bluuebunny/crossref_metadata_2025 huggingface dataset:
Correction to “Determination of polar cap boundary and daytime cusp structure using the characteristics of precipitating ions”
Authors: Troshichev O. A. , Shishkina E. M.
Published: February 2004

Particle data obtained from the Defense Meteorological Satellite Program spacecraft for periods of northward interplanetary magnetic field show that ion spectra above the polar cap arcs usually display the same character as those in the midnight auroral oval. Evidently, this means that polar cap arcs and the midnight oval arcs have the same source. At the same time, ion spectra in spikes of particle precipitation in the discrete oval vary with MLT in a regular manner, such that the flux of ions in the energy range 0.1 < Ei < 1 keV increases from midnight toward noon. This feature of ion spectra makes it possible to identify the boundary of the polar cap from the precipitation patterns when the interplanetary magnetic field is northward. The structural zones such as the cusp proper and the poleward and equatorward edges of the cusp can be separated from the daytime oval region using specific features of the ion spectra. The ion population in all these zones is composed of three parts, namely, the mantle, the cusp, and the low‐latitude boundary layer plasmas. Densities of all plasma fractions are maximal in the cusp proper and decrease when moving toward the cusp periphery.
Geometry of the Livingstone Mountains Border Fault, Nyasa (Malawi) Rift, East Africa
Authors: Wheeler W. H. , Rosendahl B. R.
Published: February 2004

We use multifold seismic reflection profiles to constrain the geometry and slip sense of a half graben border fault and the extension direction in the adjacent rift basin. Our data are from the western branch of the East African Rift System, often cited as an analog of early‐stage passive continental margin formation. In this case study, classic tilt‐block half graben clearly occur along a documented strike‐slip fault. The Livingstone Mountains Border Fault bounds the northernmost basin in the Nyasa (Malawi) Rift and is a series of straight, dextral oblique‐slip fault segments which mimic the characteristics of a parallel, underlying, prerift ductile shear zone. Structures adjacent to the border fault show extension slightly oblique to the border fault, indicating that the border fault is predominantly a strike‐slip fault, consistent with studies of border fault exposures. Data indicate overall extension in the adjacent Livingstone Basin is at a much higher angle to the strike‐slip border fault, consistent with the tilt‐block half graben architecture. This characteristic is similar to basins bounded by “weak” strike‐slip faults. Some aspects of Livingstone Basin fault geometry resemble pull‐apart, strike‐slip duplex, and extensional imbricate fan fault geometries. However, the overall inexact match suggests the Livingstone Basin may be an incipient form of these classic strike‐slip basin models.
Strike‐slip faulting at Thebes Gap, Missouri and Illinois: Implications for New Madrid tectonism
Authors: Harrison Richard W. , Schultz Art
Published: February 2004

Numerous NNE and NE striking strike‐slip faults and associated normal faults, folds, and transtensional grabens occur in the Thebes Gap area of Missouri and Illinois. These structures developed along the northwestern margin of the buried Reelfoot rift of Precambrian‐Cambrian age at the northern edge of the Mississippi embayment. They have had a long‐lived and complex structural history. This is an area of recent moderate seismicity, approximately 45 km north of the New Madrid seismic zone. Stratigraphic evidence suggests that these faults were active during the Middle Ordovician. They were subsequently reactivated between the Early Devonian and Late Cretaceous, probably in response to both the Acadian and Ouachita orogenies. Deformation during this period was characterized by strongly faulted and folded Ordovician through Devonian rocks. In places, these deformed rocks are overlain with angular unconformity by undeformed Cretaceous strata. Fault motion is interpreted as dominantly strike slip. A still younger period of reactivation involved Late Cretaceous and Cenozoic formations as young as the Miocene or Pliocene Mounds Gravel. These formations have experienced both minor high‐angle normal faulting and subsequent major, right‐lateral strike‐slip faulting. En echelon north‐south folds, ENE striking normal faults, regional fracture patterns, and drag folds indicate the right‐lateral motion for this major episode of faulting which predates deposition of Quaternary loess. Several nondefinitive lines of evidence suggest Quaternary faulting. Similar fault orientations and kinematics, as well as recent seismicity and proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.
The evolution of alkaline groundwaters in the continental intercalaire aquifer of the Irhazer Plain, Niger
Authors: Andrews J. N. , Fontes J.‐C. , Aranyossy J.‐F. , Dodo A. , Edmunds W. M. , Joseph A. , Travi Y.
Published: February 2004

This paper discusses the hydrochemical evolution of groundwaters in the multilayer artesian aquifer of the Continental Intercalaire (the mainly Jurassic Agadez‐Dabla sandstones) aquifer of northern Niger. Isotopic and chemical changes in relation to the geological setting suggest that the increasing HCO3− alkalinity of the groundwaters is caused by interaction of deep CO2 with the aquifer matrix. Alteration of feldspars by CO2 with a δ13C value of −3.0‰ accounts for the observed alkalinity and isotopic and trends. Carbon 14 ages have been estimated for recent and Holocene groundwaters which have a distinct stable isotopic (2H and 18O) signature compared with 14C dead groundwaters from further west on the Irhazer Plain. Recharge temperatures, estimated by analysis of noble gas contents, show that the 14C dead waters were recharged under conditions cooler than present averages in the region, possibly at the beginning of deglaciation (≈16 ka B.P.) or during the period 23–30 ka B.P. Trends in the hydrochemistry of U are related to the deep CO2 alteration process. Radiogenic He contents increase along the flow direction and extremely high values occur in the proximity of U ores. Denitrification in the paleowaters of the Irhazer was assessed by measurements of nitrogen/argon ratios.
Nonmonotonic matric pressure histories during constant flux infiltration into homogeneous profiles
Authors: Stonestrom David A. , Akstin Katherine C.
Published: February 2004

