bluuebunny/crossref_metadata_2025 huggingface dataset:
Heart failure as an inflammatory condition: potential role for androgens as immune modulators
Authors: Pugh Peter J. , Jones Richard D. , Jones T. Hugh , Channer Kevin S.
Published: December 2002

Heart failure has traditionally been considered a disease of the myocardium, with symptoms arising from altered haemodynamics. However, it is now recognised that, in addition to marked neuroendocrine disturbance, there is perturbation of cytokine expression in patients with heart failure, resulting in an inflammatory imbalance. This not only influences symptoms, but also plays a central role in the underlying pathophysiological processes of heart failure, leading to disease progression and poorer prognosis. Recognition of the influence of cytokines, in particular tumour necrosis factor, has opened a new avenue for potential therapies for heart failure. Current approaches involve immunomodulation, aimed at suppressing tumour necrosis factor. We suggest that androgens may potentially offer a superior therapeutic strategy by their well‐recognised non‐specific immunosuppressive and anti‐inflammatory effects. Studies of cell lines, human mononuclear cells and animals in vivo have demonstrated the ‘anti‐cytokine’ actions of androgens, and we have found a similar action in whole blood from patients with heart failure. These effects, along with the anabolic action of these agents, make androgens an attractive potential option for treatment of patients with heart failure.
Angiotensin II type 2 receptor gene polymorphism and cardiovascular phenotypes: the GLAECO and GLAOLD studies
Authors: Herrmann Stefan‐Martin , Nicaud Viviane , Schmidt‐Petersen Klaus , Pfeifer Jacqueline , Erdmann Jeanette , McDonagh Theresa , Dargie Henry J. , Paul Martin , Regitz‐Zagrosek Vera
Published: December 2002

Background:

The angiotensin II type 2 (AT2) receptor is thought to play a role in cardiovascular disorders such as neointima formation after vascular injury, cardiac hypertrophy and myocardial infarction (MI). Recently, the biallelic polymorphism G+1675A in intron 1 of the AT2 receptor gene has been associated with left ventricular posterior, septal and relative wall thickness, as well as left ventricular mass index in young hypertensive males.

Methods:

To investigate its potential role in left ventricular hypertrophy (LVH) and other cardiovascular traits, 1968 individuals from two population samples (the Glasgow Heart Scan, GLAECO and Glasgow Heart Scan Old, GLAOLD studies) with echocardiographically and electrocardiographically assessed phenotypes, were genotyped for G+1675A using allele‐specific oligonucleotide hybridization. Both studies had a similar design, only the age‐ranges differed, being 25–74 years in the GLAECO study and 55–74 years in the GLAOLD study, so that internal consistency of results could also be assessed. Since the AT2 gene is located on the X chromosome, males and females were analysed separately.

Results:

The +1675A allele frequency was 0.49 and 0.51, in the GLAECO and GLAOLD studies, respectively. In both studies, the genotype frequencies were similar in hypertensive and non‐hypertensive individuals. In the GLAOLD study, in females with episodes of coronary ischemia and MI, the AT2 +1675A allele was more common than in females with no episode (86.5% vs. 73.5%, respectively; P<0.007). This effect was not observed in males. In the same study, AT2 +1675A allele carriers were more common in males with LVH, than in those without LVH (60.3% vs. 46.0%, respectively; P=0.047). This result was unchanged after exclusion of subjects taking antihypertensive drugs (including ACE inhibitors) (64.4% vs. 47.4%, P=0.038). However, in the GLAECO study, these results could not be replicated, even when subjects >55 years of age were considered separately.

Conclusions:

Our study gives rise to a potential implication of the AT2 G+1675A polymorphism in LVH and coronary ischemia subgroups. Since these results were not consistent in both studies, but are partially in agreement with two independent investigations, further efforts should be made to elucidate the specific nature of these genotype/phenotype interactions.
Acute haemodynamic effects of oestrogen administration in male patients with chronic heart failure
Authors: Adamopoulos Stamatis , Leftheriotis Dionyssios , Sbarouni Eftihia , Karavolias George , Kremastinos Dimitrios Th
Published: December 2002

Background:

Although there are many studies concerning the effects of long‐term oestrogen administration on systemic haemodynamics in postmenopausal women, the effects of oestrogen in patients with chronic heart failure are not defined.

Aim:

The goal of this study was to evaluate the acute haemodynamic effects of oestrogen in male patients with chronic heart failure.

Methods and results:

We studied 15 men with advanced heart failure (NYHA II–IV, EF<35=). A Swan–Ganz thermodilution catheter was advanced in their pulmonary artery and central haemodynamics were assessed at baseline, after placebo administration, and following 0.625 and 1.25 mg of oestrogen infusion. Simultaneously, all patients underwent limb plethysmography. Analysis of variance with repeated measures was used to compare the sequential measurements. Following oestrogen administration, right atrial, pulmonary artery and pulmonary capillary wedge pressures, as well as systemic, pulmonary and forearm vascular resistance were decreased; cardiac output, cardiac index, stroke volume, stroke volume index, stroke work index and forearm blood flow were increased.

