bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for dissolution of fatty acids in sediment traps: Impact on flux estimates
Authors: Körtzinger Arne , Schulz‐Bull Detlef E. , Petrick Gert , Duinker Jan C.
Published: February 2004

The effect of dissolution from particulates into the supernatant solution in sediment trap sample cups has been measured for fatty acids. A mooring array with time series sediment traps was deployed in the northeast Atlantic Ocean (59°N, 21°W) for 14 months. Selected representative samples from the trap at 2200 m (poisoned with NaN3) were analyzed for total and free fatty acids in both the solution and particulate phase by means of gas chromatography‐mass spectrometry with an ion trap detector. The flux contribution of the dissolved total fatty acids (∑ DTFA) was found to be between 15 and 75% of the total flux (∑ TTFA, sum of the fluxes of total fatty acids in both particles and supernatants). Dissolved free fatty acids (∑ DFFA) represented 25–88% of the total flux of free fatty acids (∑ TFFA). Absolute concentrations of total and free fatty acids in both compartments are discussed in terms of the processes controlling the distribution between the two phases, for example, readsorption. Sample handling, poisoning, bacterial activity, and swimmers may also affect fatty acid distribution. Flux data (sum of particulate and dissolved fluxes) are presented for individual fatty acids. Also, the degree of dissolution of individual fatty acids is shown for one sample (dissolved fraction ranging between 16 and 98% of total flux).
A numerical analysis of shipboard and coastal zone color scanner time series of new production within Gulf Stream cyclonic eddies in the South Atlantic Bight
Authors: Pribble J. Raymond , Walsh John J. , Dieterle Dwight A. , Müller‐Karger Frank E.
Published: February 2004

Eddy‐induced upwelling occurs along the western edge of the Gulf Stream between Cape Canaveral, Florida, and Cape Hatteras, North Carolina, in the South Atlantic Bight (SAB). Coastal zone color scanner images of 1‐km resolution spanning the period April 13–21, 1979, were processed to examine these eddy features in relation to concurrent shipboard and current/temperature measurements at moored arrays. A quasi‐one‐dimensional (z), time‐dependent biological model, using only nitrate as a nutrient source, has been combined with a three‐dimensional physical model in an attempt to replicate the observed phytoplankton field at the northward edge of an eddy. The model is applicable only to the SAB south of the Charleston Bump, at ∼31.5°N, since no feature analogous to the bump exists in the model bathymetry. The modeled chlorophyll, nitrate, and primary production fields of the euphotic zone are very similar to those obtained from the satellite and shipboard data at the leading edges of the observed eddies south of the Charleston Bump. The horizontal and vertical simulated fluxes of nitrate and chlorophyll show that only ∼10% of the upwelled nitrate is utilized by the phytoplankton of the modeled grid box on the northern edge of the cyclone, while ∼75% is lost horizontally, with the remainder still in the euphotic zone after the 10‐day period of the model. Loss of chlorophyll due to sinking is very small in this strong upwelling region of the cyclone. The model is relatively insensitive to variations in the sinking parameterization and the external nitrate and chlorophyll fields but is very sensitive to a reduction of the maximum potential growth rate to half that measured. Given the success of this model in simulating the new production of the selected upwelling region, other upwelling regions for which measurements or successful models of physical and biological quantities and rates exist could be modeled similarly.
Classification of sea slicks by multifrequency radar techniques: New chemical insights and their geophysical implications
Authors: Hühnerfuss Heinrich , Gericke Arne , Alpers Werner , Theis Reinhard , Wismann Volkmar , Lange Philipp A.
Published: February 2004

Sea slick experiments with an airborne five‐frequency radar scatterometer were performed in the presence of surface active substances that represent different fractions of biogenic slicks (fats, amines, sugar derivatives, and fatty acids). Measurements at water temperatures of 282.2 K (9.0°C) and 290.6 K (17.4°C) showed that temperature effects appear to play a secondary role for slick‐induced water wave damping, at least in the temperature range encountered during the present experiments. Different procedures of slick generation, with and without application of a spreading solvent, indicated that the wave‐damping effect in the short‐gravity/capillary wave range, and thus the modification of backscattered radar signals, is not only dependent on the chemical structure but also on the arrangement and distribution (morphology; formation of domains) of the surface‐active compounds. Thus far this aspect, which appears to be of particular importance for biogenic sea slicks, has been completely ignored. External infrared reflection‐absorption spectroscopy laboratory measurements with infrared radiation in the wavelength range between 3.3 μm and 7 μm enabled us allowed to form a link between some important elements of the morphological structure of the monolayers and their viscoelastic characteristics, which are closely related to the wave‐damping effect of surface active compounds and to the compounds influence on remote sensing signals. Furthermore, the IRAS measurements supplied detailed insight into the relaxation process that occurs during the generation of a sea slick and on a slick‐covered undulating water surface. In particular, strong hydration/dehydration effects appear to play an important role.
The relationship between the microwave radar cross section and both wind speed and stress: Model function studies using Frontal Air‐Sea Interaction Experiment data
Authors: Weissman David E. , Davidson Kenneth L. , Brown Robert A. , Friehe Carl A. , Li Fuk
Published: February 2004

