bluuebunny/crossref_metadata_2025 huggingface dataset:
Near infrared imaging and spectroscopy of the SL‐9 impacts from Calar Alto
Authors: Herbst T. M. , Hamilton D. P. , Böhnhardt H. , Ortiz‐Moreno J. L.
Published: February 2004

Near infrared observations of the impacts of seven fragments of Comet Shoemaker‐Levy 9 with Jupiter show that precursor flashes are ubiquitous and associated with phenomena at or near the time of atmospheric entry. The comet fragments appear to be a heterogenous group: some impacts produced anomalously bright precursors, while others were completely undetectable despite expectations based on pre‐collision images. Strong CO emissions in spectra taken near maximum light point to hot molecular gas which cools within minutes. Finally, images of the disk of Jupiter in the two months after the collision show spreading of the impact structures at approximately 1.5° per day.
Characteristic non‐down‐dip‐extensional intermediate‐depth earthquakes immediately beneath the volcanic front in South Kyushu, Japan
Authors: Iguchi Masato , Ishihara Kazuhiro , Tatsumi Yoshiyuki
Published: February 2004

The hypocentral distribution and fault‐plane solutions of intermediate‐depth earthquakes in South Kyushu, Japan were investigated. The dipping seismic zone bends at a depth of 60∼70 km and continues to a depth of 180 km and the majority of the source mechanisms are down‐dip‐extension (DE). Non‐DE earthquakes are concentrated at depths of 100–120 km beneath the volcanic region, that is, upward and westward of the dipping seismic zone, and have vertical P‐ and horizontal T‐ axes. The occurrence of Non‐DE earthquakes may be related to dehydration processes at the base of the mantle wedge.
Anisotropy and crustal thickness of northern‐Tibet. New constraints for tectonic modelling
Authors: Herquel Georges , Wittlinger Gérard , Guilbert Jocelyn
Published: February 2004

In 1993 a seismological array was installed on a profile along the Golmud‐Lhasa highway from the Qaidam basin to Central Tibet. A travel time analysis for local and regional earthquakes was performed in order to better constrain the crustal structure obtained by teleseismic tomography. More information about the crustal thickness and anisotropy comes from the analysis of Moho converted P to SV waves. The two methods supplement each other and confirm the existence of crust thinner than expected accross the northern edge of the Tibetan plateau and Qaidam. P to Sv splitting analysis yields a striking similarity between the fast polarization direction and the velocity field of present‐day deformation as inferred from kinematic modelling. The two observations, the thinning of the crust and the clockwise rotation of the fast polarization direction emphasize the leading role of eastward extrusion for the absorption of the large amount of crustal shortening occuring in Central Asia.
Magnetic measurements used to identify paleoxidation fronts in deep‐sea sediments from the Madeira Abyssal Plain
Authors: Sahota J. T. S. , Robinson S. G. , Oldfield F.
Published: February 2004

We describe the results of rock‐magnetic measurements of a sediment core from the Madeira Abyssal Plain which contains multiple turbidites. Previous studies of trace element (e.g. U) concentration and observations of sediment color changes have shown that turbidite emplacement has resulted in reductive diagenesis and the formation of paleoxidation fronts. We show that variations in sediment lithology and postdepositional sedimentary processes can be characterized very sensitively using magnetic measurements. Low concentrations of magnetic minerals occur in turbidites with a high organic content, reflecting the destruction of magnetic material via the process of reductive diagenesis. In addition, fossil redox fronts are readily identified by rock‐magnetic properties.
Geometrical determination of the Love Number h2 at four tidal frequencies
Authors: Ray R. D. , Bettadpur S. , Eanes R. J. , Schrama E. J. O.
Published: February 2004

The Love number h2 is determined at the M2, N2, O1, and K1 frequencies by combining satellite altimetry with in situ ocean tidal measurements. Topex/Poseidon altimetry is used to measure the (ocean + earth) tide, while gauges at 114 island and ocean‐bottom sites determine the ocean tide; the difference sets constraints on h2. Our h2 standard errors are somewhat larger than recent VLBI estimates, but they clearly delineate the resonance in K1 at the 6‐σ level.
Measurements of the cooling at the base of Pahoehoe Flows
Authors: Keszthelyi Laszlo
Published: February 2004

Temperature measurements were made in August and October of 1994 at the base of small active pahoehoe flow lobes on Kilauea Volcano, Hawai'i. Surprisingly, after about 2 minutes of initial rapid cooling, the basal temperatures increased significantly before resuming a slower cooling trend. The recorded temperatures are also warmer than those predicted by simple conductive cooling models. Preliminary calculations suggest that these observations can be explained by the insulating effect of microfractures in the underlying flow and the kinetics of crystallization. The initial cooling may be rapid enough to super‐cool the lava such that the onset of crystallization is delayed. When crystallization does begin, it is initially rapid, releasing sufficient latent heat to re‐heat the lava. As the system equilibrates, the flow resumes a slow cooling.
Imaging of subducted lithosphere beneath South America
Authors: Engdahl E. R. , van der Hilst R. D. , Berrocal J.
Published: February 2004

