bluuebunny/crossref_metadata_2025 huggingface dataset:
Management of life-threatening airway obstruction caused by benign thyroid disease
Authors: Kadhim A L , Sheahan P , Timon C
Published: September 2006

Introduction: Goitre presenting with acute, life-threatening airway compromise is an uncommon indication for thyroid surgery. The management of this critical condition is controversial.

Aims: To investigate the incidence of life-threatening airway compromise in patients with benign goitre, to investigate the predisposing factors, and to outline an optimal management policy for such critical cases.

Methods: Retrospective review of the medical records of patients presenting with life-threatening, acute airway compromise secondary to benign thyroid disease, treated by the senior author (CT) between July 1994 and July 2005.

Results: Of a total of 505 thyroid surgery procedures over the 11-year period, five patients with benign thyroid disease had presented with life-threatening, acute airway compromise. Three of the five patients had been thyrotoxic and two of these had received an iodine load prior to airway compromise. Immediate endotracheal intubation for airway control followed by admission to the intensive care unit had been the presentation in two patients. An incidental diagnosis of tracheal compression had been made from the computed tomography (CT) scan in two patients who had non-resolved obstructive airway disease. Emergency thyroidectomy had been performed in all five patients. Significant tracheomalacia had been noted in four patients. Following thyroidectomy, two patients had required tracheostomy and one had required tracheal stenting.

Conclusion: Chronic obstructive airways disease, substernal extension and long-standing goitre are considered as risk factors for developing acute, life-threatening airway compromise in the presence of benign thyroid disease. A recent iodine load may lead to airway compromise in thyrotoxic patients. A CT scan is indicated in cases of unresponsive chronic obstructive airways disease to rule out substernal extension of non-palpable goitres. Life-threatening airway compromise secondary to benign goitres is best treated by endotracheal intubation if conservative measures fail, followed by emergency thyroidectomy. Following surgery, close observation is mandatory to exclude airway compromise due to tracheomalacia and laryngeal oedema.
Multiple laryngeal foreign bodies composed of dried fish vertebral bones: a case report
Authors: Nakahira M , Yamakawa K , Ikenaga H , Takeuchi S
Published: September 2006

We present a rare case of tracheostomy for removal of laryngeal foreign bodies consisting of three connected fish vertebral bones in a 15-month-old girl. Recent endoscopic techniques have made it possible to extract nearly all tracheobronchial foreign bodies with rigid bronchoscopes. However, the three connected foreign bodies in this report could not be extracted entirely by single endoscopy because the glottis as an exit was narrow due to severe oedema. Accordingly, tracheostomy was required to assist ventilation, prevent prolonged post-operative endotracheal intubation, remove the secondary tracheal foreign bodies and to provide a conduit for the introduction of a bronchoscope.

This suggests that tracheostomy should be considered to avoid the potential dangers of severe laryngeal oedema and to secure the route for removal of foreign bodies from the trachea when treating patients with multiple laryngeal foreign bodies and laryngeal oedema.
Computer-assisted surgery of the paranasal sinuses: technical and clinical experience with 368 patients, using the Vector Vision Compact® system
Authors: Stelter K , Andratschke M , Leunig A , Hagedorn H
Published: September 2006

Introduction: This paper presents our experience with a navigation system for functional endoscopic sinus surgery. In this study, we took particular note of the surgical indications and risks and the measurement precision and preparation time required, and we present one brief case report as an example.

Materials and methods: Between 2000 and 2004, we performed functional endoscopic sinus surgery on 368 patients at the Ludwig Maximilians University, Munich, Germany. We used the Vector Vision Compact® system (BrainLAB) with laser registration. The indications for surgery ranged from severe nasal polyps and chronic sinusitis to malignant tumours of the paranasal sinuses and skull base.

Results: The time needed for data preparation was less than five minutes. The time required for preparation and patient registration depended on the method used and the experience of the user. In the later cases, it took 11 minutes on average, using Z-Touch® registration. The clinical plausibility test produced an average deviation of 1.3 mm. The complications of system use comprised one intra-operative re-registration (18 per cent) and one complete failure (5 per cent). Despite the assistance of an accurate working computer, the anterior ethmoidal artery was incised in one case. However, in all 368 cases, we experienced no cerebrospinal fluid leaks, optic nerve lesions, retrobulbar haematomas or intracerebral bleeding. There were no deaths.

Discussion: From our experience with computer-guided surgical procedures, we conclude that computer-guided navigational systems are so accurate that the risk of misleading the surgeon is minimal. In the future, their use in certain specialized procedures will be not only sensible but mandatory. We recommend their use not only in difficult surgical situations but also in routine procedures and for surgical training.
Ice cold carbonated water: a therapy for persistent hyperawareness of pharyngeal mucus and throat clearing
Authors: Acharya A N , Mirza S , Jones N S
Published: September 2006

Chronic throat clearing or a feeling of ‘something’ at the back of the oropharynx or nasopharynx is a common cause for referral to otorhinolaryngology services. While treatment of an underlying causative condition might be expected to improve these symptoms, in many cases a clear underlying cause is not found. Currently, there is no recognized treatment which is effective against these troublesome symptoms. This observational study investigated the effectiveness of a regime of sipping ice cold carbonated water to try to break the vicious cycle of throat clearing. Seventy-two patients with these symptoms who had previously been advised to use the regime were contacted with a postal questionnaire. Sixty-three per cent of patients documented an improvement in their symptom severity score. The most severely and most frequently affected patients had the greatest benefit. We conclude that the suggested regime can be effective in breaking the vicious cycle of persistent throat-clearing.
Predictive role of Carhart's notch in pre-operative assessment for middle-ear surgery
Authors: Yasan H
Published: September 2006

Objectives: To evaluate the predictive role of the audiometric Carhart's notch for the assessment of middle-ear pathology prior to surgical intervention.

