bluuebunny/crossref_metadata_2025 huggingface dataset:
Diurnal changes in volcanic plume chemistry observed by lunar and solar occultation spectroscopy
Authors: Burton M. R. , Oppenheimer C. , Horrocks L. A. , Francis P. W.
Published: February 2004

We report the first spectroscopic measurements of volcanic gas emissions by lunar occultation. The experiment was carried out at Masaya volcano, Nicaragua in 1998 using a portable Fourier transform infrared spectrometer. Both SO2 and HCl column concentrations were determined to yield a SO2/HCl molar ratio of 2.2±0.28 (±1σ). This is significantly greater than the equivalent ratio of 1.6±0.02 (±1σ) derived from solar occultation measurements of the volcanic plume. We propose that the cause of the nocturnal increase in SO2/HCl ratio is dissolution of HCl into volcanic water droplets within the plume. This arises because the low saturated vapour pressure of water by night results in strong condensation of plume water vapour whereas by day only negligible plume water vapour condenses.
Magnetostratigraphy of the Kavaalani section (southwestern Turkey): Consequence for the origin of the Antalya calcareous nappes (Turkey) and for the Norian (Late Triassic) magnetic polarity timescale
Authors: Gallet Yves , Besse Jean , Krystyn Leopold , Marcoux Jean , Guex Jean , Théveniaut Hervé
Published: February 2004

A magnetostratigraphic study of the Kavaalani section of uppermost Carnian to Upper Norian age, located in the Antalya Calcareous Nappes (southwestern Turkey), reveals nineteen polarity intervals. This pattern correlates very well with two other polarity sequences obtained from the same nappe system (Bolücektasi Tepe and Kavur Tepe) if these sections were deposited in the same (northern) hemisphere. This new interpretation changes our previous conclusions regarding the southern hemisphere origin of the magnetic remanence of the Kavur Tepe section. The paleomagnetic data obtained from the Kavur Tepe and the Kavaalani sections therefore reflect large (∼180°) internal rotations within the Antalya nappes. These nappes were likely formed close to the northern tip of the Arabian promontory. We propose a revised yet still preliminary version of the Norian magnetic polarity sequence.
Rapid stress release caused by polymorphic transformation during the experimental deformation of quartz
Authors: Brodie K. H. , Rutter E. H.
Published: February 2004

Cylindrical samples of polycrystalline quartz were fabricated by hot pressing of crushed Brazilian quartz at 1100 and 1200°C, then deformed in extension at 1200°C at a confining pressure of 300 or 350 MPa. After initial plastic yield, samples failed with sudden and total offloading. Samples could be reloaded in compression and deformed plastically to large strains. Microscopic examination showed extensional failure had occurred with the formation of ‘veins’, oriented normal to the extension direction, containing fibers of silica with their length and c crystal axes parallel to the extension direction. From X‐ray and microstructural observations, these are inferred to have formed as mixed tridymite/cristobalite reaction products, now reverted to quartz, accommodating offloading owing to the 38% extensional strain parallel to c. Such rapid transformation and offloading can be compared to processes invoked to explain deep‐focus earthquakes in appropriate rock types, but also to the slower formation of oriented, localized reaction products in crustal shear zones.
The Field‐Dependence of AC Susceptibility in Titanomagnetites: Implications for the Anisotropy of Magnetic Susceptibility
Authors: De Wall Helga
Published: February 2004

In a case study on titanomagnetite‐bearing rocks from the Riedheim dike of (Hegau volcanics, SW‐Germany), samples of varying composition (Curie temperatures of 128 to 440 °C) have been tested for their ac field‐dependence of low‐field susceptibility. The measurements were performed in ac fields of 30 and 300 A/m. In order to quantify the field‐dependency of titanomagnetites, the parameter χHd [%] = [(χ300A/m ‐ χ30A/m) / χ300A/m] × 100 is introduced, which ranges from 4.1 to 26.5. A liear relationship has been determined between the Curie temperature of the titanomagnetites and the log χHd parameter. The anisotropy factor (P′) of the anisotropy of magnetic susceptibility (AMS) ellipsoid is significantly enhanced in the higher ac field, while the shape factor (T) appears to be insensitive to the field amplitude. However, despite these variations, the principal axes of the AMS‐ellipsoids remain unchanged in orientation.
Inner core anisotropy and heterogeneity level
Authors: Garcia Raphaël , Souriau Annie
Published: February 2004

An analysis of core phase travel times is performed in order to estimate the relative contributions of heterogeneities and anisotropy and their distribution inside the inner core. A stochastic analysis performed on the equatorial paths, which are poorly sensitive to anisotropy, indicates that the inner core exhibits a heterogeneity level smaller than 0.3% at all depths on scale lengths larger than 200 km. This result, extended to all path orientations, suggests a predominant effect of the anisotropy on travel times anomalies. A simultaneous inversion of absolute and differential core phase travel times for any path orientation favours a simple inner core model in which a large, homogeneous structure with 3% uniform anisotropy is asymmetrically surrounded by a homogeneous isotropic layer with a thickness of 100–200 km on the western hemisphere, increasing to 400 km over a large part of the eastern hemisphere.
Thermal Enhancement of Magnetic Fabrics in High Grade Gneisses
Authors: Borradaile Graham J. , Lagroix France
Published: February 2004

