bluuebunny/crossref_metadata_2025 huggingface dataset:
Current flow through high‐voltage sheaths observed by the TEMAG Experiment during TSS‐1R
Authors: Mariani F. , Candidi M. , Orsini S. , Terenzi R. , Agresti R. , Musmann G. , Rahm M. , Acuña M. , Panetta P. , Ness N. F. , Neubauer F.
Published: February 2004

During the TSS‐1R flight, conditions occurred under which very intense currents flowed through the tether wire system. The effect of these currents during the active phases of operation was clearly seen by the TEMAG sensor assembly located on the short, fixed satellite boom. Magnetic signatures appeared on the field components parallel to the boom and to the spin axis with a strong peak when the boom points closer to the ram direction. While a toroidal current flowing on the ram side of the plasma sheath may explain the main features seen by the TEMAG outboard sensor, further studies are needed for the physical interpretation of the complex electrodynamic interactions of the TSS‐ionosphere system.
Applicability of wavelet algorithm for geophysical viscoelastic flow
Authors: Vasilyev Oleg V. , Yuen David A. , Podladchikov Yuri Yu.
Published: February 2004

This paper introduces a newly developed wavelet technique for modeling of geophysical flow processes in multiple dimensions. The method utilizes the idea of collocation with the multilevel wavelet approximation. The multilevel structure of the algorithm facilitates the computational adaptation of the grid refinement in regions where sharp variations occur. We have tested this algorithm for viscoelastic flows with viscosity contrasts up to 1012. We have confirmed the findings of stress amplification in the thin highly viscous layer. The new method allows us to conduct the calculations for thin layers and high viscosity contrasts, close enough for realistic mantle‐lithospheric interaction. Our results demonstrate the potential usefulness of the wavelet technique in large‐scale numerical simulations in the geosciences.
Methyl chloride formation by gas phase thermal chlorine atom reaction with methyl iodide and methyl bromide
Authors: Goliff Wendy S. , Rowland F. Sherwood
Published: February 2004

Thermal chlorine atoms react with gaseous CH3I and CH3Br at 295K to produce CH3Cl with yields of 8.6% and 0.6%, respectively. The studies utilized radioactive 38Cl formed by the 37Cl (n,γ) 38Cl nuclear reaction in gaseous CClF3 at pressures from 760 to 4,000 torr. The initially energetic 38Cl atoms are thermalized by multiple inelastic collisions with CClF3 prior to reaction with the methyl halide. The reaction rate constant for thermal chlorine attack on CH3Br to form CH3Cl at 295K and 1–5 atmospheres pressure is (2.0±0.5) × 10−15 cm³ molecule−1 s−1. The substitution of Cl for Br/I in a methyl halide molecule cannot be a significant source of atmospheric CH3Cl because of its abundance from other sources. However, the replacement of I by Cl in other iodohalocarbons might in some cases provide a marker for the presence of atomic chlorine.
Array tracking of the volcanic tremor source at Deception Island, Antarctica
Authors: Almendros J. , Ibáñez J. M. , Alguacil G. , Del Pezzo E. , Ortiz R.
Published: February 2004

We have found experimental evidence which shows that the volcanic tremor recorded at Deception Island (South Shetland Islands, Antarctica) is a superposition in time of overlapping hybrid events. We studied data from a small aperture seismic array. Data analysis for tremor and hybrids included: (1) spectral analysis; (2) apparent slowness and back‐azimuth determination by using the zero‐lag cross‐correlation method; and (3) polarization analysis. Both types of events share these common features: (a) two dominant spectral bands at frequencies 1–3 Hz (the most energetic) and 4–8 Hz; (b) several coherent phases with the same back‐azimuth to the source and apparent slowness along the whole signal; (c) in the high frequency band, the apparent slowness is very low (around 0.17 s/km), indicating the propagation of body waves; (d) in the low frequency band, the apparent slowness is high (around 1.6 s/km), consistent with the presence of surface waves; and (e) clear P‐wave onset followed by a complex pattern of Rayleigh waves. Therefore, both types of events are strongly related because they share the same source region, the same wave‐propagation properties, and the same wave composition. Moreover, several arrivals, that resemble a single hybrid event, have been found along the tremor signals. Due to these reasons, we hypothesize that volcanic tremor of Deception Island is a superposition of hybrid type events. The source of both types could be the interaction between thaw water and hot materials in a shallow aquifer.
Retrieval of contrail microphysical properties during SUCCESS by the split‐window method
Authors: Duda David P. , Spinhirne James D. , Hart William D.
Published: February 2004

Estimates of cloud particle size and infrared optical depth were inferred from multi‐spectral observations of contrails and cirrus during the SUbsonic aircraft: Contrails and Cloud Effects Special Study (SUCCESS) experiment on 20 April 1996. The particles in a newly formed contrail were generally smaller than those in an older contrail, while the microphysics of the older contrail resembled the surrounding cirrus. Split‐window retrievals of contrails were sensitive to changes in surface temperature and surface emissivity.
Ice‐age cycles: Earth's rotation instabilities and sea‐level changes
Authors: Sabadini R. , Vermeersen L. L. A.
Published: February 2004

A new class of multilayered, viscoelastic Earth models based on PREM is applied to the modeling of Earth's rotation instabilities and associated sea‐level changes, induced by the occurrence of Pleistocene ice‐age cycles that match the oxygen isotope records over the last 0.8 Myr. The novelty of our approach stands on the usage, for the first time in post‐glacial rebound induced sea‐level studies, of a fully analytical scheme based on normal mode theory that allows to deal with complexities of the real Earth, such as lithospheric and mantle layering, sphericity and self‐gravitation. The ice models are based on ICE‐3G.

