bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of coatings and fills on flow in fractured, unsaturated tuff porous media systems
Authors: Soll Wendy , Birdsell Kay
Published: February 2004

A numerical study of a single fracture embedded in a porous matrix was performed to investigate the role of fracture coatings and fills on water movement in permeable, fractured porous media. The variables considered were conductivity and continuity of fracture coatings; location, length, and conductivity of fracture fills; combinations of fills and coatings; initial matrix saturation; and inflow boundary conditions. Results from the simulations indicate that in low‐saturation, high‐capillarity tuff systems, the conditions under which fractures act as rapid flow paths are limited. These conditions include a continuous coating with conductivity several orders of magnitude lower than that of the neighboring matrix, and large inflow rates. However, as initial matrix saturation increases, the amount of fracture flow also increases. Discontinuities in coatings substantially reduce their effectiveness in preventing matrix imbibition. The presence of any coating, however, does produce increased infiltration depths. Fills appear to be effective barriers to fracture flow.
Effects of grain‐scale mass transfer on the transport of volatile organics through sediments: 2. Column results
Authors: Werth Charles J. , Cunningham Jeffrey A. , Roberts Paul V. , Reinhard Martin
Published: February 2004

Trichloroethylene (TCE) elution profiles for purged and unswept columns are presented and simulated with the Distributed Dual Diffusion Model (DDDM) presented in the first of this two‐paper series. Elution profiles were measured at 15, 22, 30, and/or 60°C for a silica gel, a Livermore sand fraction, a Livermore clay and silt fraction, a Santa Clara sediment, and/or a Norwood soil, all at 100% relative humidity. Advection and dispersion control TCE transport through the vapor phase of purged columns. Diffusion controls TCE transport through the vapor phase of unswept columns. For both purged and unswept columns a fast and a slow desorbing fraction of TCE were observed. The DDDM effectively simulated both of these fractions. For the fast fraction the DDDM predicted desorption with no fitting parameters. For the slow fraction the DDDM was not predictive but it simulated desorption using either a single (for silica gel) or a gamma distribution (for soil and sediments) of micropore diffusion rate constant(s) and a micropore capacity factor. Micropore capacity factors obtained by fitting the DDDM to purged column results were used to predict the onset of slow desorption in unswept columns of the same solid.
Evaporation of pendant water droplets in fractures
Authors: Ho Clifford K.
Published: February 2004

This paper investigates the evaporation of pendant water droplets in fractured tuffaceous rock. The droplets are assumed to exist near asperities and cavities as a result of gravity‐dominated flow through fractures. Because of the curvature of the droplet, the vapor pressure near the liquid‐vapor interface is greater than the saturated vapor pressure of water held in the matrix at the system temperature. Expressions for the vapor pressure and evaporation rate of water droplets are developed as a function of droplet radius and relative humidity of the surroundings. The relative humidity is calculated using Kelvin's equation to account for vapor pressure lowering in the surrounding tuffaceous rock. Results indicate that the vapor pressure of water droplets is not significantly increased above the saturated vapor pressure of freestanding water when the droplet size is greater than 100μm. However, if the relative humidity of the surroundings is exactly equal to 1 or if the droplet radius is very small (≪1μm), the effects of interface curvature will enhance the evaporation of water droplets. Finally, expressions are developed to determine the minimum liquid flux required to propagate flow through either a single fracture or a network of fractures without being evaporated.
A small perturbations solution for nonequilibrium chemical transport through soils with relatively high desorption rate
Authors: Wallach Rony
Published: February 2004

An analytical solution is presented for reactive solute transport or nonuniform flow when the reaction rate or the diffusive transfer rate to stagnant water is small compared to the flow velocity or large compared to the contact time. For these cases many transport models assume local chemical or physical equilibrium for conceptual and mathematical simplification. In this paper the commonly used nonequilibrium formulation for one‐dimensional, steady‐flow transport was used as the starting point. Dimensionless variables were defined and substituted into the mass balance equations forming dimensionless equations and boundary and initial conditions. There are two characteristic timescales associated with the two rate‐limited processes: The fast characteristic timescale is related to the chemical desorption and the slow timescale is related to the convective‐dispersive transport. By scaling the first‐order rate equation that accounts for linear sorption kinetics (or the dissolved chemical exchange between mobile and stagnant porosities in structured soils), a singular perturbations problem was obtained in which a small parameter, ϵ, multiplies the time derivative. This small parameter is the ratio between the slow and fast timescales. Inner, т=O(ϵ), and outer,т=O(1), solutions were developed, and the method of matched asymptotic expansion was used to form a uniform solution over the entire time domain. The leading‐order approximation, obtained for ϵ → 0 and valid for т=O(1), yields equations that are usually obtained by the local equilibrium assumption (LEA). A initial layer, т=O (ϵ), near t=0 is formed within which the initial concentrations equilibrate. The condition under which the local equilibrium assumption is valid, ϵ=ν2/krD ≪ 1, which depends on the system parameters such as flow velocity, dispersion coefficient, and the variables. This condition was also obtained in other studies by solving the problem in either kinetic or LEA form and comparing the solutions to determine under what conditions the local equilibrium approximation is close to the kinetic solution. As ϵ decreases, the LEA is valid, and the initial layer, in which the initial concentrations reach local equilibrium, is shorter.
Multiphase flow in heterogeneous porous media from a stochastic differential geometry viewpoint
Authors: Christakos George , Hristopulos Dionissios T. , Li Xinyang
Published: February 2004