Method: In this retrospective analysis, a total of 315 operated ears of 305 patients were evaluated regarding their pre-operative pure tone audiograms and peri-operative findings. The probable relationship between the middle-ear pathologies found and the Carhart's notch found on pre-operative pure tone audiometry was investigated. Patients with conductive hearing loss who obtained at least a 10 dB improvement (at 1 and 2 kHz frequencies) in their bone conduction threshold post-operatively were included in the Carhart's notch group. The pathologies underlying Carhart's notch were compared.

Results: Three hundred and fifteen ears of 305 consecutive patients with conductive hearing loss were operated on due to middle-ear pathology. In patients with otosclerosis and tympanosclerosis, a Carhart's notch was seen at 2 kHz in 28 (93 per cent) patients but at 1 kHz in only two (7 per cent). However, in patients with chronic otitis media, a Carhart's notch was seen at 1 kHz in 10 (55 per cent) patients and at 2 kHz in eight (45 per cent) patients.

Conclusions: Otitis media with effusion, tympanosclerosis and congenital malformations should be considered in the differential diagnosis of a patient with a Carhart's notch seen on pure tone audiometry. A Carhart's notch at 2 kHz indicates stapes footplate fixation, whereas one at 1 kHz indicates a mobile stapes footplate; the footplate mobility can thus be predicted pre-operatively.
Magnetic resonance imaging scans for vestibulocochlear nerve tumours: what is actually found?
Authors: Chisholm E J , Savy L , Geyer M , Choa D
Published: September 2006

Background: Approximately 20 per cent of adult patients presenting to otolaryngology clinics have symptoms pertaining to the inner ear. These are investigated with magnetic resonance imaging (MRI) internal auditory meatus scans. This study analysed all findings from 736 sequential MRI internal auditory meatus scans performed on 731 patients over a one year period.

Methods: Six hundred and seventy-two patients were included for analysis. Of these, 419 (62.35 per cent) had normal MRI scans, 221 (32.90 per cent) had MRI findings thought to be unrelated to their presenting symptoms, 32 (4.76 per cent) had findings thought to be the cause of their symptoms, and eight (1.19 per cent) had the typical appearance of an VIIIth nerve schwannoma.

Conclusions: Magnetic resonance image scanning of the inner ears and auditory pathways yields a diagnosis of VIIIth nerve tumours of the order of 1 per cent, does not show other causes of inner-ear symptoms in a further 4 per cent, and shows incidental intra- and extracranial abnormalities in a further 33 per cent, most of which are not clinically significant.
BIRTH WEIGHT AND ADULTHOOD DISEASE AND THE CONTROVERSIES
Authors: PHILLIPS DIW
Published: September 2006

A large number of studies show that low birth weight is associated with cardiovascular disease and its risk factors including raised blood pressure, glucose intolerance and the metabolic syndrome. These findings have formed the basis for the ‘fetal origins hypothesis’. This suggests that the operation of adverse influences during intrauterine life leads to permanent alterations in fetal structure and physiology which predispose to adult disease. The process is known as developmental plasticity or programming and is strongly supported by studies in experimental animals. Ongoing research is providing important insights in to the underlying mechanisms. It is likely that adverse environmental factors during pregnancy are important, and that these include suboptimal nutrition of the mother. The long-term programming effects may be transduced by alterations in the set-point of key hormonal axes, especially the hypothalamic-pituitary-adrenal axis, and recent evidence suggests that epigenetic modification of gene expression may be a key factor. Importantly, this has the potential to produce transgenerational effects.

The hypothesis has not remained unchallenged and a wide variety of criticisms have been put forward. These include accusations that the associations are weak and overestimated due to publication bias, that there are many inconsistencies between studies, that the associations are confounded by lifestyle factors, and that there has been inappropriate adjustment for adult size. Finally many studies report that the findings in singletons do not seem to be replicated in twins. While many of these issues have been resolved, some continue to form the basis of a lively dialogue and ongoing research. Nevertheless the research findings have important implications for clinical obstetric practice and maternal-fetal medicine.
STRUCTURED TEAM TRAINING IN OBSTETRICS AND ITS IMPACT ON OUTCOME
Authors: DRAYCOTT T , CROFTS J
Published: September 2006

Obstetric caregivers must deal with a wide range of emergencies, some of which are quite uncommon, and many believe they have achieved a high level of expertise based on study rather than experience. Yet a growing body of work demonstrates that simulation training can sharpen the skills of all caregivers and promote the development of efficient teams capable of reducing the morbidity of these rare events. This paper outlines current recommendations for emergency and teamwork training in obstetrics and reviews different training methods and their effectiveness.
Therapeutic mammotome excisions: papillary lesions
Authors: Philpotts Liane
Published: September 2006

