bluuebunny/crossref_metadata_2025 huggingface dataset:
A comparison between modeled and measured clear‐sky radiative shortwave fluxes in Arctic environments, with special emphasis on diffuse radiation
Authors: Barnard J. C. , Powell D. M.
Published: October 2003

The ability of the Santa Barbara Disort Atmospheric Radiative Transfer (SBDART) model to predict clear‐sky diffuse and direct normal broadband shortwave irradiances is investigated. Model calculations of these quantities are compared with data from the Atmospheric Radiation Measurement program's Southern Great Plains (SGP) and North Slope of Alaska (NSA) sites. The model tends to consistently underestimate the direct normal irradiances at both sites by about 1%. In regard to clear‐sky diffuse irradiance, the model overestimates this quantity at the SGP site in a manner similar to what has been observed in other studies [Halthore and Schwartz, 2000]. The difference between the diffuse SBDART calculations and Halthore and Schwartz's MODTRAN calculations is very small, thus demonstrating that SBDART performs similarly to MODTRAN. SBDART is then applied to the NSA site, and here it is found that the discrepancy between the model calculations and corrected diffuse measurements (corrected for daytime offsets) [Dutton et al., 2001] is 0.4 W/m2 when averaged over the 12 cases considered here. Two cases of diffuse measurements from a shaded “black and white” pyranometer are also compared with the calculations and the discrepancy is again minimal. Thus, it appears as if the “diffuse discrepancy” that exists at the SGP site does not exist at the NSA sites. We cannot yet explain why the model predicts diffuse radiation well at one site but not at the other.
Effect of surface albedo variations on UV‐visible limb‐scattering measurements of the atmosphere
Authors: Oikarinen Liisa
Published: October 2003

In a new technique to measure stratospheric ozone profiles a near‐UV and visible spectrometer is used to detect backscattered solar light in limb‐viewing geometry. Several satellite‐based instruments using this technique will be launched in 2001–2002. A limb‐viewing instrument does not see Earth's surface or tropospheric clouds directly. However, indirect light reflected from the surface or low‐altitude clouds (which have an effect similar to a highly reflective surface) can make up tens of percents of limb radiance. Our simulations by a three‐dimensional Monte Carlo radiative transfer model show that reflection from an area at Earth's surface that extends over 1000 km along the instrument line of sight and 200 km across it contributes to the signal. The exact area depends on tangent altitude of the measurement, wavelength, surface elevation, and atmospheric conditions. Over this distance the reflectivity of the surface can vary by almost 100%, which should be taken into account in measurement data analysis. Normally, radiative transfer models that are used to analyze scattering measurements assume that the atmosphere and the surface are spherically symmetric. In such a model the surface albedo is a constant, and it is not possible to include a spatially varying surface into the model. We present an approximative method to average the reflectivity of Lambert surfaces, which can be used to estimate limb radiance over an inhomogeneous surface by a spherically symmetric model.
Uptake of HNO3 on water‐ice and coadsorption of HNO3 and HCl in the temperature range 210–235 K
Authors: Hynes Robert G. , Fernandez Miguel A. , Cox R. Anthony
Published: October 2003

The uptake of HNO3 on water‐ice films was investigated in a coated wall flow reactor under tropospheric temperature conditions. Experiments were performed in the “ice” region of the HNO3–H2O phase diagram. With HNO3 partial pressures in the range of (0.3–2.0) × 10−6 Torr, continuous uptake was observed below 215 K; whereas above 215 K, the uptake was time dependent. Using the geometric surface area of the ice film, the surface coverage at 218 K was 3.0 × 1014 molecules/cm2, decreasing to 1.5 × 1014 molecules/cm2 at 233 K; the timescales for saturation were 700 and 800 s at 218 and 233 K, respectively. The surface coverage was found to change by a factor of 2 over a 10‐fold change in HNO3 partial pressure. By assuming that the surface coverage can be represented by a Langmuir isotherm for dissociative adsorption, the enthalpy of adsorption of HNO3 onto ice was found to be −(54.0 ± 2.6) kJ/mol. At a constant HNO3 partial pressure, the maximum uptake coefficients, γ, were measured as a function of temperature, decreasing from 0.03 at 215 K down to 0.006 at 235 K. The uptake coefficients at 218 K were not significantly affected by changes in HNO3 partial pressure. The uptake of HCl at 218 K on ice surfaces previously dosed with HNO3 was found to be reversible, and the coadsorption of HNO3 with HCl indicates that HCl is displaced from surface sites by HNO3 molecules. Uptake of HNO3 on HCl‐dosed surfaces showed that HNO3 molecules displace ∼1013 molecules/cm3 of HCl. The efficiency of cirrus clouds in scavenging HNO3 is discussed, as well as the implications for chlorine activation reactions under tropospheric temperature conditions.
Hypsometric analysis of Margaritifer Sinus and origin of valley networks
Authors: Luo Wei
Published: October 2003

