bluuebunny/crossref_metadata_2025 huggingface dataset:
Evolution and dynamics of tropical river plumes in the Great Barrier Reef: An integrated remote sensing and in situ study
Authors: Burrage D. M. , Heron M. L. , Hacker J. M. , Stieglitz T. C. , Steinberg C. R. , Prytz A.
Published: December 2002

The short‐lived but intense discharge of freshwater from tropical rivers into the Great Barrier Reef (GBR) Lagoon and the associated salinity reductions are a critical consideration in marine research and management of the ecologically sensitive GBR World Heritage Area. Salinity provides a unique tracer that gives clues to the origin of river‐borne contaminants and allows the influences of storm‐induced resuspension and river discharge on turbidity to be clearly distinguished. We describe a field investigation of the evolution and dynamics of the Herbert River plume in the central GBR. Its primary goals were to use an airborne salinity mapper and in situ instruments to study the three‐dimensional structure and evolution of the plume and to lay a foundation for numerical modeling studies of its dynamics. The aircraft surveys provided a rapid assessment of the plumes spatial extent, while the in situ data revealed details of its subsurface structure. The Herbert River plume was produced by heavy rainfall associated with tropical storms during the La Nina‐dominated 1999/2000 monsoon season. In the near field, the surface expression of the plume boundaries was indicated by sharp color and salinity fronts that were clearly visible from the air and sea surface. In the far field and middle Lagoon, the plume was more dispersed and ultimately merged with the larger‐scale salinity gradients and with the remnant plume of the more distant, and larger, Burdekin River. The plume location and structure evolved in response to changing river flows, tidal and subtidal circulation, and wind. Using Garvine's Kelvin number‐based scheme, the plume was classified as intermediate in dynamical character and thus is subject to a variety of forcings. The plume evolved in response to changes in the relative intensity of tidal currents and low‐frequency circulation due to wind and western boundary current forcing. It also displayed a characteristic “hook‐shaped” structure, which has been identified previously in numerical plume model studies. This structure appeared in the presence of accelerating along‐shelf current flow and horizontal shear and it indicates that the plume circulation had a strongly three‐dimensional character. The approach demonstrates the efficacy of combining airborne and in situ methods to observe rapidly evolving coastal salinity structure and dynamics and sets the stage for future satellite‐borne studies of larger‐scale features showing contrasting salinity distributions.
Regions of estuarine convergence at high Rossby number: A solution in estuaries with elliptical cross sections
Authors: Mied Richard P. , Handler Robert A. , Donato Timothy F.
Published: December 2002

Generation of convergence regions in homogeneous rotating rectilinear estuaries is addressed. The mechanism investigated is the tilting of the planetary vorticity by the vertical shear of the along‐estuary flow, which can result in rapidly growing surface convergence regions aligned along the axis of the estuary. The complexity introduced by the bathymetry geometry and the nonlinearity of the equations has resulted in computationally intensive numerical solutions to this problem [Mied et al., 2000; Handler et al., 2001]. However, an analytical solution that will allow the study of varying parameters and the observation of general trends is possible with a judicious choice of bottom bathymetry and appropriate analytical simplifications. The equations for the along‐channel flow (V) and the cross‐channel stream function (ψ) become independent in the limit of vanishingly small rotation or large Rossby number. Consequently, we express them as an asymptotic series in the reciprocal of the Rossby number (1/Ro), and find that the choice of an elliptically shaped bottom profile allows us to solve for the leading order terms. The steady along‐channel flow is a Poiseuille flow on a nonrotating Earth, while the related cross‐channel response is a closed circulation cell with a clockwise rotation when looking in the direction of the along‐channel flow. A salient result is that the associated cross‐channel surface convergence is proportional to the Coriolis parameter (f), the maximum along‐channel velocity, and the aspect ratio (depth/width) of the channel.
Coupled dynamics of short waves and the airflow over long surface waves
Authors: Kudryavtsev V. N. , Makin V. K.
Published: December 2002

A study is presented of modulations induced by a dominant long surface wave (LW) in the coupled airflow–short wind‐generated waves (SW) system. The modulation of SWs in the gravity range results from their interaction with the LW orbital velocity and their interaction with the wind stress modulated by the LW. The modulation of waves in the capillary range is mainly due to the modulation of the rate of generation of parasitic capillaries by steep short gravity waves. The variation of the wind surface stress is described by the dynamics of the turbulent airflow over the LW with the surface roughness varying along its profile. The variation of the surface roughness is caused by the variation of the form drag supported by modulated SWs. In turn, the LW‐induced variation of the surface stress affects the SW modulation. This provides a feedback in the coupled airflow–SW system in the presence of the LW. The model results show that the amplitude of the surface roughness modulation can be large. In terms of the modulation transfer function (MTF), it can reach values of 10–20. The modulation of the form drag, which causes the modulation of the surface roughness, comes mainly from short breaking waves strongly modulated by dominant waves. The modulation of the surface roughness considerably affects the dynamics of the airflow over the LW and thus the LW wind growth rate. Models of the airflow above waves assuming a constant roughness parameter underestimate the growth rate parameter approximately two to three times as compared to the measured values. The present study shows that when the variation in the surface roughness is accounted for, the growth rate parameter increases roughly twice, which to a large extent reduces the discrepancy with measurements.
Vertical and meridional distributions of the atmospheric CO2 mixing ratio between northern midlatitudes and southern subtropics
Authors: Machida T. , Kita K. , Kondo Y. , Blake D. , Kawakami S. , Inoue G. , Ogawa T.
Published: December 2002