The Frontal Air‐Sea Interaction Experiment (FASINEX) provided a unique data set with coincident airborne scatterometer measurements of the ocean surface radar cross section (RCS) (at Ku band) and near‐surface wind and wind stress. These data have been analyzed to study new model functions which relate wind speed and surface friction velocity (square root of the kinematic wind stress) to the radar cross section and to better understand the processes in the boundary layer that have a strong influence on the radar backscatter. Studies of data from FASINEX indicate that the RCS has a different relation to the friction velocity than to the wind speed. The difference between the RCS models using these two variables depends on the polarization and the incidence angle. The radar data have been acquired from the Jet Propulsion Laboratory airborne scatterometer. These data span 10 different flight days. Stress measurements were inferred from shipboard instruments and from aircraft flying at low altitudes, closely following the scatterometer. Wide ranges of radar incidence angles and environmental conditions needed to fully develop algorithms are available from this experiment.
Estimates of the energy cycle of the oceans
Authors: Oort Abraham H. , Anderson Laurence A. , Peixoto José P.
Published: February 2004

A new formulation of the general problem of the large‐scale energetics for the global oceans is presented and analyzed. Using a variety of ocean surface observations, some of the terms in the energy balance equations, such as the time rates of change, the generation rates of available gravitational potential energy G(P) and kinetic energy G(K), and the conversion rate from available gravitational potential energy into kinetic energy C(P, K), are estimated for annual and seasonal mean conditions. An attempt is also made to measure the uncertainty of these terms in order to assess the reliability of the results. The interseasonal variability is analyzed showing that the winter hemisphere represents the most active region of the globe. Using the data and some reasonable assumptions, pictures of the energy cycle in the global oceans for yearly and seasonal conditions are constructed. The hemispheric and global dissipation rates of available gravitational potential energy D(P) and of kinetic energy D(K) are estimated as residuals, assuming that the contribution from the internal energy C(I, K) is only a minor factor. After analyzing the general consistency of the picture of the energy cycle for the oceans, the conclusion is reached that the G(P) and G(K) terms are about equally important terms needed to describe and understand the structure and dynamics of the global ocean circulation.
Baroclinic eddy generation at a sharp corner in a rotating system
Authors: Klinger Barry A.
Published: February 2004

Laboratory experiments were conducted to investigate the generation of anticyclonic gyres by separation of a surface current from a coast in a rotating, two layer system. The experiments were motivated by the hypothesis that the flow of coastal currents around capes can generate oceanic eddies, as well as by the observation of gyres at the mouths of various straits. In the experiments the gyre is formed when the current, which flows with the coast to its right if one is oriented in the downstream direction, encounters a sharp convex corner. The current overshoots the corner, loops to the right, and reattaches to the coast downstream of the corner. Between the current loop and the coast is an anticyclone whose width grows with time. If a countercurrent flows under the surface current, a similar separation in the lower layer results in the generation of a cyclone as well; under some circumstances the cyclone and anticyclone advect each other away from the coast as a heton. Previous studies on related systems found that the corner must be sufficiently sharp for a gyre to form. I show that for a very sharp corner the angle made by the corner must be above a critical value of between 40° and 45° for a gyre to form. This is in contrast to nonrotating flows of comparable Rayleigh number, which will separate from a sharp corner at virtually any angle. For angles below the critical value, the current profile downstream of the corner changes as a function of corner angle, indicating that it is the stagnation of the flow nearest the wall which causes the anticyclone to form. This stagnation is reminiscent of the two‐dimensional, nonrotating picture of viscous boundary layer dynamics forcing separation of a boundary current. However, the gyre grows more slowly when the lower layer is much thicker than the upper layer, indicating that baroclinic processes are at least quantitatively important in the generation of the gyre. By varying the initial condition of the current, it is shown that the gyre formation is not a product of the interaction of the nose of the current with the corner. In conclusion, the experiments indicate that the basic mechanism of gyre formation may be viscous boundary effects as in nonrotating systems, but that rotation tends to inhibit eddy generation while baroclinic effects tend to enhance it.
Mechanism for low‐frequency variability and salt flux in the Mediterranean salt tongue
Authors: Spall Michael A.
Published: February 2004

The role of baroclinic instability in the generation of low‐frequency variability in the interior of ocean subtropical gyres and its possible importance in the zonal flux of salt and heat within the Mediterranean salt tongue are discussed. The observed zonal enhancement of the low‐frequency variability is interpreted as the signature of baroclinic instability of the large‐scale wind‐driven flow. The zonal orientation results from the relatively weak vertical shear of the large‐scale upper ocean flow and the stabilizing influence of the planetary vorticity gradient. There is a reversal in the vertical shear of velocity at middepths in the eastern basin of the North Atlantic that results in a local middepth maximum in the zonal eddy flux of density. Linear theory predicts a vertical structure of this density flux that is nearly coincident with the observed vertical distribution of the warm, salty water of the Mediterranean salt tongue. A primitive equation model is used to investigate the nonlinear, large‐amplitude regime. The zonal eddy density (or salt) flux averaged over several wavelengths and several cycles of wave growth and breaking indicates that this mechanism may be an important component in the overall salt balance in this region.
Low to middle tropospheric profiles and biosphere/troposphere fluxes of acidic gases in the summertime Canadian taiga
Authors: Klemm O. , Talbot R. W. , Fitzgerald D. R. , Klemm K. I. , Lefer B. L.
Published: February 2004