The orientation‐distributions of AMS and AARM ellipsoids are non‐coaxial in the Kapuskasing Zone granulites. AARM is due to the preferred orientation of magnetite which mostly postdates the silicate fabric. The AMS orientation‐distribution combines susceptibility anisotropies of magnetite and the silicates. Whereas heating does not increase the bulk susceptibility, it does improve the definition of the orientation‐distributions of both AMS and AARM. However, the orientation‐distribution of AARM is most enhanced and therefore post‐heated samples emphasize the magnetite sub fabric. Thus, heating does not clarify the interpretation of the silicate fabric in this study. However, it does change the samples' AMS fabric in such a way as to reveal the magnetite subfabric which can only otherwise be detected by more tedious AARM measurements.
New kinematic models for Pacific‐North America Motion from 3 Ma to Present, II: Evidence for a “Baja California Shear Zone”
Authors: Dixon Timothy , Farina Fred , DeMets Charles , Suarez‐Vidal Francisco , Fletcher John , Marquez‐Azua Bertha , Miller Meghan , Sanchez Osvaldo , Umhoefer Paul
Published: February 2004

We use new models for present‐day Pacific‐North America motion to evaluate the tectonics of offshore regions west of the Californias. Vandenburg in coastal Alta California moves at the Pacific plate velocity within uncertainties (∼1 mm/yr) after correcting for strain accumulation on the San Andreas and San Gregorio‐Hosgri faults with a model that includes a viscoelastic lower crust. Modeled and measured velocities at coastal sites in Baja California south of the Agua Blanca fault, a region that most previous models consider Pacific plate, differ by 3–8 mm/yr, with coastal sites moving slower that the Pacific plate. We interpret these discrepancies in terms of strain accumulation on known on‐shore faults, combined with right lateral slip at a rate of 3–4 mm/yr on additional faults offshore peninsular Baja California in the Pacific. Offshore seismicity, offset Quaternary features along the west coast of Baja California, and a discrepancy between the magnetically determined spreading rate in the Gulf Rise and the total plate rate from a geological model provide independent evidence for a “Baja California shear zone.”
Crustal shortening in the Andes: Why do GPS rates differ from geological rates?
Authors: Liu Mian , Yang Youqing , Stein Seth , Zhu Yuanqing , Engeln Joe
Published: February 2004

GPS data indicate 30–40 mm yr−1 present‐day crustal shortening across the Andes, whereas geological evidence shows crustal shortening concentrated in the sub‐Andean thrust belt at a much lower rate (<15 mm yr−1). We reconcile the discrepancy between the geodetic and the geological crustal shortening using geodynamic modeling that includes timescale‐dependent crustal deformation. The GPS velocities reflect the instantaneous deformation in the Andes that includes both permanent deformation and elastic deformation that will be recovered during future earthquakes, whereas the lower geological rates reflect only the permanent deformation. The three‐dimensional viscoelastic model predicts nearly uniform short‐term velocity gradients across the Andes, similar to the GPS results, and concentrated long‐term crustal shortening in the sub‐Andean thrust zone, consistent with geological observations.
Pressure gradient measurements in volcanic diffuse gas emanations
Authors: Natale Giuseppe , Hernández Pedro , Mori Toshiya , Notsu Kenji
Published: February 2004

We describe a differential pressure measurement device which allows one to estimate fluid pressure gradients ranging from 6.3 × 10−6 to 3.15 × 10−3 atm/m in soil diffuse volcanic gas emanations. The lower limit roughly corresponds to the atmospheric (static) pressure gradient due to gravity, and should represent the minimum required value for volcanic gases to reach the Earth's surface by viscous flow. In the study of diffuse gas emanations, such as for the purpose of volcanic surveillance, such physical data supplements the geochemical monitoring of concentrations and fluxes of specific substances constituting the flowing gaseous mixture and may be used to infer volcanic mechanical states. We describe laboratory experiments with the device and report on a successful preliminary test with diffuse gas emanations on the Miharayama cone of the Izu‐Oshima volcano (Japan), where the highest fluid pressure gradients have been found to be associated with the highest CO2 fluxes and lowest CO2 concentration gradients.
Crystallization heat of impure amorphous H2O ice
Authors: Kouchi Akira , Sirono Sin‐iti
Published: February 2004

We report new results of Differential Thermal Analysis (DTA) of crystallization of impure amorphous H2O ice (a‐H2O), containing CO, CO2 and CH4 molecules. It is revealed that the heat of crystallization of impure a‐H2O is reduced by the impurities. The crystallization is not exothermic like pure a‐H2O, but endothermic when the concentration of impurities is higher than 2% regardless of molecular species. An out‐gassing rate from a model cometary nucleus is computed numerically using the experimental values. The result shows that the runaway crystallization of cometary ice never occurs and that the mechanism of outbursts should be reexamined.
An appraisal of NCEP/NCAR reanalysis MSLP data viability for climate studies in the South Pacific
Authors: Marshall Gareth J. , Harangozo Stephen A.
Published: February 2004

Fifty years of monthly mean sea level pressure (MSLP) data from the NCEP/NCAR reanalysis (hereinafter NNR) are validated against station observations in the extratropical South Pacific and West Antarctica. The period for which the NNR may be considered reliable differs markedly between regions. It is only realistic from ∼1970 across West Antarctica. A lack of surface observations entering the model causes the NNR to be poorly constrained prior to the availability of GTS‐based data in 1967: the latter coincides with a significant improvement in the NNR MSLP across the eastern South Pacific. Substantial spurious negative trends occur within the NNR MSLP at high latitudes; although the decrease is greatest prior to the advent of satellite sounder data it continues into the 1990s south of 60°S. In addition, widely used tropical and extra‐tropical circulation indices are poorly represented in the NNR data prior to the 1960s.
Influence of the Antarctic Ice Sheet on southern high latitude climate during the Cenozoic: Albedo vs topography effect
Authors: Ogura Tomo'o , Abe‐Ouchi Ayako
Published: February 2004

