bluuebunny/crossref_metadata_2025 huggingface dataset:
Sea level variation in seismic normal mode band observed with on‐ice GPS and on‐land SG at Syowa Station, Antarctica
Authors: Nawa Kazunari , Suda Naoki , Aoki Shigeru , Shibuya Kazuo , Sato Tadahiro , Fukao Yoshio
Published: May 2003

We analyze sea level variation data acquired by a differential GPS and gravity data acquired by a superconducting gravimeter (SG) at Syowa Station, Antarctica, in an eight month period of 1998. At frequencies between 0.2 and 2.5 mHz in the seismic normal mode band we observe similar spectral peaks in both of the data sets. We also observe high coherence and zero phase between the two data sets at the frequencies of these peaks. The results of response analysis and simple mode calculation suggest that the observed peaks in the SG data are due to the effects of ocean water attraction and loading associated with sea level variation, a possible cause of which is the seiche in Lützow‐Holm Bay around the station. Applying a transfer function method to both of the data sets, we can reduce the background noise due to the oceanic effects in the SG data.
Superrotation and equatorial waves in a T21 Venus‐like AGCM
Authors: Yamamoto Masaru , Takahashi Masaaki
Published: May 2003

Superrotation of more than 100 m s−1 is formed at the cloud top (65–70 km) in a T21 Venus‐like atmospheric general circulation model (Venus‐like AGCM) driven by a zonal‐mean thermal forcing. This is maintained by the Gierasch mechanism, in which meridional circulation efficiently pumps up angular momentum and various waves produce equatorward eddy momentum fluxes. In addition to the above mechanism, fast equatorial waves with a wide frequency range (including a famous 4‐day wave) enhance the cloud‐top superrotation, since the downward angular momentum flux of vertically propagating gravity waves is canceled by the upward flux of the fast equatorial waves.
Correlation of a strong lunar magnetic anomaly with a high‐albedo region of the Descartes mountains
Authors: Richmond N. C. , Hood L. L. , Halekas J. S. , Mitchell D. L. , Lin R. P. , Acuña M. , Binder A. B.
Published: May 2003

Mapping and model simulations of Lunar Prospector magnetometer measurements show that the source of the strongest known magnetic anomaly on the lunar near side (42 nanoTeslas at 18.6 km altitude) coincides approximately with a high‐albedo region of the Descartes mountains centered 60 km south‐southeast of the Apollo 16 landing site. The Descartes mountains represent primary ejecta from one or more basin‐forming events (Imbrium and/or Nectaris), supporting the hypothesis that basin ejecta materials emplaced >3.8 Gyr ago are the main sources of lunar magnetic anomalies. The higher albedo of the surface at this location is consistent with a significant role for solar wind ions in the optical maturation (or “space weathering”) of the lunar surface.
Determining pore‐throat size in Permo‐Triassic sandstones from low‐frequency electrical spectroscopy
Authors: Scott Julian B. T. , Barker Ron D.
Published: May 2003

Hydraulic conductivity or permeability, a knowledge of which is vital in modelling the movement of hydrocarbons in reservoir rocks and contaminants in aquifers, is strongly related to the intergranular pore‐throat size in sandstones. For many years attempts have been made to determine permeability from the electrical properties of rocks, but with little success. Here we have measured the complex electrical conductivity of Permo‐Triassic sandstone samples over the frequency range 0.0001–1000 Hz and show how parameters determined from the characteristic shape of the spectra correlate closely to pore‐throat size determined from mercury injection measurements.
Worldwide trend of atmospheric mercury since 1977
Authors: Slemr Franz , Brunke Ernst‐Günther , Ebinghaus Ralf , Temme Christian , Munthe John , Wängberg Ingvar , Schroeder William , Steffen Alexandra , Berg Torunn
Published: May 2003

The inventories of global anthropogenic emissions of mercury for years from 1979/1980 to 1995 suggest a substantial reduction in the 1980s and almost constant emissions afterwards. In contrast to emission inventories, measurements of atmospheric mercury suggest a concentration increase in the 1980s and a decrease in the 1990s. Here we present a first attempt to reconstruct the worldwide trend of atmospheric mercury concentrations from direct measurements since the late 1970s. In combination, long term measurements at 6 sites in the northern, 2 sites in the southern hemispheres, during 8 ship cruises over the Atlantic Ocean (1977–2000) provide a consistent picture, suggesting that atmospheric mercury concentrations increased in the late 1970s to a peak in the 1980s, then decreased to a minimum at about 1996, and have been nearly constant since. The observed trend is not consistent with the published inventories of anthropogenic emissions and the assumed ratios of anthropogenic/natural emissions, and suggests the need to improve the mercury emission inventories and to re‐evaluate the contribution of natural sources.
Large potential energy of gravity waves over a smooth surface with little convection: Simulation and observation
Authors: Kawatani Yoshio , Dhaka S. K. , Takahashi Masaaki , Tsuda Toshitaka
Published: May 2003

A numerical experiment is conducted using an Atmospheric General Circulation Model (AGCM) to investigate the presence of the large potential energy over a region of low topography and little convective activity, focusing on the tropical Atlantic region (10°E to 20°W, 0° to 20°S). It is found that gravity waves with a time period of 24 hours are excited near the Equator (∼5°–15°N) in a region of large moist heating extending vertically up to 10–13 km. The gravity waves propagate upward from this region with a bias toward the south and are manifested as large energy fluxes in the cross equatorial region. Enhanced energy fluxes are therefore simulated at 20–30 km altitude over a region with no significant source of gravity waves, and are confirmed using Global Positioning Satellite/Meteorology (GPS/MET) experiment data.
Assessment of GPS velocity accuracy for the Basin and Range Geodetic Network (BARGEN)
Authors: Davis J. L. , Bennett R. A. , Wernicke B. P.
Published: May 2003

