bluuebunny/crossref_metadata_2025 huggingface dataset:
Phylogeny, phylogeography, and geographic variation of Sylvisorex howelli (Soricidae), an endemic shrew of the Eastern Arc Mountains, Tanzania
Authors: Stanley William T. , Olson Link E.
Published: July 2005

The Eastern Arc Mountains of eastern Africa are notable for the high levels of endemism exhibited by various forest‐dwelling organisms of this ancient montane archipelago. There has been virtually no assessment of the variation among populations of small mammal species living on these unique mountains, but recent faunal surveys have produced sufficient material to initiate such studies. Cranial morphometric and DNA sequence data were examined from six populations of Sylvisorex howelli Jenkins, 1984, an endemic shrew found in several different massifs of the Eastern Arc Mountains, to assess variation across the archipelago in the context of various hypotheses of historical biogeography. Twenty‐two cranial measurements were analysed using principal components analysis. Age classes (based on tooth wear) and sex had little effect on the variation exhibited by the variables studied. Overall, specimens of S. howelli from the East Usambara Mountains are smaller than specimens from other known populations. The mitochondrial ND2 and 12S rRNA genes from representatives of each montane population of S. howelli in addition to several crocidurine taxa from eastern Africa and three soricine outgroup species were sequenced to assess phylogenetic relationships among these taxa. Neither maximum likelihood, maximum parsimony, nor Bayesian analyses support monophyly of the genus Sylvisorex, but S. howelli populations were consistently recovered as a well‐supported clade. Over 40 individuals of S. howelli from six disjunct montane ranges, comprising the entire known distribution of the species, were sequenced for 504 base pairs of ND2 to investigate phylogeographic patterns. Phylogenetic analysis recovered six reciprocally monophyletic haplotype clades grouped by locality. Branch lengths are consistent with relatively long periods of isolation among populations from the Uluguru, Ukaguru, Nguru, Nguu, East Usambara and West Usambara Mountains, with low levels of diversity observed within each population. These results are interpreted within the historical context of the Eastern Arc Mountains.
X-Ray Microanalysis of Human Cementum
Authors: Alvarez-Pérez Marco Antonio , Alvarez-Fregoso Octavio , Ortiz-López Jaime , Arzate Higinio
Published: July 2005

An energy dispersive x-ray microanalysis study was performed throughout the total length of cementum on five impacted human teeth. Mineral content of calcium, phosphorous, and magnesium were determined with an electron probe from the cemento-enamel junction to the root apex on the external surface of the cementum. The concentration profiles for calcium, phosphorous, and magnesium were compared by using Ca/P and Mg/Ca atomic percent ratio. Our findings demonstrated that the Ca/P ratio at the cemento-enamel junction showed the highest values (1.8–2.2). However, the area corresponding to the acellular extrinsic fiber cementum (AEFC) usually located on the coronal one-third of the root surface showed a Ca/P media value of 1.65. Nevertheless, on the area representing the fulcrum of the root there is an abrupt change in the Ca/P ratio, which decreases to 1.3. Our results revealed that Mg2+distribution throughout the length of human cementum reached its maximum Mg/Ca ratio value of 1.3–1.4 at.% around the fulcrum of the root and an average value of 0.03%. A remarkable finding was that the Mg/Ca ratio pattern distribution showed that in the region where the Ca/P ratio showed a decreasing tendency, the Mg/Ca ratio reached its maximum value, showing a negative correlation. In conclusion, this study has established that clear compositional differences exist between AEFC and cellular mixed stratified cementum varieties and adds new knowledge about Mg2+distribution and suggests its provocative role regulating human cementum metabolism.
At the crossroads: Making the transition to hospice
Authors: SCHULMAN-GREEN DENA , McCORKLE RUTH , CURRY LESLIE , CHERLIN EMILY , JOHNSON-HURZELER R. , BRADLEY ELIZABETH
Published: July 2005

Objective:Previous studies reveal that many terminally ill patients never receive hospice care. Among those who do receive hospice, many enroll very close to the time of death. Nationally, between 1992 and 1998, the median length of stay at hospice declined 27%, from 26 to 19 days. In our prior study of 206 patients diagnosed with terminal cancer and using hospice, we found that one-third enrolled with hospice within 1 week prior to death. Late hospice enrollment can have deleterious effects on patients and their family members. The aim of the present study was to characterize common experiences of patients and primary family caregivers as they transition to hospice, focusing on caregiver perceptions of factors that might contribute to delays in hospice enrollment.

Methods:We conducted in-depth interviews with a purposive sample of 12 caregivers selected from a population of primary family caregivers of patients with terminal cancer who enrolled with hospice in Connecticut between September 2000 and September 2001. Respondents represented different ages, genders, and kinship relationships with patients. Respondents were asked about the patient's care trajectory, how they first learned about hospice, and their experiences as they transitioned to hospice. NUD*IST software was used for qualitative data coding and analysis.

Results:Constant comparative analysis identified three themes common to the experience of transitioning to hospice: (1) caregivers' acceptance of the impending death, (2) challenges in negotiating the health care system across the continuum of care, and (3) changing patient–family dynamics.

