bluuebunny/crossref_metadata_2025 huggingface dataset:
Three‐dimensional spatial and temporal monitoring of soil water content using electrical resistivity tomography
Authors: Zhou Qi You , Shimada Jun , Sato Akira
Published: February 2004

In this paper, we propose a noninvasive method for monitoring three‐dimensional (3‐D) spatial and temporal variations of soil water content in the field, soil moisture tomography. The basic idea of the method originates from Archie's relationship between soil resistivity and water content. Initially, 88 electrodes were densely buried within a 3.5 m×3.5 m square area, and potentials at the electrodes were measured by pole‐pole and Wenner array methods at given time intervals. An inversion calculation of the 3‐D soil resistivity was then conducted based on these potential data. Next, 46 soil samples were taken at representative positions in the square, and the parameters in the Archie's relationship were measured in the laboratory. Then, the 3‐D distributions of the parameters were obtained by a distance weight interpolation method. Finally, based on Archie's relationship and the 3‐D distribution of the soil resistivity and the related parameters, 3‐D distributions of soil water content were calculated. To evaluate the obtained water content, the calculated water contents were compared with those measured by heat‐probe‐type soil moisture sensors, and a comparison between the spatial distribution patterns of calculated water content and soil bulk dry density was conducted. The 3‐D variations of the calculated water content during a rainfall event were also analyzed. The results show that there are ±0.10 cm3/cm3 errors in the calculated water content, but between the calculated and the measured water content there exists a good linear relationship. It is possible to use the calculated water content to analyze the very general 3‐D distribution characteristics of the soil moisture and investigate the 3‐D rainfall infiltration process, the redistribution of soil water after rain, and other hydrological processes in the field. The proposed method is preferred for porous media where the water resistivity is relatively stable.
Acid/base character of organic acids in a boreal stream during snowmelt
Authors: Hruška Jakub , Laudon Hjalmar , Johnson Chris E. , Köhler Stephan , Bishop Kevin
Published: February 2004

In northern regions, spring snowmelt generally results in an episodic decline of surface water pH. Natural organic acids may be an important factor in this type of pH change. We studied the variations in the acid/base character of aquatic organic acids during spring snowmelt in 1997 at Svartberget, a stream rich in total organic carbon (TOC) that is located in the boreal zone of northern Sweden. Snowmelt at Svartberget was accompanied by a drop in stream pH of up to 1.8 pH units, as well as the dilution of base cation and strong acid anion concentrations. Aluminum and TOC increased or decreased during snowmelt, depending on the sampling site within the 50‐ha catchment. Although there were distinct differences in pH, TOC, and major inorganic ions in the runoff from three subcatchments, there was very little variation in the acid/base character of TOC. Thus organic acids in the Svartberget catchment share a common set of acid/base properties despite markedly different subcatchment drainage patterns, vegetation, and soils. The dissociation behavior of organic acids at Svartberget could be described with high precision (R2 = 0.91, p < 0.001, and n = 115) by a triprotic acid analog model (pKa1 = 2.5, pKa2 = 4.0, and pKa3 = 5.8), together with the measured site density of organic acids (8.6±0.8 μeq (mg TOC)−1). A Gaussian pKa distribution (μ = 4.20 and σ = 1.43) predicted organic acid dissociation with similar precision (R2 = 0.91, p < 0.001, and n = 94). Variations in site density among the tributary streams could largely be explained by aluminum complexation. Sites with lower measured site densities had greater concentrations of organically bound Al. Thus Al binding reduces the potential release or neutralization of H+ by organic acids.
Sensitivity analysis and parameter identifiability for colloid transport in geochemically heterogeneous porous media
Authors: Sun Ning , Sun Ne‐Zheng , Elimelech Menachem , Ryan Joseph N.
Published: February 2004

Effective use of colloid transport models for heterogeneous subsurface porous media requires the development of methodologies to identify the key model parameters. The inverse problem of a two‐dimensional model for colloid transport in geochemically heterogeneous porous media is systematically investigated in this paper. Sensitivity analysis prior to the parameter identification provided valuable insights into the identifiability of the six model parameters. The hydraulic conductivity and longitudinal dispersivity were identified from tracer breakthrough data and then were used in the remaining parameter identification. The four colloid deposition and release parameters, favorable (fast) colloid deposition rate coefficient, geochemical heterogeneity, unfavorable (slow) colloid deposition rate coefficient, and colloid release rate coefficient from the unfavorable surface fraction, were found to be highly interrelated, and the inverse solution of the four‐parameter set was not unique. When either the geochemical heterogeneity or favorable colloid deposition rate coefficient is known, the other three colloid deposition and release parameters can be identified via the inverse solution if the duration of the colloid injection is sufficiently long. The colloid release rate coefficient, however, cannot be identified when using a short (pulse‐like) colloid injection. Neglecting the colloid release rate results in estimation errors of the other model parameters and thus adversely affects the subsequent prediction of colloid transport.
Effect of the number of soil layers on a modeled surface water budget
Authors: Martinez Janet E. , Duchon Claude E. , Crosson William L.
Published: February 2004

