bluuebunny/crossref_metadata_2025 huggingface dataset:
Large slip velocity of the surface rupture associated with the 1990 Luzon Earthquake
Authors: Yomogida Kiyoshi , Nakata Takashi
Published: February 2004

We found more than fifty people who provided important information on coseismic fault motion of the 1990 Luzon, the Philippines, earthquake. About thirty of them “witnessed” coseismic fault motion close to (less than 30 m) the surface rupture. The average slip duration reported was about 1 s, and some reported much less than 1 s, which is surprisingly short compared with the predicted value of about 10 s for its size (e.g., fault length: 120 km, slip: 5 m) according to scaling laws obtained from teleseismic studies. Teleseismic studies only obtain spatially and temporally averaged values of fault motion, but actual coseismic fault slip has a high degree of spatial heterogeneity. The large slip velocity over 10 m/s obtained by our study suggests a very high local stress drop (> 100 MPa). Other important information from the eyewitness accounts is that the slip velocity seems to have been nearly constant, implying that the fault slip is well described by a ramp function proposed by Haskell.
Electrical response of the Summit‐Greenland ice core to ammonium, sulphuric acid, and hydrochloric acid
Authors: Moore John C. , Wolff Eric W. , Clausen Henrik B. , Hammer Claus U. , Legrand Michel R. , Fuhrer Katrin
Published: February 2004

Electrical and chemical analysis of the GRIP ice core from Summit in central Greenland confirms that the ECM current is controlled solely by acids in the ice, though there could be different responses for different acids. The dielectric conductivity is dependent on strong acid, on sea salt chloride, and also on ammonium concentrations in the ice. The response to NH4+ is similar to that of sea salt chloride, as they both conduct only at AC frequencies, but NH4+ is approximately twice as conductive per mole. The response to the strong acids shows results consistent with earlier work, with similar responses throughout the length of the core. It seems as if all the thousands of electrical peaks in the GRIP core may be explained by the response to just three chemical species: acidity, ammonium salts, and a third component which is probably chloride.
Characteristics of luminous structures in the stratosphere above thunderstorms as imaged by low‐light video
Authors: Lyons Walter A.
Published: February 2004

An experiment was conducted in which an image‐intensified, low‐light video camera systematically monitored the stratosphere above distant (100–800 km) mesoscale convective systems over the high plains of the central U.S. for 21 nights between 6 July and 27 August 1993. Complex, luminous structures were observed above large thunderstorm clusters on eleven nights, with one storm system (7 July 1993) yielding 248 events in 410 minutes. Their duration ranged from 33 to 283 ms, with an average of 98 ms. The luminous structures, generally not visible to the naked, dark‐adapted eye, exhibited on video a wide variety of brightness levels and shapes including streaks, aurora‐like curtains, smudges, fountains and jets. The structures were often more than 10 km wide and their upper portions extended to above 50 km msl.
Application of genetic algorithms to focal mechanism determination
Authors: Kobayashi Reiji , Nakanishi Ichiro
Published: February 2004

Genetic algorithms are a new class of methods for global optimization. They resemble Monte Carlo techniques, but search for solutions more efficiently than uniform Monte Carlo sampling. In the field of geophysics, genetic algorithms have recently been used to solve some non‐linear inverse problems (e.g., earthquake location, waveform inversion, migration velocity estimation). We present an application of genetic algorithms to focal mechanism determination from first‐motion polarities of P‐waves and apply our method to two recent large events, the Kushiro‐oki earthquake of January 15, 1993 and the SW Hokkaido (Japan Sea) earthquake of July 12, 1993. Initial solution and curvature information of the objective function that gradient methods need are not required in our approach. Moreover globally optimal solutions can be efficiently obtained. Calculation of polarities based on double‐couple models is the most time‐consuming part of the source mechanism determination. The amount of calculations required by the method designed in this study is much less than that of previous grid search methods.
Comparison of plate and asthenospheric flow models for the thermal evolution of oceanic lithosphere
Authors: Stein Carol A. , Stein Seth
Published: February 2004

Although seafloor depth and heat flow for young oceanic lithosphere can be described by modeling the lithosphere as the boundary layer of a cooling halfspace, a long standing question has been why data at older ages deviate from those expected for a halfspace. Two classes of models have been proposed for these deviations. In one, heat added from below “flattens” depth and heat flow. In the other, asthenospheric flow beneath the lithosphere perturbs the depths. We compare recent versions of the model classes: the GDH1 thin‐lithosphere plate model [Stein and Stein, 1992] and an asthenospheric flow model [Phipps Morgan and Smith, 1992]. The plate model fits heat flow data better than the flow model for all cases considered, and topographic data in all but one case. The flow model significantly overpredicts depths for the North Atlantic, because the assumed asthenospheric flow in the plate motion direction would yield deepening for old ages rather than the observed flattening. Overall, the GDH1 global average model does better than this flow model, whose parameters were fit to specific plates. Moreover, plate models fit to specific plates do better than the flow model. Plate models thus appear more useful than this flow model, suggesting that deviations from a cooling halfspace are largely thermal in origin.
The saturated‐cascade model for atmospheric gravity wave spectra, and the wavelength‐period (W‐P) relations
Authors: Dewan E. M.
Published: February 2004