Conclusions:

In male patients with chronic heart failure, acute oestrogen administration improves the indices of cardiac systolic performance and decreases pulmonary and systemic vascular resistance. These findings imply a beneficial effect of oestrogen in selected patients with chronic heart failure.
Investigating the heterogeneity of the D″ region beneath the northern Pacific using a seismic array
Authors: Thomas Christine , Heesom Thomas , Kendall J. Michael
Published: December 2002

Seismic array recordings are used to study the heterogeneity of a 15° × 25° region of the lowermost mantle beneath the northern Pacific. We investigate P waves from northwestern Pacific events, 68° to 82° from the Yellowknife array in northern Canada. Anomalous arrivals (PdP) are observed 2–13.5 s after P with a slowness 0.4–1.2 s/deg smaller than P, suggesting that they are reflections from a D″ discontinuity. We use vespagrams (slant stacks) and f‐k analyses to determine travel times and slowness vectors respectively. The f‐k technique simultaneously estimates both the horizontal slowness and backazimuth of arrivals at a receiver, with better resolution than vespagrams. Travel time analysis reveals a mean discontinuity height of 241 km above the core‐mantle boundary in the region studied here. However, there appears a systematic variation in this thickness which ranges from 211 to 336 km. The f‐k analyses also reveal variations between P and PdP backazimuths, further implying the existence of lateral variations in D″ in this area. This site is thought to be a transition region from an area of mantle downwelling to a region of upwelling; thus the variations in heterogeneity in this region may be related to its proximity to a site of paleoslab accumulation.
Numerical modeling of the role of water and clay content in soils' and rocks' bulk electrical conductivity
Authors: Tabbagh Alain , Panissod Cédric , Guérin Roger , Cosenza Philippe
Published: December 2002

The influence of clay and water content in the electrical conductivity of rocks and soils has been experimentally established and is expressed by simple empirical laws: the Archie's law and the addition law between volume water conductivity and surface shale conductivity. Two independent numerical modeling techniques, the moment method and the finite difference method, are presented here and are used, first, to verify the agreement between Maxwell's equation based theoretical approaches and the empirical laws and, second, to begin to investigate for a possible effect of the microscopic geometry over macroscopic conductivity. A good agreement between simulation results and Archie's law is obtained when both randomly distributed isotropic and elongated microvolumes of conducting water are considered and a slight difference appears between these two microstructures. For low clay contents in clay‐dispersed media, the clay‐associated conductivity is shown to be proportional to a specific clay area, which is in good agreement with the addition empirical law.
Effect of windowing on lithosphere elastic thickness estimates obtained via the coherence method: Results from northern South America
Authors: Ojeda Germán Y. , Whitman Dean
Published: December 2002

The effective elastic thickness (Te) of the lithosphere is a parameter that describes the flexural strength of a plate. A method routinely used to quantify this parameter is to calculate the coherence between the two‐dimensional gravity and topography spectra. Prior to spectra calculation, data grids must be “windowed” in order to avoid edge effects. We investigated the sensitivity of Te estimates obtained via the coherence method to mirroring, Hanning and multitaper windowing techniques on synthetic data as well as on data from northern South America. These analyses suggest that the choice of windowing technique plays an important role in Te estimates and may result in discrepancies of several kilometers depending on the selected windowing method. Te results from mirrored grids tend to be greater than those from Hanning smoothed or multitapered grids. Results obtained from mirrored grids are likely to be over‐estimates. This effect may be due to artificial long wavelengths introduced into the data at the time of mirroring. Coherence estimates obtained from three subareas in northern South America indicate that the average effective elastic thickness is in the range of 29–30 km, according to Hanning and multitaper windowed data. Lateral variations across the study area could not be unequivocally determined from this study. We suggest that the resolution of the coherence method does not permit evaluation of small (i.e., ∼5 km), local Te variations. However, the efficiency and robustness of the coherence method in rendering continent‐scale estimates of elastic thickness has been confirmed.
Compositional variability in the ascending fluxes from a hydrothermal plume
Authors: Bertram Miriam A. , Cowen James P. , Thomson Richard E. , Feely Richard A.
Published: December 2002

Sequentially sampling sediment traps set with 33 day sampling intervals were deployed with current meters on three moorings in the northeast Pacific Ocean between July 1994 and May 1995. One mooring was deployed near the Main Vent field on Endeavour Ridge (On‐Axis site, 47°57.0′N, 129°05.7′W), a second, 3 km west of the Main vent site (West site), and the third, 43 km northeast of the Main vent site (East or background site). Ascending and descending particles were collected near 1600 and 2000 m depth, well above and within the top of laterally spreading hydrothermal plumes. The elemental composition of particles was used to evaluate their origins: biogenic fluxes were indicated by elevated Ca or Si, hydrothermal fluxes by elevated Fe, Mn, and Cu, and lithogenic fluxes by elevated Ti. We link temporal variability in both the ascending and descending particle composition and flux to variations in lateral transport of hydrothermal constituents and to seasonal drawdown of hydrothermal plume particles by biogenic material from the upper ocean. The relatively low hydrothermal Fe content of ascending material late in the experiment is thought to be due to uptake by descending biogenic material. These results suggest that seasonal productivity and particle export from the ocean surface can modulate the hydrothermal flux of elements to the waters above and to the sediments below.
Excess helium and neon in the southeast Pacific: Tracers for glacial meltwater
Authors: Hohmann R. , Schlosser P. , Jacobs S. , Ludin A. , Weppernig R.
Published: December 2002

