bluuebunny/crossref_metadata_2025 huggingface dataset:
Rilke's "Archaic Torso of Apollo"
Authors: Jager Bernd
Published: October 2003

What happens when in the midst of the routines of our workaday world we suddenly find ourselves in the presence of someone who regards us with intensity and demands our response? Rilke's poem explores that precise and pregnant moment when an object of scientific investigation, aesthetic contemplation or historical analysis suddenly breaks free from the constraints imposed upon it by a workaday perspective and transforms itself into a subject who beckons us to enter another world. Rilke's "Archaic Torso of Apollo" leads us beyond our mundane and naturalistic concerns, beyond a thinking and doing that seeks to appropriate and masters a natural world.To faithfully follow its meandering thought means to be led to the very source from which springs narration and metaphor. It is from this same source that springs a human world.
The Most Silent of Men: Nietzsche's Other Madness
Authors: Hooke Alexander
Published: October 2003

Silence and madness can be likened to irritating cousins. Both introduce questionable or negative elements to the ideals of dialogue and rational communication. Silence can disturb and disrupt the rational pursuit of truth, while madness can noisily provoke a mockery of any meaningful or reciprocal exchange of ideas and thoughts. In the work and life of philosopher Friedrich Nietzsche, silence and madness highlight more positive features.To study and articulate these features, this paper relies on the central themes of two prominent thinkers, the archaeological and genealogical studies from the late Michel Foucault and the revived forces of phenomenology from American philosopher Alphonso Lingis, to present the case that Nietzsche embraced a late 19th century disorder called the fugue. This disorder, what Ian Hacking calls a transient mental illness, involves nomadic life. Nietzsche exemplified such a life. His writings and experiences comprise a mixture of travels, arts of the self, willful forgetfulness, and a philosophical play with madness. From conventional perspectives, this play is viewed as irrelevant or detrimental to Nietzsche's philosophical importance. From Nietzsche's own perspective, however, this play might be appreciated as a gift from the insights of madness and the enriching contacts with silence.
Altered hypertrophic chondrocyte kinetics in GDF‐5 deficient murine tibial growth plates
Authors: Mikic B. , Clark R. T. , Battaglia T. C. , Gaschen V. , Hunziker E. B.
Published: October 2003

The growth/differentiation factors (GDFs) are a subgroup of the bone morphogenetic proteins best known for their role in joint formation and chondrogenesis. Mice deficient in one of these signaling proteins, GDF‐5, exhibit numerous skeletal abnormalities, including shortened limb bones. The primary aim of this study was determine whether GDF‐5 deficiency would alter the growth rate in growth plates from the long bones in mice and, if so, how this is achieved. Stereologic and cell kinetic parameters in proximal tibial growth plates from 5‐week‐old female GDF‐5 ‐/‐ mice and control littermates were examined. GDF‐5 deficiency resulted in a statistically significant reduction in growth rate (−14%, p = 0.03). The effect of genotype on growth rate was associated with an altered hypertrophic phase duration, with hypertrophic cells from GDF‐5 deficient mice exhibiting a significantly longer phase duration compared to control littermates (+25%, p = 0.006). These data suggest that one way in which GDF‐5 might modulate the rate of endochondral bone growth could be by affecting the duration of the hypertrophic phase in growth plate chondrocytes. © 2003 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved.
Carbonaceous aerosols over the Indian Ocean during the Indian Ocean Experiment (INDOEX): Chemical characterization, optical properties, and probable sources
Authors: Mayol‐Bracero O. L. , Gabriel R. , Andreae M. O. , Kirchstetter T. W. , Novakov T. , Ogren J. , Sheridan P. , Streets D. G.
Published: October 2003

We measured carbonaceous material and water‐soluble ionic species in the fine fraction (Dp < 1.3 μm) of aerosol samples collected on NCAR's C‐130 aircraft during the intensive field phase (February–March 1999) of the Indian Ocean Experiment (INDOEX). Polluted layers were present over most of the study region north of the equator at altitudes up to 3.2 km. The estimated aerosol mass (sum of carbonaceous and soluble ionic aerosol components) of fine‐mode particles in these layers was 15.3 ± 7.9 μg m−3. The major components were particulate organic matter (POM, 35%), SO42− (34%), black carbon (BC, 14%), and NH4+ (11%). The main difference between the composition of the marine boundary layer (MBL, 0 to ∼1.2 km), and the overlying residual continental boundary layer (1.2 to ∼3.2 km) was a higher abundance of SO42− relative to POM in the MBL, probably due to a faster conversion of SO2 into SO42− in the MBL. Our results show that carbon is a major, and sometimes dominant, contributor to the aerosol mass and that its contribution increases with altitude. Low variability was observed in the optical properties of the aerosol in the two layers. Regression analysis of the absorption coefficient at 565 nm on BC mass (BC < 4.0 μg C m−3) yielded a specific absorption cross section of 8.1 ± 0.7 m2 g−1 for the whole period. The unusually high fraction of BC and the good correlation between the absorption coefficient and BC suggest that BC was responsible for the strong light absorption observed for the polluted layers during INDOEX. High correlation between BC and total carbon (TC) (r2 = 0.86) suggest that TC is predominantly of primary origin. Good correlations were also found between the scattering coefficient at 550 nm and the estimated aerosol mass for the fine fraction. These yielded a specific scattering cross section of 4.9 ± 0.4 m2 g−1. The observed BC/TC, BC/OC, SO42−/BC, and K+/BC ratios were fairly constant throughout the period. These ratios suggest that between 60 and 80% of the aerosol in the polluted layers during INDOEX originated from fossil fuel and between 20 and 40% from biofuel combustion.
Linked behavior of twin tropical cyclones
Authors: Moustaoui M. , Teitelbaum H. , Basdevant C. , Boughaleb Y.
Published: October 2003