Tomographic images are produced for the deep structure of the Andean subduction zone beneath western South America. The data used in the imaging are the delay times of P, pP and pwP phases from relocated teleseismic earthquakes in the region. Regionally, structural features larger than about 150 km are resolved by the data. Presentations of layer anomaly maps and cross sections reveal: (1) The Nazca slab is probably continuous laterally and at depth over most regions; (2) The offset between the north and south deep earthquake zones, containing the 1994 deep Bolivia main shock and its aftershocks, can be modelled by a northwest striking and steeply northeast dipping slab structure; and (3) The Nazca slab clearly penetrates the lower mantle beneath central South America, but is partly deflected in the southern deep zone.
Rapid oscillations in Vostok and GRIP Ice Cores
Authors: Yiou P. , Jouzel J. , Johnsen S. , Rögnvaldsson Ö. E.
Published: February 2004

We investigate the spectral properties of climatic times series derived from two recent ice cores in Greenland and East Antarctica. We find that the signals behave in a similar way in the high frequency part of their spectra. The rapid oscillations found in the GRIP ice core were closely correlated to Heinrich Events. A comparable spectral feature is detected in the Vostok ice core. We discuss the possibilities of connections between the two hemispheres and proper ice sheet oscillations in the light of simple oscillating climate models.
The integral enstatite chondrite model of the Earth
Authors: Javoy M.
Published: February 2004

The only primitive meteorites that match satisfactorily both the stable isotope and redox characteristics of the Earth are the Enstatite chondrites. I present an integral Enstatite chondrite model in which the Earth is built from essentially pure EH material, which is justified by the above similarities and by the fact that most elements in these meteorites exist in very refractory phases, more so than in most other types of meteorites. This results in a rather strong chemical heterogeneity at the upper‐lower mantle boundary, which favours a two‐level mantle convection model and puts limitations on the chemical relationships between lower and upper mantle. The upper mantle differentiation from EH material calls for a more complex mechanism than simple liquid metal sinking, involving a two‐step redox mechanism, governed by pressure and temperature variations, during which the Enstatite‐Perovskite transition plays a major role. A very late accretion of 0.8% of CI type material takes into account the stable isotope differentiation of the Upper Earth (upper mantle plus outer envelopes).
Charge transfer reactions of metastable Ba(I) and Sr(I) in the CRRES G‐11b Chemical Release Experiment
Authors: Hunton D. E.
Published: February 2004

Mass resolved fluxes of Ba+ and Sr+ ions were measured with the Quadrupole Ion Mass Spectrometer during the CRRES G‐11b chemical release experiment in darkness. The flux of Sr+ relative to Ba+ at a distance of 4 km from the release point was more than ten times larger than expected based on estimated charge transfer cross sections of the ground state metals. In each metal, we have identified at least one low‐lying metastable state that is closer to charge‐transfer resonance with O+ than the ground state. These metastable states are 5s5p ³P2 in Sr at 14, 899 cm−1 above the ground state and 6s5d ³D3 in Ba at 9,597 cm−1. The Sr 5s5p ³P2 state is nearly exactly resonant with O+ (9 meV energy defect) and may have a significantly enhanced charge transfer cross section. In a proposed mechanism that may explain the measured ion fluxes, neutral metal atoms are excited to these metastable states by electron‐atom collisions early in the expansion of the neutral cloud. High energy electrons could be produced by a plasma process such as CIV. This energy is stored in the neutral cloud. The metastable atoms are ionized by near‐resonant charge exchange with ambient O+ and are detected after the cloud expands to reach the spacecraft.
GCM evaluation of a mechanism for El Niño triggering by the El Chichón ash cloud
Authors: Robock Alan , Taylor Karl E. , Stenchikov Georgiy L. , Liu Yuhe
Published: February 2004

The El Chichón volcanic eruption in 1982 was immediately followed by the strongest El Niño of the century in 1982–83. We investigate a possible mechanism proposed by Hirono whereby volcanic eruptions might trigger or enhance El Niños. Three distributions of volcanic ash aerosol in the troposphere over the eastern Pacific Ocean were used to force simulations with a modified version of the NCAR CCM1 atmospheric general circulation model for the month of April 1982, using observed sea surface temperatures. Only in the case of mid‐tropospheric heating is there a strong dynamical reaction in the atmosphere resulting in a weakening of the trade winds in the eastern Pacific Ocean north of the equator, consistent with surface wind observations and with the first part of Hirono's theory. However, the 1982 ENSO event had started before this wind anomaly, and only trade wind collapses in the western equatorial Pacific can initiate El Niños. The results suggest that, while tropospheric aerosols from volcanic eruptions can influence atmospheric circulation, the timing and location of the El Chichón eruption and the large ENSO event that followed was a coincidence, and that Hirono's mechanism was not responsible for the strength or timing of the El Niño.
26Al in seawater and 26Al/10Be as paleo‐flux tracer
Authors: Ku T. L. , Wang L. , Luo S. , Southon J. R.
Published: February 2004