A sensitivity analysis was performed to determine the effects of systematically increasing the number of soil layers in a land surface‐atmosphere model on the components of the modeled water budget. The study was done for a forested location in central Oklahoma for a 65‐day period in spring 1996 using the model called Simulator for Hydrology and Energy Exchange at the Land Surface (SHEELS). SHEELS is based on the Biosphere‐Atmosphere Transfer Scheme (BATS), except that the subsurface hydrology was substantially changed to improve representation of the soil moisture profile. The soil profile was divided into zones of thickness 0.05 m (upper), 1.25 m (root), and 1.20 m (bottom). The two principal conclusions are that (1) the water budget is very sensitive to the number of layers in the soil profile under wet conditions and (2) the water budget is much more sensitive to the number of layers in the profile than to the range of 2 orders of magnitude in saturated hydraulic conductivity considered in this study. A result of the latter conclusion is that larger errors in modeled water fluxes can occur from using an insufficient number of soil layers than from using an incorrect value of saturated hydraulic conductivity.
Characteristics of large snowfall events in the montane western United States as examined using snowpack telemetry (SNOTEL) data
Authors: Serreze Mark C. , Clark Martyn P. , Frei Allan
Published: February 2004

Daily snow water equivalent records from the snowpack telemetry archive are used to assess spatiotemporal characteristics of large snowfall events over the montane western United States. The largest mean annual (leading) events are found in the Pacific Northwest and Sierra Nevada. The mean leading event lasting up to 72 hours typically accounts for 10–23% of the water equivalent of annual snowfall, with the largest contribution in the Arizona/New Mexico sector. For most of the West, snowfall events in the top quartile of station distributions are most common during midwinter, but those for the Rocky Mountain states and Utah are more common during late winter or spring. Colorado also shows a secondary peak in large events during November. Large midwinter snowfall events in the marine sectors, Idaho, and Arizona/New Mexico are spatially coherent in that when observed at one station, they tend to occur at surrounding stations. Large events are less spatially coherent for drier inland regions. When annual snowfall is anomalously positive, there tends to be an increase in the number of snow days as well as a shift in the distributions toward the larger event sizes. Opposite relationships are observed for negative annual snowfall anomalies. These findings are in accord with recent studies using lower elevation data, demonstrating that the probability of extreme precipitation events is altered during El Nino or La Nina conditions.
Mechanisms of virus removal during transport in unsaturated porous media
Authors: Chu Yanjie , Jin Yan , Flury Markus , Yates Marylynn V.
Published: February 2004

Previous studies suggest that sorption of colloidal particles onto the air‐water interface is an important mechanism for enhanced retention and retardation during transport in unsaturated systems. In this study, bacteriophages øX174 and MS‐2 and Br− tracer were introduced into sand columns of various water contents as a step function under constant flow rates. The results showed that when a “reactive” (water washed) sand was used, the retention of both Φ;X174 and MS‐2 increased significantly at low water saturation levels. However, when an “inert” (metals and metal oxides removed) sand was used, the effect of water content was minimal, although observable. These results suggest that in the presence of reactive solid surfaces, increased reactions at the solid‐water interface rather than at the air‐water interface dominates in virus removal and transport under unsaturated conditions. A model that incorporated reactions at both the solid‐water and air‐water interfaces was developed and successfully applied to the data.
Unsaturated hydraulic conductivity function based on a soil fragmentation process
Authors: Assouline Shmuel , Tartakovsky Daniel M.
Published: February 2004

We present a new two‐parameter expression for relative hydraulic conductivity (RHC) of partially saturated soils. It is based on the premise of Assouline et al. [1998] that soil structures evolve from a uniform random fragmentation process. This assumption allows us to derive hydraulic properties of soils (water retention curves and unsaturated hydraulic conductivity) from primary properties, such as pore geometry and soil structure. We tested our RHC expression against different soil types and found that it fits data better than the widely used models of Brooks and Corey [1964] and van Genuchten [1980].
Estimating the moisture dependence of root zone water loss using conditionally averaged precipitation
Authors: Salvucci Guido D.
Published: February 2004

A new method for estimating the dependence of soil water loss on soil moisture is proposed. The novelty of the approach is the use of precipitation measurements P, conditionally averaged according to soil moisture storage S, as a surrogate for moisture‐dependent outflow (evapotranspiration (ET) plus runoff R and drainage D. The basis of the method is as follows: Soil moisture storage and its rate of change are statistically dependent, but under stationary conditions the expected value of the change in soil moisture storage over an interval
, conditioned on the storage during the interval S¯, is zero. This stationarity property, which results from the tendency of wetter soils to dry faster via enhanced drainage, runoff, and evapotranspiration, leads to the result that conditionally averaged precipitation can be used to estimate moisture‐dependent water loss, i.e.:
. As an example application, sparsely sampled soil moisture (approximately weekly to monthly) and daily precipitation data are used to estimate the daily timescale moisture‐dependent water loss function for sites in Illinois. The estimated loss function is consistent in magnitude and shape with conventional models of evapotranspiration efficiency and percolation. The estimated loss function is then used to test a physically based stochastic model for the probability distribution of soil moisture [Rodriguez‐Iturbe et al., 1999]. The observed and derived distributions of moisture are in close agreement, lending support for both the methodology and the model. Other uses for the methodology, including the study of scale dependence in water balance sensitivity to soil moisture, are discussed.
A minimalist probabilistic description of root zone soil water
Authors: Milly P. C. D.
Published: February 2004