We assess the accuracy of horizontal velocity estimates from the Basin and Range Geodetic Network (BARGEN), a continuous GPS network that has been in operation since 1996. To make this quantitative assessment, we use a procedure that we term the “whole‐error” method. In this method, the measure of the velocity errors is the root‐mean‐square (RMS) residual velocity relative to a simple geophysical model. This method produces a conservative estimate of the uncertainties, since errors in the geophysical models also contribute to the RMS residual. Using estimates from two different BARGEN subnetworks, the Northern Basin and Range and the Yucca Mountain Cluster, we determine velocity uncertainties of 0.1–0.2 mm yr−1. Since BARGEN covers a significant fraction of area of the proposed Plate Boundary Observatory component of EarthScope, our results indicate a good ability of this project to determine highly accurate long‐term horizontal crustal velocities and deformation rates in this region.
Dimethyl disulfide (DMDS) and dimethyl sulfide (DMS) emissions from biomass burning in Australia
Authors: Meinardi Simone , Simpson Isobel J. , Blake Nicola J. , Blake Donald R. , Rowland F. Sherwood
Published: May 2003

We identify dimethyl disulfide (DMDS) as the major reduced sulfur‐containing gas emitted from bushfires in Australia's Northern Territory. Like dimethyl sulfide (DMS), DMDS is oxidized in the atmosphere to sulfur dioxide (SO2) and methane sulfonic acid (MSA), which are intermediates in the formation of sulfuric acid (H2SO4). The mixing ratios of DMDS and DMS were the highest we have ever detected, with maximum values of 113 and 35 ppbv, respectively, whereas background values were below the detection limit (10 pptv). Molar emission ratios relative to carbon monoxide (CO) were [1.6 ± 0.1] × 10−5 and [6.2 ± 0.3] × 10−6, for DMDS and DMS respectively, while molar emission ratios relative to carbon dioxide (CO2) were [4.7 ± 0.4] × 10−6 and [1.4 ± 0.4] × 10−7, respectively. Assuming these observations are representative of biomass burning, we estimate that biomass burning could yield up to 175 Gg/yr of DMDS (119 Gg S/yr) and 13 Gg/yr of DMS.
Stochastic boundary conditions for coastal flow modeling
Authors: Mariano Arthur J. , Chin Toshio M. , Özgökmen Tamay M.
Published: May 2003

Recent high‐resolution radar data of surface velocity between the Florida Current and the coast allow us for the first time to deduce coastal boundary conditions for ocean models based on observations. A stochastic model is found to be a better choice for simulating properties of the observed vorticity than a model with deterministic boundary conditions. A stochastic model parameterizing boundary conditions is developed and embedded in a simple quasigeostrophic ocean model. Comparison of numerical simulations of western boundary flow with stochastic boundary conditions against simulations with traditional no‐slip and free‐slip conditions reveals significant differences in the formation of coherent mesoscale structures and the energetics of the western boundary current. Coherent structures such as dipoles and submesoscale vortices can be generated using stochastic boundary conditions. The boundary current variability becomes more energetic and “episodic” than quasi‐periodic circulation features in the simulations using the conventional boundary conditions.
Relativistic electron acceleration and precipitation during resonant interactions with whistler‐mode chorus
Authors: Horne R. B. , Thorne R. M.
Published: May 2003

Resonant interactions with whistler‐mode chorus waves provide an important process for electron loss and acceleration during storm times. We demonstrate that wave propagation significantly affects the electron scattering rates. We show that stormtime chorus waves outside the plasmapause can scatter equatorial electrons ≤60 keV into the loss cone and accelerate trapped electrons up to ∼ MeV energies at large pitch‐angles. Using ray tracing to map the waves to higher latitudes, we show that the decrease in the ratio between the electron plasma and gyro frequencies, along with the normalized chorus frequency bandwidth, enable much higher energy electrons ∼1 MeV to be scattered into the loss cone. We suggest that off equatorial pitch‐angle scattering by chorus waves is responsible for relativistic micro‐burst precipitation seen on SAMPEX. Off‐equatorial scattering at pitch‐angles well away from the loss cone also contributes to the acceleration of higher energy ≥3 MeV electrons.
Eddies revealed by SeaWiFS ocean color images in the Antarctic Divergence zone near 140°E
Authors: Hirawake Toru , Kudoh Sakae , Aoki Shigeru , Rintoul Stephen R.
Published: May 2003

Eddy‐like distributions of chlorophyll a were clearly detected in the Antarctic Divergence zone around 140°E by SeaWiFS ocean color images. The distribution was also supported by in‐situ measurements. The eddy‐like structure was associated with changes in surface and subsurface water mass properties. Extremely high levels of chlorophyll in coastal areas were transported and redistributed horizontally offshore by these eddies, and a significant effect of the huge biomass on the biological processes in the investigated area was expected. The lateral exchange between coastal and offshore waters driven by these eddies, may be an essential factor in the observed patchy structures in this region.
Relationship between North Atlantic Oscillation changes and stratospheric ozone recovery in the Northern Hemisphere in a chemistry‐climate model
Authors: Schnadt Christina , Dameris Martin
Published: May 2003