Our results show that differences in true polar wander (TPW) and TPW‐induced sea‐level changes between Earth models with a few layers and models having enough layers so that saturated continuum limits are reached, can amount factors 2 to 3. This may change conclusions derived from some earlier studies on polar wander induced changes in climate, that were based on Earth models with a limited amount of layers. The results indicate that models containing about 15 layers with a stratified lower mantle and transition zone have reached saturated continuum responses for both TPW and TPW‐induced sea‐level changes. Stratification of the lithosphere is not important. This is in contrast with the sensitivity of post‐seismic deformation models. This difference in sensitivity on the radial profile of the Earth model can be explained with simple arguments on the dependence on zonal degree.
Observations of double discontinuities in the magnetotail
Authors: Whang Y. C. , Fairfield D. , Smith E. J. , Lepping R. P. , Kokubun S. , Saito Y.
Published: February 2004

Observations of slow shocks in the Earth's magnetotail at the plasma sheet‐lobe boundaries have been well documented. We restudy the magnetic field data of two slow shocks: one was observed from Geotail on January 17, 1994 at XGSE = −92 RE, and another was observed from ISEE‐3 on February 2, 1983 at XGSE = −220 RE. In both cases, the slow shock layer was followed by an adjoining rotational discontinuity layer on the postshock side. Compound structures each composed of a slow shock layer and an adjoining rotational discontinuity layer have been recently observed in interplanetary space from Wind, Geotail and Imp‐8. Because the two successive discontinuities are very close to each other, the compound structure looks like a new kind of MHD discontinuity. It may be called a double discontinuity. Since double discontinuities exist not only in interplanetary space but also in the magnetotail region, they could be a general MHD structure in space plasma.
Cooling mechanisms and an approximate thermal budget for the 1991–1993 Mount Etna lava flow
Authors: Wooster M. J. , Wright R. , Blake S. , Rothery D. A.
Published: February 2004

The 1991–1993 eruption of Mount Etna, Sicily built a 7.2 km² aa lava flow field within the Valle del Bove. This letter provides estimates of the power losses associated with various cooling mechanisms operating during the development of the flow field, derived from time‐series analysis of nighttime satellite remote sensing data. Unlike sensors used in many previous remote sensing studies of active lava, the ERS‐1 Along Track Scanning Radiometer (ATSR) provides unsaturated measurements of spectral radiance from even very hot surfaces. This allows for more accurate solution of the lava flow endmember thermal components. We find that radiative and conductive processes dominated, with our model suggesting energy losses of similar magnitude. Radiative losses peaked about one month into the eruption, when lava flowed in open channels. Conductive losses peaked after two months, with a marked decline caused by a significant decrease in the horizontal spreading rate of lava. By the end of the eruption the 235 × 106 m³ of erupted lava is estimated to have lost only 28% of its initial thermal energy. A further 6.5 × 1017 J must be lost before the lava reaches ambient temperature.
Small comets: Naked‐eye visibility
Authors: Rizk Bashar , Dessler A. J.
Published: February 2004

We investigate an obvious consequence of the small‐comet hypothesis. We find that the 30‐ton cloud of water‐ice particles formed by a small comet would survive long enough to be an unmistakably bright object. The visual magnitude of such clouds would be between that of a bright star and the full Moon. A whole‐Earth small‐comet flux of 20/min implies the sudden appearance of at least two bright patches of light every five minutes. The two‐hour periods after sunset and before sunrise ought to produce the most spectacular sightings—intermittent punctuations of bright rapidly‐moving points of light. Because such events are not reported, we conclude that this class of object does not exist in detectable numbers.
Observations of an enhanced convection flow channel for northward turning IMF
Authors: Nilsson H. , Yamauchi M. , Mukai T. , Yamamoto T. , Moretto T.
Published: February 2004

A detailed case study of the excitation of a more than 200 km wide flow channel with ionospheric drift speeds exceeding 2 kms−1 is presented. The flow channel is excited during a slowly northward turning IMF and strong IMF By conditions. A brief southward spike in the IMF moves the flow channel equatorward. Thereafter the enhanced flow decreases, consistent with a decreasing IMF By component. The presence and location of the flow channel appear to be entirely determined by the IMF conditions. The flow channel is distinctly different from the poleward propagating convection disturbances associated with strong IMF By for strongly southward IMF Bz.
Ice‐rafted debris in the North Pacific and correlation to North Atlantic climatic events
Authors: Hewitt Antony T. , McDonald Darcy , Bornhold Brian D.
Published: February 2004