Multiphase flow of immiscible fluids is studied by means of a stochastic flow path approach. This approach is based on a differential geometric formulation that replaces the partial differential equations (PDEs) of flow by a set of ordinary differential equations (ODEs) that determine the flow paths and impose conservation of flux. It is shown that flux conservation along the flow paths involves a space transform. Other formulations of the multiphase flow equations involve Jacobian mappings. Flow realizations as well as statistical flow moments can be derived by means of the stochastic flow path method. Advantages of the stochastic flow path method include: reduction of a PDE to an ODE system, independence from perturbation approximations and Green's functions, and the freedom to use random initial conditions at the boundary. Using the stochastic flow path method, closed‐form expressions are obtained for two‐phase flow in uniaxially heterogeneous media. Two‐phase flow in a heterogeneous two‐dimensional medium is also investigated using numerical simulations.
Simulation of variable‐density flow and transport of reactive and nonreactive solutes during a tracer test at Cape Cod, Massachusetts
Authors: Zhang Hubao , Schwartz Frank W. , Wood Warren W. , Garabedian S. P. , LeBlanc D. R.
Published: February 2004

A multispecies numerical code was developed to simulate flow and mass transport with kinetic adsorption in variable‐density flow systems. The two‐dimensional code simulated the transport of bromide (Br−), a nonreactive tracer, and lithium (Li+), a reactive tracer, in a large‐scale tracer test performed in a sand‐and‐gravel aquifer at Cape Cod, Massachusetts. A two‐fraction kinetic adsorption model was implemented to simulate the interaction of Li+ with the aquifer solids. Initial estimates for some of the transport parameters were obtained from a nonlinear least squares curve‐fitting procedure, where the breakthrough curves from column experiments were matched with one‐dimensional theoretical models. The numerical code successfully simulated the basic characteristics of the two plumes in the tracer test. At early times the centers of mass of Br− and Li+ sank because the two plumes were closely coupled to the density‐driven velocity field. At later times the rate of downward movement in the Br− plume due to gravity slowed significantly because of dilution by dispersion. The downward movement of the Li+ plume was negligible because the two plumes moved in locally different velocity regimes, where Li+ transport was retarded relative to Br−. The maximum extent of downward transport of the Li+ plume was less than that of the Br− plume. This study also found that at early times the downward movement of a plume created by a three‐dimensional source could be much more extensive than the case with a two‐dimensional source having the same cross‐sectional area. The observed shape of the Br− plume at Cape Cod was simulated by adding two layers with different hydraulic conductivities at shallow depth across the region. The large dispersion and asymmetrical shape of the Li+ plume were simulated by including kinetic adsorption‐desorption reactions.
Vertical leakage and vertically averaged vertical conductance for Karst Lakes in Florida
Authors: Motz L. H.
Published: February 2004

In the karst lake district in peninsular Florida in the southeastern United States, as many as 70% of the lakes lack surface outlets, and groundwater outflow is an important part of the water budgets of these lakes. For 11 karst lakes in the Central Lake District, vertical leakage from the lakes to the upper Floridan aquifer averages 0.12 to 4.27 m yr−1. The vertically averaged vertical conductance Kv/b, a coefficient that represents the average of the vertical conductances of the hydrogeologic units between the bottom of a lake and the top of the upper Floridan aquifer, was determined to range from 0.0394 to 1.00 yr−1 for these lakes. For six of the lakes, various hydraulic parameters previously calculated by other investigators are shown to be equivalent to the Kv/b values calculated in this study. If Kv/b is determined for a lake, then vertical leakage can be estimated for other conditions of lake stage and hydraulic head in the upper Floridan aquifer, using Kv/b for the lake and Darcy's equation written for vertical flow. The methodology described in this paper for quantifying Kv/b, which requires only limited data (i.e., vertical leakage, lake stage, and hydraulic head in the upper Floridan aquifer), could be used to investigate the apparent association between relatively large Kv/b values and lake level instabilities at some lakes in the Central Lake District and similar hydrogeologic settings. This methodology for calculating vertical leakage is applicable to the Central Lake District in Florida and to other similar lake and groundwater systems.
Effective parameters in heterogeneous and homogeneous transport models with kinetic sorption
Authors: Reichle R. , Kinzelbach W. , Kinzelbach H.
Published: February 2004

Transport of dissolved tracers undergoing kinetic sorption in saturated porous media is described on the basis of a dual‐porosity model with heterogeneous and cross‐correlated sorption parameters, i.e., distribution coefficient and exchange rate. The approach is a conceptual model for reactive transport in a medium with spatially varying reaction capacity, given by the distribution coefficient, and spatially varying accessibility, given by the exchange rate. We treat the sorption parameters as a stochastic process and apply a perturbation approach. From the ensemble‐averaged spatial moments of a plume, we analytically derive formal expressions for time‐dependent effective transport parameters. For vanishing microdispersion the calculations are carried out up to second order for the effective transport velocity ueff(t) and the effective dispersion coefficient Deff(t). For large times the effective retardation is determined by the ensemble‐averaged distribution coefficient, whereas the effective dispersion is related to the sorption parameters in a more complicated way depending on the variability of the exchange rate and of the distribution coefficient. Effective sorption parameters are given. For comparison we derive exact expressions for ueff(t) and Deff(t) in a homogeneous triple‐porosity model. Unlike the simpler homogeneous dual‐porosity model, the triple‐porosity model yields a satisfactory description of the time‐dependent dispersion of the heterogeneous model. The appropriate sorption parameters for the triple‐porosity model are given as functions of the stochastic parameters.
Nonstationary stochastic analysis of steady state flow through variably saturated, heterogeneous media
Authors: Zhang Dongxiao , Winter C. L.
Published: February 2004