Sensitivity of high latitude temperature distribution to the variation of the Antarctic ice sheet is investigated using an atmospheric general circulation model coupled with a mixed layer ocean. Results suggest that cooling effect of the ice sheet is not negligible compared to the effect of atmospheric CO2 decrease such as during the Cenozoic. Cooling effect of high surface albedo of the ice sheet is enhanced over the ice sheet and slightly suppressed over the circumpolar ocean by the high topography of the ice sheet. High surface albedo and high topography of the ice sheet each causes increase and decrease of southward atmospheric heat transport respectively, whose contribution to maintaining the heat balance anomaly of atmosphere‐ocean system is comparable to that of local adjustment of radiation balance.
Mesoscale analysis of transport across the subtropical tropopause
Authors: Kowol‐Santen Johanna , Ancellet Gérard
Published: February 2004

An airborne ozone lidar has been operated on March 26 and 27, 1999 in order to document the ozone distribution near the subtropical jet (STJ) in the 5°W–15°W longitude band which corresponds to an area where the STJ accelerates and interacts strongly with mid‐latitude cyclones. The two main features observed are a tropopause fold in the region where the STJ accelerates and an intrusion of subtropical tropospheric air into the mid‐latitude lower stratosphere. A mesoscale meteorological model is applied with high vertical resolution in order to study the strong layering in the upper troposphere and lower stratosphere.
Positionally dependent 15N fractionation factors in the UV photolysis of N2O determined by high resolution FTIR spectroscopy
Authors: Turatti F. , Griffith D. W. T. , Wilson S. R. , Esler M. B. , Rahn T. , Zhang H. , Blake G. A.
Published: February 2004

Positionally dependent fractionation factors for the photolysis of isotopomers of N2O in natural abundance have been determined by high resolution FTIR spectroscopy at three photolysis wavelengths. Fractionation factors show clear 15N position and photolysis wavelength dependence and are in qualitative agreement with theoretical models but are twice as large. The fractionation factors increase with photolysis wavelength from 193 to 211 nm, with the fractionation factors at 207.6 nm for 14N15N16O, 15N14N16O and 14N14N18O equal to −66.5±5‰,−27.1±6‰ and −49±10‰, respectively.
The time‐dependence of climate sensitivity
Authors: Senior Catherine A. , Mitchell John F. B.
Published: February 2004

A doubled CO2 coupled ocean‐atmosphere experiment has been run for over 800 years. The ‘effective’ equilibrium climate sensitivity to a doubling of CO2 (the equilibrium response of the model assuming the feedbacks remained constant at the value found at any given point of the transient response) is calculated throughout the run and found to increase by around 40%. The time‐dependence is associated with differences in cloud feedback arising from inter‐hemispheric temperature differences due to the slower warming rate of the Southern Ocean. The time‐dependence of the climate response has implications for the use of simpler models in scaling GCM results to different scenarios of forcing.
Impact of the 1997–98 El Niño Event on lightning activity over Indonesia
Authors: Hamid Effrina Yanti , Kawasaki Zen‐Ichiro , Mardiana Redy
Published: February 2004

The 1997–98 El Niño was one of the strongest El Niño Southern Oscillation (ENSO) events of this century. The major impact of the sea surface temperature (SST) change during this El Niño event was the shift in convection activity from the western to the central and eastern Pacific ocean affecting the response of rain‐producing cumulonimbus. As a result, convective rainfalls were suppressed near the Western Pacific regions and the Maritime Continent including Indonesia. On the other hand, the lightning activity during the El Niño period increased in contrast (on the average by 57%). As observed by the Tropical Rainfall Measuring Mission (TRMM) Lightning Imaging Sensor and Precipitation Radar, the convective storms during the El Niño were more intense. This was supported by the evidence that the El Niño storms had greater vertical developments and thicker zones containing ice phase precipitation.
Spatial patterns of earthquake sounds and seismic source geometry
Authors: Tosi Patrizia , De Rubeis Valerio , Tertulliani Andrea , Gasparini Calvino
Published: February 2004

Earthquake sounds are heard during or immediately before an event up to several kilometres around the epicentral area. Sound data as heard by people have been collected by way of macroseismic questionnaires, showing that sound audibility does not follow isotropic patterns. The explanation of this effect is found in the behaviour of the particular radiation pattern of the P‐waves for each earthquake, in connection with its focal mechanism. This result opens the possibility to get more information about the earthquake source parameters in the future and past events, making use of non‐instrumental observations.
Visualisation of luminescence excitation‐emission timeseries: Palaeoclimate implications from a 10,000 year stalagmite record from Ireland
Authors: Baker Andy , Bolton Lucy , Brunsdon Chris , Charlton Martin , McDermott Frank
Published: February 2004