The relationship between North Atlantic Oscillation (NAO) changes and northern stratospheric ozone recovery in the near future is investigated using four timeslice scenarios (1960, 1980, 1990, 2015) of the chemistry‐climate model ECHAM4.L39(DLR)/CHEM. A wintertime NAO index composite study of the scenario “1990” and of the ECMWF reanalyses shows the typical NAO patterns: in the positive phase the stratospheric polar vortex is stronger and colder than in the negative phase. In the troposphere, the positive phase is marked by increased variance across the North Atlantic stormtrack whereas the negative phase is suggestive of blocking. Consistently, vertical stationary (transient) wave propagation is reduced (enhanced) in the positive phase. The model NAO index decreases significantly from “1990” to “2015”. This coincides with enhanced vertical stationary wave propagation and a dynamical heating of the northern polar stratosphere. Thus, tropospheric circulation changes might influence stratospheric dynamics and hence northern hemisphere ozone evolution.
Long‐term creep‐rate changes and their causes
Authors: Bokelmann Göetz H. R. , Kovach Robert L.
Published: May 2003

We discuss measurements of the long‐term creep rate from the San Juan Bautista section of the San Andreas fault. These observations of aseismic slip span a period of approximately half a century making it the longest creep record ever measured along an active fault zone. The records show systematic changes in creep rate over time scales of tens of years, and we address potential causes of these changes. In principle, they may be caused either by changes in resistive forces within the fault zone or by variations in plate‐tectonic driving forces. Such driving force variations have recently been suggested to have occurred in the same area (Western North America) and within the same time window. These should give rise to observable effects in the creep data, but we find no evidence for temporal changes in plate‐tectonic forcing at these time scales. A natural explanation for the observed long‐term changes is elastic reloading of adjacent locked portions of the San Andreas fault after large earthquakes and possibly aseismic strain release that occurs before the earthquakes.
Lithospheric thickness inferred from Australian post‐glacial sea‐level change: The influence of a ductile crustal zone
Authors: Kendall R. , Mitrovica J. X. , Sabadini R.
Published: May 2003

We investigate the influence of a crustal low viscosity zone (CLVZ) on numerical predictions of post‐glacial, late Holocene sea‐level variations in the Australian region. Specifically, we compare predictions from a model with a 15 km thick CLVZ within an otherwise elastic plate to results from a suite of models in which the thickness of a purely elastic crust‐lithosphere is varied. We conclude that previous inferences of lithospheric thickness based on differential highstands from the region represent (approximately) the thickness of the elastic layer above the CLVZ; and thus, if a CLVZ exists, these inferences may be significantly underestimating the total depth extent of the crust‐lithosphere system.
Continued anomalous warming in Australia
Authors: Nicholls Neville
Published: May 2003

Previous work, using high‐quality temperature and rainfall data sets averaged across Australia, has demonstrated that the relationship between annual mean maximum temperature and rainfall changed in the early 1970s. The relationship was still strong and negative (i.e., high temperatures tended to accompany droughts) but the temperature in the period 1973–1992 tended to be higher, for any value of rainfall, than had been the case in the earlier years. This study again uses high‐quality data averaged across Australia and the year, and demonstrates that this “anomalous warming” has intensified. Since 1993, temperatures have tended to be higher, for a given rainfall, than was the case in the 1973–1992 period (which in turn was relatively warmer than previous years). Thus the warming observed over Australia over the last few decades does not reflect changes in rainfall.
Sea‐level dependence on the NAO over the NW European Continental Shelf
Authors: Wakelin S. L. , Woodworth P. L. , Flather R. A. , Williams J. A.
Published: May 2003

The connection between changes in the North Atlantic Oscillation (NAO) and the sea level over the northwest European continental shelf is investigated for the period 1955–2000 using a two‐dimensional model of tides and storm surges. There is a clear spatial pattern in the correlation between sea level and the NAO on a winter‐mean timescale. Correlations are positive (>0.8) in the northeast and negative (<−0.7) in the south. The sensitivity of the sea level to the NAO is strongest in the southern North Sea (up to 96 mm per unit NAO index), where most of the sensitivity is present also in the non‐hydrostatic component of sea level. The relationships are validated using observed data recorded at coastal tide gauges.
Long‐term decline in carbon dioxide supersaturation in rivers across the contiguous United States
Authors: Jones Jeremy B. , Stanley Emily H. , Mulholland Patrick J.
Published: May 2003

The partial pressure CO2 (pCO2) in streams and rivers reflects both internal carbon dynamics and external biogeochemical processes in terrestrial ecosystems. CO2 is typically supersaturated in streams because rates of organic matter decomposition exceed photosynthetic uptake, and because of inflow of CO2 supersaturated ground waters. Using the U.S. Geological Survey's NASQAN database, we calculated pCO2 and dissolved inorganic carbon (DIC) concentration in 417 streams and rivers distributed across the contiguous United States over a 22‐year period. In addition to demonstrating widespread supersaturation and distinct regional variation in pCO2 across the U.S., our analysis revealed that pCO2 significantly declined 78.4 ppmv y−1 from 1973 to 1994. This decline is not attributable to changes in terrestrial weathering or in‐stream processes, but instead suggests large‐scale declines in terrestrial CO2 production and import into aquatic ecosystems during this 22‐year period.
Initial intensification of East Asian winter monsoon at about 2.75 Ma as seen in the Chinese eolian loess‐red clay deposit
Authors: Xiong S. F. , Ding Z. L. , Jiang W. Y. , Yang S. L. , Liu T. S.
Published: May 2003

