bluuebunny/crossref_metadata_2025 huggingface dataset:
Radiogenic heat production of crustal rocks: An assessment based on geochemical data
Authors: Wollenberg H. A. , Smith A. R.
Published: February 2008

A survey of the geochemical literature and unpublished data has resulted in the classification of U, Th, and K concentrations by rock type. Over 2500 data entries have been compiled, permitting calculation of their radiogenic heat production. In the igneous rocks mean heat production ranges from highs of 12‐20 heat production units (HPU: µWm−3) in some peralkaline intrusives, through ∼ 4 HPU in acidic, ∼ 2 in intermediate, and ∼ 1 in basic rocks, to a low of 0.3 HPU in ultramafic rocks. Siliceous clastic rocks generally have greater heat production (2 to 4 HPU) than do chemical sedimentary rocks, including the carbonates (0.4 to 2 HPU). The heat production of metamorphic rocks generally depends on the radioelement contents of their igneous and sedimentary predecessors, modified by metamorphic processes. Based on estimates of the proportion of the continental crust that specific rock types occupy, the weighted mean radiogenic heat production of the upper continental crust estimated from this data base is ∼ 3 HPU.
Field line draping about fast coronal mass ejecta: A source of strong out‐of‐the‐ecliptic interplanetary magnetic fields
Authors: Gosling J. T. , McComas D. J.
Published: February 2008

Fast coronal mass ejecta interact strongly with the ambient interplanetary plasma and magnetic field into which they propagate. A shock forms in front of an ejection and the slower moving ambient plasma ahead is accelerated and deflected from its path. In this paper we argue that such flow accelerations and deflections of the ambient plasma must produce a draping of the ambient interplanetary magnetic field about the ejected material similar to that which occurs in the magnetosheath surrounding the earth's magnetosphere. The draping pattern should depend upon the overall size and shape of the ejection, its speed relative to the ambient plasma ahead, the orientation of the ambient magnetic field, and the position where the shocked plasma is sampled. At some locations upstream from an ejection draping leads to an enhancement of the out‐of‐the‐ecliptic field component (BZ) at the expense of the ecliptic components (BX, BY). Although turbulence and fluctuations in the ambient field may confuse the observational situation, we suggest that draping probably plays an important role in producing intervals of strong and prolonged negative BZ in the ecliptic plane at 1 AU and thus also may be an important factor in stimulating geomagnetic activity.
A comparison of canopus ground optical data with images from the Viking UV camera
Authors: Jones A. Vallance , Gattinger R. L. , Creutzberg F. , King R. A. , Prikryl P. , Cogger L. L. , McEwen D. J. , Harris F. R. , Anger C. D. , Murphree J. S. , Koehler R. A.
Published: February 2008

Simultaneous observations of a strong auroral display by the VIKING ultraviolet imager and a meridian scanning photometer of the CANOPUS array have been obtained. These show good overall agreement between the latitude profiles inferred from the data of the two instruments and provide evidence that the images are correctly located in geographic coordinates. The relation between imager signal for vertical viewing and the 4278Å N2+ band brightness as observed from the ground has been determined. A modelling study shows that this relation is sensitive to incident electron energy and could vary by a factor of about 5 for electron energies between 2 and 10 keV. The modelling combined with provisional absolute wavelength sensitivity curves for the imager leads to values in the same range as that from the ground comparison.
Deformation across the Asal‐Ghoubbet Rift, Djibouti, Uplift and crustal extension 1979–1986
Authors: Ruegg J. C. , Kasser M.
Published: February 2008

Geodetic networks of different sizes have been established since 1973 in the Asal‐Ghoubbet rift in south‐western Afar in order to study crustal movements across an extensive plate boundary. Partial or entire remeasurements of these networks during the 1979–1986 interval provide detailed data about strain accumulation and vertical movements after a seismo‐volcanic rifting event that occured in November 1978 along this area similar to an oceanic accreting plate boundary. The results of the geodetic monitoring indicate a continuous opening of the rift zone of about 6 cm/yr since 1979. The deformation is principally distributed in the Inner Floor of the rift with a uniaxial extensional N40°E strain rate of about 15 µstrain/yr. The results of the 1979 and the 1984–85 levellings define the development of a large uplift across the rift zone amounting 15 cm during this 6 year interval. This uplift is accompanied with a relative collapse of the Inner Floor zone of about 4 cm which is associated with creep on the active faults bounding the rift. Two stages of the rifting process are successively observed in Djibouti: an abrupt rifting event in 1978 and then a continuous accumulation stage which is controled by the plate motion and partially by magmatic inflation and active creep faulting.
10Be in polar Ice: Data reflect changes in cosmic ray flux or polar meteorology
Authors: Lal D.
Published: February 2008

We have theoretically estimated the expected changes in the global cosmic ray production of 10Be in the atmosphere with changes in solar activity, and the consequent variations in its fallout in the polar regions. The global 10Be production rate is found to be about 20% higher during periods of very low solar activity, compared to the average solar modulation level observed during the past 3 solar cycles. The stratospheric 10Be fallout pattern has been derived using the fallout data for 90Sr as an analog. This fallout shows an amplitude attenuation by a factor of about three at 70°; the higher the latitude, the higher the attenuation. The results have been compared with the long time series available for 10Be in polar ice in Greenland and in Antarctica, 70°‐78° latitude. It is concluded that the observed variations in 10Be concentrations in ice cores are primarily due to climatic changes, for both short and long period variations. Thus 10Be data can be used as a proxy for climate induced meteorological changes in the polar region.
The Gulf Stream rainband
Authors: Hobbs Peter V.
Published: February 2008

