bluuebunny/crossref_metadata_2025 huggingface dataset:
A Proposed Geological Parameterization Method for Parameter Identification in Three‐Dimensional Groundwater Modeling
Authors: Sun Ne‐Zheng , Jeng Ming‐Chin , Yeh William W. ‐G.
Published: February 2004

A new parameterization method for parameter identification is presented. This method allows us to incorporate all well log data and any other geological information into the inverse solution procedure for three‐dimensional groundwater modeling. In the proposed method, unknown parameters, such as hydraulic conductivity and storage coefficient, are directly related to the geological materials. Existing well logs of an aquifer can provide information of local geological structures along the vertical direction. By using these data, as well as any other geological information available, the three‐dimensional structure of the aquifer can be estimated by means of the geostatistical method. Then, art inverse problem can be formulated, leaving fewer unknown parameters to be identified. The advantages of the proposed method are the following: (1) all existing geological and hydrogeological information available is used for parameter identification, (2) the identified parameters are independent of the complexity of the simulation model, (3( the ill‐posedness of the inverse solution is mitigated, and (4) the identified parameters are distributed and physically meaningful. In a hypothetical example, the three‐dimensional distribution of hydraulic conductivity is easily identified using the proposed method. The results indicate that the identified distributed parameter vector is very close to the “true” distribution, and the inverse solution is highly stable with respect to observation errors. The proposed methodology has enabled us to determine the three‐dimensional distribution of hydraulic conductivity and storativity in the Hemet basin, Riverside, California.
The (Least Squares) Quotient Algorithm as a Rapid Tool For Obtaining Sorption Isotherms From Column Elution Curves
Authors: van Veldhuizen M. , Appelo C. A. J. , Griffioen J.
Published: February 2004

Sorption isotherms are essential for describing transport of solutes in groundwater, and may be obtained in column experiments. In this paper a novel algorithm for the numerical computation of the sorption isotherm from the measured data is presented. The algorithm, which is quite different from classical minimization algorithms like the Marquardt process, uses the relative arrival times of dissolved components with a different sorption behavior. It has a large domain of attraction, and it is also rather inexpensive computationally. It is most effective as a preprocessor for a classical minimization process. The applicability of the algorithm is demonstrated on elution curves of K+, displaced by Ca++ in a cation exchange reaction. The speed of the algorithm allows for the use of the bootstrap method for obtaining confidence domains for different sorption sites with different exchange constants.
Downstream Fining in a Network of Gravel‐Bedded Rivers
Authors: Pizzuto James E.
Published: February 2004

A network‐based routing model is used to determine how spatial variations in sediment supply influence rates of downstream fining in a small watershed in central Pennsylvania. Gravel of a specified size distribution and lithology is supplied to the network at zero‐order basins. Once in transport, the total sample weight and moments of the grain‐size distribution are modified according to empirical functions of transport distance. Contributions from each zero‐order basin are summed to determine the total population of sizes and lithologies at any location. In the study area, resistant quartz sandstone ridges supply sediment an order of magnitude larger than other lithologies. Because these ridges occur primarily in the basin headwaters, spatial variations in supply strongly influence rates of downstream fining. Model calculations indicate that spatial variations in supply alone account for over 80% of the decrease in mean grain size along the main channel.
An Analytical Solution for the Lateral Transport of Dissolved Chemicals in Overland Flow
Authors: Rivlin (Byk) Judith , Wallach Rony
Published: February 2004

The role of overland flow dynamics on the dissolved chemical transport toward an outlet is studied herein using the solutions of the mass conservation equations for overland flow and transport. Some simplifying conditions are considered, to develop an analytical solution for both equations. The rainfall rate ƒ, the infiltration rate i ,the mass transfer coefficient k, and the soil surface concentration cs are assumed constant. The solution, which is analytical, is based on the characteristics method for the two main stages of overland flow, namely, the rising and falling stages. The first stage occurs from ponding time to the time when rainfall ceases, at which point the second stage begins. During the second stage the slope drains, and overland flow depth gradually becomes zero. Although the initial water depth for the kinematic wave equation, h0, could be chosen arbitrarily, its combination with the solute equation induces that h0 should be greater than zero, since a singularity is obtained for h0 = 0. Therefore the solution for the overland flow is developed for a general constant initial water depth, but in order to meet real initial conditions, h0 is chosen to be very small. As an initial condition for the solute equation,c(x, 0) = cs is taken. This is based on the postulation that some mixing occurs with the impact of the raindrops during the first stage of water depth buildup. The initial condition also implies that k → ∞ which, according to the convective mass transfer theory, is obtained for h → 0. An analytical solution is obtained by the characteristics method. As a result, different solutions are obtained for each subzone that composes the domain. In one subzone that belongs to the falling stage, the characteristic curve is solved by Euler's method. The concentration hydrograph decreases rapidly during the rising stage of overland flow to a constant value. During the falling stage of overland flow the concentration hydrograph increases gradually to a value larger than cs, which depends on the ratio k/(k − i). Therefore at the time of ponding and during the final period of overland flow recession, the assumption of constant k is not valid, and, although mathematically correct, physically erroneous results are obtained.
Hydrodynamics of the Capture Zone of a Partially Penetrating Well in a Confined Aquifer
Authors: Faybishenko Boris A. , Javandel Iraj , Witherspoon Paul A.
Published: February 2004