The mutual interaction of cross‐equatorial twin cyclones, its effect, and the effect of the planetary vorticity gradient on their motion are investigated using barotropic nondivergent and shallow water models. In comparing the behavior of a single cyclone to that of twin cyclones, it is found that each cyclone tends to accelerate the other and to turn its track westward. The causes of these changes are illuminated by investigating the motion of a single northern cyclone in a mean flow that resembles the one induced by a southern cyclone. The meridionally varying environmental vorticity gradient induced by the southern cyclone plays a key role in the explanation of the northern cyclone motion. This gradient tends to cancel the planetary vorticity gradient around the northern cyclone, resulting in a lower effective β that produces a weaker wave number 1 (WN1) asymmetry and consequently a slower motion. As the cyclone moves northward, the effective β increases, and so does the WN1 asymmetric circulation, which in turn accelerates the cyclone. Even in the linear case, the mean varying vorticity gradient causes the WN1 circulation to be no longer east–west, but to turn counterclockwise. This effect is due to the development of a strong anticyclonic circulation that is at a maximum in the northeast region as a consequence of vorticity conservation. When the nonlinear effects are included, the β gyres are turned further counterclockwise by the symmetric circulation, which is stronger than in the single cyclone case. Mutual interaction of tropical twin cyclones may increase the duration of the resulting Westerly Wind Bursts by reducing the poleward drift. The role of divergence effects on the twin cyclones' evolution is examined using a shallow water simulation with the same cyclone wind profile as in the nondivergent case. It is found that divergence tends to slow down the cyclone motion. We suggest that this effect is due to the potential vorticity conservation (compared to absolute vorticity conservation for nondivergent flows) that tends to reduce the produced WN1 asymmetry.
Using high temporal frequency data for CO2 inversions
Authors: Law R. M. , Rayner P. J. , Steele L. P. , Enting I. G.
Published: October 2003

Almost all previous inversions for CO2 sources and sinks from atmospheric measurements have used monthly or annual mean data. Here, we assess the potential benefits and challenges of using higher time resolution CO2 concentration data. Inversions are performed with synthetic data since there are currently only limited continuous CO2 measurements available. The use of synthetic data also enables the inversion quality to be evaluated in terms of both systematic biases in the estimated sources and the magnitude of the source uncertainties. When estimating sources for 22 large regions, we find that using high time resolution data gives large reductions in uncertainty compared to using monthly mean data. Greater reductions are achieved (around 80%) for smaller rather than larger networks (around 45%), although larger networks give lower uncertainties overall (0.35 Gt C yr−1 on average compared to 1.2 Gt C yr−1). In most cases, inversion biases are larger than the estimated uncertainties (by up to 6 Gt C yr−1) due to the assumptions made in the inversion about the spatial distribution of sources within regions. These biases can be significantly reduced by estimating the sources for smaller regions. This is demonstrated using a case study that subdivides Australia into the model grid cells. Sources are successfully estimated from high time resolution data for the individual grid cells and for the total Australian source.
A comparison of mean density and microscale density fluctuations in a CME at 10 R⊙
Authors: Lynch B. J. , Coles W. A. , Sheeley N. R.
Published: October 2003

We have observed intensity scintillation (IPS) of the radio source 0854 + 201 at 8 GHz on August 2, 2000 during the passage of a coronal mass ejection (CME) across the line of sight. The source was at a distance of 10 R⊙ over the north solar pole. Simultaneous observations with the LASCO C3 instrument allow us to model the mean density Ne and the microscale density fluctuations δNe within the CME. We find that Ne increased by a factor of 2.18 but δNe increased by only 1.76, so the ratio δNe/Ne is 19% smaller than in the pre‐CME slow wind. During the passage of the CME a short burst of enhanced turbulence doubled the IPS variance but was not visible in the C3 images. This was likely caused by a thin flux tube crossing the line of sight. Detailed modeling indicates that the diameter of the tube was 41,000 km and its density was 14.5 times the CME density.
Ozone depletion and chlorine activation in the Arctic winter 1999/2000 observed in Ny‐Ålesund
Authors: Klein Ulf , Wohltmann Ingo , Lindner Kai , Künzi Klaus F.
Published: October 2003