In this study we develop a first‐order, nonstationary stochastic model for steady state, unsaturated flow in randomly heterogeneous media. The model is applicable to the entire domain of a bounded vadose zone, unlike most of the existing stochastic models. Because of its nonstationarity, we solve it by the numerical technique of finite differences, which renders the flexibility in handling different boundary conditions, input covariance structures, and soil constitutive relationships. We illustrate the model results in one and two dimensions for soils described by the Brooks‐Corey constitutive model. It is found that the flow quantities such as suction head, effective water content, unsaturated hydraulic conductivity, and velocity are nonstationary near the water table and approach stationarity as the vertical distance from the water table increases. The stationary limits and the critical vertical distance at which stationarity is attained depend on soil types and recharge rates. The smaller the recharge rate is, the larger the critical distance; and the coarser the soil texture is, the smaller the distance. One important implication of this is that the existing simpler, gravity‐dominated flow models may provide good approximations for flow in vadose zones of large thickness and/or coarse‐textured soils although they may not be valid for vadose zones of fine‐textured soils with a shallow water table. It is also found that the vertical extent of a domain where nonstationarity is important may be estimated by solving the one‐dimensional Richards equation for mean head with average soil properties and appropriate boundary conditions. On the basis of the mean head, one may then determine whether the full, nonstationary model must be solved or whether a simpler, gavity‐dominated model will suffice. The flow quantities are also nonstationary in the horizontal direction near the lateral boundaries, as found for flow in saturated zones.
The δ13C anomaly in the northeastern Atlantic
Authors: Keir Robin , Rehder Gregor , Suess Erwin , Erlenkeuser Helmut
Published: February 2004

The δ13C of dissolved inorganic carbon was measured on samples collected at 49°N in the northeast Atlantic in January 1994. Deeper than 2000 m, δ13C exhibits the same negative correlation versus dissolved phosphate that is observed elsewhere in the deep Atlantic. Upward from 2000 m to about 600 m, δ13C shifts to values more negative than expected from the correlation with nutrients at depth, which is likely due to penetration of anthropogenic CO2. From these data, the profile of the anthropogenic δ13C decrease is calculated by using either dissolved phosphate or apparent oxygen utilization as a proxy for the preanthropogenic δ13C distribution. The shape of the anthropogenic anomaly profile derived from phosphate is similar to that of the increase in dissolved inorganic carbon derived by others in the same area. The reconstruction from oxygen utilization results in a lower estimate of the anthropogenic δ13C decrease in the upper water column, and the vertical anomaly profile is less similar to that of the dissolved inorganic carbon increase. A 13C budget for the atmosphere, ocean, and terrestrial biosphere indicates that within the range of probable ocean CO2 uptake the ratio of δ13C to inorganic carbon change should be mostly influenced by the 13C inventory change of the biosphere. However, the uncertainty in the ratio we derive prevents a strong contraint on the size of the exchangeable biosphere.
Interannual variability in soil trace gas(CO2, N2O, NO) fluxes and analysis of controllers on regional to global scales
Authors: Potter Christopher S. , Klooster Steven A.
Published: February 2004

Interannual variability in flux rates of biogenic trace gases must be quantified in order to understand the differences between short‐term trends and actual long‐term change in biosphere‐atmosphere interactions. We simulated interannual patterns (1983–1988) of global trace gas fluxes from soils using the NASA Ames Research Center version of the Carnegie‐Ames‐Stanford Approach (CASA) model in a transient simulation mode. This ecosystem model has been calibrated for simulations driven by satellite vegetation index data from the National Oceanic and Atmospheric Administration's Advanced Very High Resolution Radiometer over the mid‐1980s. The predicted interannual pattern of soil heterotropic CO2 emissions indicates that relatively large increases in global carbon flux from soils occurred about 3 years following the strong El Nino‐ Southern Oscillation event of 1983. Results for the years 1986 and 1987 showed an annual increment of +1 Pg (1015 g) C‐CO2 emitted from soils, which tended to dampen the estimated global increase in net ecosystem production with about a 2‐year lag period relative to plant carbon fixation. Zonal discrimination of model results implies that 80–90% of the yearly positive increments in soil CO2 emission during 1986–1987 were attributable to soil organic matter decomposition in the low latitudes (between 30°N and 30°S). Soils of the northern middle‐latitude zone (between 30° and 60°N) accounted for the residual of these annual increments. Total annual emissions of nitrogen trace gases (N2O and NO) from soils were estimated to vary from 2 to 4% over the time period modeled, a level of variability that is consistent with predicted interannual fluctuations in global soil CO2 fluxes. Interannual variability of precipitation in tropical and subtropical zones (30°N to 20°S) appeared to drive the dynamic inverse relationship between higher annual emissions of NO versus emissions of N2O. Global mean emission rates from natural (heterotrophic) soil sources over the period modeled (1983–1988) were estimated at 57.1 Pg C‐CO2 yr−1, 9.8 Tg (1012 g) N‐NO yr−1, and 9.7 Tg N‐N2O yr−1. Chemical fertilizer contributions to global soil N gas fluxes were estimated at between 1.3 to 7.3 Tg N‐NO yr−1 and 1.2 to 4.0 Tg N‐N2O yr−1.
The WIND‐HAARP Experiment: Initial results of high power radiowave interactions with space plasmas
Authors: Rodriguez P. , Kennedy E. J. , Keskinen M. J. , Siefring C. L. , Basu Sa. , McCarrick M. , Preston J. , Engebretson M. , Kaiser M. L. , Desch M. D. , Goetz K. , Bougeret J.‐L. , Manning R.
Published: February 2004

