bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental assessment of gas transport mechanisms in natural porous media: Parameter evaluation
Authors: Abu‐El‐Sha'r Wa'il , Abriola Linda M.
Published: February 2004

An understanding of vapor transport in natural porous media is critical to the assessment of a wide range of environmental problems. In this work a comprehensive experimental program was undertaken to evaluate the relative importance of different gaseous transport mechanisms in natural porous media. The dusty gas model was used as a framework for this evaluation. The experimental program was divided into two parts: the first emphasizes the measurement of porous media transport parameters, and the second explores flux mechanisms in organic vapor transport. Results of the first part are presented in this paper. Single and binary gas experiments were conducted to obtain governing transport parameters (coefficients of permeability, Knudsen diffusion, and diffusibility) in dry porous media. To conduct these experiments, a special experimental apparatus was built that incorporates a diffusion cell that represents an open system where the pressure gradient and absolute pressures can be regulated by controlling the flow rates of the component gases at both ends of the soil sample. Soils tested included three uniform materials, a sea sand, an Ottawa sand, and kaolinite clay, and five graded mixtures of these uniform soils. Results of the single‐gas experiments illustrate the importance of Knudsen diffusion in permeability measurements. Two new transport parameter correlations are developed from the presented data and compared with available literature correlations. The correlation for the Knudsen diffusion radius has a functional dependence upon the square root of intrinsic permeability, selected as a characteristic length of the porous medium. Binary diffusion experiments, using an equimolar pair of gases, are employed to develop a correlation for a composition independent diffusibility.
A geostatistical approach to contaminant source identification
Authors: Snodgrass Mark F. , Kitanidis Peter K.
Published: February 2004

A geostatistical approach to contaminant source estimation is presented. The problem is to estimate the release history of a conservative solute given point concentration measurements at some time after the release. A Bayesian framework is followed to derive the best estimate and to quantify the estimation error. The relation between this approach and common regularization and interpolation schemes is discussed. The performance of the method is demonstrated for transport in a simple one‐dimensional homogeneous medium, although the approach is directly applicable to transport in two‐ or three‐dimensional domains. The methodology produces a best estimate of the release history and a confidence interval. Conditional realizations of the release history are generated that are useful in visualization and risk assessment. The performance of the method with sparse data and large measurement error is examined. Emphasis is placed on formulating the estimation method in a computationally efficient manner. The method does not require the inversion of matrices whose size depends on the grid size used to resolve the solute release history. The issue of model validation is addressed.
Seasonal variations in acid‐neutralizing capacity in 13 northeast United States headwater streams
Authors: DeWalle David R. , Davies Trevor D.
Published: February 2004

Variations in acid‐neutralizing capacity (ANC) in 13 streams in the Adirondack, Catskill, and Northern Appalachian Plateau regions of the northeast United States were related to discharge, time of year, and seasonal variations in cation and anion concentrations using periodic regression analysis, ANC varied significantly with both discharge and time of year in 12 streams. Generation of ANC seasonal variations, being dependent upon the precise timing and magnitude of seasonal variations in cation and anion concentrations, was unique to each stream. Greatest seasonal ANC variations occurred in streams where seasonal variations in major anion and cation concentrations were completely out of phase. Maximum errors that could occur because of extrapolation of ANC data from one time of year to another were equal to or greater than maximum errors due to extrapolation of ANC from one discharge to another.
The influence of observation method on local concentration statistics in the subsurface
Authors: Destouni Georgia , Graham Wendy
Published: February 2004

By introducing the concept of a finest possible time resolution in concentration observations, we extend the probabilistic Lagrangiari transport formulation to account for the statistics of locally measured concentration values and their dependence on observation method for short pulse solute inputs. The outlined methodology for quantifying the ensemble expected value and variance of locally measured concentration values is relevant for transport under either unsaturated or saturated flow conditions and for different types of observation methods. The methodology is exemplified here for direct pore water sampling in aquifers (perfectly stratified/near‐field transport, or three‐dimensional isotropic and far‐field transport) and for solute that is non‐reactive or undergoes linear (reversible equilibrium or nonequilibrium, and irreversible) sorption. For nonreactive solute and for solute that undergoes irreversible sorption or equilibrium sorption‐desorption, the observation procedure greatly influences the variance of locally measured solute concentrations: both the concentration variance and the coefficient of variation decreases considerably as the sampled water volume/sampling time increases. For solute that undergoes nonequilibrium sorption‐desorption, both the concentration variance and the observation effect on the variance are considerably smaller than for nonreactive solute or solute undergoing equilibrium or irreversible sorption. The reason is that the concentration variance is highly dependent on the sorption kinetics, which implies that simple rules, based on average solute behavior, for when the sorption‐desorption process can be regarded as being in equilibrium may be irrelevant for describing the concentration variance in heterogeneous fields.
Stochastic analysis of oxygen‐limited biodegradation in three‐dimensionally heterogeneous aquifers
Authors: Miralles‐Wilhelm F. , Gelhar L. W. , Kapoor V.
Published: February 2004