A recurrent and almost stationary region of banded clouds and precipitation has been identified over the Gulf Stream off Cape Hatteras, North Carolina, in winter. This rainband is attributed to the large fluxes of heat and moisture from the warm waters of the Gulf Stream to the colder, overlying air. It is speculated that the Gulf Stream rainband could play a role in cyclogenesis, which is common off the Carolina Coast.
Characteristics of mesospheric internal gravity waves observed by MU Radar
Authors: Muraoka Y. , Kawahira K. , Sato T. , Tsuda T. , Fukao S. , Kato S.
Published: February 2008

We present mesospheric wind data from MU radar at Shigaraki (34.9°N, 136.1°E), Japan, that exhibit a wave motion with a vertical wavelength of 6 km. An analysis of the horizontal and vertical components of the observed wind velocity shows that the wave motion is due to an internal inertia‐gravity wave. It behaves like a stationary wave, similar to lee waves. With the estimated wave parameters, we can derive the mean mesospheric temperature from the dispersion relation for the inertial modes. The temperature is shown to be quite consistent with the mean state of the atmosphere. It is further shown that a scattering echo layer observed simultaneously was closely connected with the vertical propagation of the gravity waves.
Hydroxide decomposition of dimethylsulfoniopropionate to form dimethylsulfide
Authors: Dacey John W. H. , Blough Neil V.
Published: February 2008

The kinetics of DMS production resulting from reaction of OH− with DMSP were investigated as a function of hydroxide concentration and temperature. The reaction was first‐order with respect to DMSP and OH−. The second order rate constant at 20+/−1°C is 0.0044 M−1 sec−1. The activation energy for this reaction is 14.4 kcal mole−1. Our investigation indicates that the rate of reaction of DMSP with OH− is very slow at the pH of seawater (half‐life of about 8 years at 10°C), suggesting that DMSP, which may be a major precursor of DMS in seawater, decomposes in the ocean by other mechanisms. We have cultured a bacterium which produces DMS from DMSP quantitatively at rates many orders of magnitude higher than indicated by OH−1 decomposition, suggesting that enzymatic processes accelerate the production of DMS from DMSP in seawater.
Estimates of solar wind heating inside 0.3 AU
Authors: Freeman John W.
Published: February 2008

We normalize the Helios 1 proton temperature data to 0.3 AU to establish a base temperature‐velocity curve at that distance and ask what solar wind heating rates, versus velocity, closer to the sun, are required to predict that curve. The results indicate that the slope of the solar wind temperature gradient for high‐speed streams, inside 0.3 AU, is about half of that found beyond this distance. The very low‐speed wind on the other hand is found to expand adiabatically all the way out. Intermediate speed winds have enhanced heating rates in proportion to their velocities.
Local transverse ion energization in and near the polar cusp
Authors: André Mats , Koskinen Hannu , Matson Lligo , Erlandson Robert
Published: February 2008

Ion conics are often observed in the dayside polar cusp region of the magnetosphere by the polar orbiting Viking satellite. These ion distributions may be locally heated perpendicularly to the ambient magnetic field to temperatures of about 100 eV. The conics are closely associated with increased electron fluxes but may occur equatorward of the region of ions injected from the magnetosheath. They are also closely related to waves with frequencies up to about 100 Hz. The wave electric field is directed mainly perpendicular to the ambient magnetic field and shows no clear structure near the ion gyrofrequencies or their harmonics. Observations of ion conies at 90° pitch angle and the related waves indicate that the waves may cause significant ion heating, especially of heavy ions.
A prediction for the size of sunspot cycle 22
Authors: Wilson Robert M.
Published: February 2008

Based on “annual” averages, a bivariate analysis of the maximum amplitude of the sunspot cycle against its minimum amplitude and the minimum value of the aa geomagnetic index (in the vicinity of sunspot cycle minimum) results in a fit that closely matches the observable record. The bilinear fit has a high coefficient of correlation (r=0.982) and a small standard deviation (s=9.5), suggesting that it may be useful for predicting the size of a sunspot cycle 3 to 4 years before maximum amplitude occurrence. Applying the fit to Cycle 22, one infers an annual average of maximum amplitude Rmax equal to 92±19 (equivalent to 96±20, in terms of the 13‐month running mean or “smoothed” sunspot number).
Transportation of beryllium with H2O at high pressures: Implication for magma genesis in subduction zones
Authors: Tatsumi Yoshiyuki , Isoyama Hirofumi
Published: February 2008

The degree of transportation of beryllium with H2O is measured under the upper mantle P/T conditions in order to examine the incorporation of 10Be in subduction zone magmas. 5.4±0.3% of original beryllium in the starting serpentinite is extracted with H2O from the system through the dehydration reaction of serpentine at 850°C and 1.5 GPa. It follows that the partial melting of oceanic lithosphere including 10Be‐rich sediment layer is not necessarily required for inclusion of the isotope in island‐arc lavas. We suggest that the dehydration processes in the subducted slab and mantle wedge materials dragged downward by the slab subduction govern the concentration of 10Be in arc lavas.
Observations of vertical velocity over Illinois by the Flatland Radar
Authors: Green J. L. , Gage K. S. , VanZandt T. E. , Clark W. L. , Warnock J. M. , Nastrom G. D.
Published: February 2008