In the pump and treat approach to the problem of managing a contaminated aquifer, a key problem is to design an effective capture system that collects only the polluted groundwater without allowing any of it to escape. At present, it is customary to design a capture system using fully penetrating withdrawal wells. Very often, however, only part of the vertical thickness of the aquifer is contaminated, so the question may arise whether a more efficient capture system can be achieved using partially penetrating wells. Very little work has been done on the application of partially penetrating wells to this problem. A new semianalytic method that can be used in determining the geometry of the capture zone for steady state flow to a partially penetrating well that is screened from the top (or from the bottom) of a confined aquifer has been developed. By combining the velocity potentials for flow to the well with that for the regional flow field, a three‐dimensional velocity potential that can be used in determining the complete geometry of the capture surface has been developed. The results have shown that with a constant pumping rate the maximum horizontal extent of the capture surface at the top (or bottom) of the aquifer increases as the degree of penetration decreases. As one would expect, the maximum vertical extent increases as the depth of penetration increases. Thus, if one knows the actual location of the contaminant plume, an appropriate combination of the degree of penetration and pumping rate can be selected to create an effective capture zone.
Testing Transferability of Recreation Demand Models Across Regions: A Study of Corps of Engineer Reservoirs
Authors: Loomis John , Roach Brian , Ward Frank , Ready Richard
Published: February 2004

This research tests the interchangeability of two specifications of travel cost demand models for recreation at U.S. Army Corps of Engineer reservoirs in Arkansas, California, and Tennessee/Kentucky. Statistical tests of coefficient equality for both nonlinear least squares and Heckman sample selection models suggest rejecting a transferable model among all three regions. However, the nonlinear least squares models in Arkansas and Tennessee were similar enough to fail to reject the hypothesis of equal coefficients at the 0.01 significance level. Even so, interchanging the Arkansas and Tennessee nonlinear least squares coefficients produces visitor use and total benefit estimates that are more than 100% too high. However, interchanging coefficients does provide reasonably close estimates of the average consumer surplus per trip for both states using the nonlinear least squares model (±5% to 10%). This is due to similarity of the price coefficients in the two models. Thus a more limited form of transferability which focuses on average benefit per day, rather than on predicting total use and total benefits, appears promising.
Sensible Heat Flux From Arid Regions: A Simple Flux‐Variance Method
Authors: Albertson John D. , Parlange Marc B. , Katul Gabriel G. , Chu Chia‐Ren , Stricker Han , Tyler Scott
Published: February 2004

Similarity models in the inner region of the unstable atmospheric boundary layer (ABL) are generally based on four dimensional parameters: buoyancy, friction velocity, surface heat flux, and the height above the land surface. In the free convection limit the friction velocity can be neglected, thus reducing the measurement needs in practical applications. Some field measurements of the second moment of temperature have indicated that free convection scaling of this statistic may be extended into more dynamic regimes, namely, the “dynamic‐convective” and, perhaps, the “dynamic” regions of the ABL. An advantage of this approach is that the sensible heat flux can be estimated without shear stress measurements. This temperature variance similarity model is applied for a wide range of unstably stratified flows over the dry Owens Lake, in southeastern California. The simple free convection model of the temperature variance is accurate for sensible heat flux estimation across the full range of unstable atmospheric stability conditions.
Runoff Production in a Forested, Shallow Soil, Canadian Shield Basin
Authors: Peters D. L. , Buttle J. M. , Taylor C. H. , LaZerte B. D.
Published: February 2004

Storm flow in forested basins on the Canadian Shield is largely supplied by subsurface water; however, mechanisms by which this water reaches the stream remain unclear. Side slope contributions to storm flow were studied using throughflow trenches on slopes in a headwater basin near Dorset, Ontario. Discharge, soil water content, and chemical and isotopic signatures of subsurface water were monitored at each site. Four hypotheses were tested: (1) most flow occurs at the soil‐bedrock interface on shield slopes with thin soil; (2) a significant fraction of event water moves vertically to bedrock via preferential flow pathways and laterally over the bedrock surface; (3) relative preevent water contribution to subsurface flow on shield slopes is a function of soil thickness; and (4) a significant portion of event water flux in storm flow from forested basins with shallow soil cover is supplied from side slopes via subsurface flow along the soil‐bedrock interface. Hypothesis 1 was confirmed from hydrometric observations during spring and fall rainstorms. Hypotheses 2 and 3 were supported by temporal trends in dissolved organic carbon and 18O in flow at the soil‐bedrock interface and by isotopic hydrograph separations (IHSs) of hillslope runoff. Comparison with the streamflow IHS indicated that event water flux from the basin in excess of that attributable to direct precipitation onto near‐channel saturated areas could be supplied by flow along the bedrock surface (hypothesis 4). Flow at the soil‐bedrock interface on side slopes also contributed ∼25% of preevent water flux from the basin. Much of the event water component of basin storm flow may travel considerable distances via subsurface routes and is not necessarily contributed by surface runoff processes (Horton flow or saturation overland flow). Therefore the assumption that event water undergoes little interaction with the soil during its passage downslope may be unwarranted here.
Change in phytomass and net primary productivity for Siberia from the Mid‐Holocene to the Present
Authors: Monserud Robert A. , Denissenko Olga V. , Kolchugina Tatyana P. , Tchebakova Nadja M.
Published: February 2004