We present vortex‐averaged calculations of ozone loss rates between late December 1999 and mid‐March 2000 derived from data collected by the Radiometer for Atmospheric Measurements (RAM). The ground‐based microwave radiometer RAM is operated at the Arctic station of the Network for the Detection of Stratospheric Change (NDSC) at Ny‐Ålesund, Spitsbergen (79°N, 12°E). Simultaneous observations of stratospheric ozone and chlorine monoxide (ClO) profiles were performed by the RAM during winter and spring 1999/2000. Ozone was monitored continuously and ClO was observed between late February and early April. Maximum ozone loss rates of 35 ppb/d were obtained in mid‐February and in the beginning of March. The ozone loss accumulated to 41% in a layer with a thickness of approximately 10 km centered at the 475 K isentropic level. Ozone loss estimates are compared to results obtained by other groups and to model calculations showing good agreement when all results are adjusted to the same vertical resolution. Simultaneously, we have observed record ClO mixing ratios in the lower stratosphere with a peak mixing ratio of 1.25 ppb on 1 March, corresponding to the strong chemical ozone loss at the same time. The ClO observations are compared to model calculations indicating that the SLIMCAT model underestimates the amount of chlorine activation at the end of the winter in Ny‐Ålesund, in contrast to the good agreement between modeled and observed ozone loss.
Comparison of measurements and model calculations of stratospheric bromine monoxide
Authors: Sinnhuber B.‐M. , Arlander D. W. , Bovensmann H. , Burrows J. P. , Chipperfield M. P. , Enell C.‐F. , Frieß U. , Hendrick F. , Johnston P. V. , Jones R. L. , Kreher K. , Mohamed‐Tahrin N. , Müller R. , Pfeilsticker K. , Platt U. , Pommereau J.‐P. , Pundt I. , Richter A. , South A. M. , Tørnkvist K. K. , Van Roozendael M. , Wagner T. , Wittrock F.
Published: October 2003

Ground‐based zenith sky UV–visible measurements of stratospheric bromine monoxide (BrO) slant column densities are compared with simulations from the SLIMCAT three‐dimensional chemical transport model. The observations have been obtained from a network of 11 sites, covering high and midlatitudes of both hemispheres. This data set gives for the first time a near‐global picture of the distribution of stratospheric BrO from ground‐based observations and is used to test our current understanding of stratospheric bromine chemistry. In order to allow a direct comparison between observations and model calculations, a radiative transfer model has been coupled to the chemical model to calculate simulated slant column densities. The model reproduces the observations in general very well. The absolute amount of the BrO slant columns is consistent with a total stratospheric bromine loading of 20 ± 4 ppt for the period 1998–2000, in agreement with previous estimates. The seasonal and latitudinal variations of BrO are well reproduced by the model. In particular, the good agreement between the observed and modeled diurnal variation provides strong evidence that the BrO‐related bromine chemistry is correctly modeled. A discrepancy between observed and modeled BrO at high latitudes during events of chlorine activation can be resolved by increasing the rate constant for the reaction BrO + ClO → BrCl + O2to the upper limit of current recommendations. However, other possible causes of the discrepancy at high latitudes cannot be ruled out.
Cloud‐to‐ground lightning associated with the evolution of a multicell storm
Authors: Brown Rodger A. , Kaufman Cristina A. , MacGorman Donald R.
Published: October 2003

The relationship of cloud‐to‐ground (CG) lightning strikes to the stages of updraft/downdraft evolution is investigated in a multicell thunderstorm that occurred on 11 July 1989 during the North Dakota Thunderstorm Project. With only single‐Doppler radar data available for this storm, reflectivity and single‐Doppler velocity signatures are used to identify individual cells within the storm and to deduce the stage of evolution within each cell. Cell evolution appeared to follow the Thunderstorm Project model of the late 1940s: updraft growth and vertical development during the growing (cumulus) stage, updraft peaking in the upper portion of the cell and rainy downdraft descending from the middle portion during the mature stage, and lighter precipitation settling out during the dissipating stage. On 11 July, cells tended to occur in clusters, each cluster consisting of growing/mature and dissipating cells close together in both time and space. No CG strikes were detected when the convective region of the storm contained only one cluster of cells; all strikes occurred when there were two or more clusters of cells. With only two exceptions, strikes occurred in the convective region of the storm, typically closer to growing/mature cells than to dissipating cells. These observations support the hypothesis that descending precipitation creates electrical conditions conducive to flashes reaching ground. However, these observations also suggest that the greater complexity of electrical structure due to the juxtaposition of several cells is especially conducive to CG flashes and can cause CG flashes to occur earlier in a new cell's life cycle than would otherwise be the case.
Validation of temperature measurements from the airborne Raman ozone temperature and aerosol lidar during SOLVE
Authors: Burris John , McGee Thomas , Hoegy Walter , Lait Leslie , Twigg Laurence , Sumnicht Grant , Heaps William , Hostetler Chris , Bui T. Paul , Neuber Roland , McDermid I. Stuart
Published: October 2003

