bluuebunny/crossref_metadata_2025 huggingface dataset:
Compound specific radiocarbon and δ13C measurements of fatty acids in a continental aerosol sample
Authors: Matsumoto Kohei , Kawamura Kimitaka , Uchida Masao , Shibata Yasuyuki , Yoneda Minoru
Published: February 2004

Compound‐specific radiocarbon analysis of individual fatty acids was conducted for a semi‐urban aerosol sample using preparative capillary gas chromatography (PCGC) system and accelerator mass spectrometry (AMS). The aerosol fatty acids (C16 to C34) showed a typical bimodal distribution with two maxima at C16 and C26. Their carbon isotopic compositions ranged from −30.3‰ (C26) to −23.3 ‰ (C18), suggesting that they are derived from terrestrial higher plants and marine sources. Radiocarbon measurements of C16‐C22 fatty acids showed modern 14C ages, suggesting that the acids are emitted from living higher plants and possibly from marine organisms. On the other hand, C24‐C26 fatty acids that are characteristic to terrestrial plant waxes showed 14C ages of 5860 (±200) years. This suggests that some portion of higher molecular weight fatty acids have been stored in geochemical reservoirs such as soils at least for hundreds to thousands of years and then emitted to the atmosphere. These aged fatty acids could be in part transported long distances from the Asian continent through the atmosphere.
CO2 source inversions using satellite observations of the upper troposphere
Authors: Park Bernard C. , Prather Michael J.
Published: February 2004

Satellite observations of CO2 abundance in the upper troposphere can provide a major constraint for deriving the net carbon fluxes from tropical landmasses that is unavailable from current surface observations. Such global CO2 profiling with an uncertainty of about 1% (3 ppm) contains key longitudinal information needed to derive surface fluxes in a standard Bayesian inversion. Upper‐tropospheric data available from flight‐proven FTIR solar occultation measurements could provide comparable information to that from yet‐to‐be‐demonstrated column CO2 observations, which have heretofore been the focus of carbon cycle studies. A strategy for improving CO2 source inversions with either type of satellite data should focus on tropical observations and on careful evaluation of possible sampling biases affecting the observational uncertainties.
Interdecadal variability generated by interactions between Pacific and Atlantic oceans
Authors: Dima Mihai , Stefan Sabina , Dima Vasile , Borsan Dorin
Published: February 2004

Recent studies suggest that, interannual, decadal, and quasibidecadal periodicities dominate global sea surface temperature and sea level pressure variability over past hundred years. In this study, we present evidence that the quasibidecadal mode of variability can be considered in a first order approximation as resulting from a linear interaction between the dominant modes of variability in the Tropical Pacific (associated with interannual variability) and North Atlantic ocean (associated with decadal variability). A two coupled delayed action oscillators model is proposed to qualitatively explain this result.
The global magnetic field of Mars and implications for crustal evolution
Authors: Connerney J. E. P. , Acuña M. H. , Wasilewski P. J. , Kletetschka G. , Ness N. F. , Rème H. , Lin R. P. , Mitchell D. L.
Published: February 2004

The Mars Global Surveyor spacecraft obtained globally‐distributed vector magnetic field measurements approximately 400 km above the surface of Mars. These have been compiled to produce the first complete global magnetic field maps of Mars. Crustal magnetization appears dichotomized, with intense magnetization mainly confined to the ancient, heavily cratered highlands in the south. The global distribution of sources is consistent with a reversing dynamo that halted early in Mars evolution. Intense crustal magnetization requires an increased oxidation state relative to mantle‐derived rock, consistent with assimilation of an aqueous component at crustal depths.
Tomography of self‐potential anomalies of electrochemical nature
Authors: Revil A. , Ehouarne L. , Thyreault E.
Published: February 2004

Ore deposits and buried metals like pipelines behave as dipolar electrical geobatteries in which the source is due to (1) variation of the redox potential with depth, (2) oxido‐reduction reactions acting at the ore body/groundwater contact, and (3) migration of electrons in the ore body itself between the reducing and oxidizing zones. This polarization mechanism is responsible for an electrical field at the ground surface, the so‐called self‐potential anomaly. A new quick‐look tomographic algorithm is developed to locate electrical dipolar sources in the subsurface of the Earth from the analysis of these self‐potential signals. We applied this model to the self‐potential anomaly discussed by Stoll et al. [1995] in the vicinity of the KTB‐boreholes drilled during the Continental Deep Drilling Project in Germany. The source of this self‐potential signal is related to the presence of massive graphite veins associated with steeply inclined fault zones within the gneisses and observed in the KTB‐boreholes.
Importance of wind‐driven sea ice motion for the formation of Antarctic Intermediate Water in a global climate model
Authors: Saenko Oleg A. , Weaver Andrew J.
Published: February 2004