Measurements of water‐column 26Al/27Al ratios above 850 m depth in the Pacific yield values in the range 10−13–10−14, translating into 26Al concentrations of 20–200 atoms kg−1. The atomic ratio of 26Al/10Be in surface ocean is close to 1 × 10−4, at least an order lower than the atmospheric production ratio. Surface‐ocean particulate removal of Al is about 30 times more rapid than that of Be. The results of this first set of data on 26Al in seawater also suggest that the source of 26Al in the sea is dominated by spallation of Ar in the atmosphere (as opposed to eolian and cosmic‐dust inputs) and that the ratio 26Al/10Be in marine sediments can be potentially used to decipher past variations of oceanic particle flux, hence biologic productivity.
Active crustal deformation in the Marmara Sea Region, NW Anatolia, Inferred from GPS measurements
Authors: Straub Christian , Kahle Hans‐Gert
Published: February 2004

Deformation in the boundary zone between the Anatolian and Eurasian plates has been determined by means of repeated Global Positioning System (GPS) measurements. Three campaigns (1990, 1992, 1994) were carried out around the Marmara Sea. The network lies within the active earthquake belt of NW Anatolia, extending from the western part of the North Anatolian Fault Zone (NAFZ) to the Aegean extensional province. Results of the dense network consisting of 52 sites clearly reveal the westward motion of Anatolia. The rates amount to 17 mm/a ±3 mm/a on average relative to Istanbul, located at the northeastern edge of the Sea of Marmara. Based on the trajectories for the displacements of the observation sites it is concluded that the Marmara Sea forms a transition zone between the Europe fixed region of Thrace/Black Sea (Eurasia) and NW Anatolia. At the western extremity of NW Anatolia the motion bends from W to WSW(247°). The strain field calculated yields an E‐W oriented right‐lateral strike‐slip movement (average 0.12 ppm/a, maximum 0.41 ppm/a) accompanied by NE‐SW extension (average −0.12 ppm/a, maximum −0.52 ppm/a) at the eastern end of the Marmara Sea and N‐S extension at the Aegean shore line. Comparisons with the directions of T axes derived from 65 fault plane solutions of earthquakes show remarkable agreement.
Evidence for Arctic ozone depletion in late February and early March 1994
Authors: Manney G. L. , Zurek R. W. , Froidevaux L. , Waters J. W.
Published: February 2004

Significant chemical ozone (O3) loss in the 1993–94 Arctic winter occurred mainly during an unusually late cold spell of ∼10 days in late Feb/early Mar. Over the 30 d period studied (including the cold spell), observed vortex‐averaged O3 at 465 K (∼40 hPa) decreased by ∼10%. New three‐dimensional, diabatic trajectory calculations show that this observed decrease represents only about half of the net chemical loss (∼20%) during the 30 day period. The resupply of lower stratospheric O3 by transport in Feb 1994 was considerably greater than in 1993, when transport masked only about a quarter of the chemical loss in Feb/Mar. The net estimated chemical loss over 30 days in 1994 was comparable to that over the same 30 days in 1993, but mainly occurred at a faster rate during the brief cold spell. These results highlight the impact of Arctic interannual variability on the relative roles of chemistry and dynamics in O3 evolution during recent Arctic winters.
Direct simulation of electrical and hydraulic tortuosity in porous solids
Authors: Zhang Xiaodong , Knackstedt Mark A.
Published: February 2004

We directly evaluate the fluid‐flow and electrical conductivity of model three dimensional random porous medium at a microscopic level. This allows a direct test of the popular assumption that fluid‐flow and electrical current follow equivalent flow paths in porous solids. Visualisation of the fluid‐flow and electric‐current streamlines within identical porous samples show this assumption is incorrect. The tortuosity factors, characterising the geometry of the flow paths associated with fluid‐flow and electrical current transport, are directly evaluated. Fluid‐flow tortuosity is systematically larger than the electrical tortuosity, and can differ by as much as an order of magnitude at lower porosities.
The Ulysses south polar pass: Anomalous component of cosmic rays
Authors: Trattner K. J. , Marsden R. G. , Bothmer V. , Sanderson T. R. , Wenzel K.‐P. , Klecker B. , Hovestadt D.
Published: February 2004

We have expanded our previous study of latitudinal gradients of anomalous cosmic ray oxygen (8 to 12 MeV/n and 12 to 16 MeV/n) by using also helium (11 to 20 MeV/n) as an additional component and a larger ULYSSES/LET data set including the segment up to the maximum southern latitude and the pole‐to‐equator segment of the mission down to 38°S. The ULYSSES observations are compared with observations in the vicinity of the Earth, provided by SAMPEX and IMP 8. The data sets cover a time period from August 1992 to end of January 1995. Only quiet time periods which contain no increases due to solar energetic particles are taken into account. Both oxygen energy channels show a decrease of the SAMPEX to ULYSSES flux ratio which is equivalent to a positive latitudinal gradient of ∼2%/degree. However, no significant latitudinal gradient for helium was found using the IMP 8 to ULYSSES flux ratio.
Fracture criteria at the tip of fluid‐driven cracks in the Earth
Authors: Khazan Yakov M. , Fialko Yuri A.
Published: February 2004