A high‐resolution record of the flux of ice‐rafted debris in deep‐sea cores from the Northeast Pacific indicates that the major interstadials that punctuated the last glaciation are concurrent between the North Pacific and the North Atlantic. In the North Atlantic these major interstadials immediately followed episodes of massive iceberg discharge, thought to result from extensive collapse of the Laurentide icesheet. A mechanistic scenario is presented to explain how collapse of the Laurentide icesheet could cause concurrent interstadials between the two oceans.
Observations of Hurricane Hortense with two over‐the‐horizon radars
Authors: Harlan J. A. , Georges T. M.
Published: February 2004

Hurricane Hortense was observed in the Atlantic Ocean on 12 September 1996 by two high‐frequency over‐the‐horizon radars in Texas and Virginia, looking at backscatter from the ocean surface. Dual radar coverage permits construction of an unambiguous surface‐wind‐direction field and a vector surface‐current field with about 15‐km resolution in the storm's vicinity. The known location of a storm band coincides with a region of surface convergence indicated by the radar. The surface‐current field lags the wind field by about 3 h and shows the strongest ocean response to the right of the storm track, with near‐inertial rotation in the storm's wake. Analysis of surface‐wave directionality shows that it depends on the recent wind‐direction history at each point.
The first real‐time worldwide ionospheric predictions network: An advance in support of spaceborne experimentation, on‐line model validation, and space weather
Authors: Szuszczewicz E. P. , Blanchard P. , Wilkinson P. , Crowley G. , Fuller‐Rowell T. , Richards P. , Abdu M. , Bullett T. , Hanbaba R. , Lebreton J. P. , Lester M. , Lockwood M. , Millward G. , Wild M. , Pulinets S. , Reddy B. M. , Stanislawska I. , Vannaroni G. , Zolesi B.
Published: February 2004

We report on the first realtime ionospheric predictions network and its capabilities to ingest a global database and forecast F‐layer characteristics and “in situ” electron densities along the track of an orbiting spacecraft. A global network of ionosonde stations reported around‐the‐clock observations of F‐region heights and densities, and an on‐line library of models provided forecasting capabilities. Each model was tested against the incoming data; relative accuracies were intercompared to determine the best overall fit to the prevailing conditions; and the best‐fit model was used to predict ionospheric conditions on an orbit‐to‐orbit basis for the 12‐hour period following a twice‐daily model test and validation procedure. It was found that the best‐fit model often provided averaged (i.e., climatologically‐based) accuracies better than 5% in predicting the heights and critical frequencies of the F‐region peaks in the latitudinal domain of the TSS‐1R flight path. There was a sharp contrast, however, in model‐measurement comparisons involving predictions of actual, unaveraged, along‐track densities at the 295 km orbital altitude of TSS‐1R. In this case, extrema in the first‐principle models varied by as much as an order of magnitude in density predictions, and the best‐fit models were found to disagree with the “in situ” observations of Ne by as much as 140%. The discrepancies are interpreted as a manifestation of difficulties in accurately and self‐consistently modeling the external controls of solar and magnetospheric inputs and the spatial and temporal variabilities in electric fields, thermospheric winds, plasmaspheric fluxes, and chemistry.
Seismic attenuation in a partially saturated, artificial crack due to restricted contact line motion
Authors: Waite W. , Moerig R. , Spetzler H.
Published: February 2004

Attenuation and stiffness measurements have been made on partially saturated, artificial cracks over the frequency range 2 mHz to 10 Hz. The wedge‐shaped cracks are open systems composed of glass slides separated by wires. A non‐zero, frequency independent attenuation has been measured at low frequencies for these cracks. Additionally, the low frequency stiffness of a partially saturated crack is larger than that of a dry crack. For this geometry and frequency range, no dissipative fluid flow is expected. Local fluid flow models predict zero attenuation and no stiffening for these open systems. We have developed a model based on the restricted motion of the fluid meniscus to explain the measured low frequency results. In this model, physicochemical interactions between the fluid and solid are responsible for restricting motion of the three phase boundary between liquid, solid and gas (the contact line). We compare model predictions with data measured in artificial cracks partially saturated with deionized water. Contact line mobility is varied by exposing the crack surfaces to increasing concentrations of sodiumdodecylsulfate (SDS) in deionized water. Increases in low frequency attenuation (below .1 Hz) and crack stiffness correlate with increasing surface exposure to SDS. These measured trends can be qualitatively modeled by reducing meniscus mobility as the surface contamination increases.
The photochemistry of acetone in the upper troposphere: A source of odd‐hydrogen radicals
Authors: McKeen S. A. , Gierczak T. , Burkholder J. B. , Wennberg P. O. , Hanisco T. F. , Keim E. R. , Gao R.‐S. , Liu S. C. , Ravishankara A. R. , Fahey D. W.
Published: February 2004