The case will be presented for the hypothesis that over a certain wave number range all the atmospheric gravity wave spectra (and the Wavelength‐Period Relations as well) are a direct consequence of a “saturated‐cascade” of the waves.
Gobi dust storms and The Great Green Wall
Authors: Parungo Farn , Li Zhe , Li Xingsheng , Yang Dongzeng , Harris Joyce
Published: February 2004

Vast belts of forest planted across the northern arid lands of China, called “The Great Green Wall,” are probably one of the most aggressive weather modification programs in the twentieth century. The purpose is to reduce eolian transport of dust from the Gobi Desert. Preliminary data indicate a negative trend in dust‐storm frequency and duration since the 1960s. Effects on atmospheric radiation and cloud microphysics appear to be statistically insignificant in the studied period. However, only time can show any long‐term impact on our environment.
Numerical simulation of large‐scale field‐aligned current generation from finite‐amplitude magnetosonic waves
Authors: Yamauchi M.
Published: February 2004

A two‐dimensional numerical simulation of finite‐amplitude magnetohydrodynamic (MHD) magnetosonic waves is performed under a finite‐velocity background convection condition. Isothermal cases are considered for simplicity. External dissipation is introduced by assuming that the field‐aligned currents are generated in proportion to the accumulated charges. The simulation results are as follows: Paired field‐aligned currents are found from the simulated waves. The flow directions of these field‐aligned currents depend on the angle between the background convection and the wave normal, and hence two pairs of field‐aligned currents are found from a bowed wave if we look at the overall structure. The majority of these field‐aligned currents are closed within each pair rather than between two wings. These features are not observed under slow background convection. The result could be applied to the cusp current system and the substorm current system.
High‐resolution Fabry‐Perot Observations of mesospheric OH (6‐2) emissions
Authors: P. A. Greet , J. Innis , P. L. Dyson
Published: February 2004

Over the 1992/93 summer the Fabry‐Perot spectrometer at Mawson, Antarctica (67.6°S, 62.9°E), was modified to permit observations of two lines in the OH (6–2) band near λ 840 nm. Preliminary observations were obtained on 5 nights in early February. Analysis of these lines, permitting estimates of mesospheric winds and temperatures, will be presented. Lambda‐doubling of OH (6–2) Q1(2) and P1(3) lines was measured to be 5.50±0.01 pm and 19.17±0.06 pm respectively. The results show that mesospheric temperatures can be obtained from Q1(2) profiles even though the doublet is not fully resolved. This emission is significantly more intense than the P1(3) emission so its use will allow better resolution of temporal variations.
Comparison of trend analyses for Umkehr data using new and previous inversion algorithms
Authors: Reinsel Gregory C. , Tam Wing‐Kuen , Ying Lisa H.
Published: February 2004

Ozone vertical profile Umkehr data for layers 3–9 obtained from 12 stations, using both previous and new inversion algorithms, were analyzed for trends. The trends estimated for the Umkehr data from the two algorithms were compared using two data periods, 1968–1991 and 1977–1991. Both nonseasonal and seasonal trend models were fitted. The overall annual trends are found to be significantly negative, of the order of −5% per decade, for layers 7 and 8 using both inversion algorithms. The largest negative trends occur in these layers under the new algorithm, whereas in the previous algorithm the most negative trend occurs in layer 9. The trend estimates, both annual and seasonal, are substantially different between the two algorithms mainly for layers 3, 4, and 9, where trends from the new algorithm data are about 2% per decade less negative, with less appreciable differences in layers 7 and 8. The trend results from the two data periods are similar, except for layer 3 where trends become more negative, by about −2% per decade, for 1977–1991.
Apatite, phosphorus and titanium in eclogitic garnet from the upper mantle
Authors: Haggerty Stephen E. , Fung Agnes T. , Burt Donald M.
Published: February 2004

The existence of apatite exsolution lamellae in garnet supports earlier suggestions that garnet is a major repository for P in the mantle, and that P is strongly coupled to Na+Ti. The bulk P content (∼250 ppm) of mantle eclogites is unexpectedly similar to estimates for the P content (130–220 ppm) of the upper mantle; both rocks are depleted relative to chondrites and to ocean floor basalts. Eclogites have either equilibrated with the mantle at large, or have undergone secondary melting, and based on P contents are unlikely to have had subducted protoliths.
Global‐mean temperature and sea level consequences of greenhouse gas concentration stabilization
Authors: Wigley T. M. L.
Published: February 2004

The Intergovernmental Panel on Climate Change (IPCC) has defined a set of scenarios for future CO2 concentrations stabilizing at levels of 350 to 750 ppmv. Using models previously employed by IPCC, the implied global‐mean temperature and sea level changes are calculated out to 2500. While uncertainties are large, the results show that even with concerted efforts to stabilize concentrations of greenhouse gases, substantial temperature and sea level increases can be expected to occur over the next century. Increases in sea level are likely to continue for many centuries after concentration stabilization because of the extremely long time scales associated with the deep ocean (which influences thermal expansion) and with the large ice sheets of Greenland and Antarctica.
Elastic wave velocities of high density pressure‐induced amorphous GeO2
Authors: Fujisawa H. , Ito E. , Ohtaka O. , Yamanaka T.
Published: February 2004