Papillary lesions of the breast are fairly common on imaging-guided breast biopsy, and the management remains controversial. Due to the heterogeneity of histological findings, papilloma can be a challenge to the pathologist when interpreting core biopsy specimens, so some may desire the entire lesion to be removed to be confident of the diagnosis of a benign papilloma. In appropriate cases, an attempt at removal with vacuum-assisted biopsy appears a reasonable approach with the hopes of establishing a diagnosis, relieving symptoms of nipple discharge, and avoiding the cost and morbidity of surgical intervention. The management of lesions with atypia on mammotome excision will remain controversial and the prudent approach is to recommend complete surgical excision.
Three‐dimensional density model of the Nazca plate and the Andean continental margin
Authors: Tassara Andrés , Götze Hans‐Jürgen , Schmidt Sabine , Hackney Ron
Published: September 2006

We forward modeled the Bouguer anomaly in a region encompassing the Pacific Ocean (85°W) and the Andean margin (60°W) between northern Peru (5°S) and Patagonia (45°S). The three‐dimensional density model that reproduces the gravity field is a continental‐scale representation of density structure to 410 km depth that characterizes the mantle and crust of the oceanic Nazca plate, subducted slab and continental margin with a minimum number of bodies. We predefined the density of each body after studying the dependency of density on composition of crustal and mantle materials and pressure‐temperature conditions appropriate for the Andean setting. A database of independent geophysical information constrains the geometry of the top of the subducted slab, locally the Moho of the oceanic and continental crusts and, indirectly, the lithosphere‐asthenosphere boundary underneath the continental plate. Other boundaries, notably the intracrustal density discontinuity separating upper from lower crust below the continent, were not constrained and their geometry is the result of fitting the observed and calculated Bouguer anomaly during forward modeling. This contribution presents the model to the Andean geoscientific community and contains some tools, like a sensitivity analysis, that helps potential users of the model to interpret its results. We describe and discuss some of these results in order to illustrate the application of the model to the study of a wide range of phenomena (e.g., modification of oceanic plate structure by hot spots, shape of the subducted slab, thermal structure of the continental lithosphere, compensation mechanism and formation of orogenic relieve, causes of Andean segmentation).
On the steric and mass‐induced contributions to the annual sea level variations in the Mediterranean Sea
Authors: García David , Chao Benjamin F. , Del Río Jorge , Vigo Isabel , García‐Lafuente Jesús
Published: September 2006

The sea level variation (SLVtotal) is the sum of two major contributions: steric and mass‐induced. The steric SLVsteric is that resulting from the thermal and salinity changes in a given water column. It only involves volume change, hence has no gravitational effect. The mass‐induced SLVmass, on the other hand, arises from adding or subtracting water mass to or from the water column and has direct gravitational signature. We examine the closure of the seasonal SLV budget and estimate the relative importance of the two contributions in the Mediterranean Sea as a function of time. We use ocean altimetry data (from TOPEX/Poseidon, Jason 1, ERS, and ENVISAT missions) to estimate SLVtotal, temperature, and salinity data (from the Estimating the Circulation and Climate of the Ocean ocean model) to estimate SLVsteric, and time variable gravity data (from Gravity Recovery and Climate Experiment (GRACE) Project, April 2002 to July 2004) to estimate SLVmass. We find that the annual cycle of SLVtotal in the Mediterranean is mainly driven by SLVsteric but moderately offset by SLVmass. The agreement between the seasonal SLVmass estimations from SLVtotal – SLVsteric and from GRACE is quite remarkable; the annual cycle reaches the maximum value in mid‐February, almost half a cycle later than SLVtotal or SLVsteric, which peak by mid‐October and mid‐September, respectively. Thus, when sea level is rising (falling), the Mediterranean Sea is actually losing (gaining) mass. Furthermore, as SLVmass is balanced by vertical (precipitation minus evaporation, P–E) and horizontal (exchange of water with the Atlantic, Black Sea, and river runoff) mass fluxes, we compared it with the P–E determined from meteorological data to estimate the annual cycle of the horizontal flux.
Río de la Plata estuary response to wind variability in synoptic to intraseasonal scales: Barotropic response
Authors: Simionato C. G. , Meccia V. L. , Dragani W. C. , Guerrero R. , Nuñez M.
Published: September 2006

The first long‐period acoustic Doppler current profiler series collected in two locations of the Río de la Plata estuary are explored for barotropic current variability and its connection to wind variability in synoptic to intraseasonal timescales. Wind‐driven currents can be explained in terms of two modes, resulting of the estuary's geometry. The first one prevails for winds with a cross‐river component, whereas the second dominates when they blow along the estuary axis. Even though both modes imply that barotropic currents develop in a phase lag with the wind that depends on the location, northeasterly and southwesterly winds generate stronger currents than southeasterly and northwesterly winds. Barotropic response to winds occurs in around 6 hours, and an equilibrium regime is reached for processes with temporal scales more than 4 days. The temporal scales of estuarine variability replicate the wind ones, with activity in bands around 2–8, 10–12, and 18–25 days. Therefore the estuary reaches an equilibrium regime with most of atmospheric processes from synoptic to intraseasonal scales. Intraseasonal variability can be significant and even act in the same direction as the synoptic one, with important effects on circulation. These features imply that the estuary has “weather” and “climate” as the atmosphere does. Our results suggest that conditions classically thought as characteristic of “summer” or “winter” likely occur during any season with high variability. This result has important implications for those coastal species that spawn in the estuary, as they require specific conditions for their successful reproduction, and on estuary's predictability.
Vertical distribution of wave shear stress in variable water depth: Theory and field observations
Authors: Zou Qingping , Bowen Anthony J. , Hay Alex E.
Published: September 2006