The atmospheric CO2 mixing ratio was measured using a continuous measurement system onboard a Gulfstream‐II aircraft between the northern midlatitudes and the southern subtropics during the Biomass Burning and Lightning Experiment Phase A (BIBLE A) campaign in September–October 1998. The vertical distribution of CO2 over tropical regions was almost constant from the surface to an altitude of 13 km. CO2 enhancements from biomass burning and oceanic release were observed in the tropical boundary layer. Measurements in the upper troposphere indicate interhemispheric exchange was effectively suppressed between 2°N–7°N. Interhemispheric transport of air in the upper troposphere was suppressed effectively in this region. The CO2 mixing ratios in the Northern and Southern Hemispheres were almost constant, with an average value of about 365 parts per million (ppm) and 366 ppm, respectively. The correlation between the CO2 and NOy mixing ratios observed north of 7°N was apparently different from that obtained south of 2°N. This fact strongly supports the result that the north‐south boundary in the upper troposphere during BIBLE A was located around 2°N–7°N as the boundary is not necessary a permanent feature.
Inversion of multiangle sky radiance measurements for the retrieval of atmospheric optical properties 1. Algorithm
Authors: Qin Yi , Box Michael A. , Jupp David L. B.
Published: December 2002

An inversion technique is developed that retrieves single scattering albedo and phase function from multiangle sky radiance measured at the ground. A linear equation system is first derived from the radiative perturbation theory to approximately represent exiting radiance as a function of single scattering albedo and the Legendre polynomial coefficients of the phase function. However, this linear system is ill‐posed. Regularization is thus introduced to obtain a stable solution. An important and difficult step of the regularization is the determination of the regularization parameter, especially when iteration is involved in the inversion. A number of methods described in the literature that fit best into our general inversion approach, such as the L curve method, have been tried, but it is found that the regularization parameter derived from these methods is constantly too small, resulting in an unstable inversion procedure. Because of this, efforts have been made to obtain a more appropriate regularization parameter. In this paper, we focus on the development of the inversion technique. Results obtained using the technique from both synthetic and real measurements are presented by Qin et al. [2002b].
Inversion of multiangle sky radiance measurements for the retrieval of atmospheric optical properties 2. Application
Authors: Qin Yi , Jupp David L. B. , Box Michael A.
Published: December 2002

In the first paper of this series, we described an inversion scheme that retrieves single scattering albedo and phase function from multiangle sky radiance measured at the ground. In this paper, this technique is applied to synthetic Cimel measurements with varying levels of random noise. Our results show that the technique is robust. Good results have been obtained even when strong noise is present. Sensitivity studies have been conducted to analyze the influence of errors in surface albedo and total optical thickness on retrieval. No significant effects have been found due to 10% total optical thickness error, or as large as 100% surface albedo error. However, errors in both factors may have an impact on the retrieval of single scattering albedo. In this paper, the developed technique is also applied successfully to Cimel measurements provided by Aerosol Robotic Network. Retrieved optical properties are compared with those calculated from the aerosol physical properties retrieved by the Dubovik algorithm. A good agreement between the two properties was found.
The seasonal cycle of cosmogenic 14CO at the surface level: A solar cycle adjusted, zonal‐average climatology based on observations
Authors: Jöckel Patrick , Brenninkmeijer Carl A. M.
Published: December 2002

Mainly three processes determine the 14CO content of the troposphere: the cosmogenic production of 14C throughout the atmosphere, the removal (oxidation) by the hydroxyl radical (OH), and the transport of 14CO from the stratosphere into the troposphere. These characteristics make 14CO an interesting tracer for application in atmospheric dynamics and chemistry research. If 14CO observations from different times have to be compared for changes in OH or the stratosphere–troposphere exchange (STE), the varying global source strength of 14CO caused by variations in solar activity has to be taken into account. Three approaches for parameterizing solar activity with respect to the effect on the global average atmospheric 14CO production rate are developed and compared. These methods involve the sunspot number, the heliospheric potential, and atmospheric neutron monitor data. Applying further results from previous studies about the atmospheric response, a rescaling procedure for 14CO observations of different epochs to the same solar activity conditions is derived. All three approaches yield consistent results, whereby small differences provide an uncertainty estimate. The rescaling is used to compile the first solar cycle adjusted, zonal‐average 14CO climatology (cosmogenic contribution) from all currently available 14CO observations at the surface level. For this, in a first step, the smaller contribution of 14CO of noncosmogenic, that is, biogenic origin (secondary source) is estimated from CO observations and subtracted from the measurements. The resulting climatology can be used to trace changes if compared to future observations, and especially for the evaluation of OH distributions and the stratosphere–troposphere exchange in three‐dimensional global atmospheric models.
Some theoretical results concerning O3‐NOx‐VOC chemistry and NOx‐VOC indicators
Authors: Sillman Sanford , He Dongyang
Published: December 2002