Stalagmite luminescence excitation emission wavelength timeseries can provide high‐resolution palaeoclimate records. Here, we employ multidimensional visualisation techniques in order to interpret a 10,000 year luminescence record from a stalagmite from Crag Cave, SW Ireland. Our results demonstrate three periods of distinct luminescence properties: (1) 0–4,000 BP, when they are affected by overlying agriculture. (2) 4,000–9,600 BP, where there is a strong correlation between luminescence and 13C isotopic variations; we suggest the correlation demonstrates a vegetation response to climate change, (3) Before 9,600 BP, where a strong early Holocene transition is visible. Our results suggest that it took about 400–600 years for soils above the cave to stabilise after significant climate or environmental change, and that there was a complex vegetation response between 8,000 and 7,100 BP that my have been a lagged response to the “8.2 ka event”.
Surface segregation of bromine in bromide doped NaCl: Implications for the seasonal variations in Arctic ozone
Authors: Ghosal Sutapa , Shbeeb Alia , Hemminger John C.
Published: February 2004

Episodes of ozone depletion attributed to chemistry of gas phase bromine compounds in marine regions of the Arctic boundary layer have been reported at polar sunrise. Models for the source of brominated compounds in the marine Arctic troposphere have focussed on surface chemistry of sea salt ice and aerosols even though the molar ratio of Cl− to Br− in sea salt is expected to be ∼660 to 1. X‐ray photoelectron spectroscopy (XPS) studies described here show, for the first time, substantial segregation of Br− to the surface of NaCl samples with low level Br− dopant. Water vapor exposure plays an important role as it provides enhanced ionic mobility in such systems allowing the surface segregation as the system approaches thermodynamic equilibrium. Our XPS results are confirmed by scanning electron microscopy (SEM) imaging of the salt sample surface after water vapor exposure, which shows NaBr crystallites that form at the surface. Our experiments provide the first experimental evidence for surface segregation in mixed alkali halide solids. The segregation phenomenon displayed here is likely to play an important role in a wide range of atmospheric phenomena that involve surface reactions of sea salt particles and aerosols.
Quantification of stratospheric mixing from turbulence microstructure measurements
Authors: Alisse Jean‐Rémi , Haynes Peter H. , Vanneste Jacques , Sidi Claude
Published: February 2004

In the stratosphere, turbulence is confined within shallow, localised patches. The resulting vertical mixing of tracers is highly intermittent and difficult to quantify. Here a new technique is employed to estimate from high‐resolution, lower stratospheric mid‐latitude balloon data a well‐defined vertical diffusivity associated with this mixing. The technique, which is based on a stochastic model of the distribution of turbulent patches, emphasises the dependence of the diffusivity on the typical patch lifetime. Assuming a lifetime of a few hours, the diffusivity is found to be in the range 0.01–0.02m²s−1. This value is an order of magnitude smaller than those previously derived from radar measurements. The potential of the technique for the analysis of ocean microstructure measurements is noted.
Seismic and infrasonic evidences for an impulsive source of the shallow volcanic tremor at Mt. Etna, Italy
Authors: Ripepe M. , Coltelli M. , Privitera E. , Gresta S. , Moretti M. , Piccinini D.
Published: February 2004

During a seismo‐acoustic experiment we recorded volcanic tremor around the summit craters of Mt. Etna volcano. Tremor shows amplitude modulation, which disappear ≈ 900 m from the crater area. The infrasonic wavefield is coherent even at distances of ≈ 750 m. Time delay between infrasonic transient is stable around 1.3 s and is consistent with the position of the source in the Voragine crater. Amplitude modulation of tremor is well correlated (0.72) with infrasound amplitude with a time lag of 0.37 s. coherent with a shallow position of the source. Amplitude of volcanic tremor decays over increasing distances according to geometrical spreading of body waves. Tremor wavefield shows a linear polarization following the same time occourrence as the infrasonic pulses. Polarization azimuth indicates that wavefield rectilinearity is mostly due to P‐waves. We infer that most of the volcanic tremor we recorded at Mt. Etna is generated by superimposition of small impulsive sources acting at 1–2 s rate caused by pressure instability during magma degassing.
Lévy flights and earthquakes
Authors: Sotolongo‐Costa O. , Antoranz J. C. , Posadas A. , Vidal F. , Vázquez A.
Published: February 2004

Lévy flights representation is proposed to describe earthquake characteristics like the distribution of waiting times and position of hypocenters in a seismic region. Over 7500 microearthquakes and earthquakes from 1985 to 1994 were analyzed to test that its spatial and temporal distributions are such that can be described by a Lévy flight with anomalous diffusion (in this case in a subdiffusive regime). Earthquake behavior is well described through Lévy flights and Lévy distribution functions such as results show.
Seismo‐ionospheric signatures prior to M≥6.0 Taiwan earthquakes
Authors: Liu J. Y. , Chen Y. I. , Pulinets S. A. , Tsai Y. B. , Chuo Y. J.
Published: February 2004

This paper examines variations of the greatest plasma frequency in the ionosphere, foF2, recorded by the Chung‐Li ionosonde (25.0° N, 121.1° E) before M≥6.0 earthquakes during 1994–1999. The 15‐day running median and the associated inter‐quartile range are utilized as the reference and the upper or lower bounds to monitor the ionospheric foF2 variations for finding seismo‐ionospheric signatures (precursors) of the earthquakes. It is found that precursors, in the form of the recorded foF2 falling below its associated lower bound around 1200–1700 LT, appear 1–6 days prior to these earthquakes. On September 20, 1999 UT (September 21, Taiwan local time) a large Mw=7.7 earthquake struck central Taiwan near the small town of Chi‐Chi. We analyzed the foF2 and found three clear precursors 1, 3, and 4 days prior to the Chi‐Chi earthquake.
Characteristics of strong ground motion across a thrust fault tip from the September 21, 1999, Chi‐Chi, Taiwan earthquake
Authors: Huang Bor‐Shouh , Chen Kou‐Cheng , Huang Win‐Gee , Wang Jeen‐Hwa , Chang Tao‐Ming , Hwang Ruey‐Der , Chiu Hung‐Chie , Tsai Chu‐Chuan Peter
Published: February 2004