A three‐dimensional analytical model is developed to quantify the process of oxygen‐limited biodegradation as it occurs at field scales. The model incorporates the effects of chemical and microbiological heterogeneities inherent to the biodegradation process in a stochastic analysis of the coupled transport equations for a system consisting of a contaminant and an oxidizing agent, that is, oxygen, in heterogeneous and anisotropic aquifers. Natural aquifer variability, equilibrium linear sorption and Monod‐type kinetics for the microbial population constitute the sources of these heterogeneities. Calculations for hypothesized field conditions show that longitudinal macrodispersivities for the contaminant and dissolved oxygen are considerably affected by biodegradation. The effective contaminant decay rate is fundamentally found to be moderately less than the mean, while the effects are lesser for the effective retardation factor. The usual assumption of equal dispersivities for both components is found to be inadequate over most concentration ranges.
Methane oxidation and pathways of production in a Texas paddy field deduced from measurements of flux, δl3C, and δD of CH4
Authors: Tyler S. C. , Bilek R. S. , Sass R. L. , Fisher F. M.
Published: February 2004

Irrigated rice paddies are one of the few methane (CH4) sources where the management of its emissions may be possible. Before that can be initiated, however, the relationship between production, oxidation, and emission of CH4 and the processes controlling them must be better known. To that end we have made measurements of concentration and stable carbon and hydrogen isotopes of CH4 and CO2 in paddy fields along the Gulf Coast of Texas. Although only small differences in total CH4 flux (∼46.5 g m−2 clayey and ∼43 g m−2 sandy) and average δ13CH4 (seasonal averages of −56.11±1.21‰ clayey and −53.57±0.97‰ sandy) from emitted CH4 were observed in two plots with different soil textures, by making additional measurements of belowground CH4 and CO2 we learned much about processes occurring in the paddy field. We estimated that roughly 98% of the CH4 released was transported through the plant and that residence times for belowground CH4 were from about 1 to 5 hours during most of the season, indicating fast processing of both organic carbon and current photosynthesized carbon to make CH4. The percentage of CH4 made from acetate fermentation calculated using isotope data was strongly dependent on the value of the fractionation factor (α) associated with the CO2/H2 reduction pathway for CH4 formation. Using a range of reasonable values for α, we calculated that acetate fermentation was from 67 to 80% early in the season to 29 to 60% late in the season (generally decreasing as the season progressed). Most importantly, we have strong evidence that rhizospheric CH4 oxidation occurs in paddy fields. We have developed a semiempirical equation and used it to calculate the percent of CH4 oxidized as a function of total CH4 produced from field measurements of δ13CH4 under natural conditions. Because most emitted CH4 is transported by the rice plant, it was necessary to determine the isotopic fractionation CH4 underwent during its transport through the plant. This value, 12±l‰, was used to calculate oxidation percent using belowground and emitted δ13CH4 values. In Texas, oxidation of CH4 in the soil increased from ∼20 to ∼60% over the 6 week period just prior to harvest.
Evaluation of terrestrial carbon cycle models through simulations of the seasonal cycle of atmospheric CO2: First results of a model intercomparison study
Authors: Heimann M. , Esser G. , Haxeltine A. , Kaduk J. , Kicklighter D. W. , Knorr W. , Kohlmaier G. H. , McGuire A. D. , Melillo J. , Moore B. , Otto R. D. , Prentice I. C. , Sauf W. , Schloss A. , Sitch S. , Wittenberg U. , Würth G.
Published: February 2004

Results of an intercomparison among terrestrial biogeochemical models (TBMs) are reported, in which one diagnostic and five prognostic models have been run with the same long‐term climate forcing. Monthly fields of net ecosystem production (NEP), which is the difference between net primary production (NPP) and heterotrophic respiration RH, at 0.5° resolution have been generated for the terrestrial biosphere. The monthly estimates of NEP in conjunction with seasonal CO2 flux fields generated by the seasonal Hamburg Model of the Oceanic Carbon Cycle (HAMOCC3) and fossil fuel source fields were subsequently coupled to the three‐dimensional atmospheric tracer transport model TM2 forced by observed winds. The resulting simulated seasonal signal of the atmospheric CO2 concentration extracted at the grid cells corresponding to the locations of 27 background monitoring stations of the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory network is compared with measurements from these sites. The Simple Diagnostic Biosphere Model (SDBM1), which is tuned to the atmospheric CO2 concentration at five monitoring stations in the northern hemisphere, successfully reproduced the seasonal signal of CO2 at the other monitoring stations. The SDBM1 simulations confirm that the north‐south gradient in the amplitude of the atmospheric CO2 signal results from the greater northern hemisphere land area and the more pronounced seasonality of radiation and temperature in higher latitudes. In southern latitudes, ocean‐atmosphere gas exchange plays an important role in determining the seasonal signal of CO2. Most of the five prognostic models (i.e., models driven by climatic inputs) included in the intercomparison predict in the northern hemisphere a reasonably accurate seasonal cycle in terms of amplitude and, to some extent, also with respect to phase. In the tropics, however, the prognostic models generally tend to overpredict the net seasonal exchanges and stronger seasonal cycles than indicated by the diagnostic model and by observations. The differences from the observed seasonal signal of CO2 may be caused by shortcomings in the phenology algorithms of the prognostic models or by not properly considering the effects of land use and vegetation fires on CO2 fluxes between the atmosphere and terrestrial biosphere.
Role of dissolved organic matter in the marine biogeochemical cycle: Studies using an ocean biogeochemical general circulation model
Authors: Yamanaka Yasuhiro , Tajika Eiichi
Published: February 2004