An ocean‐atmosphere‐sea ice model is used to show the importance of wind‐driven sea ice motion in the formation of Antarctic Intermediate Water (AAIW). The model is able to reasonably simulate a tongue of low salinity AAIW even when the direct momentum transfer from wind to the ocean is neglected, provided that the wind stress is applied to sea ice. In contrast, when the wind stress exclusively drives the ocean, the model fails to capture the properties of AAIW. The growth and subsequent offshore transport of sea ice acts as a freshwater conduit from near‐shore regions, where AABW is formed, to subpolar regions, where AAIW is formed. Sea ice dynamics are also shown to be important in the simulation of a local salinity minimum at intermediate depths in the southern Indian Ocean and a local salinity maximum in the western Weddell Sea.
In search of greenhouse signals in the equatorial middle atmosphere
Authors: Beig Gufran , Fadnavis S.
Published: February 2004

A series of Rocketsonde and Radiosonde data (balloon) were collected over the equatorial station Thumba (8°N, 76°E), India extended for about two solar cycle period (1971‐1993). This is one of a few longest sets of rare records available from equatorial stations. These data were now analyzed using two independent and upto date new regression models, which are based on multiple function regression theory and also takes account of successive instrumental modifications and tidal effects. These experimental results are complemented with 2‐D interactive model results simulated for the same duration and found to agree well. The model accounts for the actual measured growth rate of several greenhouse gases including CO2, CH4, N2O and CFCs for this period. Results of both balloon and rocket data analysis indicate a cooling of the order of 1°K /decade in the lower stratosphere which agrees well with low latitude data by other workers. A negative trend of 2 to 3°K/decade in the lower mesosphere and a rise in cooling up to 5.6°K/decade in the upper mesosphere has been observed. A loss of trend near the stratopause is noticed in annual trend analysis. However, on seasonal scales, trend structure gets modified and shows slightly stronger cooling in winter as compared to summer in the mesosphere.
Spectral dependence of visible light absorption by carbonaceous particles emitted from coal combustion
Authors: Bond Tami C.
Published: February 2004

Optical characteristics of particles that absorb visible light are needed to model their effects on atmospheric radiation. Light absorption by particles emitted from low‐technology coal combustion has exhibited a strong spectral dependence. I investigate various explanations for this phenomenon and conclude that a spectrally dependent imaginary refractive index is the most plausible. Following previous work on the structure of amorphous carbon, I propose that both the magnitude and spectral dependence of light absorption are controlled by the size of graphitic clusters within the material, and can be described using the optical band‐gap theory. This hypothesis is an alternative to the current measurement divisions of light‐absorbing “black carbon” and non‐absorbing “organic carbon,” and offers an explanation for preferential absorption at blue wavelengths that may extend to ultraviolet wavelengths.
Viscoelastic simulation of earthquake cycle using a simple spring‐Dashpot‐mass system with a friction law
Authors: Mitsui Noa , Hirahara Kazuro
Published: February 2004

We examine the viscoelastic effect on earthquake cycle using a simple spring‐dashpot‐mass system with a laboratory‐derived friction law. The temporal change of the frictional stress is large at the early interseismic stage and gradually decreases, in contrast to the linear change in an elastic medium. This temporal change depends on the Maxwell time. The smaller relaxation time leads to the larger change of the stress accumulation rate. Such a rate change in stress accumulation may affect the seismicity at subduction zones. Moreover, we find that the smaller relaxation time produces the smaller period of earthquake cycle and that, if the system relaxation time becomes smaller than the period of earthquake cycle, the bifurcation phenomenon, where the period splits into two, occurs. It is also found that the smaller relaxation time causes the earlier occurrence of the precursory stress decrease preceding the rapid stress drop.
Trends of NAO and AO and their associations with stratospheric processes
Authors: Zhou Shuntai , Miller Alvin J. , Wang Julian , Angell James K.
Published: February 2004

Trends of NAO and AO are shown, along with trends of various stratospheric fields and dynamical processes, including geopotential height, temperature and zonal wind, as well as EP flux and its divergence, based upon 30 years (1968–1997) of NCEP/NCAR Reanalysis data. Monthly trends are estimated by using linear regression. The NAO trends are similar to the AO trends in February and March, but different in other months, particularly in May and June. Comparing the variation by month of stratospheric trends with that of the NAO and AO index, we find that the largest trends of stratospheric fields and processes are in the same active season (JFM) as that in NAO and AO, but with the timing of peak of the trends somewhat different, the stratospheric trends leading the NAO and AO trends by one month. We also find a significant trend of equatorward refraction of mid‐latitude planetary waves in January.
Preferential detection of the Lehmann discontinuity beneath continents
Authors: Gu Yu J. , Dziewonski Adam M. , Ekström Göran
Published: February 2004

We perform a global survey for the presence of the Lehmann discontinuity using ∼20,000 long‐period SS precursors. This data set is highly sensitive to upper mantle reflectors and the coverage is more complete than in previous studies. Our survey indicates that the Lehmann discontinuity is a local feature that is observed under continents more than twice as often as it is observed under oceans. We observe significant variations in travel times and waveforms associated with this shallow mantle reflector, indicating its complexity and lateral depth variations. Little signal is detected on the continent‐scale stacks of the SS precursors, which provides further evidence for the intermittent and variable nature of the Lehmann discontinuity.
Theoretical foundation for conductivity scaling
Authors: Winter C. L. , Tartakovsky Daniel M.
Published: February 2004