A series of model results is shown pertaining to ozone, reactive nitrogen (NOy), and peroxides in polluted regions. The results focus on ratios such as O3/NOy and H2O2/HNO3 that have been proposed as indicators for O3‐NOx‐VOC sensitivity. These ratios are shown to correlate with predicted NOx‐VOC sensitivity for a variety of zero‐dimensional (0‐D) and 3‐D models, but the correlation varies in situations ranging from relatively clean to highly polluted. The previously identified NOx‐VOC transition values for indicators appear to be valid for moderately polluted conditions with 80–150 ppb O3. Changes in indicator behavior are linked to odd hydrogen chemistry and in particular to changes in the ratio of O3 to primary radical production. Changes in indicator behavior are also correlated with the values of a test ratio, O3/(2H2O2+NOz) which can be evaluated against measurements. Ratios of the form ΔO3/ΔNOy, representing differences relative to background values, are proposed for analyzing NOx‐VOC sensitivity in individual urban plumes. Comparisons are made to extent‐of‐reaction parameters, which have been proposed for evaluating NOx‐VOC sensitivity.
Detailed analysis of the error associated with the rainfall retrieved by the NOAA/NESDIS Special Sensor Microwave/Imager algorithm 2. Rainfall over land
Authors: Ferraro Ralph , Li Qihang
Published: December 2002

This study has investigated the error associated with the estimation of instantaneous areal rain rate over land by the NOAA/NESDIS Office of Research and Application's Special Sensor Microwave/Imager (SSM/I) algorithm. By comparing with ground‐based rain observations from the Oklahoma Mesonet rain gage network, the error inherent in the SSM/I‐based areal rain estimate is quantified. Since the ground‐based gauges use point measurements to estimate areal rain, the gauges do not make a perfect estimate and contain an associated error. A formulation has been developed by which the difference between the SSM/I‐ and Mesonet‐based estimates is divided into two parts: one due to the error in the Mesonet and the other due to the error in the SSM/I. A separate formulation has also been developed by which the error in Mesonet‐based rain measurement is quantified according to the gage density and the statistics of rain (variance and spatial correlation). A nine‐month data set of 15‐min rain accumulation for over 100 gages from the Mesonet has been used to obtain the rain statistics and to compare with the SSM/I estimate over various spatial scales. Results show that the error for the instantaneous SSM/I rain rate over 0.5, 1.0, and 2.5‐degree boxes are approximately 150%, 100%, and 70% of the mean areal rain rate, respectively.
Summertime tropospheric ozone over China simulated with a regional chemical transport model 1. Model description and evaluation
Authors: Ma Jianzhong , Liu Hongli , Hauglustaine Didier
Published: December 2002

A three‐dimensional regional chemical transport model, extended from the Regional Acid Deposition Model (RADM) and aimed at studying the distribution and budget of tropospheric ozone and its precursors over China, is presented. The model domain covers the China region with a horizontal resolution of 100 km. In the vertical, the model extends up to the pressure level of 10 mbar for meteorological simulation, and to the local thermal tropopause for chemical integration. The meteorological fields for the model run are provided with the Fifth‐Generation National Center for Atmospheric Research (NCAR)/Penn State Mesoscale Model (MM5). In addition to updated surface emissions, aircraft emissions and lightning NOx sources are taken into account. The initial fields and lateral boundary conditions for most chemical tracers are provided with a global chemical transport model for ozone and related chemical tracers (MOZART). The model simulation is performed for the period July 1–15, 1995, which appears to be representative of meteorological conditions in summertime over China. The model results are compared with surface measurements of ozone and its precursors in China, ozone soundings in Japan, and MOZART results for the China region. The daily variation as well as geographical and vertical distribution of O3 concentration is generally well simulated by the model. It is indicated that surface ozone is controlled by photochemistry in eastern China and by transport processes in western China. Large‐scale transport of O3 and its precursors from the highest‐source‐emission regions to remote areas and the free troposphere is simulated.
On the pathways and timescales of intercontinental air pollution transport
Authors: Stohl Andreas , Eckhardt Sabine , Forster Caroline , James Paul , Spichtinger Nicole
Published: December 2002