We analyze helium (He) and neon (Ne) isotope data sets from the southeast Pacific sector of the Southern Ocean collected in 1992 and 1994 and describe a new method to estimate glacial meltwater fluxes independent of previous approaches. The waters sampled during these cruises reveal large atmospheric He and Ne excess concentrations in the upper 500 m that are derived predominantly from the dissolution of air contained in glacial ice during melting underneath and at the front of floating ice shelves at elevated hydrostatic pressure. On the stations sampled, the meltwater fractions are largest near the northern and southern ice shelf fronts of George VI Ice Shelf (1.5–2.5%), consistent with prior inferences from δ18O. The inventories of 4He and Ne with local glacial meltwater origin south of 70°S between 210°E and 295°E are (2.5 ± 0.7)1011 cm3STP 4He and (7.9 ± 2.7)1011 cm3STP Ne, respectively. The associated meltwater volumes are 430 ± 120 Gt for 4He and 400 ± 140 Gt for Ne. For an estimated seawater residence time of 2 years on the continental shelf, the amounts of glacial meltwater translate into bulk melting rates of 215 ± 170 Gt yr−1 for 4He and 200 ± 170 Gt yr−1 for Ne. The values derived from 4He are expected to be larger than those obtained from Ne because of the terrigenic He component, which accounts for 10–15% of the He excess in this region. Our regional melting rate of 200–215 Gt yr−1 is comparable to a prior estimate but subject to uncertainties resulting from the station distribution, the air‐sea gas exchange, and the estimate of the net transport through the study region.
Effects of benthic transport processes on abrupt climatic changes recorded in deep‐sea sediments: A time‐dependent modeling approach
Authors: Charbit S. , Rabouille C. , Siani G.
Published: December 2002

A one‐dimensional time‐dependent model is developed to characterize qualitatively and quantitatively the combined effects of bioturbation and burial on sedimentary signals related to abrupt climatic changes. This model is based on the widely used advection‐diffusion equation and simulates rapid climatic transitions by representing the deposition flux at the sediment‐water interface by a steep ramp function of time. This model is applied to both planktonic foraminifera abundance curves and δ18O distributions. Output signals, obtained at the bottom of the bioturbated layer for these rapid transitions, have been generated for a broad range of sedimentation rates (5–50 cm kyr−1), biodiffusion coefficients (10−3 −1 cm2 yr−1), and mixed layer thicknesses (2–15 cm). Numerical results clearly demonstrate the importance of a dynamic description of sediment mixed layers. Properties of the sedimentary response to fast transitions appear to be highly and nonlinearly dependent upon the sedimentation rate and the relative values of the original transition length and the time required to bury the signal below the mixed layer. Moreover, for low sedimentation rates (≤10 cm kyr−1) we show that signals occurring over a 50‐ to a 250‐year timescale are indistinguishable. To quantify the distortion of sedimentary signals, we determined the transition length of the bioturbated simulated signals and compare it to the initial transition length for given sets of bioturbation and sedimentation rates and mixed layer thicknesses. Comparison between model predictions and experimental results reveals a good agreement, showing that transition timescales are compatible with ice core‐derived transitions (<100 years) for environments in which bioturbation can be approximated by a diffusive process. Tests performed on δ18O distributions have illustrated the effect of bioturbation on the stratigraphic offsets between isotopic compositions of cold and warm species of foraminifera during climatic transitions.
Impact of nitrous acid photolysis on the total hydroxyl radical budget during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono study in Milan
Authors: Alicke B. , Platt U. , Stutz J.
Published: December 2002

The photolysis of nitrous acid (HONO) in the early morning hours is believed to be a significant source of hydroxyl radicals (OH), the most important daytime oxidizing species. Although the importance of this mechanism has been recognized for many years, no accurate experimental quantification is available. Here we present measurements of HONO, NO2, SO2, O3 and HCHO by Differential Optical Absorption Spectroscopy (DOAS) during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono (LOOP/PIPAPO) study in May–June 1998 in Milan, Italy. The concentration of NO and J(NO2)/J(HONO) were simultaneously monitored by in situ monitors. The photolysis frequencies of HCHO and O3 were determined with a radiative transfer model. High nocturnal HONO mixing ratios of up to 4.4 ppb were regularly observed. Elevated daytime HONO levels during cloudy periods show that the formation of HONO proceeds after sunrise and therefore also represents a source of hydroxyl radicals throughout the day. Averaged over 24 hours, HCHO photolysis is the most important source of OH in Milan, followed by either ozone or HONO photolysis. Our observations indicate that on certain days the OH production from HONO can be even more important than that from ozone photolysis. The diurnal variation of the different OH formation mechanisms shows that HONO photolysis is by far the most important source in the early hours of the morning, and can be as large as and even surpass the total OH production at noon.
Sensitivity of ozone production derived from field measurements in the Italian Po basin
Authors: Thielmann Axel , Prévôt André S. H. , Staehelin Johannes
Published: December 2002

