bluuebunny/crossref_metadata_2025 huggingface dataset:
Relativistic electron microbursts during the GEM storms
Authors: Lorentzen K. R. , Looper M. D. , Blake J. B.
Published: February 2004

Observations of relativistic (>1 MeV) electron microbursts by the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX) satellite are frequently associated with geomagnetic storms. We examine the characteristics of these microbursts during 1997 and 1998, paying particular attention to the three storms selected by the Geospace Environment Modeling (GEM) community for special study: May 15, 1997, September 25, 1998, and October 19, 1998. The relativistic electron microbursts strongly correlate with both the Dst and Kp indices and generally increase in intensity and move to lower L shells during the recovery phases of geomagnetic storms. During the recovery phases of the September and October 1998 storms, the numbers of >1 MeV electrons lost from the radiation belts to the microburst precipitation are estimated to be 2.5 × 1025 and 3.3 × 1024, respectively. In both cases, the microburst loss is a significant fraction of the total radiation belt population.
Sea surface height observations of the 34°N ‘waveguide' in the North Atlantic
Authors: Cromwell David
Published: February 2004

We present a study of the energetic zonal band at 34°N in the North Atlantic using a wavelet analysis of more than 8 years of TOPEX/POSEIDON altimeter data. It is already well‐established in the literature that this zonal ‘waveguide' is dominated by large‐scale propagating features. The wavelet analysis yields sea surface height variance at a range of periods and wavelengths, allowing us to observe and quantify evolution of the features in space and time. Signal variance west of the mid‐Atlantic ridge at 34°N is larger than to the east of the ridge: by a factor of ˜2 in the period band 0.5–0.9 years, in which baroclinic Rossby waves and eddies propagate. The period of the peak energy is reduced crossing the ridge from ˜1 year to ˜7–9 months, before rising again to the annual cycle on the other side. There is also evidence of energy peaks at periods of ˜2–4 years in the Gulf Stream region and east of the ridge.
Simultaneous retrieval of cloud motion and height from polar‐orbiter multiangle measurements
Authors: Horváth Ákos , Davies Roger
Published: February 2004

For the first time, the fully automated retrieval of cloud motion from a polar orbiter is possible using a unique technique based on multiangle imagery. The main advantages of the method are the ability to simultaneously determine cloud height along with the wind and the capability of obtaining retrievals at high latitudes (up to 82°). The first results are consistent with the prelaunch error estimates of ±3 ms−1 for wind and ±400 m for height.
Evidence of different magnetotail responses to small solar wind pressure pulses depending on IMF Bz polarity
Authors: Moldwin Mark B. , Mayerberger S. , Rassoul H. K. , Collier M. R. , Lepping R. P. , Slavin J. A. , Szabo A.
Published: February 2004

The response of the magnetotail to small flux rope associated pressure pulses depends on the IMF Bz polarity. Clear and large amplitude magnetotail reverse polarity South‐then‐North traveling compression regions (SN TCRs) are observed when the pressure pulse is associated with the northward IMF interval of the flux rope. These tail signatures correspond to small‐scale (<10 minute duration) pulses of the solar wind dynamic pressure located in front of and within the small‐scale flux ropes. Pressure pulses associated with IMF Bz southward are either absent or give rise to smaller amplitude compressions and less systematic lobe Bz rotations. These results suggest that the orientation of the IMF Bz plays a critical role in modulating the magnetotail response to solar wind dynamic pressure pulses.
New type of soliton in Bi‐ion plasmas and possible implications
Authors: Sauer K. , Dubinin E. , McKenzie J. F.
Published: February 2004

It is well known that the addition of a second ion population into a proton‐electron plasma gives rise to new low‐frequency wave modes. Here we investigate stationary structures streaming with sub‐fast speed in such a bi‐ion plasma. It is shown that a new type of stationary structure occurs as result of mode splitting effects caused by the second ion population. These so‐called ‘oscillitons' are characterized by an oscillating spatial structure superimposed on the spatial growth or decay associated with the usual single‐ion solitons. Examples of the solution of the full non‐linear equations describing stationary bi‐ion flows are given which show that ‘oscillitons' may contribute to a better understanding of diverse low‐frequency phenomena observed in the mass loaded plasma environments of Mars, Jupiter and comets.
Evidence for photochemical production of ozone at the South Pole surface
Authors: Crawford J. H. , Davis D. D. , Chen G. , Buhr M. , Oltmans S. , Weller R. , Mauldin L. , Eisele F. , Shetter R. , Lefer B. , Arimoto R. , Hogan A.
Published: February 2004

Observations of OH, NO, and actinic flux at the South Pole surface during December 1998 suggest a surprisingly active photochemical environment which should result in photochemical production of ozone. Long‐term South Pole in situ ozone data as well as sonde data also appear to support this conclusion. Other possible factors contributing to ozone variability such as stratospheric influence and the origin of air transported to the South Pole are also explored. Based on box model calculations it is estimated that photochemistry could add 2.2 to 3.6 ppbv/day of ozone to surface air parcels residing on the Antarctic polar plateau. Although the oxidizing potential of the polar plateau appears to be exceptionally high for a remote site, it is unlikely that it has a significant impact on surrounding regions such as the Southern Ocean and the Antarctic free troposphere. These new findings do suggest, however, that the enhanced oxidizing power of the polar plateau may need to be considered in interpreting the chemical history of climate proxy species in ice cores.
Composition from fast neutrons: Application to the Moon
Authors: Gasnault Olivier , Feldman William C. , Maurice Sylvestre , Genetay Isabelle , d'Uston Claude , Prettyman Thomas H. , Moore Kurt R.
Published: February 2004