The formation of Martian valley networks has been debated since their discovery. The relative roles of groundwater sapping and fluvial runoff processes have different implications on Martian paleoclimate. This paper uses a hypsometric analysis technique that has been tested on terrestrial landforms to analyze the hypsometric attributes of watershed basins in the Margaritifer Sinus region on Mars using Mars Orbiter Laser Altimeter (MOLA) gridded topographic data. On the basis of quantitative characteristics of their hypsometric attributes, the majority of the basins (covering ∼3/5 of the study area) look more like terrestrial basins of sapping origin, and a significant number of basins (covering ∼1/5 of the study area) are more fluvial like. The classification of the rest of the basin is less certain at the presently available resolution of the digital elevation model (DEM). Overlay with Viking photomosaic indicates that the classification is generally consistent with the morphology shown in Viking images. Although this analysis alone cannot make a sure determination of valley network origin, combined with other morphometric analysis, the results from this study are consistent with a valley network formation by precipitation‐recharged groundwater sapping, suggesting a warm and wet climate for early Mars.
Oxygen isotope record of the 1997–1998 El Niño in Peruvian sea catfish (Galeichthys peruvianus) otoliths
Authors: Andrus C. Fred T. , Crowe Douglas E. , Romanek Christopher S.
Published: October 2003

Sagittal otoliths of the Peruvian sea catfish Galeichthys peruvianus were collected from the north coast of Peru during and after the 1997–1998 El Niño. The otoliths were analyzed via laser microprobe and micromilling techniques for oxygen isotope composition through ontogeny to document their use as an El Niño‐Southern Oscillation (ENSO) proxy. Results were compared to theoretical calculations for the δ18O of otolith aragonite using measured sea surface temperatures (SST) and δ18O values for local seawater assuming equilibrium oxygen isotope fractionation was achieved. All otoliths recorded the 1997–1998 El Niño event as well as seasonal temperature variations. These ENSO events were recorded in otolith aragonite as significant negative excursions in δ18O that reflected the increased temperature of local marine waters. The combined otolith data were used to create a 10‐year SST record, including ENSO events and local seasonal temperature variation, validating the use of otolith δ18O as a temperature proxy.
Simulation of ocean‐ice sheet interactions during the last deglaciation
Authors: Crucifix Michel , Berger André
Published: October 2003

The last deglaciation, between 21 thousand years BP (kyr BP) and 8 kyr BP, was punctuated by a series of climatic oscillations, both in the Northern and Southern Hemispheres, often attributed to changes in ocean circulation. These oscillations are explored with an Earth system model of intermediate complexity, including a synchronous coupling between atmosphere, ocean, and ice sheet dynamics. We focused more particularly on the impact of Heinrich Event 1 (HE1) on the deglaciation process. Representation for HE1 was achieved by a parameterization of iceberg discharge included in the ice sheet model, based on paleoceanographic evidence. The model simulates the following sequence in response to the HE1: (1) The thermohaline circulation is drastically reduced as soon as HE1 starts, causing a sharp cooling in the North Atlantic and a smooth warming in the Southern Hemisphere. (2) Circulation restarts abruptly at the end of HE1, producing an intense warming in both hemispheres (up to 10°C warming in the Greenland‐North Atlantic area, with a rapidly decreasing amplitude as one moves southward). (3) Along with this warming, the melting of the North American and Eurasian ice sheets is enhanced, producing a small freshwater discharge to the North Atlantic, but there is no significant impact on Atlantic salinity and thermohaline circulation. (4) A few decades after the post‐Heinrich warm event, both the southern Atlantic and Antarctica entered a prolonged cold period caused by the reactivation of the thermohaline circulation. (5) Finally, about 1500 years later, depending on sensitivity experiments, meltwater flowing into the North Atlantic through the Hudson Strait and the Barents Sea causes a gradual vertical stratification of the northern North Atlantic. The presented simulations are compared to paleoarchives by taking into account the limits inherent to the model structure. One of the conclusions is that there is probably no direct link between the meltwater pulse 1A observed in sea level data and the onset of the Younger Dryas.
Retrieval of in situ electron density in the topside ionosphere from cosmic radio noise intensity by an artificial neural network
Authors: Maruyama Takashi
Published: October 2003

An artificial neural network (ANN) is applied to retrieve electron density at satellite height from cosmic radio noise measurements made near the plasma cutoff frequency in the topside ionosphere. Observations were made using the topside sounder on board the Ionosphere Sounding Satellite launched in 1978. The automatic gain control voltage of the sounder receiver supplied information on the spectrum of cosmic radio noise intensity. Local electron densities, which are the target of the ANN, were scaled from the plasma resonance spikes and the echo traces in the ionogram for several passes. Each pass contained about 100 frames of ionograms; it is not a very easy task to scale the local plasma parameters by an eyeball judgment for all passes. With the aid of a neural network application, we determined the in situ electron density for about 150,000 ionograms. The results were applied to global ionospheric mapping.
Measuring dynamic topography: An analysis of Southeast Asia
Authors: Wheeler Paul , White Nicky
Published: October 2003