A generalized analytical model is developed to describe the vertical distribution of wave‐induced shear stress in the presence of bottom slope, bottom friction and depth‐induced wave breaking in the shoaling region and surf zone. The theory is compared to data obtained on an unbarred beach in 3.7‐m mean water depth over a 2° bottom slope. Bottom slope and bottom friction are incorporated in the theory by including the wave energy dissipation by bottom friction in a potential wave theory for variable water depth, and coupling the wave theory with a wave bottom boundary layer (WBBL) theory over a sloping bottom. The effect of wave breaking is included through a periodic bore dissipation model. Previous studies have considered some, but not all, of these effects. Each of the three components, sloping bottom, bottom friction and wave breaking, exhibits a different vertical structure. The contributions due to bottom slope and bottom friction attain maximum strength in the WBBL, and decay with distance above the bed, approaching smaller but nonzero values at the surface. In contrast, the contribution from wave breaking is maximal at the surface, and decays linearly with depth, becoming zero at the bed. The vertical structure of the cross‐shore (u) and vertical (w) components of wave orbital velocity was measured using a coherent Doppler acoustic profiler. The measured velocity fields were used to obtain the ensemble averaged wave shear stress profiles that extend across the WBBL to a height of 30 cm above the bed. Close to the seabed, the observed and predicted 〈uw〉 profiles are similar, confirming the sensitivity of wave stress to frictional and bottom slope effects within the WBBL. Farther from the bed, however, the observed profiles fall off more rapidly with height, as w approaches quadrature with u faster than predicted. Wave breaking induced shear stresses were not observed.
Multiscale modeling of air pollutants dynamics in the northwestern Mediterranean basin during a typical summertime episode
Authors: Jiménez Pedro , Lelieveld Jos , Baldasano José M.
Published: September 2006

The complex behavior of photochemical pollutants in the northwestern Mediterranean basin (NWMB) is conditioned by the superposition of circulations of different scale and the pattern of emissions. Therefore a new approach to the modeling of air quality in the NWMB has been adopted by combining the global climate‐chemistry model ECHAM5/MESSy and the regional modeling system MM5‐EMICAT2000‐CMAQ to analyze the high levels of photochemical air pollution during a typical summertime episode. We show that this combination of models is well suited to address the range of scales involved. The complexity of the area requires the application of high spatial and temporal resolution (2 km and 1 hour) modeling to cover local to regional interactions. We address the local and large‐scale processes controlling tropospheric ozone in the NWMB, notably emissions and photochemistry, convective and advective transport, deposition processes, and stratosphere‐troposphere exchange. The simulation results indicate that the ozone buildup largely results from local photochemical production, which strongly exceeds the removal rates through transport and deposition. The contribution by advective transport is limited, associated with the stagnant meteorological conditions. In the lower troposphere, local recirculation systems are of key importance. The strength of the land‐sea breeze circulation and thermally or mechanically driven convection over the complex orography of the eastern Iberian coast can induce vertical transport and the layering of air pollution.
Oxygen and sulfur isotopic composition of volcanic sulfate aerosol at the point of emission
Authors: Mather T. A. , McCabe J. R. , Rai V. K. , Thiemens M. H. , Pyle D. M. , Heaton T. H. E. , Sloane H. J. , Fern G. R.
Published: September 2006

Volcanic sulfate aerosol is emitted from the vents of many active volcanoes, but its origin has not yet been explained. We report the first measurements of the isotopic compositions of near‐vent volcanic aerosol sulfate and use the combined sulfur and oxygen isotope systematics of the aerosol and magma at Masaya volcano, Nicaragua, to draw preliminary conclusions about the production mechanism of near‐source volcanic sulfate. The sulfate aerosol does not display a significant mass‐independent oxygen or sulfur isotopic signature, which suggests that primary volcanic aerosol does not contribute to the larger mass‐independent anomalies found in some ambient atmospheric aerosols and as preserved in ice cores. The oxygen isotope composition of the sulfate appeared to become heavier on the particle filters with increasing amount of sample collected and suggests that the δ18O value of the sulfate aerosol is <8‰. The sulfur isotopic composition of the sulfate did not vary with sample loading on the filters and had a mean δ34S value of 7.7 ± 0.8‰, similar to that of the magma (6.6 ± 0.2‰). The low Δ17O value, the δ18O value of the magma (6.6 ± 0.3‰) and the high δ18O value of atmospheric oxygen (23.5‰) suggest that known atmospheric oxidation pathways at ambient temperatures are not the major routes of production for this sulfate. Instead, the isotopic systematics of aerosol and magma are consistent with sulfate production either by high‐temperature equilibration of the magmatic gas mixture with small amounts of atmospheric oxygen or by direct emission of SO42− from the magma.
Study on acidity and acidic buffering capacity of particulate matter over Chinese eastern coastal areas in spring
Authors: Wang Wei , Liu Hongjie , Yue Xin , Li Hong , Chen Jianhua , Ren Lihong , Tang Dagang , Hatakeyama Shiro , Takami Akinori
Published: September 2006