Constant flux infiltration experiments were performed at rates less than saturated hydraulic conductivity (Ksat) on uniform columns of soils and glass beads with low initial water contents. Tensiometers measured matric pressure (ψ) histories at various depths in the 0.05‐m diameter, 0.73‐m‐tall columns. One of two devices applied the steady fluxes: one was a ceramic plate applicator that allowed monitoring of pressures above the plate, and the other was a rain applicator that sprinkled water uniformly over the surface. Two columns were used. One allowed destructive sampling for water content in a way that prevented postrun changes in water content. The other allowed prerun replacement of pore air with gases of different solubilities. Contrary to predictions based on the Richards equation, transmission zone ψ values passed through maxima, then decreased continuously as wetting fronts moved down columns. Such nonideal behavior was observed in Aiken silt loam, Hanfoird sandy loam, Delhi sand, Oakley sand, and glass beads. At an infiltration rate equal to 70% of Ksat, values of ψ at 2, 5, and 8 cm depths in the glass beads column decreased an average of 52% from their respective maxima in about 3 hours. In the soil columns the nonmonotonic behavior was less pronounced but statistically significant at all rates examined (3–59% of Ksat). Matric pressure reversals were larger, and corresponding maxima higher, when a given rate was preceded by a series of step wise increasing rates. Tests of possible explanations provided no evidence to support hypotheses involving trapped‐air dynamics, convective air flow, particle rearrangement, or experimental artifacts. The results cast doubt on the ability of the Richards equation to predict the course of constant flux infiltration including the initiation of runoff.
Minimum hydrochemical conditions allowing limestone cave development
Authors: Groves Christopher G. , Howard Alan D.
Published: February 2004

Early theoretical investigations into initiation of limestone cave development suggested that water entering small fractures approaches saturation within a short distance and thus appeared to be unable to produce much further enlargement of these fractures. The answer to this problem seems to be White's (1977) “kinetic trigger” idea, emphasizing the precipitous drop in dissolution rates as equilibrium is approached. However, minimum conditions of flow rate, passage geometry, and initial CO2 concentration may exist, below which the waters will so nearly achieve saturation that caves will be unable to develop. Modeling results indicate that under geologically reasonable PCO2 and head gradient values, the minimum initial aperture widths in which caves will develop is of the order of 100 μm. Initial apertures wider than about 500 μm will form passages very easily, even under low head gradients. There will thus be strong differential selection among initial flow paths with regard to cavern passage development.
Frequency domain analysis of time domain reflectometry waveforms: 1. Measurement of the complex dielectric permittivity of soils
Authors: Heimovaara T. J.
Published: February 2004

The S11 scatter function of a coaxial probe in the frequency domain is shown to be an accurate model for predicting waveforms of a seven‐wire coaxial probe in the time domain. Reproducibility of discrete Fourier analyses carried out on waveforms measured with the Tektronix 1502b cable tester (Tektronix, Incorporated, Beaverton, Oregon) indicated a frequency band width ranging from 20 kHz to approximately 1.5 GHz. The frequency dependent complex dielectric permittivity can be calculated from measured waveforms by inverting the S11 scatter function. Results indicate that a seven‐wire coaxial probe, connected to a 1‐m RG214 coaxial cable, emulates a coaxial tube for frequencies up to 150 MHz. Application of the frequency domain model to time domain reflectometry waveforms shows that the apparent dielectric permittivity calculated from the travel time in the probe is very dependent on the relaxation frequency of the material in which the probe is embedded. For materials with low relaxation frequencies the apparent dielectric permittivity is much lower than the static permittivity. Inversion of the frequency domain model allows for solving the frequency dependent complex dielectric permittivity of soils from measured waveforms.
Surface energy balance estimates at local and regional scales using optical remote sensing from an aircraft platform and atmospheric data collected over semiarid rangelands
Authors: Kustas W. P. , Moran M. S. , Humes K. S. , Stannard D. I. , Pinter P. J. , Hipps L. E. , Swiatek E. , Goodrich D. C.
Published: February 2004