The effect of high confining pressure on fluid‐filled crack growth is considered. Exact solutions are given for a two‐dimensional horizontal crack in an infinite elastic body using the approximation of Dugdale‐Barenblatt (DB) model. It is shown that for equilibrium cracks (i.e. for cracks on the verge of propagation) the large‐scale crack characteristics, such as fluid overpressure, apparent fracture toughness, maximum opening of the crack and crack volume, grow with increase of confining pressure. These effects result from a pressure induced fracture resistance (PIFR). If basic parameters of the DB model (tensile strength and critical crack opening displacement) are independent of confining pressure then PIFR dominates over intrinsic rock strength starting from quite shallow depth (tens to hundreds of meters).
Horizontal wave number spectra of density and temperature perturbations in the mesosphere measured during the 4 August flight of ANLC‐93
Authors: Qian Jun , Gu Yiyun Y. , Papen George C. , Gardner Chester S. , Espy Patrick J.
Published: February 2004

On 4 August 1993 during ANLC‐93 the NCAR Electra completed a round‐trip flight west from Edmonton, Alberta to the Pacific Ocean. The University of Illinois Na lidar and Utah State Michelson interferometer observations were used to study the vertical wave number (m) and zonal wave number (k) spectra of relative atmospheric density, Na abundance, OH emission intensity, and rotational temperature perturbations. The spectral indices of the m‐ and k‐spectra inferred from the lidar data are smaller than those reported by Hosteller and Gardner [1994] over the mid‐Pacific but similar to those reported by Kwon et al. [1990] over the Rocky Mountains and Great Plains. These differences may be a consequence of different gravity wave source characteristics over the Rocky Mountains compared to the equatorial mid‐Pacific region where convection is strong and orographic forcing is absent. The Na abundance spectrum closely follows a power‐law over the range from k = 2π/(1000 km) to 2π/(3 km). This observation contradicts simple gravity wave theory which predicts that the abundance spectrum should fall rapidly to zero at wave numbers larger than ∼2π/(25 km).
Influence of the discovery and Shona mantle plumes on the southern Mid‐Atlantic Ridge: Rare earth evidence
Authors: Douglass J. , Schilling J‐G. , Kingsley R. H. , Small C.
Published: February 2004

Chondrite normalized (La/Sm)n ratio variations from 66 basalt glasses dredged along the Mid‐Atlantic Ridge (MAR) from 40–54.5°S reveal two distinct geochemical anomaly highs coupled with gravity and bathymetric highs and crest‐like rather than rifted ridge‐axis morphology. The Discovery anomaly (45–49°S), located opposite the Discovery hotspot track, is irregular and shows large local variation. The Shona anomaly (50–52.5°S) is smoother and shows less local variation. These results suggest that the influential Shona mantle plume may be located on or very close to the ridge. In contrast, the dispersal of the Discovery plume, located well off the ridge, is affected in a complex manner by the Agulhas fracture zone and the asthenospheric flow field associated with the spreading MAR.
On the spatial organization of soil moisture fields
Authors: Rodriguez‐Iturbe Ignacio , Vogel Gregor K. , Rigon Riccardo , Entekhabi Dara , Castelli Fabio , Rinaldo Andrea
Published: February 2004

We examine the apparent disorder which seems to characterize the spatial structure of soil moisture by analyzing large‐scale experimental data. Specifically, we address the statistical structure of soil moisture fields under different scales of observation and find unexpected results. The variance of soil moisture follows a power law decay as function of the area at which the process is observed. The spatial correlation remains unchanged with the scale of observation and follows a power law decay typical of scaling processes. Soil moisture also shows clear scaling properties on its spatial clustering patterns. A well‐defined organization of statistical character is found to exist in soil moisture patterns linking a large range of scales through which the process manifests itself and impacts other processes. We suggest that such scaling properties are crucial to our current understanding and modeling of the dynamics of soil moisture in space and time.
Electrostatic solitary structures in non‐thermal plasmas
Authors: Cairns R. A. , Mamum A. A. , Bingham R. , Boström R. , Dendy R. O. , Nairn C. M. C. , Shukla P. K.
Published: February 2004

Solitary electrostatic structures involving density depletions have been observed in the upper ionosphere by the Freja satellite [Dovner et al., 1994]. If these are interpreted as ion sound solitons, the difficulty arises that the standard Korteweg‐de Vries description predicts structures with enhanced rather than depleted density. Here we show that the presence of non‐thermal electrons may change the nature of ion sound solitary structures and allow the existence of structures very like those observed.
Shape anisotropy versus magnetic interactions of magnetite grains: Experiments and application to AMS in granitic rocks
Authors: Grégoire Vincent , de Saint Blanquat Michel , Nédélec Anne , Bouchez Jean‐Luc
Published: February 2004

The magnetic fabric of ferromagnetic granitic rocks results from both the shape preferred orientation of individual magnetite grains and their distribution anisotropy through magnetic interactions between neighbouring grains. Measurement of the low‐field magnetic anisotropy of single multi‐domain magnetite grains shows a linear correlation between their magnetic anisotropy degree and their aspect ratio. Interactions between two elongated grains were studied experimentally using two types of grain arrangement: an “aligned” configuration and a “side‐by‐side” configuration. For a distance between the grain centers equal to approximately twice the average grain size, the magnetic susceptibility and its anisotropy are enhanced in both configurations, and the direction of kmax, the easiest magnetization axis, is stable in the “aligned” configuration, whereas it rotates toward an orthogonal direction in the “side‐by‐side” configuration. Depending on the distribution of the interacting magnetite grains, magnetic interactions may therefore either increase the whole‐rock anisotropy magnitude, or reduce it as in the given example of the granitic rocks from Madagascar.
A wavelet analysis of Plio‐Pleistocene climate indicators: A new view of periodicity evolution
Authors: Bolton Edward W. , Maasch Kirk A. , Lilly Jonathan M.
Published: February 2004