A new VHF clear‐air Doppler radar has been constructed in very flat terrain near Urbana, Illinois. This radar, called the Flatland radar, as presently configured measures a profile of the vertical component of the wind velocity every 2.5 minutes. It is found that typical time variances of vertical velocity over this very flat terrain are similar to the small variances observed during “quiet” periods near mountains. The observed absence of extended periods of large variance supports the hypothesis that the “active” periods observed near mountains are mainly due to orographic effects. The absence of such effects at Flatland should facilitate the study of other meteorological processes. For example, in the case study presented here it is suggested that the vertical motions associated with large‐scale baroclinic storms are measurable by the Flatland radar.
Has the Wharton Basin's Heat flow been perturbed by the formation of a diffuse plate boundary in the Indian Ocean?
Authors: Stein Carol A. , Hobart Michael A. , Abbott Dallas H.
Published: February 2008

The Central Indian Ocean region has heat flow higher than expected for its lithospheric age. This heat flow anomaly is thought to be associated with deformation of sediment and crust and high seismicity. To better constrain the nature of this deformation, we examine the spatial variation of the heat flow. Previous work suggested high heat flux also in the Wharton Basin to the east, which shows less seismicity and deformation. Using new values for lithospheric age from reinterpretation of the magnetic anomalies, we have reexamined the heat flow and found it no higher than expected, in contrast to the Central Indian Basin. This spatial distribution of heat flow highs and expected values is consistent with the pattern of seismicity and deformation and the predictions of the recent diffuse plate boundary model [Wiens et al., 1985] for the region.
Weak field control of remanent magnetization changes produced by uniaxial stress cycling
Authors: Lanham M. , Fuller M.
Published: February 2008

The effect of weak fields (∼0.01 mT.) upon the remanent magnetization of basalts, granodiorites and polycrystalline magnetite during uniaxial compression has been investigated. Samples carrying NRM and AF demagnetized NRM were used. The demagnetized samples showed the largest effects. In the low stress range of less than 100 bars, the influence of stress was demagnetization. In the absence of an applied field, the magnetization rotated away from the compression axis, as is commonly observed. However, with the application of a field of between .01 to .02 mT., the magnetization rotated into alignment with the field as stress was increased. AF demagnetization after the application of 1 kbar of load produced large and repeatable magnetization increases confined to a very narrow coercivity band. AF demagnetization to 10 mT. removed most of the stress induced remanence. These observations are explained in terms of enhanced remanence acquisition in the presence of stress. This reversible effect unblocks soft domain wall sections which can respond to weak applied fields, or to internal demagnetizing fields.
Magnetic rotational hysteresis study on spherical 85–160 nm Fe3O4 particles
Authors: Schmidbauer E.
Published: February 2008

Rotational hysteresis losses Wr were determined as a function of magnetic field H for dispensed spherical Fe3O4 particles of mean grain sizes 85 nm, 127 nm and 162 nm between 78 K and 294 K. The observed Wr‐H curves are compared with theoretical curves for single domain particles. The analysed particles reveal centers of high magnetic anisotropy. Such centers can be of importance during the generation of a thermoremanent magnetization, as they may be the origin of enhanced magnetic stability.
Vacuum weathering of sulfur: Temperature effects and applications to Io
Authors: Nash Douglas B. , Moses Julianne I.
Published: February 2008

We have conducted laboratory experiments on frozen sulfur to further study the vacuum‐weathering phenomenon discovered by Nash [1987]. In this report we discuss the effect of surface temperature on the initial transient and subsequent steady‐state behavior of the vacuum‐sublimation rate and the UV/VIS spectral reflectance of frozen sulfur. We show that surface temperature is a dominant parameter controlling the rate of vacuum weathering of sulfur, a finding consistent with the steep vapor pressure curve of sulfur. We set limits on the prodigious sublimation rates expected for sulfur from hot spots on Io's surface and further define the range of changes that occur in the spectral reflectance of freshly frozen sulfur. These results imply that any freshly‐frozen sulfur deposits on Io at typical Io hotspot temperatures should display major transient changes in color (and microtexture) in a matter of hours to days. These rapid changes in spectral reflectivity should be readily detectable by high time‐resolution synoptic observations of Io's spectrum in the UV/VIS by spacecraft optical instruments such as on Galileo and, in certain instances (e.g., during or immediately after large‐scale Io volcanic activity), by Earthbased telescopes. Such observations should be useful in determining the frequency of occurrence, surface location, and areal scale of any sulfur volcanic activity on Io.
Shock compression of Wüstite
Authors: Yagi T. , Fukuoka K. , Takei H. , Syono Y.
Published: February 2008