The Airborne Raman Ozone, Temperature, and Aerosol Lidar (AROTEL) participated in the recent SAGE III Ozone Loss and Validation Experiment (SOLVE) by providing profiles of aerosols, polar stratospheric clouds (PSCs), ozone, and temperature with high vertical and horizontal resolution. Temperatures were derived from just above the aircraft to ∼60 km geometric altitude with a reported vertical resolution of ∼0.6 km. The horizontal footprint varied from 4 to 70 km. This paper explores the measurement uncertainties associated with the temperature retrievals and makes comparisons with independent, coincident measurements of temperature. Measurement uncertainties range from 0.1 to ∼4 K depending on altitude and integration time. Comparisons between AROTEL and balloon sonde temperatures retrieved under clear sky conditions using both Rayleigh and Raman scattered data showed AROTEL ∼1 K colder than sonde values. Comparisons between AROTEL and the Meteorological Measurement System (MMS) on NASA's ER‐2 show AROTEL being from 2 to 3 K colder for altitudes ranging from 14 to 18 km. Temperature comparisons between AROTEL and the UK Met Office's model showed differences of ∼1 K below ∼25 km and a very strong cold bias of ∼12 K at altitudes between 30 and 35 km.
A mechanistic model of the northern annular mode
Authors: Eichelberger Scott J. , Holton J. R.
Published: October 2003

The northern annular mode (NAM) is the leading mode of variability in the Northern Hemisphere. The NAM consists of a meridional dipole of the zonal mean zonal wind that extends into the stratosphere during the winter season. During the high‐index state of the NAM, high‐latitude westerly winds are stronger than normal, leading to a stronger and colder polar vortex. Over the past few decades, observations show a trend toward higher NAM index values. To investigate whether this trend is a result of natural variability or is related to greenhouse warming, a mechanistic model is developed that provides a simple analogue of the NAM. The model represents the interaction between the zonally symmetric flow and planetary waves for two meridional modes of variation. Greenhouse warming is specified in the model by varying the radiative equilibrium meridional temperature gradient. Variations in the second meridional mode qualitatively resemble those of the observed NAM. Model runs that correspond to larger greenhouse gas concentrations yield on average higher NAM index values.
New methodology for deriving total ozone and other atmospheric variables from Brewer spectrophotometer direct sun spectra
Authors: Kerr J. B.
Published: October 2003

A new method has been developed for taking high‐quality spectral measurements of ultraviolet radiation with the Brewer spectrophotometer. Spectral measurements of direct solar radiation made routinely with the new method at Toronto between 1996 and 2001 were used to determine total ozone, aerosol optical depth, sulfur dioxide and ozone temperature. Corrections to laboratory‐based ozone absorption coefficients have been derived from the data set of these new measurements as have the temperature dependencies of standard Brewer and Dobson total ozone measurements. It was found that the temperature of atmospheric ozone has little effect on the total ozone derived from the standard algorithm used for the Brewer instrument. The new measurement method and the calibration information required to derive the atmospheric variables from the spectra are described. Results of calibrations carried out at Mauna Loa Observatory in 1997 and 2000 are presented. The records of atmospheric variables measured at Toronto between 1996 and 2001 are given.
Global free oscillations of the atmosphere and secondary planetary waves in the mesosphere and lower thermosphere region during August/September time conditions
Authors: Pogoreltsev A. I. , Fedulina I. N. , Mitchell N. J. , Muller H. G. , Luo Y. , Meek C. E. , Manson A. H.
Published: October 2003

Wind measurements made using ground‐based mesosphere and lower thermosphere radar systems at Sheffield, UK (2°W, 53°N) and Saskatoon, Canada (107°W, 52°N) show an increase in long‐period planetary wave (PW) activity at the end of August until the middle of September 1993. Some of these waves can be identified with the well‐known normal atmospheric modes; however, the westward propagating wave with zonal wave number one (m = 1) and a period of about 6.5 days observed during this time interval cannot be explained using the classical theory of free atmospheric oscillations. Analysis of the UKMO assimilated fields shows that in the stratosphere the 7‐day wave with m = 2 increases in amplitude during the time interval considered, and there exists a strong stationary planetary wave (SPW) with m = 1. A steady state two‐dimensional numerical model of planetary waves has been used to simulate the free atmospheric oscillations and secondary planetary wave, which arises from a nonlinear interaction between the second asymmetric normal mode with m = 2 (the 7‐day wave) and SPW with m = 1. The results of simulation show that an increase in long‐period PW activity during August/September can be explained by seasonal changes of the zonal mean flow, which influence the wave propagation conditions, and that one of the possible sources for the 6.5‐day wave is a nonlinear interaction between the 7‐day wave and SPW with m = 1. It is suggested that the 6.5‐day wave with m = 1 be referred to as a “secondary normal mode,” which has been generated by random meteorological motions in the lower atmosphere and involving interaction with a SPW of wave number 1.
Structure of the upper water column in the northwest North Atlantic: Modern versus Last Glacial Maximum conditions
Authors: de Vernal Anne , Hillaire‐Marcel Claude , Peltier W. Richard , Weaver Andrew J.
Published: October 2003

During the Last Glacial Maximum, the northwestern North Atlantic constituted a major conduit for Labrador and Greenland ice sheet meltwaters. Vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements (δ18O) in planktonic foraminifera. Transfer functions yield temperature and salinity and thus potential density (σθ) for the warmest (August) and coldest (February) months in the photic zone. The δ18O values in different size fractions of epipelagic (Globigerina bulloides) and mesopelagic (Neogloboquadrina pachyderma left‐coiled (Npl)) foraminifera allow us to assess σθ gradients through the pycnocline between surface and intermediate waters, based on the calibration of a σθ versus δ18O relationship from transfer function reconstructions. The size and density of Npl shells provide further constraints on these σθ gradients. The results show the development of a very strong pycnocline during the LGM with a difference of about 3 (summer) to 1.5 (winter) σθ units between surface and underlying waters. They indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow, low‐salinity buoyant layer over the northern North Atlantic. This layer depicted a strong E‐W gradient, with maximum seasonal contrast and minimum absolute σθ values westward.
Dyadic Green's functions for curved waveguides and cavities and their reformulation
Authors: Fan Guo‐Xin , Liu Qing Huo
Published: October 2003