The probabilistic response of depth‐integrated soil water to given climatic forcing can be described readily using an existing supply‐demand‐storage model. An apparently complex interaction of numerous soil, climate, and plant controls can be reduced to a relatively simple expression for the equilibrium probability density function of soil water as a function of only two dimensionless parameters. These are the index of dryness (ratio of mean potential evaporation to mean precipitation) and a dimensionless storage capacity (active root zone soil water capacity divided by mean storm depth). The first parameter is mainly controlled by climate, with surface albedo playing a subsidiary role in determining net radiation. The second is a composite of soil (through moisture retention characteristics), vegetation (through rooting characteristics), and climate (mean storm depth). This minimalist analysis captures many essential features of a more general probabilistic analysis, but with a considerable reduction in complexity and consequent elucidation of the critical controls on soil water variability. In particular, it is shown that (1) the dependence of mean soil water on the index of dryness approaches a step function in the limit of large soil water capacity; (2) soil water variance is usually maximized when the index of dryness equals 1, and the width of the peak varies inversely with dimensionless storage capacity; (3) soil water has a uniform probability density function when the index of dryness is 1 and the dimensionless storage capacity is large; and (4) the soil water probability density function is bimodal if and only if the index of dryness is <1, but this bimodality is pronounced only for artificially small values of the dimensionless storage capacity.
Interbasin groundwater flow in south central Nevada: A further comment on the discussion between Davisson et. al.. [1999a, 1999b] and Thomas [1999]
Authors: Winograd Isaac J.
Published: February 2004

In their response to the comments by Thomas [1999], Davisson et al. [1999a] dismiss a large set of potentiometric measurements pertinent to an understanding of the hydrogeology of Yucca and Frenchman Flats in southcentral Nevada. This commentary is submitted to demonstrate, first, that their dismissal of this data set is unfounded and, second, that these potentiometric data call into question the central thesis of the original paper by Davisson et al. [1999b].
Space‐time modeling of water table depth using a regionalized time series model and the Kalman Filter
Authors: Bierkens Marc F. P. , Knotters M. , Hoogland T.
Published: February 2004

The spatiotemporal variation of shallow water table depth is modeled with a regionalized version of an autoregressive exogenous (ARX) time series model. The ARX model relates the temporal variation of the water table depth at a single location to a time series of precipitation surplus. The ARX model is calibrated first at locations where time series of water table depth are available. ARX parameters at nonvisited locations are estimated through geostatistical interpolation using auxiliary information, resulting in a regionalized ARX model or RARX model. The parameters of the geostatistical model are estimated by embedding the RARX model in a space‐time Kalman filter and minimization of a maximum likelihood criterion built from the filter innovations. The resulting state estimator can be used for optimal space‐time prediction of water table depth, network optimization, and space‐time conditional simulation.
Three‐dimensional particle tracking velocimetry studies of the transition from pore dispersion to Fickian Dispersion for homogeneous porous media
Authors: Moroni Monica , Cushman John H.
Published: February 2004

Fickian models developed to simulate transport in homogeneous porous media consider the flux of the contaminant species to be proportional to the concentration gradient via a constant dispersion tensor. When a solute has traveled sufficient distance or time, the mean square displacement may begin to grow linearly with time. We define the point at which the mean square displacement goes linear as the Darcy‐scale Fickian limit. Prior to reaching this limit we say we are in the regime of pore‐scale dispersion. In this paper we examine the transition from pore‐scale dispersion to Fickian dispersion via three‐dimensional particle tracking velocimetry (3D‐PTV) in matched refractive index porous media. From the trajectories obtained via 3D‐PTV we have computed the mean square displacements, velocity distributions, velocity correlation, and classical dispersion tensors. These data indicate the transverse components of the Darcy‐scale dispersion tensor trend toward zero and that the longitudinal components go Fickian after approximately six pore diameters have been traversed.
Nitrogen mass balances and abiotic controls on N retention and yield in high‐elevation catchments of the Sierra Nevada, California, United States
Authors: Sickman James O. , Leydecker Al , Melack John M.
Published: February 2004