A biogeochemical general circulation model which includes production and consumption processes of dissolved organic matter (DOM) is developed. The semilabile and the refractory DOM are taken into account. The vertical distribution of the dissolved organic carbon (DOC) concentration and the Δ14C value obtained in our model compares well with the recent observations. It is found that the double DOC maximum zone (DDMZ) extends in the east‐west direction in the equatorial Pacific. Case studies, which change the decay time and production ratio constant, show that the horizontal distribution of DOC in the surface layer can be reproduced only when the decay time of the semilabile DOM is about half a year. The semilabile DOM exists only above a depth of 400 m, and its vertical and horizontal transport plays an important role in the marine biogeochemical cycle in the surface layer. However, below that depth, only the inert refractory DOM exists, and the role of the refractory DOM in the biogeochemical cycle is not important. The global export production due to the particulate organic matter (POM) and DOM at a depth of 100 m is estimated to be about 8 Gt C/yr and about 3 Gt C/yr, respectively. The vertical transport below 400 m is due almost entirely to POM.
Quantification of diffusive benthic fluxes of nitrate, phosphate, and silicate in the southern Atlantic Ocean
Authors: Hensen Christian , Landenberger Holger , Zabel Matthias , Schulz Horst D.
Published: February 2004

Pore water data from surface sediments and bottom water data at 180 locations were used to create distribution maps of diffusive benthic release rates of nitrate, phosphate, and silicate in the southern Atlantic Ocean for water depths ≥1000 m. Geostatistical methods of variogram analysis and kriging were used for data interpolation. Since benthic fluxes are controlled by organic matter degradation and dissolution processes and therefore by the supply of organic matter to the sediment surface, the distribution pattern of all investigated constituents should reflect a general coupling to surface water productivity. This seems to be true for the most part of the oligotrophic central South Atlantic and the upwelling area off southwest Africa. Striking regional differences in this regard, however, exist for the eastern equatorial region where unexpectedly low fluxes were calculated and the Argentine Basin where benthic fluxes are very high. The Argentine Basin obviously receives a higher input of degradable/dissolvable material, whereas in the eastern equatorial region the low benthic fluxes are possibly due to intense nutrient recycling within the water column. Estimated fluxes vary considerably over the entire region: NO3, 10–180 mmol m−2 yr−1 PO4, (−2)−11 mmol m−2 yr−1 and Si, 0–0.65 mol m−2 yr−1. Areas of highest release rates are the continental margins off southwest Africa and off Argentina. The investigated area comprises a total of approximately 32×106 km2 between 8°N and 40°–50°S. Our estimations reveal benthic release rates of 1.55×l012 mol NO3 yr−1, 3.5×l010 mol PO4 yr−1 and 2.1×1012 mol Si yr−1. Open ocean areas with middle to low fluxes contribute about 70–80% of the total estimated fluxes. The release of phosphate is probably underestimated because of core recovery artifacts and is therefore based on the assumption that fluxes are not lower than 0.25 mmol m−2 yr−1 at any location of the studied area. The investigated area represents about one tenth of the world deep ocean (without the Arctic Ocean). Assuming the South Atlantic to be representative, we calculate annual global release rates of 15×l012 mol NO3, 32×l010 mol PO4 and 20×1012 mol Si. If our estimates are correct, about 4–6% of silicate, 3–4% of nitrate, and 1% of phosphate annually produced in the surface waters are remineralized in surface sediments from water depths ≥ 1000 m.
Evidence for an earthquake cycle in NW outer Himalaya near 78°E longitude from precision levelling observations
Authors: Gahalaut V. K. , Chander R.
Published: February 2004

A levelling line along the Saharanpur‐DehraDun‐Mussoorie highway crosses the NW Outer Himalaya. The line has been surveyed over most parts of its length several times at irregular intervals since 1861. The observations show that there was coseismic uplift along the line during the great Kangra earthquake of 1905. But most benchmarks have started subsiding in the decades following the earthquake. This is seen as evidence that the upper crust along and adjoining the levelling line experiences a cyclic process of strain accumulation and release in great earthquakes.
Stratospheric HBr concentration profile obtained from far‐infrared emission spectroscopy
Authors: Nolt I. G. , Ade P. A. R. , Alboni F. , Carli B. , Carlotti M. , Cortesi U. , Epifani M. , Griffin M. J. , Hamilton P. A. , Lee C. , Lepri G. , Mencaraglia F. , Murray A. G. , Park J. H. , Park K. , Raspollini P. , Ridolfi M. , Vanek M. D.
Published: February 2004

Hydrogen bromide (HBr) is the principal bromine sink species for the ozone loss chemistry induced by bromine‐containing gases in the stratosphere. We report a 1994 balloon‐based measurement of the daytime stratospheric HBr profile between 20 and 36.5 km altitude. The average concentration result of 1.31±0.39 parts per trillion in volume (pptv) and an analysis for the concentration versus altitude profile are consistent with previously reported measurements. These results strengthen the evidence for a significantly higher HBr concentration than that predicted by current photochemical models which, on the basis of recent kinetics results, do not include significant HBr production by the reaction branch, BrO + HO2 → HBr + O3.
Field‐aligned current distributions generated by a divergent Hall current
Authors: Buchert Stephan C. , Budnik Frank
Published: February 2004