Results from the first science experiment with the new HF Active Auroral Research Program (HAARP) in Alaska are reported. The objective was to study the effects of space plasmas on high power radiowave transmission to high altitudes in the magnetosphere. Reception was done by the NASA/WIND satellite. The data suggest that structured space plasmas along the propagation path impose a power law spectrum of fluctuations on the transmitted waves, resembling scintillations. Because the transmitted waves are near ionospheric plasma frequencies, other types of wave‐plasma interactions may occur. Such measurements can provide a new diagnostic tool.
Measurements of bromine containing organic compounds at the tropical tropopause
Authors: Schauffler S. M. , Atlas E. L. , Flocke F. , Lueb R. A. , Stroud V. , Travnicek W.
Published: February 2004

The amount of bromine entering the stratosphere from organic source gases is a primary factor involved in determining the magnitude of bromine catalyzed loss of ozone. Thirty two whole air samples were collected at the tropical tropopause during the NASA STRAT Campaign in Feb., Aug., and Dec., 1996 and were analyzed for brominated organic compounds. Total organic bromine was 17.4±0.9 ppt with 55% from methyl bromide, 38% from the Halons, 6% from dibromomethane, and 0.8% from bromochloromethane and dichlorobromomethane. One flight showed the presence of 0.42 ppt of additional organic bromine from bromoform and dibromochloromethane.
Dynamical influences on atomic oxygen and 5577 Å emission rates in the lower thermosphere
Authors: Angelats i Coll M. , Forbes J. M.
Published: February 2004

Effects of the mean meridional circulation, diurnal and semidiurnal tides, and eddy and molecular diffusion on O concentrations and 5577 Å emission rates are examined. Vertical winds play an important role in producing variations in these quantites, and accounting for the equatorial emission rate structures inferred from the WINDII experiment on UARS. Smaller secondary effects are produced by tidal variations in the major species concentrations and in temperature‐dependent chemical reaction rates.
Modeling and predicting sunspot activity‐state space reconstruction + artificial neural network methods
Authors: Kulkarni D. R. , Pandya A. S. , Parikh J. C.
Published: February 2004

Ideas of state space reconstruction of dynamics are combined with nonparametric artificial neural network approach to model sunspot activity. The structural aspects of the model are for the most part determined from the sunspot data. The model gives a very good fit to the data. Further it predicts weaker solar activity in the current (23‐rd) cycle, with a maximum of 144±36.
Meteor trail induced backscatter in MST radar echoes
Authors: Reddi C. Raghava , Nair S. Muraleedharan
Published: February 2004

The amplitude variations and Doppler spectra of the 50 MHz radar echoes from meteor trails are investigated. The radar echoes from underdense meteor trails particulary during nighttime do not always fit the conventional specular reflection model. The echo was found to spread, sometimes, over as large as 8–10 km in range. In each range bin, the spread echo from the trail is produced with an altitude dependent time delay after the passage of the meteoroid producing the ionized trail. The Doppler spectra of the spread echo in each range bin is asymmetric with a high frequency wing comprised of narrow spectral peaks and successive spectral peaks amplitude decrease with frequency. These observations are interpreted as due to multiple reflections of the radar pulse between the striations generated parallel to the geomagnetic field along the length of the meteor trail. There is evidence to show that within the dynamo region the EW and NS components of the currents at lower and higher altitudes could be in opposite directions during the early morning hours of Sq electric field reversal.
Observed episodic warming at 86 and 100 km between 1990 and 1997: Effects of Mount Pinatubo Eruption
Authors: She C. Y. , Thiel Steven W. , Krueger David A.
Published: February 2004

Along with initial observations, our regular lidar temperature measurements over Fort Collins, CO (41°N, 105°W) in the rarely probed mesopause region has resulted in a unique seven‐year data set between 1990 and 1997. After the seasonal variations are removed, a clear episodic warming is observable in the time series of residual temperatures. Least squares fitting the residual temperatures to an episodic impact function plus a linear trend shows maximum temperature increases occurring in 1993 with magnitudes of 9.0±1.7 K and 12.9±1.8 K, at 86 km and 100 km, respectively. By association, we attribute the Mount Pinatubo eruption in June, 1991, as the most probable primary cause for the observed warming, supporting a connection between tropical stratospheric aerosol and temperatures in a midlatitude mesopause region. It is hoped that our lidar observation from a single location will stimulate similar investigations at other latitudes and longitudes.
A space geodetic target for mantle viscosity discrimination: Horizontal motions induced by glacial isostatic adjustment
Authors: Peltier W. R.
Published: February 2004