Significance of results:Identification of these themes from the caregivers' perspective generates hypotheses about potential delays in hospice and may ultimately be useful in the design of interventions that are consistent with caregivers' needs.
Reliability and validity of the Japanese version of the Support Team
Assessment Schedule (STAS-J)
Authors: MIYASHITA MITSUNORI , MATOBA KAZUKO , SASAHARA TOMOYO , KIZAWA YOSHIYUKI , MARUGUCHI MISAE , ABE MAYUMI , KAWA MASAKO , SHIMA YASUO
Published: July 2005

Objective: The aim of this project was to develop an
appropriate and valid instrument for assessment by medical professionals
in Japanese palliative care settings.

Methods: We developed a Japanese version of the Support Team
Assessment Schedule (STAS-J), using a back translation method, and tested
its reliability and validity. In the reliability study, 16 nurses and a
physician who work in a palliative care unit evaluated 10 hypothetical
cases twice at 3-month intervals. For the validity study, external
researchers interviewed 50 patients with matignancy and their families and
compared the results with ratings by the nurses in the palliative care
unit.

Results: Our results with hypothetical cases were: interrater
reliability weighted κ = 0.53–0.77 and intrarater reliability
weighted κ = 0.64–0.85. In the validity study comparing nurse
evaluations and the results of interviews with patients and families,
complete agreement was 36–70%, and close agreement (±1) was
74–100%. As a whole, weighted κ were low: between −0.07
and 0.51. Our results were similar to those in the United Kingdom and
Canada.

Significance of results: Although this research was conducted
under methodologically limited conditions, we concluded that the STAS-J is
a reliable tool and its validity is acceptable. The STAS-J should become a
valuable tool, not only for daily clinical use, but also for research.
Parents dying of cancer and their children
Authors: BEALE ESTELA A. , SIVESIND DEBRA , BRUERA EDUARDO
Published: July 2005

Objective: We reviewed our experience with 28 consecutive
children referred for assessment and intervention. These were the children
of patients with terminal cancer referred to the Palliative Care and
Symptom Control Service. In all cases the dying parent was a biological
parent.

Methods: Eleven parameters were assessed in each of 29
children and their incidence was calculated. The children and their
parents were seen in a semistructured interview, together as well as
separately. The parameters were: seeking reassurance (82), becoming a
caretaker (79), inability to separate from parent (79), anger about
feeling abandoned (68), despair (57), guilt (54), discipline problems,
aggressive behavior (46), denial (39), blame of others (21), and fear for
the child's own health (18).

Results: Our results suggest that children with dying parents
manifest significant distress as well as a greater understanding of their
parent's illness than is usually suspected.

Significance of results: Timely intervention by a child
psychiatrist or other mental health professional with proven competence in
working with children can help children to better cope with the death and
dying of their parent and ameliorate the process of bereavement following
the parent's death.

Because of our small sample, we cannot generalize about all of the
findings. Further research is required to characterize the level of
distress in the children and the long-term impact in their overall
adjustment to life.
Hope at the end of life: Making a case for hospice
Authors: HAWTHORNE DENISE L. , YURKOVICH NANCY J.
Published: July 2005

Hope is the anticipation of something better to come and an essential
component of life. It is a complex notion that is fundamental to the
promise of health care. Initially, hope is for cure or restoration of
health but in terminal illness, when there is no longer the possibility of
cure, hope rests in the knowledge and skill of the medical scientist to
alter the course of disease and to prolong life. It is this expectation
for renewed physical being that is the focus of every intervention. At the
end of life, when science can do no more, hope endures, but the focus of
hope changes. It becomes hope to find meaning in life, as it was lived,
and in the time that remains. For most, however, the end of life unfolds
in the scientific milieu of the hospital where the significance of
redefining hope may not be considered, and many die without hope. The
purpose of this article is to explore the meaning of hope, to highlight
the necessity of redefining hope at the end of life, and to emphasize the
importance of sanctuary in engendering hope through relationship. Hospice
is proposed as a sanctuary for the final days, where the patient, family,
and health professional discover a new meaning of hope through shared
human experience.
Comparison of mid‐oceanic earthquake epicentral differences of travel time, centroid locations, and those determined by autonomous underwater hydrophone arrays
Authors: Pan Jianfeng , Dziewonski Adam M.
Published: July 2005

Mid‐oceanic interplate earthquakes are difficult to locate accurately because they normally occur far away from land‐based seismic stations. Use of water‐borne T waves recorded by autonomous underwater hydrophone (AUH) arrays records an order of magnitude more highly accurate regional low seismicity along the north Mid‐Atlantic Ridge than the International Seismic Centre (ISC). Even though the physical meaning of an AUH locations is still not well known, AUH's small location errors are important for better constraining mid‐oceanic earthquakes. Comparison of such AUH locations with those in ISC and Harvard centroid moment tensor (CMT) location catalog, and relocated ones based on the high‐resolution bathymetry and teleseismic P phases, is made in this study. AUH locations are used as a reference to compare the teleseismically determined locations. For large earthquakes with known focal mechanisms, we find that relocated locations agree with AUH ones better than with ISC. We also note that the centroid vectors from relocated epicenters are usually larger than AUH centroid vectors. The relocated epicenters and AUH locations lie in similar azimuthal directions to the associated CMT epicenters. The larger relocated and AUH centroid vectors (than the error ellipses of AUH, CMT, and relocated ones combined) might be explained by the fault rupture process. For smaller events, relocated location confidence ellipses are usually large enough to cover AUH locations and their error ellipses. Overall, the highly accurate AUH locations can be used to confirm the mid‐oceanic earthquake hypocenters and seismicity characteristics and for detail studies of the low‐level seismicity associated with the plate motions.
Erosion of upland hillslope soil organic carbon: Coupling field measurements with a sediment transport model
Authors: Yoo Kyungsoo , Amundson Ronald , Heimsath Arjun M. , Dietrich William E.
Published: July 2005