In a horizontally homogeneous high‐latitude ionosphere a steady state Hall current closes within the E region and does not contribute to the interaction between the ionosphere and magnetosphere. When the steady state assumption is given up, Hall currents driven by a non‐zero ∂B/∂t become divergent and must transiently close via the magnetosphere. It is shown, that this process is of non‐local nature and can redistribute the field‐aligned current in space and time. At scales of tens of kilometers the effect becomes significant for frequencies at about 1 Hz and above, at larger scales even for lower frequencies. The rearrangement of the field‐aligned current is such that elongated structures tend to warp, and thus it resembles some of the typical dynamic evolution of auroral forms. Even a transient local amplification of the current density is possible.
Cool tropical temperatures shift the global δ18O‐T relationship: An explanation for the ice core δ18O ‐ borehole thermometry conflict?
Authors: Boyle Edward A.
Published: February 2004

The discrepancy between central Greenland borehole temperatures and the isotopic composition of Last Glacial Maximum ice can be explained by a shift in the δ18O‐T relationship for the hydrological cycle linked to cooler tropical temperatures. This concept is illustrated using a simple Rayleigh distillation model. An estimate for α=Δδ18 O/ΔT (LGM‐Holocene) of −0.37 ‰/°C is determined with a simple graphical technique.
How the magnetopause transition parameter works
Authors: Lockwood M. , Hapgood M. A.
Published: February 2004

The transition parameter is based on the electron characteristics close to the Earth's dayside magnetopause, but reveals systematic ordering of other, independent, data such as the ion flow, density and temperature and the rientation and strength of the magnetic field. Potentially, therefore, it is a very useful tool for resolving ambiguities in a sequence of satellite data caused by the effects of structure and motion of the boundary; however, its application has been limited because there has been no clear understanding of how it works. We present an analysis of data from the AMPTE‐UKS satellite which shows that the transition parameter orders magnetopause data because magnetic reconnection generates newly‐opened field lines which coat the boundary: a direct relationship is found with the time elapsed since the boundary‐layer field line was opened. A simple model is used to reproduce this behaviour.
Trends of airglow imager observations near Adelaide, Australia
Authors: Hecht J. H. , Walterscheid R. L. , Woithe J. , Campbell L. , Vincent R. A. , Reid I. M.
Published: February 2004

From April, 1995 to January, 1996 a nightglow imager and an airglow photometer were colocated near Adelaide, Australia. The data obtained on more than 50 clear nights revealed seasonal changes in the airglow intensities and temperatures as well as in the gravity wave activity. These temperature data are the first seasonal results from the mid‐latitude southern hemisphere mesopause region. The OH Meinel band was observed to have a rotational temperature that was warmer than the O2 Atmospheric band in the winter. There were also summer solstice maxima and winter solstice minima in the O2 Atmospheric band and OI(557.7' airglow intensities. The gravity wave activity, seen in the 50 to 80 km horizontal wavelength waves, was generally greatest in the OH Meinel layer and showed a semiannual variation with a strong summer solstice maximum. The relationship between gravity wave activity and airglow intensities disagrees somewhat with models. Compared to previous studies, the data suggest that there may be a difference in the seasonal variability of short and long period gravity waves.
Dependence of self diffusivity on P and T in molten NaAlSi2O6: Comparison of laboratory and molecular dynamics experiments
Authors: Bryce Julia G. , Spera Frank J. , Stein Daniel J.
Published: February 2004

We have used molecular dynamics (MD) simulation to investigate ionic self‐diffusivity in NaAlSi2O6 melts and glasses at pressures of 3–58 GPa and temperatures of 2500–5000 K, to evaluate the effectiveness of a two‐body potential in reproducing pressure and temperature dependence of tracer self‐diffusivities. For each species, self‐diffusivity increased with increasing temperature; with increasing pressure up to ∼15 GPa, the self‐diffusivity of O, Si, and Al increased, while mobility of Na decreased. An Arrhenian fit to self‐diffusivity data collected from simulations at temperatures above the kinetic glass transition (up to 15 GPa) gives: Species Ea Va log D* (kJ/mol) (×106m³/mol) (m²/s) Na 81±14 3.5±0.5 −6.8±0.17 Al 306±31 −5.6±1.1 −6.5±0.35 Si 294±23 −6.1±0.9 −6.9±0.26 O 302±23 −5.9±0.8 −6.6±0.26 for activation energy (Ea) and activation volume (Va). The MD‐derived Ea,o and Va,o agree with laboratory results of 275±10 kJ/mol and −6.2±0.6 cm³/mol for Ea,o and Va,o respectively [Shimizu and Kushiro, 1984] measured in experiments at 1673 to 1923 K and 0.5 to 2 GPa. Agreement with the pre‐exponential factor (D*) is poorer, with MD result of ∼10−6.6 for O and laboratory value ∼10−4.7. From ∼15 GPa–25 GPa, Va is ∼0 m³/mol for O, Si, and Al; these species have a positive Va for pressures above 25 GPa (Va,o is ∼ +1 cm³/mol). For pressures ∼15 GPa the majority of the network cations are in 5‐ or 6‐ fold coordination, and more than 20% of the O is in 3‐fold coordination. With increasing pressure, 4‐fold Si and Al decrease monotonically, while 6‐fold Si and Al increase monotonically. Pentahedral Si and Al maximize at nearly the same pressure as O self‐diffusivity.
Atmospheric gradients and the VLBI terrestrial and celestial reference frames
Authors: MacMillan D. S. , Ma C.
Published: February 2004

