bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring gravity field variability, the geoid, ocean bottom pressure fluctuations, and their dynamical implications
Authors: Condi Francis , Wunsch Carl
Published: February 2004

To obtain insight into bottom pressure variability and requirements for assimilating gravity data into an ocean general circulation model, we use recent results from a constrained global model. Bottom pressure variability, as contrasted to surface elevation variability, is examined at the annual, semiannual, Chandler‐wobble, and 4‐month periods. Surface elevation and bottom pressure variability occurs on all spatial and temporal scales resolvable by our analysis, and patterns can be quite different. A barotropic index, developed to quantify variability character, suggests the importance of steric effects at longer periods. Variability decomposition into standing, eastward, and westward traveling waves indicates a strong zonal component for both surface elevation and bottom pressure, with bottom pressure showing a greater overall tendency toward eastward propagation, and surface elevation showing a greater overall tendency toward westward propagation. Bottom pressure variability signals are estimated to be recoverable from space to spherical harmonic degree 27 for the annual cycle and 14 for the semiannual and Chandler‐wobble cycles. Mass exchange, arising from model approximations, is detectable to about degree 7. Polar motion excitation by ocean seafloor loading is found to be quantitatively important. Spurious oscillations encountered in using spherical harmonics to represent oceanic fields are suppressed using Lanczos factors.
Abrupt hydrographic changes in the equatorial Pacific and subtropical Atlantic from foraminiferal Mg/Ca indicate greenhouse origin for the thermal maximum at the Paleocene‐Eocene Boundary
Authors: Tripati Aradhna K. , Elderfield Henry
Published: February 2004

The Paleocene‐Eocene Boundary (PEB) was marked by an extraordinary climatic event, hypothesized to originate from a large perturbation to the carbon cycle which fueled global warming, the rapid dissociation of oceanic methane hydrates. The pattern of surface warming interpreted from existing sea surface temperature records is not consistent with a greenhouse origin for this event, which would have fueled sea surface warming globally. Although oxygen isotope (δ18O)‐based reconstructions indicate polar warming, results for the tropics and subtropics are ambiguous because of uncertainties associated with interpreting planktonic foraminiferal δ18O. To remedy this, we have constructed high‐resolution temperature records based on Mg/Ca of multiple species of both surface and thermocline‐dwelling planktonic foraminifera across the PEB in the equatorial Pacific and subtropical Atlantic. During the carbon isotope excursion (CIE), surface temperatures increased by 3.5°–4°C and thermocline temperatures warmed by 3°C. Estimates of surface water and thermocline salinity based on paired Mg/Ca and δ18O data indicate a pattern of hydrographic changes in the equatorial and subtropical oceans that is different from previously proposed, with a more vigorous hydrologic cycle during warming. The pattern of warming and salinity changes are consistent with this being a greenhouse‐induced global warming event, and the timing of hydrographic changes relative to the CIE supports the hypothesis that gradual warming of intermediate/deep waters triggered methane hydrate dissociation.
Sea surface temperature anomalies in the oceans at the LGM estimated from the alkenone‐U37K′ index: comparison with GCMs
Authors: Rosell‐Melé Antoni , Bard Edouard , Emeis Kay‐Christian , Grieger Bjoern , Hewitt Chris , Müller Peter J. , Schneider Ralph R.
Published: February 2004

U37K′ sea surface temperature (SST) estimates for the Last Glacial Maximum (LGM) are discussed and compared to coupled general circulation model (GCM) results. We conclude that U37K′ estimates and most numerical models agree in the magnitude of the large scale SST cooling features of the glacial ocean. There was a larger cooling in the northern than in the Southern Hemisphere. The eastern boundary currents and equatorial regions were also colder. There is a consensus between models and alkenone data for a tropical cooling of about −2°C, which is in disagreement with both a smaller cooling as suggested by the CLIMAP project reconstruction, or a more pronounced cooling as suggested from coral proxy records. The comprehensive HadCM3 simulation examined reproduces a puzzling feature of the U37K′‐SST reconstruction, i.e., the warming of the glacial north Atlantic, which needs further investigation using numerical modelling and proxy data reconstruction.
Local amplification of seismic waves from the Denali Earthquake and damaging seiches in Lake Union, Seattle, Washington
Authors: Barberopoulou Aggeliki , Qamar Anthony , Pratt Thomas L. , Creager Kenneth C. , Steele William P.
Published: February 2004

The Mw7.9 Denali, Alaska earthquake of 3 November, 2002, caused minor damage to at least 20 houseboats in Seattle, Washington by initiating water waves in Lake Union. These water waves were likely initiated during the large amplitude seismic surface waves from this earthquake. Maps of spectral amplification recorded during the Denali earthquake on the Pacific Northwest Seismic Network (PNSN) strong‐motion instruments show substantially increased shear and surface wave amplitudes coincident with the Seattle basin. Because Lake Union is situated on the Seattle basin, the size of the water waves may have been increased by local amplification of the seismic waves by the basin. Complete hazard assessments require understanding the causes of these water waves during future earthquakes.
Low Mach number bow shock locations during a magnetic cloud event: Observations and magnetohydrodynamic simulations
Authors: El‐Alaoui Mostafa , Richard Robert L. , Ashour‐Abdalla Maha , Chen Margaret W.
Published: February 2004