Interannual variations in nitrogen mass balances for the Emerald Lake watershed (ELW) and six additional headwater basins of the Sierra Nevada of California are described and used to investigate the influence of physical (snow regime, runoff, and precipitation) and chemical (N loading) forcings on the observed variability in annual catchment yield and retention of N. At ELW, annual yield of N varied by a factor of 8 (0.4–3.2 kg ha−1 yr−1) and was a linear function of runoff (R2 = 0.89 and 0.74 for dissolved inorganic nitrogen and dissolved organic nitrogen, respectively). Nitrogen yield increased faster than increases in runoff; that is, ecosystem processes enhanced N losses during years with high runoff and retarded losses during dry years. The timing of snowmelt runoff had a large effect on catchment inorganic N dynamics: nitrate pulses were greater and DIN retention was lower in years with deep, late melting snowpacks. We hypothesize that in the Sierra Nevada, labile N pools in soils are increasingly stocked during years with high snowfall amounts. These findings and modeling studies in high‐elevation watersheds suggest that if current trends toward warmer air temperatures and earlier snowmelt continue, N retention will increase in the Sierra Nevada.
On the cumulative area distribution of natural drainage basins along a coastal boundary
Authors: La Barbera P. , Lanza L. G.
Published: February 2004

The natural drainage network in a region is analyzed in order to investigate scaling properties and the form of the probability distribution for basin areas along a coastal boundary. The Horton/Strahler approach used in the classical description of the drainage network within a single basin is extended to a series of independent though conterminous basins with outlet to the sea, assuming that a regional area ratio RA, analogous to the Hortonian area ratio, holds for independent basins. A multiplicative factor Rc is also defined as the average ratio between the number of independent basins of a given order ω and those of order ω+1. The cumulative area distribution (CAD) for drainage basins that drain along the coastal boundary is obtained as a power law in the form P[A > a] ∝ a−γ, with γ = log Rc/log RA. The derived form and parameters of the CAD are shown to hold for the Liguria region of Italy (≃5700 km2 in the northern Mediterranean) as well as for the whole continental Italy (≃250,000 km2). The fractal dimension of the regional system encompassing all drainage areas of basins with outlet to the sea is derived in the form 𝒟 = 1/γ. The analytical results obtained are shown to agree with the theoretical expressions already available in the literature for optimal channel networks.
A hybrid stochastic model for multiseason streamflow simulation
Authors: Srinivas V. V. , Srinivasan K.
Published: February 2004

A hybrid model is presented for stochastic simulation of multiseason streamflows. This involves partial prewhitening of the streamflows using a parsimonious linear periodic parametric model, followed by resampling the resulting residuals using moving block bootstrap to obtain innovations and subsequently postblackening these innovations to generate synthetic replicates. This model is simple and is efficient in reproducing both linear and nonlinear dependence inherent in the observed streamflows. The first part of this paper demonstrates the hybrid character of the model through stochastic simulations performed using monthly streamflows of Weber River (Utah) that exhibit a complex dependence structure. In the latter part of the paper the hybrid model is shown to be efficient in simulating multiseason streamflows, through an example of the San Juan River (New Mexico). This model ensures annual‐to‐monthly consistency without the need for any adjustment procedures. Furthermore, the hybrid model is able to preserve both within‐year and cross‐year monthly serial correlations for multiple lags. Also, it is seen to be consistent in predicting the reservoir storage (validation) statistic at low as well as high demand levels.
In search of preferential flow paths in structured porous media using a simple genetic algorithm
Authors: Gwo Jin‐Ping
Published: February 2004

Fracture network and preferential flow path images from exposed outcrops of geological formations, exposed soil pedon faces, and extracted soil columns and rock cores are often used to conceptualize and construct models to predict the fate and transport of subsurface contaminants. Both the scale resolutions inherent in these observations and the upscaling methods used to obtain macroscopic flow and transport parameters may result in uncertainties in the prediction. We present a mechanistic‐based approach that utilizes a discrete fracture flow and transport model, a distributed and high performance computational architecture, and a genetic‐based search algorithm to invert scale‐ representative, equivalent fracture networks or the preferential flow paths. Synthetic breakthrough curves (BTCs) and exposed structural information from known fracture networks in hypothetical soil columns are presented to the search algorithm. Using three genetic operators, a simple genetic algorithm (SGA) is able to invert the correct pictures of simple but not complex fracture networks. Solute transport experiments using soil columns often assume that the structure of soil columns is laterally uniform with respect to the macroscopic transport direction and the transport process is longitudinally one‐ dimensional. This assumption and the one BTC thus collected for each injection of solutes, even with flow interruptions, are not sufficient to guide the search algorithm toward the global optimum. Additional information (e.g., multiple solute BTCs along a cross section of the soil column) is necessary for the SGA to invert the correct fracture network. Three SGA population statistics, fracture network uncertainty, informatic entropy, and matrix‐fracture contact area, are proposed to measure the uncertainty of SGA near optima. A positive correlation between the reduction of these statistics and the level of relevant information to better confine the SGA search space was found. The SGA search algorithm is then applied to a laboratory solute transport problem. Multiple scenarios of search constraints, derived from visually traced surface features, are examined. The hypothesis that variation in fracture aperture may reduce the uncertainty of SGA near optima is also tested. The results from these applications suggest that there is a certain degree of uncertainty regarding the flowing nature of the exposed fracture segments that are visually traced. The uncertainty of SGA near optima is not improved by incorporating fracture aperture information into the fracture networks. Breakthrough curves thus calculated have marginal improvement, relative to the uniform aperture SGA near optima, in fitting the observations. The lack of improvement may be caused by the relative uniform structure of the soil and the scale of the problem. It is further suggested that in applying the search algorithm to laboratory and field problems, one explores only the search scenarios that relevant information and search constraints may warrant.
On the importance of atmospheric inputs of inorganic nitrogen species on the productivity of the Eastern Mediterranean Sea
Authors: Kouvarakis G. , Mihalopoulos N. , Tselepides A. , Stavrakakis S.
Published: February 2004