Ozone, nitric oxides, and total reactive nitrogen, measured at two stations in the vicinity of Milan, Italy, are used to infer information on the reactive organic gas (ROG) versus NOx sensitivity of ozone production. At the rural station, ozone production per NOx consumed is less efficient when the advected air masses originate from Milan. This lower efficiency is indicative of ROG‐sensitive ozone production. Furthermore, the indicator variables H2O2/NOz, HCHO/NOy, and O3/NOz are applied to both sets of data. The data set with lower ozone production efficiency consistently shows lower indicator values. These findings corroborate the interpretation that ozone production within the Po basin has a tendency to be NOx sensitive and that ROG‐sensitive ozone production is only possible within the Milan urban plume. Important links to model calculations for the domain are highlighted.
Sources of upper tropospheric HOx over the South Pacific Convergence Zone: A case study
Authors: Mari Céline , Saüt Carine , Jacob Daniel J. , Ravetta François , Anderson Bruce , Avery Melody A. , Blake Donald R. , Brune William H. , Faloona Ian , Gregory G. L. , Heikes Brian G. , Sachse Glen W. , Sandholm Scott T. , Singh Hanwant B. , Talbot Robert W. , Tan David , Vay Stephanie
Published: December 2002

A zero‐dimensional (0‐D) model has been applied to study the sources of hydrogen oxide radicals (HOx = HO2 + OH) in the tropical upper troposphere during the Pacific Exploratory Mission in the tropics (PEM‐Tropics B) aircraft mission over the South Pacific in March–April 1999. Observations made across the Southern Pacific Convergence Zone (SPCZ) and the southern branch of the Intertropical Convergence Zone (ITCZ) provided the opportunity to contrast the relative contributions of different sources of HOx, in a nitrogen oxide radical (NOx)‐limited regime, in relatively pristine tropical air. The primary sources of HOx vary significantly along the flight track, in correlation with the supply of water vapor. The latitudinal variation of HOx sources is found to be controlled also by the levels of NOx and primary HOx production rates P(HOx). Budget calculations in the 8‐ to 12‐km altitude range show that the reaction O(1D) + H2O is a major HOx source in the cloud region traversed by the aircraft, including SPCZ and the southern branch of the ITCZ. Production from acetone becomes significant in drier region south of 20°S and can become dominant where water vapor mixing ratios lie under 200 ppmv. Over the SPCZ region, in the cloud outflow, CH3 OOH transported by convection accounts for 22% to 64% of the total primary source. Oxidation of methane amplifies the primary HOx source by 1–1.8 in the dry regions.
Are the northern plains of Mars a frozen ocean?
Authors: Janhunen P.
Published: December 2002

In this brief report we consider the possibility that the northern plains of Mars would today be a frozen ocean, covered by a rather thin (at most of the order of a few hundred meters) layer of volcanic and impact debris and dust that prevents the ice beneath from being directly observed and thermally protects it from summertime sublimation (according to current models, subsurface ice in the high latitudes is stable under current climatic conditions). The frozen ocean hypothesis would naturally explain the striking topographic flatness of the northern plains. We show that the frozen ocean is plausible in terms of current models of paleoclimatic development. We also discuss the possibility that a remnant salty brine ocean could still exist under the ice and that electric currents flowing in it would be responsible for the recently observed ∼40 nT Northern Hemisphere magnetic anomalies. The latter hypothesis could be tested by suitably placed surface magnetometers.
A MILLENNIUM OF GEOMAGNETISM
Authors: Stern David P.
Published: December 2002

The history of geomagnetism began around the year 1000 with the discovery in China of the magnetic compass. Methodical studies of the Earth's field started in 1600 with William Gilbert'sDe Magnete[Gilbert, 1600] and continued with the work of (among others) Edmond Halley, Charles Augustin de Coulomb, Carl Friedrich Gauss, and Edward Sabine. The discovery of electromagnetism by Hans Christian Oersted and André‐Marie Ampére led Michael Faraday to the notion of fluid dynamos, and the observation of sunspot magnetism by George Ellery Hale led Sir Joseph Larmor in 1919 to the idea that such dynamos could sustain themselves naturally in convecting conducting fluids. From that came modern dynamo theory, of both the solar and terrestrial magnetic fields. Paleomagnetic studies revealed that the Earth's dipole had undergone reversals in the distant past, and these became the critical evidence in establishing plate tectonics. Finally, the recent availability of scientific spacecraft has demonstrated the intricacy of the Earth's distant magnetic field, as well as the existence of magnetic fields associated with other planets and with satellites in our solar system.
Modeling laminar sheet flow over rough surfaces
Authors: Myers T. G.
Published: December 2002

A mathematical model for two‐dimensional laminar flow over a rough surface is developed. Explicit formulae are presented for the height and average and maximum velocities in terms of measurable quantities and a friction factor. The correction factor α, the ratio of the average to maximum velocity, is also discussed and shown to vary significantly from the value on a smooth surface. Predictions for the film height and velocities are presented and compared with previous experiments. Good agreement is obtained between the theory and experiments. The saline technique for measuring velocities is shown to significantly underpredict the fluid velocity. The Manning, Chezy, and Darcy‐Weisbach formulae all overpredict the velocity in the laminar flow regime. It is also shown that there is a relation between the correction factor and the height or inundation ratio, but there is no relation to the Reynolds number in laminar flow.
Iron in the Sargasso Sea: Implications for the processes controlling dissolved Fe distribution in the ocean
Authors: Wu Jingfeng , Boyle Edward
Published: December 2002