The analytical results of the acidity and buffering capacity of particulate matter sampled by aircraft over Chinese eastern coastal areas in March and early April 2002 are presented. The flight region covered the coastal areas from Zhuhai, Guangdong province, to Dalian, Liaoning province, and the northeastern coastal areas around Dalian, Liaoning province, with the later being the key flight areas. The results show that total suspended particles (TSP) generally appear to be acidic, having no buffering capacity for acidification; the acidity of TSP in northern areas is lower than that in southern areas, whereas the acidity of TSP in the bordering region of the northern areas and the southern areas is relatively high, the discrimination of the acidity of TSP in different areas could be up to more than 100 times. The acidity of particulate matter increases as its diameter decreases, indicating that fine particles have strong acidity. Both in northern areas and in southern areas, particulate matter with diameters larger than 11 μm has acidic buffering capacity, but particulate matter with diameters smaller than 2.1 μm appears to be acidic, having no buffering capacity. Although the pollution level of particulate matter at high altitudes is lower, its acidification is stronger than that at ground level. The regional acidification of particulate matter at high altitudes is an important reason why some areas in China suffer acidic precipitation.
Polar stratospheric clouds in the 1998–2003 Antarctic vortex: Microphysical modeling and Polar Ozone and Aerosol Measurement (POAM) III observations
Authors: Benson C. M. , Drdla K. , Nedoluha G. E. , Shettle E. P. , Alfred J. , Hoppel K. W.
Published: September 2006

The Integrated Microphysics and Aerosol Chemistry on Trajectories (IMPACT) model is used to study polar stratospheric cloud (PSC) formation and evolution in the Antarctic vortex. The model is applied to individual air parcel trajectories driven by UK Met Office (UKMO) wind and temperature fields. The IMPACT model calculates the parcel microphysics, including the formation and sedimentation of ice, nitric acid trihydrate (NAT), sulfuric acid tetrahydrate (SAT), and supercooled ternary solution (STS) aerosols. Model results are validated by comparison with data obtained by the Polar Ozone and Aerosol Measurement (POAM) III solar occultation instrument and are examined for 6 years of POAM data (1998–2003). Comparisons of POAM water vapor and aerosol extinction measurements to the model results help to constrain three microphysical parameters influencing the formation and growth of both type I and type II PSCs. Principally, measurements of aerosol extinction prove to be valuable in differentiating model runs; the relationship of aerosol extinction to temperature is determined by the various particle types as they form and grow. Comparison of IMPACT calculations of this relationship to POAM measurements suggests that the initial fraction of nuclei available for heterogeneous NAT freezing is approximately 0.02% of all aerosols. Constraints are also placed on the accommodation coefficient of ice and the NAT‐ice lattice compatibility. However, these two parameters have similar effects on the extinction‐temperature relationship, and thus a range of values are permissible for each.
Dynamics of metal‐silicate separation in a terrestrial magma ocean
Authors: Höink Tobias , Schmalzl Jörg , Hansen Ulrich
Published: September 2006

In a terrestrial magma ocean, the metal‐silicate separation involved small metal droplets. Our goal is to better understand the dynamics of the metal droplet scenario. The mechanism of sedimentation in a vigorously convecting and strongly rotating magma ocean may differ significantly from settling droplets in a still fluid. In order to systematically study the parameter dependence on the style of motion we utilize two‐dimensional and three‐dimensional numerical convection models combined with a tracer‐based sedimentation method. We investigate the characteristic flow patterns resulting from the competing effects of convection and droplet settling and find three styles of motion: a temperature‐dominated style where most droplets remain suspended, a droplet‐dominated style where the droplets separate from the fluid, and a style of repetitive motion. We find that the droplet‐dominated style is relevant to the magma ocean. In this scenario the droplets settle and form a dense bottom layer. One of the key findings of this work is that the formation of the dense bottom layer, and therefore the separation of metal droplets from the liquid silicate, occurs on a characteristic timescale, which is identical with the Stokes' settling time. Finally, we study the chemical interaction of settling metal droplets and liquid silicate and discuss how accurately a simple parameterized model can describe the chemical equilibration in the metal‐rain scenario of a terrestrial magma ocean. We find agreement between the parameterized model and our two‐dimensional model. Our simulations, which include thermal convection into the metal‐rain model, confirm the fundamental observation that metal droplets are not permanently suspended in the convecting silicate melt, but that they sink and rapidly form a dense layer at the base of the magma ocean.
Limitations in correlation of regional relative geomagnetic paleointensity
Authors: McMillan D. G. , Constable C. G.
Published: September 2006