This paper presents results of a 1‐year simulation of the transport of six passive tracers, released over the continents according to an emission inventory for carbon monoxide (CO). Lagrangian concepts are introduced to derive age spectra of the tracer concentrations on a global grid in order to determine the timescales and pathways of pollution export from the continents. Calculating these age spectra is equivalent to simulating many (quasi continuous) plumes, each starting at a different time, which are subsequently merged. Movies of the tracer dispersion have been made available on an Internet website. It is found that emissions from Asia experience the fastest vertical transport, whereas European emissions have the strongest tendency to remain in the lower troposphere. European emissions are transported primarily into the Arctic and appear to be the major contributor to the Arctic haze problem. Tracers from an upwind continent first arrive over a receptor continent in the upper troposphere, typically after some 4 days. Only later foreign tracers also arrive in the lower troposphere. Assuming a 2‐day lifetime, the domestic tracers dominate total tracer columns over all continents except over Australia where foreign tracers account for 20% of the tracer mass. In contrast, for a 20‐day lifetime even continents with high domestic emissions receive more than half of their tracer burden from foreign continents. Three special regions were identified where tracers are transported to, and tracer dilution is slow. Future field studies therefore should be deployed in the following regions: (1) In the winter, the Asia tracer accumulates over Indonesia and the Indian Ocean, a region speculated to be a stratospheric fountain. (2) In the summer, the highest concentrations of the Asia tracer are found in the Middle East. (3) In the summer, the highest concentrations of the North America tracer are found in the Mediterranean.
Spectral characteristics and predictability of the NAO assessed through Singular Spectral Analysis
Authors: Gámiz‐Fortis S. R. , Pozo‐Vázquez D. , Esteban‐Parra M. J. , Castro‐Díez Y.
Published: December 2002

For the period 1826–2000, we analyze the spectral characteristics of the winter North Atlantic Oscillation (NAO) index and its predictability based on Singular Spectral Analysis (SSA) and Autoregressive Moving Average (ARMA) models. In the first part, SSA is applied to the winter NAO index to isolate its main spectral characteristics. Based on the SSA, a reconstruction (filtering) of the winter NAO index series was carried out. Results of the SSA indicate that the winter NAO index can be broken down into some modulated amplitude oscillations with periods around 7.7 and 4.8 years, some oscillations associated with a broadband peak of period around 2.4 years along with nonlinear trends. The sum of these components, the SSA‐filtered series, explains 56% of the variance of the raw winter NAO index. The SSA‐filtered series is particularly reliable, reproducing the NAO phase during extreme events (winter NAO index ≥ 1 or ≤ −1); for this subset of events, the phase of the actual and SSA‐filtered series shows to be the same in 91% of the cases. The high positive values observed in the winter NAO index in the last eighties and nineties appear to be associated with the simultaneous presence of a positive trend, starting in the early eighties and of unprecedented steepness, and an oscillation with period around 7.7 years, having very high amplitude. In the second part, an ARMA model has been fitted to the filtered winter NAO index and a forecasting experiment was conducted; results are tested against the raw winter NAO index. Results show that the ARMA modeling has useful 1‐year‐ahead forecasting abilities. Particularly, over the period 1986–2000, not used to fit the model, the model skill is 27.8% better than climatology and 43.3% better than persistence (38.5% and 47.6%, respectively, when taking into account only extreme NAO events). Additionally, percentage of cases in which the NAO phase was accurately predicted proved to be 80% (88% for extreme NAO events). For 2001/2002 and 2002/2003 winters, persistence in the negative phase of the NAO is predicted, having an index value close to −1.
FORTE satellite observations of very narrow radiofrequency pulses associated with the initiation of negative cloud‐to‐ground lightning strokes
Authors: Jacobson Abram R. , Shao Xuan‐Min
Published: December 2002

The FORTE satellite's radiofreqency receiver/recorder system has been used to study extremely narrow (∼100 ns width) radiofrequency pulses accompanying the initiation of negative cloud‐to‐ground strokes. These pulses have been observed from the ground for over two decades. The FORTE space‐based observations are substantially consistent with the prior ground‐based results, at least in regard to pulsewidth, distance‐scaled pulse amplitude, and the pulses' basic association with negative cloud‐to‐ground strokes, relative to either positive cloud‐to‐ground or intracloud strokes. New results from the FORTE observations include (1) information on the radiation pattern (versus elevation angle), (2) the tendency of the underlying fast‐pulse radiation process to occur preferentially in marine, rather than dry‐land, locations, and (3) the high degree of linear polarization of the radiated signal. These three new results were not accessible to ground‐based measurements, which do not sample elevation angles other than zero, whose signal distortion with overland propagation paths (at zero elevation angle) tends to confuse the issue of the (land versus sea) location affinity of the pulse source itself, and whose received signal is a fortiori linearly polarized because of the adjacent ground plane. The narrow radiofrequency pulse that accompanies negative cloud‐to‐ground strokes provides a useful identifier, in the satellite's radiofrequency datastream, of the occurrence of this particular kind of stroke. Additionally, the observations reported here indicate that the radiating element is a single, vertical current stalk, rather than a collection of randomly oriented, mutually incoherent dipoles, such as are believed to be responsible for most very high frequency signals from lightning.
Spectroscopic water vapor sensor for rapid response measurements of humidity in the troposphere
Authors: Kebabian Paul L. , Kolb Charles E. , Freedman Andrew
Published: December 2002