During the magnetic storm on October 18–19, 1998 a magnetic cloud encountered the Earth's magnetosphere. As the cloud passed, the solar wind density decreased dramatically, and as a consequence the solar wind magnetosonic Mach number dropped markedly, approaching 1 at times. Magnetohydrodynamic (MHD) simulations, driven by upstream interplanetary magnetic field (IMF) and solar wind parameters observed on WIND and ACE showed that during the interval of the lowest density, the subsolar distance of the bow shock (BS) reached as much as 50 RE. IMP‐8 spacecraft observations of the expansion and subsequent retreat of the BS support the finding that the shock reached a considerable distance upstream. Surprisingly, at times the BS moved sunward at a speed approaching the magnetosonic speed of the solar wind.
Profiles of Mercury in the snow pack at Station Nord, Greenland shortly after polar sunrise
Authors: Ferrari Christophe P. , Dommergue Aurélien , Boutron Claude F. , Jitaru Petru , Adams Freddy C.
Published: February 2004

Mercury (Hg) species have been measured in the snow pack at Station Nord, Greenland both in the snow and in the air of snow from February 25 to March 15, 2002, during twilight and low solar irradiation periods. More than 99% of Hg is in the snow itself (∼94–97% as Hg2+ and ∼5% as MeHg+) while less than 1% is in the interstitial air of snow as Hg°. Gaseous Elemental Mercury (Hg°) concentrations, decreased exponentially with depth from ∼1.5 ng/m3 outside to ∼0.1 ng/m3 at 120 cm depth in the snow air. Hg° incorporation flux to the snow pack has been evaluated to ∼5.8–7.0 pg/m2/h which is weak, indicating that this process does not change significantly the Hg content in the snow. We believe that this decrease in the air of snow is the result of fast oxidation processes of Hg° rather than adsorption of Hg° onto snow surfaces.
Estimation and representation of long‐term (>40 year) trends of Northern‐Hemisphere‐gridded surface temperature: A note of caution
Authors: Soon Willie W.‐H. , Legates David R. , Baliunas Sallie L.
Published: February 2004

Several quantitative estimates of surface instrumental temperature trends in the late 20th century are compared by using published results and our independent analyses. These estimates highlight a significant sensitivity to the method of analysis, the treatment of data, and the choice of data presentation (i.e., size of the smoothing filter window). Providing an accurate description of both quantitative uncertainties and sensitivity to the treatment of data is recommended as well as avoiding subjective data‐padding procedures.
Nadir observations of sprites from the International Space Station
Authors: Blanc E. , Farges T. , Roche R. , Brebion D. , Hua T. , Labarthe A. , Melnikov V.
Published: February 2004

The experiment LSO (Lightning and Sprite Observations) is dedicated to the optical study, from the International Space Station, of sprites occurring in the upper atmosphere above thunderstorms. The objectives were to study these phenomena and to validate a new measurement concept for future measurements of sprites from space at the nadir. The first measurements were performed in the frame of the flight of the French Astronaut Claudie Haigneré (mission Andromède) in October 2001. Observations were performed by two microcameras, one in the visible and near‐infrared and the other equipped with a moderately wide band filter at 761 nm. This filter includes the most intense N2 1P emission of the sprites and partly the oxygen absorption A band of the atmosphere. The light emissions from sprites occurring in the middle and upper atmosphere are then differentiated from the emissions from lightning, occurring more deeply in the atmosphere and then more absorbed. This paper presents the first observations of sprites from space at the nadir and statistics about the respective intensities of lightning and sprites emissions as observed with this experiment.
FAST observations of the solar illumination dependence of upflowing electron beams in the auroral zone
Authors: Cattell C. , Dombeck J. , Yusof W. , Carlson C. , McFadden J.
Published: February 2004

Electron beams accelerated upward out of the ionosphere are commonly observed in the auroral acceleration region. We present a statistical study of their distribution in magnetic local time, invariant latitude, and altitude, and its dependence on whether the ionospheric foot point of the satellite is illuminated or dark. The occurrence probability maximizes at ∼12% near 70° invariant latitude (ILAT) and midnight when the ionosphere is in darkness, and at ∼1% near ∼78° ILAT from ∼0600 to 1300 magnetic local time (MLT) when the ionosphere is illuminated. When the ionosphere is in darkness, there is approximately an order of magnitude increase in the probability from ∼1000 to ∼4000 km in almost all local time sectors. When the ionosphere is sunlit, the rapid increase begins at a higher altitude, ∼2500 km. The probability also increases with solar zenith angle, with the increase being slower and occurring at a higher solar zenith angle at lower altitudes. These observations are consistent with a scale‐height and density‐dependent mechanism for the parallel potential in the downward current region. More than 90% of the observed upflowing electron beams have characteristic energies between ∼50 and ∼300 eV. The statistical results suggest that there are many more beams with durations of <5 s (latitude widths of <0.2°) and with lower energies.
A Quantitative model for terrestrial foreshock radio emissions: 1. Predicted properties
Authors: Kuncic Z. , Cairns I. H. , Knock S. A.
Published: February 2004