Phytomass (live plant mass) and net primary productivity are major components of the terrestrial carbon balance. A major location for phytomass storage is the subcontinent of Siberia, which is dominated by extensive reaches of taiga (boreal forest). The responsiveness of the phytomass component of the carbon pool is examined by comparing vegetation in the mid‐Holocene (4600–6000 years before present) to modern potential vegetation. The mid‐Holocene was warmer and moister in middle and northern Siberia than today, producing conditions ideal for boreal forest growth. As a result, both northern and middle taiga were dominated by shade‐tolerant dark‐needled species that thrive in moist climates. Today, shade‐tolerant dark‐needled taiga is restricted to western Siberia and the highlands of central Siberia, with its central and eastern components in the mid‐Holocene replaced today by light‐demanding light‐needled species with lower productivity and phytomass. Total phytomass in Siberia in the mid‐Holocene was 105.0 ± 3.1 Pg, compared to 85.9 ± 3.2 Pg in modern times, a loss of 19.1 ± 3.1 Pg of phytomass. The reduction in dark‐needled northern and middle taiga classes results in a loss of 28.8 Pg, while the expansion of the corresponding light‐needled taiga results in a gain of 13.5 Pg, a net loss of 15.3 Pg. The loss is actually greater, because the modern figures are for potential vegetation and not adjusted for agriculture and other anthropogenic disturbances. Given long periods for vegetation to approach equilibrium with climate, the phytomass component of the carbon pool is responsive to climate change. Changes in net primary productivity (NPP) for Siberia between the mid‐Holocene and the present were not as large as changes in phytomass. A minor decrease in NPP (0.6 Pg yr−1, 10%) has occurred under our cooler modern climate, primarily due to the shift from dark‐needled taiga in the mid‐Holocene to light‐needled taiga today.
Temporal variations in dissolved methane deep in the Lake Agassiz Peatlands, Minnesota
Authors: Romanowicz Edwin A. , Siegel Donald I. , Chanton Jeffrey P. , Glaser Paul H.
Published: February 2004

A study (August 1990 to July 1991) of profiles of dissolved CH4 concentrations, diffusive flux of CH4, and CH4 production rates of 45 sites in the Lake Agassiz Peatlands in northern Minnesota shows that dissolved CH4 deep in the peat (> 1 m depth) mobilized easily to the vadose zone. During August 1990 the dissolved CH4 concentrations at some depths at some sites were supersaturated with respect to one atmosphere partial pressure of CH4. At one site (2.5 m depth) the concentration of dissolved CH4 in the peat pore‐water was 140 mg L−1. In July 1991, at no site did the concentration of dissolved CH4 in the peat pore water exceed 40 mg L−1 in the peat profile. The average calculated diffusive flux of CH4 decreased from 95 to 45 mg m−2 d−1 between 1990 and 1991. Gaseous CH4 was more in evidence in 1990 than in 1991. In 1990, CH4 at many depths bubbled vigorously when peat pore water was sampled. At some sites there was sufficient pore pressure to eject slugs of water forcibly from piezometers. Similarly, dissolved inorganic carbon (DIC) consisting of H2CO3, CO2, HCO3− and CO32− decreased between the sampling times from an average for both bogs and fens in 1990 of 62 mg C L−1 to 38 mg C L−1 in 1991. A dynamic mechanism must exist which traps CH4 deep in the peat column allowing gaseous CH4 to build up, increasing dissolved CH4. Other times, CH4 passes freely from deep peat to the vadose zone. We suggest as a hypothesis that a confining layer of trapped CH4 bubbles forms at depth in the peat, trapping gaseous CH4. The duration of the “bubble confining layer” is uncertain. We propose two hypotheses. (1) The confining layer is usually present and deteriorates after a major climatic event such as a drought, or (2) the confining layer forms and collapses seasonally with seasonal variations in the water table elevation.
High‐resolution holocene and late glacial atmospheric CO2 record: variability tied to changes in thermohaline circulation
Authors: Figge Regina A. , White James W. C.
Published: February 2004

Here we present results from a new method for detecting changes in atmospheric CO2 based on δ13C analyses of selected peat components from a peat core in southern South America. The paleo‐CO2‐record has decadal resolution spanning the last 14,000 radiocarbon years and compares well with Antarctic ice core CO2 data. Sharp peaks in CO2 are detected during the late glacial, specifically at 10,200, 11,600, and 12,900 years B.P. When compared to two deep‐sea records interpreted to reflect changes in thermohaline circulation, these CO2 pulses appear to relate to degassing events of the ocean associated with reinitiation of the thermohaline circulation occurring at this time. Concomitant decreases in atmospheric Δ14C during the late glacial are also consistent with a deep oceanic carbon source for the large atmospheric pulses in CO2. Results from a simple three‐box model indicate that the magnitude of the CO2 released during these degassing events is compatible with our observations. The rate of degassing, however, is much slower than that observed in the paleo‐CO2‐record. Two broad Holocene CO2 excursions are also identified with peaks at 4,200 and 7,700 years B.P. The driving mechanism behind these excursions appears to be different than those in the late glacial.
The preindustrial atmospheric14CO2 latitudinal gradient as related to exchanges among atmospheric, oceanic, and terrestrial reservoirs
Authors: Braziunas Thomas F. , Fung Inez Y. , Stuiver Minze
Published: February 2004