Wavelet analysis offers an alternative to Fourier based time‐series analysis, and is particularly useful when the amplitudes and periods of dominant cycles are time dependent. We analyze climatic records derived from oxygen isotopic ratios of marine sediment cores with modified Morlet wavelets. We use a normalization of the Morlet wavelets which allows direct correspondence with Fourier analysis. This provides a direct view of the oscillations at various frequencies, and illustrates the nature of the time‐dependence of the dominant cycles.
Mass accommodation of aniline, phenol and toluene on aqueous droplets
Authors: Heal M. R. , Pilling M. J. , Titcombe P. E. , Whitaker B. J.
Published: February 2004

Mass accommodation coefficients on aqueous droplets have been measured for two substituted aromatic compounds using a droplet train apparatus and detection in the gas phase by laser induced fluorescence. Values of (1.8±0.5) × 10−2 and (2.7±0.5) × 10−2 have been obtained at 283 K for aniline and phenol, respectively. Mass accommodation of toluene was below the limit of detection of 1.0 × 10−3. Phenol and aniline are chosen as models for polar and oxygenated species formed as Cy intermediates in the oxidation of less soluble aromatic hydrocarbon precursors. The measurements indicate that mass accommodation of such species could be a significant pathway for the removal of tropospheric hydrocarbons.
A spectral survey of the Crisium Basin Region of the Moon
Authors: Blewett D. T. , Hawke B. R. , Lucey P. G. , Spudis P. D.
Published: February 2004

The Crisium basin region harbors a number of interesting features, including geochemical and radar anomalies, light plains units and possible hidden mare deposits (cryptomaria). This report presents preliminary results of a telescopic near‐infrared spectral study concerning a variety of surface units in the Crisium region. Observations were made of Mare Crisium, light plains deposits north of Taruntius crater, and the terra associated with the Crisium basin.
Observations of inertia‐gravity wave motions in the stratosphere over Jicamarca, Peru
Authors: Riggin Dennis , Fritts David C. , Fawcett Clinton D. , Kudeki Erhan
Published: February 2004

We present results obtained with the MST radar at Jicamarca, Peru over 10 days in January, 1993. During this campaign, inertia‐gravity waves with observed periods of ∼36 hours were seen in the stratosphere (19–30 km). The radar was operated with a high (400‐m) range resolution allowing accurate determination of wave propagation characteristics. The large variation of wave amplitude (∼2–10 ms−1) with height and time suggests a superposition of several wave motions. As consistent with upward energy propagation, the phase fronts descended with time, and a vertical wavelength of ∼5 km was inferred from the rate of this phase descent. Orbital ellipses imply largely zonal propagation with an intrinsic period of roughly 30 hours, somewhat less than the observed period. The shorter intrinsic period suggests eastward wave propagation, in opposition to the predominantly westward mean motion.
Results of the Ulysses fast latitude scan: Magnetic field observations
Authors: Smith E. J. , Balogh A. , Burton M. E. , Erdös G. , Forsyth R. J.
Published: February 2004

The rapid crossing of the solar equatorial region by Ulysses as it returned from the south pole resulted in 7 crossings of the heliospheric current sheet between 10°S and 20°N and 10 distinct solar wind interaction regions between 18°S and 22°N. Both the extent of the current sheet and the latitude interval containing the interaction regions are a factor of ≈ 2 less than were observed by Ulysses when it left the equatorial region in 1993. A map of the current sheet in heliographic latitude and Carrington longitude reveals two folds corresponding to 4 magnetic sectors. The coronal holes associated with the sectors, the interaction regions and high‐speed streams have been identified. Two sectors were associated with a pair of asymmetrically‐placed polar coronal holes whereas the other two sectors coincided with a pair of near‐equatorial coronal holes on opposite sides of the equator.
Are Neptune's highly dispersed whistlers really Z‐mode radiation?
Authors: Farrell W. M.
Published: February 2004

Evidence is presented that the unusual lightning‐generated whistler signals detected very near Neptune are possibly impulsive emissions propagating in the z‐mode. Unlike terrestrial whistlers in the plasmasphere, the Neptunian emissions might be propagating in a region where the plasma‐to‐cyclotron frequency ratio is much less than one. If the nightside plasma density is indeed low, the z‐mode will extend down to unusually low frequencies. The observed events may then be interpreted as z‐mode instead of the whistler mode. Propagation in the z‐mode may explain many of the unusual emission features, including the low frequency limit of 6 kHz and the very large dispersions. Given an atmospheric emission source, this result suggests that Neptune's ionospheric electron density is relatively low. In order for the dispersive events to be observed at Voyager in the z‐mode, some locations in the nightside ionosphere are required to have densities as low as about 100 cm−3. A possible magnetospheric source for the emission is also discussed.
Relative paleointensity in sediments: A Pseudo‐Thellier Approach
Authors: Tauxe L. , Pick T. , Kok Y. S.
Published: February 2004