This paper summarizes measured photodissociation quantum yields for acetone in the 290‐320 nm wavelength region for pressures and temperatures characteristic of the upper troposphere. Calculations combine this laboratory data with trace gas concentrations obtained during the NASA and NOAA sponsored Stratospheric Tracers of Atmospheric Transport (STRAT) field campaign, in which measurements of OH, HO2, odd‐nitrogen, and other compounds were collected over Hawaii, and west of California during fall and winter of 1995/1996. OH and HO2 concentrations within 2 to 5 km layers just below the tropopause are ∼50% larger than expected from O3, CH4, and H2O chemistry alone. Although not measured during STRAT, acetone is inferred from CO measurements and acetone‐CO correlations from a previous field study. These inferred acetone levels are a significant source of odd‐hydrogen radicals that can explain a large part of the discrepancy in the upper troposphere. For lower altitudes, the inferred acetone makes a negligible contribution to HOx (HO+HO2), but influences NOy partitioning. A major fraction of HOx production by acetone is through CH2O formation, and the HOx discrepancy can also be explained by CH2O levels in the 20 to 50 pptv range, regardless of the source.
Tropospheric sulfate distribution during SUCCESS: Contributions from jet exhaust and surface sources
Authors: Dibb Jack E. , Talbot Robert W. , Loomis Matthew B.
Published: February 2004

The distribution of SO4= aerosol over the central US during SUCCESS indicates that surface sources of SO4= and SO2 in the western US caused SO4= enhancements up to 10 km altitude. The mean (median) SO4= mixing ratio in the mid‐ and upper‐troposphere increased from 24 (16) pptv over the Pacific ocean to 58 (29) pptv over the central plains. Above 10 km the SO4= mixing ratio was essentially the same in both regions, and also when the geographic classifications were further partitioned into upper tropospheric and lower stratospheric categories (mean near 40 pptv). No obvious enhancements of SO4= could be detected in jet exhaust plumes, but this may reflect the difficulty of keeping a large airborne sampling platform within a turbulent wake for time periods longer than a few seconds. Expected SO4= enhancements (based on observed CO2 enhancements and emission factors for these two species) were generally much smaller than the variability of ambient SO4= mixing ratios, so our null result does not mean that aircraft do not emit H2SO4.
Predicted electron precipitation for a filled loss cone at the top of the auroral electron acceleration region
Authors: Calvert W.
Published: February 2004

The electron precipitation flux and energy flux for a filled loss cone at the top of the auroral electron acceleration region have been calculated for the actual height for the top of the acceleration region. The resulting flux and energy flux are thus found to be more than sufficient to account for the aurora, thereby contradicting Knight's well‐known theory for electron precipitation during an auroral substorm.
A comparison of different techniques for relative paleointensity
Authors: Valet Jean‐Pierre , Meynadier Laure
Published: February 2004

Parallel relative paleointensity records that are supposed to display the same geomagnetic variations often show discrepancies. We compared various techniques of normalization with different parameters involving alternating fields (a.f.) and thermal demagnetization of sediment samples spanning the same period from the Indian and the Pacific oceans. The results are basically unchanged using any technique. There is also no causal relationship between changes in rock magnetic properties and mismatch between the two records. Thus, discrepancies between parallel records do not depend on methods for relative paleointensity, and any technique can be used with confidence, provided that the characteristic component has been properly isolated and the sediments are magnetically homogeneous. Complications are more likely due to subtle variations in the sediment remanent magnetization acquisition. These results point to the importance of sedimentological (lithology and physical properties) factors in controling the process of magnetization.
Transverse z‐mode waves in the terrestrial electron foreshock
Authors: Bale S. D. , Kellogg P. J. , Goetz K. , Monson S. J.
Published: February 2004

We examine the phase relation between two orthogonal electric field components for several hundred waveform measurements of intense electron plasma waves in the terrestrial electron foreshock. In general, the phase shift at the carrier frequency is not zero or π as would be expected if the waves were purely electrostatic Langmuir waves, but is a function of the angle between the antennas and the interplanetary magnetic field (IMF). When the antennas are field aligned, the phase shift between the components is large; this value recedes smoothly to zero as the antenna is rotated away from the IMF direction. When solar wind density fluctuations are considered, this is consistent with the dispersion of the electromagnetic z‐mode and we assert that the electron foreshock is populated by transverse z‐mode waves, not purely longitudinal Langmuir waves. This has implications for conversion to freely propagating modes and large‐amplitude saturation mechanisms.
The origin of magnetic anomalies in lower crustal rocks, Labrador
Authors: Kletetschka Günther , Stout James H.
Published: February 2004

Mid‐ to lower crustal granulites near Wilson Lake in Central Labrador exhibit pronounced aeromagnetic anomalies. Areas characterized by high and low field strength correlate with the Wilson Lake allochthon and the surrounding autochthon respectively. The induced magnetization in both units has mean values of 0.34 A/m (allochthon) and 0.33 A/m (autochthon). However, the mean values of remanent magnetizations are 9.2 A/m (allochthon) and 3.3 A/m (autochthon) in directions contributing to the present geomagnetic field. Therefore, the remanent magnetization plays the main role in generating the observed magnetic anomaly. Thermal demagnetizations indicate that titanhematite is stable to 585–600 °C. The absence of significant Verwey transitions indicates that titanhematite is the predominant carrier in some rocks and a significant carrier along with magnetite in others. Any interpretation of the magnetic anomalies above these rocks must consider magnetic remanence as the principle anomaly source.
Using the sunspot cycle to date ice cores
Authors: Steig Eric J. , Morse David L. , Waddington Edwin D. , Polissar Pratigya J.
Published: February 2004