Two samples of amorphous GeO2 were prepared at room temperature by compression of α ‐quartz type crystals at 13 and 20GPa. The former sample has a density of 4.42(6) Mg/m³ and the latter 5.34(2) Mg/m³. The elastic wave velocities, νp and νs of each sample were measured under pressures up to 4GPa at room temperature. The results are: (1) Both νp and νs are faster in the sample with higher density. (2) Even the velocities of the sample with lower density are faster than those of both α ‐quartz type crystal and a conventional amorphous phase whose density is less than 4Mg/m³. Since the pressure derivative of νp is larger than that of νs, the difference between νp and νs becomes greater with increasing pressure.
Soluble acidic species in air and snow at Summit, Greenland
Authors: Dibb Jack E. , Talbot Robert W. , Bergin Michael H.
Published: February 2004

Simultaneous measurements of the concentrations of soluble acidic species in the gas, aerosol and snow phases at Summit, Greenland were made during summer 1993. Mean concentrations of gas phase HCOOH, CH3COOH, and HNO3 (49±28, 32±17 and 0.9±0.6 nmol m−3 STP, respectively) exceeded the concentrations of aerosol‐associated HCOO−, CH3COO−, and NO3− by 1–3 orders of magnitude. On average, SO2 concentrations (0.9±0.6 nmol m−3 STP) were approximately 1/3 those of aerosol SO4=, but this ratio varied widely due largely to changes in the concentration of aerosol SO4=. Concentrations of aerosol SO4= plus SO2 consistently exceeded the sum of aerosol NO3− plus HNO3, yet NO3− was 3–20 times as abundant as SO4= in surface snow. Gas phase concentrations of HCOOH and CH3COOH at Summit were unexpectedly as large as those previously reported for several high latitude continental sites. However, carboxylate concentrations in snow were lower than those of SO4=. Our observation of post‐depositional loss of these carboxylic acids within hours after a snowfall must partially explain the low concentrations found in snow. The relative abundance of soluble acids in summer snow at Summit was opposite of that in the overlying atmosphere. Our results highlight the need for improved understanding of the processes controlling transfer of soluble atmospheric species between air and snow.
Effective viscosity of partially melted ice in the ammonia‐water system
Authors: Arakawa M. , Maeno N.
Published: February 2004

The steady‐state deformation of partially melted ice in the ammonia‐water system was studied by means of a concentric cylinder viscometer in shear stresses, 10 kPa∼0.1 MPa, temperatures, 180∼210 K and NH3 contents, 4.0∼8.4%. The flow law found was of a non‐Newtonian power‐law type; the stress exponent was 4.0±0.1. The activation energy at constant melt fractions was 33.7±0.8 kJ/mol, which was close to that of viscosity for aqueous ammonia solutions. However, the effective viscosity of partially melted ice estimated at 0.1 MPa was 107 ∼ 1010 Pa s, which is about ten orders of magnitudes larger and smaller than that of the ammonia‐water mixture in the liquid and solid phases (below a peritectic point, 176 K), respectively.
Jovian seismic waves and their detection
Authors: Hunten Donald M. , Hoffmann William F. , Sprague Ann L.
Published: February 2004

The impacts of the pieces of Comet Shoemaker‐Levy 9 should generate strong waves and fronts. Those that start out downward within a few degrees of vertical can travel large distances before reaching the surface again, and may probe to depths (13000 km) as great as the metallic‐hydrogen boundary. It is shown that the wave fronts should be detectable through their stratospheric heating and cooling, by imaging in the 7.8 µm band of CH4, which is very temperature sensitive (radiance ∝ T12.3). In addition to the “seismic” waves, the experiment should be able to detect slower‐moving ducted acoustic waves near the tropopause and still slower gravity waves.
Comet Shoemaker‐Levy‐9 impact with Jupiter: Aeronomical predictions
Authors: Cravens T. E.
Published: February 2004

The fragments of comet Shoemaker‐Levy‐9 will enter the atmosphere of Jupiter during July 20–26, 1994. Significant amounts of water vapor will be injected into the upper atmosphere of Jupiter either from the comet itself or from the lower atmosphere of Jupiter. The photochemistry of both the neutral gas and the ionosphere will be greatly altered by the influx of this water vapor or the atomic oxygen generated by the dissociation of the water. Enhanced abundances of H2O (or other species such as NH3) in the atmosphere above the homopause should persist for at least a year and should be globally distributed. The odd oxygen (i.e., O or H2O or OH) associated with the cometary water influx alters the ion chemistry by removing H+ ions, which also has the effect of reducing the ionospheric electron density because H+ is ordinarily the main ion species in the Jovian ionosphere. The density of H3+, both in the auroral and non‐auroral ionosphere, will also be reduced due to presence of water. This ion species has been detected spectroscopically at Jupiter, and a drop in its abundance should be detectable. The major ion species will become H3O+ which could reach a peak density as high as 104 cm−3 in the non‐auroral ionosphere and 105 cm−3 in the auroral ionosphere. It should be possible to detect this ion species spectroscopically from Earth‐based observatories.
Stream interfaces and energetic ions closer than expected: Analyses of Pioneers 10 and 11 observations
Authors: Intriligator Devrie S. , Siscoe George L.
Published: February 2004