A model of mantle viscosity recently obtained on the basis of the inversion of glacial isostatic adjustment data is herein shown to predict a highly characteristic signature in tangential motion due to this cause.
Correlative stratospheric ozone measurements with the airborne UV DIAL system during TOTE/VOTE
Authors: Grant William B. , Fenn Marta A. , Browell Edward V. , McGee Thomas J. , Singh Upendra N. , Gross Michael R. , McDermid I. Stuart , Froidevaux Lucien , Wang Pi‐Huang
Published: February 2004

The airborne UV differential absorption lidar (DIAL) system participated in the Tropical Ozone Transport Experiment/Vortex Ozone Transport Experiment (TOTE/VOTE) in late 1995/early 1996. This mission afforded the opportunity to compare the DIAL system's stratospheric ozone measuring capability with other remote‐sensing instruments through correlative measurements over a latitude range from the tropics to the Arctic. These instruments included ground‐based DIAL and space‐based stratospheric instruments: HALOE; MLS; and SAGE II. The ozone profiles generally agreed within random error estimates for the various instruments in the middle of the profiles in the tropics, but regions of significant systematic differences, especially near or below the tropopause or at the higher altitudes were also found. The comparisons strongly suggest that the airborne UV DIAL system can play a valuable role as a mobile lower‐stratospheric ozone validation instrument.
CIRRIS‐1A limb spectral measurements of mesospheric 9.6‐µm airglow and ozone
Authors: Zhou D. K. , Mlynczak M. G. , Bingham G. E. , Wise J. O. , Nadile R. M.
Published: February 2004

Limb infrared spectral measurements of the 9.6‐µm mesospheric ozone airglow were made by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS‐1A) during one flight of the space shuttle Discovery (April 28th to May 6th 1991). A significant difference between ozone nightglow and dayglow is observed. The measured spectrally integrated ozone ν3 fundamental band radiance profile is used to retrieve the ozone (ν3 = 1) excited state density. Modeled ozone (ν3 = 1) vibrational temperatures are used to infer the total ozone density. Night and day ozone abundance profiles inferred from ozone 9.6‐µm infrared spectral emissions and comparisons with photochemical model calculations are reported. The observed ozone abundance is significantly larger than predicted by the photochemical model.
Tidal instability as the source for Io's magnetic signature
Authors: Kerswell Richard R. , Malkus Willem V. R.
Published: February 2004

Recent observations from the Galileo spacecraft suggest that Io, the innermost of Jupiter's satellites, has a magnetic signature. Remanent magnetization appears inadequate to explain this signal and, given the huge tidal heating of Io's mantle, a convectively‐stirred molten core seems unlikely. Instead, we propose that Io's magnetic field may be a direct consequence of hydromagnetic instabilities driven in its molten core by Jupiter's tides. Laboratory realisations of such ‘tidal' instabilities confirm their potency as a means for extreme ‘stirring’ and dissipation. The energy to sustain Io's magnetic field would then come ultimately from Jupiter's rotational energy rather than an internal source as currently favoured in the Earth's case.
Long‐term climato‐limnological oscillation during the past 2.5 million years printed in Lake Baikal sediments
Authors: Kashiwaya Kenji , Ryugo Masayuki , Sakai Hideo , Kawai Takayoshi
Published: February 2004

The physical properties of long sediment cores (BDP96) obtained from the Academician Ridge of Lake Baikal, eastern Siberia, show that the changes in the climato‐limnological environment of the continental interior during the past 2.5 m.y. clearly reflected global climatic change. Oscillation in water content and grain size, which are closely related to biogenic productivity, coincides with marine δ 18O variation. The values for water content and grain size are large during interglacial periods and small during glacial periods. Milankovitch parameters were also imprinted in the sediments over the past 2.5 m.y.: a 400‐ky period as well as a 100‐ky period due to eccentricitical parameters is found in addition to other orbital parameter (a 40‐ky period of obliquitical and a 20‐ky period of precessional parameter). This indicates that change in solar insolation was closely related to long term variations in climato‐limnological regime in this area.
Recent increase in the length of the melt season of perennial Arctic sea ice
Authors: Smith Douglas M.
Published: February 2004

General circulation models predict that greenhouse gas induced global warming will be amplified in the Arctic as a result of temperature‐albedo feedback. Whilst recent observations of decreasing Arctic sea ice extent are consistent with this scenario, the possibility that such a trend is attributable to local effects at the ice margins rather than to atmospheric warming cannot be dismissed. In the absence of direct air temperature measurements, warming over Arctic sea ice may be inferred from an increasing duration of the summer melt season. Analysis presented here of the dates of spring melt and autumn freeze‐up observed over a large fraction of perennial Arctic sea ice using passive microwave data from the SMMR and SSM/I from 1979 to 1996 reveals an increase of 5.3 days (8%) per decade in the number of melt days per summer.
Generation of nonthermal electron distributions by turbulent waves near the Sun
Authors: Roberts D. Aaron , Miller James A.
Published: February 2004

We present a model for the generation of the nonthermal electron distributions observed in interplanetary space and required in some solar wind acceleration and coronal heating theories. The particles are accelerated by fast mode waves generated by an unspecified mechanism (perhaps reconnection associated with microflares) in the upper chromosphere or lower transition region. The waves interact and cascade to higher wavenumbers where they eventually energize electrons out of an initially Maxwellian distribution. Coulomb collisions limit the number that are accelerated. As the electrons are driven to higher energy they more readily escape from the acceleration site. Escape limits the efficiency of the acceleration at high energies. The distributions do not extend into the ultrarelativistic regime like those generated under solar flare conditions, but do have significant nonthermal tails.
Cerenkov emissions of ion acoustic‐like waves generated by electron beams emitted during TSS 1R
Authors: Huang C. Y. , Burke W. J. , Hardy D. A. , Gough M. P. , Olson D. G. , Gentile L. C. , Gilchrist B. E. , Bonifazi C. , Raitt W. J. , Thompson D. C.
Published: February 2004