Remotely sensed data in the visible, near‐infrared, and thermal‐infrared wave bands were collected from a low‐flying aircraft during the Monsoon '90 field experiment. Monsoon '90 was a multidisciplinary experiment conducted in a semiarid watershed. It had as one of its objectives the quantification of hydrometeorological fluxes during the “monsoon” or wet season. The remote sensing observations along with micrometeprological and atmospheric boundary layer (ABL) data were used to compute the surface energy balance over a range of spatial scales. The procedure involved averaging multiple pixels along transects flown over the meteorological and flux (METFLUX) stations. Average values of the spectral reflectance and thermal‐infrared temperatures were computed for pixels of order 10−1 to 101 km in length and were used with atmospheric data for evaluating net radiation (Rn), soil heat flux (G), and sensible (H) and latent (LE) heat fluxes at these same length scales. The model employs a single‐layer resistance approach for estimating H that requires wind speed and air temperature in the ABL and a remotely sensed surface temperature. The values of Rn and G are estimated from remote sensing information together with near‐surface observations of air temperature, relative humidity, and solar radiation. Finally, LE is solved as the residual term in the surface energy balance equation. Model calculations were compared to measurements from the METFLUX network for three days having different environmental conditions. Average percent differences for the three days between model and the METFLUX estimates of the local fluxes were about 5% for Rn, 20% for G and H, and 15% for LE. Larger differences occurred during partly cloudy conditions because of errors in interpreting the remote sensing data and the higher spatial and temporal variation in the energy fluxes. Minor variations in modeled energy fluxes were observed when the pixel size representing the remote sensing inputs changed from 0.2 to 2 km. Regional scale estimates of the surface energy balance using bulk ABL properties for the model parameters and input variables and the 10‐km pixel data differed from the METFLUX network averages by about 4% for Rn, 10% for G and H, and 15% for LE. Model sensitivity in calculating the turbulent fluxes H and LE to possible variations in key model parameters (i.e., the roughness lengths for heat and momentum) was found to be fairly significant. Therefore the reliability of the methods for estimating key model parameters and potential errors needs further testing over different ecosystems and environmental conditions.
Basin‐scale solar irradiance estimates in semiarid regions using GOES 7
Authors: Pinker R. T. , Kustas W. P. , Laszlo I. , Moran M. S. , Huete A. R.
Published: February 2004

Semiarid regions exhibit large temporal and spatial variability in surface conditions and, therefore, pose a challenge for estimating components of the surface energy budget. In particular, it is difficult to estimate the evapotranspiration component of the hydrological cycle. Because evapotranspiration is strongly controlled by absorbed solar radiation, an attempt has been made here to evaluate the accuracy at which the downward shortwave irradiance (SW ↓) can be estimated from satellites on basin scale. It was demonstrated that even under highly variable cloud conditions, satellite estimates of SW ↓ daily means were within 10% of measured values, while 5‐day means were within 3% of measured values. Such accuracies are of relevance for hydrological modeling at watershed and basin scales.
Comparison of laser and field measurements of vegetation height and canopy cover
Authors: Weltz Mark A. , Ritchie Jerry C. , Fox H. Dale
Published: February 2004

Distribution of vegetation properties is fundamental for understanding vegetation patterns and characteristics, improving estimates of infiltration, evapotranspiration, and soil erosion. A laser altimeter mounted in a small airplane was used to measure surface patterns of the landscape on the U.S. Department of Agriculture's Agricultural Research Service Walnut Gulch experimental watershed near Tombstone, Arizona. The airborne laser altimeter is a pulsed gallium‐arsenide diode laser, transmitting and receiving 4000 pulses per second at a wavelength of 0.904 μm. The laser has a 1‐mrad field of view and is designed to have a vertical recording precision of 0.05 m on a single measurement. Aircraft altitude varied between 100 and 300 m for the flights. Digital data from the laser were collected with a portable computer and analyzed to provide information on changes in vegetation height, spatial patterns, and patchiness of vegetation cover. The laser‐measured vegetation properties of plant height and canopy cover (>0.3 m) were not significantly different than field measurements made using the line‐intercept transect method at seven of the eight sites evaluated. Although the laser measurements of canopy height were not significantly different from the ground measurements, the laser consistently overestimated canopy cover less than 0.3 m in height and underestimated canopy cover greater than 0.5 m. New techniques to discriminate the background noise in the laser return signal in sparsely populated shrub communities are necessary before this technique will be fully useful in estimating canopy cover on rangelands. These studies indicate the potential of airborne laser to measure vegetation patterns quickly and quantitatively. The laser also has the ability to separate and map distinctly different plant communities.
Interactions between regional surface fluxes and the atmospheric boundary layer over a heterogeneous watershed
Authors: Hipps Lawrence E. , Swiatek Edward , Kustas William P.
Published: February 2004

The interactions between surface fluxes of sensible and latent heat and the properties of the atmospheric boundary layer (ABL) were studied for the Walnut Gulch watershed. The properties of the ABL were estimated from radiosonde measurements. Application of integrated simplified conservation equations resulted in estimates of regional fluxes that were greatly different from surface values, and often had the wrong sign. A simple modification was made to the equations, based upon the temporal changes in temperature and humidity above the ABL, assuming that such changes resulted from horizontal advection. Subsidence was assumed to be insignificant. Application of the new integrated conservation equations resulted in a dramatic improvement in the regional flux estimates. Such estimates were reasonably close to the surface measurements. Spatial variations in surface energy balance which resulted from the convective rain events affected only the properties of the lower 15 m of the atmosphere. The length scale of variations in surface moisture of about 10 km was not sufficient to affect the regional scale processes.
A model for real‐time quantitative rainfall forecasting using remote sensing: 2. Case studies
Authors: French Mark N. , Andrieu Hervé , Krajewski Witold F.
Published: February 2004