Gradients in the atmospheric refractive index can lead to errors in estimated vertical and horizontal station coordinates. These errors produce systematic errors in the terrestrial and celestial reference frames determined from our very long baseline interferometry (VLBI) measurements. Estimation of gradients for our global VLBI data set changes the terrestrial reference frame length scale by −0.7 ppb and produces station position adjustments that vary approximately monotonically with latitude. Estimating gradients reduces the radio source declinations by an amount that peaks at about 0.5 mas near the equator and decreases toward the poles. VLBI gradient estimates are consistent with gradients derived from a global three‐dimensional model of assimilated meteorological data. Both indicate that mean atmospheric delay gradients point toward the equator in both the northern and southern hemispheres. The correlation coefficient between VLBI and meteorological model gradients for VLBI sessions for the VLBI antenna at Westford, Massachusetts was 0.56.
Ion beams observed in the near Earth plasma sheet region on May 10, 1996
Authors: Parks G. K. , Skoug R. M. , Spencer S. L. , McCarthy M. P. , Lin R. P. , Larson D. , McFadden J. , Rème H. , Sanderson T. R.
Published: February 2004

This Letter reports observations of ion distributions made by the Wind 3D plasma experiment on May 10, 1996 during the 0400 UT substorm. The observations come from the 3D ion analyzer with a geometrical factor two orders of magnitude larger than most of the similar instruments flown through the near‐earth geomagnetic tail. This has permitted observations of detailed ion beam characteristics during the passage of the spacecraft across the plasma sheet boundary into the lobe where the density is very low. The plasma initially consists of cold and warm components, with an additional hot component observed as the spacecraft approaches the plasma sheet‐lobe interface. The beams originate from the warm component, which is the most dynamic. The Wind detector was even able to detect a weak beam inside the lobe where the density is ≲0.01 cm−3. Some of these observations are new and are not completely explained by current theories.
P‐wave arrival time inversion by using the τ‐p method: Application to the Mt. Vesuvius Volcano, southern Italy
Authors: De Matteis Raffaella , Zollo Aldo , Virieux Jean
Published: February 2004

In this paper we have applied a τ‐p inversion method based on a non linear approach to a set of first P‐arrival times from a 2‐D active seismic experiment performed at Mt. Vesuvius in 1994. The initial seismic investigation is devoted to the study of the shallow structure and the τ‐p method has been used for modelling velocity variations of a spherically concentric medium which is a better approximation than a flat layer of the Vesuvius geometry. We are able to obtain detailed 1‐D velocity models along different specified sections of the recorded seismic, line. These sections span different depth ranges and indicate strong lateral and vertical P‐velocity variations in the first 1 km of the volcano structure with values ranging from about 1.5 km/s at the surface to 3.5–4.0 km/s at depth. The average 1‐D concentric model obtained in this study can be used as a reasonable starting model for iterative high‐resolution tomographies of Vesuvius velocity structures.
Upper mesosphere temperatures in summer: WINDII observations and comparisons
Authors: Shepherd M. G. , Dudhia A. , López‐Puertas M. , Evans W. F. J.
Published: February 2004

Atmospheric temperature measurements from the Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite (UARS), determined from the observed Rayleigh scattering are presented. Infrared radiances predicted from these profiles are compared with measurements from the Improved Stratospheric and Mesospheric Sounder on UARS for nine cases of spatial and temporal coincidence with an effective difference of about 5–10 K in the height range 70–85 km. A comparison with monthly averaged SME results and Rayleigh lidar temperature observations at mid‐latitudes taken 8 years earlier indicated that WINDII temperatures were cooler on average by 10 K; this is consistent with a temperature decrease of 1.5 K/year inferred from the SME and lidar results. At high latitudes the agreement between falling spheres and WINDII was found to be very good.
Sensitivity of a GCM to changes in the droplet effective radius parameterization
Authors: Dandin Philippe , Pontikis Constantin , Hicks Elizabeth
Published: February 2004

The French Community Climate model (ARPEGE‐climat) has been used in relation to four different warm cloud droplet effective radius parameterizations in order to simulate the January and July climatologies. Two of these parameterizations depend upon the cloud character (maritime or continental). The comparison between the results of the different simulations reveals that the model is very sensitive to the effective radius parameterization change. This change induces differences up to 30Wm−2 in the global values of the radiative fluxes at the top of the atmosphere and at the surface level. Important differences are also induced in the zonally averaged short‐wave cloud radiative forcing, cloudiness and precipitation. At smaller scales, non negligible precipitation and surface temperature changes are also observed. The comparison between the simulation results obtained by using model versions containing the above parameterizations reveals that two of them considerably improve the agreement between model and climatological cloudiness, thus allowing a pertinent choice of the most appropriate cloud droplet effective radius parameterization.
Traversal of the nightside magnetosphere at 10 to 15 Re during northward IMF
Authors: Nishida A. , Mukai T. , Yamamoto T. , Saito Y. , Kokubun S. , Lepping R. P.
Published: February 2004