Little is known about the role of vegetated hillslope sediment transport in the soil C cycle and soil‐atmosphere C exchange. We combined a hillslope sediment transport model with empirical soil C measurements to quantify the erosion and temporal storage of soil organic carbon (SOC) within two grasslands in central California. The sites have contrasting erosional mechanisms: biological perturbation (Tennessee Valley (TV)) versus clay‐rich soil creep (Black Diamond (BD)). The average SOC erosion rates from convex slopes were 1.4–2.7 g C m−2 yr−1 at TV and 5–8 g C m−2 yr−1 at BD, values that are <10% of above ground net primary productivity (ANPP) at both sites. The eroded soil accumulates on depositional slopes. The long term SOC accumulation (or C sink) rates are ∼1.9 g C m−2 yr−1 in the TV hollow and 1.7–2.8 g C m−2 yr−1 in the BD footslope. We found that the hillslope C sink is driven primarily by the burial of in situ plant production rather than preservation of eroded SOC, a finding that differs from existing hypotheses. At TV, the net sequestration of atmospheric C by long‐term hollow evacuation and refilling depends on the fate of the C exported from the zero order watershed. This study suggests that erosion and deposition are coupled processes that create a previously unrecognized C sink in undisturbed upland watersheds, with a potential to substantially affect the global C balance presently, and over geological timescales.
Comparison of three modeling approaches for simulating denitrification and nitrous oxide emissions from loam‐textured arable soils
Authors: Li Yong , Chen Deli , Zhang Yuming , Edis Robert , Ding Hong
Published: July 2005

Soil denitrification fluxes and nitrous oxide (N2O) emissions from the soil surface simulated by a Water and Nitrogen Management Model (WNMM), with three different gas modules, are compared to measurement data sets from two irrigated wheat‐maize systems at two locations in the North China Plain (NCP) (2 years of measurement at the Luancheng site and 1 year of measurement at the Fengqiu site). The three gas modules are the WNMM gas module, the DAYCENT gas module, and the DNDC gas module. The term gas module used in this paper refers to the model component which simulates N2O emission from the processes of soil nitrification and denitrification. Soil water, temperature, organic matter decomposition, other nitrogen (N) transformations, such as mineralization and immobilization, and crop growth are simulated by the WNMM platform. For the 2‐year data set from Luancheng, the three gas modules generate similar soil mineral N dynamics in the 0–20 cm topsoil. The daily time step, simply structured WNMM gas module consistently performs the best among the three gas modules for predicting soil denitrification fluxes (R2 = 0.28, n = 39, p = 0.0006) and N2O emissions (R2 = 0.45, n = 36, p < 0.0001). Up to 73, 43, and 22% of total N2O emissions are nitrification‐induced as simulated by the DNDC, DAYCENT, and WNMM gas modules respectively, in this well‐drained loam soil during the 2‐year simulation. When applied to the 1‐year data set at the Fengqiu site, the WNMM gas module consistently performs better in estimating N2O emissions (R2 = 0.54, n = 35, p < 0.0001) compared to the other two modules. Simulations using the DNDC and DAYCENT gas modules explain over 40% of the temporal variation of N2O emission from the soil. Further testing on different soils and different agroecosystems is needed to confirm the superior performance of the WNMM gas module observed in this simulation study.
Isotopic composition of Antarctic Dry Valley nitrate: Implications for NOy sources and cycling in Antarctica
Authors: Michalski G. , Bockheim J. G. , Kendall C. , Thiemens M.
Published: July 2005

Nitrates minerals from the Dry Valleys of Antarctica have been analyzed for their oxygen and nitrogen isotopic compositions. The 15N was depleted with δ15N values ranging from −9.5 to −26.2‰, whereas the 17O and 18O isotopes were highly enriched (with excess 17O) with δ18O values spanning 62–76‰ and Δ17O values from 28.9 to 32.7‰. These are the largest 17O enrichments observed in any known mineral. The oxygen isotopes indicate that nitrate is from a combination of tropospheric transport of photochemically produced HNO3 and HNO3 formed in the stratosphere.
An update on the ring exosphere and plasma disc of Saturn
Authors: Ip W.‐H.
Published: July 2005

A re‐examination of the mass budget of the ring exosphere of Saturn – as prompted by the most recent Cassini measurements in the vicinity of the ring system ‐ indicates that the corresponding number density could reach the level of 2–3 × 105 cm−3 at maximum. Such extended exospheric structure in equilibrium with a thin ring plasma disc could be an important supplier of suprathermal oxygen ions of a few tens of keV in the Saturnian magnetosphere.
Local time distribution of low and middle latitude ground magnetic disturbances at sawtooth injections of 18–19 April 2002
Authors: Kitamura Kentarou , Kawano Hideaki , Ohtani Shin‐ichi , Yoshikawa Akimasa , Yumoto Kiyohumi
Published: July 2005