An empirical study of corotating interaction regions (CIRs) observed between 3.9 AU and 5.9 AU on Pioneers 10 and 11 shows that the main corotation energetic ion population (CEIP), which is associated with the trailing reverse shock, terminates within the CIR at a definite, structural boundary, which we show here is the stream interface. This new result has significant implications for solar wind and energetic particle modeling. In particular it implies either that the reverse shock forms closer to the stream interface than models suggest or that the theories that treat the generation and transport of these energetic ions, such as preshock Fermi acceleration and cross‐field diffusion must be combined or extended. We test these scenarios by comparing the CEIP intensity profiles on the two sides of the stream interface. We find that while each automatically accounts for one or two aspects of the results none of them alone can account for all of our empirical results.
A theoretical model of cooling viscous gravity currents with temperature‐dependent viscosity
Authors: Bercovici David
Published: February 2004

Gravity current theory has applications to any geophysical phenomena involving the spreading of fluid on a horizontal interface. Many geological gravity currents (e.g., lava flows and mantle plume heads) are composed of cooling fluid with temperature‐dependent viscosity. An axisymmetric gravity current theory accounting for these thermo‐viscous effects is thus presented and explored here. Unlike isoviscous gravity currents [Huppert, 1982], cooling variable‐viscosity currents do not conserve shape and can undergo a somewhat exotic evolution. For large viscosity contrasts between cold and hot fluid, a constant volume, initially hot, domed current collapses rapidly into a flat plateau with a steep edge. Gravity currents ejected at a constant volume flux from a central conduit also spread with a flattened plateau shape. Continuously fed currents that have a large hot initial volume develop an outwardly propagating interior plateau. Regardless of initial state, continuously‐fed, variable‐viscosity currents grow primarily by thickening; this contrasts signficantly from isoviscous currents which grow almost entirely by spreading.
Airglow response to vertically standing gravity waves
Authors: Hines Colin O. , Tarasick David W.
Published: February 2004

There is currently much interest in fluctuations of airglow emissions caused by atmospheric gravity waves. The fluctuations of brightness tend to be found in phase (or occasionally in antiphase) with the fluctuations of measured temperature, whereas current theory tends to anticipate substantial phase differences. We suggest here that the discrepancy results from failure of the common theoretical assumption that the relevant gravity waves are dominated by a single upgoing component: that, instead, there is an accompanying downgoing component of comparable magnitude, produced by reflection. In the case of total reflection, simple, steady state chemistry and vertical viewing, the phase difference is necessarily zero (or 180°).
DAC measurement of perovskite conductivity and implications for the distribution of mineral phases in the lower mantle
Authors: Duba Alfred G. , Wanamaker Barbara J.
Published: February 2004

Measurements of the electrical conductivity of olivine buffered by magnesiowüstite can increase by more than two orders of magnitude if as little as 2 × 10−3 percent of the magnesiowüstite is allowed to form a parallel conduction path between the electrodes. These results are used, in concert with recent petrologic studies of the distribution of iron between perovskite and magnesiowüstite that have been synthesized from iron‐bearing olivine, to show how most of the inconsistencies in diamond‐anvil‐cell electrical conductivity measurements of perovskite may be explained by the presence of highly conductive, through‐going magnesiowüstite layers in laser‐heated samples, including those synthesized from pyroxene. Without electrical conductivity measurements on perovskite uncontaminated with secondary phases, current laboratory data can be interpreted—within constraints provided by the electrical conductivity of the mantle from geomagnetic studies—as requiring that either the conductivity of perovskite is not much different from magnesiowüstite or that magnesiowüstite in the lower mantle is distributed heterogeneously as an interconnected through‐going phase.
GPS measured rates of deformation in the northern San Francisco Bay Region, California, 1990–1993
Authors: Williams S. D. P. , Svarc J. L. , Lisowski M. , Prescott W. H.
Published: February 2004

A 100‐km‐long, 13‐station profile extending across the San Andreas fault system north of San Francisco Bay was measured 7 times between March 1990 and January 1993 with the Global Positioning System (GPS). The data have been processed using the Bernese Version 3.2 software. Data from a continental‐scale fiducial network were included in the solutions to aid orbit improvement and provide a consistent reference frame. We find 33 ± 2 mm/yr of fault‐parallel (N33°W) shear evenly distributed southwest and northeast of the Rodgers Creek fault and a near linear velocity gradient across the profile. The profile spans most of the zone of active deformation associated with the San Andreas fault system. Shear is negligible at the east end of the profile near the Great Valley. Additional shear of a few millimeters per year is likely beyond Point Reyes Head, the west end of the profile. We observe no systematic convergence upon the fault. The GPS measured velocities are similar to those derived previously from trilateration. The velocity change across the GPS profile (31–35 mm/yr) plus that west of the profile (0–3 mm/yr) and that observed with VLBI east of the Sierra Nevada Mountains (∼10–12 mm/yr) accounts for the North American‐Pacific plate rate (46–47 mm/yr).
The effect of windspeed on sea surface temperature retrieval from space
Authors: Harris A. R. , Brown S. J. , Mason I. M.
Published: February 2004