We report features of acidic gases in the troposphere from 9 to 5000 m altitude above ground over the Canadian taiga in the summer of 1990, The measurements were conducted at a 30‐m meteorological tower and from the NASA Wallops Electra aircraft as part of the joint U.S.‐Canadian Arctic Boundary Layer Expedition (ABLE) 3B Northern Wetland Studies (NOWES). We sampled air for acidic gases using the mist chamber collector coupled with subsequent analysis using ion chromatogaphy. At the tower we collected samples at two heights during a 13‐day period, including diurnal studies. Using eddy flux and profile data, we estimated the biosphere/troposphere fluxes of nitric, formic, and acetic acids and sulfur dioxide. For the organic acids, emissions from the taiga in the afternoon hours and deposition during the predawn morning hours were observed. The flux intensities alone were however not high enough to explain the observed changes in mixing ratios. The measured deposition fluxes of nitric acid were high enough to have a significant influence on its mixing ratio in the boundary layer. On three days we measured vertical profiles of nitric, formic, and acetic acids through the lower to midtroposphere. We found that the chemical composition of the troposphere was extremely heterogenous. Pronounced layers of polluted air were readily apparent from our measurements. Local photochemical production and episodic long‐range transport of trace components, originating from biomass burning and possibly industrial emissions, appear to have a strong influence on the composition of the troposphere and biosphere/troposphere fluxes of acidic gases at this site.
Transport out of the lower stratospheric Arctic vortex by Rossby wave breaking
Authors: Waugh D. W. , Plumb R. A. , Atkinson R. J. , Schoeberl M. R. , Lait L. R. , Newman P. A. , Loewenstein M. , Toohey D. W. , Avallone L. M. , Webster C. R. , May R. D.
Published: February 2004

The fine‐scale structure in lower stratospheric tracer transport during the period of the two Arctic Airborne Stratospheric Expeditions (January and February 1989; December 1991 to March 1992) is investigated using contour advection with surgery calculations. These calculations show that Rossby wave breaking is an ongoing occurrence during these periods and that air is ejected from the polar vortex in the form of long filamentary structures. There is good qualitative agreement between these filaments and measurements of chemical tracers taken aboard the NASA ER‐2 aircraft. The ejected air generally remains filamentary and is stretched and mixed with midlatitude air as it is wrapped around the vortex. This process transfers vortex air into midlatitudes and also produces a narrow region of fine‐scale filaments surrounding the polar vortex. Among other things, this makes it difficult to define a vortex edge. The calculations also show that strong stirring can occur inside as well as outside the vortex.
Branching ratios for the O(1D) + N2O reaction
Authors: Cantrell Christopher A. , Shetter Richard E. , Calvert Jack G.
Published: February 2004

Laboratory studies of the branching ratio of the reaction of electronically excited oxygen atoms, O(1D), with nitrous oxide, N2O, were performed by measuring the loss of N2O and the formation of products in a static optical cell interfaced to a Fourier transform spectrometer system. The results agree well with the most recent measurements, and a critical evaluation of the available data results in a factor of 2 reduction in the uncertainty. The ratio k1b/k1 is the fraction of reaction leading to the production of NO (reaction (1b)) relative to the total reaction of O(1D) with N2O (reaction (1)). The present recommendation for this ratio as it pertains to atmospheric reactions is 0.61±0.08 (95% confidence interval). The consequences of this result in terms of stratospheric NOy production and field measurements of ozone photolysis rates are discussed.
Two‐hundred‐year record of biogenic sulfur in a south Greenland ice core (20D)
Authors: Whung P.‐Y. , Saltzman E. S. , Spencer M. J. , Mayewski P. A. , Gundestrup N.
Published: February 2004

The concentration of methanesulfonic acid (MSA) was determined in a shallow south central Greenland ice core (20D). This study provides a high‐resolution record of the DMS‐derived biogenic sulfur in Greenland precipitation over the past 200 years. The mean concentration of MSA is 3.30 ppb (σ = 2.38 ppb, n = 1134). The general trend of MSA is an increase from 3.01 to 4.10 ppb between 1767 and 1900, followed by a steady decrease to 2.34 ppb at the present time. This trend is in marked contrast to that of non‐sea‐salt sulfate (nss SO42−), which increases dramatically after 1900 due to the input of anthropogenic sulfur. The MSA fraction ((MSA/(MSA + nss SO42−))* 100) ranges from a mean of 15% in preindustrial ice to less than 5% in recent ice. These MSA fractions suggest that approximately 15 to 40% of the sulfur in recent Greenland ice is of biological origin. It is suggested that there is a significant low‐latitude component to the biogenic sulfur in the core and that variations in the MSA fraction reflect changes in the relative strengths of low‐ and high‐latitude inputs. The data show no evidence for a strong dependence of dimethyl sulfide (DMS) emissions on sea surface temperature during the last century. There is also no indication that the yield of MSA from DMS oxidation has been altered by increased NOx levels over the North Atlantic during this period.
Multilevel cloud retrieval using multispectral HIRS and AVHRR data: Nighttime oceanic analysis
Authors: Baum Bryan A. , Arduini Robert F. , Wielicki Bruce A. , Minnis Patrick , Tsay Si‐Chee
Published: February 2004