Time domain correlations of common features among relative paleointensity records from sedimentary cores are invaluable to paleomagnetism and paleoclimatology. Sediments with high accumulation rates might now provide millennial scale correlations of temporal variations in the geomagnetic dipole moment. Errors in the ages of paleomagnetic data samples, however, can make such correlations difficult and unreliable. We use spectral methods to assess the level of coherence expected among individual and stacked high‐resolution simulated paleointensity records for the time interval 0–75 ka. Correlations between individual paleointensity records are systematically degraded with decreased sedimentation rate and increased magnitude of age errors. We find that with optimistic age errors and interpolation of depth sampled data to evenly spaced time series, only short period signal in high‐resolution relative paleointensity is corrupted. For currently available methods of establishing chronologies, we estimate the minimum characteristic timescale of correlative features between pairs of regional stacked records at about 4.5 kyr. From an analysis of NAPIS‐75 and SAPIS data, it appears that the limit is inherent to the regional stacks and not a consequence of comparison of distant, independent data sets. A detailed comparison of the NAPIS‐75 and SAPIS stacks shows that this limit is likely larger, perhaps 6 kyr. At long periods the two regional stacks are more poorly correlated than those from our simulations, suggesting somewhat larger age errors in the individual paleointensity records.
Role of wind stress and heat fluxes in interannual‐to‐decadal variability of air‐sea CO2 and O2 fluxes in the North Atlantic
Authors: Friedrich T. , Oschlies A. , Eden C.
Published: September 2006

A coupled ecosystem‐circulation model of the North Atlantic is used to examine the individual contributions by wind stress and surface heat fluxes to naturally driven interannual‐to‐decadal variability of air‐sea fluxes of CO2 and O2 during 1948–2002. The model results indicate that variations in O2 fluxes are mainly driven by variations in surface heat fluxes in the extratropics (15°N to 70°N), and by wind stress in the tropics (10°S to 15°N). Conversely, variations in simulated CO2 fluxes are predominantly wind‐stress driven over the entire model domain (18°S to 70°N); while variability in piston velocity and surface heat fluxes is less important. The simulated uptake of O2 by the North Atlantic amounts to 70 ± 11 Tmol yr−1 to which the subpolar region (45°N to 70°N) contributes by 62 ± 10 Tmol yr−1. Whereas the subpolar North Atlantic takes up more than 2/3 of the total carbon absorbed by the North Atlantic in our model (about 0.3 Pg C yr−1), interannual variability of air‐sea CO2 fluxes reaches similar values (about 0.01 Pg C yr−1 each) in the subpolar (45°N to 70°N), the subtropical (15°N to 45°N) and the equatorial (10°S to 15°N) Atlantic.
Changing trends in the tropical Indian Ocean SST during La Niña years
Authors: Chowdary J. S. , Gnanaseelan C. , Vaid B. H. , Salvekar P. S.
Published: September 2006

The Tropical Indian Ocean (TIO) was characterized by anomalous sea surface cooling during the La Niña years (winter season) before 1976. Analysis of Hadley center Ice Sea Surface Temperature (HadISST) showed that the cooling (SST anomalies < −0.1°C) started during the boreal summer over most of the TIO (69% area) in the La Niña composites of 1958–1976, and which enhanced by the following winter, resulting in basin‐wide cooling (98%). The upwelling biennial Rossby wave propagation from the east to the western Indian Ocean enhanced the cooling during boreal summer to the following winter. However, the La Niña composites of 1976–2001 showed strong warming over the TIO in boreal summer, which even though weakened in the following winter, did not cause any basin‐wide cooling. The variability in the latent heat flux anomalies after 1976 was found to be consistent with the SST anomalies.
Pore network geometry in low permeability argillites from magnetic fabric data and oriented mercury injections
Authors: Esteban Lionel , Géraud Yves , Bouchez Jean Luc
Published: September 2006

The relationship between mineral fabric and pore network geometry anisotropy is studied for representative clay‐rich lithologies from the Callovo‐Oxfordian formation of the Andra Laboratory (Paris Basin, France), sampled from the oblique borehole‐core #EST211. Comparisons between standard magnetic fabric measurements (AMS) that give the mineral fabric, high pressure mercury injections parallel to the AMS axes, that reflect the pore structure parameter and AMS measurement after impregnation with a ferrofluid at different pressures, giving the shape of the pore networks, allow us to propose three pore models. (1) In the silt‐enriched specimens the transfer pathway is found to be controlled by vertical pathways. (2) In the carbonate‐enriched specimens the best transfer pathway is parallel to bedding, and in this plane is almost isotropic in spite of an anisotropic pore structure. (3) In the clay‐enriched specimens, at the site of the Andra Laboratory, the transfer pathway is also parallel to bedding and ∼20% higher parallel to both the magnetic lineation and the pore shape preferred orientation.
Source location of the 26 sec microseism from cross‐correlations of ambient seismic noise
Authors: Shapiro N. M. , Ritzwoller M. H. , Bensen G. D.
Published: September 2006