A three‐dimensional global tracer transport model (derived from a general circulation model) simulates geographic variations in atmospheric Δ14C in response to oceanic boundary conditions. Regional atmosphere‐ocean 14CO2 fluxes are controlled by regional wind‐dependent gas exchange coefficients (E), air‐sea pCO2 differences (ΔpCO2) and oceanic 14C/12C deficiencies. We find that various preindustrial oceanic scenarios reconstructed from reasonable sets of such air‐sea variables all produce model latitudinal gradients in atmospheric Δ14CO2 (the “NS Δ14C”) significantly greater than the measured preindustrial NS Δ14C of +4.4 ± 0.5‰ (45°N to 45°S), as estimated from pre‐twentieth century tree rings. The NS Δ14C is insensitive to regional ΔpCO2 but is strongly contingent on the chosen values for surface ocean Δ14C and E of southern high latitudes (>50°S). The simultaneous seasonality in sea ice extent and high‐latitude wind speeds may in part explain the discrepancy between modeled and measured preindustrial NS Δ14C. Terrestrial 14C sinks with longer turnover times (such as peatlands) also potentially may help to reduce the NS Δ14C. With our best estimates for preindustrial surface ocean Δ14C, ΔpCO2, and E values for other regions, we find a “best fit” ocean scenario in which the preindustrial southern surface ocean Δ14C is −95 ± 10 ‰, its ΔpCO2 is 0 ± 20 ppmv, and its E is 0.088 ± 0.010 M m−2 yr−1 μatm−1 (about 20% reduced from the widely accepted value of 0.110). An independent estimate of +6.5 ± 0.5 kg yr−1 for the net preindustrial oceanic 14C uptake is an important constraint on global mean and Antarctic E.
Oceanic primary production: 2. Estimation at global scale from satellite (Coastal Zone Color Scanner) chlorophyll
Authors: Antoine David , André Jean‐Michel , Morel André
Published: February 2004

A fast method has been proposed [Antoine and Morel, this issue] to compute the oceanic primary production from the upper ocean chlorophyll‐like pigment concentration, as it can be routinely detected by a spaceborne ocean color sensor. This method is applied here to the monthly global maps of the photosynthetic pigments that were derived from the coastal zone color scanner (CZCS) data archive [Feldman et al., 1989]. The photosynthetically active radiation (PAR) field is computed from the astronomical constant and by using an atmospheric model, thereafter combined with averaged cloud information, derived from the International Satellite Cloud Climatology Project (ISCCP). The aim is to assess the seasonal evolution, as well as the spatial distribution of the photosynthetic carbon fixation within the world ocean and for a “climatological year”, to the extent that both the chlorophyll information and the cloud coverage statistics actually are averages obtained over several years. The computed global annual production actually ranges between 36.5 and 45.6 Gt C yr−1 according to the assumption which is made (0.8 or 1) about the ratio of active‐to‐total pigments (recall that chlorophyll and pheopigments are not radiometrically resolved by CZCS). The relative contributions to the global productivity of the various oceans and zonal belts are examined. By considering the hypotheses needed in such computations, the nature of the data used as inputs, and the results of the sensitivity studies, the global numbers have to be cautiously considered. Improving the reliability of the primary production estimates implies (1) new global data sets allowing a higher temporal resolution and a better coverage, (2) progress in the knowledge of physiological responses of phytoplankton and therefore refinements of the time and space dependent parameterizations of these responses.
An atlas of the distribution of calcium carbonate in sediments of the deep sea
Authors: Archer David E.
Published: February 2004

Historical observations of the concentration of calcium carbonate in global deep sea sediments are compiled and compared with a new gridded field of seawater CO3= concentration to reveal regional variations in the calcite lysocline. The most obvious mode of variability of the calcite lysocline is the thickness of the lysocline (defined here as the difference in overlying water carbonate saturation, ΔCO3=, between high and low calcite sediments) with a thicker lysocline in the Atlantic than in the Pacific. I attribute this variation to differences in the delivery rate of terriginous material. A recent model for the lower glacial atmospheric pCO2 proposed to change the relationship between the depth of the lysocline and the ΔCO3= of the water column by changing the rain rate ratio of organic carbon to calcite production (the “rain ratio model”: Archer and Maier‐Reimer, 1994). I search the data set for analogs to the proposed glacial world, by looking for a link between the regional climate at the sea surface and the depth of the lysocline below. The ΔCO3= at the carbonate compensation depth (CCD) in the tropics appears to be 10–20 μmol kg−1 ΔCO3= more undersaturated than in high latitudes, but this is smaller than the ∼40 μmol kg−1 shift required by the model. In addition, the general resemblance of the glacial lysocline to the present day requires that the proposed shift in ΔCO3= at the CCD be globally uniform rather than locally variable, as climate forcing would probably generate. I conclude that the rain ratio model would probably require some globally uniform perturbation during glacial time, such as a change in ocean Si content, if it is to explain the entire pCO2 decrease observed in the glacial atmosphere. Finally, I grid the sedimentary data to estimate that the inventory CaCO3 which is available to neutralize fossil fuel CO2 is approximately 1600 Gt carbon, a quantity which may be exceeded by fossil fuel release in the next several centuries.
Assimilation of surface data in a one‐dimensional physical‐biogeochemical model of the surface ocean: 2. Adjusting a simple trophic model to chlorophyll, temperature, nitrate, and pCO2 data
Authors: Prunet Pascal , Minster Jean‐François , Echevin Vincent , Dadou Isabelle
Published: February 2004

