the T3‐dependent co‐repressor‐to‐coactivator switch being gene‐specific for both co‐regulator categories.
Analysis of molecular diffusion in ftsK cell‐division mutants using laser surgery
Authors: Goksör Mattias , Diez Alfredo , Enger Johan , Hanstorp Dag , Nyström Thomas
Published: August 2003

Escherichia coli cells that lack the carboxy‐terminal part of FtsK fail to segregate their chromosomes properly during cytokinesis and tend to form chains. These chains are possibly formed as a result of DNA being trapped in the division planes or a failure to fuse the membrane during septum formation. If so, small molecules might diffuse between the apparent cell compartments. To investigate this theory, we developed an optical workstation that allows simultaneous imaging of and surgical operations on cellular objects in the sub‐micrometre range. By surgical incisions of E. coli cell poles, diffusion of propidium iodide (PI) can be followed in real time. This analysis showed that PI was unable to diffuse from one cell equivalent to another in chain‐forming ftsK mutants. Thus, the cytoplasm of the cell compartments in the chains seems to be fully separated.
Cdyl: a new transcriptional co‐repressor
Authors: Caron Cécile , Pivot‐Pajot Christophe , van Grunsven Leo A , Col Edwige , Lestrat Cécile , Rousseaux Sophie , Khochbin Saadi
Published: August 2003

Cdyl (chromodomain‐Y‐like) is a chromodomain‐containing protein that is predominantly expressed during mouse spermiogenesis. In its carboxy‐terminal portion, there is a domain with homology to the coenzyme A (CoA) pocket of the enoyl‐CoA hydratase/isomerase, which is shown here to be able to bind CoA and histone deacetylases (HDACs). It also efficiently represses transcription. Moreover, the binding of Hdac1 represses the ability of Cdyl to bind CoA, and a Cdyl–CoA interaction only occurs in the absence of HDACs. These data suggest that Cdyl is primarily a transcriptional co‐repressor. However, the degradation of cellular Hdac1 and Hdac2, as observed here in the elongating spermatids, may provide an HDAC‐free environment in which Cdyl could bind CoA and participate in the global chromatin remodelling that occurs in these cells.
An interaction between frataxin and Isu1/Nfs1 that is crucial for Fe/S cluster synthesis on Isu1
Authors: Gerber Jana , Mühlenhoff Ulrich , Lill Roland
Published: August 2003

Depletion of the mitochondrial matrix protein frataxin is the molecular cause of the neurodegenerative disease Friedreich ataxia. The function of frataxin is unclear, although recent studies have suggested a function of frataxin (yeast Yfh1) in iron/sulphur (Fe/S) protein biogenesis. Here, we show that Yfh1 specifically binds to the central Fe/S‐cluster (ISC)‐assembly complex, which is composed of the scaffold protein Isu1 and the cysteine desulphurase Nfs1. Association between Yfh1 and Isu1/Nfs1 was markedly increased by ferrous iron, but did not depend on ISCs on Isu1. Functional analyses in vivo showed an involvement of Yfh1 in de novo ISC synthesis on Isu1. Our data demonstrate a crucial function of Yfh1 in Fe/S protein biogenesis by defining its function in an early step of this essential process. The iron‐dependent binding of Yfh1 to Isu1/Nfs1 suggests a role of frataxin/Yfh1 in iron loading of the Isu scaffold proteins.
Loss of eyes in zebrafish caused by mutation of chokh/rx3
Authors: Loosli Felix , Staub Wendy , Finger‐Baier Karin C , Ober Elke A , Verkade Heather , Wittbrodt Joachim , Baier Herwig
Published: August 2003

The vertebrate eye forms by specification of the retina anlage and subsequent morphogenesis of the optic vesicles, from which the neural retina differentiates. chokh (chk) mutant zebrafish lack eyes from the earliest stages in development. Marker gene analysis indicates that retinal fate is specified normally, but optic vesicle evagination and neuronal differentiation are blocked. We show that the chk gene encodes the homeodomain‐containing transcription factor, Rx3. Loss of Rx3 function in another teleost, medaka, has also been shown to result in an eyeless phenotype. The medaka rx3 locus can fully rescue the zebrafish mutant phenotype. We provide evidence that the regulation of rx3 is evolutionarily conserved, whereas the downstream cascade contains significant differences in gene regulation. Thus, these mutations in orthologous genes allow us to study the evolution of vertebrate eye development at the molecular level.
Mechanisms for changes in soil carbon storage with pasture toPinus radiataland‐use change
Authors: Halliday Joanne C. , Tate Kevin R. , McMurtrie Ross E. , Scott Neal A.
Published: August 2003

In this study, we simulated pasture toPinus radiataland‐use change with theGenericDecompositionAndYield (G'DAY) ecosystem model to examine mechanisms responsible for the change in soil carbon (C) under pine. We parameterized the model for paired sites in New Zealand. Our simulations successfully reproduced empirical trends in ecosystem productivity and soil inorganic nitrogen (N), and modeled an increase in soil C and a small decline in soil N after 30 years under pine. We determined the mechanisms contributing to soil C change based on an established hypothesis that attributes increases in soil C storage to three main factors: increased ecosystem N inputs relative to outputs, increased C/N ratios in plant and soil, or a shift of N from plant to soil. The mechanisms we attributed to the simulated increase in soil C under pine were increased soil C inputs through tree litterfall, and an increase in the soil C/N ratio. In the first 7 years following pine establishment, a decline in soil C was simulated; this was matched by a decline in soil N. The simulated longer‐term increase in soil C with afforestation by pine contrasts with results from published field studies, which show either a decline or no change in soil C under pine. The discrepancy between measured and simulated changes in soil C was attributed to the G'DAY model overestimating the transfer of litter C into the mineral soil.