Hugoniot compression curve of wüstite (Fe1‐xO) was studied up to 120 GPa using a double‐stage light‐gas gun. Pore‐free polycrystalline wüstite was grown by the floating zone method and platelet specimens, typically 10 × 14 × 2 mm³, were prepared. The inclined mirror method was adopted to record the shock compression state and both the impedance matching solution and the free surface approximation were used to deduce the Hugoniot compression curve. A discontinuous increase in density was observed at around 70 GPa. This result is consistent with the previous shock compression experiment using hot‐pressed specimen. The nature of this discontinuity is discussed.
Dehydration mechanism in the Antarctic stratosphere during winter
Authors: Ramaswamy V.
Published: February 2008

The growth of ice nuclei through deposition of water vapor at temperatures below frost point is investigated in the context of the Antarctic winter stratosphere. The altitude and the ambient water vapor mixing ratio, as well as the size of the nuclei determine the ice particle growth rate, with higher altitudes requiring colder temperatures for ice deposition. The magnitude of the temperature decrease below the frost point and its evolution over the winter determine the residence time of the growing ice particles and the loss of water vapor at any altitude. A winter‐long simulation, using the observed South Pole daily temperatures, suggests that, in the limit of weak latitudinal mixing over the austral winter, considerable dehydration can occur within the polar vortex, with the higher altitudes (above 22 km.) experiencing the least losses.
O3 and NO2 ground‐based measurements by visible spectrometry during Arctic winter and spring 1988
Authors: Pommereau Jean Pierre , Goutail Florence
Published: February 2008

Ozone and nitrogen dioxide have been monitored by ground‐based visible spectrometry from ESRANGE base at Kiruna in Sweden (68N, 22E) from mid January until early April 1988. Stratospheric winter was exceptionally long and cold this year and spring final warming developed only in March. Ozone column was found to increase slowly during this period from 400 DU to 450 DU in the average. After February 15, several rapid decreases by 30% lasting a few days have been observed in correlation with advection from the North West. They are indicative of the presence of an ozone minimum above polar regions during the period. The diurnal variation amplitude is in agreement with the current NOX photochemistry assuming the NO2 layer centered around 30 km. As already observed in the Southern polar regions, the day to day and seasonal NO2 variations are closely associated with stratospheric temperature. Calculations and comparison with other experimental data show that this behaviour cannot de interpreted with the current photochemistry.
The morphology and meteorology of southern hemisphere spring total ozone mini‐holes
Authors: Newman Paul A. , Lait Leslie R. , Schoeberl Mark R.
Published: February 2008

Rapid ozone decreases near the base of the Antarctic Penninsula have recently been observed in total ozone maps produced from the Total Ozone Mapping Spectrometer (TOMS). These rapid decreases have been labeled mini‐holes because of their relatively small horizontal scales (1000‐3000 km) with respect to the larger scale ozone hole. The mini‐holes do not show a preferential genesis region, but they do tend to intensify most strongly over the Antarctic Penninsula and the East Antarctica ice sheet. Typical time scales are on the order of 1‐5 days. The mini‐holes have been analyzed using a digital filter. Two mini‐holes case studies from 1987 show: 1) a strong correlation of the total ozone mini‐hole with a temperature mini‐hole (i.e. a negative temperature perturbation), 2) a westward tilt with altitude of the temperature mini‐hole. 3) the mini‐hole in ozone is phase shifted slightly to the east of a high in the geopotential height field, and 4) the mini‐hole is phase shifted slightly to the west of a local low in the Ertel's potential vorticity (Epv) field (note that an Epv low is generally associated with cyclonic flow in the southern hemisphere).
Slip budget and potential for a M7 earthquake in central California
Authors: Harris Ruth A. , Archuleta Ralph J.
Published: February 2008

The slip rate budget of the San Andreas fault (SAF) in central California, which is approximately 33 mm/yr, is accounted for by a change in the slip release mechanism along the fault. In the NW section of the fault, between Bear Valley and Monarch Peak, creep apparently accounts for the slip budget with the seismicity contributing negligibly. The section at Parkfield marks the transition from a creeping to a locked fault trace. Since the M8 1857 earthquake five M6 earthquakes have occurred but have not completely accounted for the slip budget. Southeast of Parkfield, the SAF has been locked since 1857. From Cholame to Bitterwater Valley this section now lags the deep slip by the amount of slip released in 1857; consequently faulting in this section could occur at the time of the next Parkfield earthquake. If this earthquake releases the slip deficit accumulated in the transition zone and in the locked zone, the earthquake will have a moment‐magnitude M7.2.
Description of substorms in the tail incorporating boundary layer and neutral line effects
Authors: Lyons L. R. , Nishida A.
Published: February 2008

We propose a description of the substorm expansion phase that includes the formation of a neutral line in the relatively near‐earth portion of the tail plasma sheet and phenomena observed in the plasma sheet boundary layer (PSBL). Our proposal is based on previously published observations of the central plasma sheet and PSBL from ISEE‐1 at |x| < 22 Re (GSM coordinates) and of the source region for the PSBL from ISEE‐3 near x = −80 Re, as well as on an inferred spatial association of auroral arcs with the PSBL and neutral line signatures observed by other satellites. Specifically, we propose that substorm onset results from the formation of a neutral line within the preexisting source region for the PSBL. The source region is presumably the tail current sheet, which we suggest extends well earthward of 80 Re. Both before and after the neutral line forms, auroral field‐aligned currents and large ion flows remain confined to the PSBL earthward of the source region.
The effect of strong velocity shears on incoherent scatter spectra: A new interpretation of unusual high latitude spectra
Authors: Swartz Wesley E. , Providakes James F. , Kelley Michael C. , Vickrey James F.
Published: February 2008