A one‐dimensional coupled physical bio‐geochemical model of the surface ocean was constrained to reproduce the seasonal evolution of surface chlorophyll, temperature and nitrate concentration by adjusting the parameters of a simple trophic system using a variational technique. It is found that assimilation of surface chlorophyll data only not allow a robust constraint of the simulated trophic cycle. When surface chlorophyll, temperature and nitrate data are used simultaneously, seven linear combinations of the model parameters can be adjusted. While temperature values are useful to constrain vertical diffusion below the mixed layer, the seasonal nitrate evolution (2 values/year) is a strong constraint on the balance between vertical diffusion and particle sinking rate. The three types of surface information provide robust constraints on the model parameters and on the main carbon fluxes within the euphotic layer. For the model to reproduce observed surface pCO2 concentrations, it is found as necessary to adjust the C/N ratios. An example is given, where the C/N ratio for net organic matter export from euphotic zone is increased to 12±1 and the C/N ratio for detritus remineralization is decreased to 3.3±2, rather than the canonical value of 7.
Atmosphere‐wetland carbon exchanges: Scale dependency of CO2 and CH4 exchange on the developmental topography of a peatland
Authors: Waddington J. M. , Roulet N. T.
Published: February 2004

Measurement of the spatial variability of CH4 emissions and net CO2 ecosystem exchange were made in a boreal peatland in northern Sweden in the summers of 1992 and 1993. Variability was monitored at the microscale (hummocks and hollows), mesoscale (ridges, lawns and pools), and macroscale (landforms) to assess the role of peatland topography on the magnitude and variability of the fluxes. The general trend is for topographically lower areas, such as hollows, pools, or peatland margins, to have higher CH4 emissions and lower CO2 uptake than the adjacent topographically higher areas such as hummocks, ridges, and plateaus. However, the greatest difference occurs at the microtopographic scale because the maximum differences in water table position and temperature occur at the microscale. The CH4 flux at the margins of the peatland was three to four times greater than that observed at the central plateau sites. Net CO2 uptake was also greatest at the margin sites. A combined meso‐macro topographic model (MMF) was used to estimate the total peatland CH4 and CO2 exchange. The model indicates that a failure to measure the exchange of carbon from peatland pools can result in a large overestimate of the total peatland NEE and therefore carbon accumulation rates.
Differential effective medium modeling of rock elastic moduli with critical porosity constraints
Authors: Mukerji Tapan , Berryman Jim , Mavko Gary , Berge Patricia
Published: February 2004

Rocks generally have a percolation porosity at which they lose rigidity and fall apart. Percolation behavior is a purely geometrical property, independent of any physical properties, and is a powerful constraint on any valid velocity‐porosity relation. We show how the conventional Differential Effective Medium (DEM) theory can be modified to incorporate percolation of elastic moduli in rocks by taking the material at the critical porosity as one of the constituents of a two‐phase composite. Any desired percolation porosity can be specified as an input. In contrast, the conventional DEM model always predicts percolation at a porosity of either 0 or 100 percent. Most sedimentary rocks however have intermediate percolation porosities and are therefore not well represented by the conventional theory. The modified DEM model incorporates percolation behavior, and at the same time is always consistent with the Hashin‐Shtrikman bounds. The predictions compare favorably with laboratory sandstone data.
Atlantic Arctic cyclones and the mild Siberian winters of the 1980s
Authors: Rogers Jeffrey C. , Mosley‐Thompson Ellen
Published: February 2004

The winters of the 1980s were among the warmest on record over northern Siberia. Daily and monthly sea level pressures, 500 mb heights, and an index of Atlantic storm track extent (toward the northeast) and intensity, are used to examine atmospheric circulation variability during extremely warm and cold winter months in Siberia. In recent years, the comparatively warm months are associated with an increased frequency in the passage of intense Atlantic cyclones that enter the extreme northeastern Atlantic and traverse the Barents and Kara Seas. These arctic cyclones bring strong westerly flow into Siberia along with passages of extensive cyclone warm sectors. Conversely, the surface mean Siberian anticyclone and large‐scale features such as the North Atlantic Oscillation appear to have little effect on warm Siberian winters.
Beat‐type Langmuir wave emissions associated with a type III solar radio burst: Evidence of parametric decay
Authors: Hospodarsky G. B. , Gurnett D. A.
Published: February 2004

Recent measurements from the plasma wave instrument on the Galileo spacecraft have shown that Langmuir waves observed in conjunction with a type III solar radio burst contain many beat‐type waveforms, with beat frequencies ranging from about 150 to 650 Hz. Strong evidence exists that the beat pattern is produced by two closely spaced narrowband components. The most likely candidates for these two waves are a beam‐generated Langmuir wave and an oppositely propagating Langmuir wave produced by parametric decay. In the parametric decay process, nonlinear interactions cause the beam‐driven Langmuir wave to decay into a Langmuir wave and a low‐frequency ion sound wave. Comparisons of the observed beat frequency are in good agreement with theoretical predictions for a three‐wave parametric decay process. Weak low‐frequency emissions are also sometimes observed at the predicted frequency of the ion sound wave.
Revised age calibration points for the geomagnetic polarity time scale
Authors: Wei Wuchang
Published: February 2004