Scaling of conductivity with the support volume of experiments has been the subject of many recent experimental and theoretical studies. However, to date there have been few attempts to relate such scaling, or the lack thereof, to microscopic properties of porous media through theory. We demonstrate that when a pore network can be represented as a collection of hierarchical trees, scalability of the pore geometry leads to scalability of conductivity. We also derive geometrical and topological conditions under which the scaling exponent takes on specific values 1/2 and 3/4. The former is consistent with universal scaling observed by Neuman [1994], while the latter agrees with the allometric scaling laws derived by West et al. [1997].
Inter‐annual variability of summertime CO concentrations in the Northern Hemisphere explained by boreal forest fires in North America and Russia
Authors: Wotawa Gerhard , Novelli P. C. , Trainer M. , Granier C.
Published: February 2004

Background measurements of Carbon Monoxide in the extra‐tropical Northern Hemisphere during the 1990s showed no clear trends, but significant inter‐annual variations. In this study, the measured summertime averaged CO concentrations north of 30° N were correlated with area burned by forest fires in North America and Russia. According to a linear regression analysis, 14% of the CO variability in the extra‐tropical Northern Hemisphere can be explained by boreal forest area burnt in North America, 53% by area burnt in Russia, and 63% by the combination of both. There are strong indications that the officially reported Russian fire areas are significantly underestimated. By statistically correcting these areas, we can show that, on the average, boreal burning provides a summertime CO source term comparable with all anthropogenic sources in the United States and Europe.
Time domain random walk method to simulate transport by advection‐dispersion and matrix diffusion in fracture networks
Authors: Delay Frédérick , Bodin Jacques
Published: February 2004

A method is proposed to calculate in one step the residence time of a particle by advection‐dispersion and matrix diffusion in a bond of a fracture network. The calculation is very rapid and avoids the discretization of Eulerian methods or the multiple leaps of classical Lagrangian approaches. The method is accurate in most flow conditions prevailing in fracture networks. Therefore, the method will be useful to evaluate the conditions in which the different transport mechanisms are of influence at the scale of the entire network.
Thermospheric vertical wind activity maps derived from Dynamics Explorer‐2 WATS observations
Authors: Innis J. L. , Conde M.
Published: February 2004

Large‐scale distribution of thermospheric vertical wind activity was studied using observations from the Wind and Temperature Spectrometer on the Dynamics Explorer‐2 satellite. We calculated the vertical velocity standard deviation, σ(Vz), within a sliding window of width 120 seconds, corresponding to an along‐track distance of ∼900 km. Maps of σ(Vz) in local magnetic time and invariant latitude reveal a high‐latitude region of enhanced activity that largely fills the polar cap. Activity appears to be a maximum in the midnight‐dawn sector of the cap, possibly at the nominal auroral oval latitude. We provisionally interpret our results as evidence of polar cap gravity waves with sources in or near the midnight‐dawn auroral oval. Waves propagating poleward effectively fill the cap with vertical wind oscillations. Equatorward propagating waves move approximately parallel to the local thermospheric wind, resulting in the possibility of critical‐layer dissipation.
Synorogenic crustal fluid infiltration in the Idaho‐Montana Thrust Belt
Authors: Bebout Gray E. , Anastasio David J. , Holl James E.
Published: February 2004

Mississippian carbonates in the Sevier thrust belt in Idaho‐Montana show shifts in δ18OV‐SMOW, from marine carbonate values to as low as +11‰, which are best explained by exchange with externally‐derived, low‐δ18O fluids. Late‐stage, synkinematic calcite veins are depleted in 18O relative to the host‐rocks and earlier‐formed veins, many having δ18O of +5 to +10‰. These veins could have equilibrated with H2O with δ18O of −7.5 to +2.5‰, perhaps reflecting infiltration of the Sevier thrust wedge by nearshore meteoric waters to depths of ∼10 km. Calcite veins in the hangingwall and footwall of the Pioneer Metamorphic Core Complex, produced during later Paleogene extension, have δ18O of −8.7 to +1.4‰ consistent with equilibration with meteoric waters with δ18O as low as −14‰. Transition from a Cretaceous crustal fluid regime influenced by the nearby Western Interior Seaway to one influenced by lower‐δ18O, more inland meteoric waters is consistent with seaway retreat during thrust wedge emergence and Paleogene uplift and subaerial volcanism.
Formation of molecular chlorine in dark condition: Heterogeneous reaction of ozone with sea salt in the presence of ferric ion
Authors: Sadanaga Yasuhiro , Hirokawa Jun , Akimoto Hajime
Published: February 2004

Uptake coefficients of O3 on NaCl and synthetic sea salt (SSS) were found to be enhanced from < 10−5 to ∼ 3.5 × 10−2 in the presence of water‐soluble Fe3+ in the Fe/Na weight ratio larger than 0.1%. Cl2 release was observed without radiation in the reaction of O3 and a FeCl3/NaCl mixture with surface adsorbed water at the yields of 0.48 and 0.28 for Fe/Na ratio of 1.0 and 0.5 weight %, respectively. Only Br2 release was observed for a FeCl3/SSS sample. These results imply that when bromide is deficient in sea salt, Cl2 would be released from the sea salt with the coexistence of Fe3+. The estimate was made to show that the Cl2 releasing rate can be high enough to explain sporadically observed Cl2 at nighttime in a coastal area.
Chemiions and nanoparticle formation in diesel engine exhaust
Authors: Yu Fangqun
Published: February 2004