We present detailed quantitative results from a theoretical model for fundamental (fp) and second harmonic (2fp) radio emission generated in Earth's foreshock by beam‐driven Langmuir waves. The model is the first to self‐consistently incorporate all key aspects of foreshock physics: reflection and acceleration of incident solar wind electrons at the bow shock, generation of unstable electron beams in the foreshock, stochastic growth of Langmuir waves and their conversion to electromagnetic waves via nonlinear processes. The physical properties of the foreshock electron beams, Langmuir waves and electromagnetic emissivities are calculated as a function of position for nominal solar wind conditions. Variations in the bow shock's location and characteristics with changes in the solar wind parameters are included. The predicted fluxes of fp and 2fp radiation are explored over a wide range of solar wind conditions. We find that the 2fp flux is most sensitive to the electron and ion temperatures and the solar wind speed and that the radio fluxes of both fp and 2fp radiation also vary significantly with the solar wind electron number density, and proportion of nonthermal electrons. Our macroscopic model provides a powerful and unique diagnostic tool with which to interpret observational data from various spacecraft under a range of solar wind conditions.
Kinetic Alfvén waves: Linear theory and a particle‐in‐cell simulation
Authors: Gary S. Peter , Nishimura Kazumi
Published: February 2004

An Alfvén‐cyclotron fluctuation of sufficiently short wavelength has a strong proton cyclotron resonance at propagation parallel to the background magnetic field Bo in a homogeneous, collisionless electron‐proton plasma. As k∥, the wavevector component parallel to Bo, decreases, the proton cyclotron wave‐particle interaction becomes nonresonant, and the electron Landau resonance becomes effective at propagation oblique to Bo. Here linear Vlasov theory is used to determine the dispersion and damping properties of Alfvén‐cyclotron fluctuations associated with the transition from the proton cyclotron resonance regime to the electron Landau resonance regime. Also, a particle‐in‐cell plasma simulation is used to examine the electron response to the initial imposition of an Alfvén‐cyclotron wave in the electron Landau resonance regime. The computation shows heating of the electrons in the direction parallel to Bo and the formation of a beam in the direction of the parallel component of k.
Nonlinear stationary waves and solitons in ion beam‐plasma configuration
Authors: Dubinin E. , Sauer K. , McKenzie J. F.
Published: February 2004

A fully nonlinear treatment for stationary waves in a cold plasma with an ion beam propagating parallel to the magnetic field is carried out in the framework of Hall MHD. It is shown that the linearly unstable system can evolve into a steady nonlinear configuration in which both ion populations undergo a coherent helical motion guided by the magnetic field. The complete system of equations can be reduced to two coupled differential equations for the transverse proton (or beam ion) speed and the phase difference between the wave motion of both ion fluids. In the case of a weak beam these equations possess a phase‐portrait integral which describes the main dynamical features of the system. A soliton‐type solution with a core filled by smaller‐scale oscillations is found for the transverse components of the ion velocities and magnetic field. It is suggested that gyrophased bunched ion beams associated with large‐amplitude quasi‐monochromatic ULF waves often observed in the ion foreshock are a manifestation of these fully nonlinear structures. A driver for such oscilliton‐like structures is provided by a linear instability in which the wave is exponentially growing. The momentum exchange between two different ion populations, mediated by the magnetic field stresses, leads to the formation of a steady nonlinear wave‐oscilliton.
Coupling between earthquake swarms and volcanic unrest at the Alban Hills Volcano (central Italy) modeled through elastic stress transfer
Authors: Feuillet N. , Nostro C. , Chiarabba C. , Cocco M.
Published: February 2004

We study a seismic swarm that occurred in 1989–1990 at the Alban Hills volcano and interpret the seismicity pattern in terms of Coulomb stress changes caused by magma intrusion in a local volcanic source and the extensional tectonic stress field. We first image the three‐dimensional (3‐D) structure of the volcano through a tomographic inversion of P waves and S‐P arrival times recorded by a temporary local network. A high Vp and Vp/Vs body exists beneath the area of most recent volcanic activity, which we interpret as a solidified magma body delimiting the position of the volcanic source. We have relocated 661 events (M ≤ 4.0) using this 3‐D velocity model and we have computed 64 fault plane solutions. Elevation changes, measured between 1951 and 1994 along a 33‐km‐long line crossing the western part of the volcano, reveal an uplift of 0.3 m. We model these data to constrain the position and geometry of the volcanic source. We compute the vertical deformation in a homogeneous half‐space, testing different volcanic sources (spherical magma chamber, sill and dike). We model the Coulomb stress changes caused by the local volcanic source and the regional tectonic stress field. The inflation of magma generates an increase of Coulomb stress larger than 0.5 MPa in the area where the seismicity is located. More than 85% of fault plane solutions are consistent with the stress perturbations induced by the volcanic source. We conclude that microearthquakes at the Alban Hills are promoted by elastic stress changes caused by volcanic unrest episodes.
Paleomagnetic constraints on deformation models for uppermost oceanic crust exposed at the Hess Deep Rift: Implications for axial processes at the East Pacific Rise
Authors: Varga Robert J. , Karson Jeffrey A. , Gee Jeffrey S.
Published: February 2004