The performance of a real‐time physically based rainfall forecasting model is examined using radar, satellite, and ground station data for a region of Oklahoma. Model formulation is described in an accompanying paper (French and Krajewski, this issue). Spatially distributed radar reflectivity observations are coupled with model physics and uncertainty analysis through (1) linearization of model dynamics and (2) a Kalman filter formulation. Operationally available remote sensing observations from radar and satellite, and surface meteorologic stations define boundary conditions of the two‐dimensional rainfall model. The spatially distributed rainfall is represented by a two‐dimensional field of cloud columns, and model physics define the evolution of vertically integrated liquid water content (the model state) in space and time. Rainfall forecasts are evaluated using least squares criteria such as mean error of forecasted rainfall intensity, root mean square error of forecasted rainfall intensity, and correlation coefficient between spatially distributed forecasted and observed rainfall rates. The model performs well compared with two alternative real‐time forecasting strategies: persistence and advection forecasting.
Estimation of mountain front recharge to regional aquifers: 1. Development of an Analytical Hydroclimatic Model
Authors: Chavez Adolfo , Davis Stanley N. , Sorooshian Soroosh
Published: February 2004

This paper addresses the hydroclimatic modeling of mountain front recharge to regional aquifers. An analytical relationship between the mean seasonal precipitation and runoff is obtained based on a conceptualization of the hydrologic processes occurring in hard rock mountainous terrain and a derived‐distribution approach where the input variables are considered to be stochastic and their probability distributions are transformed into the probability distribution of the output variable by using the deterministic physical process. In a first‐order approximation a relationship between the seasonal values of precipitation and runoff is obtained. An analytical model of the seasonal streamflow is then developed where initial abstraction and the long‐term effective subsurface outflow, or mountain front recharge, are viewed as unknown model parameters. In addition, a procedure that combines the water balance equation with a relationship provided by the so‐called “vegetal equilibrium hypothesis,” and which enables the estimation of effective soil‐related parameters jointly with the mean seasonal evapotranspiration and surface runoff, is introduced. This procedure is applied to a mountainous watershed in southern Arizona.
Channel routing independent of length subdivision
Authors: Diskin Mordechai H. , Ding Yan
Published: February 2004

Flood routing in a given reach of a prismatic channel is the process of deriving the downstream outflow hydrograph from a known inflow hydrograph at the upstream end of the channel reach. The process can be carried out by solving the basic St.‐Venant (S‐V) equation numerically or by using a lumped model, also called a hydrologic or black‐box model, which requires calibration with observed data. The model should also be capable of reproducing the flow hydrograph at one or more intermediate points along the channel reach. This requires that at least one of the model parameters be proportional to the length of the channel reach. Another desired property of the routing model is that the outflow hydrograph produced at the downstream end of a channel reach be the same when the model is applied to the entire reach, as one unit, or when the model is applied to a number of sections or subdivisions of the channel reach in series, using the outflow of one section as inflow to the next section. The resulting outflow hydrograph at the downstream end of the reach should thus be independent of the number or lengths of the subdivisions. The above desired properties of the routing model impose certain conditions on the model or, if the model is linear, on its impulse response function (IRF). The conditions are derived in this paper and applied to two models: the linear channel model and the diffusion analogy model.
Dissolved and colloidal contaminant transport in a partially clogged fracture
Authors: Kessler John H. , Hunt James R.
Published: February 2004

A water‐saturated fracture, partially clogged with porous material coating the fracture surfaces, is considered. Fluid flow and contaminant transport in this fracture are significantly altered relative to an unclogged fracture. Analytical expressions are developed for the water velocities in the clogged and the unclogged regions in the fracture and the asymptotic longitudinal dispersion coefficient for the system. For highly adsorbing dissolved contaminants or large colloids, the slow diffusion within the porous region causes enhanced dispersion. In a standard tracer test, colloidal contaminants will arrive earlier than dissolved tracers for either one of two reasons: (1) colloids confined to the unclogged portion of the fracture will have a larger average velocity or (2) colloids that can diffuse into the porous region have very low Brownian dififusivities, resulting in a large longitudinal dispersion due to the inverse relationship between Taylor dispersion and Brownian diffusion. The average velocity or asymptotic longitudinal dispersion coefficient can be orders of magnitude greater than that for a molecular tracer.
Stratospheric contribution to the global bomb radiocarbon inventory: Model versus observation
Authors: Broecker Wallace S. , Peng Tsung‐Hung
Published: February 2004

An attempt is made, through modeling, to account for the decline in the 14C/C ratio in atmospheric CO2 after its bomb‐test‐induced peak in 1963. The model suggests that as of 1964 about one third of the bomb 14C remained in the stratosphere and that it was released to the troposphere with an e‐folding time of about seven years. By contrast, measurements carried out in the stratosphere suggest that at that time the excess was closer to one quarter of the total and that the e‐folding time for its decline was 3±1 years. The anomaly between model and observation cannot be attributed solely to an inadequacy in the representation of the terrestrial biosphere. Rather, it must reflect either an inadequacy in the ocean model or in the measured stratospheric inventories.
CARAIB: A global model of terrestrial biological productivity
Authors: Warnant P. , François L. , Strivay D. , Gérard J.‐C.
Published: February 2004