The nanoparticles (diameter < 50 nm) emitted by diesel engines have received increasing attention due to their potential health effects. We propose that chemiions generated during combustion play an important role in the formation of these nanoparticles. The predicted nanoparticle properties based on our chemiion theory closely match measurements in terms of total nanoparticle concentrations, and their sensitivity to fuel sulfur contents and second stage dilution conditions, while the classical homogeneous nucleation fails to explain these observed properties. Our study indicates that total number of nanoparticles formed is very sensitive to chemiion concentrations, and we propose a technique to effectively reduce vehicle nanoparticle emissions by removing ions in the exhaust.
Cloud structure anomalies over the tropical Pacific during the 1997/98 El Niño
Authors: Cess Robert D. , Zhang Minghua , Wang Pi‐Huan , Wielicki Bruce A.
Published: February 2004

Satellite measurements of both cloud vertical structure and cloud‐radiative forcing have been used to show that during the strong 1997/98 El Niño there was a substantial change in cloud vertical structure over the tropical Pacific Ocean. Relative to normal years, cloud altitudes were lower in the western portion of the Pacific and higher in the eastern portion. The reason for these redistributions was a collapse of the Walker circulation and enhanced large‐scale upward motion over the eastern Pacific, both caused by the lack of a zonal sea surface temperature gradient during the El Niño. It is proposed that these cloud structure changes, which significantly impact satellite measurements of the tropical Pacific's radiation budget, would serve as one useful means of testing cloud‐climate interactions in climate models.
Trends in Italian total cloud amount, 1951‐1996
Authors: Maugeri M. , Bagnati Z. , Brunetti M. , Nanni T.
Published: February 2004

Trends in Italian total cloud amount are analysed for the period 1951‐1996. The data are a set of 35 station records that were extracted from the 3‐hourly Italian Air Force dataset. A method is discussed to obtain daily mean cloud amounts avoiding biases due to missing observations: less than 2% of the days have no observations, but more than 20% of them have at least one missing value. Trend analysis is applied to regional Northern and Southern Italy average series. Seasonal and annual trends were estimated by means of least squares linear fitting. Significance was tested using the non parametric Mann‐Kendall test. The results show that there is a highly significant negative trend in total cloud amount all over Italy. It is evident in all seasons and is particularly steep in winter where both in Northern and Southern Italy the decrease exceeds 1 okta in 50 years.
The equation of state of iron to 450 GPa: Another high pressure solid phase?
Authors: Brown Michael J.
Published: February 2004

At the 75% confidence level, Hugoniot data for iron exhibit a small volume‐change discontinuity at 200 GPa, the same pressure as a previously observed discontinuity in sound velocity. The sharpness of the discontinuity is consistent with a solid‐solid rather than solid‐liquid transition. Thus, another solid phase of iron (besides the hexagonal close‐packed ϵ‐phase) may be stable at temperatures above 4000 K and pressures above 200 GPa. While the Hugoniot data provide no structural constraint, the new phase is about 0.7% less dense than ϵ‐iron. Since the slope of the phase boundary between ϵ‐iron and the new phase is not known, the stable phase of iron under Earth inner core conditions remains uncertain. Efforts to understand the origin of inner core seismic anisotropy will require determination of the new phase structure, its elastic anisotropy, and its regime of stability.
Structure of Emiliania huxleyi blooms in the Black Sea surface waters as detected by SeaWIFS imagery
Authors: Cokacar Tulay , Kubilay Nilgun , Oguz Temel
Published: February 2004

The temporal and spatial characteristics of coccolithoprid Emiliania huxleyi blooms in the surface waters of the Black Sea are studied using the SeaWIFS mean normalized water‐leaving radiances data for 1998‐2000. It is shown that the Black Sea consistently experiences high reflectance patches of coccolith platelets throughout the basin each year during the May‐July period. Although the Black Sea is masked by clouds, the data also suggest enhanced activity for some period during autumn and early winter. Their spatial patterns resemble very closely the circulation system derived from the altimeter data, and exhibit pronounced differences between cyclones and anticyclones. The cyclonic cell, which covers the entire interior part of the basin, appears as a more favourable site for more intense bloom formation. This is related with its relatively shallower mixed layer thickness and stronger mixed layer average water leaving radiance.
The existence of a tertiary ozone maximum in the high‐latitude middle mesosphere
Authors: Marsh Daniel , Smith Anne , Brasseur Guy , Kaufmann Martin , Grossmann Klaus
Published: February 2004