During the Tethered Satellite System reflight the Spacecraft Particle Correlation Experiment detected fluxes of energetic electrons and ions that were simultaneously modulated at low frequencies during firings of both the fast pulsed electron gun (FPEG) and the electron generator assembly (EGA). The modulations have been interpreted as signatures of large‐amplitude, ion acoustic‐like waves excited in Cerenkov interactions between electron beams and ambient plasmas as the shuttle moved at supersonic speeds across the ionospheric magnetic field. We present examples of particle modulations observed during steady beam emissions. Measurements show that (1) most electron modulations were at frequencies of several hundred Hertz and (2) ions modulated at similar frequencies appeared at spectral energy peaks during shuttle negative charging events. Detection of modulated ion fluxes confirms the Cerenkov emission hypothesis. Observed frequency variations indicate that the EGA beam underwent more spatial spreading than the FPEG beam.
Reflected solar wind ions and downward accelerated ionospheric ions during the January 1997 magnetic cloud event
Authors: Dempsey D. L. , Burch J. L. , Huddleston M. M. , Pollock C. J. , Waite J. H. , Wüest M. , Moore T. E. , Shelley E. G.
Published: February 2004

On January 11, 1997, at 03:40:00 UT, while Polar was traveling up the dusk flank toward apogee, two ion instruments, TIDE and TIMAS, detected upflowing H+ with an energy/pitch‐angle dispersion resembling an ionospheric reflection of freshly injected solar wind ions. In the same region of space, TIDE and TIMAS observed cold beams of O+ and H+ traveling down the field line with equal bulk velocities. We interpret these ion signatures as concurrent observations of mirrored solar wind ions and downward accelerated ionospheric ions. By 03:42:00, an energy/pitch‐angle dispersion of downward moving ions at very low energies was clearly evident in the TIDE data. This additional signature is interpreted as an indication of reconnection on the same field line in the southern hemisphere. We explain this unique combination of plasma distributions in terms of high‐latitude reconnection and magnetic field line convection during northward‐IMF conditions associated with the January 1997 magnetic cloud event.
Electric field measurements of directly converted lower hybrid waves at a density striation
Authors: Rosenberg S. , Gekelman W.
Published: February 2004

Previous experiments at the Large Plasma Device (LAPD) at UCLA provide evidence that whistler waves incident on a field‐aligned density striation will produce lower hybrid waves via a linear mode‐coupling mechanism [Bamber, et. al, 1994; Bamber, et. al, 1995]. These experiments were limited in that only the magnetic fields of the waves were measured. Recent experiments at the LAPD directly measure the whistler and lower hybrid wave electric fields. The lower hybrid wave electric field amplitude is 0.8 times the incident electric field. These measurements are well within theory and allow us to make some estimates about the conversion efficiency of the linear conversion mechanism.
Fluctuations in tides and geomagnetic variations
Authors: Kohsiek A. , Kiefer M. , Meek C. E. , Manson A. H.
Published: February 2004

Middle atmosphere tidal winds and the daily geomagnetic Sq‐variation show a day‐to‐day variability, both with a local behaviour. Due to the main cause of the Sq‐variation, the ionospheric dynamo effect, day‐to‐day fluctuation of Sq could be raised by fluctuations in tides. This coupling of fluctuations is investigated with radar wind data measured at Saskatoon at around 100 km height and with magnetic data from four observatories in the vicinity of the radar. We show that our definition of fluctuations exhibits properties of atmospheric tides in the winds and that the magnetic data can be assumed to represent a local behaviour. We find that there are some significant correlations between fluctuations in winds and magnetic variations. Apparently the local fluctuation of geomagnetic variations is weakly coupled not only to the fluctuations of the semidiurnal tides but also to those of the mean winds.
The aurora during the passage of the May 27, 1996 magnetic cloud
Authors: Frey H. U. , Mende S. B. , Vo H. B. , Doolittle J. H. , Weatherwax A. T. , Rosenberg T. J.
Published: February 2004

On May 27, 1996 two all‐sky cameras in Antarctica observed the aurora during the passage of a magnetic cloud. Compression of the magnetosphere by the solar wind dynamic pressure pulse in front of the magnetic cloud caused a short, strong, and localized blue auroral emission which moved towards noon in the late morning sector. The emission was caused by electrons of 8 keV energy. The high dynamic pressure caused a diffuse large‐scale (at least 3 h MLT and 5° latitude) blue emission on closed field lines. The high energy electron precipitation disappeared after the enhanced solar wind dynamic pressure region had passed the sub‐solar magnetopause.
Solar energetic particles inside magnetic clouds observed with the Wind spacecraft
Authors: Mazur J. E. , Mason G. M. , Dwyer J. R. , von Rosenvinge T. T.
Published: February 2004