In the surface water of the winter Sargasso Sea, “dissolved” Fe concentrations (defined as iron that passes through a filter with an 0.4 micrometer diameter pore size) decrease with increasing latitude from 0.8 nM at 26°N to 0.2 nM at 31°N. It does not appear that this pattern can be explained solely by spatial variations of eolian Fe deposition. Vertical mixing, phytoplankton growth and particle scavenging all appear to play important roles in controlling dissolved Fe distributions in the surface water. Concentrations of dissolved Fe in the subsurface waters increase with increasing depth from ∼0.2 nM at ∼200 m to ∼0.6 nM at depths below 1000 m, reflecting an imbalance between Fe removal by particle scavenging and Fe regeneration from microbial decomposition of organic matter sinking from the euphotic zone. Simple model calculations suggest that scavenging loss of Fe and ventilation of low preformed Fe high P water from source region may create deep ocean Fe:P concentration ratios (5 × 10−4 for the Atlantic and 1.2 × 10−4 for the Pacific) that are much lower than the ratios of Fe to P regenerated from the organic matter sinking from the euphotic zone (24–74 × 10−4 for the Atlantic and 11–32 × 10−4 for the Pacific). We hypothesize that this low Fe:P ratio may be the driving force for Fe limitation of algal growth observed in high nutrient low chlorophyll oceans and that regional changes of Fe:C ratios in organic matter sinking from the euphotic zone may play an important role in regulating dissolved Fe concentrations in the deep waters of the world ocean.
An evaluation of physical and biogeochemical processes regulating perennial suboxic conditions in the water column of the Arabian Sea
Authors: Sarma V. V. S. S.
Published: December 2002

Monthly oxygen budgets for the subsurface Arabian Sea (100–1000 m) are constructed on the basis of Modular Ocean Model and recently collected oxygen data. The model results are in agreement with the observed pattern. The model results revealed that oxygen minimum zone (OMZ) in the Arabian Sea is regulated largely by physical processes in association with biogeochemical cycling of oxygen. This results in perennial suboxic conditions in the water column with no significant seasonal variability. Maintenance of OMZ during nonmonsoon seasons, when oligotrophic conditions prevail in surface layers, occurs through low supply of oxygen by physical pump aided by continued oxygen consumption in the oxidation of organic matter produced during monsoons. On the other hand, formation of anoxic conditions during monsoons, when higher sinking fluxes of carbon occur, is prevented by higher flux of oxygen by the physical pump. Hence, suboxic conditions in the Arabian Sea are maintained by physical pump with moderation from monsoonal biological pump. The residence time of the Arabian Sea intermediate waters (100–1000 m) was computed to be 6.5 years with rapid replacement during monsoons. The oxygen consumption rates are also high during monsoons compared with nonmonsoon seasons. The carbon regeneration rates computed based on the water mass‐mixing model, bacterial carbon demand, and electron transport system activity in the subsurface layers are in agreement with oxygen consumption rates estimated based on this model.
Methane‐limited methanotrophy in tidal freshwater swamps
Authors: Megonigal J. Patrick , Schlesinger William. H.
Published: December 2002

We investigated the relationship between CH4 production and oxidation in two tidal freshwater wetland forests in order to determine whether CH4 oxidation efficiency was limited by O2 or CH4. Methane oxidation was measured in situ over a 16‐month period with bi‐monthly applications of the inhibitor CH3F. Oxidation consumed 52 ± 10 and 81 ± 9% of diffusive CH4 emissions on the two sites. Methane oxidation rates were linearly related to gross CH4 emissions on both sites (r2 = 0.96), demonstrating the process was CH4‐limited. This interpretation is consistent with the fact that the apparent activation energies for the potential CH4 production and oxidation differed by <4 kJ mol−1. Apparent activation energies calculated from field emissions data were also similar for the two processes. The high CH4 oxidation efficiency on these sites may be attributed to relatively low rates of methane production, a deep oxidizing zone (5–10 cm), and low cover of understory vegetation capable of CH4 transport. If our results are typical of forested wetlands, CH4 oxidation efficiency in forested wetlands will not change in response to soil warming.
Modeling global annual N2O and NO emissions from fertilized fields
Authors: Bouwman A. F. , Boumans L. J. M. , Batjes N. H.
Published: December 2002

Information from 846 N2O emission measurements in agricultural fields and 99 measurements for NO emissions was used to describe the influence of various factors regulating emissions from mineral soils in models for calculating global N2O and NO emissions. Only those factors having a significant influence on N2O and NO emissions were included in the models. For N2O these were (1) environmental factors (climate, soil organic C content, soil texture, drainage and soil pH); (2) management‐related factors (N application rate per fertilizer type, type of crop, with major differences between grass, legumes and other annual crops); and (3) factors related to the measurements (length of measurement period and frequency of measurements). The most important controls on NO emission include the N application rate per fertilizer type, soil organic‐C content and soil drainage. Calculated global annual N2O‐N and NO‐N emissions from fertilized agricultural fields amount to 2.8 and 1.6 Mtonne, respectively. The global mean fertilizer‐induced emissions for N2O and NO amount to 0.9% and 0.7%, respectively, of the N applied. These overall results account for the spatial variability of the main N2O and NO emission controls on the landscape scale.
Slabs in the lower mantle and their modulation of plume formation
Authors: Tan Eh , Gurnis Michael , Han Lijie
Published: December 2002