Modeling and observations provide evidence of the existence of a tertiary ozone maximum in the middle mesosphere restricted to winter high‐latitudes. This local maximum occurs at approximately 72 km altitude, at latitudes just equatorward of the polar night terminator. Model analysis indicates that this maximum is the result of a decrease in atomic oxygen losses by catalytic cycles involving the odd‐hydrogen species OH and HO2. In the middle mesosphere, at high latitudes, the atmosphere becomes optically thick to ultra‐violet radiation at wavelengths below 185 nm. Since photolysis of water vapor is the primary source of odd‐hydrogen, reduced ultra‐violet radiation results in less odd‐hydrogen and consequently lower oxygen loss rates. The consequent increase in atomic oxygen results in higher ozone because atomic oxygen recombination remains the only significant source of ozone in the mesosphere.
Non‐uniform PSC occurrence within the Arctic Polar Vortex
Authors: Müller Marion , Neuber Roland , Beyerle Georg , Kyrö E. , Kivi R. , Wöste L.
Published: February 2004

A multi‐year dataset of lidar measurements of polar stratospheric clouds (PSCs) from two sites in the Arctic (Sodankylä, 67°N, 27°E, and Ny‐Ålesund, 79°N, 12°E) has been analyzed with respect to the existence temperature of different PSC types. Due to the location of the measurement sites relative to the polar vortex, their observations are most of the time representative of vortex edge and vortex center conditions, respectively. The comparison of the aerosol lidar measurements with local and trajectory temperatures reveals that PSC occurrence is favored at the edge of the Arctic polar vortex. One possibility discussed here is a differential distribution of water vapor that could be responsible for the non‐uniform threshold temperatures and thus differential PSC occurrence within the polar vortex.
Low‐frequency variability of the Antarctic Circumpolar Wave
Authors: Carril Andrea F. , Navarra Antonio
Published: February 2004

This study evaluates the Antarctic Circumpolar Wave (ACW) variability in the Southern Ocean using a 27‐year series of sea surface temperature (SST) and sea level pressure (SLP). From a cross‐covariance analysis we find that the strongest covariation between the extratropical wavenumber‐2 in SST and in SLP is during the austral summer in the South Pacific Ocean. Examination of the time series reveals two timescales of variability. A wavenumber‐2 structure in SST and SLP anomalies correlates well at interannual (IA) timescales, when ENSO‐driven teleconnections seem to energize the ACW. Moreover, in the 1973‐1999 epoch, the ACW has been modulated by interdecadal (ID) variability possibly related to the Southern Oscillation.
Aeromagnetic lineaments, basement structure and Kimberlite emplacement in Andhra Pradesh, India
Authors: Sarma B. S. P. , Verma B. K.
Published: February 2004

Magnetic lineaments reveal a wealth of structural detail. The aeromagnetic lineaments of the Wajrakarur Kimberlite Field (WKF) of South India are classified into shear, dyke and contact lineaments through 2‐D modelling. The shear lineaments and the dyke lineaments in the Anantapur region, exhibit a conjugate relationship suggesting a near E‐W compression. Modelling studies suggest a possible dextral displacement of the dykes by the shearing movements in the Anantapur region. The aeromagnetic map of the WKF shows, in addition to the conspicuous lineaments, certain confined magnetic anomalous zones, in the vicinity of kimberlites, which may manifest high magmatic permeability zones. The ENE‐WSW lineaments passing through these magnetic anomalous zones may control the emplacement of kimberlies in the WKF.
2‐cm GPS altimetry over Crater Lake
Authors: Treuhaft Robert N. , Lowe Stephen T. , Zuffada Cinzia , Chao Yi
Published: February 2004

Differences in electromagnetic path delay, between direct Global Positioning System (GPS) signals and those reflected from the surface of Crater Lake, have led to lake surface height estimates with 2‐cm precision in 1 second. This is the first high‐precision altimetric demonstration with GPS from sufficient altitude (≈ 480 m) to probe fundamental experimental errors, which bear on future air‐and spaceborne passive GPS altimetry. It also serves as the first demonstration of a new approach to altimetric remote sensing in the coastal region, an area that is poorly measured by conventional radar altimetry. Time‐series analyses suggest that tropospheric and thermal noise fluctuations dominate the altimetric error in this experiment. Estimating the differential delay from several simultaneously visible satellites may enable tropospheric error estimation and correction. Thermal noise on the reflected signal will be reduced with fully polarimetric observations and larger antenna apertures.
Birnessite catalysis of the Maillard Reaction: Its significance in natural humification
Authors: Jokic A. , Frenkel A. I. , Vairavamurthy M. A. , Huang P. M.
Published: February 2004

Although mineral colloids are known to play a significant role in transforming organic matter in soils and sediments, there still are many gaps in our understanding of the mechanisms of organic‐mineral interactions. In this study, we investigated the role of a major oxide‐mineral birnessite (a form of Mn(IV) oxide) in catalyzing the condensation reaction between sugars and amino acids, the Maillard reaction, for forming humic substances. The Maillard reaction is perceived to be a major pathway in natural humification. Using a suite of spectroscopic methods (including ESR, XANES, EXAFS and 13C NMR), our results show that Mn(IV) oxide markedly accelerates the Maillard reaction between glucose and glycine at ranges of temperatures and pH typical of natural environments. These results demonstrate the importance of manganese oxide catalysis in the Maillard reaction, and its significance in the natural abiotic formation of humic substances.
Single‐crystal elasticity of γ‐(Mg0.91Fe0.09(2SiO4 to high pressures and to high temperatures
Authors: Sinogeikin Stanislav V. , Bass Jay D. , Katsura Tomoo
Published: February 2004