Studies of oceanic crust exposed in tectonic windows and in ophiolites have revealed the importance of normal faulting and attendant tilting of upper crustal rock units in the accretion process at oceanic spreading centers. We present paleomagnetic remanence data from 45 fully oriented samples from dikes, gabbros and a small number of basaltic lavas from fast spread crust exposed along the Hess Deep Rift. Over ∼25 km along this escarpment, dikes and dike‐subparallel fault zones dip consistently away from the East Pacific Rise (EPR) while lava flows dip toward the ridge. Underlying gabbro is less deformed but contains widely spaced, low‐angle fractures, tentatively interpreted as shear zones. As expected from the crustal age (∼1.07–1.48 Ma), most remanence data indicate reversed polarity magnetization and are compatible with the expected range of secular variation at the site. Overly steep and directionally scattered gabbro remanence and observed low‐angle shear structures within this unit are tentatively interpreted as the manifestation of three‐dimensional strain along anastomosing shear zones. Although some remanence directions are incompatible with any plausible deformation history, and thus likely reflect orientation errors, the overall data set is consistent with a model involving sequential rotations on (1) outward dipping, EPR‐parallel (∼N‐S) normal faults and (2) Hess Deep Rift‐parallel (∼E‐W) normal faults Average rotations for these sequential events are 22° to the east (defined by the mean dike attitude) and 10° to the south (estimated by bathymetry), respectively. This model best explains the remanence data, observed dikes and lava orientations, presence of dike‐parallel fault zones, and the observation of steep, little deformed dikes cutting both east dipping dikes and faults. The data support a structural model for spreading at the EPR in which outcrop‐scale faulting and rotation is linked to subaxial subsidence and to consequent development of dominantly outward facing normal faults close to the spreading axis. Because these faults form within the neovolcanic zone, they are subject to burial and are expected to have subdued to little surface expression.
Differential uplift and tilt of Pleistocene reef platforms and Quaternary slip rate on the Morne‐Piton normal fault (Guadeloupe, French West Indies)
Authors: Feuillet N. , Tapponnier P. , Manighetti I. , Villemant B. , King G. C. P.
Published: February 2004

The Guadeloupe islands are cut by normal faults that accommodate oblique convergence between the North American and Caribbean plates. Such faults are responsible for part of the shallow seismicity and have producedM≥ 5 damaging earthquakes. To better assess the seismic hazard in Guadeloupe, we quantify the slip rate on one of the largest fault (Morne‐Piton). This roughly E‐W fault crosses the island of Marie‐Galante and uplifts a flight of reef terraces. From geomorphic analysis, we mapped three main terraces. New U/Th datings show that they formed during the latest interglacials, ∼120 and ∼240 kyr ago. Correlation with SPECMAP isotopic records implies that the Marie‐Galante plateau emerged during the ∼330 ka highstand. Topographic profiles show that the terraces and the plateau are deformed by faulting. Elastic modeling of their shape constrains the geometry of the fault (70–80° dip, 5 km depth) and its slip rate (0.5 ± 0.2 mm/yr). Given its length (50 km), depth, and slip rate, this fault might produce maximumM∼ 6.5 earthquakes with a recurrence time of 1400 to 3300 years, or more likely smaller events such as theM∼ 5.5 16 May 1851 and 3 August 1992 shocks that might recur every 400 to 1000 years. We also show that all the islands and terraces are tilted westward perpendicularly to the trench. La Désirade closest to the trench is uplifted by 276 m, whereas subsidence (−70 m) is observed 10 km east of the volcanic arc. This tilt probably resulted from a transient deformation episode at the subduction interface that predated the late Pleistocene.
Using satellite‐derived ice concentration to represent Antarctic coastal polynyas in ocean climate models
Authors: Stössel Achim , Markus Thorsten
Published: February 2004

The focus of this paper is on the representation of Antarctic coastal polynyas in global ice‐ocean general circulation models (OGCMs), in particular their local, regional, and high‐frequency behavior. This is verified with the aid of daily ice concentration derived from satellite passive microwave data using the “NASA Team 2” (NT2) and the bootstrap (BS) algorithms. Large systematic regional and temporal discrepancies arise, some of which are related to the type of convection parameterization used in the model. An attempt is made to improve the fresh‐water flux associated with melting and freezing in Antarctic coastal polynyas by ingesting (assimilating) satellite ice concentration where it comes to determining the thermodynamics of the open‐water fraction of a model grid cell. Since the NT2 coastal open‐water fraction (polynyas) tends to be less extensive than the simulated one in the decisive season and region, assimilating NT2 coastal ice concentration yields overall reduced net freezing rates, smaller formation rates of Antarctic Bottom Water, and a stronger southward flow of North Atlantic Deep Water across 30°S. Enhanced net freezing rates occur regionally when NT2 coastal ice concentration is assimilated, concomitant with a more realistic ice thickness distribution and accumulation of High‐Salinity Shelf Water. Assimilating BS rather than NT2 coastal ice concentration, the differences to the non‐assimilated simulation are generally smaller and of opposite sign. This suggests that the model reproduces coastal ice concentration in closer agreement with the BS data than with the NT2 data, while more realistic features emerge when NT2 data are assimilated.
Arctic oscillation response to the 1991 Pinatubo eruption in the SKYHI general circulation model with a realistic quasi‐biennial oscillation
Authors: Stenchikov Georgiy , Hamilton Kevin , Robock Alan , Ramaswamy V. , Schwarzkopf M. Daniel
Published: February 2004