Theoretical models of dynamic topography, generated by subducting slabs and consistent with the observed geoid, predict ∼1–2 km of subsidence on wavelengths of 102–103 km. The demonstrable existence of such subsidence has important implications for understanding sedimentary basin formation, relative sea level changes, as well as the Earth's viscosity and density structure. Here we present the results of a combined analysis of subsidence data from oceanic marginal basins and their fringing continental shelves. We have chosen to analyze a large area of Southeast Asia where dynamical predictions are believed to be well constrained by the history of subduction. Our joint analysis constrains the maximum amplitude of dynamic subsidence to be ∼300 m with a range of 0–500 m, significantly less than predicted. Actively spreading marginal basins have no resolvable dynamic subsidence, but after removing the effects of crustal thickness variation, a few inactive marginal basins are consistently 200–500 m deeper than normal. Adjacent continental sedimentary basins record a possible dynamic subsidence of 0–500 m, although wavelengths are shorter than expected (∼102 km). There is also disagreement between the predicted and observed distribution of anomalous subsidence as well as inconsistencies in initiation and duration. These results suggest that mass excess within the mantle, represented by subducted slabs, has little discernible effect on surface topography. Instead, subsidence and marine inundations throughout Southeast Asia are predominantly controlled by lithospheric extension and or by foreland loading. The spatial and temporal distribution of anomalous subsidence suggests that it might not be caused by dynamic topography associated with subducting slabs. A large discrepancy between predicted and observed dynamic topography could be reconciled by changing the density structure of subducted slabs, by supporting mass excess with a marked increase in viscosity at depth, or by decoupling slabs from the surface with a very low viscosity layer.
Lithospheric folding in Iberia
Authors: Cloetingh S. , Burov E. , Beekman F. , Andeweg B. , Andriessen P. A. M. , Garcia‐Castellanos D. , de Vicente G. , Vegas R.
Published: October 2003

Integration of stress indicator data, gravity data, crustal kinematics data, and analysis of topography and recent vertical motions demonstrates the occurrence of consistently oriented spatial patterns of large‐scale Alpine to recent intraplate deformation in Iberia. The inferred upper crustal and lithospheric deformation patterns and the timing of the associated expressions at or near the surface support the existence of a close coupling with plate boundary processes operating at the margins of Iberia. Patterns of lithosphere and upper crustal folds are oriented perpendicular to the main axis of present‐day intraplate compression in Iberia inferred from structural analysis of stress indicator data and focal mechanism solutions. These findings suggest the presence of lithospheric folds, with wavelengths compatible with theoretical predictions of folding wavelengths of Variscan lithosphere. Stress‐induced intraplate deformation set up by plate interactions is compatible with indications for the absence of present‐day deep mantle‐lithosphere interactions inferred from seismic tomography.
Optimal experimental design for parameter estimation in column outflow experiments
Authors: Altmann‐Dieses Angelika E. , Schlöder Johannes P. , Bock Hans Georg , Richter Otto
Published: October 2003

Inverse modeling is increasingly used for water flow and reactive solute transport in the unsaturated zone to determine unknown parameters, e.g., soil hydraulic parameters, degradation rates or dispersion coefficients. However, experimental data are frequently not suitable for parameter estimation leading instead to practically singular estimation problems. Optimal experimental design aims at identifying experimental conditions and sampling schemes that deliver measurement data which are most sensitive to unknown parameters. A new numerical approach to optimize experimental designs for parameter estimation in coupled partial differential equations (PDEs) and ordinary differential equation (ODEs) arising from transport and degradation processes is presented. The optimal experimental design problem is embedded in the framework of optimal control theory. This results in an intricate, nonlinear, constrained optimization problem that is solved by a direct approach based on a structured SQP method. These methods are used to investigate several scenarios for a column outflow experiment in a simulation study. Simultaneously, experimental conditions, such as irrigation schemes, substance concentrations, and sampling schemes are optimized. Result is an enormous reduction of parameter uncertainty. Additionally, it is demonstrated that it is possible to estimate both soil hydraulic and solute transport parameters together in one experiment on the basis of leachate data only. The usefulness of the numerical approach for practical applications is discussed.
Seepage into an underground opening constructed in unsaturated fractured rock under evaporative conditions
Authors: Trautz Robert C. , Wang Joseph S. Y.
Published: October 2003

Liquid‐release tests, performed in boreholes above an underground opening constructed in unsaturated fractured rock, are used in this study to evaluate seepage into a waste emplacement drift. Evidence for the existence of a capillary barrier at the ceiling of the drift is presented based on field observations (including spreading of the wetting front across the ceiling and water movement up fractures exposed in the ceiling before seepage begins). The capillary barrier mechanism has the potential to divert water around the opening, resulting in no seepage when the percolation flux is at or below the seepage threshold flux. Liquid‐release tests are used to demonstrate that a seepage threshold exists and to measure the magnitude of the seepage threshold flux for three test zones that seeped. The seepage data are interpreted using analytical techniques to estimate the test‐specific strength of the rock capillary forces (α−1) that prevent water from seeping into the drift. Evaporation increases the seepage threshold flux, making it more difficult for water to seep into the drift and producing artificially inflated α−1 values. With adjustments for evaporation, the minimum test‐specific threshold is 1600 mm/yr, with a corresponding α−1 value of 0.027 m.
Macrodispersivity for transport in arbitrary nonuniform flow fields: Asymptotic and preasymptotic results
Authors: Lunati Ivan , Attinger Sabine , Kinzelbach Wolfgang
Published: October 2003