Two of the seven Cenozoic age calibration points in the widely used Cande and Kent's geomagnetic polarity time scale have recently been revised. The rest of the five calibration points are revised here based on recently available radioisotopic dates and magnetostratigraphic data. Ages of the magnetic reversals are recalculated using the revised calibration points. Differences between the present time scale and Cande and Kent's revised time scale are generally less than 0.3 m.y., the largest (up to 1.3 m.y.) being in the early Miocene.
Passive microwave‐derived snow melt regions on the Greenland Ice Sheet
Authors: Abdalati Waleed , Steffen Konrad
Published: February 2004

By comparing data from the Special Sensor Microwave Imager (SSM/I) to field data, a melt threshold of the cross‐polarized gradient ratio (XPGR), which is a normalized difference between the 19 GHz horizontally‐polarized and 37 GHz vertically polarized brightness temperatures, is determined. This threshold, XPGR = −0.025, is used to classify dry and wet snow. The annual areal extent of melt is mapped for the years 1988 through 1991, and inter‐annual variations of melt extent are examined. The results show that the melt extent varied from a low of 38.3% of the ice sheet (1990) to a high of 41.7% (1991) during the years 1988–1991.
Continuous GPS monitoring of elastic strain in the Northern Cascadia Subduction Zone
Authors: Dragert H. , Hyndman R. D.
Published: February 2004

Previous monitoring and modeling of crustal deformation across the northern Cascadia margin at Vancouver Is. has provided strong evidence that the subduction thrust fault is locked and may generate future great earthquakes. The recent establishment of the Western Canada Deformation Array (WCDA), a network of continuous GPS trackers in southwestern British Columbia, provides a new tool for monitoring crustal strain and thereby helps to assess the earthquake hazard in this region. 17 months of continuous data from the three longest running WCDA sites (Penticton, Victoria, Holberg) indicate: 1.) A 7 mm/yr easterly motion of Victoria relative to Penticton. Victoria is located in the forearc at the southeastern end of Vancouver Is., 230 km from trench axis, whereas Penticton is located behind the arc, 520 km from the trench axis, and assumed fixed on the stable North American plate; 2.) A 3 mm/yr northwesterly motion and 10 mm/yr uplift (with a large uncertainty) of Holberg relative to Penticton. Holberg is located on the northern‐most part of Vancouver Is., 50 km from the trench and near the plate triple junction; and 3.) The presence of probably seasonal variations in the apparent relative positions of the two coastal sites with respect to Penticton. The landward motion of Victoria agrees with the deformation predicted by elastic dislocation models of the interseismic period for a great subduction‐thrust earthquake as constrained by previous deformation data. Although not as well resolved, the motion of Holberg, roughly parallel to the margin, is significantly different and is inconsistent with simple subduction models. The non‐linear variations in measured position are dominated by an annual period probably resulting from seasonal biases in the precise orbit estimates or in the modeling of tropospheric delays or tidal effects.
Preliminary results from the Sprites94 Aircraft Campaign: 1. Red sprites
Authors: Sentman D. D. , Wescott E. M. , Osborne D. L. , Hampton D. L. , Heavner M. J.
Published: February 2004

The dual jet aircraft Sprites94 campaign yielded the first color imagery and unambiguously triangulated physical dimensions and heights of upper atmospheric optical emissions associated with thunderstorm systems. Low light level television images, in both color and in black and white (B/W), obtained during the campaign show that there are at least two distinctively different types of optical emissions spanning part or all of the distance between the anvil tops and the ionosphere. The first of these emissions, dubbed “sprites” after their elusive nature, are luminous structures of brief (< 16 ms) duration with a red main body that typically spans the altitude range 50–90 km, and possessing lateral dimensions of 5–30 km. Faint bluish tendrils often extend downward from the main body of sprites, occasionally appearing to reach cloud tops near 20 km. In this paper the principal characteristics of red sprites as observed during the Sprites94 campaign are described. The second distinctive type of emissions, “blue jets,” are described in a companion paper [Wescott et al., this issue].
The effect of the impact of comet Shoemaker Levy‐9 on Jupiter's aurorae
Authors: Miller S. , Achilleos N. , Dinelli B. M. , Lam H. A. , Tennyson J. , Jagod M.‐F. , Geballe T. R. , Trafton L. M. , Joseph R. D. , Ballester G. E. , Baines K. , Brooke T. Y. , Orton G.
Published: February 2004

We present infrared spectra and images of the jovian aurorae taken at wavelengths sensitive to the H3+ molecular ion during the period around the impact of Comet Shoemaker Levy‐9. The spectra were obtained using CGS4 on the United Kingdom Infrared Telescope and the images using NSFcam on NASA's Infrared Telescope Facility. Comparison with spectra obtained in May, 1993, shows that while the relative intensities of the northern and southern auroral zones prior to and during impact week (July 16–22, 1994) were broadly comparable with those of 1993, a few days after the last collision the northern aurora was considerably enhanced and its southern counterpart somewhat depressed. The north/south auroral ratio was returning to more normal values a week later. The effect of material drifting from the impact sites to the southern auroral zone is discussed in relation to these results.
An explanation of synchrotron radiation enhancement following the impact of Shoemaker‐Levy 9 with Jupiter
Authors: Brecht Stephen H. , Pesses Mark , Lyon John G. , Gladd N. T. , McDonald S. W.
Published: February 2004