We present a method for normalizing sedimentary records for estimating relative paleointensity of the geomagnetic field, similar to that successfully used to obtain absolute paleointensity from thermally blocked remanences. It has the advantages that it is more effective in removing unwanted viscous remanence, thereby improving agreement among various records and that it allows the estimation of the uncertainty in the relative paleointensity calculated.
Quick aftershock relocation of the 1994 Shikotan Earthquake and its fault planes
Authors: Hurukawa Nobuo
Published: February 2004

The 1994 Shikotan earthquake of Mw 8.2 occurred near the western Kurile trench where the Pacific plate is subducting beneath the North American plate. Although its mechanism is thrust‐type, it is not a typical low‐angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary. In order to determine which of the two nodal planes of the main shock was the fault plane, we relocated the main shock and all aftershocks with M > 5.3 using a modified joint hypocenter determination method. Earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east‐southeastward with a dip of 70°. This plane is about 80 to 150 km long and 70 km wide. The main shock occurred at the north‐northeastern bottom of this plane, which is almost parallel to one of the two nodal planes of the main shock determined by Harvard University, which has a strike of N51°E and a dip of 76°. Thus we conclude that this plane is the fault plane, that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast. In addition to the aftershocks aligned with this fault plane, there is a secondary alignment, which is subparallel to the main fault plane and about 50 km east, where the largest aftershock of Mw 7.3 occurred on Oct. 9. Since several aftershocks occurred on this secondary fault plane on the same day as the main shock, it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock.
Silicon molecular ions in the D‐region
Authors: Kopp Ernest , Balsiger Franz , Murad Edmond
Published: February 2004

During a recent rocket campaign to study the phenomenology of noctilucent clouds (NLC‐93), mass spectrometer measurements showed the presence of ions at m/e=45 and 61. These ions are attributed to SiOH+ and SiO2H+; the former is formed by reaction of Si+ with H2O and the latter is formed by reaction of SiOH+ with O3. The data provide the first observation of a chemical sequence of reactions beginning with the ablation of meteoric elements and a sequential reaction scheme.
On the origin of the fluctuations in the length of day and in the geomagnetic field on a decadal time scale
Authors: Duhau Silvia , Martínez Ernesto A.
Published: February 2004

There is, at present, strong evidence that on a decadal time scale the excess length of day variations are caused by the exchange of angular momentum between the liquid core and the solid mantle. Nevertheless the mechanism which facilitates the momentum exchange is still not understood. In the present work a mechanism by which the magnetospheric equatorial ring current system controls the momentum exchange is introduced, some empirical insights about that mechanism are obtained from relevant data and the magnitudes of the involved magnetic fields are evaluated from these data.
State of stress in southern Italy from borehole breakout and focal mechanism data
Authors: Amato A. , Montone P. , Cesaro M.
Published: February 2004

We present new wellbore breakout data from oil exploration wells drilled in southern Peninsular Italy, from the Tyrrhenian shelf through the Apenninic mountain belt and foredeep, eastward to the undeformed Adria foreland. From the analysis of 64 wells, we observe Shmin oriented around NE‐SW, perpendicular to the trend of the Apennines, both within the belt and in the eastern foredeep. Some variations are observed in the few wells analyzed on the Tyrrhenian shelf, possibly due to local tectonic structures, such as transverse NE‐SW oriented extensional basins. The Apulian platform overthrust by the Apenninic mountains at 3–4 km depth, shows a very consistent direction of Shmin oriented N40°–50°E, in agreement with the stress regime inferred from focal mechanisms of strong earthquakes at depths of 10–15 km, which show NE extension, mostly accomplished by normal faulting. The overlying sedimentary and allochthonous units of the Apenninic belt exhibit the same NE Shmin direction, but show a larger scatter. Breakout data demonstrate that Quaternary compressional tectonism has ended, as Shmin is oriented NE also in the undeformed foreland as far as 50 km NE from the seismic belt. In the easternmost sector of the Adria foreland there are suggestions of a nearly isotropic horizontal stress field, as most wells do not show significant ellipticity.
Dynamical model of oscillatory zoning in plagioclase with nonlinear partition relation
Authors: L'Heureux Ivan , Fowler Anthony D.
Published: February 2004

We present a nonlinear dynamical model for oscillatory zoning in plagioclase based on a simple isothermal constitutive undercooling mechanism. A phenomenological partitioning is introduced to relate the concentration of An in the melt at the interface with the concentration in the solid. The non‐linearities in the model result from the coupling of the growth velocity with the local An concentration and from the boundary condition at the interface. The consideration of a nonlinear boundary condition is new and generalizes previous nonlinear growth models. It is shown that parameter values exist for which oscillatory solutions are possible via a Hopf bifurcation. As the system is driven further out of equilibrium, the model shows the development of chaotic solutions via a period‐doubling sequence.
A new quality check for absolute palaeointensities of the Earth magnetic field
Authors: Haag M. , Dunn J. R. , Fuller M.
Published: February 2004