The effect of windspeed on water emissivity, whilst being negligible around normal incidence, becomes significant above angles of about 50°. We calculate the effect of windspeed on retrieved sea surface temperature and show that errors become significant for the potentially very accurate Along Track Scanning Radiometer (ATSR, carried on board ESA's first remote sensing satellite, ERS‐1) since brightness temperatures measured at ≈56°, as well as those measured at nadir, are used to provide improved atmospheric correction. We show that when an SST retrieval algorithm generated assuming zero windspeed is applied to brightness temperatures calculated for windspeeds of 5, 10 and 15 m/s, a potential error of up to 0.4 K is introduced. Since coincident windspeed data can be obtained from the ERS‐1 radar altimeter, accurate correction can be made for this effect and we provide a preliminary algorithm for the correction of ATSR SST data.
Column abundance measurements of atmospheric hydroxyl at 45°S
Authors: Wood S. W. , Keep D. J. , Burnett C. R. , Burnett E. B.
Published: February 2004

The first Southern Hemisphere measurements of the vertical column abundance of atmospheric hydroxyl (OH) have been obtained at Lauder, New Zealand (45°S) with a PEPSIOS instrument measuring the absorption of sunlight at 308 nm. The variation of column OH with solar zenith angle is similar to that measured at other sites. However average annual abundances of OH are about 20% higher than those found by similar measurements at 40°N. Minimum OH abundances, about 10% less than average levels at 40°N, are observed during austral spring. The OH abundance abruptly increases by 30% in early summer and remains at the elevated level until late the following winter.
Comparison between the lattice dynamics and molecular dynamics methods: Calculation results for MgSiO3 perovskite
Authors: Matsui Masanori , Price Geoffrey D. , Patel Atul
Published: February 2004

The lattice dynamics (LD) and molecular dynamics (MD) methods have been used to calculate the structure, bulk modulus, and volume thermal expansivity of MgSiO3 perovskite, in order to investigate the reliability of the two simulation techniques over a wide range of temperature and pressure conditions. At an intermediate temperature of 500 K and zero pressure, the LD and MD values are in exellent agreement for both the structure and bulk modulus of MgSiO3 perovskite. At high temperatures and zero pressure, however, the LD method, which is based on the quasi‐harmonic approximation, increasingly overestimates the molar volume of MgSiO3 perovskite because of the neglect of higher‐order anharmonic terms. At the high temperatures and high pressures prevailing in the lower mantle, the errors in the LD values for both the molar volume and bulk modulus, relative to the MD values, are generally small or negligible. However, since anharmonicity decreases substantially with pressure but increases rapidly with temperature, the error in the LD simulated volume thermal expansivity is serious, especially in the lower pressure region.
Aerosol particles in the upper troposphere and lower stratosphere: Elemental composition and morphology of individual particles in northern midlatitudes
Authors: Sheridan Patrick J. , Brock Charles A. , Wilson James C.
Published: February 2004

Atmospheric particles were collected in the midlatitude upper troposphere (UT) and lower stratosphere (LS) by inertial impaction for subsequent electron microscopy and individual particle elemental analysis. More than 97% of particles analyzed on impactor substrates exposed in the LS contained only O and S in detectable quantites; these particles are believed to be acidic sulfate. Nonsulfate materials seen in the remaining particles included soot, other c‐rich substances and crustal materials. Although not predominantly sulfate, usually carried a sulfur‐rich coating in the LS. Samples collected very near and just below the tropopause were also dominated by sulfates. The fraction of sulfate particles analyzed on impactor substrates exposed in the UT was 91–94% of the total particle concentration. Nonsulfate substances observed in the UT samples included crustal‐type materials, hydrated marine salts, carbon‐rich materials of several types, and metal‐containing substances of uncertain origin. Most of these UT particles were not coated with detectable quantities of sulfate.
Classification of the tailward drifting magnetic structures in the distant tail
Authors: Nishida A. , Yamamoto T. , Tsuruda K. , Hayakawa H. , Matsuoka A. , Kokubun S. , Nakamura M. , Kawano H.
Published: February 2004

The magnetic field observed at the neutral sheet crossings in the distant tail at |x| = 200‐210 Re can be classified into three types. At the sharp and isolated crossings (Type A), the Bz component is positive on average and the tailward extension of the LLBL seems to be the viable explanation, but the presence of large and IMF‐dependent By component suggests that the field lines are not closed but are connected to IMF at both ends. When the neutral sheet crossings occur multiple times, Type B or C is observed. Type B is characterized by the bipolar magnetic signature and represents a plasmoid or flux rope. Type C is characterized by magnetic oscillations with typical time scales of a few tens of seconds. These oscillations may represent the magnetic loops or spirals produced by the tearing. In all cases, the direction of the drift motion derived from the electric and magnetic field data is directed predominantly tailward.
The Freja Project
Authors: Lundin R. , Haerendel G. , Grahn S.
Published: February 2004

Freja is a joint Swedish and German scientific satellite project to study the interaction between hot magnetospheric plasma and the topside atmosphere/ionosphere. This interaction leads to a strong energization of magnetospheric and ionospheric plasma and an associated erosion and loss of matter from the terrestrial atmosphere. Using novel plasma instruments and a high data rate Freja have provided a number of “firsts” in high resolution plasma diagnostics from satellites. Freja's high spatial/temporal resolution permits studies of meso‐ and micro‐scale phenomena in the 100‐m range for particles and in the 10‐m range for electric and magnetic fields.