Near fault tip strong motion records from the northern part of the major earthquake (Mw = 7.6), namely the Chi‐Chi earthquake on September 21, 1999 in central Taiwan demonstrated systematic differences on the hanging wall and footwall, and simulated by the finite element method. The extraordinary ground motion differences on either side of the northern fault tip can be explained by a 2‐dimension kinematic source model with fault rupture breaking to surface. In this study, the earthquake faulting was considered as bilateral from the center of a low angle thrust fault which is 30 km in length with a dip angle of 31°. Based on waveform modeling, the source rupture velocity, rise‐time and dislocation of 2.0 km/sec, 5 sec and 6 meters, respectively are suggested. The results of this study show that on the northern part of the Chi‐Chi earthquake fault there was lower rupture velocity and longer rise‐time of the fault slip than that previously reported. Furthermore, the effects of surface breaking from the fault movement contributed large ground deformations near the fault tip and, consequently, induced extensive damage.
Wavelet spectra and chaos in thermal convection modelling
Authors: Vecsey Luděk , Matyska Ctirad
Published: February 2004

Thermal convection in planetary bodies represents a chaotic dynamical system, which can be mathematically described by a set of nonlinear equations. We have studied classical Boussinesq approximation of thermal convection with no inertial forces. Even for a low Rayleigh number (105) the convection is chaotic and the wavelet analysis of temperature, kinetic energy and surface heat flow time series demonstrates that wavelet spectra are able to yield an insight into the multiscale temporal dynamics of the convecting systems.
A study of the effects of transducer size on physical modeling experiments for recovering anisotropic elastic parameters
Authors: Li Ruiping , Okoye Patrick , Uren Norm
Published: February 2004

The effect of finite size transducers on elastic parameters recovered from laboratory measurements has been studied in this paper. Ultrasonic transmission experiments in the physical modeling laboratory were used to acquire the first arrival traveltime data at different ray angles, to simulate walkaway VSP surveys in the field. The elastic parameters of the materials were then recovered by our developed inversion techniques, using velocities at different directions inverted from the first arrival traveltimes. In our laboratory experiments, “point” transducers and “large” transducers were used to carry out the transmission experiments. The finite size of the transducers introduced systematic errors in the first break picks along the survey line, and hence the determined velocity field was inaccurate. These systematic errors cannot be corrected by the inversion technique. Numerical simulations were also conducted to study the differences between experiments using large and point transducers. From our experimental measurements, accurate elastic parameter values are obtained when the ratio of the sample‐thickness to transducer‐diameter is greater than 36. Decreasing the size of the transducers is highly recommended when conducting laboratory experiments to recover elastic parameters. A method of offset correction is also implemented in an attempt to decrease the measurement errors.
On the decrease of Arctic sea ice volume
Authors: Hilmer Michael , Lemke Peter
Published: February 2004

The decrease of Arctic sea ice volume is investigated using a dynamic‐thermodynamic sea ice model. The model was forced with NCEP/NCAR reanalysis winds and surface air temperatures in a hindcast simulation of the period 1958–1998. The simulation reveals pronounced decadal variability (10–12 years) along with a significant linear negative trend of total Arctic sea ice volume which amounts to −4%/decade. The decrease is apparent throughout the annual cycle with largest amplitudes from September to December. Regionally the strongest thinning of ice thickness occurs in the East Siberian Sea with magnitudes up to −30 cm/decade. The simulation also reveals some positive trends in the Baffin Bay/Labrador Sea and north of the Canadian Archipelago.
Ozone destruction and production rates between spring and autumn in the Arctic stratosphere
Authors: Fahey D. W. , Gao R. S. , Del Negro L. A. , Keim E. R. , Kawa S. R. , Salawitch R. J. , Wennberg P. O. , Hanisco T. F. , Lanzendorf E. J. , Perkins K. K. , Lloyd S. A. , Swartz W. H. , Proffitt M. H. , Margitan J. J. , Wilson J. C. , Stimpfle R. M. , Cohen R. C. , McElroy C. T. , Webster C. R. , Loewenstein M. , Elkins J. W. , Bui T. P.
Published: February 2004

In situ measurements of radical and long‐lived species were made in the lower Arctic stratosphere (18 to 20 km) between spring and early autumn in 1997. The measurements include O3, ClO, OH, HO2, NO, NO2, N2O, CO, and overhead O3. A photochemical box model constrained by these and other observations is used to compute the diurnally averaged destruction and production rates of O3 in this region. The rates show a strong dependence on solar exposure and ambient O3. Total destruction rates, which reach 19%/month in summer, reveal the predominant role of NOx and HOx catalytic cycles throughout the period. Production of O3 is significant only in midsummer air parcels. A comparison of observed O3 changes with destruction rates and transport effects indicates the predominant role of destruction in spring and an increased role of transport by early autumn.
A model study of temperature anomaly propagation from the subtropics to tropics within the South Atlantic Thermocline
Authors: Lazar Alban , Murtugudde Ragu , Busalacchi Antonio J.
Published: February 2004