The nightside magnetosphere under the northward IMF condition is not flat at the distance of 10 to 15 Re but reveals a variety of interesting features. The magnetospheric boundary layer consists of the tailward flowing outer layer and the earthward flowing inner layer. In the dawn as well as the dusk flank regions there are large amplitude oscillations with periods of 8 to 15 min which show the character of the slow mode or the mirror mode waves. Moreover, around the midnight meridian the ions and electrons are injected earthward at intervals of 1 to 2 hours. The westward drift of the injected ions produces the energy‐dispersive ion signatures in the dusk region. The electric field Ey is positive on average at this distance while in the distant tail it has been found to be negative on average. These observations of Ey are compatible with the magnetic reconnection in the magnetotail when the twisting of the neutral sheet is taken into account.
Precambrian length of day and the validity of tidal rhythmite paleotidal values
Authors: Williams George E.
Published: February 2004

Paleotidal records obtained from sedimentary tidal rhythmites may be systematically abbreviated and so may give incorrect paleotidal and paleorotational values. The validity of determined values, including past length of day (l.o.d.), can be assessed by testing for internal self‐consistency through application of the laws of celestial mechanics. Three independent values obtained from the ∼620‐Ma Elatina‐Reynella rhythmites in South Australia (14.1 sidereal months/year, 401 sidereal days/year, and 19.5 years for the lunar nodal period), when employed in different equations that make allowance for lunar and solar tidal effects, each give a lunar semimajor axis in the range of 96.5–96.9% of the present figure. Such self‐consistency strongly supports the validity of the derived l.o.d. of 21.9 hours at ∼620 Ma. The validity of the estimated l.o.d. of 20.9 hours at ∼900 Ma (revised value, Big Cottonwood rhythmites, Utah) and of 17.1–18.9 hours at ∼2.5 Ga (Weeli Wolli rhythmites, Western Australia) cannot be assessed in that way because each data set has only one directly determined value. The derived mean rate of lunar retreat of 2.16 cm/year since ∼620 Ma averts a close approach of the Moon at least since 3 Ga and a lower rate of retreat seems likely during the Proterozoic.
Combined effect of geomagnetic field and gravity on the formation of crystals
Authors: Lee M. C. , Lee C. H.
Published: February 2004

It has been observed that, in the 1988 Shuttle Discovery experiments, crystals grew uniformly throughout the solution and also uniformly on a membrane in the experimental chamber. This was very different from those grown in laboratories on Earth, where the crystals grew only on the vertical membrane and then only at the bottom half of the membrane [Scaife et al., 1990]. We propose that the combined effect of gravity (
' and geomagnetic field (
', in the form of
drifts of ions, controls the growth of crystals in aqueous solutions. Based on this theory, the observed distinct difference between space‐grown crystals and those grown in laboratories on Earth can be reasonably explained. We have conducted concept‐proof experiments on crystal growth under gravity and different magnetic fields in the laboratory. Our experimental results have confirmed the
effect, and showed that the uniformity of crystal growth as well as the size and yield of grown crystals can indeed be controlled by the combined effect of gravity and magnetic field. This work is conducive to the understanding of formation of crystals in nature. Moreover, it may be based on to develop a practical technique for industrial growth of crystals.
Earthquake scaling laws for creeping and non‐creeping faults
Authors: Amelung Falk , King Geoffrey
Published: February 2004

The dependence of the summed moment release on the fault dimension differs between non‐creeping faults and creeping faults or volcanic regions. This can be attributed to different earthquake scaling laws. The number N of events with fault length L scales for non‐creeping faults as N(L' ∼ L−2 and for creeping faults as N(L' ∼ L−3. This difference offers a means for mapping the distribution of creep in the seismogenic crust.
³He in Indonesian Seas: Inferences on deep pathways
Authors: Top Z. , Gordon A. , Jean‐Baptiste P. , Fieux M. , Ilahude G. , Muchtar M.
Published: February 2004

Helium isotope measurements from the Indonesian Seas, and from the Java‐Australia Dynamic Experiment cruises define mantle ³He sources and deep water spreading patterns. ³He sources in the Sulawesi Sea and in the Makassar Strait are found, but these are prevented from spreading into the Banda Sea and the Indian Ocean by blocking sills. A major mantle source is identified below 2000m in the Flores Sea. The ³He distribution suggests that the Banda Sea water migrates westward along the floor of the Flores Sea, upwells and then advects the high ³He Flores signal. A tongue of higher‐than‐ambient ³He on the Indian Ocean side of the Flores chain indicates a deep outflow of the Flores and the Banda Sea water into the Indian Ocean near 1300m.
A combined first‐arrival travel time and reflection coherency optimization approach to velocity estimation
Authors: Pullammanappallil Sathish K. , Louie John N.
Published: February 2004