For many ice cores, the snow accumulation rate is too low to preserve annual stratigraphy, precluding direct measurement of annual layer thickness. For selected Holocene sections of the Taylor Dome core, East Antarctica, we instead use high‐resolution 10Be measurements to establish a nominal 11‐year thickness, taking advantage of the solar cycle in cosmogenic isotope production. We compare measured thicknesses with the layer thickness profile predicted by a finite element ice flow model. The results are in good agreement, supporting the assumption that the length of the solar cycle has remained essentially constant throughout the Holocene. For ice cores where annual layers are not preserved, the 10Be 11‐year layer method can be used as an independent check on flow‐model estimates of layer thickness and to estimate past accumulation rates. It should be possible to accurately date ice cores by counting 11‐year layers detected with continuous high‐resolution 10Be measurements.
Phase transformations in serpentine and transportation of water into the lower mantle
Authors: Irifune Tetsuo , Kubo Norifumi , Isshiki Maiko , Yamasaki Yuji
Published: February 2004

Phase transformations in serpentine, the major hydrous mineral in the upper part of the subducting slabs, have been studied at pressures to 26 GPa and at temperatures between 500 and 1400°C. While serpentine completely dehydrates at temperatures higher than 600–800°C and at pressures to 12 GPa, phase assemblages including some dense hydrous magnesium silicates (DHMS) such as phases A, E, superhydrous B and D were formed at higher pressures. Phase D was found to possess a stability field of particularly wide pressure and temperature regime, suggesting that this phase may play an important role in transportation of water into the lower mantle via subduction of cold slabs.
Turbulence measurements by the DC‐8 Meteorological Measurement System
Authors: Chan K. R. , Dean‐Day J. , Bowen S. W. , Bui T. P.
Published: February 2004

The instrumentation of a new MMS on the NASA DC‐8 aircraft is briefly described. A method to compute the turbulent dissipation rate, ε, is discussed in light of some apparent inconsistencies between high and medium altitude aircraft data and available theory. Examples of turbulence measurements during encounters of a wake vortex, a field of wave clouds, and persistent contrails are illustrated.
Global and regional surface‐wave inversions: A spherical‐spline parameterization
Authors: Wang Zheng , Tromp Jeroen , Ekström Göran
Published: February 2004

A surface‐wave phase‐velocity inversion scheme based upon a compactly supported cubic B‐spline basis on a triangular grid of knots with approximately equal inter‐knot spacing is implemented to perform global, regional and variable resolution inversions. Numerical results show that the inverted phase‐velocity maps based upon this method are similar to those obtained using a global spherical‐harmonic representation. Nonlinear inversions incorporating ray refraction are feasible based upon the spherical‐spline model parameterization and the resulting maps are only slightly different from those based upon the great‐circle approximation. A multiresolution analysis is introduced to obtain finer resolution in regions with good ray coverage and lower resolution in regions with poor coverage.
What does control Vp/Vs in granular rocks?
Authors: Manificat Guillaume , Guéguen Yves
Published: February 2004

The compressionnal Vp and shear Vs velocities of rocks are known to depend on composition and porosity. In the case of high porosity, poorly consolidated dry rocks, [Winkler, 1983] showed that Vp/Vs is essentially constant and close to 1.56, in disagreement with theoretical predictions. Winkler suggested that this discrepancy could be attributed to either packing models or contact stiffnesses models. We have investigated first the influence of packing models using results derived directly for disordered packings [Digby, 1981] and for ordered ones. Identical Poisson's ratio values, lower than the experimental values, are obtained for close packings and random ones. This shows that the role of packing is a minor one. In agreement with the conclusion of [Palciauskas, 1992], the role of contact stiffnesses appears to be the main one. We show that experimental results can be explained by a simple and robust roughness model. Averaging over a distribution of microcontacts implies that only half of these contribute to shear so that the ratio of both stiffnesses has a value close to that previously derived by Palciauskas on the basis of a more complex oblique contact model. The observed average Poisson's ratio value of 0.14–0.15 and Vp/Vs value of 1.56 is a consequence of a symmetric asperity distribution and of the asymmetry of shear.
Role of the temperature ratio in the linear stability of the quasi‐neutral sheet tearing mode
Authors: Sitnov M. I. , Malova H. V. , Sharma A. S.
Published: February 2004

The linear stability criterion of the tearing mode in the magnetotail current sheet with nonzero normal component of the equilibrium magnetic field first obtained by Lembege and Pellat [1982] considered the electrons to be trapped in the current sheet. This condition is significantly modified when electron‐to‐ion temperature ratio is small, due to the contribution of transient orbits to the perturbed electron density integrated over the flux tube. In contrast to the previous result marginal stability may be reached under realistic conditions in the near‐Earth tail current sheet during late substorm growth phase.
DC electric field measurement in the SEEK Campaign
Authors: Nakamura M. , Noda H. , Yoshikawa I. , Iwagami N. , Hirahara M. , Yamamoto M. , Fukao S.
Published: February 2004