The Freja satellite was successfully launched on October 6, 1992 into an orbit with 63° inclination, an apogee of 1750 km and perigee of 600 km.
Vertical profile measurements of carbonylsulfide in the stratosphere
Authors: Engel A. , Schmidt U.
Published: February 2004

Measurements of COS in the altitude region between 17 and 30 km were made, using a whole air sampling technique with subsequent gaschromatographic analysis. The data show COS mixing‐ratios from about 200 pptv at 17 km decreasing to less then 20 pptv at about 28 km. This behaviour is in qualitative agreement with the model‐calculations by Turco et al. (1981). From the correlation with CFCl3 and CF2Cl2 the lifetime with respect to removal in the stratosphere is calculated to be 69±28 years. This corresponds to a sink of between 47 and 112 * 109 g of COS per year in the stratosphere. Comparing this number to the estimated fluxes needed to sustain the background sulfuric‐acid aerosol confirms that most of the non‐volcanic aerosol is produced by the oxidation of COS in the stratosphere.
Self‐lubricated mantle convection: Two‐dimensional models
Authors: Lenardic A. , Kaula W. M.
Published: February 2004

We present results from convection models allowing for self‐lubrication of downflows. Models impose a line source of chemically light, low viscosity material at the top of a convecting layer of temperature‐dependent viscosity material. Low viscosity surface material serves as an analog to hydrated sediment/crust and the high viscosity upper portion of the convecting layer as an analog to mantle lithosphere. Slow near surface motion in the convecting layer entrains low viscosity material into zones of downflow, which has a lubricating effect. Once entrained lubricant is deeper than the cold high viscosity portion of the convecting layer, rapid upper boundary layer overturn occurs and system properties change (e.g., heat flux doubles). This marks transition to a lubricated state. Before and after transition, transport properties are dominantly determined by, respectively, the viscosity of mantle lithosphere and that of interior mantle. Lubricated and nonlubricated states appear as distinct regions in system output space suggesting that exchange between them is akin to a phase transition. That such exchange depends on a near surface lubricant implies that the geodynamics of planets lacking such lubricants may fundamentally differ from that of planets possessing them.
Dense plasmas in the distant magnetotail as observed by GEOTAIL
Authors: Yamamoto T. , Matsuoka A. , Tsuruda K. , Hayakawa H. , Nishida A. , Nakamura M. , Kokubun S.
Published: February 2004

It is found that dense plasma is a very common plasma regime in the earth's magnetotail, especially beyond 150RE behind the earth. Plasma density in the tail lobe inferred from spacecraft potential measurements is often comparable with that in the tail current sheet. This observation suggests that the tail lobe is rich in cold plasmas. In the distant current sheet, plasma density sometimes exceeds 1 cm−3. The high‐density current sheet accompanies northward magnetic field, coming out from both the dawn and dusk tail flanks. Two possible models are discussed; one is highly stretched LLBL (low latitude boundary layer) that spreads to the whole current sheet in the distant tail, and the other is disappearance of the distant magnetotail during northward IMF.
Horizontal crustal motion in the central and eastern Mediterranean inferred from satellite laser ranging measurements
Authors: Smith David E. , Kolenkiewicz Ron , Robbins John W. , Dunn Peter J. , Torrence Mark H.
Published: February 2004

Four campaigns to acquire Satellite Laser Ranging (SLR) measurements at sites in the Mediterranean region have been completed. These measurements to the LAGEOS satellite, made largely by mobile systems, cover a time span beginning in November 1985 and ending in June 1993. The range data from 18 sites in the central and eastern Mediterranean have been simultaneously analyzed with data acquired by the remainder of the global laser tracking network. Estimates of horizontal motion were placed into a regional, northern Europe‐fixed, kinematic reference frame. Uncertainties are on the order of 5 mm/yr for sites having at least four occupations by mobile systems and approach 1 mm/yr for permanently located sites with long histories of tracking. The resulting relative motion between sites in the Aegean exhibit characteristics of broadly distributed pattern of radial extension, but at rates that are about 50% larger than those implied from studies of seismic strain rates based on seismicity of magnitude 6 or greater across the region. The motion estimated for sites in Turkey exhibit velocity components associated with the westward motion of the Anatolian Block relative to Eurasia. These results provide a present‐day “snapshot” of ongoing deformational processes as experienced by the locations occupied by SLR systems.
Some effects of anisotropy on velocity contrasts between subducting lithosphere and overriding mantle
Authors: Shoberg Tom , Bina Craig R.
Published: February 2004

We compute velocity anisotropy for three models of preferred crystal alignment due to finite strain in the mantle which, when juxtaposed with computed anisotropy in subducted lithosphere and neglecting other effects, give velocity contrasts that we compare with those observed. We find a strong dip dependence for computed velocity contrasts due to slow axis alignment in the overriding mantle perpendicular to the slab‐mantle interface. Moreover, for an isotropic mantle wedge or convergence‐parallel flow, it is difficult to produce greater velocity in the subducting slab than the overlying mantle for near‐vertical propagation even with high strain rates. We do, however, obtain positive contrasts using a dip axis‐parallel flow model, which is the only one that yields contrasts that approach observations from the Japan Trench.
10s‐period volcanic tremors observed over a wide area in southwestern Japan
Authors: Kawakatsu Hitoshi , Ohminato Takao , Ito Hisao
Published: February 2004