To assess the importance of the atmospheric deposition of nitrogen (N) on the productivity of the eastern Mediterranean Sea, measurements of both wet and dry deposition of dissolved inorganic nitrogen (DIN) have been performed at a remote coastal area in the island of Crete (Finokalia) during a 3‐year period (1996–1999). The estimation of dry deposition of DIN is based on measurements of both gaseous (HNO3 and NH3) and particulate phase (NO3− and NH4+) nitrogen compounds. The results of the wet and dry deposition obtained at Finokalia have been compared with data of particulate organic nitrogen (PON) obtained during two yearly (1994–1995 and 1997–1998) surveys (CINCS and MATER) in the Cretan Sea by using sediment traps deployed at 200 and 500 m depths. Our results show that the atmospheric deposition of DIN can account for up to 370% of the measured PON in the sediment traps, indicating that atmospheric pathway alone can sufficiently account for the measured new nitrogen production. On the basis of the primary productivity induced by the imported DIN and the productivity of the southeastern Mediterranean derived from in situ measurements a mean f ratio of 0.24 is calculated indicating that from the N point of view, the eastern Mediterranean can no longer be considered as among the most oligotrophic seas of the world. Other elements, most probably phosphorus (P), can account for the oligotrophic character of the eastern Mediterranean Sea. To our knowledge this is the first attempt to understand the role of the atmospheric input of nitrogen on the productivity of the eastern Mediterranean Sea.
Variations in slab dip along the subducting Nazca Plate, as related to stress patterns and moment release of intermediate‐depth seismicity and to surface volcanism
Authors: Chen Po‐Fei , Bina Craig R. , Okal Emile A.
Published: February 2004

The subducting Nazca Plate shows a high degree of along‐strike heterogeneity in terms of intermediate‐depth seismicity (∼70–300 km), orientations of slab stress, and volcanism. We compile the intermediate‐depth earthquakes of South America from the Harvard Centroid Moment Tensor (CMT) catalogue to determine along‐strike dip variations, and we explore the variable level of correlation between these observations. Primary results are three‐fold: (1) Consistency among orientation of tension axes, highest level seismicity, and occurrence of volcanism is associated with steeply‐dipping regions (20°–30°). (2) Volcanism and intermediate‐depth seismicity exhibit no direct correlation, suggesting that earthquake faulting is not a necessary condition for transport of dehydrated fluids out to the mantle wedge for initiation of melting. (3) Comparison of slab thermal structures between regions with and without volcanism suggests that for certain wedge widths, the maximum temperature in the mantle wedge is higher for the former than for the latter.
Regional variations in volatile composition: Isotopic evidence for carbonate recycling in the Central American volcanic arc
Authors: Snyder Glen , Poreda Robert , Hunt Andrew , Fehn Udo
Published: February 2004

Gas data were collected from geothermal production fields, fumaroles, and hot springs in Central America in order to investigate the relation between volatile output and spatial distribution of volcanic systems. The 3He/4He ratios are 6.5 ± 0.7 Ra throughout the region, indicating that helium is predominantly of mantle origin and is largely independent of variations in the characteristics of the arc. Lower ratios produced by radiogenic production within the Chortis Block are restricted to the Berlín geothermal field and the region behind the volcanic front. Ratios of CO2/3He are inversely related to the distance between the volcanic system and the trench. In the southwestern portion of the arc, where the arc‐trench gap is short and the subduction angle is shallow (Miravalles, Costa Rica), decarbonation is enhanced relative to the mantle helium flux resulting in higher CO2/3He. In the northwest, where the gap is greater and the subduction angle steeper (Ahuachapán, El Salvador), decarbonation decreases relative to the helium flux. While variations in the carbon isotopic signature have traditionally been linked to the composition of the subducted sediments, the Central American data provide evidence that other factors within the convergent plate boundary such as arc‐trench gap, crustal thickness, and subduction angle play an important role in controlling the flux of CO2 from the subducting slab. The Central American Volcanic Arc gases show no apparent contribution of carbon dioxide derived from subducted organic sediments. Shallow crustal processes, including partitioning and isotopic fractionation, account for the minor deviations from direct mixing of mantle and carbonate‐derived end‐members. Given that the Central American arc system is not unique in terms of the composition of the subducted sediments or the volcanic output, previous interpretations of global volcanic flux in terms of carbonate and sediment output should be reconsidered. Carbon‐helium relationships in Central America require that only 0.3–3.3% of the subducted carbon is released in volcanic eruptions, while the rest is presumably reintroduced into the deeper mantle. This is generally an order of magnitude lower than global averages and is limited by the availability flux of mineral‐bound water and the temperature of release. The δ13C and CO2/3He ratios suggest that even though the amount of carbon that is released from the slab and subducted sediments is relatively low in Central America, it still makes up 86–98% of the total carbon released from arc volcanics.
A dramatic Atlantic dissolution event at the onset of the last glaciation
Authors: Broecker Wallace , Clark Elizabeth
Published: February 2004