The loess‐paleosol‐red clay sequence in the Chinese Loess Plateau provides a record of the evolution of atmospheric circulation and monsoon climate over East Asia during the last 7–8 Ma. Detailed analyses of the Baishui and Jingchuan sections show that the grain size of eolian loess increased abruptly at about 2.75 Ma, which is accompanied with a reversal of depositional pattern from the red clay to loess‐paleosol deposits, suggesting that the dust transporting circulation was reorganized. This is the earliest clear expression of the East Asian winter monsoon intensification at the Pliocene‐Pleistocene climate transition, coincident with the initiation of major Northern Hemisphere glaciation over the Eurasian Arctic and Northeast Asia, implying that at the early stage of the Pliocene‐Pleistocene global cooling the East Asian winter monsoon circulation had been closely linked with the build up of ice sheet and climate changes over the high latitudes of Northern Hemisphere. The intensified winter monsoon winds would have in turn acted as an important positive feedback in strengthening global cooling by increasing albedo and dust loading.
Downslope convection north of Elephant Island, Antarctica: Influence on deep waters and dependence on ENSO
Authors: Meredith Michael P. , Hughes Chris W. , Foden Peter R.
Published: May 2003

We present a long time series (1992–2001) of bottom temperature from 1040m on the continental slope north of Elephant Island, Antarctic Peninsula. A strong annual signal is apparent, with minimum temperatures during or following the austral winter, and a range similar to that found in much shallower waters on the adjacent shelf. Individual convective events are observable as large‐amplitude cold spikes that are confined to the period of seasonally coldest temperatures. These plumes are dense enough to seasonally displace the Circumpolar Deep Water, and directly inject cold water into the deep open ocean. The coldest water occurred when anomalous sea ice conditions were prevalent, caused by the strong 1997/98 ENSO event. We thus expect repeats of such strong convective events on ENSO timescales. The observed long‐term warming and reduction in sea ice along the Peninsula may, however, act to suppress this mode of ventilating the deep Southern Ocean.
Nucleation rate of particles in the lower atmosphere: Estimated time needed to reach pseudo‐steady state and sensitivity to H2SO4 gas concentration
Authors: Yu Fangqun
Published: May 2003

Using a kinetic model, we estimate the time‐needed (t0) to establish a pseudo‐steady state nucleation when sulfuric acid concentration ([H2SO4]) suddenly increases to a certain fixed level. We find that t0 is roughly inversely proportional to [H2SO4]. The assumption of instantaneously achieved pseudo‐steady state concentration of critical clusters, on which the classical nucleation theories are based, is no longer valid when t0 is longer than the time period that [H2SO4] can be treated as constant. Under the lower marine atmospheric conditions considered in this study, the nucleation rate predicted by ion‐mediated nucleation theory is very sensitive to [H2SO4] when [H2SO4] is low (<∼7 × 106/cm3) but such a sensitivity reduces significantly as [H2SO4] increases, which is quite different from that predicted with classical binary and ternary homogeneous nucleation theories.
Initiation of deformation of the Eastern California Shear Zone: Constraints from Garlock fault geometry and GPS observations
Authors: Gan Weijun , Zhang Peizhen , Shen Zheng‐Kang , Prescott W. H. , Svarc J. L.
Published: May 2003

We suggest a 2‐stage deformation model for the Eastern California Shear Zone (ECSZ) to explain the geometry of the Garlock fault trace. We assume the Garlock fault was originally straight and then was gradually curved by right‐lateral shear deformation across the ECSZ. In our 2‐stage deformation model, the first stage involves uniform shear deformation across the eastern part of the shear zone, and the second stage involves uniform shear deformation across the entire shear zone. In addition to the current shape of the Garlock fault, our model incorporates constraints on contemporary deformation rates provided by GPS observations. We find that the best fitting age for initiation of shear in eastern part of the ECSZ is about 5.0 ± 0.4 Ma, and that deformation of the western part started about 1.6 Myr later.
El Niño Tropical Pacific Ocean surface current and temperature evolution in 2002 and outlook for early 2003
Authors: Lagerloef Gary S. E. , Lukas Roger , Bonjean Fabrice , Gunn John T. , Mitchum Gary T. , Bourassa Mark , Busalacchi Antonio J.
Published: May 2003

The timing and magnitude of the 2002–2003 El Niño/Southern Oscillation (ENSO) warm episode has been monitored for the first time with near real time satellite‐derived surface current (SC) fields in addition to the operational temperature, wind and sea level satellite and in situ measurements previously used. The record of the past decade shows that dominant SC anomalies generally lead ENSO sea surface temperature (SST) anomalies by 2.5–3 months, and that a rapid SC anomaly reversal has coincided with the peak SST of warm events. During September to December 2002, SST anomalies increased and spread eastward in conjunction with strong, sustained eastward SC anomalies that began in July. The SC anomaly peaked in early October, followed by a sharp decrease in November and December to negative values in January. This was much like the SC sequence during the same months of the 1997–1998 El Niño when the SST anomaly peaked in December 1997. The recent SST anomalies were maximum in November 2002 and declined thereafter. These SC and SST trends signify that the present warm event has peaked and SST anomalies will continue to decline in early 2003.
Timing of abrupt climate change: A precise clock
Authors: Rahmstorf Stefan
Published: May 2003

Many paleoclimatic data reveal a ∼1,500 year cyclicity of unknown origin. A crucial question is how stable and regular this cycle is. An analysis of the GISP2 ice core record from Greenland reveals that abrupt climate events appear to be paced by a 1,470‐year cycle with a period that is probably stable to within a few percent; with 95% confidence the period is maintained to better than 12% over at least 23 cycles. This highly precise clock points to an origin outside the Earth system; oscillatory modes within the Earth system can be expected to be far more irregular in period.
Structure of oceanic core complexes: Constraints from seafloor gravity measurements made at the Atlantis Massif
Authors: Nooner Scott L. , Sasagawa Glenn S. , Blackman Donna K. , Zumberge Mark A.
Published: May 2003