CARAIB, a mechanistic model of carbon assimilation in the biosphere estimates the net primary productivity (NPP) of the continental vegetation on a grid of 1° × 1° in latitude and longitude. The model considers the annual and diurnal cycles. It is based on the coupling of the three following submodels; a leaf assimilation model including estimates of stomatal conductance and leaf respiration, a canopy model describing principally the radiative transfer through the foliage, and a wood respiration model. Present‐day climate and vegetation characteristics allow the discrimination between ecotypes. In particular, specific information on vegetation distribution and properties is successfully used at four levels; the leaf physiological level, the plant level, the ecosystem level, and the global level. The productivity determined by the CARAIB model is compared with local measurements and empirical estimates showing a good agreement with a global value of 65 Gt C yr−1. The sensitivity of the model to the diurnal cycle and to the abundance of C4 species is also tested. The productivity slightly decreases (10%) when the diurnal cycle of the temperature is neglected. By contrast, neglecting the diurnal cycle of solar irradiance produces unrealistically high values of NPP. Even if the importance of this increase would presumably be reduced by the coupling of CARAIB with a nutrient cycle model, this test emphasizes the key role of the diurnal cycle in a mechanistic model of the NPP. Uncertainties on the abundance and spatial distribution of C4 plants may cause errors in the NPP estimates, however, as demonstrated by two sensitivity tests, these errors are certainly lower than 10% at the global scale as shown by two tests.
Limiting future atmospheric carbon dioxide
Authors: Sarmiento Jorge L. , Le Quéré Corinne , Pacala Stephen W.
Published: February 2004

We estimate anthropogenic carbon emissions required to stabilize future atmospheric CO2 at various levels ranging from 350 ppm to 750 ppm. Over the next three centuries, uptake by the ocean and terrestrial biosphere would permit emissions to be 3 to 6 times greater than the total atmospheric increase, with each of them contributing approximately equal amounts. Owing to the nonlinear dependence of oceanic and terrestrial biospheric uptake on CO2 concentration, the uptake by these two sinks decreases substantially at higher atmospheric CO2 levels. The uptake also decreases with increased atmospheric CO2 growth rate. All the stabilization scenarios require a substantial future reduction in emissions.
Spatial and temporal distribution of tropical biomass burning
Authors: Hao Wei Min , Liu Mei‐Huey
Published: February 2004

A database for the spatial and temporal distribution of the amount of biomass burned in tropical America, Africa, and Asia during the late 1970s is presented with a resolution of 5° latitude × 5° longitude. The sources of burning in each grid cell have been quantified. Savanna fires, shifting cultivation, deforestation, fuel wood use, and burning of agricultural residues contribute about 50, 24, 10, 11, and 5%, respectively, of total biomass burned in the tropics. Savanna fires dominate in tropical Africa, and forest fires dominate in tropical Asia. A similar amount of biomass is burned from forest and savanna fires in tropical America. The distribution of biomass burned monthly during the dry season has been derived for each grid cell using the seasonal cycles of surface ozone concentrations. Land use changes during the last decade could have a profound impact on the amount of biomass burned and the amount of trace gases and aerosol particles emitted.
Uncertainties in future CO2 projections
Authors: Craig S. G. , Holmén K. J.
Published: February 2004

The perceived budget imbalance in the global carbon cycle has been suggested to result from, among other processes, CO2 fertilization of the terrestrial biosphere and/or enhanced regrowth of previously felled temperate forest. These two processes are incorporated into a box diffusion model of the ocean‐atmosphere system coupled to a five‐box terrestrial biosphere. The extent to which historical fossil fuel and land use change emission data can be reconciled with the observed atmospheric CO2 concentration record is examined. Furthermore, the sensitivity of future CO2 projections to the nature of the budget imbalance is investigated. It is found that the CO2 record can accommodate a carbon budget balanced by CO2 fertilization but that the balance with forest regrowth is more difficult. Future CO2 projections are found to be sensitive to how the carbon budget is balanced, even relative to uncertainties in future emissions.
An overview of the EASOE Campaign
Authors: Pyle J. A. , Harris N. R. P. , Farman J. C. , Arnold F. , Braathen G. , Cox R. A. , Faucon P. , Jones R. L. , Megie G. , O'Neill A. , Platt U. , Pommereau J. ‐P. , Schmidt U. , Stordal F.
Published: February 2004

The scientific planning of the EASOE campaign is outlined and the various constituent and meteorological data sets are described.
Rare earth element concentrations and speciation in alkaline lakes from the western U.S.A.
Authors: Johannesson Kevin H. , Lyons W. Berry , Bird David A.
Published: February 2004