Unusual seismic oscillations with a period of 10 seconds were observed over a wide area of southwestern Japan. Several lines of evidence indicate that the origin of these 10s waves must be around the Aso volcano, located in the central part of Kyushu Island, Japan. Although a 10s period is unusually long for a volcanic tremor and no corresponding surface activity at the crater was reported by the local observatory, the volcanic origin of the tremor is indisputable. A further astonishing aspects of the observation is that there exists a strong correlation between the onset of 10s waves observed remotely and cessation of high‐frequency (>1Hz) volcanic tremors at the Aso volcano. The Aso volcano appears to be trembling with a 10s period without this having been noticed. Since seismic monitoring of volcanic activity is limited to high frequencies (above 1 Hz) at the most of the volcanoes in the world, long‐period tremors of the type observed here might be a widespread phenomenon that has been overlooked.
On the energy principle and ion tearing in the magnetotail
Authors: Brittnacher M. , Quest K. B. , Karimabadi H.
Published: February 2004

We re‐examine the use of the energy principle as applied to the tearing instability in the magnetotail. We demonstrate that when a magnetic field component normal to the current sheet is present, electron pitch‐angle diffusion (PAD) either by micro‐turbulence or by chaotic orbits cannot remove the strong stabilization of the tearing mode caused by electron compressibility. We find that our conclusions are in agreement with those of Pellat et al. [1991], who argued on the basis of canonical Py conservation that the stabilization of the ion tearing mode cannot be removed by the introduction of PAD. Our results are at variance with those of Kuznetsova and Zelenyi [1991], who argued that the application of the energy principle used by Pellat et al. [1991] is incorrect, and that tearing is in fact unstable in the limit of strong PAD. We show that the disagreement between these two studies can be traced to an incorrect orbit evaluation first introduced by Coroniti [1980] and subsequently used by Kuznetsova and Zelenyi [1991].
The one hundredth year of Rudolf Wolf's death: Do we have the correct reconstruction of solar activity?
Authors: Hoyt Douglas V. , Schatten Kenneth H. , Nesmes‐Ribes Elizabeth
Published: February 2004

In the one hundred years since Wolf died, little effort has gone into research to see if improved reconstructions of sunspot numbers can be made. We have gathered more than 349,000 observations of daily sunspot group counts from more than 350 observers active from 1610 to 1993. Based upon group counts alone, it is possible to make an objective and homogeneous reconstruction of sunspot numbers. From our study, it appears that the Sun has steadily increased in activity since 1700 with the exception of a brief decrease in the Dalton Minimum (1795–1823). The significant results here are the greater depth of the Dalton Minimum, the generally lower activity throughout the 1700's, and the gradual rise in activity from the Maunder Minimum to the present day. This solar activity reconstruction is quite similar to those Wolf published before 1868 rather than the revised Wolf reconstructions after 1873 which used geomagnetic fluctuations.
Plasma wave excitation on meteor trails in the equatorial electrojet
Authors: Chapin Elaine , Kudeki Erhan
Published: February 2004

The unusual properties of meteor echoes recently observed at Jicamarca [Chapin and Kudeki, 1994] are attributed to the growth and propagation of plasma irregularities along meteor trails deposited within the equatorial electrojet. It is suggested that trails at electrojet heights must carry intense discharge currents that excite two‐stream and/or gradient drift instabilities for irregularity growth. The direction of electron motion responsible for the discharge current agrees with the Doppler shift of the high frequency components in meteor echo signals.
A comparison of eastern North American seismic strain‐rates to glacial rebound strain‐rates
Authors: James Thomas S. , Bent Allison L.
Published: February 2004

Glacial rebound strain‐rates computed using a simple Laurentide glacial loading model are of the order of 10−9 per year within the region of glaciation and extending several hundred kilometers beyond. The horizontal strain‐rates receive approximately equal contributions from horizontal and vertical velocities, a consequence of the spherical geometry adopted for the Earth model. In the eastern United States and southeastern Canada the computed strain‐rates are 1–3 orders of magnitude greater than an estimate of the average seismic strain‐rate [Anderson, 1986] and ∼1 order of magnitude greater than predicted erosional strain‐rates. The predicted glacial rebound strain‐rates are not, in general, oriented in such a way as to augment the observed state of deviatoric stress, possibly explaining why the seismic strain‐rates are much smaller than the glacial rebound strain‐rates. An exception to this may be seismically active regions in the St. Lawrence valley.
The June‐July 1993 seismo‐acoustic event at CoAxial segment, Juan de Fuca Ridge: Evidence for a lateral dike injection
Authors: Dziak Robert P. , Fox Christopher G. , Schreiner Anthony E.
Published: February 2004