Measurements of the CaCO3 content of the CaCO3 size index and of foraminifera weights demonstrate that a prominent dissolution event occurred in the western equatorial Atlantic at the onset of the last glacial period. The decrease in CO3= ion concentration appears to have been too large to be accounted for by the ocean acidification associated with the demise of excess interglacial biomass. Rather, it appears to have been the result of a temporary strengthening of the penetration of the glacial equivalent Antarctic Bottom Water into the Atlantic. The co‐occurrence of massive Ethmodiscus rex deposition in the eastern equatorial Atlantic bears witness to a reorganization of circulation in the Atlantic. This reorganization may well reflect a temporary collapse of conveyor circulation at the onset of the last glaciation.
Variability of tropical upper tropospheric humidity 1979–1998
Authors: Bates John J. , Jackson Darren L. , Bréon Francois‐Marie , Bergen Zachary D.
Published: February 2004

We update the time series of upper tropospheric humidity observations, begun in 1979 through May 1998, which includes the major El Niño event of 1997–1998. The intercalibration of different satellites is updated and compared to a physically based intercalibration. The results show excellent agreement and indicate that the main source of intersatellite bias is the known filter response function of the different instruments. Interannual variability of spatial fields is dominated by the major El Niño events in the 1979–1998 time period. Tropical average anomaly time series of upper tropospheric humidity, however, are dominated by a pronounced seasonal preference in extremes. Large deviations from the anomaly time series are twice as likely to occur in boreal winter and spring as in boreal summer and fall. During boreal winter and spring, the tropical basic state circulation permits the opening of a westerly wave duct such that midlatitude Rossby waves can propagate into the subtropics and tropics. We hypothesize that variation in the Rossby wave activity modulates the vertical water vapor flux and is responsible for large variations in the tropical upper tropospheric humidity time series.
Upper tropospheric humidity algorithm assessment
Authors: Jackson Darren L. , Bates John J.
Published: February 2004

This study assesses a common analytic expression used to compute upper tropospheric humidity (UTH) from satellite brightness temperatures at 6.7 μm. Vertical averaging methods for UTH were found to have significant impact on the algorithm. The temperature lapse parameter β had more latitudinal variance than previously found; however, large vertical gradients in midlatitude profiles degraded UTH retrievals. The scaled reference pressure parameter P0 did sufficiently improve the radiance to humidity relationship with exception to midlatitude profiles where P0 exceeds 1.7. A new method for computing the reference pressure parameter is presented using HIRS channel 6 observations. Error analysis of radiance to humidity relationship indicates that absolute UTH errors increase with increasing humidity with largest errors of 15% per 1 K bias between simulated and observed brightness temperatures.
Long‐term variations of UV‐B irradiance over Canada estimated from Brewer observations and derived from ozone and pyranometer measurements
Authors: Fioletov V. E. , McArthur L. J. B. , Kerr J. B. , Wardle D. I.
Published: February 2004

Routine uniform spectral UV‐B measurements with Brewer spectrophotometers in the Canadian network began in 1989. This relatively short duration of UV measurements militates against reliable detection of long‐term changes in UV. A statistical model has been developed to extend the record of UV back to the early 1960s. It estimates UV values (at individual wavelengths and spectrally integrated) from global solar radiation, total ozone, dew point temperature, and snow cover. The model results are demonstrated to be in good agreement with the measurements. For example, the standard deviation of the difference between monthly values of measured and derived erythemally weighted UV irradiation is 3.3% for summer months. The major source of error in the model estimates is probably linked to rare occurrences of absorbing aerosols in the atmosphere. Long records of reliable measurements of total ozone, global solar radiation, and other parameters made it possible to derive UV‐B values at three Canadian stations from the mid‐1960s. Trends in derived erythemally weighted UV at two stations (Toronto and Edmonton) are similar to those expected from total ozone trends although the estimated error of the UV trends is more than 2 times larger. However, the increase in annual UV at Churchill (59°N) in 1979–1997 was found to be more than twice that expected from the ozone decline. This is a result of longterm changes in snow cover and clouds.
Shrubland fluxes of methyl bromide and methyl chloride
Authors: Rhew Robert C. , Miller Benjamin R. , Vollmer Martin K. , Weiss Ray F.
Published: February 2004