During a magnetic storm of 18 April 2002, quasi‐periodic variations of the low‐energy electron flux were observed by the LANL satellites at geosynchronous orbit; this phenomenon has been called the “sawtooth event.” During this event, on the ground, magnetic bays and Pi 2 pulsations took place corresponding to each enhancement of the particle flux, and they had features typical to usual substorms. However, unlike typical substorms, the ACE satellite observed no apparent northward turnings of the IMF corresponding to the sawtooth event. In this study, we used ground magnetic data from middle‐ and low‐latitude stations which are distributed widely in the longitudinal direction, selected from the CPMN (Circum‐Pan Pacific Magnetometer Network) and INTERMAGNET stations and compared the magnetic variations during the sawtooth event with that of the typical substorm (Lester et al., 1984). We found that the local time distribution of the polarization axis of the Pi 2 pulsations show a good agreement with that for a typical substorm, except that the local time width of the expected current wedge was 12 hours. On the other hand, the H component is predominant in the amplitude of the magnetic bay on the ground; the distribution of the H component also suggests a 12‐hour‐wide current wedge, which did not develop much in time. From these features, it is suggested that a current wedge was formed during this sawtooth event, and it generated the Pi 2 pulsations on the ground. However, the local time width of the current wedges is much wider than typical substorms, and its uniqueness causes the ground features different from typical substorm‐associated magnetic variations on the ground.
Evidence for the tongue of ionization under northward interplanetary magnetic field conditions
Authors: Middleton H. R. , Pryse S. E. , Kersley L. , Bust G. S. , Fremouw E. J. , Secan J. A. , Denig W. F.
Published: July 2005

The activities of the International Ionospheric Tomography Community open up new possibilities of simultaneously imaging the large‐scale spatial structure of the ionosphere in different longitude sectors. In the study, tomography receiver chains in Scandinavia and Greenland were used to provide a wide view of the plasma density structure in the winter, magnetic postnoon sector under conditions of stable, positive interplanetary magnetic field Bz component. The spatial distributions of the plasma are discussed in light of a high‐latitude plasma convection pattern pertinent to the conditions, which is supported by DMSP flow measurements. The observations are consistent with a tongue of dayside photoionization being drawn antisunward by the convection pattern to form an arc of enhanced plasma density around the periphery of the polar cap.
Occurrence statistics of cold, streaming ions in the near‐Earth magnetotail: Survey of Polar‐TIDE observations
Authors: Liemohn M. W. , Moore T. E. , Craven P. D. , Maddox W. , Nagy A. F. , Kozyra J. U.
Published: July 2005

Results are presented from a survey of cold ion observations in the near‐Earth magnetotail using data from the Polar Thermal Ion Dynamics Experiment (TIDE). During the interval from July to December of 2001, Polar had its apogee (∼9.5RE) near the equatorial plane in the tail region of the magnetosphere. It is shown that a lobal wind is ubiquitous in the inner tail, with low‐energy (<300 eV) ions streaming from the ionosphere downtail. These lobal winds often pass through the plasma sheet, forming bidirectional streams, in addition to the unidirectional beams seen at higher magnetic latitudes. The observance of bidirectional streams is inversely, although weakly, correlated with geomagnetic activity. Bidirectional streams are interpreted as indicating the minimum size of the closed flux tube region. The reduced frequency of bidirectional streams with activity level times is consistent with the thinning of the plasma sheet during these times. It is inferred from the universality of these observations during Polar's passage through the inner tail region that the ionosphere is a continuous supplier of plasma to the near‐Earth magnetosphere. The high occurrence rate of these streams means that during geomagnetic disturbances, it is not necessary to wait for outflow and magnetospheric circulation in order to supply the inner magnetosphere with ionospheric ions; these cold streams are an immediately available supply of ionospheric‐origin particles.
Simultaneous appearance of energy‐dispersed ion signatures of ionospheric and magnetotail origins in the near‐Earth plasma sheet
Authors: Kazama Y. , Mukai T.
Published: July 2005

The present paper reports on properties of multiple energy‐dispersed ion signatures observed by Geotail in the near‐Earth plasma sheet. The dispersed ion signatures are widely observed in the nightside tail region, and they occur not only in disturbed magnetospheric conditions but also in quiet conditions. According to the statistical analysis, the dispersed ion signatures are accompanied by earthward bulk flows, magnetic fluctuations, dipolarizations, and electron pressure anisotropy. It is noted that the dispersed ions have a wide pitch‐angle distribution, which suggests that the ions come from the magnetotail in which the magnetic field is much weaker than that in the observation point. Our most remarkable finding is that the dispersed ions of the magnetotail origin are sometimes (∼40% of the total) accompanied by highly collimated dispersed ions, probably of the ionospheric origin. On the basis of results from the correlative analysis of the two types, we propose a model of tail configuration changes which explains the observed signatures. This model indicates two suggestions: The region of ion acceleration above the polar ionosphere may be mapped to the middle/distant tail regions, and the ion acceleration is triggered by the tail activities probably through propagation of Alfvénic disturbances from the tail to the ionosphere.
Nonlinear coupling of Alfvén waves with widely different cross‐field wavelengths in space plasmas
Authors: Voitenko Yuriy M. , Goossens Marcel
Published: July 2005