Numerical mantle convection models indicate that subducting slabs can reach the core‐mantle boundary (CMB) for a wide range of assumed material properties and plate tectonic histories. An increase in lower mantle viscosity, a phase transition at 660 km depth, depth‐dependent thermal expansivity, and depth‐dependent thermal diffusivity do not preclude model slabs from reaching the CMB. We find that ancient slabs could be associated with lateral temperature anomalies ∼500°C cooler than ambient mantle. Plausible increases of thermal conductivity with depth will not cause slabs to diffuse away. Regional spherical models with actual plate evolutionary models show that slabs are unlikely to be continuous from the upper mantle to the CMB, even for radially simple mantle structures. The observation from tomography showing only a few continuous slab‐like features from the surface to the CMB may be a result of complex plate kinematics, not mantle layering. There are important consequences of deeply penetrating slabs. Our models show that plumes preferentially develop on the edge of slabs. In areas on the CMB free of slabs, plume formation and eruption are expected to be frequent while the basal thermal boundary layer would be thin. However, in areas beneath slabs, the basal thermal boundary layer would be thicker and plume formation infrequent. Beneath slabs, a substantial amount of hot mantle can be trapped over long periods of time, leading to “mega‐plume” formation. We predict that patches of low seismic velocity may be found beneath large‐scale high seismic velocity structures at the core‐mantle boundary. We find that the location, buoyancy, and geochemistry of mega‐plumes will differ from those plumes forming at the edge of slabs. Various geophysical and geochemical implications of this finding are discussed.
Dunite distribution in the Oman Ophiolite: Implications for melt flux through porous dunite conduits
Authors: Braun Michael G. , Kelemen Peter B.
Published: December 2002

Dunites in the mantle section of the Oman ophiolite represent conduits for chemically isolated melt transport through the shallow mantle beneath oceanic spreading centers. These dunite melt conduits exhibit a scale‐invariant power law relationship between width and cumulative abundance, as measured over 4 orders of magnitude. We use this size/frequency distribution to assess several hypotheses for dunite formation and estimate the total melt flux that a dunite network can accommodate beneath an oceanic spreading center. Dunites, measured from one‐dimensional lithologic sections and digital image mosaics at a variety of length scales, range in width from ∼3 mm to ∼100 m and follow a power law with a slope of ∼1.1. Extrapolation of the power law predicts that dunites as wide as 3.5 km may exist in the melting region beneath a mid‐ocean ridge. Alternatively, perhaps the widest dunites we observe (∼100 m) represent a maximum size. Modeling of dunites as diffusive reaction zones around melt‐filled hydrofractures cannot explain the existence of dunites wider than ∼10 m in Oman. Instead, dunites may represent high porosity conduits formed by reactive porous flow. Using the observed size/frequency relationship, the assumption that dunites form a coalescing network and the requirement that flux is conserved where dunites merge, we estimate the total flux through a porous dunite network and the fraction of that flux that remains chemically isolated. Our flux model predicts that the porosity in a dunite scales with the width. For maximum porosities of ∼1–4% in the widest dunites, a network of porous dunite conduits with the abundances observed in Oman can supply a sufficient flux of melt (of which > 95% remains chemically unequilibrated with shallow residual peridotites) to satisfy the observed mid‐ocean ridge flux.
Dynamic phase boundaries of olivine‐wadsleyite in subduction zones in the western Pacific
Authors: Jing Zhi‐Cheng , Ning Jie‐Yuan , Wang Shu‐Guang , Zang Shao‐Xian
Published: December 2002

A modified coupling scheme is proposed to calculate the thermal structures and the kinetics of olivine to wadsleyite phase transformation in subduction zones, which assures a high computational precision. The phase and thermal structures of some subduction zones in the western Pacific region are calculated. Computational results show that most subduction zones don't have large wedges of metastable olivine, which lets the mechanisms of transformational faulting have difficulty explaining deep seismicity.
Late Pleistocene paleomagnetic secular variation from the Sea of Galilee, Israel
Authors: Marco Shmuel
Published: December 2002

Stable magnetization of laminated lacustrine Lisan Formation show typical paleomagnetic secular variation and a possible geomagnetic field excursion. 14C ages from the top and assumed 0.9 mm/yr deposition rate constrain the recorded section between 29–28 ka and 22–23 ka. Samples were recovered from two trenches at the southwestern shore of the Sea of Galilee, a graben within the Dead Sea Transform system. The angle between the two site mean directions is 21°, but retilting the beds to horizontal reduces it to 7°, indicating pre‐folding, probably depositional magnetization. Aberrations of field directions at one locality, where VGPs deviate >40° from the geographic north, and low NRM intensities between 29–28 ka and 25–24 ka, are contemporaneous with the Mono Lake Excursion. If the correlation is correct, the new data support the hypothesis that the excursion was global, justifying its utilization as a chronological datum.
Multidecadal streamflow regimes in the interior western United States: Implications for the vulnerability of water resources
Authors: Jain Shaleen , Woodhouse Connie A. , Hoerling Martin P.
Published: December 2002