We have developed a closed‐path water vapor sensor based on optical absorption of an atomic argon emission line that is suitable for rapid response (10 Hz bandwidth) humidity measurements in the lower and middle troposphere. The sensor uses an argon emission line at 935.4 nm that can be Zeeman‐split into two components, only one of which is strongly absorbed by a water absorption line at 10,687.36 cm−1 (∼935.6 nm). The sensor exhibits a noise figure‐of‐merit of 40 ppmv Hz−1/2 at low humidities (below 0.5%); the noise level slowly rises to 60 ppmv Hz−1/2 as water vapor mixing ratios reach 2.5%. The performance of this sensor was compared to that of a chilled mirror hygrometer and a capacitance‐based polymer sensor, all of which were installed on board a Twin Otter airplane during an atmospheric humidity measurement campaign conducted northeast of Hawaii. Over a range of water vapor volume mixing ratios of 0.1–3% (at altitudes of 50–3000 m), the sensors were shown to agree with one another within 5% of the measurement in regions of slowly changing humidity. However, in regions of large humidity gradients, the optical sensor (with the use of an appropriate inlet tube) was able to track water vapor features on the scale of tens of meters or less that neither the slow‐response chilled mirror hygrometer nor the capacitance‐based sensor could adequately reproduce. The optical sensor was also able to track humidity in the vicinity of clouds and discern fine structure within the cloud itself.
Uniplanar circularly polarized slot‐ring antenna architectures
Authors: Fries Matthias K. , Vahldieck Rüdiger
Published: December 2002

This paper presents a novel printed uniplanar antenna architecture for circular polarization. The structure consists of a single‐fed slot‐ring antenna with asymmetrically placed perturbations. The influence of different kinds of perturbations and substrates on the size of the antenna, its impedance bandwidth, and its axial ratio bandwidth is investigated. Various feed circuits based on coplanar waveguides (CPWs), coaxial line, and microstrip are investigated as well. Low‐cost applications such as tagging antennas at 2.45 GHz are tested in combination with a coaxial line and CPW feed circuit. It was found that antennas achieving an impedance bandwidth over 60% and an axial ratio bandwidth up to 15% can be realized without the need of airbridges and rf‐substrates.
Irregularities of the topside ionosphere observed by GPS/MET radio occultation
Authors: Hocke K. , Igarashi K. , Pavelyev A.
Published: December 2002

Large‐scale fluctuations (vertical scales ∼40–60 km) of total electron content (TEC) are retrieved from phase path fluctuations of GPS radio occultation links of the GPS/MET experiment. The large‐scale TEC fluctuations at observation heights 400–600 km are maximal at local times from 20:00 to 24:00 h. The fluctuations mainly occur on the summer hemisphere at low magnetic latitudes 0–30°N and seem to be concentrated over Africa and Arabia. The derived global distribution of TEC fluctuations around solar minimum (June/July 1995) is assumed to be closely related to the occurrence of spread F and radio scintillations. The meridional distribution of the background electron density (averaged for 19:00–23:00 LT) has a maximum in the topside ionosphere at around 10°N, beyond an anomaly structure of the F2 peak layer. The meridional location of the anomaly structure agrees with the location of enhanced TEC fluctuations. Both phenomena are possibly related to the enhancement of upward ion velocity in the postsunset ionosphere at equatorial latitudes. Large TEC depletions of 1–20 TEC‐units are present at observation heights 200–400 km in many TEC profiles of the equatorial ionosphere after sunset. The TEC depletions possibly indicate plasma bubbles on their way from the lower ionosphere to the topside ionosphere. GPS navigation signal loss due to spread F or high‐latitude irregularities is not found in the GPS/MET data of June/July 1995.
Estimating the sources and transport of nutrients in the Waikato River Basin, New Zealand
Authors: Alexander Richard B. , Elliott Alexander H. , Shankar Ude , McBride Graham B.
Published: December 2002

We calibrated SPARROW (Spatially Referenced Regression on Watershed Attributes) surface water‐quality models using measurements of total nitrogen and total phosphorus from 37 sites in the 13,900‐km2 Waikato River Basin, the largest watershed on the North Island of New Zealand. This first application of SPARROW outside of the United States included watersheds representative of a wide range of natural and cultural conditions and water‐resources data that were well suited for calibrating and validating the models. We applied the spatially distributed model to a drainage network of nearly 5000 stream reaches and 75 lakes and reservoirs to empirically estimate the rates of nutrient delivery (and their levels of uncertainty) from point and diffuse sources to streams, lakes, and watershed outlets. The resulting models displayed relatively small errors; predictions of stream yield (kg ha−1 yr−1) were typically within 30% or less of the observed values at the monitoring sites. There was strong evidence of the accuracy of the model estimates of nutrient sources and the natural rates of nutrient attenuation in surface waters. Estimated loss rates for streams, lakes, and reservoirs agreed closely with experimental measurements and empirical models from New Zealand, North America, and Europe as well as with previous U.S. SPARROW models. The results indicate that the SPARROW modeling technique provides a reliable method for relating experimental data and observations from small catchments to the transport of nutrients in the surface waters of large river basins.
Testing the distributed water table predictions of TOPMODEL (allowing for uncertainty in model calibration): The death of TOPMODEL?
Authors: Blazkova Sarka , Beven Keith , Tacheci Pavel , Kulasova Alena
Published: December 2002