Multiscale activity and dissipation of Alfvén waves play an important role in a number of space and astrophysical plasmas. A popular approach to study the evolution and damping of MHD Alfvén waves assumes a gradual evolution of the wave energy to small dissipative length scales. This can be done by local nonlinear interactions among MHD waves with comparable wavelengths resulting in turbulent cascades or by phase mixing and resonant absorption. We investigate an alternative nonlocal transport of wave energy from large MHD length scales directly into the dissipation range formed by the kinetic Alfvén waves (KAWs). KAWs have very short wavelengths across the magnetic field irrespectively of their frequency. We focus on the nonlinear mechanism for the excitation of KAWs by MHD Alfvén waves via resonant decay AW → KAW1 + KAW2. The resonant decay conditions can be satisfied in a rarified plasmas, where the gas/magnetic pressure ratio is less than the electron/ion mass ratio. The decay is efficient at low amplitudes of the magnetic field in the MHD waves, B/B0 ∼ 10−2. In turn, the nonlinearly driven KAWs have sufficiently short wavelengths for the dissipative effects to become significant. Therefore the cross‐scale nonlinear coupling of Alfvén waves can provide a mechanism for the replenishment of the dissipation range and the consequent energization in space plasmas. Two relevant examples of this scenario in the solar corona and auroral zones are discussed.
Polar study of ionospheric ion outflow versus energy input
Authors: Zheng Yihua , Moore Thomas E. , Mozer Forrest S. , Russell Christopher T. , Strangeway Robert J.
Published: July 2005

A statistical study of the ion outflow versus energy input is performed by using multi‐instrument data (TIDE, EFI, MFI, HYDRA) from Polar during its perigee auroral passes in the year 2000. Several important physical quantities connected to the ion outflow have been investigated, including the Poynting flux from the perturbation fields (below 1/6 Hz), the electron density, temperature, and the electron energy flux. The perturbation fields used here to calculate the Poynting flux may be associated with the small‐scale quasi‐static field structures of the field‐aligned currents or/and the very low frequency Alfvén waves (below 1/6 Hz), which are both proven to be important energy sources for powering the aurora. Our results show that the field‐aligned ion outflow flux correlates best with the Earth‐directed Poynting flux and the precipitating electron density and also demonstrates almost no correlation with the electron energy flux and temperature. The findings from this Polar study are similar to those from FAST. The general corroboration between the independent data sets of the two spacecraft suggests that the empirical ion outflow scaling laws can be established, which will be beneficial to global simulation efforts. Our results show that at 6000 km altitudes fi = 106.836±0.028S0.535±0.086 and fi = 106.650±0.063ne0.484±0.147, where fi is the total field‐aligned ion outflow flux in 1/cm2/s, S is the Poynting flux in ergs/cm2/s, and ne is the electron density in 1/cm3.
Simultaneous inversion for the Earth's mantle viscosity and ice mass imbalance in Antarctica and Greenland
Authors: Tosi N. , Sabadini R. , Marotta A. M. , Vermeersen L. L. A.
Published: July 2005

Redistribution of mass in the Earth due to Pleistocene deglaciation and to present‐day glacial melting induces secular changes in the Earth's gravitational field. The Earth is affected today by the former mechanism because of the viscous memory of the mantle and by the latter because of ongoing surface mass redistribution and related elastic response. A self‐consistent procedure allows us to invert simultaneously for the lower and upper mantle viscosity and for the present‐day mass imbalance in Antarctica and Greenland using the observed time variations of the long‐wavelength gravity field from satellite laser ranging (SLR) analyses. The procedure is based on our normal mode relaxation theory for the forward modeling and a newly developed inversion scheme based on the Levenberg‐Marquardt method. We obtain a large viscosity increase across the 670‐km depth transition zone separating the upper and the lower mantle, with the lower mantle viscosity varying over the range 5 × 1021 to 1022 Pa s and the less resolved upper mantle viscosity of the order of 1020 Pa s. When Antarctica is the only present‐day source, its rate of melting is −240 Gt yr−1, corresponding to a sea level rise of 0.7 mm yr−1; when Greenland is added as a source of ice loss, the rates of melting are −280 Gt yr−1 for Antarctica and −60 Gt yr−1 for Greenland, corresponding to sea level rises of 0.8 and 0.2 mm yr−1. SLR data indicate that ice melting in the polar regions of the Earth is ongoing.
Computational study of seismic waves in homogeneous dynamic‐porosity media with thermal and fluid relaxation: Gauging Biot theory
Authors: Quiroga‐Goode G. , Jiménez‐Hernández S. , Pérez‐Flores M. A. , Padilla‐Hernández R.
Published: July 2005

The attenuation effects predicted by Hickey's poroelastic theory (Hpt) are quantified by means of seismic modeling in an unbounded, homogeneous, isotropic porous model fully saturated with water and with oil. The numerical results are compared to those predicted by Biot poroelastic theory (Bpt). As opposed to Bpt, Hpt accounts for thermomechanical coupling and viscous fluid relaxation and adequately models the transient fluctuations of porosity and mass densities as the wave compresses and dilates the porous medium during propagation. Despite all these theoretical improvements over Bpt, the numerical results show that both theories produce remarkably similar waveforms. Without considering thermal relaxation, Hpt produces less than 1% higher‐amplitude attenuation and velocity dispersion than Bpt. The major contrasts correspond to the slow P wave. Thermomechanical coupling affects the fast P wave: seismic amplitudes are 1% smaller and some dispersion for the oil‐permeated case can be observed. It produces no effects on the fast S or the slow P wave. Therefore these numerical experiments appear to substantiate what Biot assumed at the outset of his theoretical developments: that the effects of transient oscillations of porosity during wave propagation are negligible in terms of velocity dispersion and amplitude attenuation. Furthermore it is confirmed that in a homogeneous porous medium, the combined dissipation mechanisms mentioned are not adequate to explain the total amount of energy dissipation observed in the field or laboratory.
Eastern North Atlantic Mode Waters during POMME (September 2000–2001)
Authors: Reverdin G. , Assenbaum M. , Prieur L.
Published: July 2005