A water mass flow formed by the Benguela Current and the South Equatorial Current connects the eastern subtropics to the western tropics through the Atlantic upper thermocline. We perform a process study with an Atlantic OGCM to examine whether and how synthetic subtropical mixed layer heat anomalies would employ this corridor to reach low‐latitudes. Our results suggest that it is a realistic scenario and that the time scale and trajectory of the movement can be explained to first approximation by time‐mean flow advection, since salinity compensation is tempering the density perturbation. In addition, wave processes seem to influence strongly the evolution of the intensity and the shape of the anomalies. It is apparent that an approach using both perspectives is necessary to fully understand and predict subsurface oceanic teleconnections.
New “Fresnel‐Zone” estimates for shear‐wave splitting observations from finite‐difference modeling
Authors: Rümpker Georg , Ryberg Trond
Published: February 2004

We employ full finite‐difference modeling to study effects of teleseismic shear‐wave splitting in 2D upper‐mantle models with lateral variations of anisotropy. In our models the anisotropy is confined to a layer at variable depth within the top 550 km of the upper mantle. We consider propagation of plane shear wavefronts and investigate the effects of lateral variations in symmetry‐axis orientation of orthorhombic olivine. Splitting parameters obtained from the synthetic waveforms exhibit characteristic variations as functions of frequency and polarization of the incident shear wave. We estimate the effective Fresnel zones (sensitivity range) from the lateral variations of splitting parameters. This leads to constraints for the extent of homogeneous anisotropic domains and for the depth of inhomogeneous regions.
Earthquake triggering in the North and East Aegean Plate Boundaries due to the Anatolia Westward Motion
Authors: Papazachos B. C. , Karakaisis G. F. , Papazachos C. B. , Scordilis E. M.
Published: February 2004

Historical and instrumental data of the last five centuries show that major earthquakes in the Marmara Sea area are followed by high strong‐earthquake seismicity in the Aegean area. During the first phase of this excitation period, which lasts about 3 years, strong shallow earthquakes concentrate almost exclusively along the Northern Boundary of the Aegean plate. Within 1–5 years after the first strong earthquake along this boundary, strong‐earthquake seismicity also increases in the Eastern Aegean Boundary. On the basis of current ideas on active tectonics and the previous observations, we expect the generation of several mainshocks with a mean magnitude of M=6.5 along the Northern Aegean Boundary during the next 3 years, following the recent large Izmit (NW Turkey) earthquake (1999.8.17, M=7.4).
Caribbean sea surface temperatures: Two‐to‐three degrees cooler than present during the Little Ice Age
Authors: Winter Amos , Ishioroshi Hiroshi , Watanabe Tsuyoshi , Oba Tadamichi , Christy John
Published: February 2004

We determined the seasonal environmental conditions during the Little Ice Age (LIA) by interpreting isotope proxies in the coral skeleton of Montastrea faveolata from the northeast Caribbean. The oxygen isotope composition was determined for three time intervals during the LIA (1700–1705, 1780–1785, 1810–1815), thought to correspond to the coldest intervals. The period 1984–1989 was used to represent modern calibration conditions. We determined that SSTs from the LIA intervals are nearly 2–3°C cooler than present. LIA cooling in the Caribbean may have resulted from regional oceanic and atmospheric circulation differences, especially in winter. We propose that a trough of cold air from the north Atlantic may have extended farther south than present, into the northern Caribbean. Although there are indications from Pacific corals that seasonality was greater during the LIA, this does not seem to be the case for the Caribbean.
Horizontal gradients in the wet path delay derived from four years of microwave radiometer data
Authors: Gradinarsky Lubomir P. , Elgered Gunnar
Published: February 2004

We have analyzed four years of inferred wet path delay data from a microwave radiometer operating at 21.0 and 31.4 GHz. We have applied a four parameter gradient model to the wet delays, using different lengths of the time series for the gradient estimation. The mean gradient, averaged over 15 to 1440 minutes, varies between 0.9 and 0.4 mm and has a preferred direction towards the north‐east. Increasing the averaging time causes the estimated gradient to decrease. The 15 minutes mean gradient is 1.3 mm for the summer months and 0.7 mm for the winter months. Structure function results are also presented.
The nonlinear response of stratospheric ozone to NOx and ClOx perturbations
Authors: Yang Peicai , Brasseur Guy P.
Published: February 2004

A mathematical analysis of the stratospheric photochemical system (gas phase reactions only) shows the existence of potential catastrophe mechanisms which could produce a dramatic reduction in the ozone concentration near 25 km altitude. The conditions leading to such catastrophe correspond to a relatively modest (i.e., factor 2–2.5) increase in the stratospheric source of reactive nitrogen (NOx). For a tenfold increase in the source of reactive chlorine (ClOx), the ozone system exhibits a large amplitude oscillatory behavior with a period of several tens of years. Transport processes could, however, damp these dramatic changes resulting from the nonlinear nature of the stratospheric chemical system.
El Niño, water vapor, and the global positioning system
Authors: Foster James , Bevis Michael , Schroeder Thomas , Merrifield Mark , Businger Steven , Dorn Susanne , Marcus Steven , Dickey Jean , Bar‐Sever Yoaz
Published: February 2004