We use homogenization theory to investigate the asymptotic macrodispersion in arbitrary nonuniform velocity fields, which show small‐scale fluctuations. In the first part of the paper, a multiple‐scale expansion analysis is performed to study transport phenomena in the asymptotic limit ε ≪ 1, where ε represents the ratio between typical lengths of the small and large scale. In this limit the effects of small‐scale velocity fluctuations on the transport behavior are described by a macrodispersive term, and our analysis provides an additional local equation that allows calculating the macrodispersive tensor. For Darcian flow fields we show that the macrodispersivity is a fourth‐rank tensor. If dispersion/diffusion can be neglected, it depends only on the direction of the mean flow with respect to the principal axes of anisotropy of the medium. Hence the macrodispersivity represents a medium property. In the second part of the paper, we heuristically extend the theory to finite ε effects. Our results differ from those obtained in the common probabilistic approach employing ensemble averages. This demonstrates that standard ensemble averaging does not consistently account for finite scale effects: it tends to overestimate the dispersion coefficient in the single realization.
Coupling of the solar wind to temporal fluctuations in ground magnetic fields
Authors: Weigel R. S. , Vassiliadis D. , Klimas A. J.
Published: October 2003

A study of the coupling of the solar wind to temporal fluctuations in high–latitude ground magnetic fields is presented. The fluctuation measure considered is the absolute value of the north‐south horizontal field time derivative (∣dBx/dt∣) averaged over a 30–minute interval. The fluctuation level is predicted using a nonlinear mapping of solar wind plasma and field measurements. The predictability of ground magnetic field fluctuations is shown to depend on both local time and latitude. For lower polar cap magnetometer locations, the coupling is highest at the local times that have the highest average fluctuation level and lowest at the local times that have the lowest average fluctuation level. The highest level of coupling is at auroral‐zone latitudes in the post‐midnight sector. The relative influence of different solar wind inputs is shown to be highly dependent on spatial location.
Satellite observation of Chromophoric Dissolved Organic Matter (CDOM) variability in the wake of hurricanes and typhoons
Authors: Hoge Frank E. , Lyon Paul E.
Published: October 2003

Satellite observation of Chromophoric Dissolved Organic Matter (CDOM) absorption coefficient variability in the wake of numerous hurricanes and typhoons is reported here for the first time. Storm‐induced vertically‐mixed CDOM from deeper depths has a higher absorption coefficient than the photochemically degraded CDOM within the undisturbed pre‐storm upper mixed layer. Principal findings are: (1) Little variability is observed prior to storm encounter at which time the CDOM‐defined wake rapidly develops a notable right side asymmetry. (2) The more robust right‐side CDOM absorption coefficient elevation is visible up to ∼30days depending on storm intensity. In a way that is similar to existing sea surface temperature imagery applications, the techniques in this paper are proposed as a complementary new research tool for the study of atmosphere‐ocean interactions.
Atmospheric models, GPS and InSAR measurements of the tropospheric water vapour field over Mount Etna
Authors: Wadge G. , Webley P. W. , James I. N. , Bingley R. , Dodson A. , Waugh S. , Veneboer T. , Puglisi G. , Mattia M. , Baker D. , Edwards S. C. , Edwards S. J. , Clarke P. J.
Published: October 2003

Dynamic models of atmospheric movement over the Mount Etna volcano are used to calculate the path delays affecting radar caused by variable water vapour in the troposphere. We compare these model results with the equivalent differential radar interferogram generated by two ERS‐2 SAR images taken 35 days apart and the water vapour delay retrievals from a network of fourteen GPS stations distributed over the volcano. The atmospheric model delay field agrees well with the long‐wavelength spatial differences measured by InSAR and those measured by GPS.
Using a CFC effective age to estimate propagation and storage of climate anomalies in the deep western North Atlantic Ocean
Authors: Fine Rana A. , Rhein Monika , Andrié Chantal
Published: October 2003

1990s chlorofluorocarbon (CFC) observations are used to estimate an effective age of 20 years for North Atlantic Deep Water (NADW) at the equator. The effective age is found by subtracting a “relic” age from pCFC‐11 age. The effective age is several to 10 years younger at the equator than other methods. From the effective age equatorward “effective” spreading rates of 1–2 cm/s are found, which are similar for the NADW components. Effective spreading rates take into account recirculation gyres, along‐equator flow, and mixing, which slow spreading of climate anomalies from the North Atlantic to the Southern Hemisphere. The difference between direct velocities and tracer effective spreading rates suggests that the buffering effect due to storage, in the western North Atlantic and equatorial region, is about 20 years. Even so, warming and freshening due to greenhouse gases will be first felt in the deep waters of the western North Atlantic.
Phase‐steepened Alfvén waves, proton perpendicular energization and the creation of magnetic holes and magnetic decreases: The ponderomotive force
Authors: Tsurutani B. T. , Dasgupta B. , Galvan C. , Neugebauer M. , Lakhina G. S. , Arballo J. K. , Winterhalter D. , Goldstein B. E. , Buti B.
Published: October 2003

Solar wind protons detected within Magnetic Holes (MHs) and Magnetic Decreases (MDs) are found to be preferentially heated perpendicular to 0. The MHs/MDs are associated with the phase‐steepened edges of nonlinear Alfvén waves. The proton anisotropies can lead to the proton cyclotron and mirror mode plasma instabilities. We examine the Ponderomotive Force (PF), a phenomenon due to wave pressure gradients, and show that for this plasma regime and for phase‐steepened Alfvén waves, the PF proton acceleration/energization will primarily be orthogonal to B0. It is suggested that accelerated ions create the MHs/MDs by a diamagnetic effect.
Assessing the robustness of zonal mean climate change detection
Authors: Thorne Peter W. , Jones Phil D. , Osborn Tim J. , Davies Trevor D. , Tett Simon F. B. , Parker David E. , Stott Peter A. , Jones Gareth S. , Allen Myles R.
Published: October 2003