Intense velocity shears that are unresolved within the scattering volume can distort incoherent scatter spectra in ways that could be confused with the effects of non‐Maxwellian plasmas or ion hot spots. These spectra lose the usual double humped characteristic of the more familiar incoherent scatter spectral shapes, and standard analysis (ignoring velocity shears) of such spectra yields severe under estimates of the electron temperature and over estimates of the ion temperature, with an implied, but erroneous, result that Te < Ti. High resolution velocity measurements from the HILAT satellite demonstrate that such strong shears do exist at high latitudes.
The distribution of random segment lengths
Authors: Penland Cecile
Published: February 2008

Choice of the correct distribution of sediment thicknesses is necessary in studying reflection of acoustic rays from randomly layered sediments and in many seismic applications. We consider a set of N segment lengths, {1i}, i=1, 2, 3,..., N, whose combined length is L. Three cases are of interest: 1) L and N are known constants, 2) the number of segments N is a known constant but L is a random variable with given expectation value , and 3) both N and L are random variables with given expectation values  and , respectively. The distribution of segments lengths is calculated for each of the three cases under the assumption that any set {1i} is as probable as any other set fulfilling the same conditions. The expressions are simple and easy to implement.
Age measurement of the submarine montagnais impact crater
Authors: Bottomley Richard , York Derek
Published: February 2008

Seven laser‐generated 40Ar/39Ar age spectra of melt‐rocks from the newly‐described (submarine) Montagnais Crater are presented. While the age spectra are not completely straight forward to interpret, the evidence is very strong that the impact occurred approximately 51 m.y. ago. Thus the Montagnais event is associated with neither the K‐T nor the North American tektite events. Such an age is also totally out of phase with the 26–32 m.y. cycles proposed recently for the meteorite impact and extinction records, as it falls roughly midway between two of the most precisely dated points in such proposed cycles (the K‐T boundary and the North American tektite event).
Geometry and treatment of fiducial networks: Effect on GPS baseline precision in South America
Authors: Freymueller Jeffrey T. , Golombek Matthew P.
Published: February 2008

A covariance analysis shows that Global Positioning System (GPS) baseline precision in northern South America is substantially improved when fiducial stations (used to improve satellite orbit solutions and establish a reference frame) in North America are supplemented by stations in Hawaii, Australia and New Zealand. The formal errors for a variety of fiducial networks, some including stations in South America, are almost identical when their locations are held fixed. However, the consider error, which is the computed sensitivity to uncertainties in the fiducial station locations and is an estimate of the systematic error, is strongly dependent on the fiducial network geometry. If fiducial station locations are estimated with small a priori uncertainties, the various networks are practically identical, although the total uncertainty is slightly larger for the fiducials‐fixed networks. The sensitivity analysis indicates that the baselines of interest are very sensitive to uncertainties in the locations of the closest fiducial stations. If the uncertainty in the fiducial station locations is reduced to approximately 1 cm from the 4 cm assumed, any of the networks used in this analysis would be acceptable for GPS geodesy in northern South America.
Mineralogy of insoluble particles in the Vostok Antarctic ice core over the last climatic cycle (150 kyr)
Authors: Gaudichet A. , De Angelis M. , Lefevre R. , Petit J. R. , Korotkevitch Y. S. , Petrov V. N.
Published: February 2008

Mineralogical characterisation of insoluble microparticles entrapped in ice layers successively deposited on the Antarctic continent is a useful tool for paleoclimate reconstruction. Indeed, it is likely to provide information on the distribution of potential source areas and of climatic conditions prevailing over different time periods. A first study, covering the last 30 kyr and including the end of the last glacial age, has shown that, over central East Antarctica, continental input was soil derived and originated probably from South America. In this work, the time period covered is l60 kyrs which includes a complete climate cycle. Clay species and particle size considerations suggest that local sources and Australia have been of minor importance for the studied area over the last 160 kyr. They support the hypothesis of colder and drier conditions prevailing over the source areas during glacial extrema. Lastly the predominance of illite, feldspar and quartz in association with presumably weathered volcanic products is consistent with a continental input originating from South America for the East Antarctic area, but is not in complete agreement with the results of general circulation models.
P‐coda at distances 80° – 120° and structure beneath subduction zones: Example of Chile
Authors: Souriau Annie
Published: February 2008

Strong phases are sometimes observed between P and PP for earthquakes at epicentral distances 80° – 120°. The present study analyzes as an example broadband data from a Chilean earthquake recorded in Europe by the NARS network, and by worldwide distributed GEOSCOPE stations. Clear phases are observed in the P‐coda only for the European stations.

Underside reflections at upper mantle discontinuities beneath the PP bounce point at the Mid‐Atlantic Ridge are unable to explain these phases. A discontinuity in the lowermost mantle at the top of D″ is also discarded as a possible explanation.

Reflections and conversions at a strong reflector about 200 km deep beneath Chile provide a satisfying explanation of the observations. The P‐coda is dominated by waves leaving the focus as S‐waves. The focal solution and the resulting radiation pattern explain the variations with azimuth and epicentral distance of the phases observed in the P‐coda.