In the interior western United States, increased demand for water coupled with the uncertain nature of anthropogenic and natural hydroclimatic variations add challenges to the task of assessing the adequacy of the existing regional water resources systems. Current availability of relatively short instrumental streamflow records further limits the diagnosis of multidecadal and longer time variations. Here we develop a long‐term perspective of streamflow variations using a 285‐year long tree‐ring reconstruction at Middle Boulder Creek, Colorado. Analysis of the reconstructed streamflow provides useful insights for assessing vulnerability: (a) a wider range of hydrologic variations on multidecadal time scales, not seen in the instrumental record, (b) wet/dry regimes show disparate fluctuations across various flow thresholds, and (c) temporal changes in the flow probabilities have varied “flavors” corresponding to wet and dry regimes and their spatial extent. Based on these results, we discuss implications for the climate‐related vulnerability of regional water resources.
Coordinated observations of Pc3 pulsations near cusp latitudes
Authors: Matsuoka Hitoshi , Yukimatu A. Sessai , Yamagishi H. , Sato N. , Sofko G. J. , Fraser B. J. , Ponomarenko P. , Liu R. , Goka T.
Published: December 2002

In spite of accumulated observations of ULF pulsations, there are no satisfactory explanations for the generation and transmission mechanisms of Pc3 pulsations at very high latitudes. We studied the characteristics of the high‐latitude Pc3 pulsations by using data acquired on the ground by magnetometer arrays, in the ionosphere by the Super Dual Auroral Radar Network (SuperDARN) of HF radars, and in space by the Geotail satellite. The observations revealed that narrowband Pc3 pulsations are occasionally observed simultaneously in magnetic field data on the ground and in Doppler velocity data acquired by the HF radars in the intervals of small interplanetary magnetic field (IMF) cone angles. We find that there is a clear peak of the Pc3 power near the cusp latitudes and that the power of pulsations decreases very steeply with latitude. At times, there are periods of high coherence between the pulsations in the dawn magnetosheath and on the ground, although the spectra of the magnetosheath magnetic field variations exhibit broadband signatures. The Poynting flux in the Pc3 band increases in the magnetosheath when narrowband Pc3 pulsations are observed in the cusp region. The results suggest that the driving source is located in the magnetosheath and that part of the MHD energy in the magnetosheath propagates to the ionospheric cusp. We suggest that the transmission of Pc3 pulsations in the cusp region requires not only a non‐MHD mechanism as suggested (e.g., modulated precipitation of trapped electrons) but also an MHD wave incident into the ionosphere.
Observations of plasma injection into the ring current during substorm expansive phase
Authors: Frank L. A. , Paterson W. R. , Sigwarth J. B.
Published: December 2002

The injection of plasmas during the expansive phase of four substorms was investigated with global auroral images and simultaneous measurements of plasmas and magnetic fields in the plasma sheet near the magnetic equator. The high‐resolution images were gained at far‐ultraviolet wavelengths with the Earth Camera on board the Polar spacecraft and the observations of plasmas and magnetic fields were acquired with the Geotail spacecraft at radial distances in the range of 11 to 15 RE. For each of the substorms an ion flow burst was detected with maximum speeds in the range of 200 to 400 km/s and durations of several minutes. The ion bulk flow was directed earthward. For the first time auroral images recorded the position of the flow bursts as the leading edge of the westward or eastward traveling surge during the expansive phase of the substorm. The time intervals from the substorm onset as recorded by the camera until the detection of the flow pulse at the Geotail spacecraft ranged from 3 to 11 min. With the exception of one event which was located near the duskside magnetopause, the ion velocity distributions were characterized by the same densities and temperatures during and after the flow pulse for each of the individual events. For three of the events the electron temperature increased by a factor of about 2 after passage of the flow pulse. For the fourth event the spacecraft was not in the plasma sheet prior to the flow pulse, and hence this temperature increase could not be determined. Substantial fluctuations of the magnetic fields accompany the flow pulses. The electron and ion spectra were smoothly varying during the flow pulses without evidence of the highly structured spectral features due to combined gradient and electric field drifts which are well documented for particle injections near the 6.6‐RE synchronous orbit. The measurements at the Geotail spacecraft position support the existence of the previously proposed “injection front” for plasmas which is due to transient earthward convection during the expansive phase of substorms. This convection occurs during the diversion of the equatorial current sheet into the ionosphere at locations inside the Geotail position.
Altitude‐time development of sprites
Authors: McHarg Matthew G. , Haaland Ryan K. , Moudry Dana , Stenbaek‐Nielsen Hans C.
Published: December 2002

Data from sprites using a 16‐channel, multi‐anode photometer (MAP) have been recorded at 0.1 ms resolution. The majority of the sprites have onsets at an altitude of 70–75 km and subsequently propagate both upward and downward from this initial altitude. The statistical lifetime of the emissions measured by the blue‐sensitive MAP is approximately 1.3 ms. The velocities of propagation are between 107 and 108m s−1, with larger velocities being measured at higher altitudes. The larger propagation velocities of the upward and downward sprite luminosity channels are consistent with the characteristics of highly over‐voltage streamers in the mesosphere.
Statistical distributions of field‐aligned electron events in the near‐equatorial magnetosphere observed by the Low Energy Plasma Analyzer on CRRES
Authors: Abel G. A. , Fazakerley A. N. , Johnstone A. D.
Published: December 2002