The rare earth element (REE) concentrations of lake water from five alkaline lakes (i.e., Mono, Walker, Abert, Summer, and Goose Lakes) within the Great Basin of the western U.S.A. are reported. All of the lakes exhibit HREE‐enriched shale‐normalized patterns. The speciation of the REEs was determined and, in all cases, species greater than 99% of each of the REEs exist as Ln(CO3)2‐ complexes. The only exception to this is Summer Lake where minor amounts of phosphate species were also predicted. The large enrichments in the HREEs observed in these lakes are the result of the formation of stable carbonate complexes in solution where the HREEs preferentially form stronger carbonate complexes than the LREEs. Activity product calculations for REE phosphate coprecipitates in these lakes indicate the lakes are close to saturation with respect to these phases and suggest that these precipitates may limit the maximum dissolved REE concentrations in the lakes.
Production of volatile organohalogens by phytoplankton cultures
Authors: Tokarczyk Ryszard , Moore Robert M.
Published: February 2004

Natural volatile halocarbons are important as carriers of reactive halogens to the troposphere and, in the case of the more stable compounds, to the stratosphere. Bromoform (CHBr3) has been of particular interest as a potential source of bromine which might account for sudden ozone depletion events in the Arctic boundary layer. The oceans have been shown to be major contributors of volatile halocarbons to the atmosphere, but the sources of halocarbons within them have been unknown except for macrophytic algae which are normally confined to the coastal zone. Here we report experiments that demonstrate that certain unialgal cultures of marine phytoplankton produce a suite of halocarbons (CHBr3, CHBr2Cl, CH2Br2). The production rate of each of these halocarbons is dependent on both species and growth stage. Chloroiodomethane which also appeared in the cultures could be attributable to photochemical production from a precursor (CH2I2). Great caution should be shown in extrapolating the rates estimated from these controlled experiments to the marine environment.
Energy parameters of precipitating auroral electrons obtained by using photometric observations
Authors: Ono Takayuki , Morishima Kei
Published: February 2004

An average energy and a total energy flux are estimated for active discrete auroras by using the intensity ratios of auroral emissions. They were obtained by using a multi‐channel photometer which has a narrow field of view directed to the magnetic zenith of Syowa Station, Antarctica in 1990. For the evaluation of the energy parameters, we used an intensity ratio of measured auroral emission line and band such as 844.6 nm (OI) and 670.5 nm (N2 1PG) comparing with the results of model calculations. Data analysis for active discrete auroras associated with auroral break‐up and a westward traveling surge events showed that there is rapid change of the average energy as well as the total energy flux of the precipitating auroral electrons associated with discrete arcs. A relationship between the average energy and the total energy flux of electrons showed that there is a significant consistency with the “ohmic relation” predicted for a field aligned acceleration of precipitating electrons due to the electric potential difference along the magnetic field line.
Abnormal Lg coda Q in Beijing Area
Authors: Chun Kin‐Yip , Liu J. , Zhu T. , Shih X. R.
Published: February 2004

This paper presents the results of an Lg coda Q study in the Beijing area of China. The data originate from the Beijing Telemetered Network; the Q (=Q0ƒη) measurement technique is the stacked spectral ratio method (SSR). The study area, roughly 250 km in radius, is sampled repeatedly by scattered coda waves recorded at epicentral distances between 190 and 422 km. The results point to 1‐Hz Q (Q0) as low as 150 and η as high as 0.95, in a jarring incongruity with the ambient attenuation characteristics about the study region. The Lg coda Q0 is found varying inversely with η. The unequivocality with which such a relationship becomes unravelled comes about somewhat unexpectedly given the small spatial confine of the study area. If high coda attenuation (low Q0) and high η are taken to correlate with a high level of tectonic activity in a broad sense, a view generally held to be statistically accurate, then the Beijing area belongs to the same league in Eurasia, whose members include such well known “earthquake countries” as the Himalayas, the Tibetan Plateau, the Burmese Arc, and the Tianshan Mountains.
Sensitivity of the ice‐divide position in Greenland to climate change
Authors: Anandakrishnan S. , Alley R. B. , Waddington E. D.
Published: February 2004

Model calculations of depth‐age relations for deep ice cores in central Greenland are sensitive to stability of the ice‐divide position. In addition, the folding of layers observed in the deep ice could be instigated by divide migration changing the velocity and particle paths of ice flow. We use simple steady‐state calculations to show that lateral divide migration of between 10 km and 50 km and elevation change of approximately 100 m is likely on glacial‐interglacial time scales, enough to affect model dating. The ice‐divide location appears to be most sensitive to the position of the ice‐sheet margins. By contrast, the ice‐divide elevation is most sensitive to the accumulation rate, the temperature profile, and the ice‐stiffness profile.
Solution of the Chapman‐Ferraro problem with an arbitrary magnetopause
Authors: Toffoletto F. R. , Hilmer R. V. , Hill T. W. , Voigt G.‐H.
Published: February 2004

We present a global model of the magnetic field of the magnetosphere that includes the effects of the Chapman‐Ferraro currents at the magnetopause. In contrast to earlier models, the magnetopause shape is arbitrary, thus allowing the use of more realistic geometries. The internal magnetospheric field model of Hilmer and Voigt [1993], is completely shielded within the magnetopause by solving the Laplace equation with Neumann boundary conditions using a finite difference method on a non‐orthogonal, curvilinear grid. The resulting model magnetosphere is perfectly closed although the method can also be applied with more general boundary conditions, to generate a set of open models based on the approach of Toffoletto and Hill [1989, 1993]. The purpose of this paper is to demonstrate the feasibility of a purely numerical approach to solving the Chapman‐Ferraro problem with arbitrary magnetopause shape and boundary conditions.
The North Sea pole tide described through a tide‐surge numerical model
Authors: Tsimplis M. N. , Flather R. A. , Vassie J. M.
Published: February 2004