Sound velocities and elastic moduli have been measured on γ‐(Mg0.91Fe0.09)2SiO4 (ringwoodite) single‐crystals to 16 GPa and to 923K by Brillouin spectroscopy. A third‐order finite‐strain fit to the data yields pressure derivatives of 4.1(2) and 1.3(1) for the adiabatic bulk modulus (KS) and shear modulus (μ) respectively. Mg‐rich α, β, and γ (Mg,Fe)2SiO4 have identical values of ∂KS/∂P and of ∂μ/∂P within the experimental uncertainties. ∂KS/∂T and ∂μ/∂T for γ‐(Mg,Fe)2SiO4 are −0.021 and −0.016 GPa/K respectively. Our results indicate that the shear and compressional impedance contrasts associated with β‐ → γ‐(Mg,Fe)2SiO4 transition are sufficient to produce a visible discontinuity at 520 km even with a moderate (30–50%) amount of olivine. The generally low visibility of the 520 km discontinuity is likely due to its width and large amplitude topographic variations.
An investigation of motions of the equatorial anomaly crest
Authors: Yeh K. C. , Franke S. J. , Andreeva E. S. , Kunitsyn V. E.
Published: February 2004

Using more than 350 ionospheric images reconstructed tomographically, studies on the motion of the anomaly crest and its geophysical implications are carried out. On an average day, the crest forms at 09:00 LT and, in the next two hours, moves poleward with a speed of about 1° per hour as it intensifies. This poleward motion is slowed as the crest reaches its highest latitude where it stays for several hours until early afternoon. Thereafter, the crest starts to weaken as it recedes with a speed of about 0.5° per hour equatorward. During 12:00 ‐ 14:00 LT, the crest latitude is found to correlate with the fountain strength and the total number of electrons in a cross sectional plane at the observational longitude of the whole equatorial ionosphere.
Carbon balance in East European tundra
Authors: Heikkinen Juha E. P. , Virtanen Tarmo , Huttunen Jari T. , Elsakov Vladimir , Martikainen Pertti J.
Published: February 2004

We studied the carbon dioxide and methane fluxes from early June to mid‐September 2001 in the Russian tundra of northeast Europe. Gas fluxes were measured with chamber techniques to determine the seasonal (100 days) carbon gas balance for terrestrial ecosystems representing various vegetation types. Also, the gas balance for aquatic ecosystems in the region was measured. The 2001 fluxes were compared to colder and wetter season fluxes from 1999. The Sphagnum sp. dominated peat plateau fen and Carex sp. and Sphagnum sp. dominated intermediate flarks were carbon sinks of 106 and 110 g C m−2, respectively. In addition, methane emissions were highest from these sites. Other terrestrial surfaces lost carbon to the atmosphere (28–118 g C m−2). The thermokarst lake and the river had seasonal carbon losses of 15 and 34 g C m−2, respectively. For areal integration, the distributions of the various functional surfaces were classified based on Landsat TM satellite image and on‐site validation. This data was used to integrate the carbon fluxes for the entire Lek Vorkuta catchment. The upscaling indicated that the catchment (114 km2) lost 4 (±3.5) Gg C to the atmosphere in summer 2001. The results suggest that predicted warming in the tundra region would induce a substantial loss of carbon. In the warm summer of 2001, the carbon gas released from the whole northeast European tundra (area 205,000 km2) was 8 Tg C when calculated from the Lek Vorkuta data.
A test of the magnetospheric source of traveling convection vortices
Authors: Lam M. M. , Rodger A. S.
Published: February 2004

Traveling convection vortices (TCVs) are a powerful tool for probing the nature of the coupling between the solar wind, the magnetosphere, and the ionosphere. There is no reliable model of the plasma concentration in the magnetosphere, resulting in uncertainties about the factors controlling the scale size, the motion, and the numbers of field‐aligned currents associated with TCV events. There is also uncertainty about whether TCV generation is current driven, voltage driven, or even driven by some more complex source. We use conjugate ground‐based magnetometer data from the Greenland magnetometer chain and Antarctica to test the nature of the magnetospheric source of 18 TCV events associated with changes in the magnetopause dynamic pressure. This is achieved by statistically comparing two groups of TCV events: for one group the conjugate ionospheres are of similar conductivity, and for the other group the conductivities of the conjugate ionospheres differ by an order of magnitude. Statistically, we find that conjugate TCV events are of similar intensity in both hemispheres regardless of any difference in conductivity between the two hemispheres. We propose that this is evidence in favor of a constant current source for TCVs where the amplitude of a TCV is controlled by the local plasma concentration, the magnetic field strength, and the acceleration of the plasma.
A modeling study on the climate impacts of black carbon aerosols
Authors: Wang Chien
Published: February 2004