We assess the robustness of previous optimal detection and attribution studies considering zonal‐mean temperatures. Principal results, which have consistently pointed towards a demonstrable anthropogenic influence on recently observed upper air temperatures, are confirmed. Importantly our detection results are not critically dependent on the inclusion of stratospheric as well as tropospheric temperatures. We find that detection is dependent on input field pre‐processing choices, and on the choice of detection algorithm. There are a number of cases where either no signals are detected, or results fail a consistency test.
Midlatitude circulation patterns associated with decadal and interannual Pacific Ocean variability
Authors: Frauenfeld Oliver W. , Davis Robert E.
Published: October 2003

The exact nature of the interaction between the Pacific Ocean and the climate of the Northern Hemisphere is still in large part uncertain. To investigate these interactions, canonical correlation analysis is applied to relate midlatitude atmospheric circulation variability with Pacific Ocean SST variability. The leading mode corresponds closely to decadal PDO‐like variability and the second mode is comparable to ENSO. Consequently, we identified different atmospheric circulation patterns related to the spatially similar, but temporally different modes of SST variability. Circulation variability over Eurasia is linked with the decadal SST variability, while the interannual SST variability is linked to circulation variability over the eastern Pacific. This suggests that decadal SST variability, in part, could be forced by the atmosphere. Furthermore, while the PDO switched back into its negative phase in the late 1990s, the decadal SST variability as related to circulation did not. Instead, the interannual mode has shifted into a negative phase, indicating a change in the nature of ocean‐atmosphere interaction in the late 1990s.
The effect of increasing solar activity on the Sun's total and open magnetic flux during multiple cycles: Implications for solar forcing of climate
Authors: Lean J. L. , Wang Y.‐M. , Sheeley N. R.
Published: October 2003

We investigate the relationship between solar irradiance and cosmogenic isotope variations by simulating with a flux transport model the effect of solar activity on the Sun's total and open magnetic flux. As the total amount of magnetic flux deposited in successive cycles increases, the polar fields build up, producing a secular increase in the open flux that controls the interplanetary magnetic field which modulates the cosmic ray flux that produces cosmogenic isotopes. Non‐axisymmetric fields at lower latitudes decay on time scales of less than a year; as a result the total magnetic flux at the solar surface, which controls the Sun's irradiance, lacks an upward trend during cycle minima. This suggests that secular increases in cosmogenic and geomagnetic proxies of solar activity may not necessarily imply equivalent secular trends in solar irradiance. Questions therefore arise about the interpretation of Sun‐climate relationships, which typically assume that the proxies imply radiative forcing.
Avalanches at the core‐mantle boundary
Authors: Muller Richard A.
Published: October 2003

The partial collapse of topographic structure at the core‐mantle boundary (CMB) in avalanches, slumps or turbidity flows, would cause sudden temperature changes in both the upper core and the lower mantle. Although such collapses are hypothetical, it is interesting to investigate the potential consequences. Downwelling from such events could disrupt core convection cells and trigger geomagnetic excursions and reversals. Buoyant sediment from the freezing of the inner core is hypothesized to rebuild the avalanched structures. Large avalanches could trigger mantle plumes. Oblique extraterrestrial impacts impart high shear to the CMB, and can trigger one or more simultaneous avalanches, yielding observed coincidences between craters, tektite fields and reversals. A triggered avalanche can explain the coincidence between the formation of the largest known volcanic province (the Ontong‐Java Plateau), the start of the 35 Myr Cretaceous geomagnetic quiet period, and reported coincidences between large flood basalts and extinctions.
Thermal Conductivity Measurements in Porous Mixtures of Methane Hydrate and Quartz Sand
Authors: Waite W. F. , deMartin B. J. , Kirby S. H. , Pinkston J. , Ruppel C. D.
Published: October 2003

Using von Herzen and Maxwell's needle probe method, we measured thermal conductivity in four porous mixtures of quartz sand and methane gas hydrate, with hydrate composing 0, 33, 67 and 100% of the solid volume. Thermal conductivities were measured at a constant methane pore pressure of 24.8 MPa between −20 and +15°C, and at a constant temperature of −10°C between 3.5 and 27.6 MPa methane pore pressure. Thermal conductivity decreased with increasing temperature and increased with increasing methane pore pressure. Both dependencies weakened with increasing hydrate content. Despite the high thermal conductivity of quartz relative to methane hydrate, the largest thermal conductivity was measured in the mixture containing 33% hydrate rather than in hydrate‐free sand. This suggests gas hydrate enhanced grain‐to‐grain heat transfer, perhaps due to intergranular contact growth during hydrate synthesis. These results for gas‐filled porous mixtures can help constrain thermal conductivity estimates in porous, gas hydrate‐bearing systems.
A step increase in streamflow in the conterminous United States
Authors: McCabe Gregory J. , Wolock David M.
Published: October 2003