Dyadic Green's functions (DGFs) for continuously curved waveguides are important for the feeding and radiation problems of cylindrically conformal slotted‐waveguide arrays. The major difficulty in the construction of these DGFs in curved waveguides and cavities is that there are no entire‐domain TE or TM modes with respect to the curving direction, while the longitudinal‐section electric (LSE) and magnetic (LSM) modes do not have the complete orthogonality in terms of the dot product as required by the conventional Ohm‐Rayleigh method as practiced in literature. Therefore, the conventional Ohm‐Rayleigh method for constructing DGFs is not applicable to curved waveguides. In this work, the DGFs are constructed with the help of the Lorentz reciprocity theorem and the mode orthogonality based on the concept of power flow, and by adding the source singularity terms. To reduce the orders of singularity of DGFs in their application to waveguide walls, the common form of DGFs is then reformulated into a form convenient for numerical computation by both forward and backward derivation procedures. Finally, a general procedure is proposed for the reformulation of DGFs for common types of waveguides. The DGFs derived are applicable to problems with curved waveguide junctions, and coupling and radiating slots for conformal slotted‐waveguide antennas.
Three‐dimensional subionospheric VLF field diffraction by a truncated highly conducting cylinder and its application to the Trimpi effect problem
Authors: Soloviev O. V. , Hayakawa M.
Published: October 2003

By means of a three‐dimensional full‐wave analytical‐numerical technique we consider the diffraction of a VLF point source field by a localized perturbation in the lower ionosphere, which is taken as a truncated highly conducting cylinder. The surface impedance concept is additionally used to model the Earth‐ionosphere waveguide. Our approach is based on the preliminary asymptotic integration of the rigorous two‐dimensional integral equation in order to facilitate its further numerical handling, and an original computational algorithm is proposed to obtain a solution of the approximate equation. By reducing CPU time, the procedure developed enables us to study both small and comparatively large irregularities. The theoretical computations have yielded the following findings: (1) the transverse dimension of the reflecting area, which can explain the experimental result, may be reduced as compared with that suggested before, (2) scattering may be significant not only in the forward direction but also in the backward direction and out‐of‐the‐way directions, and (3) the same ionospheric perturbation produces a noticeably smaller effect on subionospheric VLF radio wave propagation for daytime conditions than for nighttime ones.
Study of mean vertical motions over Gadanki (13.5°N, 79.2°E), a tropical station, using Indian MST radar
Authors: Jagannadha Rao V. V. M. , Venkat Ratnam M. , Narayana Rao D.
Published: October 2003

Long‐term mean vertical velocities observed by the Mesosphere‐Stratosphere‐Troposphere (MST) radar over a tropical station, Gadanki, India (13.5°N, 79.2°E), are presented for the first time in this paper. Profiles of mean vertical velocities show wave like structure with a vertical wavelength of ∼6 km, and the observed values range from 3 to 20 cm s−1 on average. During monsoon and postmonsoon seasons, larger magnitudes are observed up to 20 cm s−1. From the present study, an interesting feature, reversal in vertical velocities from downward to upward between 5 and 10 km during the monsoon season, is observed. This upward motion in long term averaged vertical velocity is thought to be due to reversal in wind direction around this height range and also due to horizontal velocity convergence, which is frequently observed over this region. One more reversal is observed near the Tropical Easterly Jet (TEJ) (around 16 km), which is from downward to upward and always showing minimum vertical velocities close to zero. This reversal can be attributed to instabilities associated with the jet streams. Large negative values are observed in the lower troposphere below 6 km, which are attributed to large vertical wind variances observed in this region indicating gravity wave activity.
On stochastic modeling of flow in multimodal heterogeneous formations
Authors: Lu Zhiming , Zhang Dongxiao
Published: October 2003

Most existing stochastic models are developed for unimodal porous media that may be well characterized with only the first two statistical moments. However, the distribution of hydraulic properties, such as hydraulic conductivity, may possess a multiplicity of modes; thus the first two moments may not be adequate to characterize properties of such porous media. In turn, the stochastic models developed for unimodal porous media may not be applicable to flow and transport in a multimodal heterogeneous porous medium. This study investigates under what circumstances the second‐order moment‐based stochastic models are applicable to multimodal heterogeneous porous media. We assume that a porous medium is composed of a number of materials (categories), each of which may have a different mean, variance, and correlation scale. The distribution of materials in the domain is characterized by indicator random variables. We first derive analytical expressions for the mean and covariance of the log saturated hydraulic conductivity (ln Ks) of the multimodal porous medium in terms of categorical proportions, transition probability among categories, and covariances of indicator random variables. We express the covariance in terms of the statistics of materials in the porous medium, which allows us to accurately evaluate the variance and the correlation length of the composite ln Ks field. We then solve the second‐order moment equations for the “equivalent” unimodal field with an exponential covariance with a single correlation scale computed for the composite field. On the other hand, we conduct two sets of Monte Carlo simulations: one with multimodal random fields, and the other with “equivalent” unimodal random fields. Examples for porous media with two materials are given. Numerical experiments show that a bimodal ln Ks field may be well approximated by an equivalent unimodal field when one of the two modes is dominant, under which condition the applicability of the second‐order moment‐based model is subject to the same limitation of relatively small variance as that for unimodal fields. When the bimodal distribution has two more or less equally important modes, although it cannot be adequately represented by an equivalent unimodal distribution, the second‐order moment‐based stochastic model seems to be applicable to systems with larger composite variances than it does for an one‐mode‐dominant distribution.
Uncertainty of nitrate‐N load computations for agricultural watersheds
Authors: Guo Yiping , Markus Momcilo , Demissie Misganaw
Published: October 2003