A three‐dimensional interactive aerosol‐climate model has been developed and used to study the climatic impact of black carbon (BC) aerosols. When compared with the model's natural variability, significant global‐scale changes caused by BC aerosols occurred in surface latent and sensible heat flux, surface net long‐wave radiative flux, planetary boundary layer height, convective precipitation (all negative), and low‐cloud coverage (positive), all closely related to the hydrological cycle. The most significant regional change caused by BC revealed in this study is in precipitation that occurs in the tropics (shift of precipitation center in the ITCZ) and in the middle and high latitudes of the Northern Hemisphere (change in snow depth). Influenced by BC caused changes in cloud cover and surface albedo, the interactive model provides smaller positive all‐sky forcing at the top of atmosphere (TOA) and larger negative forcing at the surface than the offline diagnostics (the direct forcings). The actual solar radiative forcings by BC derived from the interactive model also exhibit significant interannual variations that are up to 4 times as large as their means. Based on the revealed changes in cloud radiative forcing by BC, a non‐Twomey‐Albrecht indirect forcing by BC that alters radiative budgets by changing cloud cover via thermodynamics rather than microphysics is also defined. It has been demonstrated that with an absolute amount more than 2 times higher than that of the TOA forcing, the surface forcing by BC is a very important factor in analyzing the climatic impact of BC. The result of this study suggests that with a constant annual emission of 14 TgC, BC aerosols do not cause a significant change in global‐mean surface temperature. The calculated surface temperature change is determined by a subtle balance among changes in surface energy budget as well as in the hydrological cycle, all caused by BC forcing and often compensate each other. The result of this study shows that the influences of BC aerosols on climate and environment are more significant in regional scale than in global scale. Important feedbacks between BC radiative effects and climate dynamics revealed in this study suggest the importance of using interactive aerosol‐climate models to address the issues related to the climate impacts of aerosols.
Correlation between speeds of coronal mass ejections and the intensity of geomagnetic storms
Authors: Yurchyshyn Vasyl , Wang Haimin , Abramenko Valentyna
Published: February 2004

We studied the relationship between the projected speed of coronal mass ejections (CMEs), determined from a sequence of Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph Experiment (SOHO/LASCO) images, and the hourly averaged magnitude of the Bz component of the magnetic field in an interplanetary ejecta, as measured by the Advanced Composition Explorer (ACE) magnetometer in the Geocentric Solar Magnetospheric Coordinate System (GSM). For CMEs that originate at the central part of the solar disk we found that the intensity of Bz is correlated with the projected speed of the CME, Vp. The relationship is more pronounced for very fast ejecta (Vp > 1200 km/s), while slower events display larger scatter. We also present data which support earlier conclusions about the correlation of Bz and the Dst index of geomagnetic activity. A possible application of the results to space weather forecasting is discussed.
Evaluation of cubic law based models describing single‐phase flow through a rough‐walled fracture
Authors: Konzuk Julie S. , Kueper Bernard H.
Published: February 2004

This study provides an evaluation of various modifications of the cubic law, expanding upon previous work as follows: (1) Experimentally measured flow rates and apertures are the basis for the evaluation; (2) a rock fracture is used rather than an analog or numerically simulated fracture; (3) the fracture is not disturbed at any point during the testing; and (4) detailed measurements of the apertures and the top and bottom fracture surface profiles (931,988 measurements in total) are obtained, enabling assessment of the impact of fracture surface undulation and model discretization on the simulated flow rates. The cubic law calculated with either the geometric mean aperture or incorporating surface roughness factors provided reasonable (±10%) estimates of the observed flow rates for Re < 1. The cubic law applied locally (LCL) over‐predicted the observed flow rates by at least 1.9 times. Modifying the LCL to incorporate a solution for tapered plates and correcting for surface undulation reduced the over‐prediction to at least 1.75 times the measured flow rates. The primary conclusions that we can draw from this work are as follows: (1) There appears to be merit to conducting further studies of the cubic law applied at the single‐fracture scale to determine whether similar results are achievable in all fracture types; and (2) the current understanding of when the LCL will provide an adequate representation of the true flow behavior is not entirely correct; more investigation into the effect of fracture surface undulation and other causes of abrupt aperture change (e.g., rock debris trapped within the fracture plane) is required.
Hydrochemical implications of groundwater mixing: An example from the Southern Laramie Basin, Wyoming
Authors: Mazor E. , Drever J. I. , Finley J. , Huntoon P. W. , Lundy D. A.
Published: February 2004

The southern Laramie Basin groundwater system was studied to explore how standard thermodynamic chemical calculations can produce misleading results with respect to water‐rock interactions when groundwaters with different chemical compositions mix. Geological and hydrological data determined the direction of flow to be NW in the Casper aquifers, as well as in the Redbeds aquifers. Hydrological and structural data were used to identify wells having mixtures of groundwater. The chemical data revealed that waters in the different aquifers are distinguishable by their chemical compositions and that mixtures have intermediate compositions. The different chemistries of the mixed groundwater samples are identical to those predicted by geochemical evolution paths, including calcite precipitation, evolution toward equilibration with gypsum, and Ca‐Mg ion exchange.
Contaminant spreading in stratified soils with fractal permeability distribution
Authors: Kemblowski Marian W. , Wen Jet‐Chau
Published: February 2004