Planetary neutron leakage fluxes provide a measure of surface composition. However to be used in geological studies, a quantitative relationship between measured fluxes and surface composition is needed. The present work shows that neutron production is expected to be a function of the atomic mass, and that the fast leakage flux in the energy range between 0.6 and 8 MeV is linearly related to the average soil atomic mass. This result is consistent with laboratory measurements, and with Lunar Prospector observations of the Moon. When calibrated with returned lunar samples, this relationship is used to construct a map of the average atomic mass of lunar soils.
Observations of the 2‐day wave in UARS MLS temperature and ozone measurements
Authors: Azeem S. M. I. , Palo S. E. , Wu D. L. , Froidevaux L.
Published: February 2004

Mesospheric ozone and temperature data obtained by the Microwave Limb Sounder (MLS) on board the Upper Atmosphere Research Satellite (UARS) have been analyzed to elucidate quasi‐two day wave activity. Data from January 1993 were analyzed to investigate the evolution and structure of the two day wave. During this period, the wave amplitude in ozone attained its maximum value in late January near 30° in the summer hemisphere. The evolution of the wave amplitude indicates a shift of the peak amplitude to higher latitudes with increasing height. Correlation of the two day wave phase observed in MLS ozone and temperature measurements indicates that the perturbations are out of phase. During the same period, the amplitudes of the perturbations in temperature and ozone were positively correlated. The results suggest that the variations in ozone are photochemically driven in the mesosphere region via changes in reaction rates that are strongly temperature dependent.
Energetic radiation associated with lightning stepped‐leaders
Authors: Moore C. B. , Eack K. B. , Aulich G. D. , Rison W.
Published: February 2004

With the use of a NaI scintillation detector, bursts of radiation with energies in excess of 1 MeV were recorded at a mountain‐top observatory immediately before three, nearby cloud‐to‐ground, negative lightning strikes. Coincident recordings of the electric field changes due to the discharges showed that, in each case, the bursts began between 1 and 2 milliseconds before and continued until the onset of the first return stroke. This radiation was associated with approaching stepped‐leaders and may have influenced their development.
Isotopic fractionation of methane in the stratosphere and its effect on free tropospheric isotopic compositions
Authors: McCarthy M. C. , Connell P. , Boering K. A.
Published: February 2004

Kinetic isotope effects (KIEs) for the oxidation of CH4 by OH, Cl, and O(¹D) were incorporated into a 2D model of the atmosphere to examine how sensitive the carbon isotopic composition of CH4 in the free troposphere is to three influences: realistic stratospheric chemistry and transport, tropospheric Cl chemistry, and use of new, experimentally‐determined KIEs for the OH and O(¹D) sinks. At steady‐state, our results indicate that stratospheric chemistry and transport enrich tropospheric δ13CH4 by 0.5 to 0.6‰, tropospheric Cl chemistry as modeled enriches δ13CH4 by ∼0.3‰, and the new KIE for the OH sink depletes modeled global δ13CH4 by >1‰. Ignoring the stratosphere (and Cl chemistry in general) in models therefore happens to partially compensate for use of the previously accepted KIE for OH when comparisons with observations of free tropospheric δ13CH4 are made. In contrast, including only one of these influences increases the error relative to including none. Thus, all 3 effects are of sufficient magnitude to warrant their inclusion in inverse models in order to reduce uncertainties in the CH4 budget.
Mantle control of plate boundary deformation
Authors: Melbourne Tim , Helmberger Don
Published: February 2004

The seismic wavefield propagating along the recently instrumented Pacific‐North American plate boundary (California) displays remarkable variation, with regional shear waves arriving at coastal stations up to 20 seconds earlier than equidistant stations in eastern California. Broadband modeling of this data reveals that coastal paths sample fast upper mantle typical of Miocene‐aged ocean plate (>50 Km thickness). Inland paths sample slower uppermost mantle, with the seismic lithosphere, or lid, measuring less than 5 Km thick, characteristic of the Basin and Range extensional province. The boundary in the uppermost mantle between these provinces is sharp, expressing the juxtaposition of the stronger Pacific plate with weaker continental North America. The lid step coincides with regionally maximum dextral strain rates measured with GPS, suggesting the uppermost mantle modulates long term, regional‐scale continental margin deformation and evolution.
Plasma transport at the magnetospheric boundary due to reconnection in Kelvin‐Helmholtz vortices
Authors: Nykyri K. , Otto A.
Published: February 2004