Water quality samples for most streams are collected at variable frequencies within monitoring periods of different lengths. On the basis of discrete concentration data obtained from these monitoring studies, loads of various pollutants passing through a gaging station for selected periods may be calculated using various load estimation methods. In this paper, nitrate‐N load estimates were compared with their “true” values, calculated using 6 years of daily nitrate‐N concentration and average discharge data at an agricultural watershed in central Illinois. A Monte Carlo subsampling study was conducted to simulate different sampling scenarios for variable sampling frequencies and different monitoring durations. Load calculations were compared for each sampling scenario based on rating curve, ratio estimator, and flow‐weighted average estimator. In addition, two bias correction techniques (minimum variance unbiased estimator (MVUE) and smearing estimator) were applied to the rating curve method. The monitoring durations were 1, 2, 3, and 6 years, and the sampling frequencies ranged from weekly to bimonthly. The results demonstrated that a desired accuracy of the estimates could be achieved either by sampling more frequently or by monitoring the site longer. Although the ratio and the flow‐weighted average estimators had a small negative bias, in most cases rating curve estimators were positively biased when applied to the study site. Also, neither of the two bias correction techniques, MVUE and smearing estimator, decreased this positive bias. On the contrary, those techniques produced a higher bias, which resulted in increased root‐mean‐square error (RMSE). The rating curve uncorrected for bias, the simple ratio, and the flow‐weighted estimator had a significantly smaller RMSE for all sampling frequencies and all periods of record than the bias‐corrected rating curve methods.
The dominance of electron plasma waves near a reconnection X‐line region
Authors: Farrell W. M. , Desch M. D. , Kaiser M. L. , Goetz K.
Published: October 2003

As previously reported by Oieroset et al. [2000], the Wind spacecraft made a fortuitous near‐encounter in April 1999 with an active X‐line reconnection region in the geomagnetic tail. The plasma flow signatures included two reversals of bulk flow velocity from earthward to tailward, and then tailward to earthward. We report here on the associated plasma wave observations made concurrently with the near‐encounter with the X‐line. Specifically, we find that emissions at the local upper hybrid frequency intensify greatly for short periods, with amplitudes exceeding 40 mV/m detected in the region. We discuss the upper hybrid bursts' possible importance in the electron diffusion region.
Elastic Moduli of Jadeite‐Enstatite Majorite
Authors: Reichmann Hans J. , Sinogeikin Stanislav V. , Bass Jay D. , Gasparik Tibor
Published: October 2003

The adiabatic bulk (KS) and shear (G) moduli of a polycrystalline majorite‐garnet solid solution with composition (Na0.92Mg2.08)(Mg0.02Al1.06Si0.92)Si3O12 were measured at ambient conditions by Brillouin spectroscopy. KS and G were found to be 171.6 (3.5) GPa and 103.5 (2.0) GPa, respectively. Assuming a linear dependence of the elastic moduli on composition for the Mg2Si2O6 (enstatite‐majorite, En‐Mj) – NaAlSi2O6 (jadeite‐majorite, Jd‐Mj) join, the calculated KS and G of the fictive Jd‐Mj end‐member are 178 and 125 GPa, respectively. At ambient conditions, the shear velocity change associated with the pyroxene to majorite transition increases dramatically with increasing Na content in the system. In contrast, there is virtually no shear velocity increase associated with the pyroxene to majorite transition in MgSiO3. If this relationship holds at high pressures and temperatures, it suggests that for mineral assemblages containing an abundance of large radius cations such as Ca and Na, the pyroxene→garnet reaction will produce higher shear velocity gradients than assemblages that are relatively deficient in these elements. Such chemical effects could play a significant role in explaining high seismic velocity gradients in the transition zone.
Tropical Pacific decadal variability and global warming
Authors: Bratcher Amy J. , Giese Benjamin S.
Published: October 2003

An analysis of ocean surface temperature records show that low frequency changes of tropical Pacific temperature lead global surface air temperature changes by about 4 years. Anomalies of tropical Pacific surface temperature are in turn preceded by subsurface temperature anomalies in the southern tropical Pacific by approximately 7 years. The results suggest that much of the decade to decade variations in global air temperature may be attributed to tropical Pacific decadal variability. The results also suggest that subsurface temperature anomalies in the southern tropical Pacific can be used as a predictor for decadal variations of global surface air temperature. Since the southern tropical Pacific temperature shows a distinct cooling over the last 8 years, the possibility exists that the warming trend in global surface air temperature observed since the late 1970's may soon weaken.
Freshening of the Labrador Sea surface waters in the 1990s: Another great salinity anomaly?
Authors: Häkkinen Sirpa
Published: October 2003