Using the DSV Alvin, the relative seafloor gravimeter ROVDOG was deployed at 18 sites on the Atlantis Massif (located at the ridge‐transform intersection of the Mid‐Atlantic Ridge and the Atlantis Transform Fault near 30°N, 42°W). These data along with previously collected shipboard gravity and bathymetry provide constraints on the density structure of this oceanic core complex. A series of quasi 3‐D forward models suggests that symmetric east and west‐dipping density interfaces bound the core of the massif with dip angles of 16°–24° in the east and 16°–28° in the west, creating a wedge with a density of 3150–3250 kg/m3. The dip angle in the east is steeper than that of the surface slope, suggesting that the detachment fault surface does not coincide with the density boundary. The resulting low‐density layer is interpreted as a zone of serpentinization.
Ground surface temperatures in Canada: Spatial and temporal variability
Authors: Beltrami Hugo , Gosselin C. , Mareschal J. C.
Published: May 2003

Past changes in the Earth's surface energy balance are recorded in the ground as perturbations of the subsurface thermal regime. Here we reconstruct ground surface temperature histories (GSTH) from temperature versus depth profiles measured at 246 sites distributed across Canada. We show that the ground has warmed about 0.7 K in the last 100 years. Spatial variability is significant and indicates that the largest warming is in the southern areas of Canada. The apparent signal for the “Little Ice Age” (LIA) does not appear to be homogeneous across Canada.
The source of Benguela Niños in the South Atlantic Ocean
Authors: Florenchie Pierre , Lutjeharms Johann R. E. , Reason C. J. C. , Masson S. , Rouault M.
Published: May 2003

The intermittent occurrence of anomalous warm events in the upwelling regions of the Pacific – El Niños – has been intensively studied. Pacific Niños have striking effects on the local ecosystem, hence on the fisheries, and on rainfall. Similar dramatic events have been observed in the South Atlantic off the coasts of Angola and Namibia and named Benguela Niños. They tend not to occur in unison with their Pacific counterpart and may thus have unrelated forcing mechanisms. Using an ocean general circulation model, forced by real winds and verified with satellite data, it is shown that Benguela Niños are generated by specific wind stress events in the west‐central equatorial Atlantic, and progress from there as subsurface temperature anomalies that eventually outcropped only at the south‐west African coast. These results suggest that it now may be possible to predict the occurrence of these disruptive events with a lead‐time of 2 months.
Analysis of deep‐penetrating radar surveys of West Antarctica, US‐ITASE 2001
Authors: Welch Brian C. , Jacobel Robert W.
Published: May 2003

We collected 1850 km of ground‐based radio echo‐sounding (RES) data in West Antarctica along the 2001 US leg of the International Trans‐Antarctic Scientific Expedition traverse (US‐ITASE). These data represent the first high‐resolution measurements of ice thickness and internal stratigraphy for portions of this area that bear on questions about the stability of the West Antarctic Ice Sheet (WAIS). Internal layers depicting isochrones have been traced continuously for much of the profile length and a date from the Byrd Deep Core is ascribed to one of these isochrones from which we estimate vertical velocities across the traverse route. Comparison of our ice thickness measurements with BEDMAP show good agreement in regions where the database is well constrained by data coverage. Where the BEDMAP dataset was forced to interpolate, differences are as high as 45% of the ice thickness.
Interactions between the Atlantic Multidecadal Oscillation, El Niño/La Niña, and the PNA in winter Mississippi Valley stream flow
Authors: Rogers Jeffrey C. , Coleman Jill S. M.
Published: May 2003

Winter streamgage data at 554 locations in the U.S. Geological Survey's Hydro‐Climatic Data Network are used to evaluate interactions between the Atlantic multidecadal oscillation (AMO), the Pacific/North American (PNA) teleconnection pattern, and warm and cold equatorial Pacific Niño 3.4 events in producing Mississippi River basin discharge variations. The AMO is linked to statistically significant stream flow differences over the upper Mississippi Valley, as well as low (high) winter stream flow from 1930–1959 (1965–1994). Its influence in the lower Mississippi Valley is however not as apparent because of 4 consecutive wet winters, 1949–1952, that disrupt the AMO warm/dry period. Persistent PNA zonal flow, and a La Niña event, occur during these winters and they are closely linked to high Tennessee and Ohio River valley stream levels. PNA‐influenced stream flow on these rivers has a greater long‐term winter impact on the lower Mississippi basin than does flow from the upper Mississippi.
Coherence of Antarctic sea levels, Southern Hemisphere Annular Mode, and flow through Drake Passage
Authors: Hughes Chris W. , Woodworth Philip L. , Meredith Michael P. , Stepanov Vladimir , Whitworth Thomas , Pyne Alexander R.
Published: May 2003

It is known from small sets of tide gauges that sub‐surface pressure (sea level corrected for the inverse barometer effect) around Antarctica varies coherently around about half of the continent, and that this coherent signal is related to atmospheric forcing in the form of the Antarctic Oscillation, or Southern Hemisphere Annular Mode. We here confirm that this coherence extends to a more extensive network of tide gauges, and to parts of the continental shelf far from the shore, as measured by bottom pressure gauges. We use time series from an eddy‐permitting ocean model with realistic forcing to relate the coherent mode to fluctuations in transport through Drake Passage, and confirm, using a 1° resolution barotropic model, that the fluctuations are predominantly due to barotropic dynamics, although baroclinic dynamics are expected to play an increasing role at interannual timescales.
High resolution DNS of jet stream generated tropopausal turbulence
Authors: Joseph B. , Mahalov A. , Nicolaenko B. , Tse K. L.
Published: May 2003