DC electric fields were measured by the Electric Field Detector ‐ Beam experiment (EFD‐B) onboard the sounding rocket S‐310‐26 above the E‐region ionosphere during the Sporadic‐E Experiment over Kyushu (SEEK) campaign. The sounding rocket was launched into the ionosphere when a strong quasi‐periodic (QP) echo structure appeared. The EFD‐B measured both the electric field and the magnetic field from X+169 s until X+232 s (altitude of 167 km to 173 km). Accuracy of the measurements were 0.19 mV/m for the electric field and 1.9 nT for the magnetic field. The magnetic field measurements were in very good agreement with a model field (IGRF 95). The electric fields, which were projections of the ionospheric electric fields to the altitude of the observation point along the magnetic field line, reached to 11.5 mV/m at maximum. The observed electric field is much larger than expected, and is associated with the 4 km periodic structure of the electric field which may be related to the atmospheric gravity wave activity in the E region.
Ion reflection by the TSS‐1R satellite
Authors: Papadopoulos K. , Chang C. ‐L. , Drobot A.
Published: February 2004

The results of the TSS‐1R mission generated several scientific puzzles. First the current collection was much more efficient than predicted on the basis of theoretical models, and previous laboratory and rocket experiments. Second, a sharp transition in the interaction physics occurred at threshold potentials between 5–10 V. Third, a significant population of suprathermal electrons, heated ionospheric ions, and enhanced plasma waves were observed in the ram direction, following the transition. The letter contains a preliminary examination of the extent to which these phenomena are related to the interaction of the impinging ambient ram O+ ions with the sheath surrounding the TSS satellite.
The role of extensional instability in creating Ganymede grooved terrain: Insights from Galileo High‐Resolution Stereo Imaging
Authors: Collins Geoffrey C. , Head James W. , Pappalardo Robert T.
Published: February 2004

Galileo stereo images covering about 1500 km² of Uruk Sulcus on Ganymede have revealed two scales of ridges; (1) large‐scale ridges and troughs spaced ∼6 km apart, corresponding to the “grooves” seen in Voyager images, and (2) small‐scale ridges spaced hundreds of meters apart superimposed on the large‐scale ridges. We interpret the small‐scale ridges to be the result of tilt‐block normal faulting of the surface brittle layer, while the large‐scale ridges may be due to necking of the brittle layer over a ductile substrate. The geometry of the tilt blocks revealed in Galileo images leads to a minimum estimation of 51% to 58% extensional strain in the area. The strain estimate, when incorporated into a model for the formation of grooved terrain by necking of a brittle layer undergoing extension, leads us to estimate a thermal gradient of ∼20 K/km and a strain rate of ∼10−14 s−1 during groove formation.
Factors influencing the locations of hot spots determined by the hot‐spotting technique
Authors: Wessel Paul , Kroenke Loren W.
Published: February 2004

Seafloor beneath hot‐spot‐produced seamounts have crustal flow lines that intersect at the hot spot locations, provided there is more than one stage rotation and that hot spots are stationary. Convolving seamount shapes with their associated flow lines yields an image of cumulative volcano amplitude (CVA). We call the technique of correlating local CVA maxima with hot spot locations “hot‐spotting”. This technique is geometrical and requires no age information for seamounts or seafloor. We analyze synthetic and actual seamount data and demonstrate that factors such as across‐trail scatter in seamount locations, inaccurate stage poles, and migration of hot spots all exert strong influences on the locations and appearances of CVA maxima. The interpretation of raw CVA images is therefore not straightforward.
Position determination of red sprites by scattering of VLF subionospheric transmissions
Authors: Rodger Craig J. , Dowden Richard L.
Published: February 2004

VLF sprites are identified by high angle scattering of VLF transmissions by the highly conducting plasma columns which are observed as the luminous structure of “red sprites”. By using multiple receivers and/or transmitters the location of the sprite plasma can be determined using existing VLF methods. It is shown that the complex electrical structure of sprites leads to uncertainties in the position determination. However, these are normally no more than the lateral width of the sprite structure itself.
Interstellar pickup hydrogen observations at large heliocentric distances
Authors: Mihalov J. D. , Gazis P. R.
Published: February 2004

Possible signatures of interstellar pickup hydrogen have been identified in data from the Pioneer 10 and 11 Ames plasma analyzers at locations out to beyond the orbit of Saturn, and at a wide range of longitudes in the heliosphere, both upstream and downstream in the interstellar wind. These signatures provide an extension of pickup ion observations out to beyond 15 AU heliocentric distance, including near where the maximum pickup hydrogen flux is expected. A depletion of interstellar pickup hydrogen downstream from the Sun in the interstellar flow may be indicated. These signatures are consistent with Ulysses pickup ion measurements.
Variations of carbon monoxide density in the total atmospheric column over Russia between 1970 and 1995: Upward trend and disturbances, attributed to the influence of volcanic aerosols and forest fires
Authors: Yurganov Leonid N. , Grechko Eugeny I. , Dzhola Anatoly V.
Published: February 2004

The analysis of total column spectroscopic CO observations over Russia revealed an upward linear trend between 1970 and 1995 with a rate of about 1.0 ppbv/year or 0.96%/year. A similar trend was reported earlier for the CO total column over Switzerland between 1950 and 1987. This rate is almost 3 times higher, than the rate of CO increase between 1920 and 1950, obtained from ice core data. Main disturbances of CO tropospheric concentration coincided with vast wildfires in the central Russia in 1972 and volcanic eruptions. Stratospheric volcanic aerosol probably influence the concentration of tropospheric OH radicals, which destroy CO molecules. The aerosol scatters photochemically active UV radiation and, in the same time, triggers the stratospheric ozone photochemical destruction. Diminished total column ozone UV absorption can offset the increase of UV scattering due to additional aerosol. Studying these processes is important for a prediction of further CO and OH long‐term variations in the global atmosphere.
Simple parameterization of the absorption of the solar Lyman‐alpha line
Authors: Chabrillat Simon , Kockarts Gaston
Published: February 2004