Solar energetic particles can be used to probe the structure of magnetic clouds. Since impulsive flare particles are accelerated within active regions, their presence inside a magnetic cloud implies that the cloud's magnetic field connects to an active region at the sun. We report on the fluxes and composition of low energy ions inside 13 magnetic clouds observed with instrumentation on the Wind spacecraft from November 1994 to February 1997. The STEP subsystem of the EPACT experiment on Wind resolves ³He and 4He and the most abundant heavy ion species from ∼20 keV/nucleon to ∼1 MeV/nucleon. Using STEP, we are able to measure the energetic particle composition in an energy range previously unexplored in the context of magnetic clouds. We find that when STEP measured significant ion fluxes inside a cloud, they were most likely from impulsive solar flares; this was the case in 4 events. We find that the 1/10/97 magnetic cloud decreased the interplanetary fluxes of ∼100 keV/nucleon ions by a factor of ∼10²; this was probably because the cloud disconnected Wind from the interplanetary particle source beyond 1 AU. In contrast, we observed particles from several impulsive solar flares inside the 10/18/95 event with fluxes ∼10³ higher than the fluxes measured inside the 1/10/97 cloud.
Neural network models predicting the magnetospheric response to the 1997 January Halo‐CME event
Authors: Wu J.‐G. , Lundstedt H. , Wintoft P. , Detman T. R.
Published: February 2004

A magnetic cloud associated with the 1997 January 6 halo coronal mass ejection (CME) impacted the magnetosphere on January 10. With the WIND solar wind observations we make predictions 1–3 hours ahead of the magnetospheric response (Dst) to the halo‐CME event. The recently developed neural network models with different solar wind input parameters are applied in this study. A major geomagnetic storm triggered by the cloud is accurately predicted by the models with inputs: (a) P1/2, V Bz, (b) B, N, V, Bs, and (c) B, By, Bz, N, V. Further, the three models can predict the effect of the density enhancement at the rear of the cloud which might be associated with the disappearing filament observed on January 6, 1997.
Stimulated emissions around second harmonic of Tromsø heater frequency observed by long‐distance diagnostic HF tools
Authors: Blagoveshchenskaya N. F. , Kornienko V. A. , Rietveld M. T. , Thidé B. , Brekke A. , Moskvin I. V. , Nozdrachev S.
Published: February 2004

Observations of stimulated electromagnetic emission (SEE) around the second harmonic of Tromsø heater frequency carried out by long‐distance diagnostic HF tools are presented. Diagnostic tools are located at a distance of 1200 km from the Tromsø HF heater. Observed SEE spectra show: (1) spectral broadening up to 30 kHz; (2) frequency shift of the maximum amplitude in the SEE spectra from the heater second harmonic frequency 8080 kHz by 16–20 kHz; (3) dependence of the maximum amplitude on the heater power level. The detected features in the SEE spectra have not been observed before in ionospheric heating experiments and may be the second harmonic of the downshifted maximum. The strongest candidate is the coalescense (head‐on collisions) of Langmuir waves produced in the heated volume.
The magnetospheric response to the CME passage of January 10–11, 1997, as seen at geosynchronous orbit
Authors: Thomsen M. F. , Borovsky J. E. , McComas D. J. , Elphic R. C. , Maurice S.
Published: February 2004

The response of the magnetosphere to the passage of the January 10–11, 1997 coronal mass ejection (CME) is described from the vantage point of geosynchronous orbit. Salient aspects of the observed response include 1) the global compression of the magnetosphere, including plasma sheet density enhancements and geosynchronous magnetopause crossings; 2) strongly stretched magnetotail field, with attendant substorm activity; 3) enhanced magnetospheric convection, leading to plasmaspheric erosion and dayside drainage; 4) no detectable superdense plasma sheet; and 5) propagating plasma‐sheet density fronts. The various aspects are related to the variations in the solar wind and interplanetary magnetic field impinging on the magnetosphere.
Reactive uptake of ozone by liquid organic compounds
Authors: de Gouw Joost A. , Lovejoy Edward R.
Published: February 2004

The reaction probability of ozone on the surface of several different organic liquids is measured. Ozone reacts efficiently (γ≈10−2‐10−3) with organic liquids containing double bonds (1‐tridecene, α‐pinene, toluene, methacrolein and canola oil), and much less efficiently with an aldehyde, a ketone (tridecanal, 2‐tridecanone; γ≈10−4), an alkane, an alcohol and an acid (tridecane, 1‐tridecanol, tridecanoic acid; γ≤10−5). The results suggest that heterogeneous reactions with organic aerosol can be an important loss process for tropospheric ozone, if the aerosol contains unsaturated organic material.
Global ionospheric TEC variations during January 10, 1997 storm
Authors: Ho C. M. , Mannucci A. J. , Lindqwister U. J. , Pi X. , Tsurutani B. T. , Sparks L. , Iijima B. A. , Wilson B. D. , Harris I. , Reyes M. J.
Published: February 2004