The Kelvin‐Helmholtz (KH) mode has long been considered for viscous interaction at the magnetospheric boundary but it is not expected to produce significant mass transport. The presented results indicate that the Kelvin‐Helmholtz instability can indeed cause a transfer of mass into the magnetotail during times of northward IMF. The vortex motion of KH waves can generate a strongly twisted magnetic field with multiple current layers. Magnetic reconnection in the strong current layers inside the vortices can detach high density plasma filaments from the magnetosheath. This may explain observed high density and low temperature filaments in the magnetosphere and the correlation of the plasma sheet density and the solar wind density. We present a two‐dimensional study of reconnection and mass transport in KH vortices depending on magnetosheath and magnetospheric plasma and field properties. For individual waves the average mass entry velocities is determined to be several km/s.
Sixteen years of Florida Current Transport at 27° N
Authors: Baringer Molly O'Neil , Larsen Jimmy C.
Published: February 2004

Daily transports of the Florida Current have been inferred since 1982 through the use of submerged submarine telephone cables that measure the voltage difference across the Straits of Florida. Using all sixteen years of data, the annual cycle ranges from a minimum of 30 Sv in January, to a maximum of 33.5 Sv in July. The annual cycle is not stable throughout the entire period however: the first eight years show a slightly larger peak‐to‐peak annual range of 5 Sv, while the second eight years have a semi‐annual cycle with a distinct minimum in July and peak‐to‐peak range of 4 Sv. Filtered Florida Current transports contain a two to three year variation between 2 and 3 Sv in amplitude and a decadal variation of about ±2 Sv. The decadal changes in the Florida Current transport are significantly correlated (R=0.75 at 95% significance) to the North Atlantic Oscillation Index.
Direct estimation of absolute precipitable water in oceanic regions by GPS tracking of a coastal buoy
Authors: Chadwell C. David , Bock Yehuda
Published: February 2004

A buoy‐based GPS receiver and meteorological sensor are used to estimate directly the absolute precipitable water (PW) overlying a coastal ocean site 8 km from shore. During an 11‐day experiment, one‐second GPS data collected at the buoy and at a shore station are combined with 30‐second data from four distant GPS stations to estimate the buoy position, zenith wet delay, phase biases, and receiver and satellite clocks using double‐differenced phase processing with ambiguity resolution. GPS‐derived PW at the buoy compared to radiosonde measurements (20) and to half‐hourly GPS‐PW values (384) from the nearby shore station show an rms agreement of ±1.5 mm and ±1.8 mm, respectively. Hourly means (170) of the GPS‐measured vertical motion of the buoy show a ±24 mm rms agreement with a NOAA tide gauge, equivalent to about 4 mm of PW. GPS‐derived PW from buoys may have the potential to improve weather forecasting, calibration of satellite‐based sensors, and climate studies.
Crustal deformation measured by GPS in the South Iceland Seismic Zone due to two large earthquakes in June 2000
Authors: Árnadóttir Thóra , Hreinsdóttir Sigrún , Gudmundsson Gunnar , Einarsson Páll , Heinert Michael , Völksen Christof
Published: February 2004

Two large earthquakes struck the South Iceland Seismic Zone in June 2000, the first on June 17 (MW=6.5) and the second on June 21 (MW=6.4). These are the largest earthquakes in the area in the past 88 years. A network of GPS stations was remeasured following the earthquakes. The whole network was last measured in 1995, and partly in 1999. We correct for the interseismic motion from 1995 to 2000, to obtain the coseismic displacements. The largest coseismic motion we observe is about 0.55 m in the epicentral area of the June 17 event. We model the surface deformation for the two earthquakes using rectangular dislocations in an elastic half space. Best fit uniform slip models indicate that the events occurred on two parallel, N‐S vertical faults, with right‐lateral strike slip motion. This is the same style of faulting believed to have occurred in large historical earthquake sequences in South Iceland.
Unstable near‐surface boundary conditions in summer on top of the Greenland Ice Sheet
Authors: Cullen Nicolas J. , Steffen Konrad
Published: February 2004

The surface energy balance for the interior of the Greenland ice sheet in summer 2000 is described. The most important feature of the energy balance is that net all‐wave radiation is positive. Peak global radiation values of 800 W m−2 provide energy at the snow surface that results in the turbulent fluxes of sensible and latent heat being directed into the atmosphere. Heating at the surface gives rise to unstable near‐surface atmospheric conditions, with sensible heat fluxes typically between 10‐20 W m−2. Daily mean values of the subsurface heat flux are small and directed downwards from the surface as the snow cover warms during the summer season. Analysis of the gradient Richardson number for the past three summers shows that unstable conditions are common, with frequencies between 11‐43% for a 2.5 month period. The unstable conditions in summer appear to be important in controlling katabatic forcing over the ice sheet.
Last interglacial coral record of enhanced insolation seasonality and seawater 18O enrichment in the Ryukyu Islands, northwest Pacific
Authors: Suzuki Atsushi , Gagan Michael K. , De Deckker Patrick , Omura Akio , Yukino Izuru , Kawahata Hodaka
Published: February 2004