Stratospheric aerosol clouds from large tropical volcanic eruptions can be expected to alter the atmospheric radiative balance for a period of up to several years. Observations following several previous major eruptions suggest that one effect of the radiative perturbations is to cause anomalies in the Northern Hemisphere extratropical winter tropospheric circulation that can be broadly characterized as positive excursions of the Arctic Oscillation (AO). We report on a modeling investigation of the radiative and dynamical mechanisms that may account for the observed AO anomalies following eruptions. We focus on the best observed and strongest 20th century eruption, that of Mt. Pinatubo on 15 June 1991. The impact of the Pinatubo eruption on the climate has been the focus of a number of earlier modeling studies, but all of these previous studies used models with no quasi‐biennial oscillation (QBO) in the tropical stratosphere. The QBO is a very prominent feature of interannual variability of tropical stratospheric circulation and could have a profound effect on the global atmospheric response to volcanic radiative forcing. Thus a complete study of the atmospheric variability following volcanic eruptions should include a realistic representation of the tropical QBO. Here we address, for the first time, this important issue. We employed a version of the SKYHI troposphere‐stratosphere‐mesosphere model that effectively assimilates observed zonal mean winds in the tropical stratosphere to simulate a very realistic QBO. We performed an ensemble of 24 simulations for the period 1 June 1991 to 31 May 1993. These simulations included a realistic prescription of the stratospheric aerosol layer based on satellite observations. These integrations are compared to control integrations with no volcanic aerosol. The model produced a reasonably realistic representation of the positive AO response in boreal winter that is usually observed after major eruptions. Detailed analysis shows that the aerosol perturbations to the tropospheric winter circulation are affected significantly by the phase of the QBO, with a westerly QBO phase in the lower stratosphere resulting in an enhancement of the aerosol effect on the AO. Improved quantification of the QBO effect on climate sensitivity helps to better understand mechanisms of the stratospheric contribution to natural and externally forced climate variability.
Measurements of stratospheric volcanic aerosol optical depth from NOAA TIROS Observational Vertical Sounder (TOVS) observations
Authors: Pierangelo Clémence , Chédin Alain , Chazette Patrick
Published: February 2004

We show that the infrared optical depth of stratospheric volcanic aerosols produced by the eruption of Mount Pinatubo in June 1991 may be retrieved from the observations of the High‐Resolution Infrared Radiation Sounder (HIRS‐2) on board the polar meteorological satellites of the National Oceanic and Atmospheric Administration (NOAA). Evolution of the concentration in time and in space, in particular the migration of the aerosols from the tropics to the Northern and Southern Hemispheres, is found to be consistent with our knowledge of the consequences of this eruption. The method relies on the analysis of the differences between the satellite observations and simulations from an aerosol‐free radiative transfer model using collocated radiosonde data as the prime input. Thus aerosol optical depths are retrieved directly without making assumptions about the aerosol size distribution or absorption coefficient. The aerosol optical depths reached a maximum in August 1991 in the tropical zone (0.055 at 8.3 μm, 0.03 at 4.0 μm, and 0.02 at 11.1 μm). The peak occurred in November 1991 in the southern midlatitudes and in March/April 1992 in the northern midlatitudes. A reanalysis of the almost 25 year archive of NOAA TIROS‐N Operational Vertical Sounder (TOVS) observations holds considerable promise for improved knowledge of the atmosphere loading in volcanic aerosols.
Evaluation of operational radiances for the Measurements of Pollution in the Troposphere (MOPITT) instrument CO thermal band channels
Authors: Deeter M. N. , Emmons L. K. , Francis G. L. , Edwards D. P. , Gille J. C. , Warner J. X. , Khattatov B. , Ziskin D. , Lamarque J.‐F. , Ho S.‐P. , Yudin V. , Attie J.‐L. , Packman D. , Chen J. , Mao D. , Drummond James R. , Novelli Paul , Sachse Glen
Published: February 2004

The ability of operational radiative transfer models to accurately predict remote sensing instrument observations (e.g., calibrated radiances) over a wide variety of geophysical situations is critical to the performance of trace gas retrieval algorithms. As part of the validation of the Measurements of Pollution in the Troposphere (MOPITT) satellite instrument, we present a technique for comparing operational calibrated thermal band (4.7 μm) Earth‐view MOPITT radiances with corresponding values calculated using the MOPITT operational radiative transfer model. In situ carbon monoxide (CO) profiles sampled from aircraft in coordination with MOPITT overpasses serve as the foundation for MOPITT validation. Characteristics of radiance errors due to in situ sampling characteristics, CO temporal and spatial variability, and surface emissivity are discussed. Results indicate that radiance biases for most of the MOPITT thermal channel radiances are typically on the order of 1%. Observed radiance biases are largest and most variable for the pressure modulation cell difference‐signal radiances, probably because of the lack of in situ data in the upper troposphere and lower stratosphere.
Validation of Measurements of Pollution in the Troposphere (MOPITT) CO retrievals with aircraft in situ profiles
Authors: Emmons L. K. , Deeter M. N. , Gille J. C. , Edwards D. P. , Attié J.‐L. , Warner J. , Ziskin D. , Francis G. , Khattatov B. , Yudin V. , Lamarque J.‐F. , Ho S.‐P. , Mao D. , Chen J. S. , Drummond J. , Novelli P. , Sachse G. , Coffey M. T. , Hannigan J. W. , Gerbig C. , Kawakami S. , Kondo Y. , Takegawa N. , Schlager H. , Baehr J. , Ziereis H.
Published: February 2004