Tropopausal turbulence (TT), generated by jet streams, is examined, for different nonhomogeneous basic state forcing profiles, through high resolution three‐dimensional (3D) direct numerical simulations (DNS). Turbulent core regions, on either side of the jet, are characterized by a dramatic decrease in Brunt‐Väisälä frequency (N), minima in gradient Richardson number (Rig) and shear length scales, and maxima in buoyancy Reynolds number and buoyancy length scales. The edges of turbulent mixing layers are marked by N2‐bulges, which provides an alternate mechanism for multiple tropopauses. While temperature variance peaks in the vicinity of these N2‐bulges, velocity variances peak within the turbulent core. Multiple branches in the scaling of flux Richardson number with Rig are found typical for TT, a result having implications to the problem of turbulence parameterization.
Influence of SDZ RAD vs. MMF on gastric emptying in renal transplant recipients
Authors: Maes Bart D , Evenepoel Pieter , Kuypers Dirk , Geypens Benny , Ghoos Yvo , Vanrenterghem Yves
Published: May 2003

SDZ RAD and mycophenolate mofetil (MMF) are increasingly used in the prevention of renal allograft rejection. SDZ RAD, having a macrolide structure, and MMF, known with gastrointestinal side‐effects, may have gastric motility modifying properties. Gastric emptying was examined 1 yr after renal transplantation in eight patients taking corticosteroids (CS), cyclosporin A (CsA) and SDZ RAD and six patients treated with CS, CsA and MMF. Comparing the two groups, no significant differences in gastric emptying of solids and liquids were noted. Compared with normal volunteers, solid gastric emptying was faster in the SDZ RAD group and similar in the MMF group. It is concluded that in stable renal transplant recipients treated with MMF, gastric emptying was normal. Because of the impact on drug absorption and gastrointestinal symptoms, further studies are indicated to corroborate the potential prokinetic properties of SDZ RAD.
Steroid‐free immunosuppression during and after liver transplantation – a 3‐yr follow‐up report
Authors: Pirenne Jacques , Aerts Raymond , Koshiba Takaaki , Gelder Frank Van , Roskams Tania , Schetz Marie , Verhaegen Marleen , Lauwers Peter , Fevery Johan , Nevens Frederik
Published: May 2003

Abstract:  Background/aims: Steroids are traditionally used in liver transplantation as a part of a triple or quadruple immunosuppressive regimen. Steroids act non‐specifically and cause multiple side‐effects. Most liver transplantation centers reduce the dosage of steroids and eventually withdraw them after various time intervals. A few steroid‐free trials have been recently conducted after liver transplantation but long‐term data are not yet available. In addition, in these trials steroids were usually given during surgery. We report the long‐term (median = 40 months) follow‐up data of a prospective pilot study designed to determine whether liver transplantation could be performed with no steroids at all (neither during nor after surgery).

Methods: Twenty‐one consecutive liver transplantations in 20 adult patients between August 1998 and July 1999 were prospectively included in an ab initio steroid‐free immunosuppressive protocol. Mean age was 54 yr (40–67 yr). Tacrolimus (through levels, 8–10 ng/mL) and azathioprine (1–2 mg/kg) were started after liver transplantation. Patients were not given steroids during or after liver transplantation except in the event of rejection or in case of tacrolimus or azathioprine toxicity requiring significant dose reduction and/or withdrawal.

Results: There has been no case of primary graft dysfunction or non‐function. Eleven of 21 liver transplantations (52%) received no steroids throughout the whole study. Rejection developed in five of 21 liver transplantations (23.5%). These rejections responded to standard i.v. steroids (plus ATG in one patient), followed by an oral steroid taper stopped 3 months after rejection. Steroids were transiently given in six liver transplantations for non‐immune reasons: two with tacrolimus‐induced neurotoxicity, three cases where azathioprine was discontinued, and one for an allergic reaction; four of these six patients are off steroids at last follow‐up. The 3‐yr graft and patient survival is 95 and 100%, respectively.

Conclusions: Steroids are not necessary in more than 50% of liver transplantations. Steroids were transiently needed to treat acute rejection in 23.5% liver transplantations and for toxicity of calcineurin inhibitors or azathioprine or other reason in 28%. Of the patients who received steroids, the majority (70%) was eventually taken off steroids. This prospective single‐center pilot study shows that liver transplantation without steroids is feasible and yields no penalty in terms of acute and chronic rejection, immune graft loss, graft function, patient and graft survival.
Chronic liver disease in kidney recipients with hepatitis C virus infection
Authors: Giordano Helena M , França Alex VC , Meirelles Luciana , Escanhoela Cecília AF , Nishimura Nancy F , Santos Raquel LS , Quadros Kélcia RS , Mazzali Marilda , Alves‐Filho Gentil , Soares Elza C
Published: May 2003

Abstract: Background:  The prevalence of anti‐hepatitis C virus (HCV) positive test is higher among patients in dialysis and in kidney recipients than in general population. Hepatitis C virus infection is the main cause of chronic liver disease in renal transplant patients. Liver biopsy and virological analysis were performed to clarify the grade of liver damage in kidney recipients.

Methods:  Renal recipients patients with at least 5 yr under immunosuppression were submitted to clinical and laboratory analysis. Patients who tested anti‐HCV positive were candidates to liver biopsy with no regard to transaminase levels.