We present a calibrated, high‐resolution 18O/16O and 13C/12C record for a well‐preserved Last Interglacial Porites sp. coral (U‐Th age of 127±6 ka) from the sea‐level high‐stand terrace of Yonaguni Island, Japan. Seasonal variations in the δ18O and δ13C values for the fossil coral are greater than those observed in modern coral records from the same reef setting and appear to be driven by the enhanced insolation seasonality in the northern hemisphere during the Last Interglacial maximum. The 18O enrichment of 1.1‰ in the fossil coral compared to the modern analogue cannot be due entirely to a reduction in sea‐surface temperature because corals in this region are already growing at their lower thermal limit. Instead, most of the 18O enrichment must be due to a change in the δ18O of the surface seawater, probably in response to enhanced evaporation of the ocean or a higher volume flux of the Kuroshio Current.
Stochastic ion heating at the magnetopause due to kinetic Alfvén waves
Authors: Johnson Jay R. , Cheng C. Z.
Published: February 2004

The magnetopause and boundary layer are typically characterized by large amplitude transverse wave activity with frequencies below the ion cyclotron frequency. The signatures of the transverse waves suggest that they are kinetic Alfvén waves with wavelength on the order of the ion gyroradius [Johnson and Cheng, 1997a; Johnson et al., 2001]. We investigate ion motion in the presence of large amplitude kinetic Alfvén waves with wavelength the order of ρi and demonstrate that for sufficiently large wave amplitude (δB⟂/B0 > 0.05) the particle orbits become stochastic. As a result, low energy particles in the core of the ion distribution can migrate to higher energy through the stochastic sea leading to an increase in T⟂ and a broadening of the distribution. This process can explain transverse ion energization and formation of conies which have been observed near the magnetopause in both the magnetosheath and low‐latitude boundary layer.
A cloud resolving model as a cloud parameterization in the NCAR Community Climate System Model: Preliminary results
Authors: Khairoutdinov Marat F. , Randall David A.
Published: February 2004

Preliminary results of a short climate simulation with a 2‐D cloud resolving model (CRM) installed into each grid column of an NCAR Community Climate System Model (CCSM) are presented. The CRM replaces the conventional convective and stratiform cloud parameterizations, and allows for explicit computation of the global cloud fraction distribution for radiation computations. The extreme computational cost of the combined CCSM/CRM model has thus far limited us to a two‐month long climate simulation (December‐January) using 2.8° × 2.8° resolution. The simulated geographical distributions of the total rainfall, precipitable water, cloud cover, and Earth radiation budget, for the month of January, look very reasonable.
Secular changes to the ENSO‐U.S. hurricane relationship
Authors: Elsner James B. , Bossak Brian H. , Niu Xu‐Feng
Published: February 2004

Analysis of the statistical relationship between annual U.S. hurricane activity and the El Niño‐Southern oscillation (ENSO) is performed. The legitimacy of considering annual U.S. hurricane counts as a Poisson process is checked. Then, Poisson regression is used to model the ENSO‐U.S. hurricane connection. A bivariate regression model verifies a significant negative correspondence between tropical Pacific sea‐surface temperature (SST) and U.S. hurricane activity. When equatorial SSTs are cold, U.S. hurricanes are more likely. Secular changes to the ENSO‐U.S. hurricane relationship are examined using moving regressions. A nonlinear downward trend in the relationship's strength is evident. Variations in sea‐level pressures over the extra‐tropical North Atlantic Ocean during months immediately prior to the hurricane season provide an explanation for a portion of this secular variability. Atmospheric synoptic conditions associated with the North Atlantic oscillation (NAO) result in hurricanes tracking parallel to southern latitudes en route to the United States.
Stratospheric CO2 isotopic anomalies and SF6 and CFC Tracer Concentrations in the Arctic Polar Vortex
Authors: Alexander B. , Vollmer M. K. , Jackson T. , Weiss R. F. , Thiemens M. H.
Published: February 2004

Isotopic measurements (δ17O and δ18O) of CO2 along with concentration measurements of SF6, CCl3F (CFC‐11), CCl2F2 (CFC‐12) and CCl2FCClF2 (CFC‐113) in stratospheric samples collected within the Arctic polar vortex are reported. These are the first simultaneous measurements of the concentration of fluorinated compounds and the complete oxygen isotopic composition of CO2 in the middle atmosphere. A mass‐independent anomaly in the oxygen isotopic composition of CO2 is observed that arises from isotopic exchange with stratospheric O(¹D) derived from O3 photolysis. The data exhibit a strong anti‐correlation between the Δ17O (the degree of the mass‐independent anomaly) and molecular tracer concentrations. The potential ability of this isotopic proxy to trace mesospheric and stratospheric transport is discussed.
Kuroshio Stream path variation and its associated velocity structures south of Shikoku, Japan
Authors: Zhu Xiao‐Hua , Kaneko Arata , Saito Tsutomu , Gohda Noriaki
Published: February 2004

During 1993‐1995, twelve repeat observations of the Kuroshio south of Shikoku, Japan were carried out for obtaining a vertical velocity section of the upper 300m, using a towed‐type acoustic Doppler current profiler (ADCP). Among the twelve observations, the Kuroshio took the onshore path 9 times and the offshore path 3 times. The cross‐stream velocity distribution around the Kuroshio stream axis is asymmetric (steeper on the onshore side than on the offshore side) for the onshore path while it is symmetric for the offshore one. The core with a maximum velocity is submerged to 100‐200m depths for the onshore case and located at the near surface for the offshore case. In the combined analysis with the Rapid Bulletin of Ocean Conditions, the Kuroshio mainly took an onshore path with stream‐axis positions less than 80km from Cape Ashizuri, but the distance was increased over 150km at the frequency once a year.
Solar wind electron halo depletions at 90° pitch angle
Authors: Gosling J. T. , Skoug R. M. , Feldman W. C.
Published: February 2004