The impact of comet Shoemaker‐Levy 9 (SL‐9) with Jupiter generated a marked increase in synchrotron radiation levels, contrary to predictions that cometary dust would reduce the observed level of synchrotron radiation. The observed increase can be explained by the acceleration of magnetospheric electrons by shock waves emanating from fragment impact points and propagating upward into the Jovian magnetosphere.
Overlapping cusp ion injections: An explanation invoking magnetopause reconnection
Authors: Lockwood M.
Published: February 2004

An explanation of overlapping cusp ion injections is presented using the pulsating cusp model of the effects of magnetopause reconnection. It is shown that two populations of cusp ions, covering separated energy ranges, can be seen simultaneously by low‐ or mid‐altitude satellites because of the combined effect of the acceleration and the straightening of newly‐opened field lines as they evolve away from the reconnection site. Observations of such signatures, recently reported in data from the Viking and Freja satellites, are discussed in terms of pulsed and steady reconnection.
Carbon kinetic isotope effect in the reaction of CH4 with Cl atoms
Authors: Saueressig G. , Bergamaschi P. , Crowley J. N. , Fischer H. , Harris G. W.
Published: February 2004

The carbon kinetic isotope effect in the reaction between Cl and CH4 (KIECl) has been measured using tunable diode laser absorption spectroscopy to determine 13CH4/12CH4 ratios. Cl atoms were generated by the irradition of Cl2 in static mixtures of Cl2/CH4/N2 or Cl2/CH4/N2/O2. Both methods resulted in a (KIECl) of 1.066±0.002 at 297 K. The KIECl displayed a slight temperature dependence, increasing to 1.075±0.005 at 223 K. This result suggests a significant influence of the title reaction on the stratospheric CH4 isotopic composition and may help to resolve discrepancies between measurements of stratospheric 13CH4/12CH4 profiles and laboratory measurements of KIEOH.
Geomagnetic transmission of solar energetic protons during the geomagnetic disturbances of October 1989
Authors: Boberg P. R. , Tylka A. J. , Adams J. H. , Flückiger E. O. , Kobel E.
Published: February 2004

We present orbit‐averaged geomagnetic transmission measurements during the large solar energetic particle events of October 1989 using proton data from the NOAA‐10 and GOES‐7 satellites. We compare the measurements to geomagnetic transmission calculations determined by tracing particle trajectories through the combination of the International Geomagnetic Reference Field (IGRF) model and the 1989 Tsyganenko magnetospheric magnetic field model. We modify the effective ‘ring current’ parameter in the 1989 Tsyganenko model based on the Dst data. We compare our results to calculations employing only the IGRF and to a parameterization of geomagnetically quiet‐time cutoff rigidities derived from Cosmos/Intercosmos observations. Our 3‐hour orbit‐averaged results have ∼15% accuracy during the October 1989 events.
Stream interfaces and energetic ions II: Ulysses test of Pioneer results
Authors: Intriligator Devrie S. , Siscoe George L. , Wibberenz Gerd , Kunow Horst , Gosling John T.
Published: February 2004

Ulysses measurements of energetic and solar wind particles taken near 5 AU between 20 and 30 degrees south latitude during a well‐developed recurring corotating interaction region (CIR) show that the CIR's corotating energetic ion population (CEIP) associated with the trailing reverse shock starts within the CIR at the stream interface. This is consistent with an earlier result obtained by Pioneers 10 and 11 in the ecliptic plane between 4 and 6 AU. The Ulysses/Pioneer finding is noteworthy since the stream interface is not magnetically connected to the reverse shock, but lies 12–17 corotation hours from it. Thus, the finding seems to be inconsistent with the basic model that generates CEIP particles at the reverse shock and propagates them along field lines. Eliminating the inconsistency probably entails an extension of the standard model such as cross‐field diffusion or a non‐shock energization process operating near the stream interface closer to the sun.
Efficiency of formation of CH3O in the reaction of CH3O2 with ClO
Authors: Biggs P. , Canosa‐Mas C. E. , Fracheboud J.‐M. , Shallcross D. E. , Wayne R. P.
Published: February 2004

A discharge‐flow apparatus was used to determine the branching ratio α for the channel of the reaction of ClO with CH3O2 that leads to the formation of CH3O. The experiments were performed at 2 Torr pressure and at room temperature. ClO was the excess reactant and was measured mass spectrometrically; CH3O was detected by laser‐induced fluorescence. The value of α was shown to depend on the fraction β of the reaction of CH3O2 with Cl atoms that leads to the formation of CH3O. For β = 0, 0.5 and 1, the derived values of α are 0.28±0.07, 0.32±0.08 and 0.42±0.09, respectively. Comparison with other published results suggests the possibility of three significant product channels for the reaction of CH3O2 with ClO.
The role of shock acceleration on synchrotron radiation following SL‐9 impact
Authors: Brecht Stephen H. , Pesses Mark E. , de Pater Imke , Gladd N. T. , Lyon John G.
Published: February 2004