The absorption of the solar Lyman‐alpha line by the terrestrial atmosphere is calculated, taking in account the wavelength variations of the emission line and of the O2 cross‐section, as well as the temperature dependence of the cross‐section. A new parameterization is developed to reproduce in atmospheric models the results of this high‐resolution calculation, up to an attenuation of 1010 for the incident solar radiation. The error made in most of existing models when computing the Lyman‐alpha contribution to photo dissociation rates in the middle atmosphere, using a constant O2 cross‐section of 10−20 cm², is shown to be important and this can affect the loss rate of mesospheric constituents such as H2O or CH4.
Asymmetric multiple auroral arcs and inertial Alfvén waves
Authors: Trondsen T. S. , Cogger L. L. , Samson J. C.
Published: February 2004

High‐resolution optical observations by the University of Calgary Portable Auroral Imager show a frequent occurrence of asymmetric multiple small‐scale auroral arc structures during auroral substorms. Whereas the classical multiple arc array tends to exhibit a fairly symmetrical configuration, with parallel motions within individual discrete arcs being opposite in direction across the center of the arc array, the multiple arcs to be discussed herein are distinguished by the presence of discrete arcs strictly equatorward of the two bright counter‐streaming arcs that would ordinarily define the center of the arc array. The intensity of these parallel equatorward‐lying arcs were in most cases found to decrease rapidly in the equatorward direction. By considering the topology of the structures and the spacing between arcs, observations are found to be consistent with recent theories suggesting inertial Alfvén waves as a possible cause of fine‐scale auroral arcs.
Patterns of deep seismicity reflect buoyancy stresses due to phase transitions
Authors: Bina Craig R.
Published: February 2004

Thermal perturbation of mantle phase relations in subduction zones gives rise to significant buoyancy anomalies. Finite element modeling of stresses arising from these anomalies reveals transition from principal tension to compression near ∼400 km depth, down‐dip compression over ∼400–690 km (peaking at ∼550 km), and transition to rapidly fading tension below ∼690 km. Such features, even when complicated by olivine metastability, are consistent with observed patterns of deep seismicity. That such a simple model, neglecting all effects other than buoyancy anomalies due to temperature and to thermal perturbation of olivine phase relations, successfully generates so many observed features of deep seismicity suggests that these buoyancy anomalies are significant contributors to the stress field in subducting slabs. It also suggests that the depth distribution of deep seismicity may largely reflect the state of stress in the slab rather than simply a particular mechanism of stress release.
Interhemispheric differences in stratospheric water vapour during late winter, in version 4 MLS measurements
Authors: Morrey M. W. , Harwood R. S.
Published: February 2004

Observations of stratospheric water vapour, made by the Microwave Limb Sounder (MLS) during the 1992 and 1993 Arctic and 1992 Antarctic late winters have now been produced using version 4 of the retrieval software. These improved measurements are analysed as equivalent latitude zonal means. Major interhemispheric differences are revealed in the water vapour content of the vortex in the lower stratosphere. This technique emphasises mixing ratio gradients at the edges of both polar vortices, and a local maximum at the edge of the Antarctic vortex. There are some small interhemispheric differences in mixing ratios in mid‐latitudes, but they are not strongly related to the dehydration of the Antarctic vortex. A mixing ratio gradient across the interior of the Antarctic vortex at 530K indicates it is not isentropically mixed. A strong local maximum in mixing ratio at the centre of the Antarctic vortex in the mid‐stratosphere indicates it is not well mixed in the mid‐stratosphere also. There is little evidence of significant structure inside the Arctic vortex.
Effect of the overflows on the circulation in the subpolar North Atlantic: A regional model study
Authors: Redler René , Böning Claus W.
Published: February 2004

An ocean circulation model for process studies of the Subpolar North Atlantic is developed based on the Geophysical Fluid Dynamics Laboratory (GFDL) Modular Ocean Model (MOM) code. The basic model configuration is identical with that of the high‐resolution model (with a grid size of 1/3° × 2/5°) of the World Ocean Circulation Experiment (WOCE) Community Modeling Effort (CME), except that the domain of integration is confined to the area from 43° to 65°N. Open boundary conditions are used for the inflows and outflows across the northern and southern boundaries. A comparison with the CME model covering the whole North Atlantic (from 15°S to 65°N) shows that the regional model, with inflow conditions at 43°N from a CME solution, is able to reproduce the CME results for the subpolar area. Thus the potential of a regional model lies in its use as an efficient tool for numerical experiments aiming at an identification of the key physical processes that determine the circulation and water mass transformations in the subpolar gyre. This study deals primarily with the representation and role of the overflow waters that enter the domain at the northern boundary. Sensitivity experiments show the effect of closed versus open boundaries, of different hydrographic conditions at inflow points, and of the representation of the narrow Faeroe Bank Channel. The representation of overflow processes in the Denmark Strait is the main controlling mechanism for the net transport of the deep boundary current along the Greenland continental slope and further downstream. Changes in the Faeroe Bank Channel throughflow conditions have a comparatively smaller effect on the deep transport in the western basin but strongly affect the water mass characteristics in the eastern North Atlantic. The deep water transport at Cape Farewell and further downstream is enhanced compared to the combined Denmark Strait and Iceland‐Scotland overflows. This enhancement can be attributed to a barotropic recirculation in the Irminger Basin which is very sensitive to the outflow conditions in the Denmark Strait. The representation of both overflow regions determine the upper layer circulation in the Irminger and Iceland Basins, in particular the path of the North Atlantic Current.
Modeling the vertical distribution of chlorophyll in the California Current System
Authors: Millán‐Núñez Roberto , Alvarez‐Borrego Saúl , Trees Charles C.
Published: February 2004