Stochastic analysis of flow and transport in the subsurface usually assumes that the soil permeability is a stationary, homogeneous stochastic process with a finite variance. Some field data suggest, however, that the permeability distributions may have a fractal character with long‐range correlations. It is of interest to investigate how the fractal character of permeability distribution influences the spreading and mixing process in porous media. The results of our analysis of this problem for perfectly stratified media with fractal distribution of permeability along the vertical are presented. Results were obtained for the transient and asymptotic dispersivities in the longitudinal direction. The results show that the macroscopic asymptotic dispersivity depends strongly on the fractal dimension of vertical permeability distribution. Specifically, the higher the fractal dimension, the lower the value of macroscopic dispersivity. The macroscopic dispersivity was found to be problem‐scale dependent in transient (development) and asymptotic phases. Variance of fluctuation of concentration was also analyzed and found to be dependent on the fractal dimension. In this case, the higher fractal dimension results in more mixing of pore water and therefore smoother (smaller σα2) concentration distribution.
Exact Scheffé‐type confidence intervals for output from groundwater flow models: 2. Combined use of hydrogeologic information and calibration data
Authors: Cooley Richard L.
Published: February 2004

Calibration data (observed values corresponding to model‐computed values of dependent variables) are incorporated into a general method of computing exact Scheffé‐type confidence intervals analogous to the confidence intervals developed in part 1 (Cooley, this issue) for a function of parameters derived from a groundwater flow model. Parameter uncertainty is specified by a distribution of parameters conditioned on the calibration data. This distribution was obtained as a posterior distribution by applying Bayes' theorem to the hydrogeologically derived prior distribution of parameters from part 1 and a distribution of differences between the calibration data and corresponding model‐computed dependent variables. Tests show that the new confidence intervals can be much smaller than the intervals of part 1 because the prior parameter variance‐covariance structure is altered so that combinations of parameters that give poor model fit to the data are unlikely. The confidence intervals of part 1 and the new confidence intervals can be effectively employed in a sequential method of model construction whereby new information is used to reduce confidence interval widths at each stage.
Solution of the shallow water equations by least squares collocation
Authors: Laible Jeffrey P. , Pinder George F.
Published: February 2004

A method of solution of the shallow water equations in their primitive form that yield solutions free of numerical oscillations, is presented. The method is based on the least squares collocation concept. The focus is on the accuracy of the solution procedure. Comparison of the numerical solution with analytic solutions for problems of irregular geometry are presented. Key features are the ability of the method to solve the equations in an irregular domain with a completely orthogonal computational mesh and the inherent nondissipative noise control of the temporal and spatial approximations.
Probabilistic sensitivity analysis for one‐dimensional reactive transport in porous media
Authors: Cawlfield Jeffrey D. , Wu Ming‐Chee
Published: February 2004

A reliability approach for probabilistic modeling of reactive transport in porous media provides two important quantitative results: (1) an estimate of the probability that dimensionless concentration equals or exceeds some specified level and (2) a probabilistic sensitivity measure which quantifies the relative importance of each uncertain variable with respect to the probabilistic outcome. The approach is potentially attractive because it can provide both a probability estimate and probabilistic sensitivity measures; this is especially important for relatively low probability events where Monte Carlo simulation may require hundreds of thousands of realizations for reasonable results. The reliability method can incorporate marginal probability distribution functions (PDF) and correlation between uncertain variables, and the general method can be used with existing analytical or numerical solutions. However, a first‐order reliability approach provides only an approximate probability measure; the accuracy is a function of performance criterion and statistical characteristics of the uncertain variables. The methodology and results here focus on probabilistic sensitivity measures which indicate the importance of any uncertain variable to the probabilistic outcome. In this work, one‐dimensional reactive transport is investigated with the following uncertain variables: groundwater flow velocity, diffusion coefficient, dispersivity, distribution coefficient, porosity, and bulk density. We examine how probabilistic outcome and sensitivity are influenced by choice of marginal PDF, correlation, and magnitude of uncertainty for the variables. We also compare the probabilistic sensitivity results to typical deterministic sensitivity measures. Results indicate that the probabilistic outcome is most sensitive to likely changes in flow velocity and the reaction terms. Diffusion coefficient can also be an important uncertain variable but only when it has significantly higher uncertainty (coefficient of variation) than any other variable. For some cases shown in this paper, dispersivity and diffusion coefficient can be treated as deterministic variables with little impact on the probabilistic outcome.
Incorporating demand uncertainty in water supply headworks simulation
Authors: Ng Wan Sing , Kuczera George
Published: February 2004

Simulation is used to evaluate the future performance of water supply headworks systems. Typically, most of the uncertainties associated with the use of demand models are ignored in the simulation. A simulation methodology is presented which makes allowance for the uncertainties associated with the use of demand and streamflow models. The demand uncertainties considered are natural, climatic, socioeconomic, and model parameter uncertainty. The methodology is illustrated using two case studies which consider a simple stationary demand model and the widely used trend extrapolation demand model. The results show that ignoring demand uncertainties (as well as streamflow model parameter uncertainty) can significantly bias the expected reliability. This bias depends on the magnitude of demand uncertainty which in turn depends on model structure, length of data available for calibration, and uncertainty in future socioeconomic variables. Moreover, this bias tends to increase as streamflow variability decreases. To guard against overoptimistic assessment of system performance, it is suggested that allowance be made for demand uncertainty (as well as streamflow model parameter uncertainty) in headworks simulation.