The reflector at 200 km beneath Chile may be the upper boundary of a piece of slab detached from the Nazca plate. Alternatively, it may result from the chemical differenciation of the slab during its subduction. Modelling P‐coda generated in other subduction zones may help to specify this differenciation process.
Distribution of the pCO2 in surface seawater of the western and central equatorial Pacific during the 1986/87 El Niño/Southern oscillation event
Authors: Inoue Hisayuki , Sugimura Yukio
Published: February 2008

Measurements of the partial pressure of CO2 in surface seawater (pCO2) of the central and western equatorial Pacific were made in January and February 1987, with the main objective of studying variations in CO2 exchange between the air and the sea during the El Niño/Southern Oscillation (ENSO) event.

In January 1987, the western equatorial Pacific had pCO2 distributions similar to those during non‐ENSO periods, despite the fact that large variations in pCO2 had occurred during the 1982/83 ENSO event.

The pCO2 along 180° and 160°E was fairly constant (336.7 µatm to 355.7 µatm), while along 160°W it varied remarkably (342.8 µatm to 409.4 µatm). A maximum appeared near the equator, and the pCO2 was quite high from 3°N to 5°S (365.7 µatm to 409.4 µatm).

In January and February 1987, the pCO2 in the surface seawater of the central equatorial Pacific was disturbed due to the ENSO event, but there seems to have been a net positive exchange of CO2 between the sea and air, compared to the 1982/83 ENSO event.
Mars thermospheric general circulation model: Calculations for the arrival of Phobos at Mars
Authors: Bougher S. W. , Dickinson R. E. , Roble R. G. , Ridley E. C.
Published: February 2008

The NCAR thermospheric general circulation model (TGCM) for the Earth's thermosphere has been modified to examine the three‐dimensional structure and circulation of the upper mesosphere and thermosphere of Mars (MTGCM). The computational framework and major processes unique to a CO2 thermosphere are similar to those utilized in a recent Venus TGCM. Mean orbital, seasonal, and solar conditions are specified. An Equinox version of the MTGCM is used to predict the Mars solar driven global circulation and structure for a non‐dusty (quiet) lower atmosphere at the time of arrival of the two Phobos spacecraft.
A large‐scale ionospheric depletion by intense radio wave heating
Authors: Wright J. W. , Kopka H. , Stubbe P.
Published: February 2008

A large (100 km N/S), stable, smoothly‐structured and significant depletion (15% in number density) of the daytime Tromsø F‐region was produced inadvertently during a Heater polarisation and beam‐forming procedure. We show that the depletion coincided with the passage of an atmospheric gravity wave of natural origin which served as a large‐scale ‘seed‘ depletion for the self‐focussing instability.
On the possibility of quasi‐static convection in the quiet magnetotail
Authors: Kivelson Margaret G. , Spence Harlan E.
Published: February 2008

The magnetotail is known to serve as a reservoir of energy transferred into the terrestrial magnetosphere from the solar wind. In principle, the stored energy can be dissipated impulsively, as in a substorm, or steadily through the process of steady adiabatic plasma convection. However, some theoretical arguments have suggested that quasi‐static adiabatic convection cannot occur throughout the magnetotail because of the structure of the magnetic field. Here we reexamine the question. We show that in a magnetotail of finite width, downtail pressure gradients depend strongly on the ratio of the potential across half the tail to the ion temperature in the far tail (60 RE). For pertinent quiet time ratios (∼3), a Tsyganenko quiet‐time magnetic field model is consistent with steady convection.
Merging of aircraft vortex trails: Similarities to magnetic field merging
Authors: Gurnett Donald A.
Published: February 2008

This paper discusses the phenomenological and formal similarities between the merging of aircraft vortex trails and the merging of magnetic field lines in a plasma. High‐resolution photographs are shown of smoke trails from the wing tips of an airplane. These photographs show that the two vortex trails merge together downstream of the aircraft in a way similar to the merging of oppositely directed magnetic field lines in a plasma. Although there are some differences, this correspondence is apparently related to the fact that the vorticity equation in a fluid has the same mathematical form as the magnetic field equation in a MHD plasma. In both cases the merging proceeds at a rate considerably faster than would be predicted from classical estimates of the viscosity and resistivity. The enhanced merging rate in the fluid case appears to result from turbulence that increases the diffusion rate in the merging region.
Energetic electron components at geosynchronous orbit
Authors: Cayton T. E. , Belian R. D. , Gary S. P. , Fritz T. A. , Baker D. N.
Published: February 2008

Energy distribution functions have been derived from energetic (30–2000 keV) electron fluxes observed simultaneously by three geosynchronous orbit satellites throughout the year 1986. These distributions, as well as others derived from empirical models of outer magnetospheric electron fluxes, can be resolved into two distinct relativistic Maxwellian components which are each fully parameterized by a density and a temperature. The resulting four‐parameter model of magnetospheric energetic electrons yields the following results: Higher energy (300–2000 keV) “hard” electrons are characterized by Th ≃200 keV and nh ∼ 10−4 cm−3; nh decreases during substorms, but Th shows very little change on a substorm (hourly) time scale. Lower energy (30–300 keV) “soft” electrons have nominal parameter values Ts ∼25 keV and ns ∼ 5 × 10−3 cm−3; intense substorm‐related injections and extreme temporal variability characterize this component. This four parameter characterization presents a new, simplified procedure for the interpretation of energetic electron data in the outer magnetosphere.
Results of the first statistical study of Pioneer Venus Orbiter plasma observations in the distant Venus tail: Evidence for a hemispheric asymmetry in the pickup of ionospheric ions
Authors: Intriligator Devrie S.
Published: February 2008