Strong depletions in solar wind electron halo distribution functions, centered on and roughly symmetric about 90° pitch angle, are present in at least 10% of data obtained by the Los Alamos SWEPAM experiment on the ACE spacecraft. Sunward‐directed conics are also present in the electron data, occur in conjunction with the 90° depletions, but are less common than depletions. We suggest that on open field lines both depletions and conics arise from focusing and mirroring effects associated with field line connection to magnetic field enhancements farther out in the heliosphere. The focusing and mirroring produces field‐aligned, counterstreaming fluxes of suprathermal electrons somewhat similar to that observed on closed field lines. Our observations provide strong evidence that the antisunward‐directed portion of the electron halo on open field lines at times results primarily from mirroring of back scattered strahl and/or shock‐heated electrons from far out in the heliosphere.
Experimentally determined postspinel transformation boundary in Mg2SiO4 using MgO as an internal pressure standard and its geophysical implications
Authors: Fei Y. , Van Orman J. , Li J. , van Westrenen W. , Sanloup C. , Minarik W. , Hirose K. , Komabayashi T. , Walter M. , Funakoshi K.
Published: February 2004

We have determined the postspinel transformation boundary in Mg2SiO4 by combining quench technique with in situ pressure measurements, using multiple internal pressure standards including Au, MgO, and Pt. The experimentally determined boundary is in general agreement with previous in situ measurements in which the Au scale of Anderson et al. [1989] was used to calculate pressure: Using this pressure scale, it occurs at significantly lower pressures compared to that corresponding to the 660‐km seismic discontinuity. In this study, we also report new experimental data on the transformation boundary determined using MgO as an internal standard. The results show that the transition boundary is located at pressures close to the 660‐km discontinuity using the MgO pressure scale of Speziale et al. [2001] and can be represented by a linear equation, P(GPa) = 25.12 − 0.0013T(°C). The Clapeyron slope for the postspinel transition boundary is precisely determined and is significantly less negative than previous estimates. Our results, based on the MgO pressure scale, support the conventional hypothesis that the postspinel transformation is responsible for the observed 660‐km seismic discontinuity.
Cokriged estimation of aquifer transmissivity as an indirect solution of the inverse problem: A practical approach
Authors: Ahmed Shakeel , De Marsily G.
Published: February 2004

A simple approach to indirectly address the inverse problem in steady state for aquifer transmissivity has been studied. The data on transmissivity and water level have simultaneously been used to produce the spatial distribution of transrnissivity through cokriging. A simple relation between transmissivity and head was used to calculate coherent head covariance and head‐transmissivity cross‐covariance based on a chosen transmissivity covariance. Two theoretical aquifer models were studied: one with simple and almost parallel flow and the other with a complex flow and source terms. The results were compared with the theoretical values. The comparison shows that a better estimation both in terms of the estimated values of transmissivities and in terms of the standard deviation of the estimation errors is obtained when water levels combined with transmissivity are used than in case of the estimation with transmissivity alone, provided the groundwater flow direction in a close neighborhood of the estimation point is carefully calculated.
A composite hydraulic and statistical flow‐routing method
Authors: Morel‐Seytoux Hubert J. , Fahmy Hussam , Lamagat Jean‐Pierre
Published: February 2004

A simple and efficient method for flow routing, combining the kinematic wave equation with a statistical procedure, is introduced. It accounts for the nonlinearity and the dispersion of the flood wave propagation phenomenon and for lateral flow. The method is flexible, because it can be used to simulate a variety of flow variables, for example, water stage or discharge. Its calibration is based on historical records at both ends of the reach, and does not require geometric cross‐section or longitudinal data. An application to the White Nile in Sudan demonstrates the practicality and accuracy of the method.
The Effect of streambed topography on surface‐subsurface water exchange in mountain catchments
Authors: Harvey Judson W. , Bencala Kenneth E.
Published: February 2004

A numerical hydrological simulation suggested that water exchange between stream channels and adjacent aquifers is enhanced by convexities and concavities in streambed topography. At St. Kevin Gulch, an effluent stream in the Rocky Mountains of Colorado, subsurface hydraulic gradients and movement of ionic tracers indicated that stream water was locally recharged into well‐defined flow paths through the alluvium. Stream water‐filled flow paths in the alluvium (referred to as substream flow paths) returned to the stream a short distance downstream (1 to 10 m). Recharge to the substream flow paths occurred where stream water slope increased, at the transition from pools (<1%) to steeper channel units (5–20%). Return of substream flow paths to the stream occurred where stream water slope decreased, at the transition from steeper channel units to pools. A net water flux calculation is typically used to characterize water and solute fluxes between surface and subsurface zones of catchments. Along our study reach at St. Kevin Gulch the net inflow of water from subsurface to stream (1.6 mL s−1 m−1) underestimated the gross inflow (2.7 mL s−1 m−1) by 40%. The influence of streambed topography is to enhance hydrological fluxes between stream water and subsurface zones and to prolong water‐sediment contact times; these effects could have important consequences for solute transport, retention, and transformation in catchments.
A hierarchical and empirical Bayes Approach for the regional Pearson type III distribution
Authors: Ribeiro‐Correa Joseph , Rousselle Jean
Published: February 2004