The observed Labrador Sea surface salinities for 1951–2001 in region [55W–40W, 45N–55N] show freshening in the 1990s which may rival the Great Salinity Anomaly (GSA) of the 1970s [Dickson et al., 1988]. The 1990s freshening is distinct in the lowest range of salinity values associated with the coastal waters. The variability of the highest salinity values, provided by the North Atlantic Current entering the Labrador Sea, shows that the high salinity Atlantic waters were not widely present in the 1970's and 1990s. This can be interpreted as weakened transport of saline waters to the area. This explanation is consistent with an Arctic‐North Atlantic model results forced by NCEP/NCAR Reanalysis data (for 1958–2001) which suggest that these periods are associated with a reduced meridional overturning. The model also associates the coastal freshening with southward current anomalies which are well correlated with the number of icebergs crossing 48N.
Inflow interruption by meteorological forcing in the Strait of Gibraltar
Authors: García Lafuente Jesús , Delgado Javier , Criado Francisco
Published: October 2003

A case of extreme meteorologically forced fluctuation of net flow through the Strait of Gibraltar is analysed. The Atlantic water inflow was interrupted during some days and the net flow reached a peak of −1.5 Sv towards the Atlantic Ocean. In spite of the rapid increase of atmospheric pressure that triggered this episode, the expected inflow contribution to the net flow induced by pressure variation should not exceed 75% of the mean inflow, insufficient to reverse the inflow. Wind stress acting on the upper layer can induce important inflow and therefore net flow fluctuations. A simple model is proposed in which wind stress intensity as a function of frequency determines the inflow response. For low frequency fluctuations and moderate wind speeds the model predicts a gain that, if added to the atmospheric pressure effect, could bring the inflow fluctuation peak beyond the mean, thus explaining the inflow interruption.
Onset of convection with temperature‐ and depth‐dependent viscosity
Authors: Korenaga Jun , Jordan Thomas H.
Published: October 2003

We derive a scaling law for the onset of convection in an incompressible fluid cooled from above with temperature‐ and depth‐dependent viscosity, on the basis of 2‐D numerical simulation. Rayleigh numbers up to 107 are considered. The activation energy is varied from 0 to 200 kJ mol−1, and a variation of up to 103 is considered in depth‐dependent reference viscosity. Our scaling law is shown to be able to handle a variety of buoyancy distributions, including highly non‐Gaussian and multimodal distributions, with a tightly constrained critical Rayleigh number.
Ice concentration and distribution near the south pole of Mars: Synthesis of odyssey and global surveyor analyses
Authors: Tokar R. L. , Feldman W. C. , Prettyman T. H. , Moore K. R. , Lawrence D. J. , Elphic R. C. , Kreslavsky M. A. , Head J. W. , Mustard J. F. , Boynton W. V.
Published: October 2003

Mars Odyssey Gamma‐Ray Spectrometer (GRS) neutron spectrometer data are analyzed to determine the concentration and boundary of buried water ice near the south pole. The measurements are consistent with a circumpolar layer of average ice concentration from 35 to 100% by weight and superposed dust with thickness density product 30 to 40 g/cm2. The region of buried water ice extends from near the south pole to latitudes 48S to 58S. The equatorward boundary of the ice‐rich region compares favorably with the boundary of an ice‐rich dust mantle inferred from Mars Orbiter Laser Altimeter data and the locations of dissected terrain inferred from Mars Orbiter Camera images. The ice‐rich mantle is identified as the source of enhanced hydrogen sensed by the neutron spectrometer.
Inner radiation belt electron lifetimes due to whistler‐induced electron precipitation (WEP) driven losses
Authors: Rodger Craig J. , Clilverd Mark A.
Published: October 2003

Wave‐particle interactions driven by whistler mode waves in the inner Van Allan belt is an important loss process for the energetic electrons found in this region. In this paper we seek to investigate the significance of Whistler‐Induced Electron Precipitation (WEP) to inner belt electron lifetimes, by combining experimental satellite results, ionospheric remote observations, and global lightning distributions. We find that long‐term WEP driven losses at L = 2.23 are more significant than all other inner radiation belt loss processes for electron kinetic energies in the range 40–350 keV. This suggests a faster depletion rate and thus lower lifetimes than previously calculated. Thunderstorm generated whistlers are an important factor for determining the lifetimes of medium energy electrons in the inner belt.
Operational forecasts of the geomagnetic Dst index
Authors: Lundstedt H. , Gleisner H. , Wintoft P.
Published: October 2003

We here present a model for real time forecasting of the geomagnetic index Dst. The model consists of a recurrent neural network that has been optimized to be as small as possible without degrading the accuracy. It is driven solely by hourly averages of the solar wind magnetic field component Bz, particle density n, and velocity V, which means that the model does not rely on observed Dst. In an evaluation based on more than 40,000 hours of solar wind and Dst data, it is shown that this model has smaller errors than other models currently in operational use. A complete description of the model is given in an appendix.
Calculation of actinic fluxes with a coupled atmosphere–snow radiative transfer model
Authors: Lee‐Taylor Julia , Madronich Sasha
Published: October 2003