A multispectral, multiresolution (MSMR) method is developed for analyzing scenes of overlapping cloud layers. The MSMR method is applied to data from the NOAA 11 advanced very high resolution radiometer (AVHRR) and the high‐resolution infrared radiometer sounder (HIRS‐2). The data are from a nighttime oceanic scene in which a semitransparent cirrus veil overlays a large‐scale stratus cloud. Low‐cloud and clear‐sky radiances are determined using a spatial coherence technique. Middle to upper level cloud pressures and radiances are estimated from HIRS‐2 15‐μm CO2 band radiometric data. The MSMR method improves the interpretation of a nighttime, oceanic scene containing thin cirrus over a large‐scale stratiform cloud. If, for example, the same scene is analyzed using only the AVHRR 10.8‐μm channel, the accompanying retrieved cloud heights are found to be between the cirrus and stratus cloud heights and are incorrectly identified as midlevel altostratus clouds. Theoretical radiative transfer model results for both water droplet spheres and randomly oriented hexagonal ice crystals are compared to observed AVHRR brightness temperature differences (BTD) between the 3.7‐ and 10.8‐μm channels (BTD34) and between the 10.8‐ and 12‐μm channels (BTD45) to distinguish among the effects of cloud optical depth, particle size, and phase for both single‐layer clouds and overlapping two‐layer clouds. Theoretical BTD calculations are used to estimate the range of effective particle sizes for each cloud layer. The data for the cirrus in the case study region near Bermuda are consistent with theoretical results for relatively small randomly oriented hexagonal ice crystals. The observed BTD34 and BTD45 values are lower for the cirrus above a lower‐level cloud than for single‐level cirrus with no underlying cloud. In certain cases the BTD analysis provides a way to distinguish between clouds composed of supercooled water droplets rather than ice particles. Analysis of nighttime data permits determination of stratus infrared optical depths smaller than 4.
Evaluation of water vapor distribution in general circulation models using satellite observations
Authors: Soden Brian J. , Bretherton Francis P.
Published: February 2004

This paper presents a comparison of the water vapor distribution obtained from two general circulation models, the European Centre for Medium‐Range Weather Forecasts (ECMWF) model and the National Center for Atmospheric Reseach (NCAR) Community Climate Model (CCM), with satellite observations of total precipitable water (TPW) from SSM/I and upper tropospheric relative humidity (UTH) from GOES. Overall, both models are successful in capturing the primary features of the observed water vapor distribution and its seasonal variation. For the ECMWF model, however, a systematic moist bias in TPW is noted over well‐known stratocumulus regions in the eastern subtropical oceans. Comparison with radiosonde profiles suggests that this problem is attributable to difficulties in modeling the shallowness of the boundary layer and large vertical water vapor gradients which characterize these regions. In comparison, the CCM is more successful in capturing the low values of TPW in the stratocumulus regions, although it tends to exhibit a dry bias over the eastern half of the subtropical oceans and a corresponding moist bias in the western half. The CCM also significantly overestimates the daily variability of the moisture fields in convective regions, suggesting a problem in simulating the temporal nature of moisture transport by deep convection. Comparison of the monthly mean UTH distribution indicates generally larger discrepancies than were noted for TPW owing to the greater influence of large‐scale dynamical processes in determining the distribution of UTH. In particular, the ECMWF model exhibits a distinct dry bias along the ITCZ and a moist bias over the subtropical descending branches of the Hadley cell, suggesting an underprediction in the strength of the Hadley circulation. The CCM, on the other hand, demonstrates greater discrepancies in UTH than are observed for the ECMWF model, but none that are as clearly correlated with well‐known features of the large‐scale circulation.
Heterogeneous chemistry of trichloroacetyl chloride in the atmosphere
Authors: George C. , Lagrange J. , Lagrange P. , Mirabel P. , Pallares C. , Ponche J. L.
Published: February 2004

The heterogeneous chemistry of trichloroacetyl chloride was studied using two different techniques allowing direct measurements of the uptake rate by water droplets and of the homogeneous aqueous phase hydrolysis rate. The first technique used was the droplet train technique for the study of the gas/liquid interaction which yielded uptake coefficients lower than 10−3 and estimates of the Henry's law constant H of 2 M atm−1 and of the hydrolysis rate constant kh of 500 s−1 for pH < 3.5. The second technique used was a stopped‐flow method for the homogeneous aqueous phase study. The results led to a hydrolysis rate constant of 150 s−1 in pure water for pH between 4.8 and 5.8 and strongly catalyzed by hydrogen and hydroxide ions. The results show that trichloroacetyl chloride can react readily with water leading to short residence time in the atmosphere.
Tethered‐balloon measurements of actinic flux in a cloud‐capped marine boundary layer
Authors: Vilà‐Guerau de Arellano Jordi , Duynkerke Peter G. , van Weele Michiel
Published: February 2004