Regional information has proved to be particularly valuable for estimating the higher‐order parameters of flood series distributions. This has suggested the use of a hierarchical approach for regional curve fitting, in which higher‐order moment ratios, such as the coefficient of skewness and the coefficient of kurtosis, are estimated over larger areas than lower‐order moment ratios, such as the coefficient of variation. This philosophy is applied here for the Pearson type III distribution and is combined with an empirical Bayes approach for the estimation of the scale parameter. This work is specifically aimed at estimating flood frequencies and quantiles at sites with short record lengths. Some simulation experiments are reported for an evaluation of the performance of the method, and an application on a set of 59 Ontarian flood series having long record length plus two example stations with short record length is described for illustrative purposes.
Mixing cell models for nonlinear nonequilibrium single species adsorption and transport
Authors: Bajracharya K. , Barry D. A.
Published: February 2004

The oft‐used “standard” mixing cell model describing reactive solute transport is extended to cater for nonequilibrium reactions. For tracer transport, the standard model is second‐order accurate in the space and time discretization used. However, an error analysis of the standard model reveals that its accuracy is degraded when reactions are included. An “improved” model which maintains second‐order accuracy is developed. The improved mixing cell model is demonstrated to be more accurate than the standard model. The solution obtained from the improved model is found to agree very well with the results of a numerical Crank‐Nicolson solution for various isotherms. The improved mixing cell predictions are also shown to agree very well with the exact solution for the two‐site adsorption model, where a linear isotherm is considered. Application of the improved model was illustrated by simulating the experimental data from a laboratory Ca‐K exchange experiment in which a solution containing Ca was passed through a column filled with K‐saturated soil. The model was used in conjunction with the experimentally determined nonlinear adsorption isotherm to predict the experimental breakthrough data. By changing the value of kinetic coefficient, it was demonstrated that the predictions varied markedly. However, the simulations suggest that the equilibrium model is more appropriate than the assumption of nonequilibrium.
Upscaling of permeability of anisotropic heterogeneous formations: 1. The general framework
Authors: Indelman P. , Dagan G.
Published: February 2004

In numerical simulations of flow through heterogeneous formations, the domain is partitioned into numerical elements. The solution requires assigning physical properties to each numerical block. The process of transferring information from the scale of actual heterogeneity to that of the numerical elements is known as upscaling. We consider steady, one‐phase flow and the only property of interest is the permeability, which is regarded as a random space function, and the same is true for the upscaled conductivity. In this paper we establish the necessary and sufficient conditions to be satisfied by upscaling. The necessary conditions are expressed with the aid of the global response of the formation, e.g., the total flux caused by a constant pressure head drop applied on the boundaries. The requirement is that the expected value and the variance of the total flux are the same in the actual and upscaled domains. These are supplemented by local conditions which stipulate that space averages of flow variables over the numerical blocks in the upscaled domain tend to those in the actual formation when the elements size tends to 0. The result of this analysis is that the upscaled permeability must be such as to ensure the equality, in a statistical sense, between the space averaged dissipation in the two media. By assuming an unbounded domain, average uniform flow and stationarity, simplified relationships between the moments of the dissipation in the upscaled and actual media are derived. It is shown that the effective permeability of the two media is the same. The approach is illustrated for stratified formations for which exact composition rules are possible. Even in this simple case the upscaled permeability is a tensor, characterized at second order by two mean components and three covariance functions.
Kernel flood frequency estimators: Bandwidth selection and kernel choice
Authors: Lall Upmanu , Moon Young‐il , Bosworth Ken
Published: February 2004

Kernel density estimation methods have recently been introduced as viable and flexible alternatives to parametric methods for flood frequency estimation. Key properties of such estimators are reviewed in this paper. Attention is focused on the selection of the kernel function and the bandwidth. These are the parameters of the method. Existing techniques for kernel and bandwidth selection are applied to three situations: Gaussian data, skewed data (three‐parameter gamma), and mixture data. The intent was to investigate issues relevant to parameter estimation as well as to the likely performance of these methods with the small sample sizes typical in hydrology. Bandwidths chosen by minimizing a performance criterion related to the distribution function lead to much smaller mean square errors of tail probabilities than those chosen by cross‐validation methods designed for density estimation. However, this can lead to estimates that degenerate to the empirical distribution function, and hence to an unusable flood frequency curve. Variable bandwidths with heavy tailed kernels appear to do best. Kernel estimators are increasingly more competitive in terms of mean square error of estimate as the underlying distribution gets more complex.
Calibration of rainfall‐runoff models: Application of global optimization to the Sacramento Soil Moisture Accounting Model
Authors: Sorooshian Soroosh , Duan Qingyun , Gupta Vijai Kumar
Published: February 2004