Flux measurements in coastal sage scrub, chamise chaparral, and creosote bush scrub environments show that methyl bromide (CH3Br) and methyl chloride (CH3Cl), compounds that are involved in stratospheric ozone depletion, are both produced and consumed by southern California shrubland ecosystems. CH3Br and CH3Cl are produced in association with a variety of plants and are consumed by the soils, although there is a large variability in the fluxes, depending on predominant vegetation and environmental conditions. At sites with a net uptake of both compounds the fluxes of CH3Cl and CH3Br show a strong correlation, with a molar ratio of roughly 40:1, pointing to a similar mechanism of consumption. In contrast, the net production rates of these compounds show no apparent correlation with each other. The average observed net CH3Br uptake rates are an order of magnitude smaller than the previously reported average soil consumption rates assigned to shrublands. Extrapolations from our field measurements suggest that shrublands globally have a maximum net consumption of <1 Gg yr−1 for CH3Br and <20 Gg yr−1 for CH3Cl and may, in fact, be net sources for these compounds. Consequently, the measured net fluxes from shrubland ecosystems can account for part of the present imbalance in the CH3Br budget by adding a new source term and potentially reducing the soil sink term. These results also suggest that while shrubland soil consumption of CH3Cl may be small, soils in general may be a globally significant sink for CH3Cl.
Predicted hygroscopic growth of sea salt aerosol
Authors: Ming Yi , Russell Lynn M.
Published: February 2004

Organic species in sea salt particles can significantly reduce hygroscopic growth in subsaturated conditions, an important uncertainty in the radiative effect of aerosol particles on the atmosphere. This hygroscopic behavior is predicted with a numerical model of the the organic‐water, electrolyte‐water, and organicelectrolyte interactions in complex mixtures of organic species and inorganic ions. The results show a 15% decrease in hygroscopic growth above 75% relative humidity for particles that include as little as 30% organic mass. Organic compositions of 50% organic mass reduce hygroscopic growth by 25%. This prediction relies on particle chemical composition estimated from measurements of insoluble organic species in marine‐derived particles and of soluble organic species measured in seawater. Twenty insoluble and four soluble organic species are used to represent the behavior of sea salt organic composition. The hygroscopic growth is strongly sensitive to the organic fraction that is soluble or slightly soluble, although variations among different soluble or insoluble species are small above the sodium chloride deliquescence point. Interactions between organic and electrolyte species depend primarily on the “salting out” behavior of NaCl with alkanes, carboxylic acids, and alcohols, although interactions with other inorganic ions in sea salt were estimated to cause small changes in the hygroscopic growth. The predicted growth factors for sea salt with < 30% organic species are consistent with growth factors measured for ambient marine‐derived particles by another group [Berg et al., 1998; Swietlicki et al, 2000; Zhou et al, 2001]. This coincidence suggests that the less‐hygroscopic particles could indicate the presence of marine organic compounds, although multiple combinations of inorganic and anthropogenic organic species would also satisfy the measured behavior.
Climate memory of snow mass as soil moisture over central Eurasia
Authors: Shinoda Masato
Published: February 2004

The interseasonal carryover of the central Eurasian snow mass anomaly as a subsequent soil moisture anomaly is studied on the basis of observational data. Regional focus is placed on the semiarid region north of the Caspian‐Aral Seas, included in central Eurasia, for which the snow cover exhibits a significant correlation with the Indian summer monsoon rainfall. In general, over this region the snow depth reaches a yearly maximum during late February to early March, while the soil moisture exhibits a maximum in early April due to snowmelt and attenuates to a minimum during midsummer. On the interannual basis, a larger (smaller) yearly maximum snow depth leads, through a later (earlier) snow disappearance, to a higher (lower) soil moisture. This carryover of the land‐surface anomalies was observed in a limited region, represented by Ural'sk (51°15′N, 51°24′E), which has the following climatic and soil conditions: (1) The yearly maximum snow depth represents a major portion of the soil water upon snow disappearance. When this is not the case, the maximum snow‐depth‐soil‐moisture correlation is weakened due to the input of meltwater that is produced prior to reaching maximum snow depth (during the snow‐increasing phase) and/or input of rainfall during the cold season. (2) The yearly maximum soil moisture during snow disappearance is lower than the field capacity. When this is not so, snow mass anomalies exceeding the field capacity are not maintained, due to the loss of excessive meltwater as runoff. In addition, the potential effect of seasonally frozen soil on the carryover is addressed. Even at Ural'sk, the carried‐over soil moisture anomaly has reduced amplitude during the relatively dry spring. These results suggest that the soil moisture anomaly may not have a direct effect on the Indian summer monsoon through land‐surface‐atmosphere interaction.
Validation of POAM III aerosols: Comparison to SAGE II and HALOE
Authors: Randall C. E. , Bevilacqua R. M. , Lumpe J. D. , Hoppel K. W.
Published: February 2004