As part of the Atlantic Stratocumulus Experiment (ASTEX), more than 34 tethered‐balloon soundings were carried out on Santa Maria Island, Azores. The main purpose of the soundings was to measure vertical profiles of actinic flux under different meteorological conditions. In addition, vertical profiles of temperature, relative humidity, and wind speed and direction were measured. The actinic flux was measured with a photoelectrical detector with a spectral response that ranges from 330 nm to 390 nm. It is in this region where the photodissociation of nitrogen dioxide, the main precursor of ozone in the troposphere, takes place. Several vertical profiles of actinic flux under clear and cloudy conditions are presented. These profiles show the different behavior of the actinic flux below, in, and above clouds. These observations are complemented with detailed measurements of cloud characteristics; relevant cloud properties for this study are the cloud‐base and cloud‐top heights and the cloud optical depth. A slightly increasing tendency for the actinic flux in the whole atmospheric boundary layer was observed under clear sky conditions. Under the presence of clouds and compared with clear sky values measured at the same solar zenith angle and at the surface, lower values were observed below cloud (ratio ranging from 0.39 to 0.92) and higher at the top of the cloud (ratio ranging from 1.68 to 2.32). In the cloud an increase in the values of actinic flux with height was measured. The actinic flux measurements are evaluated against values obtained from a multilayer delta‐Eddington model. An excellent agreement is found for the soundings made under total overcast conditions.
Ozone productivity of atmospheric organics
Authors: Bowman Frank M. , Seinfeld John H.
Published: February 2004

A technique is developed to determine the amount of ozone and other products, such as nitric acid and peroxyacetylnitrate (PAN), generated by the individual organic components of a complex atmospheric organic/NOx mixture. The technique is applied to the SAPRC 90 photochemical mechanism to study the individual contributions of carbonyls, aromatics, alkanes, alkenes, and carbon monoxide to ozone, nitric acid, PAN, and free radical production at varying organic to NOx ratios typical of atmospheric conditions.
The natural thermoluminescence of meteorites: 7. Ordinary chondrites from the Elephant Moraine region, Antarctica
Authors: Benoit P. H. , Roth J. , Sears H. , Sears D. W. G.
Published: February 2004

We report natural and induced thermoluminescence (TL) measurements for meteorites from the Elephant Moraine region (76°17′S, 157°20′E) of Antarctica. We use our data to identify fragmented meteorites (i.e., “pairings”); our dataset of 107 samples represents at most 73 separate meteorite falls. Pairing groups are generally confined to single icefields, or to adjacent icefields, but a small proportion cross widely separated icefields in the region, suggesting that the fields can be considered as a single unit. Meteorites from this region have high natural TL levels, which indicates that they have small terrestrial surface exposure ages (<12,500 years). There do not appear to be significant differences in natural TL levels (and hence surface exposure ages) between individual blue icefields in the region. The proportion of reheated meteorites from the Elephant Moraine region is similar to that of other Antarctic sites and modern falls, consistent with the uniformity of the meteoritic flux in this regard. An unusual subset of H‐chondrites, with high induced TL peak temperatures, is absent among the data for meteorites collected in the Elephant Moraine region, which stresses their similarity to modern falls. We suggest that the Elephant Moraine icefields formed through shallow ablation of the ice. Unlike the Allan Hills sites to the south, lateral transport is probably less important relative to the infall of meteorites in concentrating meteorites on these icefields.
Equatorial Atlantic sea surface temperature for the last 30 kyr: A comparison of U37k′, δ18O and foraminiferal assemblage temperature estimates
Authors: Sikes Elisabeth L. , Keigwin Lloyd D.
Published: February 2004

A recently developed technique for determining past sea surface temperatures (SST), based on an analysis of the unsaturation ratio of long chain C37 methyl alkenones produced by Prymnesiophyceae phytoplankton (U37k′), has been applied to an upper Quaternary sediment core from the equatorial Atlantic. U37k′ temperature estimates were compared to those obtained from δ18O of the planktonic foraminifer Globigerinoides sacculifer and of planktonic foraminiferal assemblages for the last glacial cycle. The alkenone method showed 1.8°C cooling at the last glacial maximum, about 1/2 to 1/3 of the decrease shown by the isotopic method (6.3°C) and foraminiferal modern analogue technique estimates for the warm season (3.8°C). Warm season foraminiferal assemblage estimates based on transfer functions are out of phase with the other estimates, showing a 1.4°C drop at the last glacial maximum with an additional 0.9°C drop in the deglaciation. Increased alkenone abundances, total organic carbon percentage and foraminiferal accumulation rates in the last glaciation indicate an increase in productivity of as much as 4 times over present day. These changes are thought to be due to increased upwelling caused by enhanced winds during the glaciation. If U37k′ estimates are correct, as much as 50–70% (up to 4.5°C) of estimated δ18O and modern analogue temperature changes in the last glaciation may have been due to changes in thermocline depth, whereas transfer functions seem more strongly influenced by seasonality changes. This indicates these estimates may be influenced as strongly by other factors as they are by SST, which in the equatorial Atlantic was only reduced slightly in the last glaciation.
A simplified radiative transfer equation for application in ocean microwave remote sensing
Authors: Guissard Albert , Sobieski Piotr
Published: February 2004