In Brecht et al. [1995] shock acceleration was proposed to explain the enhanced synchrotron radiation levels that followed the impact of SL‐9 on Jupiter. This paper presents preliminary estimates of the expected synchrotron radiation levels following a fragment impact. The estimates rely on an analytic description of the diffusive shock acceleration and compare favorably with radio telescope data. The agreement between the calculations and data add support to the idea that the shock acceleration process may have been operative in the Jovian magnetosphere.
Magnetic flux ropes at the high‐latitude magnetopause
Authors: Berchem Jean , Raeder Joachim , Ashour‐Abdalla Maha
Published: February 2004

We examine the consequences of magnetic reconnection at the high‐latitude magnetopause using a three‐dimensional global magnetohydrodynamic simulation of the solar wind interaction with the Earth's magneto sphere. Magnetic field lines from the simulation reveal the formation of magnetic flux ropes during periods with northward interplanetary magnetic field. These flux ropes result from multiple reconnection processes between the lobes field lines and draped magnetosheath field lines that are convected around the flank of the magnetosphere. The flux ropes identified in the simulation are consistent with features observed in the magnetic field measured by Hawkeye‐1 during some high‐latitude magnetopause crossings.
Laboratory investigation of matrix imbibition from a flowing fracture
Authors: Tidwell Vincent C. , Glass Robert J. , Peplinski William
Published: February 2004

Predicting fluid flow and transport behavior in unsaturated, fractured rock is greatly simplified where matrix imbibition can be modeled as a linear function of the square root of time (t1/2); however, such treatment implicitly assumes homogenous matrix properties. To investigate matrix heterogeneity effects, we perform a simple experiment in which x‐ray imaging is used to measure the imbibition of water from a flowing fracture into a slab of volcanic tuff. Experimental results show matrix imbibition to follow a linear t1/2 relationship even though the saturated hydraulic conductivity of the tuff varies by over four orders of magnitude.
Mesospheric temperature inversions with overlying nearly adiabatic lapse rate: An Indication of a well‐mixed turbulent layer
Authors: Whiteway James A. , Carswell Allan I. , Ward William E.
Published: February 2004

The Rayleigh lidar technique was applied to study the thermal structure of the middle atmosphere. Observations were carried out on a routine basis for one year (130 clear nights) at the main campus of York University near Toronto (44°N,80°W). Mesospheric temperature inversions were generally found to occur below a height of 70 km during winter and above during summer. The most interesting aspect of our observations was that the inversions were often associated with an overlying nearly adiabatic lapse rate which extended for several kilometres. We interpret this as being an indication (or signature) of a well‐mixed turbulent layer. A one‐dimensional numerical model was applied to demonstrate that a well‐defined turbulent layer within the mesosphere can bring about a thermal structure quite similar to that which was commonly observed—an inversion with overlying nearly adiabatic lapse.
Flux and images of Jupiter at 13, 22 and 36 cm before, during and after SL‐9 impacts
Authors: Dulk G. A. , Leblanc Y. , Hunstead R. W.
Published: February 2004

Two radio telescopes in Australia, the Australia Telescope and the Molonglo Observatory Synthesis Telescope were used to observe Jupiter before, during and after the impacts of comet Shoemaker‐Levy 9 in July 1994. The telescopes observed at wavelengths of 13, 22 and 36 cm and produced 2‐D images of Jupiter–s synchrotron radiation belts, showing that the brightness of a portion of these belts was strongly affected by the comet impacts. Starting about one day after the first impact and reaching a peak soon after the time of the last impact the integrated flux density increased by approximately 25–30% at 13 and 22 cm and 40% at 36 cm.
The relationship between solar UV irradiance and total ozone from observations over southern Argentina
Authors: Bojkov Rumen D. , Fioletov Vitali E. , Diaz Susana B.
Published: February 2004

Solar ultraviolet (UV) radiation at 300 and 305 nm, measured by a Biospherical Instruments high resolution scanning spectroradiometer at Ushuaia, southern Argentina (55°S, 68°W), as a part of the US National Science Foundation Network for Polar Regions, was compared with total ozone satellite measurements. A statistical relationship between UV and total ozone was derived. On the basis of this relationship, the differences in 300 and 305 nm irradiance between 1979–1983 and 1989–1993 intervals are estimated; for October, the 15% observed decline of total ozone has led to irradiance increases of 80% at 300 nm and 35% at 305 nm. During the days with “ozone hole” conditions, the 300 nm irradiance is as high as it would be at the summer solstice three months later, and is ∼4 times higher than the UV irradiance corresponding to the “normal” ozone condition for early October, as further illustrated for October 1994. Inclusion of the 340 nm cloudy‐dependent predictor is discussed.
Post‐SL9 sulfur photochemistry on Jupiter
Authors: Moses Julianne I. , Allen Mark , Gladstone G. Randall
Published: February 2004

We have modeled the photochemical evolution of the sulfur‐containing species that were observed in Jupiter's stratosphere after the SL9 impacts. We find that most of the sulfur is converted to S8 in the first few days. Other important sulfur reservoirs are CS, whose abundance increases markedly with time, and possibly H2CS, HNCS, and NS, whose abundances depend on kinetic reaction rates that are unknown at the present. We discuss the temporal variation of the major sulfur compounds, make abundance and compositional predictions useful for comparisons with observations, and discuss the possible condensation of sulfur‐containing species.