We describe statistical comparisons between Polar Ozone and Aerosol Measurement (POAM) III and Stratosphere Aerosol and Gas Experiment (SAGE) II measurements of aerosol extinction in 1998 and 1999. SAGE II and POAM III are in qualitative agreement, and show that since the launch of POAM III in March of 1998, stratospheric aerosol extinctions at visible and near‐IR wavelengths have remained at background levels. We present quantitative differences between the SAGE II and POAM III extinctions at 1.02 μm and 0.45 μm for temporally and spatially coincident measurements. At 1.02 μm the instruments agree to within about ±30% from 10 to 22 km, where most of the aerosol extinction lies. Differences at 0.45 μm are similar to 1.02 μm in the southern hemisphere, but much larger in the northern hemisphere. We show that differences between SAGE II and POAM III slant path optical depths closely resemble the aerosol extinction differences at 1.02 μm, but not at 0.45 μm. On the basis of these results we conclude that the aerosol extinction differences at 1.02 μm arise from differences in the slant path optical depth measurements of the two instruments, not from species separation differences in the retrieval algorithms. However, we tentatively attribute the aerosol extinction differences at 0.45 μm to an error in the NO2/aerosol species separation in the SAGE II retrievals. We present theoretical simulations incorporating the maximum plausible systematic pointing or timing errors in the POAM III instrument. We conclude that these errors cannot explain the 1.02 μm optical depth or aerosol extinction differences, although it is possible that they contribute to the observed differences. We thus attribute these differences to fundamental radiometric differences between POAM III and SAGE II that remain to be resolved. We also compare derived surface areas and volume densities from POAM III, SAGE II, and the Halogen Occultation Experiment (HALOE). The statistical differences can be explained by the aerosol extinction differences in the SAGE II comparisons, and by the lack of sensitivity on the part of POAM III and SAGE II to very small aerosols in the HALOE comparisons. Nevertheless, we show qualitative agreement between all three instruments. The results presented here show that the POAM III aerosol measurements are valid for scientific studies.
Spectra and correlations of climate data from days to decades
Authors: Weber Rudolf O. , Talkner Peter
Published: February 2004

The correlations of several daily surface meteorological parameters such as maximum, minimum, and mean temperature, diurnal temperature range, pressure, precipitation, and relative air humidity are analyzed by partly complementary methods being effective on different timescales: power spectral analysis, second‐ and higher‐degree detrended fluctuation analysis, Hurst analysis, and the direct estimation of the autocorrelation in the time domain. Data from American continental and maritime and European low‐elevation and mountain stations are used to see possible site dependencies. For all station types and locations, all meteorological parameters show correlations from the shortest to the longest statistically reliable timescales of about three decades. The correlations partly show a clear power law scaling with site‐dependent exponents. Mainly, the short‐time behavior of the correlations depends on the station type and differs considerably among the various meteorological parameters. In particular, the detrended fluctuation and the Hurst analyses reveal a possible power low behavior for long timescales which is less well resolved or even may remain unrecognized by the classical power spectral analysis and from the autocorrelation. The long‐time behavior of the American temperatures is governed by power laws. The corresponding exponents coincide for all temperatures except for the daily temperature range with different values for the maritime and the continental stations. From the European temperatures those from low‐elevation stations also scale quite well, whereas temperatures from mountain stations do not.
Temperature dependence of the Brewer ultraviolet data
Authors: Weatherhead E. , Theisen D. , Stevermer A. , Enagonio J. , Rabinovitch B. , Disterhoft P. , Lantz K. , Meltzer R. , Sabburg J. , DeLuisi J. , Rives J. , Shreffler J.
Published: February 2004

We characterize the temperature dependence of the U.S. Environmental Protection Agency/University of Georgia network of Brewer spectrophotometers as used to measure solar ultraviolet (UV) radiation. The instruments used in this study are operated in partnership with the National Park Service at 14 national park sites and in 7 urban areas. The daily and seasonal measurements of UV radiation provided by the instruments can be affected by changes in the internal instrument temperatures at the sites. These effects can lead to errors on the order of ±10% in the resulting spectral data and of the same order of magnitude for CIE‐weighted UV. Fortunately, the temperature dependence for each instrument can be quantified and the data corrected, improving the accuracy to values closer to the levels attainable with high‐quality calibration and operation. The temperature dependence of the Brewers is found to vary significantly among the different instruments. A 0.8% per degree Celsius dependence can result in temperature effects as large as 12% at sites where temperatures can vary by 15°C in 1 day. These effects can result in a ±5% error in the spectral irradiance. The errors to the spectral irradiance vary seasonally in a manner that is not random: in the warmer summertime the temperature dependence of the instruments can cause the irradiances to be underestimated, while during the colder winters the effect will be to overestimate UV amounts. In the part of the spectrum above 325 nm, the temperature dependence is generally independent of wavelength. Below 325 nm the temperature effects vary as a function of wavelength over a range of values and are generally largest at the shortest wavelengths. Because changes in temperature from one calibration to the next can affect an instrument's response, understanding the temperature effects is necessary to ensure that artificial trends are not introduced into the Brewer data records.