Absolute palaeointensity determinations of recent lavas from Mt. Etna have been carried out using the Koenigsberger‐Thellier‐Thellier (KTT) method but with two different data presentations. The first, which is the standard method, compares the natural remanent magnetization (NRM) demagnetized and the thermoremanent magnetization (TRM) acquired in successive temperature intervals cumulatively. The second compares the NRM and TRM in the successive intervals in an incremental manner. The latter method appears to distinguish aberrant behaviour better than the classical method. Such aberrant behaviour can be related to changes in hysteresis ratio parameters, saturation remanent magnetization to saturation magnetization and remanent coercive force to coercive force, which are reflected by displacements in the Day et al. (1977) plot. These changes in hysteresis parameters are caused by irreversible changes in domain state or transformations of magnetic phases brought about by the thermal cycling. The changes in hysteresis parameters serve as a useful quality factor for absolute palaeointensity determinations.
The heterogeneous generation of N2O from exhaust gases of combustion: A laboratory study
Authors: Pires M. , Rossi M. J.
Published: February 2004

The heterogeneous reaction of NO, SO2 and O2 in the presence of condensed or adsorbed H2O results in high yields of N2O under conditions mimicking flue gas from fossil fuel combustion. We observed a strong influence of the nature of the substrate surface on the rate of N2O formation. The maximum rate of N2O formation of 350 ppm h−1 occurred on soot and fly ash at relative humidities approaching 100% at 368K final yields of 80–100% N2O. The mechanism corresponds to a complex multiphase system in which NO2 seems to be a key species. The observed abundance of NO2 does not correspond to the one predicted by the simple mechanism by Lyon and Cole (1988).
Unusual wave phenomena near interplanetary shocks at high latitudes
Authors: Thejappa G. , Wentzel Donat G. , MacDowall R. J. , Stone R. G.
Published: February 2004

We report on several interplanetary shocks that are unusual because waves at about 10 Hz are highly electrostatic in the upstream region yet highly electromagnetic in the downstream region. These shocks, detected by the Unified Radio and Plasma Wave Experiment (URAP) on Ulysses are supercritical reverse shocks, which occurred predominantly at high heliographic latitudes. The level of wave activity is observed to be independent of the angle between the magnetic field and the shock normal, the Mach number, and the change in the ratio of ion thermal pressure to magnetic pressure from upstream to downstream regions. Since the energy in the upstream electrostatic waves is small compared to the downstream electromagnetic waves, mode conversion from electrostatic to electromagnetic at the shock is not a viable mechanism. The upstream and downstream waves are likely to be generated by separate mechanisms, with lower hybrid waves being the most probable candidates for the upstream waves and electromagnetic lower hybrid or whistlers for the downstream waves.
Simulation of the stratospheric Quasi‐Biennial Oscillation using a general circulation model
Authors: Takahashi Masaaki
Published: February 2004

The quasi‐biennial oscillation is fairly well simulated by use of a T21 60‐layer general circulation model with moist convective adjustment. The model is the first version of the Center for Climate System Research/National Institute for Environmental Studies (CCSR/NIES) general circulation model. The vertical resolution is approximately 500m in the upper troposphere and lower stratosphere. The damping time for the maximum wavenumber in the fourth‐order horizontal diffusion is 20 days, being about one‐order of magnitude less than that in standard general circulation models. The period of the oscillation is 1.5 years, which is slightly shorter than that of the observed quasi‐biennial oscillation. The simulated oscillation occurs in the middle stratosphere, being slightly higher than that observed in the equatorial lower stratosphere. The amplitude of the zonal‐wind associated with the oscillation is 20 ms−1 which is comparable to the observed value.
Inaccuracies in seismicity and magnitude data used by Varotsos and Coworkers
Authors: Wyss M.
Published: February 2004

The claims of successful earthquake predictions by VAN are based on magnitudes said to be Ms (surface wave). However, they are larger by 1.0 unit, on the average, than those published in the Preliminary Determination of Epicenters (PDE), the authoritative source for Ms values. This discrepancy arises because VAN calculate Ms from ML (local magnitude) using the incorrect transformation Ms(VAN)=ML+0.5. Least squares regressions, based on the PDE data for Greece, yield Ms=l.50ML−2.62 and Ms=1.82mb−4.16 instead. An important part of many author's evaluations of VAN's claims is an assessment of whether their performance is better than that expected by random chance. If the random chance probability is defined using standard (PDE) seismicity data and magnitudes, whereas VAN's claims are based on a non‐standard scale, the significance of VAN's successes will be overestimated strongly. Additional discrepancies are introduced because Ms(VAN) is based on preliminary ML values), or sometimes on newspaper reports, rather than those published in the final bulletin of the Seismological Institute of the National Observatory Athens (SI‐NOA). The correct final magnitude should be used in all studies claiming success and evaluating these claims years after the earthquakes occurred. Inaccuracies in presenting an earthquake catalog also exist in Varotsos et al. [1981b], who claimed a one‐to‐one correlation of seismic electric signals (SES) with the list of earthquakes with mostly ML>2.9 published by the SI‐NOA. In fact, VAN had used instead a list called “Ten Days Preliminary Seismogram Readings at Athens” which is not a bulletin and contains no epicenters. As a consequence 37% of the earthquakes reported in the SI‐NOA Monthly Bulletin (including the largest one) were not contained in the list of VAN, and 40% of the earthquakes VAN claimed had occurred, were not in the SI‐NOA Bulletin. In addition, VAN added another 25% of events to the list. These latter events were identified as added, but there is no evidence that they were not explosions or other cultural disturbances. It is concluded that some of VAN's claims of correlations between SESs and earthquakes, and some of the evaluations of these claims, are based on incorrect earthquake lists.
Wavelet analysis of multiscale permeabilities in the subsurface
Authors: Li Bai‐Lian , Loehle Craig
Published: February 2004