Conceptual rainfall‐runoff models are difficult to calibrate by means of automatic methods; one major reason for this is the inability of conventional procedures to locate the globally optimal set of parameters. This paper investigates the consistency with which two global optimization methods, the shuffled complex evolution (SCE‐UA) method (developed by the authors) and the multistart simplex (MSX) method, are able to find the optimal parameter set during calibration of the Sacramento soil moisture accounting model (SAC‐SMA) of the National Weather Service River Forecast System (NWSRFS). In the first phase of this study, error‐free synthetic data are used to conduct a comparative evaluation of the algorithms under “ideal” conditions. In 10 independent trials of each algorithm in which 13 parameters of the SAC‐SMA model were optimized simultaneously, the SCE‐UA method achieved a 100% success rate in locating the precise global optimum (i.e., the “true” parameter values) while the MSX method failed in all trials even with more than twice the number of function evaluations. In the second phase, historical data from the Leaf River watershed are used to conduct a comparative evaluation of the algorithms under “real” conditions, using two different estimation criteria, DRMS and HMLE; the SCE‐UA algorithm obtained consistently lower function values and more closely grouped parameter estimates, while using one‐third fewer function evaluations than the MSX algorithm.
Modeling moisture movement in revegetating waste heaps: 2. Application to oil shale wastes
Authors: Connell L. D. , Bell P. R. , Haverkamp R.
Published: February 2004

The application of a model for the movement of water within waste dumps, described in a previous paper, requires the estimation of a range of physical characteristics. Parameters relating to the transfer of liquid water, water vapor, heat, and air within the waste dump must be estimated in addition to surface parameters which determine the interaction between subsurface processs and the atmospheric boundary layer. Three different methods are used to estimate the hydraulic conductivity and moisture retentivity: an inverse analysis based on field measurements of moisture movement; an application of the instantaneous profile method; and the Haverkamp‐Parlange method. The water vapor‐air diffusivity and intrinsic permeability of air are estimated, as well as the thermal properties of the various waste materials. The model presented previously is refined through a series of sensitivity analyses and applied to simulate the water movement observed within a lysimeter. Model predictions were particularly sensitive to the surface roughness. Evaporation from a bare surface was found to be related primarily to the surface moisture content, most evaporation occurring directly after rainfall. The contribution of vapor transport to cumulative evaporation was not significant in comparison to the contribution of liquid flow, even for long periods of dry surface conditions. Finally, the model is applied to predict the moisture movement within waste dumps that could be expected from an oil shale‐mining operation.
State space model for river temperature prediction
Authors: Bravo Hector R. , Krajewski Witold F. , Holly Forrest M.
Published: February 2004

A stochastic state space model for the estimation of river temperature is presented, setting the stage for its implementation in optimal control algorithms. Physical processes modeled include advection, diffusion, and environmental heat exchange; the mathematical formulation is one dimensional. The deterministic formulation uses a hybrid characteristics‐finite differences numerical scheme for the solution of the governing equations. The stochastic formulation accounts for uncertainty due to model assumptions, errors in the model inputs and parameters, and river temperature measurements. Model use is demonstrated by the estimation of temperatures in a 5‐mile (8 km) reach of the Des Plaines River, Illinois, below the Joliet power station. River temperature measurements and hydrological and meteorological data are used to estimate the model parameters; model formulation and limitations are assessed based on the model application results. The stochastic formulation improves river temperature estimation, as measured by the mean, variance‐covariance, correlation, and range of the residuals.
Analysis of short‐run domestic water supply transfers under uncertainty
Authors: Smith Mark Griffin , Marin Carlos M.
Published: February 2004

From the perspective of water supply managers, supply reliability can be more important than economic benefit. This study uses four alternative models of water supply allocation to examine issues of reliability and welfare maximization arising from short‐run inter‐city water transfers. The results of this work show that the economic gain from water transfers may be relatively small. However, water transfers can significantly improve system reliability, thus providing strong incentives for transfer arrangements among water authorities. We apply the models in a case study on the island of Cyprus.
Statistical analysis with an ordered categorical regressor: The effect of rainfall on attendance
Authors: Solow Andrew R. , Starczak Victoria E.
Published: February 2004

This paper describes an approach to the statistical analysis of a linear model in which one regressor is an ordered categorical variable. The approach is based on fitting a model in which the ordered categorical variable is replaced by an estimate of the mean in each category of the underlying continuous variable. Significance is assessed using a randomization test. An application to estimating and testing the effect of rainfall on attendance at the Sydney Easter Show is presented.
Metamodels and nonpoint pollution policy in agriculture
Authors: Bouzaher Aziz , Lakshminarayan P. G. , Cabe Richard , Carriquiry Alicia , Gassman Philip W. , Shogren Jason F.
Published: February 2004