Monthly mean sea level values from tide gauges at the coasts of the North Sea are compared with the monthly means from an operational tide‐surge numerical model for the time period 1955–1984. The model describes most of the variability at all frequencies except the annual. Most of the energy around the pole tide frequency is also reproduced by the model and since its tidal forcing does not include the equilibrium pole tide frequencies it is concluded that the deviations from the equilibrium pole tide are of meteorological origin. The east‐west wind stress component is found to be energetic at this frequency thus providing the meteorological forcing. The annual cycle due to steric effects is also estimated. The meteorological correction modifies the determined sea‐level secular trends by up to 0.8mm/yr for this 30 year period for stations in the eastern North Sea.
An inquiry into the cirrus‐cloud thermostat effect for tropical sea surface temperature
Authors: Lau K.‐M. , Sui C.‐H. , Chou M. ‐D. , Tao W.‐K.
Published: February 2004

In this paper, we investigate the relative importance of local vs remote control on cloud radiative forcing using a cumulus ensemble model. It is found that cloud and surface radiation forcings are much more sensitive to the mean vertical motion associated with large scale tropical circulation than to the local SST. When the local SST is increased with the mean vertical motion held constant, increased surface latent and sensible heat flux associated with enhanced moisture recycling is found to be the primary mechanism for cooling the ocean surface. Large changes in surface shortwave fluxes are related to changes in cloudiness induced by changes in the large scale circulation. These results are consistent with a number of earlier empirical studies, which raised concerns regarding the validity of the cirrus‐thermostat hypothesis (Ramanathan and Collins, 1991). It is argued that for a better understanding of cloud feedback, both local and remote controls need to be considered and that a cumulus ensemble model is a powerful tool that should be explored for such purpose.
Southern hemisphere mid‐latitude seasonal cycle in total column nitric acid
Authors: Jones N. B. , Koike M , Matthews W. A. , McNamara B. M.
Published: February 2004

Total column ground based HNO3 measurements were made at Lauder, New Zealand (45.0°S, 169.7°E). Approximately 760 infra‐red spectra were recorded over the period from October 1990 to October of 1993. Two micro‐windows, near 870 cm−1, were analyzed using a non‐linear least squares spectral fitting technique. A seasonal cycle has been established with an amplitude of 27%, a minimum in February, and an annual mean of 1.2 × 1016 molecules cm−2. The seasonal phase, amplitude and absolute amounts of HNO3 were found to be consistent with similar high resolution studies from Northern Hemisphere sites and with satellite measurements. Sensitivity tests indicated that the retrieved column in the stratosphere is generally insensitive to the temperature and assumed HNO3 vertical profile.
Dynamic topography compared with residual depth anomalies in oceans and implications for age‐depth curves
Authors: Kido Motoyuki , Seno Tetsuzo
Published: February 2004

Ocean depth is affected by dynamic topography caused by mantle flow. Regional bathymetric deviations from the cooling plate age‐depth curve, called residual depth anomalies, can therefore be used as indicators of dynamic topography in oceans. In this work, we first evaluated the oceanic residual depth anomalies. We then compute the dynamic topography for the flow induced by density perturbations converted from seismic tomography models by assuming δρ∝δν. We found that the predicted dynamic topography correlates with the depth anomalies when the density perturbations in the shallow part of the upper mantle were inferred from slab densities, not from tomographic models. We estimated a new age‐depth curve based on depths corrected for dynamic topography. This corrected age‐depth curve shows that the corrected depths for old seafloor (70∼110 Ma) are a few hundred meters deeper than those uncorrected.
Freja observations of narrow inverted‐V electron precipitation by the Two‐Dimensional Electron Spectrometer
Authors: Boehm M. H. , Paschmann G. , Clemmons J. , Haerendel G. , Eliasson L. , Lundin R.
Published: February 2004

Observations of several steady, ∼1–5 km scale inverted‐V's by the Freja F7 Two‐dimensional Electron Spectrometer (TESP) are described. Such narrow structures are not common, but provide an opportunity for observing edge precipitation and the movement of arcs through the plasma. Velocities of inverted‐V potential structures in the plasma frame can be derived from the observed time delay between precipitating and mirrored electrons. These velocities determine whether horizontal plasma flow into a potential structure can provide the source population for arc edge precipitation. It is found that the intensity of the arc edge precipitation is not associated in any expected way with this velocity, indicating another source of plasma for arc edge precipitation is required.
Ozone and nitrogen dioxide vertical distributions by UV‐visible solar occultation from balloons
Authors: Pommereau Jean‐Pierre , Piquard Jacques
Published: February 2004