Annual minimum, median, and maximum daily streamflow for 400 sites in the conterminous United States (U.S.), measured during 1941–1999, were examined to identify the temporal and spatial character of changes in streamflow statistics. Results indicate a noticeable increase in annual minimum and median daily streamflow around 1970, and a less significant mixed pattern of increases and decreases in annual maximum daily streamflow. These changes in annual streamflow statistics primarily occurred in the eastern U.S. In addition, the streamflow increases appear as a step change rather than as a gradual trend and coincide with an increase in precipitation.
Resonant acoustic spectroscopy of microfracture in a Westerly granite sample
Authors: Lebedev A. V. , Bredikhin V. V. , Soustova I. A. , Sutin A. M. , Kusunose K.
Published: October 2003

The experimental setup for precision acoustic measurements of the elastic tensor of structurally inhomogeneous materials has been designed and fabricated. The achieved accuracy of measurements is high enough for studying a fine structure of rocks. It is shown that resonant acoustic spectroscopy is a useful tool for measuring the small content of oriented microcracks that can be used for diagnostics of early stages of fracture when oriented microcracking occurs. Elastic characteristics of a Westerly granite sample have been investigated. The elastic tensor has been found to be hexagonal, oriented with respect to the rift plane. The obtained data have shown the presence of oriented microcracks and have been explained sensibly by a model of microcracks.
Sources of spatial variability in light absorbing components along an equatorial transect from 165°E to 150°W
Authors: Simeon Jennifer , Roesler Collin , Pegau W. Scott , Dupouy Cécile
Published: October 2003

Spatial variability of major light‐absorbing components in seawater was analyzed at the equator from 165°E to 150°W during the Zonal Flux Cruise aboard the R/V Thompson from 20 April to 10 May 1996. Spectral absorption coefficients were separated into phytoplankton, nonphytoplankton chromophoric particulate material (CPM) and chromophoric dissolved organic material (CDOM). CPM and phytoplankton absorption account for about 20% and 80% of the total particulate absorption, respectively, above 100 m. The <0.2 μm CDOM absorption accounts for nearly 80% of the total absorption below 100 m. A significant portion of spatial variability in particulate absorption was due to conservative processes in the upper 100 m. Non‐conservative spatial variability of phytoplankton absorption was zonally determined by the biomass changes of a spectrally invariant taxonomic community and vertically by photoacclimation. Distributions of size‐fractionated CDOM absorption are suggestive of the presence of new (0.2 to 0.7 μm) and old (<0.2 μm) DOM pools. Photochemical reactions and microbial activity are nonconservative processes that act upon these pools, respectively. New DOM was found primarily in the upper water column, while an analysis of variance showed that <0.2 μm CDOM originating from deep water composes the background CDOM in the Equatorial Pacific.
Arctic Oscillation response to the 1991 Mount Pinatubo eruption: Effects of volcanic aerosols and ozone depletion
Authors: Stenchikov Georgiy , Robock Alan , Ramaswamy V. , Schwarzkopf M. Daniel , Hamilton Kevin , Ramachandran S.
Published: October 2003

Observations show that strong equatorial volcanic eruptions have been followed by a pronounced positive phase of the Arctic Oscillation (AO) for one or two Northern Hemisphere winters. It has been previously assumed that this effect is forced by strengthening of the equator‐to‐pole temperature gradient in the lower stratosphere, caused by aerosol radiative heating in the tropics. To understand atmospheric processes that cause the AO response, we studied the impact of the 1991 Mount Pinatubo eruption, which produced the largest global volcanic aerosol cloud in the twentieth century. A series of control and perturbation experiments were conducted with the GFDL SKYHI general circulation model to examine the evolution of the circulation in the 2 years following the Pinatubo eruption. In one set of perturbation experiments, the full radiative effects of the observed Pinatubo aerosol cloud were included, while in another only the effects of the aerosols in reducing the solar flux in the troposphere were included, and the aerosol heating effects in the stratosphere were suppressed. A third set of perturbation experiments imposed the stratospheric ozone losses observed in the post‐Pinatubo period. We conducted ensembles of four to eight realizations for each case. Forced by aerosols, SKYHI produces a statistically significant positive phase of the AO in winter, as observed. Ozone depletion causes a positive phase of the AO in late winter and early spring by cooling the lower stratosphere in high latitudes, strengthening the polar night jet, and delaying the final warming. A positive phase of the AO was also produced in the experiment with only the tropospheric effect of aerosols, showing that aerosol heating in the lower tropical stratosphere is not necessary to force positive AO response, as was previously assumed. Aerosol‐induced tropospheric cooling in the subtropics decreases the meridional temperature gradient in the winter troposphere between 30°N and 60°N. The corresponding reduction of mean zonal energy and amplitudes of planetary waves in the troposphere decreases wave activity flux into the lower stratosphere. The resulting strengthening of the polar vortex forces a positive phase of the AO. We suggest that this mechanism can also contribute to the observed long‐term AO trend being caused by greenhouse gas increases because they also weaken the tropospheric meridional temperature gradient due to polar amplification of warming.
Parametrization of ternary nucleation rates for H2SO4‐NH3‐H2O vapors
Authors: Napari I. , Noppel M. , Vehkamäki H. , Kulmala M.
Published: October 2003