Results:  Forty‐five patients tested anti‐HCV positive and 42 anti‐HCV negative. Twenty‐six anti‐HCV and RNA‐HCV positive patients were submitted to liver biopsy. Seventy‐three percentage of these patients presented chronic active hepatitis, from these only one patient presented cirrhosis. Only 29% of the anti‐HCV positive group presented elevated alanine aminotransferase levels. Anti‐HCV positive patients presented longer previous time on dialysis and less rejection episodes than the group anti‐HCV negative (p < 0.05). All anti‐HCV positive patients but one tested RNA‐HCV positive by polymerase chain reaction (PCR).

Conclusions:  In this series the prevalence of anti‐HCV positive is 51.7%. Most of the patients presented liver damage in histology caused by HCV. However, we found only mild or minimal fibrosis and inflammatory activity grade, despite 10 yr of HCV infection and 5 yr of immunosuppressive treatment. Only one patient presented cirrhosis (4%). Performing serial liver biopsies in a long‐term follow‐up is needed to clarify the impact of HCV infection in renal transplant patients.
The impact of mycophenolate mofetil dosing patterns on clinical outcome after renal transplantation
Authors: Pelletier Ronald P , Akin Baris , Henry Mitchell L , Bumgardner Ginny L , Elkhammas Elmahdi A , Rajab Amer , Ferguson Ronald M
Published: May 2003

Abstract: Background:  Mycophenolate mofetil (MMF) has proven to be a very effective drug for the prevention of acute rejection following renal transplantation when dosed as prescribed at 2 or 3 g/d. However, circumstances arise in clinical transplantation where the dose must be lowered, either to avoid drug toxicity or because of concurrent infection. The impact on the incidence of acute rejection and graft survival when the MMF dose must be lowered has not previously been investigated.

Methods:  In this study, a cohort of 721 kidney transplant recipients who received immunosuppression using MMF in conjunction with cyclosporine and prednisone and OKT3 (n = 425) or Simulect (n = 296) induction were evaluated. Clinical outcomes were compared and contrasted between patients with and without MMF dose changes within the first year post‐transplantation.

Results:  The majority of patients (70.3%, n = 507) had at least one dose change within the first post‐transplant year. Compared with the 214 patients who did not have a dose change, these patients had a much higher incidence of acute rejection within the first post‐transplant year (23.3% vs. 3.7%, p < 0.001). This resulted in a significantly decreased 3‐yr death‐censored graft survival (76.3% vs. 88.3%, p = 0.003). The incidence of acute rejection for patients who had a dose change was highest if the dose change occurred within the first post‐transplant month (34.4%). The incidence of acute rejection for the dose change patients was influenced by recipient ethnicity (African‐American vs. Caucasian) and the type of induction agent used (OKT3 vs. Simulect).

Conclusion:  Altering the dose of MMF within the first post‐transplant year correlated with a significantly worse clinical outcome in this cohort of renal transplant recipients. These data suggest that avoidance of MMF dose changes within the first year after renal transplantation would result in improved graft survival.
Effect of cyclosporin pharmacokinetics on renal allograft outcome in African‐Americans
Authors: Emovon Osemwegie E , King Judy AC , Holt Cindy Op't , Singleton Barbara , Howell David , Browne Barry J
Published: May 2003

Abstract:  African‐Americans (A‐As) experience inferior outcome after transplantation compared with other ethnic groups. Bioavailability of cyclosporin (CsA) has been implicated as a possible contributing factor. This paper describes the outcome of 32 A‐A recipients of de novo renal allograft who received CsA‐based triple immunotherapy according to individual pharmacokinetic profiles. Patients received CsA‐microemulsion q 12 h, dosed initially at 3.5 mg/kg (8 am) and 3.0 mg/kg (8 pm). The am and pm doses were independently adjusted to achieve a 12‐h area under the concentration–time curve (AUC0−12) of 6600–7200 nghr/mL and morning trough level (C0) of 250–325 ng/mL, respectively. Mean age was 43 ± 12 yr, 37% (12) female. Mean AUC0−12 in 1 wk, 1, 3, 6, and 12 months were 7810 ± 1880 nghr/mL, 9057 ± 2097 nghr/mL, 7674 ± 1912 nghr/mL, 7132 ± 2040 nghr/mL, and 6503 ± 1410 ngl/h with corresponding C0 of 301 ± 79 ng/mL, 316 ± 66 ng/mL, 275 ± 59 ng/mL, 273 ± 66 ng/mL, and 224 ± 49 ng/mL, respectively. Acute rejection occurred in two patients (6%) 1 yr after transplantation. Prospective use of CsA pharmocokinetic profiles improves renal allograft outcome in A‐As.
Exercise capacity and muscle structure in kidney recipient and twin donor
Authors: Painter Patricia , Taylor Jasmine , Wolcott Shoshana , Krasnoff Joanne , Adey Deborah , Tomlanovich Stephen , Stock Peter , Topp Kimberly
Published: May 2003