Pioneer Venus Orbiter plasma and magnetometer observations from the first nine tail seasons of crossings of the Venus wake are used to study ion pickup in the far wake of an unmagnetized object embedded in the solar wind. This first statistical study treats all of the plasma spectra containing pickup ions in the vicinity of the Venus tail. We find a hemispheric asymmetry in the pickup of ionospheric ions, with approximately four times more O+ events observed in the “northern” magnetic hemisphere (where Z″ > O), i.e., the induced electric field points outward, (away from the ionopause boundary) than in the “southern” (Z″ < O) magnetic hemisphere. Out of a total of 167 large O+ events, 125, or 75%, occurred in the northern hemisphere when position is calculated in terms of Venus radii and 129 or 77% occurred in the “northern” hemisphere when position is expressed in gyroradii. This hemispheric asymmetry in ion pickup is consistent with the prediction of the Cloutier et al. (1974) mass loading model for Venusian ions above the ionopause boundary.
Structures of the West African Craton Margin across southern Mauritania inferred from a 450‐km geoelectrical profile
Authors: Ritz M. , Robineau B. , Vassal J. , Bellion Y. , Dukhan M.
Published: February 2008

Magnetotelluric (MT) measurements were carried out at 20 sites, extending 450 km across southern Mauritania in order to study lithospheric structures related to the West African craton (WAC) margin. The MT profile starts to the west on the Senegal‐Mauritania basin (S‐M basin), traverses across the Mauritanides orogenic belt, and terminates on the western border of the WAC (Taoudeni basin). Distortion effects due to local shallow inhomogeneities are present in nearly all of the basin data. In such a situation, the preliminary interpretation of the data was done by using 1D inversions based upon rotationally invariant parameters. Such distortion is not apparent for the belt and craton sites, and 1D inversions were followed by 2D modeling. The models produced reveal a clear crustal subdivision into a resistive upper crust underlain by a two‐layer lower crust with two conductors, one at mid‐crustal depths (supposed fluid‐produced) beneath the S‐M basin and the second at the base of the crust beneath the WAC. The 14‐km‐thick conductive material below the Mauritanides belt is interpreted as large imbricated thrusts representing the deep roots of the Mauritanides nappes. The models also show that significant contrasts in resistivity extend deep in the lithosphere between the cratonic area and the Senegal microplate.
Whistler wings from moving electrodes in a magnetized laboratory plasma
Authors: Stenzel R. L. , Urrutia J. M.
Published: February 2008

In a large laboratory plasma the current pattern set up by moving electrodes has been measured. It is observed that the current flows oblique to the magnetic field
at an angle given by the electrode speed across
and the current penetration along
which is controlled by whistler waves. The current pattern, characterized as “whistler wings”, occurs irrespective of whether the electrodes collect electrons/ions or emit fast electron beams. These results are relevant to active experiments in space involving electrodynamic tethers, beam injections and large space stations.
The 1988 Antarctic ozone depletion: Comparison with previous year depletions
Authors: Schoeberl Mark R. , Stolarski Richard S. , Krueger Arlin J.
Published: February 2008

The 1988 spring Antarctic ozone depletion was observed by TOMS to be substantially smaller than in recent years. The minimum polar total ozone values declined only 15% during September 1988 compared to nearly 50% during September 1987. At southern midlatitudes, exceptionally high total ozone values were recorded beginning in July 1988. The total integrated southern hemispheric ozone increased rapidly during the Austral spring, approaching 1980 levels during October. The high midlatitude total ozone values were associated with a substantial increase in eddy activity as indicated by the standard deviation in total ozone in the zonal band 30°–60°S. The standard deviation also correlates with the QBO cycling of the tropical winds. Mechanisms through which the increased midlatitude eddy activity could disrupt the formation of the Antarctic ozone hole are briefly discussed.
Settling particles with positive Ce anomalies from the Japan Sea
Authors: Masuzawa Toshiyuki , Koyama Mutsuo
Published: February 2008

Rare earth element patterns of settling particles collected at five water depths (890 to 3,240 m) of the Japan Sea show significant positive Ce anomalies. The very surface sediment exhibits a slightly positive one. Excess Ce content over the Ce/La ratio of average shale increases with increasing excess Mn content from 890 to 1,870 m, and it possibly remains constant below this depth. These results give evidence for the removal of Ce in association with the removal of Mn from seawater by settling particles.
Helium isotopes and tectonics in southern Italy
Authors: Sano Yuji , Wakita Hiroshi , Italiano Francesco , Nuccio Mario P.
Published: February 2008