For inversion purposes in remote sensing applications, it is very useful to dispose of a simple, but nevertheless accurate enough, procedure for calculating brightness temperatures as received by spaceborne radiometers when observing the Earth surface through the atmosphere. Starting from an idea of Grody, a contracted form of the radiative transfer equation is proposed. It has the form of the equation for an attenuating atmosphere at constant temperature, above a lossy dielectric rough surface, under the specular approximation. However, it includes corrections for the atmospheric temperature profile and for the surface diffuse scattering. This last correction is an extension of that first proposed by Wentz. The resulting form of the equation and the importance of the correction terms are discussed for the practical case of the ocean surface. This equation has been used by the authors for the retrieval of geophysical parameters of the ocean surface and of the atmosphere from combined radiometric and radar measurements.
Bending and unbending of an elastic lithosphere: The Cenozoic history of the Apennine and Dinaride foredeep basins
Authors: Kruse Sarah E. , Royden Leigh H.
Published: February 2004

The Adriatic region forms an intermediate continental foreland overthrust along its northeastern margin by the southwest vergent Dinaric thrust belt in Eocene‐Oligocene time and along its southwestern margin by the northeast vergent Apennine thrust belt in Pliocene‐Quaternary time. Orogenic activity within these thrust belts was accompanied by the development of two superposed foredeep basin systems of opposite polarity and different ages. Using well log, biostratigraphic, and seismostratigraphic data, the geometry of this composite basin system was reconstructed along three profiles at beginning of Quaternary, middle Pliocene, beginning Pliocene, and beginning Eocene time. Modeling of reconstructed geometries using a thin elastic sheet approximation yields a range of acceptable effective elastic plate thicknesses for the central Adriatic region of Te = 5–10 km for Eocene‐Oligocene flexure and Te = 10–15 km for Pliocene‐Quaternary flexure (although an upper bound for Te could not be established on one of the three profiles). These results are consistent with a constant effective elastic plate thickness of Te = 10 km for the Adriatic lithosphere and preclude the possibility that significant weakening of the Adriatic plate occurred between flexural events. Modeling of incremental deflections between Pliocene and Quaternary time gives results consistent with constant values of Te = 10 km in the central Adriatic and Te = 15 km in the northern Adriatic and Po Plain and shows little evidence for weakening of the plate during Pliocene‐Quaternary time. Thus within the resolution of the data presented in this paper, there is little evidence for viscous relaxation of the lithosphere on time scales between about 2 and 50 m.y. Analysis of bending of an idealized lithosphere with a simple brittle‐elastic‐ductile rheology, and a low to moderate thermal gradient suggests that the small values of Te observed within the Adriatic region can be readily understood as the result of bending of the lithosphere to unusually high curvature (4 × 10−6 m−1) and do not require unusually high temperatures within the foreland lithosphere. The same rheological model is also consistent with the absence of significant inelastic yielding for at least 50 m.y. after the cessation of loading. An apparent unbending of the Adriatic lithosphere began in early Quaternary time, approximately coeval with the cessation of major thrusting within the Apennine thrust belt. The three‐dimensional pattern of Quaternary deflection makes it difficult to attribute this phenomenon to local depositional processes and suggests that unbending reflects a fundamental change in the subduction process in early Quaternary time. Our preferred interpretation is that unbending is the result of a diminution of forces acting on the subducted Adriatic lithosphere at mantle depths.
Extension versus compression during the Miocene tectonic evolution of the Betic chain. Late folding of normal fault systems
Authors: Crespo‐Blanc Ana , Orozco Miguel , Garcia‐Dueñas Víctor
Published: February 2004

The westernmost part of the Mediterranean Alpine Belt is represented by the Betic‐Rif orogenic belt, around the Gibraltar Arc, which in turn surrounds the Alboran Basin. In the Betic Chain, early and middle Miocene crustal thinning of the Alboran basement is well established, as extensional low‐angle normal faults and detachment faults, developed in both ductile and brittle conditions, thinned a previously thickened crust. In the Alboran Domain of the central Betics, two main extensional episodes are evidenced: a Langhian one, with a north‐northwestward transport direction, followed by a west‐southwestward extension, Serravallian in age. Therefore all the units heretofore considered to be thrust nappes are, in reality, extensional units bounded by low‐angle normal faults. The cortical segment studied formed the basement of the Miocene Alboran Basin, in which progressively deeper basement units were covered by younger marine sediments as a result of extensional denudation processes. The age of these sediments clearly dates the faulting. The extensional evolution during the Miocene is much more complex than the past models suggest. During the upper Miocene, these extensional systems were folded as the result of a compressive regime, which allowed them to be well exposed. Compression in the Gibraltar Arc is nearly contemporaneous with extension, and the westward migration of the compression through its footwall is related with the extensional spreading.
Paleomagnetism and rotation constraints for the middle Miocene southwestern Nevada volcanic field
Authors: Hudson Mark R. , Sawyer David A. , Warren Richard G.
Published: February 2004