A parametrization of nucleation rates for H2O‐H2SO4‐NH3 vapors in atmospheric conditions is developed. The parametrization is based on nucleation rates obtained from a self‐consistent model of ternary nucleation, including state‐of‐art thermodynamics, H2O‐H2SO4 hydration model, and rigorous treatment of nucleation kinetics. The parametrized nucleation rates are shown to be within one order of magnitude from those given by the full model with enhanced accuracy at higher nucleation rates. Parametrizations for particle numbers and radius of the critical nucleus are given as a function of nucleation rate and temperature. The parametrizations are valid for temperatures 240–300 K, relative humidities 5–95%, sulfuric acid concentrations 104–109 molecules cm−3, ammonia mixing ratios 0.1–100 ppt, and nucleation rates 10−5–106 cm−3 s−1.
Mixing events revealed by anomalous tracer relationships in the Arctic vortex during winter 1999/2000
Authors: Jost Hans‐Jürg , Loewenstein Max , Greenblatt Jeffery B. , Podolske James R. , Bui T. Paul , Hurst Dale F. , Elkins James W. , Herman Robert L. , Webster Christopher R. , Schauffler Sue M. , Atlas Elliot L. , Newman Paul A. , Lait Leslie R. , Wofsy Steven C.
Published: October 2003

During the 1999/2000 Arctic winter SAGE III–Ozone Loss and Validation Experiment (SOLVE) campaign, high‐resolution, in situ tracer data measured aboard the NASA ER‐2 high‐altitude aircraft revealed anomalous mixing events within the polar vortex. From January to March 2000 in the 350–500 K potential temperature range, we found mixing events during 15% of the flight time on average with significant maxima at potential temperatures of 450, 410, and 380 K. The events were spread throughout the vortex but showed a distinct minimum at 73° N and a peak at 85°N equivalent latitude. About 60% of the observed mixing events were less than 13 km wide. Based on a case study of tracer‐tracer relationships, an objective simple method is introduced to detect such events using the linear nitrous oxide (N2O):potential temperature relationship observed deep in the vortex. Rigorous analysis and supporting evidence from total water data corroborated the validity of the method. These results suggest mixing across the polar vortex edge occurred preferentially in layers at select altitudes in the Arctic winter 1999/2000.
Response of Antarctic (ODP Site 690) planktonic foraminifera to the Paleocene–Eocene thermal maximum: Faunal evidence for ocean/climate change
Authors: Kelly D. Clay
Published: October 2003

High‐resolution study of Antarctic planktonic foraminiferal assemblages (Ocean Drilling Program Site 690, Weddell Sea) shows that these microplankton underwent a stepwise series of changes during the Paleocene–Eocene thermal maximum (PETM). Initiation of this response coincides with the onset of the carbon isotope excursion (CIE) but precedes the benthic foraminiferal mass extinction. The “top‐to‐bottom” succession in the biotic response indicates that the surface ocean/atmosphere was affected before the deep sea. The earliest stage of the faunal response entailed a conspicuous turnover within the shallow‐dwelling genus Acarinina and a succession of stratigraphic first appearances. The genus Morozovella, large (>180 μm) biserial planktonics, and A. wilcoxensis are all restricted to the lower CIE within this PETM section. Acarininid populations crashed as the ocean/climate system ameliorated during the CIE recovery, reflecting atypical surface water conditions. This transient decline in acarininids is paralleled by a marked increase in carbonate content of sediments. It is postulated that this interval of carbonate enrichment, and its unusual microfauna, reflects enhanced carbon storage within reservoirs of the global carbon cycle other than the marine carbonate system [sensu Broecker et al., 1993; Ravizza et al., 2001].
Paleostress field reconstruction and revised tectonic history of the Donbas fold and thrust belt (Ukraine and Russia)
Authors: Saintot Aline , Stephenson Randell , Brem Arjan , Stovba Sergiy , Privalov Vitaliy
Published: October 2003

In the WNW‐ESE Donbas fold belt (DF), inversion of 3500 microtectonic data collected at 135 sites, in Proterozoic, Devonian, Carboniferous, and Cretaceous competent rocks allowed reconstruction of 123 local stress states. Accordingly, four successive paleostress fields reveal the tectonic evolution of the DF. At the numerous sites that have been affected by polyphase tectonics, the chronology between local paleostress states (also paleostress fields) was established using classical criteria (crosscutting striae, pre‐ or post‐folding stress states, stratigraphic control). The oldest event is an extensional stress field with NNE‐SSW σ3. It corresponds to the rifting phases that generated the basin in Devonian times and its early Visean reactivation. Later, the DF was affected by a transtension, with NW‐SE σ3 characterizing Early Permian tectonism, including the development of the “Main Anticline” of the DF and the pronounced uplift of its southern margin and Ukrainian Shield. Two paleostress fields characterize the Cretaceous/Paleocene inversion of the DF, which was accompanied by folding and thrusting. Both are compressional in type but differ by the trend of σ1, which was first NW‐SE and subsequently N‐S. The discrete paleostress history of the DF allows a revised interpretation of its tectonic evolution with significant implications for understanding the geodynamic evolution of the southern margin of the East European Craton.
Refining the footwall cooling history of a rift flank uplift, Rio Grande rift, New Mexico
Authors: House M. A. , Kelley S. A. , Roy M.
Published: October 2003