Very strong, narrow band Rayleigh wave arrivals peaking near 26 sec are observed in cross‐correlations of long time sequences of ambient noise records on US, European, and African stations with apparent arrival times that are typically smaller than expected for propagation along the great‐circle linking the stations. Use of these apparent travel times to locate the source of narrow band arrivals shows that the waves originate off the west African coast in the Gulf of Guinea and propagate with an average speed of about 3.5 km/s; i.e., close to the expected group speed of Rayleigh waves at this period. Using data from different months demonstrate that the source location is temporally stable with amplitudes that maximize during the southern hemisphere winter. A microseism with similar features but with a slightly broader spectral peak is observed at stations in East Asia and in the western Pacific, and apparently originates in the North Fiji Basin. The nearly antipodal location of the two source regions leads to the hypothesis that the 26 sec signals are excited by a single source located in the Gulf of Guinea. The Pacific inter‐station cross‐correlations may be for major‐arc propagation.
Large increase in heavy rainfall associated with tropical cyclone landfalls in Korea after the late 1970s
Authors: Kim Joo‐Hong , Ho Chang‐Hoi , Lee Min‐Hee , Jeong Jee‐Hoon , Chen Deliang
Published: September 2006

This study presents a new demonstration of the abrupt increase in the heavy rainfall events (≥100 mm day−1) during August–September in Korea around the late 1970s. The accumulated heavy rainfall averaged for the two months over 12 stations was 57 mm during 1954–77 (ID1); however, it changed to 103 mm during 1978–2005 (ID2). This change is found to be associated with landfalling tropical cyclones (TCs). The most plausible mechanism that accounts for the TC–heavy rainfall relationship is an enhanced TC–upper‐tropospheric trough (UTT) interaction, which results from a southward shift of the upper‐tropospheric jet in East Asia during ID2. While the intensity and duration of the landfalling TCs in Korea does not appear to exhibit such an interdecadal change based on the data available, the enhanced TC–UTT interaction increases the upper(lower)‐tropospheric divergence (convergence) and coherent ascending motion, which strengthen the frontal zone around Korea.
Role of vertical ion convection in the high‐latitude ionospheric plasma distribution
Authors: Deng Y. , Ridley A. J.
Published: September 2006

We use the Global Ionosphere‐Thermosphere Model (GITM) to simulate the ionospheric reaction to a simple step change of the high‐latitude forcing terms during the first hour of electric field enhancement. In response to the enhanced convection electric field, both the convection velocity and Joule heating increase dramatically. The changes in NmF2 present that the tongue extends across the polar cap and the troughs stretch longitudinally. The calculated total electron content (TEC) can vary by 15 TECU and have a similar pattern to the changes of NmF2. The changes in the vertical ion drift can be upward 100 m/s on the dayside and downward 100 m/s on the nightside as a consequence of the changes in the E × B drift. Approximately, hmF2 ascends where ViR is upward and descends where ViR is downward. In general, the response of the ionosphere to the enhanced E‐field is that the F2 layer moves upward on the dayside and enhances at all altitudes on the nightside. Below the F2 peak (250 km altitude), the region of decreasing electron density coincides with the upward ViR on the dayside, and the reverse is true on the nightside. Above the F2 peak (450 km altitude), the features related with both horizontal convection and vertical advection are present. The vertical ion drift sets up a vertical circulation in the noon‐midnight meridional plane during the early stage of E‐field enhancement in addition to the widely accepted horizontal two cell convection. According to the circulation, the significant sources of tongue ionization are not only the plasma from the lower latitudes, but also from the low altitudes on the dayside. While the vertical circulation is not well organized after 6‐hour E‐field enhancement, the contribution of vertical ion convection is still significant. Although the vertical E × B drift in Apex coordinates is more complex and variable than that in a simple dipole magnetic field, the main characteristics are the same, which indicate the significance of the vertical circulation for the electron density distribution in reality during the early stage of E‐field enhancement. The Joule heating drives upwelling of the atmosphere and modifies the O/N2 ratio. Meanwhile, the enhanced neutral advection twists the O/N2 ratio pattern a little bit. However, the changes in the O/N2 ratio have relatively poor correlation with the variation of electron density during the first hour of E‐field enhanced time.
Characteristics of field‐aligned density depletion irregularities in the auroral ionosphere that duct Z‐ and X‐mode waves
Authors: James H. G.
Published: September 2006

The small‐scale and two‐point nature of the Observations of Electric‐field Distributions in the Ionospheric Plasma—A Unique Strategy C (OEDIPUS‐C, OC) dual‐payload propagation experiment in the auroral ionosphere in 1995 has permitted improved measurements of the parameters of magnetic field‐aligned density irregularities. Comparatively strong and dispersed pulses were observed at frequencies f just above the electron plasma frequency fp when the electron gyrofrequency fc was less than fp. The waves are interpreted as quasielectrostatic Z‐mode propagation with dispersion surfaces close to those of the Langmuir solutions in wave vector space, albeit at somewhat lower refractive indices of about 50. If mission length surveys of the Z‐wave intensities are aligned with histories of fp at the payload and of the strength of X‐ and fast Z‐mode ionospheric reflection echoes, a strong positive correlation is found at momentary relative depletions of the ambient density. These observations are taken as evidence of ducting in the field‐aligned depletions. The spectra of these strong Z‐mode transmissions are similar to those of slow Z ducted spectra observed at similar f, fp, and fc values in the OEDIPUS‐A experiment in 1989. The magnitudes of the density depletions are found to lie in the range 7–21% and to have cross‐field dimensions of a few kilometers. The present duct dimensions are of the same order as the previous findings from ionospheric X‐mode electromagnetic echoes on OC, but the depletions are up to 10 times deeper. Measurements of ducting irregularities can lead to insights into their formation. This will be important for our understanding of the interfaces of the ionospheric or magnetospheric topologies where irregularity formation is an important link in the large‐scale flow of energy.
Origins of plasmaspheric hiss
Authors: Meredith Nigel P. , Horne Richard B. , Clilverd Mark A. , Horsfall David , Thorne Richard M. , Anderson Roger R.
Published: September 2006