Four hydrographic surveys in the northeast Atlantic (38°–45°N, 15°–21°W) carried out during the Programme Océan Multidisciplinaire Méso Echelle (POMME) experiment (September 2000–2001) are used to investigate the water masses in the upper layers corresponding to Eastern North Atlantic Mode Waters. A large meridional gradient in isopycnal temperature/salinity is witnessed which has no counterpart in climatology and is associated with an anomalous eastward current near 41°N. Waters tend to be warmer/more salty, somewhat more stratified, and less oxygenated on isopycnal surfaces in the southern part of the domain. In addition, there is an overlying zonal gradient of properties, in particular, north of the jet, consistent with earlier descriptions. However, these large‐scale distributions also change significantly through the POMME year, in particular, between the February and early April surveys, which we attribute to (1) the arrival of a 2001 vintage of mode waters, in particular, in the northeastern part of the domain and to (2) stirring by the mesoscale motions, which contribute to down‐gradient transport (equivalent diffusion coefficient of 2000 m2/s for σ = 27.10). On a smaller scale, there are noticeable changes in properties between surveys, some of which can be shown by quasi‐Lagrangian diagnostics to result from advection by the horizontal circulation. In particular, in the southwest corner of the domain between the surveys P1 (February 2001) and P2 (April 2001), horizontal isopycnal advection is responsible for a large cooling (freshening) and oxygen increase, or in the northeast corner, where new oxygenated and freshly ventilated water (in particular for surface σΘ = 27.05 kg/m3) penetrates during that period. In other regions, or for a longer period, water masses are often difficult to track as a result of dispersion or stirring by the eddies and too small of a POMME domain.
A seasonal study of diatom dynamics in the North Atlantic during the POMME experiment (2001): Evidence for Si limitation of the spring bloom
Authors: Leblanc K. , Leynaert A. , Fernandez I. C. , Rimmelin P. , Moutin T. , Raimbault P. , Ras J. , Quéguiner B.
Published: July 2005

The Si cycle in the northeast Atlantic (40°–43.5°N, 15°–21°W) was investigated in the winter, spring, and late summer during the Programme Océan Multidisciplinaire Méso Echelle (POMME) (2001). The aim of this study was to determine the principal causes of the onset and subsequent decline of the diatom bloom, with an emphasis on nutritional limitation processes. The siliceous compartment dynamics was characterized through silicic acid distribution, size‐fractionated biogenic silica and Si uptake rates, Si uptake kinetics (KS and Vmax), and export rates. The results of the POMME cruises indicated an important seasonal variability of the siliceous compartment in the North Atlantic together with a spatial variability following a south‐north gradient in parallel to the increasing stock of nutrients. Here we present the first kinetic evidences for Si limitation of the diatom spring bloom in the northeast Atlantic, supporting previous reports of potentially limiting silicic acid concentrations in this region. Integrated Si uptake rates were very low throughout the survey, except at the northern anticyclonic eddy site, where a Pseudo‐nitzschia bloom was observed during spring and ranged between 0.04 and 11.2 mmol m−2 d−1, which is comparable to values obtained in oligotrophic regions. The overall annual Si production budget for the entire POMME area (375,000 km2) was extrapolated to 9.8 × 109 mol Si yr−1, while Si export fluxes at 400 m only represented 3% of the surface production.
Impact of the spatiotemporal variability of the nutrient flux on primary productivity in the ocean
Authors: Pasquero C. , Bracco A. , Provenzale A.
Published: July 2005

Oceanic carbon uptake depends on the productivity of the marine ecosystem. Here we study the dependence of primary productivity on the spatial and temporal variability of the nutrient flux and the functional form used to parameterize it. We show that primary productivity is significantly affected by the form of the nutrient input. For a restoring flux, used to parameterize nutrient input by upwelling, primary productivity depends on the size and/or temporal duration of the upwelling events. For a fixed‐flux nutrient input, we show that high‐nutrient, low‐chlorophyll (HNLC) regions can easily appear, without necessarily implying the lack of some micronutrient. These results have interesting implications on the interpretation of primary productivity estimates from observational data and ocean circulation models, and indicate a way to obtain upper and lower bounds to primary productivity in coarse‐resolution models.
Observed mean and mesoscale upper ocean circulation in the midlatitude northeast Atlantic
Authors: Le Cann Bernard , Assenbaum Michel , Gascard Jean‐Claude , Reverdin Gilles
Published: July 2005