The 1997–1998 El Niño had a profound impact on atmospheric circulation in the tropical Pacific and affected weather patterns world‐wide. Precipitable water estimates from Global Positioning System (GPS) sites in the western tropical Pacific capture the sudden onset of large‐scale subsidence, a phenomenon proposed as a possible mechanism driving the eventual decline of El Niño episodes. The atmospheric drying associated with this anomalous high‐pressure ridge and the turnabout as the warm episode transitions into the subsequent La Niña are clearly visible in the GPS observations.
Difference in radiosonde temperature trend for the period 1979–1998 of MSU data and the period 1959–1998 twice as long
Authors: Angell James K.
Published: February 2004

The difference in temperature trend for the 20‐year period 1979–1998 and 40‐year period 1959–1998 is estimated from a 63‐station global radiosonde network. The variability of radiosonde‐station temperature trends, as measured by their standard deviation, is about twice as great for 1979–1998 as 1959–1998. The cooling trend in the 100–50 mb layer of the low stratosphere is similar in polar, temperate and tropical zones, and about twice as great during 1979–1998 as 1959–1998. The cooling trend in the 300–100 mb layer of extratropics is also greater during 1979–1998 than 1959–1998, but the slight tropical warming is almost the same for the 2 periods. The warming trend in the tropospheric 850–300 mb layer is similar during 1959–1998 and 1979–1998, except in the south temperate zone where there is indicated to be cooling during 1979–1998. At the surface of the north polar zone the warming trend during 1979–1998 is nearly 3 times the warming during 1959–1998. In the global average the surface and 850–300 mb warmings are the same during 1959–1998, but the surface warms relative to the 850–300 mb layer during 1979–1998.
On the control of stratospheric humidity
Authors: Sherwood Steven C. , Dessler Andrew E.
Published: February 2004

We present a hypothesis on the dehydration and transfer of air from the tropical troposphere into the stratosphere. The hypothesis is based on the existence of a thick “tropopause layer,” in which vertical and horizontal mixing are both significant. Air is rapidly dehydrated upon entering this layer in vigorous convective overshoots, then slowly ascends through the layer before fully entering the stratosphere. Dehydration and genuine entry into the stratosphere are separate processes that happen on much different time scales.
An estimate of the impact of observed ozone losses on stratospheric temperature
Authors: Langematz Ulrike
Published: February 2004

The climatic impact of the observed stratospheric ozone changes since 1980 was studied in simulations with the Berlin Climate Middle Atmosphere Model (CMAM). The model was run with prescribed ozone climatologies of the years 1980 and 2000, derived from the newest WMO assessment of ozone trends. It is shown that in the northern hemisphere stratosphere, the temperature decreases as a reaction to the 20 year ozone changes. Whereas the patterns of the observed stratospheric cooling for that period are reproduced in the model, its magnitude is underestimated, indicating an impact of other factors on stratospheric temperature.
Bromoform as a source of stratospheric bromine
Authors: Sturges William T. , Oram David E. , Carpenter Lucy J. , Penkett Stuart A. , Engel Andreas
Published: February 2004

We have measured bromoform (CHBr3) in the troposphere and lower stratosphere (sea level to 17 km) from balloons, aircraft and ground stations. The concentrations ranged from 2 to 20 ppt at sea level, and 0.1 to 1 ppt in the upper troposphere. Above the tropopause the concentrations declined sharply to less than 0.01 ppt above 14 km. CHBr3 accounted for 3% of total measured organic bromine (Bro) at the extratropical tropopause, and appeared to potentially contribute at least 9% of reactive bromine (Bry) in stratospheric air of mean age less than 1 year. Inclusion of dibromomethane and the mixed bromochloromethanes increased these figures to about 10% of Bro and 20% of Bry respectively. Observations of CHBr3 in both Arctic and mid‐latitudinal stratospheric air, and in air masses with mean ages of more than 1.5 years, suggests that the CHBr3 in these locations originates predominantly from extratropical stratosphere‐troposphere exchange.
An overview of LOA SAGE III inversion algorithm
Authors: Bazureau A. , Brogniez C. , Lenoble J.
Published: February 2004

We present here the inversion algorithm implemented by the Laboratoire d'Optique Atmosphérique, University of Lille, France, for the analysis of solar and lunar occultation data from the Stratospheric Aerosol and Gas Experiment III (SAGE III). The first flight of SAGE III is planned to be launched in late fall 2000 on the polar orbit spacecraft METEOR 3M. We present first the forward model algorithm for calculating atmospheric transmittances in four of the SAGE III channels: the solar ones, around 440 nm and 600 nm, and the lunar ones, around 413 nm and 660 nm. Then the inversion algorithm is introduced, accomplished in two sequential steps. The first one is the spatial inversion of the simulated slant optical thickness profile leading to the extinction coefficient profile. The second is the spectral inversion of the extinction coefficient at each altitude to separate gas and aerosol contributions. Lastly, error analysis is conducted by a Monte Carlo technique and discussed: the retrieved gas densities and aerosol extinction profiles favourably compare to the corresponding input profiles.
the excitation of the Chandler wobble
Authors: Gross Richard S.
Published: February 2004

The Chandler wobble is an excited resonance of the Earth's rotation having a period of about 14 months. Although it has been under investigation for more than a century, its excitation mechanism has remained elusive. Here, the angular momentum of the atmosphere computed from the products of a numerical weather prediction analysis system and the angular momentum of the oceans computed from a global oceanic general circulation model driven by observed surface winds and fluxes are used to show that during 1985.0–1996.0 the Chandler wobble was excited by a combination of atmospheric and oceanic processes, with the dominant excitation mechanism being ocean‐bottom pressure fluctuations.
Subtropical SST dipole events in the southern Indian Ocean
Authors: Behera Swadhin K. , Yamagata Toshio
Published: February 2004