We present a nonlinear optimization method for two‐dimensional velocity estimation in strongly heterogeneous media. We achieve this by designing a simulated‐annealing algorithm to simultaneously maximize reflection coherency as well as minimize first‐arrival travel time residuals. Relatively shallow velocity structure is constrained by first‐arrival times, while coherency information from deeper reflections (if present' helps constrain deeper velocities. Prestack migration using the optimized velocities images reflections with greater continuity, compared with other velocity estimation methods. Using synthetic and real data we demonstrate that migrations through velocities obtained using our coherency criterion reconstruct basin‐boundary structures more accurately than through those obtained using only first‐arrival times. Images from shot gathers collected along COCORP Mojave line 5 across the Garlock fault in Cantil Valley, California show new evidence of links between Garlock fault branches and sub‐horizontal structures in the upper crust. Imaging reflections and estimating velocities using coherency annealing is more effective and less expensive than picking reflection times from shot gathers recorded complex regions.
The elastic constants of a pyrope‐grossular‐almandine garnet to 20 Gpa
Authors: Chai Mu , Brown J. Michael , Slutsky Leon J.
Published: February 2004

Laser‐induced phonon spectroscopy has been applied to the determination of the elastic constants and equation of state at 25°C of a natural garnet of composition Py51.6Al31.7Gr15.8Sp0.9 to a pressure of 20 GPa. Moduli are linear with pressure. The adiabatic bulk modulus in GPa is given by K=170.8 + 4.09 P and the shear modulus is µ=94.7 + 1.76P. The derivative of the shear modulus with respect to temperature at constant density is derived from the temperature and pressure dependencies of the elastic constants. The constant pressure derivatives of the mean longitudinal (Vp' and shear (Vs' velocities are tabulated. At 298K and 1bar (∂1nVp/∂1nρ'p=1.7, (∂1nVs/∂1nρ'p=1.5 and (∂1nVs/∂1nVp'p=0.9. The corresponding values calculated at 1000 K and 20 GPa are 1.6, 1.7 and 1.1.
Energy spectral characteristics of auroral electron microburst precipitation
Authors: Reinard A. A. , Skoug R. M. , Datta S. , Parks G. K.
Published: February 2004

We consider data from a rocket experiment designed to study auroral microburst precipitation. Our rocket instruments had high energy spectral resolution which allowed us to characterize the electron energy spectra. Data from the field aligned electron detector show that the majority of the spectra fit an exponential form in the 45–70 keV energy range. Approximately 15% of the spectra fit a power law form for high energies (70–150 keV' and 45% fit an additional exponential form for low energies (20–45 keV'. The multi‐component spectra appeared during both microburst and non‐burst times. The e‐folding energies for the 45–70 keV energy range increased as the flux increased. Some of these features can be explained by a cyclotron wave‐particle interaction mechanism. We also observed a weak peak in the energy spectrum at about 45 keV, suggesting the existence of field‐aligned potential drops associated with microburst production.
Substorm precipitation in the polar cap and associated Pc 5 modulation
Authors: Weatherwax A. T. , Rosenberg T. J. , Maclennan C. G. , Doolittle J. H.
Published: February 2004

This paper reports substorm‐related cosmic radio noise absorption events observed deep into the polar cap, well poleward of the typical nightside auroral oval. We find that such events usually occur in the late expansion/recovery phase of a substorm during moderate‐to‐strong planetary disturbances (Kp=3–8' and at times of high solar wind speed conditions. We present riometer data from U.S. manned and automatic geophysical observatories in Antarctica to track the morphology and progression of auroral absorption features over 5 hours of local time at ≥80° magnetic latitude. The azimuthal motions observed, westward pre‐midnight, eastward post‐midnight, are similar to the dynamics expected for lower latitude substorm‐related auroral absorption. ULF modulation of the absorption (and hence of the causative fluxes of precipitating energetic electrons' are often observed. These modulations are usually dominated by spectral peaks between 1–4 mHz and, in the one case examined in detail, were confined to a narrow, ∼1° latitude band embedded within more uniform precipitation. Pc 5 (150 to 600 s periods' magnetic variations with similar spectral peaks, and auroral arcs are often observed concurrently. Several mechanisms for producing the particle modulations are examined within the context of these observations.
Energy budget of the Tidal Hydrodynamic Model FES94.1
Authors: Lyard Florent H. , Le Provost Christian
Published: February 2004

This paper presents a detailed energy budget of the M2 tide over the world ocean, based on the hydrodynamic solution FES94.1. The global energy input by the astronomical forcing, deduced from the (2,2) spherical harmonics of the M2 FES94.1 solution, is 2.35 TW. A quarter of this input takes place over the South Atlantic Ocean. This energy is dissipated by bottom friction over the main continental shelves, among which 40% over the North Atlantic Ocean. The Pacific Ocean, the Indian Ocean and the South Atlantic Ocean receive more energy than they dissipate. By contrast the Atlantic Ocean and the Arctic Ocean show a large deficit, compensated by a net influx of energy coming from the other basins. One third of the total M2 energy input by astronomical forcing over the world ocean flows northward through the Equatorial Atlantic. Detailed energy dissipation estimates are computed over the different areas of dissipation and compared to the previous estimates.
A 50–70 year climatic oscillation over the North Pacific and North America
Authors: Minobe Shoshiro
Published: February 2004

The chronology of interdecadal climatic regime shifts is examined, using instrumental data over the North Pacific, North America and the tropical oceans, and reconstructed climate records for North America. In the North Pacific and North America, climatic regime shifts around 1890 and in the 1920s with alternating polarities are detected, whose spatial structure is similar to that of the previously‐known climatic shifts observed in the 1940s and 1970s. Sea‐surface temperatures in the tropical Indian Ocean‐maritime continent region exhibit changes corresponding to these four shifts. Spectra obtained by the Multi‐Taper‐Method suggest that these regime shifts are associated with 50–70 year climate variability over the North Pacific and North America.