Remote sensing of ocean color provides data on the average photosynthetic pigment concentration in the first optical depth. To model primary productivity in the water column, estimates of the vertical distribution of pigment concentration are required. We used a Gaussian distribution function proposed by Platt et al. [1988] to represent the pigment vertical profile with four parameters. Empirical relationships were derived to estimate these parameters for the California Current System between 28° and 37°N, using California Cooperative Oceanic Fisheries Investigations (CalCOFI) data (1978–1992). The studied area was divided into six spatial subregions and temporally into warm and cool seasons. Regression models were developed for each subregion and season to estimate each of the parameters as functions of surface chlorophyll. Comparison of chlorophyll profiles obtained during the 1994 CalCOFI cruises (not used for constructing the models) with those estimated with our models shows a general agreement. Assuming a homogeneous biomass profile resulted in underestimation of integrated primary productivity (pp) by as much as 30%, whereas the modeled profiles gave equal or overestimated pp (up to 23%), with respect to the values derived from the real 1994 profiles.
Modeling the signal transfer of sea water δ18O to the δ18O of atmospheric oxygen using a diagnostic box model for the terrestrial and marine biosphere
Authors: Leuenberger Markus C.
Published: February 2004

We make use of a simple diagnostic box model to determine the sensitivities of the influencing parameters for the isotopic signal transfer of seawater oxygen to atmospheric oxygen. We calculate the δ18O of atmospheric oxygen from prescribed oxygen fluxes of the living and dead biomes on land and in the ocean, respectively. The model is driven by an assumed (experiment 1) or measured (experiments 2 and 3) temporal seawater δ18O signal and a land biomass estimation. In experiment 1, we calculated the required changes of several model parameters in order to study fast variations of δ18O of atmospheric oxygen as seen in the Greenland Ice Core Project (GRIP) ice at depths assigned to the Eemian time period. Our calculations support evidence of stratigraphic problems at these depths in the GRIP ice core. In experiment 2, we adjusted the model output, which was driven by the benthic seawater δ18O record from V19‐30, to the measured Greenland Ice Sheet Project 2 δ18O record of atmospheric oxygen for the last 110,000 years, by varying the model parameter. Single and multi‐parameter matchings were performed. The results for single‐parameter runs exceed the uncertainty ranges for most of the parameters, while multiparameter variations are well within these ranges. The model calculations are most sensitive to the land respiration factor. Our results support the findings of Van de Water et al. [1994] that the fractionations associated with biomes activities were most probably lower during cold periods, which could point to a combination of fractionations with different temperature dependencies. The model results indicate periods of higher marine biological activity during the ice age than today. Temporal variations of the model parameters show a double peak around 10000 and 8000 years ago, which could be associated with meltwater pulses, as shown in experiment 3. However, they are hardly the well‐known Fairbanks [Fairbanks et al., 1992] pulses since these occur 3000 to 4000 years earlier.
CH4 and δ18O of O2 records from Antarctic and Greenland ice: A clue for stratigraphic disturbance in the bottom part of the Greenland Ice Core Project and the Greenland Ice Sheet Project 2 ice cores
Authors: Chappellaz Jérôme , Brook Ed , Blunier Thomas , Malaizé Bruno
Published: February 2004

The suggestion of climatic instability during the last interglacial period (Eem), based on the bottom 10% of the Greenland Ice core Project (GRIP) isotopic profile, has been questioned because the bottom record from the neighboring Greenland Ice Sheet Project 2 (GISP2) core (28 km away) is strikingly different over the same interval and because records of the δ18O of atmospheric O2 from both cores showed unexpected rapid fluctuations. Here we present detailed methane records from the Vostok (Antarctica), GRIP, and GISP2 cores over the relevant intervals. The GRIP and GISP2 data show rapid and large changes in methane concentration, which are correlative with variations of the δ18O of the ice, while the Vostok record shows no such variations. This discrepancy reinforces the suggestion that the bottom sections of the Greenland records are disturbed. By combining the methane data with measurements of δ18O of O2 in the same samples, we attempt to constrain the nature of the stratigraphic disturbance and the age of the analyzed ice samples. Our results suggest that ice layers from part of the last interglacial period exist in the lower section of both ice cores and that some of the apparent climate instabilities in the GRIP core would be the result of a mixture of ice from the last interglacial with ice from the beginning of the last glaciation or from the penultimate glaciation.