Exercise capacity and muscle function are known to be abnormal in patients with renal disease. We present a case study in which we studied a kidney transplant recipient who received a kidney from his identical twin. Testing included maximal exercise testing with measurement of oxygen uptake (VO2max), isokinetic muscle function testing, body composition analysis using dual energy X‐ray absorptiometry (DEXA) imaging and quality of life using The Medical Outcomes Short Form (SF‐36) questionnaire. Muscle biopsies were also analysed for fibre composition and size and ultrastructure. We found that the twin recipient had lower values for VO2max, muscle strength, muscle mass and quality of life scales (physical domains) compared with the twin donor. Muscle fibre composition was identical in the twins, however, muscle fibres size was reduced in the twin donor in Type I, and Type IIA fibre types. The twin recipient also showed lower fibre density (volume percentage) and greater intrafibrillar space than the donor. The twins were both sedentary, thus we conclude that the low exercise capacity and abnormalities observed in the recipient are characteristics of renal failure, and not the result of physical deconditioning, nor was it related to prednisone therapy, which may negatively affect muscle function.
The use of an anti‐CD25 monoclonal antibody and mycophenolate mofetil enables the use of a low‐dose tacrolimus and early withdrawal of steroids in renal transplant recipients
Authors: Kuypers DRJ , Evenepoel P , Maes B , Coosemans W , Pirenne J , Vanrenterghem Y
Published: May 2003

Abstract: Background: Reducing calcineurin‐inhibitor‐induced nephrotoxicity and simultaneously avoiding long‐term steroid related side‐effects is a desirable goal in renal transplantation. We examined the hypothesis that using anti‐CD25 monoclonal antibody induction and mycophenolate mofetil (MMF) would allow the lowering of target pre‐dose blood concentrations of tacrolimus immediately after transplantation and subsequently stopping steroids at 5 months.

Methods: Eighty‐two kidney recipients were enrolled in a single‐center study comparing two tacrolimus‐based protocols. Group I (n = 41) patients received a standard‐dose tacrolimus (blood concentration 10–15 ng/mL) with MMF and a standard dose corticosteroid. Group II (n = 41) patients were treated with a low‐dose tacrolimus (blood concentration 5–10 ng/mL) and MMF, a low‐dose corticosteroid (stopped after 5 months) and induction with daclizumab.

Results: Patient (95.1 versus 100%) and graft survival (92.6 versus 97.5%) at 1 yr were not different between groups. Patients of group II experienced significantly less acute rejections than group I (17.1 versus 41.4% p = 0.03). Delayed graft function occurred less often in group II (5 versus 12% p = 0.43). Graft function at 1 yr was significantly better in group II (serum creatinine 1.49 versus 1.69 mg/dL and creatinine clearance 59.6 versus 49 mL/min; p < 0.05). Corticosteroids could be stopped after 5 months in 82.9% of group II patients.

Conclusion: A regimen consisting of anti‐CD25 monoclonal antibody induction and MMF allows the safe and efficient use of low‐target pre‐dose trough concentrations of tacrolimus and enables the early discontinuation of steroids. Preliminary results indicate a better 1‐yr graft function compared to a normal‐dose tacrolimus regimen.
Pancreas transplantation in crossmatch‐positive recipients
Authors: Khwaja Khalid , Wijkstrom Martin , Gruessner Angelika , Noreen Harriet , Sutherland David ER , Humar Abhinav , Kandaswamy Raja , Gruessner Rainer WG
Published: May 2003

Abstract: Background: Prolonged cold preservation time can unfavorably affect outcome in pancreas transplantation. To reduce this ischemic time, cadaver pancreas grafts, in selected cases, are sometimes transplanted before crossmatch results are known. We report our experience with pancreas transplants in recipients with either current or historically positive T‐ or B‐cell crossmatches.

Methods: Crossmatch‐positive pancreas transplants were identified using a computerized database. T‐cell crossmatches were performed using an antihuman‐globulin‐augmented complement‐dependent cytotoxicity (CDC) test; B‐cell crossmatches were performed using an extended incubation CDC test. All patients received anti‐T‐cell induction therapy and either cyclosporine (1987–1993) or tacrolimus‐based (1994–2001) immunosuppression. More recent recipients (2000–2001) also received intravenous gamma globulin and postoperative plasmapheresis.

Results: Between October 1, 1987 and March 31, 2001, of a total of 1076 pancreas transplants performed, 59 (5.48%) were crossmatch‐positive. Of these, 8 had a current T‐cell‐positive crossmatch and 15 had a current B‐cell‐positive crossmatch. One recipient was both current B‐ and T‐positive, and the rest were past B‐ and/or T‐cell positive. One‐year pancreas graft survival for current T‐ and B‐cell crossmatch‐positive transplants was 63% and 67%, respectively. T‐ or B‐cell crossmatch‐negative transplants had a 1‐yr survival of 70%. In the T‐cell crossmatch‐positive group, four grafts are still functioning (follow‐up range, 2–12 yr), one patient died with a functioning graft at 4 months, and four grafts failed (one each from pancreatitis, infection, primary nonfunction, and vascular thrombosis). No grafts were lost to rejection. In the B‐cell crossmatch‐positive group, six grafts are still functioning (follow‐up range, 2–11 yr) and nine have failed (four from chronic rejection, three from vascular thromboses, and two from pancreatitis). Crossmatch‐positive cases were significantly more likely to be retransplants (70.8%) than crossmatch‐negative cases (14.8%, p < 0.0001). In a multivariate analysis, crossmatch positivity did not affect pancreas graft outcome, whereas retransplants had a significant impact on outcome (relative risk 1.84, p < 0.0001).

Conclusions: (i) Pancreas transplants performed in the setting of a positive current crossmatch may have long‐term function. (ii) With current immunosuppressive protocols, graft loss from hyperacute and acute rejection may be prevented in current crossmatch‐positive pancreas transplants. Chronic rejection was only seen in B‐cell crossmatch‐positive cases. (iii) High rates of technical graft loss in crossmatch‐positive cases may reflect a high frequency of retransplants in this group.