Low energy (≤100 eV–10 keV) field‐aligned electrons are often observed by the Low Energy Plasma Analyzer (LEPA) on the CRRES satellite. These electrons usually occur in bursts of <10 min duration and are mostly bidirectional, though opposing fluxes are not always equal. The events can be seen from L‐values of 5 outward (to at least L = 7) and from 0800 magnetic local time (MLT) through midnight to 1400 MLT. Larger numbers of events were seen at the outer edge of CRRES' coverage and in the evening and early morning sectors, when the apogee of CRRES was at higher latitudes. The bursts normally occur within 20 min of substorm onset. High‐latitude, low‐altitude spacecraft often observe upgoing field‐aligned electron beams. We suggest that these are the source of the field‐aligned electron beams seen by CRRES near the equator.
Radial dependence of relativistic electron fluxes for storm main phase development
Authors: Kim Hee‐Jeong , Rostoker Gordon , Kamide Y.
Published: December 2002

Satellite observations have revealed that the flux variations of outer belt relativistic electrons during the main phase of a magnetic storm exhibit a strong radial dependence. This L dependence is characterized as a small increase or decrease near the inner edge of the belt (L ∼ 3) and a large decrease inits outer region (L ∼ 5). Extending the study by Kim and Chan [1997] of relativistic electron flux decreases at geostationary orbit, we investigate the characteristic radial dependence in terms of the fully adiabatic response of relativistic electrons to magnetic field perturbations. Using Liouville's theorem and the conservation of the first and third adiabatic invariants, we calculate storm main phase fluxes of equatorially mirroring electrons by adiabatically evolving the prestorm values. A quiet time electron distribution model is constructed from the CRRES satellite data. The radial structure of magnetic field perturbations and the spatial and energy dependence of the quiet time electron distribution are found to affect the main phase fluxes through adiabatic processes. In response to the field perturbations, adiabatic flux changes become larger at higher L shells where electrons can experience strong deceleration and considerable radial displacement. The nonmonotonic energy spectrum at the inner edge of the outer belt, which is featured in our quiet time electron model, can yield a slight flux increase in that region even during adiabatic deceleration. The results of this study suggest that a fully adiabatic treatment can provide an important component of the explanation for the general pattern of large scale changes in the radial profile of relativistic electron fluxes during the storm main phase.
MHD simulations of the solar wind interaction with Mercury
Authors: Ip Wing‐Huen , Kopp Andreas
Published: December 2002

A numerical MHD code is used to simulate the dynamical responses of Mercury's magnetosphere to different orientations of the interplanetary magnetic field (IMF) and values of the solar wind dynamical pressure. It is found that the IMF orientation is very effective in changing the size of the polar cap and, hence, the surface area subject to direct solar wind sputtering. Even though the polar cap size is not significantly changed by the solar wind dynamic pressure variation for a fixed IMF direction, the global configuration and size of the Hermean magnetosphere are highly responsive. The observed time variations of the atomic sodium emission at Mercury, hence, might indeed be correlated with the solar wind condition.
Excitation of left‐hand‐polarized nonlinear Alfvén waves by an ion beam in a plasma
Authors: Shevchenko V. I. , Galinsky V. L. , Ride S. K.
Published: December 2002

The nonlinear problem of MHD wave excitation in plasma by an ion beam with a ring distribution function was solved. We studied how the steepened wave profiles grew out of low‐frequency Alfvén fluctuations excited by the ion beam in plasma. Two types of nonlinearities are taken into account: (1) strong nonlinearity of resonant ions (beam ions) due to trapping and bounce‐oscillation effects and (2) weak nonlinearity of nonresonant particles (plasma particles) that leads to mode coupling and steepening of the wave profile. The spectral method in concert with a hybrid method of resonant simulation was used in this study. The wave excitation, saturation, and subsequent nonlinear evolution were studied.
A new model of the location of the plasmapause: CRRES results
Authors: Moldwin Mark B. , Downward L. , Rassoul H. K. , Amin R. , Anderson R. R.
Published: December 2002

A new empirical model of the plasmapause location has been developed using density data from the plasma wave receiver onboard the CRRES spacecraft for nearly 1000 orbits. The “plasmapause” is identified here as the innermost sharp gradient in density (change of a factor of 5 in <0.5 L). Such a sharp gradient was observed on 73% of the CRRES inbound and outbound orbits that returned data. The plasmapause location is expressed as a linear function of Kp (previous 12 hour maximum) and local time. The model gives the linear best fit location of the plasmapause as well as the standard deviations of the model parameters. We found a slight noon‐midnight asymmetry with the plasmapause located on average an L shell farther from the Earth at midnight than in the noon sector. This is in the opposite sense to the noon‐midnight asymmetry found previously. Significant variability (with standard deviations up to +/− 1 L shell) in the plasmapause location is seen and suggests that though the mean plasmapause is roughly circular, the instantaneous plasmapause has significant time variable localized structure at all local times but most especially in the duskside sector.