Lagrangian instruments and altimetry data are used to investigate the upper (0 to ∼500 m) mean and mesoscale circulations in a region of the midlatitude northeast Atlantic (36°–47°N, 13°–23°W), a formation and subduction area of Subpolar Mode Water. Lagrangian data were collected between September 2000 and September 2001 with isobaric subsurface floats, totaling 34.0 float years, and surface drifting buoys, totaling 27.9 buoy years. The near‐surface (0–100 m) mean circulation is dominated by two weak (∼5 cm/s) eastward currents which veer southward in the domain. In the 100‐ to 500‐m‐deep layer, these eastward mean currents retroflect westward and form two anticyclonic circulation cells, opened to the west and separated by a cyclonic cell. Eddy kinetic energy is decreasing from the northwest to the southeast of the area, from ∼100–200 (cm/s)2 to ∼20–30 (cm/s)2. Long‐lived anticyclones and cyclones display mean coherent displacements, both to the southwest. Westward eddy propagation speeds, close to that of long Rossby waves, increase southward and are consistent with a superposition of beta effect and advection by mean currents. Southward eddy displacements are coherent with the observed mean currents. In the north, anticyclones are seen to consist of Central and Subpolar Mode Water eddies, most of them likely originating from the eastern boundary, whereas in the south, most anticyclonic features result from the influence of “Mediterranean Water Eddies” (meddies) on the upper layers. Cyclonic activity is concentrated in “cyclonic zones,” which are seen to exchange floats and water properties.
Comparative vertical distributions of iron in the Japan Sea, the Bering Sea, and the western North Pacific Ocean
Authors: Takata Hyoe , Kuma Kenshi , Iwade Shoei , Isoda Yutaka , Kuroda Hiroshi , Senjyu Tomoharu
Published: July 2005

The vertical distributions of dissolvable (unfiltered) Fe concentrations in semi‐closed oceanic regions, such as the Japan Sea and the Bering Sea, are characterized by a gradual increase with depth in the intermediate and deep waters. However, there is a rapid decrease in the dissolvable Fe concentration over the narrow depth range between deep and bottom waters with constantly lower concentrations observed in the bottom waters of the Japan Sea (Japan Basin), probably from the injection of newly formed bottom water. In addition, the rapid increase in dissolvable Fe concentrations in bottom waters in the western North Pacific Ocean may be due to the resuspension of sediments from the seafloor or the slope. However, there are no differences of labile dissolved (filtered) Fe concentrations and Fe(III) hydroxide solubility between deep and bottom waters, revealing that dissolved Fe concentrations in deep waters may be controlled primarily by Fe(III) complexation with natural organic ligands. Dissolved Fe concentrations, humic‐type fluorescence intensity, and Fe(III) solubility correlate well with PO4 with different slopes between intermediate and deep waters in the North Pacific Ocean. However, there is no different depth regime between them in semi‐closed oceanic regions. The most statistically significant correlation between the Fe(III) solubility and fluorescence intensity was found with a nearly linear relation in intermediate and deep waters at all stations of the semi‐closed and open oceanic regions. This result suggests that the distributions of humic‐type fluorescent organic matter may be responsible for Fe(III) solubility and dissolved Fe concentrations in deep oceanic waters.
A model perspective on total tropospheric O3 column variability and implications for satellite observations
Authors: de Laat A. T. J. , Aben I. , Roelofs G. J.
Published: July 2005

In recent years several methods have been developed that derive total tropospheric O3 columns from satellite measurements. However, one issue that has not been paid much attention to is the interpretation of (extratropical) total tropospheric O3 columns. Different processes contribute to the total tropospheric O3 column: stratosphere‐troposphere exchange, tropospheric O3 production and loss, transport and the height of the tropopause. Each process contributes differently to the total tropospheric O3 column variability depending on season, geographical location, and altitude. This paper investigates the contribution of these different processes on total tropospheric O3 column variability using a chemistry‐climate model simulation of tropospheric O3, and reflects on the implications for total tropospheric O3 column measurements. On the basis of tropospheric O3 column (satellite) measurements and without other sources of information (e.g., model simulations, observations of other trace species) it is not possible to determine the separate contributions by the aforementioned processes to the extratropical total tropospheric O3 column variability. Furthermore, typical extratropical synoptic‐scale (daily) total tropospheric O3 column variability is of the order of 10 DU (1‐σ value), implying the errors in (satellite) measurements should be of the order of magnitude at maximum (∼10 DU) for daily measurements. For tropical total tropospheric O3 column (satellite) measurements the requirements are less stringent because the most important variability occurs on seasonal timescales. Errors in tropical total tropospheric O3 column (TTOC) measurements should be of the order of 5 DU for monthly means.
Soil moisture initialization for climate prediction: Characterization of model and observation errors
Authors: Ni‐Meister Wenge , Walker Jeffrey P. , Houser Paul R.
Published: July 2005