Middle Miocene rocks of the southwestern Nevada volcanic field (SWNVF) lie across the projection of the Walker Lane belt within the Basin and Range province and thus provide an interesting opportunity to test for late Cenozoic vertical‐axis rotation. Paleomagnetic data from individual ash flow sheets document no significant relative vertical‐axis rotation among localities within central SWNVF, an area of relatively low stratal tilts and widely spaced faults. A time‐averaged mean paleomagnetic direction (D = 351.4°, I = 52.7°, α95= 4.5°) calculated from data from numerous separate rock units suggests that the central SWNVF underwent minimal counterclockwise vertical‐axis rotation (R = −7.1° ± 6.6°) with respect to the North American craton. No clockwise vertical‐axis rotation is found to support projection of dextral faults of the Walker Lane beneath the central SWNVF. Clockwise rotation of variable magnitude is common at numerous sites from southern and western margins of the field. These clockwise rotations probably reflect dextral shear strain developed at the interface between the little extended central SWNVF block and more strongly extended areas to the south and southwest of the field. Negligible rotation of 11.45‐Ma to 13.25‐Ma tuffs relative to the central SWNVF was found at the southeast margin of the field where 90° clockwise rotation at the northwest termination of the Las Vegas Valley shear zone had been postulated. Any clockwise rotation in this area must predate 13.25 Ma, and thus dextral shear within this part of the Walker Lane belt was not synchronous or connected across the southern margin of the field. Small counterclockwise vertical‐axis rotation relative to the craton, as found for the central SWNVF block, might be a regional feature in the western Great Basin.
Correction to “Effective water table depth to describe initial conditions prior to storm rainfall in humid regions” by Peter A. Troch, François P. De Troch, and Wilfried Brutsaert
Authors: Troch Peter A. , De Troch François P. , Brutsaert Wilfried
Published: February 2004

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Effect of cationic surfactants on organic liquid‐water capillary pressure‐saturation relationships
Authors: Demond A. H. , Desai F. N. , Hayes K. F.
Published: February 2004

Many solutes, either naturally occurring or introduced, are surface active and sorb preferentially at the interfaces of subsurface systems. In multiphase systems, the sorption of surfactants affects the capillary pressure‐saturation relationships, fundamental constitutive relationships in the modeling of multiphase flow. In this study, the impact of surfactant sorption on capillary pressure relationships for organic liquid‐waters systems was demonstrated by qualitatively correlating measurements of sorption and zeta potential, with interfacial tension and contact angle and, in turn, quantitatively relating these measurements to changes in capillary pressure‐saturation relationships for o‐xylene‐water‐quartz systems containing a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The results show that the sorption of CTAB causes the naturally hydrophilic system to become hydrophobic, as evidenced by a change in the contact angle from about 10°–15° to 155° or 180°, depending on the pH. This change in hydrophilicity is reflected in the zeta potential of the system which goes from negative to positive as the aqueous phase CTAB concentration increases. The spontaneous imbibition capillary pressure‐saturation relationship is more sensitive to the sorption of CTAB than the drainage relationship. To predict the observed changes in both capillary pressure‐saturation relationships, a modified form of Leverett's function was used where roughness and curvature corrections were incorporated into the intrinsic contact angle to give an operational contact angle. A comparison of the measured and predicted capillary pressure‐saturation relationships showed reasonable agreement.
Toward the development of a multidirectional vegetation index
Authors: Chehbouni A. , Kerr Y. H. , Qi J. , Huete A. R. , Sorooshian S.
Published: February 2004

Vegetation‐related information is critical for modeling hydrological processes. Remotely sensed spectral data provide powerful means to characterize vegetation status. However, the non‐Lambertian behavior of most surfaces induces a large view/Sun angle dependence. Two approaches are possible to correct such contamination. One approach consists of using directional reflectance models; the other consists of normalizing the Sun/view angle effects directly on vegetation indices that have the advantage of being less sensitive to surface anisotropy than individual reflectances. Ground‐based multiple view direction/angle measurements made over a semiarid grassland canopy at the Walnut Gulch experiment watershed (Monsoon '90 experiment) were used to develop and to validate a semiempirical model to normalize the MSAVI (modified soil‐adjusted vegetation index) response to a nadir, regardless of view/direction angle. We further advanced this model to account simultaneously for both Sun and view angle variations by introducing a shadow parameterization. The results showed that this model can be used to monitor the vegetation status using a single view/Sun configuration throughout the growing season. We therefore believe that we have taken a further step toward the development of a multidirectional vegetation index.
Transport of chromium and selenium in the suboxic zone of a shallow aquifer: Influence of redox and adsorption reactions
Authors: Kent D. B. , Davis J. A. , Anderson L. C. D. , Rea B. A. , Waite T. D.
Published: February 2004