A light and easily handled balloon‐borne uv‐visible spectrometer was designed for investigating ozone photochemistry in the Arctic winter. The optical sonde was flown 10 times during the EASOE campaign at Kiruna in Northern Sweden from November 1991 until March 1992. The flights gave the first simultaneous measurements of the vertical distributions of ozone and nitrogen dioxide in the Arctic winter.
Discrimination of hydrothermal mound structures using transient electromagnetic methods
Authors: Evans Rob L. , Everett Mark E.
Published: February 2004

We present numerical modeling results to support the use of seafloor transient electromagnetic (EM) techniques in characterizing the buried component of active hydrothermal mounds. We construct 2‐D electrical models of a volcanic‐hosted sulphide mound and compute the EM fields created by a transient electric dipole source deployed on the seafloor. The time it takes for fields to diffuse between the source and receivers is diagnostic of the intervening electrical conductivity. In the case considered, the highly conductive, outcropping sulphide mound is essentially invisible to the EM probe, exposing the moderately conducting alteration and upflow zone below. Transient EM responses are measurably different for the model featuring concentrated upflow compared to the model containing a spatially broad fluid supply beneath the mound.
Yellowstone: A continental midplate (hot spot) swell
Authors: Waschbusch P. J. , McNutt M. K.
Published: February 2004

The Yellowstone hot spot has been identified mainly by its track of age‐progressive volcanics; many smaller scale tectonic features serve to hide the long‐wavelength hot spot‐related swell. By employing averaging and filtering techniques, we are able to identify a swell in both the gravity and topography and use them to constrain the apparent depth of compensation of the Yellowstone hot spot at 70±10 km. This value is comparable to the deepest compensation depths for swells on old oceanic lithosphere. A compensation depth within the mid‐ to lower lithosphere combined with the only 15 m.y. known duration of the hot spot suggests either dynamic thinning of the thermal plate or compensation by upwelling in a low‐viscosity asthenosphere, with some combination of the two explanations being consistent with seismic tomography results. Thus in many ways the Yellowstone hot spot appears quite similar to the oceanic analogues.
A possible influence of recent polar stratospheric coolings on the troposphere in the northern hemisphere winter
Authors: Kodera Kunihiko , Yamazaki Koji
Published: February 2004

A possible influence of the recent cooling trends in the polar stratosphere on the tropospheric circulation in the Northern Hemisphere winter is studied over the period from 1979 to 1992. Changes in circulation associated with cooling trends in the stratosphere are compared with those triggered by heating due to volcanic aerosols in the stratosphere, which are considered as a prototype of the atmospheric responses to an external forcing. In both cases, strengthening of the stratospheric polar night jets are observed in early winter and perturbations in zonal‐mean zonal winds propagate down into the troposphere by forming dipole type anomalies which are associated with changes in planetary waves.
New sources for the hot oxygen geocorona
Authors: Richards P. G. , Hickey M. P. , Torr D. G.
Published: February 2004

This paper investigates new sources of thermospheric non thermal (hot) oxygen due to exothermic reactions involving numerous minor (ion and neutral) and metastable species. Numerical calculations are performed for low latitude, daytime, winter conditions, with moderately high solar activity and low magnetic activity. Under these conditions we find that the quenching of metastable species are a significant source of hot oxygen, with kinetic energy production rates a factor of ten higher than those due to previously considered O2+ and NO+ dissociative recombination reactions. Some of the most significant new sources of hot oxygen are reactions involving quenching of O+(²D), O(¹D), N(²D), O+(²P) and vibrationally excited N2 by atomic oxygen.
Wave environment inside an inverted‐V electron event observed by Freja
Authors: Stasiewicz K. , Gustafsson G. , Holmgren G. , Holback B. , Eliasson L. , Kintner P. M. , Zanetti L.
Published: February 2004

We present an analysis of the wave environment observed inside an inverted‐V electron event at an altitude of 1700 km, occurring in the upward directed current with intensity of a few µAm−2. During the analyzed event we observe that precipitating auroral electrons (∼ 2 keV) generate intense (40 mV/m) auroral hiss with peak power concentrated at the lower hybrid frequency flh ≈ fpi, and weak Langmuir waves at fpe. The low frequency turbulence observed within the event is found to be composed of a mixture of Alfvén waves, O+ cyclotron waves, multi‐ion resonances, and ion sound waves. The LH waves appear to interact modulationally with O+ and ion sound waves. From the observed values of flh and multi‐ion resonance frequencies it is possible to estimate three‐ion composition of plasma with representative values of [23, 19, 58] percent for normalized number densities of [H+, He+, O+], respectively.
UV‐B in Germany higher in 1993 than in 1992
Authors: Seckmeyer G. , Mayer B. , Erb R. , Bernhard G.
Published: February 2004

A comparison of spectral UV measurements between 1992 and 1993 showed increased levels of UV‐B radiation in late spring and early summer of 1993 caused by reduced total ozone columns. The monthly averaged total ozone columns in 1993 were the lowest since ozone was systematically recorded in Southern Germany. The data also show that UV‐A radiation was lower in 1993 than in 1992, due to differences in cloudiness between the two years. Our data demonstrate the impact of clouds and aerosols on UV‐B irradiances which must be considered in addition to stratospheric ozone change when interpreting changes in UV‐B irradiances.