A one‐dimensional atmospheric radiative transfer model has been extended to include scattering and absorption by multiple layers of snow. Empirical values for scattering coefficients for wet and dry snow and for absorption by impurities are derived from previous observations of snow albedo and irradiance attenuation depth, thus avoiding the uncertainties inherent in modeling the optical properties of ensembles of individual snow grains. Vertical profiles of spectral actinic flux within the model snowpack are computed and compared to those of down‐welling spectral irradiance. The ratio of these two quantities is a strong function of solar zenith angle near the snow surface but rapidly approaches ∼0.25 (the isotropic limit) at depths greater than a few centimeters. Calculated rates of in‐snow nitrate (NO3−) photolysis confirm that this process can explain at least part of the enhanced NOx concentrations observed in the atmospheric boundary layer above snow.
Twenty years of revised Dobson total ozone measurements in Oslo, Norway
Authors: Svendby T. M. , Dahlback A.
Published: October 2003

Total ozone measurements using the Dobson spectrophotometer 56 (D56) have been performed on a regular basis in Oslo (59.9°N, 10.7°E), Norway, from 1978 to 1998. The data set for the entire period of observations has been critically examined. In this paper we present the results of the homogenization process and discuss the data quality of the record. Much effort has been made to optimize the zenith sky charts used for CC′ zenith observations. The charts have been constructed using a semiempirical method, where a large number of quasi‐simultaneous observations of direct Sun and zenith observations have been used in combination with a radiative transfer model. The same radiative transfer model has been used for constructing AD and CD zenith sky charts for various optical thicknesses of cloud cover. When the D56 ozone observations started up in 1978 the SO2 level in Oslo was significant. High concentrations of SO2 will generally influence the measurements of Dobson total ozone and might give fictitious ozone trends. Without the SO2 corrections the revised Oslo Dobson data shows a year‐round ozone decrease of −5.22 ± 0.63% per decade from 1978 to 1998, while after SO2 corrections the decrease is reduced to −4.68 ± 0.63% per decade. The Dobson data from Oslo are compared to ozone data from Brewer spectrometer 42 and to Total Ozone Mapping Spectrometer (TOMS) daily overpass data from satellites Nimbus 7, Meteor 3, and Earth Probe. The mean and standard deviation of the monthly percentage difference between Dobson and TOMS amount to −0.91 ± 1.41%.
A new approach in space‐time analysis of multivariate hydrological data: Application to Brazil's Nordeste region rainfall
Authors: Sicard Emeline , Sabatier Robert , Niel Hélène , Cadier Eric
Published: October 2003

The objective of this paper is to implement an original method for spatial and multivariate data, combining a method of three‐way array analysis (STATIS) with geostatistical tools. The variables of interest are the monthly amounts of rainfall in the Nordeste region of Brazil, recorded from 1937 to 1975. The principle of the technique is the calculation of a linear combination of the initial variables, containing a large part of the initial variability and taking into account the spatial dependencies. It is a promising method that is able to analyze triple variability: spatial, seasonal, and interannual. In our case, the first component obtained discriminates a group of rain gauges, corresponding approximately to the Agreste, from all the others. The monthly variables of July and August strongly influence this separation. Furthermore, an annual study brings out the stability of the spatial structure of components calculated for each year.
Radar observations of the kinematic, microphysical, and precipitation characteristics of two MCSs in TRMM LBA
Authors: Cifelli Robert , Petersen Walter A. , Carey Lawrence D. , Rutledge Steven A. , da Silva Dias Maria A. F.
Published: October 2003

Dual‐Doppler and polarimetric radar observations are used to analyze two mesoscale convective systems (MCSs) that occurred during the Tropical Rainfall Measuring Mission Large‐Scale Biosphere‐Atmosphere field campaign. The MCSs formed in different meteorological regimes, based on profiles of atmospheric wind and thermodynamic data. The first MCS event (26 January 1999) was a squall line that formed in low‐level easterly flow and had an intense leading line of convection. In contrast, the 25 February 1999 MCS formed in low‐level westerly flow and was best characterized by stratiform precipitation with embedded convective elements. The radar analyses suggest that the MCSs were distinct in terms of overall vertical structure characteristics. In particular, polarimetric radar cross sections indicated the presence of an active mixed phase zone in the easterly MCS that was largely absent in the westerly case. The easterly MCS had considerably more precipitation ice in the middle to upper troposphere compared to the westerly MCS. Composite analyses showed that the easterly MCS had higher peak reflectivities and a smaller reflectivity gradient above the 0°C level in convective regions of the storm compared to the westerly MCS event. Moreover, mean profiles of both vertical air motion and vertical mass transport in the convective portion of the easterly MCS were larger (over a factor of 2 at some heights below the 0°C level) than those in the westerly event. These observations suggest that the easterly and westerly wind regimes in the southwest Amazon region produce convection with different vertical structure characteristics, similar to regimes elsewhere in the global tropics (e.g., maritime continent).