Apatite fission track (AFT) and (U‐Th)/He data from the Sandia Mountains and Hagan embayment provide new insights into the thermal and tectonic evolution of the eastern flank of the Rio Grande rift in northern New Mexico. AFT and (U‐Th)/He data reveal rapid cooling in the Sandia Mountains between 22 and 17 Ma, followed by a decrease in cooling rate at 16 to 14 Ma that temporally corresponds to a hiatus in deposition in the Albuquerque basin. A second increase in cooling rate at approximately 14 Ma was followed by continued slow cooling until present. Cooling ages from Jurassic to Permian sandstones in the Hagan embayment northeast of the Sandia Mountains are used to constrain the thermal conditions in Oligocene time that are necessary to map cooling histories into exhumation histories, thereby providing a limit on the amount of section removed during rift flank development. Thermal modeling, geologic constraints, and low‐temperature thermochronology are used to demonstrate that the heat flow in the Sandia Mountain region was at least 25 mW/m2 higher during Oligocene time compared to today. Furthermore, at least 3.1 km of material has been exhumed from the Sandia Mountains and 2.4 km of rock uplift occurred during flexural tilting of the block since middle Miocene time.
Estimation of hydraulic properties of vertically heterogeneous forest soil from transient matric pressure data
Authors: Kosugi Ken'ichirou , Inoue Mitsuhiro
Published: October 2003

Conventional methods for determining the hydraulic properties of unsaturated soil are laborious and time consuming. Although the inverse method can be an effective alternative, it occasionally produces nonunique solutions. The problem becomes more difficult when the inverse method is applied to vertically heterogeneous soil profiles. This study evaluated the method proposed by Kosugi and Nakayama, which estimates retention and hydraulic conductivity functions simultaneously for each horizontal layer of a vertically heterogeneous soil using transient matric pressure profiles. Artificial rainfall experiments were conducted on an undisturbed forest soil sample, and 14 unknown parameters that are contained in both retention and conductivity functions were estimated for seven layers. The estimated hydraulic properties corresponded well with those measured using conventional methods. Various initial parameter guesses converged at very similar final parameters, indicating the unique, stable solution. In addition, the effects of model selection, the soil pore tortuosity parameter, and experimental errors on the estimation results are discussed.
Perturbations of the sodium layer: controlled by chemistry or dynamics?
Authors: Xu Jiyao , Smith A. K.
Published: October 2003

The chemical lifetime of the mesospheric sodium layer is calculated from the eigenvalues and eigenvectors of the sodium chemical system. This method determines a lifetime that is an excellent estimate of the relaxation time of the sodium chemical system. The lifetime is more than a day in the vicinity of the mesospheric sodium layer and is much longer than the traditionally defined chemical lifetime for sodium of a few minutes. This verifies the assumption often made that transport determines the sodium perturbations in the presence of gravity waves and other rapid air motions. At the bottom of the sodium layer, below about 85 km, photochemistry is the dominant process.
Effect of clouds on photolysis and oxidants in the troposphere
Authors: Tie Xuexi , Madronich Sasha , Walters Stacy , Zhang Renyi , Rasch Phil , Collins William
Published: October 2003

Cloud layers in the troposphere influence photolysis rates (J values) and hence concentrations of chemical species. In order to study the impact of clouds on photolysis rates and oxidants, we have developed a simplified version of the National Center for Atmospheric Research (NCAR) Tropospheric Ultraviolet‐Visible (TUV) model and have coupled the simplified TUV (otherwise known as the fast TUV (FTUV)) into the NCAR/Atmospheric Chemistry Division global transport chemical model (Model for Ozone and Related Chemical Tracers (MOZART‐2)). The FTUV model has the same physical processes as the TUV model, except that the wavelength bins between 121 and 750 nm are reduced from 140 to 17. As a result, FTUV is about 8 times faster than the original TUV. Differences in the calculated photolysis rates between TUV and FTUV are generally less than 5% in the troposphere. Subgrid vertical distributions of clouds are also considered in the calculation of photolysis rates in MOZART‐2. The method used in this study is a mixed maximum and random overlap scheme. The subgrid method increases the computation time for photolysis rates by a factor of 3 compared to a simple method in which clouds are uniformly distributed over the MOZART‐2 grids. Our calculation shows that the uniform cloud distribution method tends to significantly overestimate back scattering on the top of clouds and overestimates the impact on photochemistry in the troposphere. The results suggest that clouds have important impacts on tropospheric chemistry. Global mean OH concentration increases by about 20% due to the impact of clouds. As a result, the calculated CH4 lifetime changes to 11 years for clear sky and 9 years for cloudy sky. The latter value is closer to the methane lifetime estimated from previous studies. Calculated CO surface concentrations are compared with observed values, showing an improvement when the impact of clouds on the photolysis rates is taken into account. Clouds also have important impacts on tropospheric ozone budget. Our calculation suggest that because of clouds, the globally averaged photolysis rates of J[O3], J[CH2O], and J[NO2] are enhanced in the troposphere by about 12, 13, and 13%, respectively, leading to an 8% increase in the tropospheric O3 concentrations. Our study suggests that clouds strongly influence photolysis rates and hence play an important role in controlling the concentrations of the tropospheric oxidants. Such effects should be carefully considered and included in regional and global chemical transport models.