Plasmaspheric hiss is an electromagnetic wave emission responsible for electron loss from the radiation belts, particularly in the slot region (2 < L < 3). There are two leading theories for the origin of plasmaspheric hiss: in situ amplification of wave turbulence in space and lightning‐generated whistlers. Here we analyze CRRES wave data together with the global distribution of lightning to test both theories. Using the entire CRRES wave database, we split the data into seven frequency bands between 0.1 and 5 kHz and examine the ionospheric mapping of the wave intensities in the slot region as a function of season, magnetospheric location, and magnetic activity. The wave intensities peak in the frequency range 0.2–0.5 kHz and become progressively smaller at higher frequencies. The wave intensities at low frequencies, f < 1 kHz, are independent of lightning flash rate, are stronger on the dayside, and peak during the equinoxes. In contrast, the wave intensities at high frequencies, f > 2 kHz, increase with flash rate, are stronger on the nightside, and peak during the boreal summer. The wave intensities increase with magnetic activity for all frequencies on the dayside but are independent of magnetic activity on the nightside. The data suggest that in situ amplification of wave turbulence in space is the main source of wave power below 1 kHz, whereas wave power above 2 kHz is more related to lightning‐generated whistlers. The results suggest that natural plasma turbulence should dominate the loss of relativistic (approximately MeV) electrons in the slot region 2 < L < 3.
Plate force due to bending at subduction zones
Authors: Buffett Bruce A.
Published: September 2006

Bending of the lithosphere at subduction zones generates stresses that contribute to the force balance on plates. We determine the net horizontal force on subducting plates by imposing a simple kinematic description of strain in the equations that govern the mechanical equilibrium of a thin viscous sheet. The magnitude of the force depends on the velocity, thickness, and curvature of the subducting plate. Using representative values for old oceanic lithosphere, we obtain an effective horizontal force that is nearly 40% of the buoyancy force due to slabs in the upper mantle.
Rates of carbon dioxide plume degassing from Mount Etna volcano
Authors: Aiuppa A. , Federico C. , Giudice G. , Gurrieri S. , Liuzzo M. , Shinohara H. , Favara R. , Valenza M.
Published: September 2006

We report here on the real‐time measurement of CO2 and SO2 concentrations in the near‐vent volcanic gas plume of Mount Etna, acquired by the use of a field portable gas analyzer during a series of periodic field surveys on the volcano's summit. During the investigated period (September 2004 to September 2005), the plume CO2/SO2 ratio ranged from 1.9 to 10.8, with contrasting composition for Northeast and Voragine crater plumes. Scaling the above CO2/SO2 ratios by UV spectroscopy determined SO2 emission rates, we estimate CO2 emission rates from the volcano in the range 0.9–67.5 kt d−1 (average, 9 kt d−1). About 2 kt of CO2 were emitted daily on average during quiescent passive degassing, whereas CO2 emission rates from Etna's summit were 10–40 times larger during the 2004–2005 effusive event (with a cumulative CO2 release of ∼3800 kt during the 6 months of the eruption). Such a syneruptive increase, ascribed to the replenishment of the shallow (<6 km) volcanic plumbing system by CO2‐rich (0.25 wt %) more primitive magmas, supports the potential of CO2 output rates as key parameters for volcanic hazard assessment.
Three subtropical fronts in the North Pacific: Observational evidence for mode water‐induced subsurface frontogenesis
Authors: Kobashi Fumiaki , Mitsudera Humio , Xie Shang‐Ping
Published: September 2006

Subsurface fronts in the subtropical North Pacific were investigated by constructing a high‐resolution temperature climatology. Three distinct subtropical fronts (STFs) are identified, which are the southern, northern and eastern STFs according to their relative geographical locations. The southern STF extends along 19°–21°N west of the dateline, while the northern and eastern STFs appear along 21°–24°N and 26°N in the western and central subtropical gyre, respectively. Our analysis showed that each of these STFs is associated with large negative meridional potential vorticity (PV) gradient in the thermocline below the front. The northern STF is located on the southern edge of the Kuroshio recirculation, where the negative PV gradient occurs within a narrow density range and is maintained by the low PV core of the subtropical mode water (STMW). On the other hand, the negative PV gradient at the eastern and southern STFs spans over a wide density range. The eastern STF forms near the center axis of the subtropical gyre, north of which the upper and lower portions of the central mode water (CMW) converge, forming a thick low PV pool that maintains the negative PV gradient on the front. Similarly, at the southern STF, the negative PV gradient is due to a low PV pool to the north, with the southernmost portion of the STMW stacked above the upper CMW advected from the central subtropical gyre. It is concluded that the mode waters are essential for the North Pacific STFs.