Validation of the Measurements of Pollution in the Troposphere (MOPITT) retrievals of carbon monoxide (CO) has been performed with a varied set of correlative data. These include in situ observations from a regular program of aircraft observations at five sites ranging from the Arctic to the tropical South Pacific Ocean. Additional in situ profiles are available from several short‐term research campaigns situated over North and South America, Africa, and the North and South Pacific Oceans. These correlative measurements are a crucial component of the validation of the retrieved CO profiles and columns from MOPITT. The current validation results indicate good quantitative agreement between MOPITT and in situ profiles, with an average bias less than 20 ppbv at all levels. Comparisons with measurements that were timed to sample profiles coincident with MOPITT overpasses show much less variability in the biases than those made by various groups as part of research field experiments. The validation results vary somewhat with location, as well as a change in the bias between the Phase 1 and Phase 2 retrievals (before and after a change in the instrument configuration due to a cooler failure). During Phase 1, a positive bias is found in the lower troposphere at cleaner locations, such as over the Pacific Ocean, with smaller biases at continental sites. However, the Phase 2 CO retrievals show a negative bias at the Pacific Ocean sites. These validation comparisons provide critical assessments of the retrievals and will be used, in conjunction with ongoing improvements to the retrieval algorithms, to further reduce the retrieval biases in future data versions.
Effects of crustal heterogeneity on the morphology of chasmata, Venus
Authors: Bleamaster Leslie F. , Hansen Vicki L.
Published: February 2004

The Ix‐Chel, Kuanja, and Vir‐ava Chasmata (IKVC) are a 7000‐km‐long collection of discontinuous topographic troughs and deformation suites. Collectively, they account for approximately 12.5% of the ∼55,000 linear km of chasmata on Venus; however, morphologically the IKVC differs significantly from the majority (75%) of Venusian chasmata because it lacks corona features. Coronae represent notable volumes of material both erupted onto the surface and intruded into the crust. Together with chasmata, coronae may also be important indicators of Venus's interior convective processes as well as significant contributors to Venus's heat loss. Although IKVC lacks coronae, detailed geologic and structural mapping along its length highlights previously unrecognized structural and volcanic relationships indicative of local uplift, collapse, and volcanism we call pseudocoronae. In light of this mapping, previous corona formation models (theoretical and numerical) are evaluated, and an amended hypothesis (diapir stagnation) is presented for pseudocorona formation. The diapir stagnation model proposes that variations of the crustal thickness perturb corona formation and thus affect their resultant surface morphology. Chasmata are accompanied by corona development when forming in regions of relatively thin, or normal (plains‐type), crust (<20 km) but lack corona features when influenced by crustal heterogeneities (mechanical and chemical) at depth associated with thick crustal plateau roots (35–80 km (e.g., Ovda, Thetis, and Phoebe Regios)). Beneath crustal plateaus, diapiric rise is inhibited by (1) the presence of a low‐density crustal keel that creates a deep‐seated density trap and (2) a composition‐dependent mechanically weak crust‐mantle boundary layer. Diapir stagnation can be characterized or accompanied by minimal broad doming of the surface, formation of radial and concentric extension structures, lateral dike propagation, and collapse, all of which may be accompanied by limited volume surface eruptions of the lowest density melt phases. Through time, the crust‐mantle boundary layer may repeatedly lift and subside through conductive heating and viscous flow, which may allow more voluminous melt migration and eruption; however, true coronae fail to develop.
Microwave dielectric loss in oxides: Theory and experiment
Authors: Aupi Xavi , Breeze Jonathan , Ljepojevic Neboysha , Dunne Lawrence J. , Malde Nishil , Axelsson Anna-Karin , Alford Neil McN.
Published: February 2004

We present a model that provides a description of the microwave dielectric loss in oxides. The dielectric loss (tan δ) in single crystal and polycrystalline MgO and Al2O3 is measured over the temperature range 70–300 K. We are able to model the dielectric loss in terms of a two-phonon difference model. There are two key parameters in this model: The third derivative, φ3, of the lattice potential and the linewidth, γ, of the thermal phonons. In polycrystalline samples, rather than considering the different mechanisms of extrinsic loss, it is assumed that the main effect of extrinsic factors is a modification of the linewidth of the thermal phonons. By varying γ(T), it is shown that the model can describe the loss in both single crystals and polycrystallines materials. In single crystal and polycrystalline MgO, we use γ as a fitting parameter. In single crystal and polycrystalline Al2O3, we obtain γ(T) by Raman spectroscopy. The theory gives the right order of magnitude of the measured loss.
Photoluminescence study of low temperature epitaxial growth Yb-doped AlxGa1−xAs
Authors: Sato K. , Takamasu T. , Kido G.
Published: February 2004

Yb-doped AlxGa1−xAs (x=0–1) was fabricated by low temperature epitaxial growth using a molecular beam epitaxy method. Photoluminescence (PL) measurements were performed in a temperature range between 1.6 and 150 K. Three sharp PL peaks due to intra-4f transition of Yb were observed around λ=1 μm in samples with x⩾0.3, whereas samples with x<0.3 show no PL peak in this region. Irrespective of wide variety of the Al contents x, PL intensities of these peaks show a similar rapid thermal quenching above 100 K. Furthermore, a broad and intense PL band was found at around 1.4 eV.
Resonant Raman effect enhanced by surface plasmon excitation of CdSe nanocrystals embedded in thin SiO2 films
Authors: Brioude A. , Bellessa J. , Rabaste S. , Champagnon B. , Sphanel L. , Mugnier J. , Plenet J. C.
Published: February 2004