Sea surface temperature (SST) anomalies in the subtropical southern Indian Ocean show interannual dipole events that are seasonally phase‐locked to the austral summer. A positive phase of the event is characterized by cold SST anomalies in the eastern part i.e. off Australia and warm SST anomalies in the southwestern part, south of Madagascar. Such an event is found to produce above normal rainfall over many regions in south‐central Africa. The cooling of SST in the eastern part is mainly caused by the enhanced evaporation. This is associated with stronger winds along the eastern edge of the subtropical high, which is strengthened and shifted slightly to the south during the event. On the other hand, relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part. Evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the Indian Ocean.
Currents in Korea‐Tsushima Strait during summer 1999
Authors: Perkins H. , Teague W. J. , Jacobs G. A. , Chang K. I. , Suk M.‐S.
Published: February 2004

Results are presented from continuous current measurements across Korea‐Tsushima Strait between May and October 1999. The data are from eleven bottom‐mounted Acoustic Doppler Current Profilers that recorded full‐depth profiles of currents along two lines, one at each end of the Strait. The two sections show markedly different mean flow regimes. At the southern entrance, the cross‐section flow varies smoothly across the channel, showing a broad maximum at mid‐channel. The northern section is marked by strong spatial variability but in the mean consists of two streams, one on each side of the strait. Between the two is a regime of highly variable flow with a weak mean, presumably indicating the wake from Tsushima Island. Flow variability in time is described by statistical measures and by representative snapshots.
A note on contact stress and closure in models of rock joints and faults
Authors: Beeler N. M. , Hickman S. H.
Published: February 2004

We have re‐examined asperity deformation predicted by joint closure models based on Greenwood and Williamson [1966] which use a statistical representation of loaded, rough surfaces. Although such models assume small elastic strains within contacting asperities (Hertzian contact) and well predict the observed dependence of closure on normal stress, large elastic normal strains measured in experiments violate the model assumptions. This inconsistency between observations and models can be resolved. The model dependence of closure on macroscopic normal stress results primarily from the statistics of the surface topography, and the functional dependence of closure on normal stress can be independent of assumed contact‐scale elastic interactions. Thus, a joint model of the Greenwood and Williamson kind, modified to allow a portion of the elastic deformation to occur outside of the asperity contact region, predicts macroscopic behavior consistent with Hertzian models. Contact stresses derived from previously published models of this kind may be in error.
Concentration variations of tropospheric nitrous oxide over Japan
Authors: Ishijima Kentaro , Nakazawa Takakiyo , Sugawara Satoshi , Aoki Shuji , Saeki Tazu
Published: February 2004

Aircraft measurements of the tropospheric N2O concentration were made over Japan during the period from October 1991 to June 1999. The observed values of the N2O concentration showed clear evidence of the secular increase, with mean rates of 0.50 to 0.64 ppbv/yr for selected height intervals of 0–2, 2–4, 4–6, 6–8 km and 8 km‐tropopause. Although the seasonality of the N2O concentration was hardly observable throughout the troposphere, interannual variations with periods of about 2 years were clearly found. The average N2O concentrations over the observation period for the above 5 height intervals were almost identical with each other, showing no appreciable vertical gradient of the concentration. This suggests that N2O emissions from the ground surface around Japan are very weak and the emitted N2O is mixed well in the troposphere.
1 Hz Lg Q tomography in central Asia
Authors: Phillips W. Scott , Hartse Hans E. , Taylor Steven R. , Randall George E.
Published: February 2004

We have applied tomographic techniques to a data set of over 1700, regional distance, Lg amplitudes from 12 stations for paths inside a 30° by 40° region of Central Asia. Our purpose is to create high resolution path correction maps for use in regional distance source discrimination and magnitude determination, as well as to study Lg propagation characteristics in one of the most heterogeneous portions of the earth. For 1.0 Hz data, tomography reduced variance 33%, relative to a best fit, uniform Q model. LgQ varied with geologic region, with low values in Tibet, the Tien Shan and the Pamir range (Q=200 to 400), intermediate values in basins such as the Tarim (Q=500) and high values for platforms and older crust (Q>800). The relatively efficient propagation across the Tarim differs from the poor propagation that is generally observed across sedimentary basins.
The Indian Ocean SST dipole simulated in a coupled general circulation model
Authors: Iizuka Satoshi , Matsuura Tomonori , Yamagata Toshio
Published: February 2004

We are successful in simulating the recently discovered ocean‐atmosphere coupled phenomenon called the Indian Ocean Dipole for the first time, using a coupled general circulation model without flux correction. During the analyzed 50 years of model integration, the anomalous climate events have appeared 8 times over the Indian Ocean (IO). They are characterized by the cooling of the sea surface temperature (SST) in the southeastern tropical IO and the warming of the SST in the western tropical IO, associated with the anomalous easterly winds along the equator. The spatial pattern of the anomalous SST shows an east‐west dipole mode (DM) structure that is similar to the recent reports. The simulated DM events are independent of the El Niño simulated in the same model. The heat budget analysis shows that the tropical air‐sea interaction, which is strongly influenced by ocean dynamics, is crucial in generating the model DM events.