The distributed predictions of the original version of TOPMODEL are here compared with distributed observations of water table levels in the Uhlirska catchment in the Jizera Mountains, Czech Republic. The calibration of the model has been carried out within the GLUE framework, which allows the estimation of uncertainties in predicting the distributed patterns of the water table at different times. Many of the water table levels are predicted within the limits of uncertainty, but it is shown that the predictions could be improved by the calculation of a local effective transmissivity value (or local upslope contributing areas) at each observation site. These effective transmissivities show a similar relationship to the topographic index as found in a previous study of a small catchment in Norway. Some of the anomalies can be explained by deficiencies in the topographic analysis but this may also be an indication of possible structural deficiencies in the model. Interpretation is, however, difficult, and it remains to be seen whether these anomalies might be avoided in more dynamic distributed models.
Visual attributes of a rock and their relationship to permeability: A comparison of digital image and minipermeameter data
Authors: Tidwell Vincent C. , Wilson John L.
Published: December 2002

What is the relationship between the visual attributes of a rock sample and its permeability, and how might such information be used in aquifer/reservoir characterization? We investigated these questions by way of three meter‐scale blocks of rock, two sandstones, and one volcanic tuff. Each rock exhibits visual and permeability patterns that differ in geometry, intensity, and scale. Using a gas minipermeameter, hundreds to thousands of permeability values were collected on grids at centimeter‐scale resolution from each block face and compared to the digital visual image of the same face. We found no significant direct correlation between the permeability measurements and any objective textural measure drawn from the corresponding digital images, despite the obvious resemblance of the permeability maps and visual images. Hypothesizing that the human eye relies on spatial correlation to synthesize information, we calculated and compared semivariograms for both the maps and the images. Semivariogram shape, anisotropy ratio, and principal axes orientation were consistent for the maps and images of each rock but different between rocks. To explore this similarity further, we compared discrete features appearing in map/image pairs, using a difference of Gaussian edge filter to segment (i.e., delineate) the spatial features. The filter consistently colocated visually sharp features, such as sedimentological bounding surfaces, in both the map and the image. Additionally, cumulative distribution functions characterizing the size, shape, and orientation of the segmented features were statistically indistinguishable between a permeability map and its corresponding visual image but statistically different between rocks. These results suggest that it may not always be possible to use visual images (photographs or scans) of outcrops to directly map permeability, even with a training set of punctual permeability data. In particular, defining such relations may be difficult where the scales of analysis and/or intensity of heterogeneity are limited (e.g., within a given facies) as is the case here. Where direct mapping is not possible, these results suggest that visual images can still be used to delineate spatial permeability patterns, especially to locate boundaries where sharp permeability contrasts occur. Other surrogate measurements of permeability, in particular the various geophysical methods, may exhibit similar behavior.
Global sinks of PCBs: A critical assessment of the vapor‐phase hydroxy radical sink emphasizing field diagnostics and model assumptions
Authors: Axelman Johan , Gustafsson Örjan
Published: December 2002

Polychlorinated biphenyls (PCBs) are ubiquitous contaminants in the global biogeosphere. Based on extrapolation of reaction rates determined at temperatures in laboratory experiments that were 60–100 degrees above global average tropospheric temperatures, it has been suggested that the gas‐phase reaction with the hydroxy radical (HO·) in the troposphere constitutes the strongly dominating sink for PCBs. An assessment of a broad set of field observations relevant to the actual environmental behavior of individual PCB congeners suggests that such an assertion should be treated with some caution. First, if the proposed reaction rates were applied to published tropospheric contents of individual PCB congeners, a continuous order‐of‐magnitude depletion of the lighter congeners relative to more chlorinated ones would be predicted. However, a large shift in PCB fingerprint is inconsistent with congener‐specific sediment archives, where a disproportionate historical depletion of lighter PCBs cannot be found. Alternatively, such HO·‐reaction rates would require a continuous source flux of PCBs to today's environment grossly enriched (again by several orders‐of‐magnitude) in lighter PCB congeners to counterbalance the implied selective congener losses; a scenario that is not supported by available information on emission rates. Further, the existence of a latitudinal trend in tropospheric concentrations, where the highest concentrations are found at lower latitudes, suggests that the fate of PCBs is controlled by temperature‐driven partitioning processes rather than a HO·‐reaction sink, which would be expected to be more efficient at lower latitudes. Finally, the observed tropospheric variability of individual PCB concentrations conform poorly with both the absolute values and congeneric trends in predicted reaction lifetimes. A reconciliation of these apparent discrepancies is attempted.
Landscape level differences in soil carbon and nitrogen: Implications for soil carbon sequestration
Authors: Garten Charles T. , Ashwood Tom L.
Published: December 2002