In this article, the Raman signal of CdSe nanocrystals well dispersed in a very thin SiO2 film (20 nm) has been investigated by surface plasmon excitation in a resonant Raman spectroscopy experiment. In order to perform the excitation, the thin SiO2 layer containing nanocrystals is deposited on a well-defined silver layer. The surface plasmon excitation increases the sensitivity of the Raman experiment, compared to the conventional setup, and allows the observation of a small number of nanocrystals (around 5000). The luminescence has also been measured and its dependence with the separation between the metal layer and CdSe nanocrystals is analyzed. In particular the quenching of the luminescence for thin film has been used to obtain only the Raman signal in resonant configuration.
On the scaling of thermal stresses in passivated nanointerconnects
Authors: Sharma P. , Ganti S. , Ardebili H. , Alizadeh A.
Published: February 2004

Much work has been done in the approximation of the stress state of microelectronic interconnects on chips. The thermally induced stresses in passivated interconnects are of interest as they are used as input in interconnect reliability failure models (stress-driven void growth, electromigration-driven void growth). The classical continuum mechanics and physics typically used is, however, intrinsically size independent. This is in contradiction to the physical fact that at the size scale of a few nanometers, the elastic state is size dependent and a departure from classical mechanics is expected. In this work, we address the various physical causes (and the affiliated mathematical modeling) of the size dependency of mechanical stresses in nanointerconnects. In essence, we present scaling laws for mechanical stresses valid for nanosized interconnects.
Effect of ultraviolet–ozone treatment of indium–tin–oxide on electrical properties of organic light emitting diodes
Authors: Kim Soo Young , Lee Jong-Lam , Kim Ki-Beom , Tak Yoon-Heung
Published: February 2004

We report the change of surface electronic structure of indium–tin–oxide (ITO) as a function of ultraviolet (UV)–ozone treatment time. The voltage of organic light emitting diodes at a current density of 100 mA/cm2 was reduced as the surface treatment time using UV–ozone was lengthened. X-ray photoelectron spectroscopy results showed that the relative concentration of carbon atoms decreased, but oxygen concentration increased relatively with UV–ozone treatment. This led to the increase in the ITO work function via the reduction of operation voltage.
Modeling a resistive wall mode control system of the bang–bang type
Authors: Jensen T. H.
Published: February 2004

Feedback stabilization of the resistive wall mode is usually accomplished by using linear amplifiers. In this paper a study is made of a possibility of controlling resistive wall modes using switches instead of linear amplifiers, i.e., using bang–bang control. The motivation is that bang–bang control systems may be cheaper than conventional feedback systems. A distinct disadvantage of the bang–bang system is complexity due to its inherent nonlinearity. Further studies, particularly of engineering issues, are needed to determine the attractiveness of a bang–bang system.
Bose–Einstein condensation and intermediate state of the photon gas
Authors: Tsintsadze Levan N.
Published: February 2004

The possibility of the establishment of equilibrium between a photon and a dense photon bunch is studied. The condition of production of the Bose–Einstein condensate is obtained in the case when the density of plasma does not change. It is shown that the inhomogeneity of density of photons leads to a new intermediate state of the photon gas.
Low to high confinement transition theory of finite-beta drift-wave driven shear flow and its comparison with data from DIII-D
Authors: Guzdar P. N. , Kleva R. G. , Groebner R. J. , Gohil P.
Published: February 2004

Shear flow stabilization of edge turbulence in tokamaks has been the accepted paradigm for the improvement in confinement observed in high (H) confinement mode plasmas. Results on the generation of zonal flow and fields in finite β plasmas are presented. This theory yields a criterion for bifurcation from low to high (L–H) confinement mode, proportional to Te/Ln, where Te is the electron temperature and Ln is the density scale-length at the steepest part of the density gradient. When this parameter exceeds a critical value (mostly determined by the strength of the toroidal magnetic field), the transition occurs. The predicted threshold based on this parameter shows good agreement with edge measurements on discharges undergoing L–H transitions in DIII-D [J. L. Luxon, R. Anderson, F. Batty et al., in Proceedings of the 11th Conference on Plasma Physics and Controlled Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. The observed differences in the transitions with the reversal of the toroidal magnetic field are reconciled in terms of this critical parameter due to the differences in the density gradient scale-lengths in the edge. The theory also provides a possible explanation for lowered threshold power, pellet injection H modes in DIII-D, thereby providing a unified picture of the varied observations on the L–H transition.
Tuned transition from a quantum well to a quantum wire investigated by magnetophonon resonance
Authors: Schneider D. , Brink C. , Schlachetzki A. , Ploner G. , Strasser G. , Gornik E.
Published: February 2004

This article describes experimental investigations of the transition from a two-dimensional electron gas to a quasi-one-dimensional quantum wire by the magnetophonon effect, tuned by Schottky gates in GaAs/AlGaAs. We present a model of the depletion region linked to the gates. The measurements allow the band-edge effective mass to be determined from two to one dimension between 89.5 and 348 K. We performed the measurements with a single, isolated quantum wire in magnetic fields up to 17 T.
Regular and stochastic orbits of ions in a highly prolate field-reversed configuration
Authors: Landsman A. S. , Cohen S. A. , Glasser A. H.
Published: February 2004