Wavelet analysis is a new mathematical theory and calculation method for separating and sorting structures on different time scales at different times, and on different spatial scales at different locations. This method has been used to identify spatial heterogeneity of geologic structures and to estimate spatial scales of geophysical parameters in the subsurface. We used the integral wavelet transform to analyze the spatial variability of permeability in the alluvial fan deposits in Radioactive Waste Management Site Area 5 of Nevada. The mother wavelet which we used is the “Mexican Hat” function. A wavelet variance is defined to detect the characteristic scales of non‐periodically spaced spatial structures. Results showed heterogeneity of spatial structure in permeability at hierarchical scales and difference of scales between transects in spatially distributed permeability. These multiscale features of spatial variability of permeability provide an explanation for the strong quasi‐periodic behavior in the horizontal and vertical semivariograms. A comparison among wavelets, fractals, and traditional geostatistics is also given.
surface ozone at high latitudes
Authors: Theodorsen Alexander , Henriksen Kjell , Bersås Sølvi , Ørnes Hilde , Sirota Vitaly , Vasiliev Alexei
Published: February 2004

Surface ozone is measured at 70°N and 78°N with analysers having response time of 1 and 20 sec, and characteristic ozone depletions due to polluted air are revealed. Using the rapid instrumental time response, significant variations are found to occur within a few seconds. It is hard to find any ozone enhancements due to polluted air, and local ozone production seems to have minor importance. Therefore no significantly enhanced ozone levels due to local and long‐range transported car exhaust are likely to occur at high latitudes. Additional depletions due to dry and wet depositions are probably occurring.
An explanation for type 1 radar echoes from the midlatitude E‐region ionosphere
Authors: Haldoupis C. , Schlegel K. , Farley D. T.
Published: February 2004

Type 1 radar echoes from the midlatitude E‐region are comparatively rare, but we now have many nighttime examples. These observations imply that large electric fields, of the order of 15 mV/m or more, must exist at times in the plasma, even during quiet magnetic conditions. We suggest here that such fields can be generated by the same polarization process as at the magnetic equator, but with the geometry “turned on its side.” That is, we assume that there are sharp horizontal conductivity gradients associated with patchy nighttime metallic ion layers that play the same role that vertical gradients play at the equator. Sharp gradients in the zonal direction, particularly, could lead to polarization fields more than an order of magnitude greater than the ambient dynamo fields and sufficient to excite the two‐stream instability implied by the radar data. Only a small percentage of the metallic ion patches are like to have the right geometry and be at the right altitude, however, which perhaps explains why the type 1 echoes are seen only occasionally.
Recent Climatic Change in the World's Drylands
Authors: Hulme Mike
Published: February 2004

Precipitation and temperature trends in nine dryland regions are analysed for the period 1900 to 1994. No widespread desiccation in dryland climates is found, the African Sahel being the only region to demonstrate a significant drying trend. All dryland regions have warmed, however, with the majority of the warming probably being unrelated to regional dryland effects. This warming may have contributed to a worsening of the P/PE ratio in many of these dryland regions. Three African dryland regions are alone in showing a significant negative correlation between precipitation and temperature, contrasting with the relationship for global land areas of warmer years/decades being also wetter years/decades. The relative lack of warming in the Sahel is noted and increased atmospheric dust resulting from the increased desiccation of the region is suggested as a possible explanation.
Phase coupling in Langmuir wave packets: Possible evidence of three‐wave interactions in the upstream solar wind
Authors: Bale S. D. , Burgess D. , Kellogg P. J. , Goetz K. , Howard R. L. , Monson S. J.
Published: February 2004

Some theories of the generation of 2ωpe radiation, in the upstream solar wind, invoke the notion of nonlinear wave‐wave interactions. We present observations, from the WIND spacecraft, of an event in the upstream solar wind with first and second harmonic emissions. The bicoherence spectrum of this event shows coherence amongst components that suggest three‐wave interactions of the type described in (Cairns and Melrose, 1985). We discuss this result and its theoretical context.
Seismic detection of a thin laterally varying boundary layer at the base of the mantle beneath the central‐Pacific
Authors: Garnero Edward J. , Helmberger Donald V.
Published: February 2004

We explore lowermost mantle structure beneath the Pacific with long‐period recordings of the seismic core phases SKS, SPdKS, and SKKS from 25 deep earthquakes. SPdKS and SKKS are anomalously delayed relative to SKS for lower mantle paths beneath the southwest Pacific. Late SPdKS arrivals are explained by a laterally varying mantle‐side boundary layer at the CMB, having P‐velocity reductions of up to 10% and thickness up to 40 km. This layer is detected beneath a tomographically resolved large‐scale low velocity feature in the lower mantle beneath the central‐Pacific. SKS, SPdKS, and SKKS data for the generally faster‐than‐average circum‐Pacific lower mantle are well‐fit by models lacking any such low‐velocity boundary layer. The slow boundary layer beneath the central Pacific may be a localized zone of partial melt, or perhaps a chemically distinct layer, with its location linked to overlying upwelling motions.