Complex mathematical simulation models are generally used for quantitative measurement of the fate of agricultural chemicals in soil. But it is less efficient to use them directly for regional water quality assessments because of the large number of simulations required to cover the entire region and because the entire set of simulation runs must be repeated for each new policy. To make regional water quality impact assessment on a timely basis, a simplified technique called metamodeling is suggested. A metamodel summarizes the input‐output relationships in a complex simulation model designed to mimic actual processes such as groundwater leaching. Metamodels are constructed and validated to predict groundwater and surface water concentrations of major corn and sorghum herbicides in the Corn Belt and Lake States regions of the United States. The usefulness of metamodeling in the evaluation of agricultural nonpoint pollution policies is illustrated using an integrated environmental economic modeling system. For the baseline scenario, we estimate that 1.2% of the regional soils will lead to groundwater detection of atrazine exceeding 0.12 Mg/L, which compares well with the findings of an Environmental Protection Agency monitoring survey. The results suggest no‐till practices could significantly reduce surface water concentration and a water quality policy, such as an atrazine ban, could increase soil erosion despite the conservation compliance provisions.
Lmoment diagrams should replace product moment diagrams
Authors: Vogel Richard M. , Fennessey Neil M.
Published: February 2004

It is well known that product moment ratio estimators of the coefficient of variationCν, skewness γ, and kurtosis κ exhibit substantial bias and variance for the small (n≤ 100) samples normally encountered in hydrologic applications. Consequently,Lmoment ratio estimators, termedLcoefficient of variation τ2,Lskewness τ3, andLkurtosis τ4are now advocated because they are nearly unbiased for all underlying distributions. The advantages of L moment ratio estimators over product moment ratio estimators are not limited to small samples. Monte Carlo experiments reveal that product moment estimators ofCνand γ are also remarkably biased for extremely large samples (n≥ 1000) from highly skewed distributions. A case study using large samples (n≥ 5000) of average daily streamflow in Massachusetts reveals that conventional moment diagrams based on estimates of product momentsCν, γ, and κ reveal almost no information about the distributional properties of daily streamflow, whereasLmoment diagrams based on estimators of τ2, τ3, and τ4enabled us to discriminate among alternate distributional hypotheses.
Initialization for generating single‐site and multisite low‐order periodic autoregressive and moving average processes
Authors: Salas Jose D. , Abdelmohsen Magdy W.
Published: February 2004

Single‐site and multisite periodic autoregressive and moving average (PARMA) processes have been suggested for modeling and simulation of hydrologic processes. Generation of synthetic samples based on such models requires knowledge of the initial conditions, i.e., the values of the process at times prior to t = 1. In this paper an initialization procedure for generating univariate and multivariate PAR (1), PAR (2), and PARMA (1, 1) processes is described. The procedure is based on generating the initial values of the process in such a way that the variance‐covariance structure of the process is preserved. The initialization procedure introduced herein is exact and easy to use. Examples are included to explain the applicability of the proposed approach.
Measurement of variation in soil solute tracer concentration across a range of effective pore sizes
Authors: Harvey Judson W.
Published: February 2004

Solute transport concepts in soil are based on speculation that solutes are distributed nonuniformly within large and small pores. Solute concentrations have not previously been measured across a range of pore sizes and examined in relation to soil hydrological properties. For this study, modified pressure cells were used to measure variation in concentration of a solute tracer across a range of pore sizes. Intact cores were removed from the site of a field tracer experiment, and soil water was eluted from 10 or more discrete classes of pore size. Simultaneous changes in water content and unsaturated hydraulic conductivity were determined on cores using standard pressure cell techniques. Bromide tracer concentration varied by as much as 100% across the range of pore sizes sampled. Immediately following application of the bromide tracer on field plots, bromide was most concentrated in the largest pores; concentrations were lower in pores of progressively smaller sizes. After 27 days, bromide was most dilute in the largest pores and concentrations were higher in the smaller pores. A sharp, threefold decrease in specific water capacity during elution indicated separation of two major pore size classes at a pressure of 47 cm H2O and a corresponding effective pore diameter of 70 μm. Variation in tracer concentration, on the other hand, was spread across the entire range of pore sizes investigated in this study. A two‐porosity characterization of the transport domain, based on water retention criteria, only broadly characterized the pattern of variation in tracer concentration across pore size classes during transport through a macroporous soil.
Tracer experiments in fractured rocks: Matrix diffusion and the validity of models
Authors: Maloszewski Piotr , Zuber Andrzej
Published: February 2004

Several published tracer tests are reexamined using the single fracture dispersion model (SFDM), i.e., a solution to the transport equation in which fractured rock is represented by a single fracture and the tracer is allowed to diffuse into the matrix. The model has three fitting parameters, i.e., the mean time of flow, dispersivity, and a diffusion parameter which combines such physical parameters as matrix porosity, coefficient of matrix diffusion, and adjusted fracture aperture. The model is easily calibrated yielding as good, or better, fits as did the models applied in original works, which were based on an assumption of negligible matrix diffusion and were characterized by larger numbers of fitting parameters. The SFDM better describes the short‐term transport in investigated systems and/or their parameters than models applied so far. Validation of the model was obtained by showing that the values of its physical parameters either agree with those known from other methods or are within expected ranges. Another validation was achieved for tests performed in the same pair of wells with two tracers characterized by distinctly different coefficients of molecular diffusion. In spite of distinct differences in the shapes of the experimental curves, the SFDM yielded the same values of the fracture aperture, matrix porosity, and intrinsic dispersivity. The ratio of the diffusion coefficients in the matrix was close to that known from the diffusion coefficients in free water.