The leading mode of the empirical orthogonal functions of the air‐temperature reconstructed from tree‐rings in North America exhibits a spatial distribution that is reminiscent of instrumentally observed air‐temperature differences associated with the regime shifts. The temporal evolution of this mode is characterized by a 50–70 year oscillation in the eighteenth and nineteenth centuries. This result, combined with the results of the analyses of the instrumental data, indicates that the 50–70 year oscillation is prevalent from the eighteenth century to the present in North America.
Frequency‐Shifted Signature of the HF Pump in the Ionospheric Focused Heating Experiment
Authors: Rodriguez Paul , Siefring Carl L. , Bernhardt Paul A. , Haas Daniel G. , Baumback Mark M.
Published: February 2004

Ionospheric heating experiments have begun to examine interactions at altitudes where the heater HF wave frequency matches the local electron plasma frequency. We discuss the frequency‐shifted signature observed by radiowave receivers on a rocket launched into the HF beam and approaching the interaction altitude. The frequency shifts associated with the upgoing (transmitted) and the downgoing (reflected) waves arise from the Doppler effect and changes in the wave vector. The characteristic spectral signature provides a method to locate the reflection altitude accurately. Generally, the ratio of intensities of upgoing and downgoing waves decreases as the reflection altitude is approached.
The Relation Between Geomagnetic Variations and Their Time Derivatives and Implications for Estimation of Induction Risks
Authors: Viljanen Ari
Published: February 2004

By using the IMAGE magnetometer network data, we compare the geomagnetic variation field B and its time derivative dB/dt in and near the auroral region. We show that although the auroral electrojet is the main reason for large B's, it cannot alone produce large dB/dt's, so smaller‐scale current systems are important. This is evidenced by the horizontal field: the geographic north component (X) is clearly larger than the eastward one (Y) in the auroral region, but dX/dt and dY/dt are nearly equal. This result is important when geomagnetic induction risks on man‐made conductors are estimated. The key quantity is the horizontal geoelectric field, and contrary to what is often assumed, it can have large values in any direction, not just parallel to the electrojet.
T‐Matrix computations of zenith‐enhanced lidar backscatter from horizontally oriented ice plates
Authors: Mishchenko M. I. , Wielaard D. J. , Carlson B. E.
Published: February 2004

Zenith‐enhanced backscattering (ZEB) of a lidar beam by cirrus clouds is a remarkable phenomenon usually explained in terms of specular reflection from large plane facets of horizontally oriented ice plates. Since the standard geometric optics approximation (GO) may be inapplicable in many cases, especially in analyzing infrared measurements, and ignores physical optics effects, we use the recently improved exact T‐matrix method to compute the scattering of light by ice plates at visible and infrared wavelengths. Computations for horizontally and randomly oriented thin disks and oblate spheroids with size parameters up to 50 show that while all particles produce a strong Fraunhofer diffraction peak centered at exactly the forward‐scattering direction, a strong and narrow ZEB peak can be produced only by horizontally oriented disks but not by horizontally oriented spheroids or particles in random orientation. This finding demonstrates that ZEB can be produced even by particles which are not in the GO domain of size parameters and supports the traditional interpretation of ZEB. Also, we have found that the angular width of the ZEB peak for horizontally oriented disks is equal to half the width of the Fraunhofer diffraction peak. This result can be used in practice to derive a lower estimate of ice particle sizes from high angular resolution measurements of ZEB. We show that our exact T‐matrix computations can explain the peculiar zenith‐angle dependence of depolarization observed by Platt et al. [1978] in the visible and can be interpreted qualitatively in terms of the modified Kirchhoff approximation.
The Seasonal and Long Term Changes in Mesospheric Water Vapor
Authors: Chandra S. , Jackman C. H. , Fleming E. L. , Russell J. M.
Published: February 2004

This study explores the feasibility of identifying long term changes in mesospheric water vapor as a result of increasing level of methane in the atmosphere and the solar cycle variation of Lyman α. The study is based on recent measurements of water vapor in the mesosphere and the solar Lyman α flux from the UARS (Upper Atmosphere Research Satellite) HALOE (Halogen Occultation Experiment) and the SOLSTICE (Solar Stellar Iradiance Comparison Experiment) instruments during the declining phase of the solar cycle 22. The solar activity during this period decreased from a near maximum to a near minimum level. The analysis of these data sets, in conjunction with the NASA/GSFC two dimensional chemistry and transport model suggests that on a seasonal time scale, the temporal changes in mesospheric water vapor are largely controlled by the vertical advection associated with the meridional circulation. On the time scale of a solar cycle, H2O may vary by about 30–40 % near the mesopause height (∼80 km) to about 1–2% in the lower mesosphere (60–65 km) caused by the solar cycle modulation of Lyman α. In comparison, the secular increase in H2O related to methane increase in the atmosphere is about 0.4% /year at all heights in the mesosphere.