The CoAxial segment (Juan de Fuca Ridge) was the site of an intense swarm of earthquakes that began at 21:43 GMT on June 26, 1993 (Julian Day 177). The swarm started near 46°15′N and migrated northward over the next 40 hours to ∼46°36′N, where the majority of 676 events occurred during the following 3 weeks of activity. The earthquakes propagated NNE at a velocity of 0.3±0.1 m s−1 from the southern to northern swarm sites. The activity went undetected by land‐based seismic networks along the Oregon and Washington coasts, suggesting that the earthquakes were all M ≤ 4.0. The character of this earthquake swarm is very similar to dike injections observed at Krafla and Kilauea Volcanoes. The earthquake activity and subsequent migration probably represent a lateral dike injection into faults and fissures comprising the CoAxial segment. The reservoir acting as the dike's source likely resides beneath, or to the south of, the initial southern swarm of earthquakes. The large magma supply at Axial Volcano cannot be ruled out as the source for the CoAxial dike, even though Axial Volcano exhibited no earthquake activity related to the CoAxial swarm. The T‐wave earthquake swarm reported here is the first deep‐ocean observation of volcanic seismicity associated with what most likely was a mid‐ocean ridge dike injection event.
Methane hydrate stability in seawater
Authors: Dickens Gerald R. , Quinby‐Hunt Mary S.
Published: February 2004

Experimental data are presented for methane hydrate stability conditions in seawater (S ≈ 33.5‰). For the pressure range of 2.75–10.0 MPa, at any given pressure, the dissociation temperature of mcthane hydrate is depressed by approximately −1.1°C relative to the pure methane‐pure water system. These experimental results are consistent with previously reported thermodynamic predictions and experimental results obtained with artificial seawater. Collectively these results provide a minimum constraint concerning depth ranges over which methane hydrate is stable in the oceanic environment.
Lamellae in D″?: An alternative model for lower mantle anomalies
Authors: Weber M.
Published: February 2004

Typical 1‐D velocity models of anomalies in the lowermost mantle show a positive velocity jump of 2–3% in the bottom few hundred kilometers of the mantle, the core‐mantle transition zone. With synthetic seismograms it is demonstrated that a thin lamella of about 20 km thickness in D″ can produce similar seismic signals, for P and for S waves. A reduction of the thickness and/or the velocity contrast of this lamella will render it seismically invisible. The intermittent detection of anomalies in the lower mantle could therefore be due to the intermittent existence of inhomogeneities or, if lamellae exist in D″, be produced by variations in their thickness, velocity contrast and/or undulation. This demonstrates the uncertainty in our present knowledge of the D″ structure.
Permeability differences between surface‐derived and deep drillhole core samples
Authors: Morrow C. A. , Lockner D. A.
Published: February 2004

Laboratory tests reveal that the permeability of samples obtained from deep boreholes is often lower and more sensitive to pressure than the permeability of common surface‐derived crystalline rocks reported in the literature. We attribute the differences in permeability behavior to the fact that surface rocks have histories of unloading, weathering and retrograde metamorphism which are not comparable to that of the deeper rocks. Weathering products that line cracks and pores of surface rocks and make these openings more difficult to close as pressure increases may account for the relatively low pressure‐sensitivity of permeability. Stress‐relief cracking in the borehole samples can also reduce the pressure sensitivity. These results have important implications for models that incorporate assumptions about the transport properties of rock at depth, such as models of heat transport or fluid pressure buildup, because many models are based on the properties of common surface‐derived rocks. Other physical properties that are controlled by cracks and pores, such as seismic velocity and electrical resistivity, may be similarly affected by differences between surface‐derived and deep rocks.
A shallow double seismic zone beneath the central New Hebrides (Vanuatu): evidence for fragmentation and accretion of the descending plate?
Authors: Prévot Richard , Chatelain J‐L. , Roecker S. W. , Grasso J‐R.
Published: February 2004

A shallow double seismic zone (SDSZ) has been found in the descending Australian plate beneath the central part of the New Hebrides island arc, directly above a large gap in intermediate depth seismicity and between two seismic boundaries. Ambient seismicity occurs mostly in the upper part of the SDSZ, while earthquakes in the lower part occur in clusters (swarms or aftershocks of large earthquakes). The distance between the upper and lower levels of the SDSZ is 50–70 km, and they are joined at 80 km depth by a near‐horizontal band of seismicity. Thrust‐faulting mechanisms predominate for earthquakes in the upper level of the SDSZ. Those in the lower level, however, appear to be normal faulting, despite their being aftershocks of large thrust events. We suggest that with the absence of a pull from the detached lithosphere the upper part of the Australian plate in the region of the SDSZ is resistant to subduction, and thus the downward displacements caused by large earthquakes in the adjoining regions result in a localized rebound. The location of the aftershocks within the plate suggests that a new plate boundary is forming, which will eventually replace that outlined by the residual seismicity in the upper level. Thus the leading edge is decoupling, and the boundary will eventually shift back to the lower level of the SDSZ.
Generation of electrostatic waves as a consequence of chaotic ion acceleration in the neutral sheet
Authors: Burinskaya T. , Schriver D. , Ashour‐Abdalla M.
Published: February 2004

The stability of ion distributions with velocity space holes caused by chaotic ion acceleration in the vicinity of the field reversal region in the Earth's magnetotail is investigated. It is shown that such distributions are unstable to electrostatic waves with wave vector directed along the Sun‐Earth line. The solution of the quasi‐linear equation shows that the saturation of the instability occurs due to velocity space trapping of the low‐energy background ions and results in a flattening of the reduced ion distribution function in the region of the original velocity space hole. The energy level of the excited waves in the vicinity of the Earth's midplane is estimated as a function of the initial size of the empty velocity space region.