The objective of this research was to understand how land cover and topography act, independently or together, as determinants of soil carbon and nitrogen storage over a complex terrain. Such information could help to direct land management for the purpose of carbon sequestration. Soils were sampled under different land covers and at different topographic positions on the mostly forested 14,000 ha Oak Ridge Reservation in Tennessee, USA. Most of the soil carbon stock, to a 40‐cm soil depth, was found to reside in the surface 20 cm of mineral soil. Surface soil carbon and nitrogen stocks were partitioned into particulate (≥53 μm) and mineral‐associated organic matter (<53 μm). Generally, soils under pasture had greater nitrogen availability, greater carbon and nitrogen stocks, and lower C:N ratios than soils under transitional vegetation and forests. The effects of topography were usually secondary to those of land cover. Because of greater soil carbon stocks, and greater allocation of soil carbon to mineral‐associated organic matter (a long‐term pool), we conclude that soil carbon sequestration, but not necessarily total ecosystem carbon storage, is greater under pastures than under forests. The implications of landscape‐level variation in soil carbon and nitrogen for carbon sequestration are discussed at several different levels: (1) nitrogen limitations to soil carbon storage; (2) controls on soil carbon turnover as a result of litter chemistry and soil carbon partitioning; (3) residual effects of past land use history; and (4) statistical limitations to the quantification of soil carbon stocks.
A new estimate of the CaCO3 to organic carbon export ratio
Authors: Sarmiento J. L. , Dunne J. , Gnanadesikan A. , Key R. M. , Matsumoto K. , Slater R.
Published: December 2002

We use an ocean biogeochemical‐transport box model of the top 100 m of the water column to estimate the CaCO3 to organic carbon export ratio from observations of the vertical gradients of potential alkalinity and nitrate. We find a global average molar export ratio of 0.06 ± 0.03. This is substantially smaller than earlier estimates of 0.25 on which a majority of ocean biogeochemical models had based their parameterization of CaCO3 production. Contrary to the pattern of coccolithophore blooms determined from satellite observations, which show high latitude predominance, we find maximum export ratios in the equatorial region and generally smaller ratios in the subtropical and subpolar gyres. Our results suggest a dominant contribution to global calcification by low‐latitude nonbloom forming coccolithophores or other organisms such as foraminifera and pteropods.
A high‐resolution calibration of Sr/Ca thermometry using the Caribbean coral Montastraea annularis
Authors: Swart P. K. , Elderfield H. , Greaves M. J.
Published: December 2002

A relationship has been established between the Sr/Ca ratio in the skeleton of the scleractinian coral Montastraea annularis and sea surface water temperature in south Florida. In order to obtain this correlation, specimens of Montastraea annularis were transplanted to a site at a local reef where every two to three months throughout a 2‐year period the corals were stained with Alizarin‐red S and where water temperature, which annually ranges between ∼20° and 30°C, was continually monitored. At the end of the experimental period the coral skeleton was sampled at a rate of ∼50 samples per year, each sample corresponding to only around 20 μg of calcium carbonate. For the 2.5‐year period, the Sr/Ca ratio exhibited excellent correlation in the first year (R2 = 0.83; Sr/Ca (mmol/mol) = 10.11 − 0.0452 × SST (°C)), but a rather poorer correlation in the second year (R2 = 0.68; Sr/Ca (mmol/mol) = 10.09 − 0.0406 × SST (°C)). Averaging the data into monthly values for year 1, we determined a relationship of (Sr/Ca (mmol/mol) = 10.165 − 0.0471 × SST (°C). On the basis of the excellent correlation between temperature and Sr/Ca, we feel that this relationship is the most accurate. Discrepancies in the second year are suggested to arise from slight sampling errors relative to the stain lines.
Mantle dynamics, element recycling, and magma genesis beneath the Kermadec Arc‐Havre Trough
Authors: Haase Karsten M. , Worthington Tim J. , Stoffers Peter , Garbe‐Schönberg Dieter , Wright Ian
Published: December 2002

New geochemical and isotopic data are presented for lavas from three sites in the Havre Trough‐Lau Basin back arc and six volcanoes along the Kermadec arc. The back arc basalts range from MORB‐like to arc‐like in composition and contain a variable contribution from the underlying slab. The least contaminated MORB‐like back arc lavas from 24°–29°S are low degree partial melts of a source with Pacific MORB isotopic characteristics. A transition occurs at 30°S between the strongly depleted northern Kermadec (and Tonga) arc lavas and the mildly depleted southern Kermadec arc lavas. This transition does not correlate with changes in the back arc extension rate or width but may reflect inhibited mantle wedge replenishment behind the shallower‐dipping northern Kermadec‐Tonga slab. Northern Kermadec lavas require mixing between two components: (1) depleted Havre Trough mantle and (2) fluid derived from altered MORB crust with a slight input of sediment lead. Inter‐volcano differences in fluid compositions probably reflect local variations on the subducting slab rather than mineralogical variation in the mantle wedge. Southern Kermadec lavas require an additional component: (3) Pacific sediment melt. This sediment melt is only detected where the subduction rate is <7 cm/year, and requires thermal heating of the slab to >650°C before passing through the sub‐arc melt generation zone.
Wolf–Darwin lineament and plume–ridge interaction in northern Galápagos
Authors: Harpp Karen , Geist Dennis
Published: December 2002