Ion dynamics in a field-reversed configuration are explored for a highly elongated device, with emphasis placed on ions having positive canonical angular momentum. Due to angular invariance, the equations of motion are that of a two degree-of-freedom system with spatial variables ρ and ζ. As a result of separation of time scales of motion caused by large elongation, there is a conserved adiabatic invariant, Jρ, which breaks down during the crossing of the phase-space separatrix. For integrable motion, which conserves Jρ, an approximate one-dimensional effective potential was obtained by averaging over the fast radial motion. This averaged potential has the shape of either a double or single symmetric well centered about ζ=0. The condition for the approach to the separatrix and therefore the breakdown of the adiabatic invariance of Jρ is derived and studied under variation of Jρ and conserved angular momentum, πφ. Since repeated violation of Jρ results in chaotic motion, this condition can be used to predict whether an ion (or distribution of ions) with given initial conditions will undergo chaotic motion.
Fabrication of ferromagnetic nanocluster rods by magnetic trapping
Authors: Huh Seung H. , Nakajima Atsushi , Kaya Koji
Published: February 2004

In a one-pot fabrication at room temperature, both an iron-neodymium-dysprosium-boron permanent magnet (Fe66Nd28Dy4B1) and cobalt (Co) metal have been directly converted into the corresponding ferromagnetic nanometer-scale cluster (nanocluster) rods using pulsed-laser ablation combined with magnetic-field trapping. The morphology of the produced nanomaterials was analyzed by electron microscopy and the composition by electron energy-loss spectroscopy, and it was found that one-dimensional structured soft magnets, up to ∼150 nm in length, consist of magnetic clusters a few nanometers in diameter. The mechanism and driving behind their growth process and their magnetic evolution have been proposed.
The interaction of error fields and resistive wall modes
Authors: Gimblett C. G. , Hastie R. J.
Published: February 2004

An investigation is presented of the effect of an error field on the growth of a resistive wall mode (RWM). This issue is of importance to many toroidal confinement devices, but particularly to the proposed International Thermonuclear Experimental Reactor (ITER) [ITER Physics Basis, Nucl. Fusion 39, 2175 (1999)], where if advanced tokamak performance is required, then the RWM instability is especially vulnerable. The paper includes a discussion of error field amplification when RWM marginal stability is approached, and it is pointed out that error field current is the fixed quantity in this calculation, not the error field flux, which is essentially an eigenvalue of the calculation. The key issue concerns the effect of plasma rotation on the RWM. The distinction is made between the resistive wall tearing mode (RWTM), which is stabilized by modest plasma rotation, and the ideal RWM, which is not. The importance of the joint torques that are present when an error field and an RWM of the same helicity coexist is investigated. Using torque balance a simulation is presented of the effect of reducing error field amplitude on the duration of a stable discharge. This shows features in accord with experimental observations from the DIII-D device [J. L. Luxon et al., Plasma Physics and Controlled Fusion Research (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p.159].
Scaling of forced magnetic reconnection in the Hall-magnetohydrodynamic Taylor problem
Authors: Fitzpatrick Richard
Published: February 2004

Two-dimensional, incompressible, zero guide-field, nonlinear Hall-MHD (magnetohydrodynamical) simulations are used to investigate the scaling of the rate of forced magnetic reconnection in the so-called Taylor problem. In this problem, a small-amplitude boundary perturbation is suddenly applied to a tearing stable, slab plasma equilibrium; the perturbation being such as to drive magnetic reconnection within the plasma. This type of reconnection, which is not due to an intrinsic plasma instability, is generally known as “forced reconnection.” The inclusion of the Hall term in the plasma Ohm’s law is found to greatly accelerate the rate of magnetic reconnection. In the linear Hall-MHD regime, the peak instantaneous reconnection rate is found to scale like dΨ/dt∼diη1/3Ⅺ0, where Ψ is the reconnected magnetic flux, di the collisionless ion skin depth, η the resistivity, and Ⅺ0 the amplitude of the boundary perturbation. In the nonlinear Hall-MHD regime, the peak reconnection rate is found to scale like dΨ/dt∼di3/2Ⅺ02.
Selective excitation of erbium in silicon-infiltrated silica colloidal photonic crystals
Authors: Kalkman J. , de Bres E. , Polman A. , Jun Y. , Norris D. J. , ’t Hart D. C. , Hoogenboom J. P. , van Blaaderen A.
Published: February 2004

Optically active erbium ions in the silica and silicon sections of a Si-infiltrated silica colloidal photonic crystal can be separately addressed. A face-centered cubic colloidal crystal composed of 860 nm silica colloids was made by self-assembly under controlled drying conditions. It was then infiltrated with Si using chemical vapor deposition at 550 °C. Next, the photonic crystal was doped with erbium ions by 2 MeV ion implantation. The erbium ions were activated by thermal anneals at 400 and 750 °C, and showed clear photoluminescence at 1.5 μm in both the Si and silica parts of the photonic crystal. By varying measurement temperature and excitation wavelength the erbium ions were selectively excited in Si and/or silica. In this way the local optical density of states in these photonic crystals can be selectively probed. The emission linewidth for Er3+ in crystalline Si is relatively narrow and fits well within the calculated photonic band gap. The long luminescence lifetime of Er in Si makes these photonic crystals an ideal geometry to measure effects of the optical density of states on spontaneous emission.