The ionospheric storm evolution process was monitored during the January 10, 1997 magnetic cloud event, through measurements of the ionospheric total electron content (TEC) from 150 GPS stations. The first significant response of the ionospheric TEC to the geomagnetic storm was at 0300 UT as an auroral/subauroral enhancement around the Alaskan evening sector. This enhancement then extended to both noon and midnight. Around 0900 UT, the enhancement at noon broke from the subauroral band and moved to lower latitudes. This day side northern hemisphere enhancement also corresponded to a conjugate geomagnetic latitude enhancement in the southern hemisphere and lasted about 5 hours. At 1500 UT a large middle latitude enhancement appeared over Mexico and the southern US, and persisted until 2200 UT. The enhancement was probably caused by the equatorward neutral wind which pushed the plasma up. On the basis of this assumption, the kinetic energy of the neutral wind which caused the middle latitude enhancement is estimated as ∼4.1×l09 Joules. This is about 0.03% of solar wind energy impinging on the magnetosphere and about 3% of the energy deposited on polar cap ionosphere. After 2000 UT, a negative phase gradually became stronger (especially in the southern hemisphere), although the northern subauroral enhancement persisted one more day. The entire ionosphere gradually recovered to normal on January 12. Thus, large middle latitude enhancement, equatorward motion of the dayside enhancement (probably related to a TID), the persistence of the subauroral enhancement, and the conjugate features at both hemispheres are the main characteristics of this storm.
Reply [to “Comment on ‘A new hydrous silicate, a water reservoir, in the upper part of the lower mantle’ by Eiji Ohtani, Hiroki Mizobata, Yasuhiro Kudoh, Toshiro Nagase, Haruo Arashi, Hisayoshi Yurimoto, and Isoji Miyagi”]
Authors: Ohtani Eiji , Mizobata Hiroki , Kudoh Yasuhiro , Nagase Toshiro , Arashi Haruo , Yurimoto Hisayoshi , Miyagi Isoji
Published: February 2004

Phase G reported by Ohtani et al. [1997] and Kudoh et al. [1997a] is identical with the new phase D reported by Kuroda and Irifune [1998] and Yang et al. [1997]. However, there is ambiguity on existence of phase D defined by Liu [1987]. There are following possibilities on existence of Liu's phase D; (1) the product was a mixture of phase G and the other contaminant phases, (2) it realy exists stably in different pressure and temperature conditions from those studied by our works, or (3) the phase is a metastable phase formed due to a short run duration and/or no sealing of water in the diamond anvil cell. Therefore, it is not appropriate to use the name phase D for the dense hydrous magnesium silicate phase G reported by us [Ohtani et al., 1997].
Heat flow in the Southwest Japan Arc and its implication for thermal processes under arcs
Authors: Furukawa Yoshitsugu , Shinjoe Hironao , Nishimura Susumu
Published: February 2004

We present 35 new heat flow measurements for the Kinki district in the eastern part of the southwest Japan arc. Heat flow distribution in this region shows zonal structure parallel to the trench. In the across‐arc heat flow profile there are two high heat flow peaks: one is located at the volcanic front and the other is between the south coast of this arc and the trench. The high heat flow at the volcanic front is probably caused by the induced flow in the mantle wedge. The high heat flow off the south coast is located in the zone where slab depth is 10∼20 km, and is immediately to the ocean side of the boundary at which P‐wave velocity increases landward in the upper crust. We thus consider the high heat flow is caused by the uplift of accreted materials along the backstop in the accretionary prism, assuming that seismic velocity is an indicator of rigidity of rocks. The upward flow velocity is estimated to be ∼1 mm/yr using a simple one‐dimensional erosion model, which is consistent with that estimated from the present heights of marine terraces.
Tidal variations of noctilucent clouds measured at 69°N latitude by groundbased lidar
Authors: von Zahn U. , von Cossart G. , Fiedler J. , Rees D.
Published: February 2004

During June/July 1997 we observed with a groundbased lidar noctilucent clouds (NLCs) overhead the ALOMAR observatory in Northern Norway (69°N, 16°E). These daylight observations of NLC were made possible by use of a very small field‐of‐view for the lidar receiving telescope in combination with a narrowband double‐etalon Fabry‐Perot interferometer in front of the photon counting detectors. During 148 hours of lidar measurements, NLCs were observed for 69 hours. Thus, the mean occurrence frequency of NLC was 46%. The observed NLCs exhibited marked variations of the layer altitude and backscatter ratio with local time (LT). The temporal behaviour of both the NLC altitude and NLC backscatter ratio are dominated by a semidiurnal variation. The NLC altitude attains maxima near 13 LT and 01 LT and minima near 07 LT and 19 LT. The backscatter ratio clearly maximizes at times of minimum NLC layer altitude. These observations point to a strong control of variations in NLC altitude and backscatter ratio by a stable semidiurnal tide. The mean centroid NLC altitude is 82.7 km.
Measurements of polytropic index in the January 10–11, 1997 magnetic cloud observed by WIND
Authors: Osherovich Vladimir A. , Fainberg J. , Stone R. G. , Fitzenreiter R. , Viñas A. F.
Published: February 2004

The polytropic index γ is a key parameter in the modeling of interplanetary magnetic clouds. In contrast to other models, the self‐similar model of Osherovich et al [1993a] suggested γ < 1 in clouds. The first measurements [Osherovich et al, 1993b] showed that γ ≈ γe = 0.4 ‐ 0.5 in magnetic clouds demonstrating the dominant role of electrons over protons (Te/Tp ≈ 6‐7 at 1 AU). For the January 10‐11, 1997 cloud observed by WIND, we found that the polytropric relation Te = FNeγe−1 is valid with γe = 0.52 ± 0.04 and F = 1.97 105 ± 0.12 105 (cgs units) over the number density range 1 < Ne < 10 cm−3. The constant F is half the value found for other clouds studied at 1 AU, while γe is essentially the same. We believe that the small value of F should be attributed to a later stage of the self‐similar evolution of this cloud as compared to other clouds studied previously at 1 AU.