The Wolf–Darwin Lineament (WDL), located in the northwestern sector of the Galápagos Archipelago, lies between the focus of the Galápagos hot spot and the Galápagos Spreading Center. Consequently, most researchers have attributed its origin to the interaction between the plume and the adjacent ridge. We propose that the WDL is caused only partially by the plume–ridge interaction, and instead that it is primarily the result of tensional stresses emanating from the inside corner of the transform fault at 91°W. An additional factor that amplifies the tension in this region is the oblique orientation of the major transform fault with respect to the Nazca plate's spreading direction. This setting creates a transtensional zone whereby strain is partitioned into strike‐slip motion along the transform and extension throughout the inside corner of the ridge–transform system. The area under tension is magmatic owing to the overlapping effects of the ridge and the Galápagos plume. The extensional model predicts no age‐progressive volcanism, which is supported by observed age relationships. The WDL volcanoes define two distinct chemical groups: lavas erupted south of Wolf Island have compositions similar to those produced along the GSC west of 93°W, while those from the northern WDL resemble GSC lavas from the segment directly north of the lineament. This geographic distribution implies that the WDL is supplied by the same type of plume‐affected mantle as the segment of the GSC that produced the lithosphere underlying the volcanoes. The observed WDL geochemical gradients are consistent with the extension model; the region under tension simply taps hybrid products of mixing at the margins of the subridge convection system and the periphery of the plume. Essentially, the stress field around the transform fault, normally not observable in a typical midocean ridge setting, is illuminated by the presence of melt from the adjacent hot spot.
Strongly underwound magnetic fields in co‐rotating rarefaction regions: Observations and Implications
Authors: Murphy N. , Smith E. J. , Schwadron N. A.
Published: December 2002

Observations of the magnetic field orientation in co‐rotating rarefaction regions (CRRs) reveals that the field can be significantly more radial than predicted by the Parker model. In particular, CRRs sampled by the Ulysses spacecraft beyond 4 AU from the sun often show average field orientations deviating by more than 30° from the expected Archimedian spiral and lasting many days. These observations are explained by a model combining footpoint motion between fast and slow solar wind streams at the source surface with the effects of velocity shear across coronal hole boundaries.
Radiative forcing by aerosols over Bay of Bengal region
Authors: Satheesh S. K.
Published: December 2002

Estimates of aerosol radiative (short wave and long wave) forcing over Bay of Bengal region are made from observations conducted as part of validation experiment of Indian Remote Sensing satellite, IRS‐P4. Aerosol visible optical depths were as high as 0.6 and aerosol single scattering albedo were as low as 0.85 indicating the presence of significant amount of absorbing aerosols. The presence of aerosol over Bay of Bengal decreases the short wave radiation arriving at the surface by as much as 38 W m−2 and increases the top of the atmosphere reflected radiation by 7 W m−2. In the long wave region, the corresponding forcing values are +11 W m−2 (increase) at the surface and +3 W m−2 (decrease). The short wave atmospheric absorption translates to an atmospheric heating of 0.5° to 1°K/day which is an increase of ∼60–80% of the aerosol‐free solar heating.
Cosmic electron gradients in the inner heliosphere
Authors: Clem John , Evenson Paul , Heber Bernd
Published: December 2002

We report the first determination of the radial gradient of cosmic ray electrons in the inner heliosphere at rigidities of 1.2 and 2.5 GV from 1 to 5 AU. Since this determination was made during the A+ solar polarity state, it also constitutes the only determination for particles in a polarity state opposite to their charge sign. We find that the radial gradient for electrons is indistinguishable from that for positive particles measured at the same time. We have found no significant latitude gradient in either 1.2 or 2.5 GeV electrons. Lack of the ability to study time evolution greatly hampers interpretation of our results.
Microbiological degradation of atmospheric organic compounds
Authors: Ariya Parisa A. , Nepotchatykh Oleg , Ignatova Olga , Amyot Marc
Published: December 2002

Until now, aerosol transformation was assumed to be via chemical or physical processes. Here we present evidence that an important class of organic aerosols – dicarboxylic acids (DCA) – can be efficiently transformed by existing airborne microbes (bacteria and fungi) in the boundary layer. Isotopic studies indicate that microbiological entities transform and use DCA as nutrients. Several observed products are toxicants or pathogens. Identified volatile products indicate that DCA can be recycled back to the atmosphere via microbiological processes. Thus, biodegradation could be an important atmospheric transformation pathway for organic compounds.
Multistage moisture transport into the interior of northern Mexico during the North American summer monsoon
Authors: Fawcett Peter J. , Stalker James R. , Gutzler David S.
Published: December 2002

The summertime sources and transport pathways of water vapor into the interior of southwestern North America are examined in a high‐resolution mesoscale model simulation. A complex multi‐stage transport pathway is associated with a pronounced diurnal cycle of deep convection and low‐level wind systems. Daytime thermal pumping of moisture from the Gulf of California towards the Sierra Madre Occidental (SMO) leads to widespread, deep convection. At night, land surface and atmospheric cooling generate drainage flows down both sides of the SMO. A nocturnal, low‐level jet forms above the western foothills and transports moisture north into the Sonoran Desert. Moist air draining to the east mixes with onshore flow from Gulf of Mexico and flows into the northern Chihuahuan Desert. The diurnal flow of moisture up and down the SMO and the formation of nocturnal, low‐level jets transport moisture into the core regions of the NA monsoon in NW Mexico.