While it has been shown that soil moisture data assimilation techniques can be used to constrain land surface model predictions with remotely sensed soil moisture observations to provide optimal climate model surface and root zone soil moisture initialization, a good understanding and quantification of both model and observation error are required. In this paper we therefore evaluate the catchment‐based land surface model (CLSM) and scanning multichannel microwave radiometer (SMMR) soil moisture estimation errors using long‐term in situ soil moisture measurements available for Eurasia. Generally, the CLSM surface and root zone soil moisture was found to be biased less than 0.08 vol/vol dry in dry climate and frozen soil areas and biased over 0.08 vol/vol (as high as 0.16 vol/vol) wet in wet climate areas. Moreover, the CLSM suffered from an underestimation in surface zone seasonal soil moisture variation. While the SMMR soil moisture estimates were also biased, less than 0.05 vol/vol dry in dry climate and over 0.10 vol/vol (as high as 0.2 vol/vol) wet in wet climate, they generally had accurate seasonal variations. This error characterization study is crucial for practical Eurasian data assimilation, as unbiased observations and model predictions, and reliable knowledge of relative observed and model predicted soil moisture errors are key data assimilation assumptions. This study therefore provides the error information required for data assimilation and emphasizes the need for careful bias representation when assimilating SMMR data into the CLSM. The potential deficiencies in this error assessment are acknowledged and discussed, including the disparate time‐space representation of the various soil moisture sources.
Pore‐scale simulation of biomass growth along the transverse mixing zone of a model two‐dimensional porous medium
Authors: Knutson C. E. , Werth C. J. , Valocchi A. J.
Published: July 2005

The success of in situ bioremediation projects depends on the mixing of contaminants and nutrients in the presence of microbes. In this work, a pore‐scale model is developed to simulate biomass growth that is controlled by the mixing of an electron donor and acceptor. A homogeneous packing of cylinders representing solid grains is used as the model two‐dimensional porous medium. The system is initially seeded with microbes in computational cells located at grain‐water interfaces. The solutes enter the system completely unmixed; each solute is input over one half of the inlet boundary. Solute mixing is controlled by molecular diffusion transverse to the flow direction, and solutes are biotransformed according to dual Monod kinetics only where biomass is present. Simulation of biomass growth requires calculation of the water flow field as well as transport and reaction of solutes. The lattice Boltzmann method is used to obtain the flow field. Transport and reaction of the solutes is modeled by a finite volume discretization of the advection‐diffusion‐reaction equation. Biomass is allowed to grow and spread by means of a cellular automata algorithm. Model parameters are systematically varied to understand their effects on biomass development. Base case parameter values are obtained from batch experiments reported in the literature and are modified to achieve agreement between simulation results and previously reported micromodel experimental results. The most significant mechanisms that control biomass development are shear strength of new biomass and solute degradation rates. The biomass growth model achieves good qualitative agreement with experimental results.
Mean flow and turbulence in vegetated open channel flow
Authors: Defina Andrea , Bixio Anna Chiara
Published: July 2005

Vegetation affects the mean and turbulent flow structure in surface water bodies, thus impacting the local transport processes of contaminants and sediments. The present paper explores the capability of two different mathematical models to predict fully developed one‐dimensional open channel flow in the presence of rigid, complex‐shaped vegetation with leaves, submerged or emergent. The flow is described by applying two different turbulence closure schemes, both of which are based on the Boussinesq eddy viscosity model: a suitably modified к − ε model and a two‐layer model based on the mixing length approach. To describe the turbulence structure within and above the canopy a turbulent kinetic energy budget equation was added to the two‐layer model. The results of the models were compared with experimental data where simple cylinders, plastic plant prototypes, or real plants, all arranged in a scattered pattern, were employed. Since good agreement between the results of the models and measurements was found in comparing velocity and turbulent shear stress, the models could potentially be used to assess vegetative resistance. Significant disagreement was found when comparing measured and computed eddy viscosity distributions, streamwise turbulence intensity, and most of the terms comprising the turbulent kinetic energy budget.
Recent observed changes in severe storms over the United Kingdom and Iceland
Authors: Alexander Lisa V. , Tett Simon F. B. , Jonsson Trausti
Published: July 2005

Severe storms defined as 3‐hourly pressure changes exceeding an extreme magnitude, were carefully manually quality‐controlled and analyzed at stations in the UK and Iceland which had at least 45 years of digitized data. Iceland showed significant distribution differences between the periods before and after 1980 with a tendency towards less extreme severe events in latter decades. In contrast, the UK regions have tended towards larger magnitude events in recent decades, particularly in the more southerly regions. There has been a significant increase in the number of severe storms over the UK as a whole since the 1950s, however, this may not be unusual in longer‐term variability. For both the UK and Iceland in winter these changes in severe storms appear to be related to changes in the North Atlantic Oscillation (NAO) but UK changes during October to December do not appear to be related to changes in the NAO.
Mixing estimates from a large‐scale hydrographic survey in the North Atlantic
Authors: Walter Maren , Mertens Christian , Rhein Monika
Published: July 2005

A large‐scale hydrographic survey from 2003 (RV Meteor cruise M59/2) is used to map turbulent mixing by means of eddy diffusivities from finescale shear and strain in the subpolar North Atlantic, covering various hydrographic and bathymetric conditions. Results from the analysis indicate small (O(10−5) m2s−1) diffusivities below the Labrador Sea Water layer at mid‐depth in the open ocean. Higher values exceeding 10−4 m2s−1 are found in the abyss close to rough topography and over the flanks of the Mid‐Atlantic Ridge. The strongest mixing with diffusivities of 10−3 m2s−1 occurs in the Deep Western Boundary Current off Flemish Cap. The results of this study convey the need to map mixing globally from existing sets of CTD/LADCP data as well as its feasibility: the similarities and differences in mixing patterns as compared to other studies indicate that large scale patterns of small scale processes are still not well known and understood.