Breakthrough of Cr(VI) (chromate), Se(VI) (selenate), and O2 (dissolved oxygen) was observed in tracer tests conducted in a shallow, sand and gravel aquifer with mildly reducing conditions. Loss of Cr, probably due to reduction of Cr(VI) to Cr(III) and irreversible sorption of Cr(III), occurred along with slight retardation of Cr(VI), owing to reversible sorption. Reduction of Se(VI) and O2 was thermodynamically feasible but did not occur, indicating conditions, were unfavorable to microbial reduction. Cr(VI) reduction by constituents of aquifer sediments did not achieve local equilibrium during transport. The reduction rate was probably limited by incomplete contact between Cr(VI) transported along predominant flow paths and reductants located in regions within aquifer sediments of comparatively low permeability. Scatter in the amount of Cr reduction calculated from individual breakthrough curves at identical distances downgradient probably resulted from heterogeneities in the distribution of reductants in the sediments. Predictive modeling of the transport and fate of redox‐sensitive solutes cannot be based strictly on thermodynamic considerations; knowledge of reaction rates is critical. Potentially important mass transfer rate limitations between solutes and reactants in sediments as well as heterogeneities in the distribution of redox properties in aquifers complicate determination of limiting rates for use in predictive simulations of the transport of redox‐sensitive contaminants in groundwater.
The universal structure of the groundwater flow equations
Authors: Beckie Roger , Aldama Alvaro A. , Wood Eric F.
Published: February 2004

Most groundwater flow models are not sufficiently detailed to allow an explicit representation of all dynamical scales. Instead, most models are constructed at such a coarse scale of resolution that unresolved subgrid variability often exists. It is therefore important to understand the interaction between unresolved dynamics and explicitly resolved dynamics. The concept of universality is central to this interaction and is here related to the problem of rescaling models of groundwater flow. We examine when it is possible to construct an accurate model for the explicitly resolved large scales, without an explicit description of the subgrid scale dynamics. We demonstrate how unresolved subgrid scale dynamics interact with resolved scale dynamics. We show that a universally valid resolved scale model can be constructed if the resolved dynamics are sufficiently independent of the details of the subgrid scale dynamics. In that event, a resolved scale model is composed of a universal structure and accompanying model parameters. The model parameters represent the effect of unresolved dynamics upon resolved dynamics. We examine two possible model structures for groundwater flow. We show theoretically, and numerically, that a local Darcy law is a universally valid resolved scale model if the resolved and subgrid scales of the hydraulic conductivity are separated in scale by a so‐called spectral gap. If, however, the hydraulic conductivity possesses many scales of variability, then a more general nonlocal Darcy law is a more appropriate model structure. When the nonlocal Darcy's law is more appropriate, numerical experiments suggest that errors using a local Darcy's law with effective parameters are most significant at the smallest resolving scale of the model, and are minimal at scales between 8 and 16 times the resolving scale.
A one‐dimensional ice thermodynamics model for the Laurentian Great Lakes
Authors: Croley Thomas E. , Assel Raymond A.
Published: February 2004

Great Lakes hydrologic research requires the use of continuous‐simulation daily ice cover models over long time periods in the absence of field observations. They must be physically based, rather than statistically based, for use under conditions different than those under which they were derived. But they also must match existing conditions for which data exist. A review discloses that existing ice dynamics models do not meet all of these criteria; a new one that does is based here on a prismatic ice pack heat balance, ice growth and temperature constraints, and thermodynamic flux terms from companion water heat balance and storage equations. The prismatic ice model is a good first step to understanding complex geometries and is supportable through the use of lake‐averaged energy fluxes. The ice model is integrated into an existing lake thermodynamics and one‐dimensional heat storage model, and the resulting combination is calibrated for Laurentian Great Lakes applications. Simulation experiments are used to analyze the model's strengths and limitations and to explore its relevance. Comparisons between model output and existing data allow consideration of the ice climatology of the Great Lakes; the climatology description is extended through use of the new model. Promising potential model extensions include spatial extension, additional parameterizations for wind‐ice movement, snow, and albedo, and inclusions of remotely sensed data.
Probability distributions for flood warning systems
Authors: Kelly Karen S. , Krzysztofowicz Roman
Published: February 2004

Engineering design, optimal operation, evaluation of performance, and benefit‐cost analysis of a local flood warning system require an explicit and extensive characterization of uncertainties in terms of probability distributions. Such a characterization is obtained via a Bayesian Processor of Forecasts (BPF) which provides (1) a prior description of uncertainty about flood occurrence and crest height, (2) a stochastic characterization of the forecaster in terms of likelihood functions, and (3) a posterior description of uncertainty about flood occurrence and crest height, conditional on a flood crest forecast. The theoretical novelty of our BPF is that a posterior distribution can be constructed for any prior distribution, parametric or nonparametric, the generality essential in light of the variety of models used as flood crest distributions. The conceptual novelty of the BPF opens a new research paradigm (which provides distributions for real‐time decision making based on forecasts) that adjoins the classical flood frequency analysis (which has provided probability distributions for planning and design).