Geodynamic evolution of southern Italy can be understood within the framework of the Mediterranean‐Alpine System. Subduction of a plate along the Sicily‐Calabrian forearc under the Tyrrhenian Sea has been suggested by many geophysicists, although it is not yet confirmed and remains somewhat controversial. Helium isotope ratios provide useful information on the geotectonic structure of the region. We report here the ³He/4He ratios of terrestrial gas samples from southern Italy. The observed ³He/4He ratios are relatively high in the Eolian volcanic arc region and low in the other areas. Dichotomous explanations are presented. Firstly volcanic arc‐forearc hypothesis suggests the subduction along the Sicily‐Calabrian forearc. Secondly horizontal transport hypothesis is described based on the relationship between the ratios and radial distance from the recent spreading basin in Southern Tyrrhenian Sea.
The nature of the pressure‐induced metallization of FeO and its implications to the core‐mantle boundary
Authors: Sherman David M.
Published: February 2008

The pressure and temperature‐induced metallization of FeO discovered by Knittle et al [1986] is here argued to result from a Mott transition associated with increased Fe(3d)‐Fe(3d) orbital overlap at high pressures. The metallic bonding in the Fe(3d) t2g band may account for the 4% volume decrease of FeO associated with the metallization transition. If so, a structural change (B1→B2 or B1→B8) or spin‐pairing transition may not need to be invoked to explain the high pressure phase transition in FeO. Below the Neel temperature of FeO, antiferromagnetic ordering of Fe spins forces the Fe (t2g) electrons to be localized. Since the Neel temperature increases with pressure, no metallization transition of FeO was observed by Yagi et al. [1985] in their high‐pressure measurements at 300K. Neither (Mg, Fe)O and (Mg,Fe)SiO3 can undergo a Mott transition at high pressure and temperature. Consequently, it is here argued that a lower mantle containing only these phases should be electrically insulating. Finally, the formation of itinerant d‐electrons in FeO may be a necessary, if not sufficient, condition for the apparent alloying of FeO with Fe. Such alloying may allow oxygen to be incorporated into the outer core.
Dynamical influences from thermal‐chemical instabilities at the core‐mantle boundary
Authors: Hansen Ulrich , Yuen David A.
Published: February 2008

Two‐dimensional, time‐dependent calculations show that the thermal and flow structures can be influenced by the lower‐mantle thermal‐chemical instabilities. The style of the core‐mantle boundary (CMB) deformation in thermal‐chemical convection is different from that obtained in thermal convection. The amplitude of CMB hills is reduced greatly from the depth‐dependence of thermal expansivity, found in recent high‐pressure experiments.
On the use of spectral methods for the determination of fractal dimension
Authors: Hough S. E.
Published: February 2008

This paper discusses the use of fractal theory for quantitative analysis of profiles from two‐dimensional surfaces. The theoretical relationship between spectral parameters and fractal dimension is examined, including the conditions under which the derived relationship between spectral parameters and fractal dimension by Voss (1985) is valid, and the limitations in making inferences from spectral parameters. Applications of fractal theory to geophysical data are also discussed. In particular, it is shown that an amplitude spectrum with a decay corresponding to a fractal dimension of 1.5 can result from the concatenation of time series with decays corresponding to different fractal dimensions. It has been shown that the spectral density of a fractal distribution will be characterized by a power‐law decay, but this paper illustrates that a power‐law decay is not sufficient to identify a fractal distribution. Although this paper discusses applications to the study of Earth topography, the results are applicable to the study of any one‐dimensional profile.
Seawater and porewater fluorescence in the Santa Barbara Basin
Authors: Chen Robert F. , Bada Jeffrey L.
Published: February 2008

The fluorescence of filtered seawater and porewaters from the Santa Barbara Basin has been measured. Porewater fluorescence exceeded that in the overlying seawater by a factor of 10–500. The water column profile of fluorescence can be explained by photochemical degradation of fluorescent components in surface waters and diffusion of “marine humic substances” from the sediments into basin bottom waters. Porewater fluorescence increases linearly with depth to at least 2 m and correlates well with titration alkalinity and ammonium ion concentration. The sources and the type of molecules responsible for fluorescence remain unknown.
Genesis of the Southern Oscillation within the atmosphere: Illustration with global general circulation models
Authors: Hameed Sultan , Sperber Kenneth R. , Cess Robert D.
Published: February 2008

In this study we compare simulations of climate in two general circulation models: a coupled GCM in which the atmosphere and ocean interact dynamically and a slab GCM in which the ocean is represented by a static layer. W. L. Gates and G. L. Potter carried out multiyear simulations of global climate with these two models at the Lawrence Livermore National Laboratory. These simulations have no imposed conditions on the nature of the interannual variability. We present results showing that the slab model generates the signal of the Southern Oscillation in atmospheric pressure during the northern spring season but the signal is not propagated to other seasons. The coupled model manifests the Southern Oscillation in other seasons and in several climatic variables in which it is found in nature.
On the disproportionate role of tropospheric ozone as a filter against solar UV‐B radiation
Authors: Brühl C. , Crutzen P. J.
Published: February 2008

Increases in tropospheric ozone due to photochemical production, mostly due to growing industrial and technological NOx‐ emissions, in the industrialized northern hemisphere can overcompensate for increased UV‐B radiation resulting from ozone depletions due to chlorine‐catalyzed reactions in the stratosphere. This is especially the case in the summer months, because during this period a large fraction of the UV, which reaches the surface as diffuse radiation, is scattered by air molecules, droplets and aerosol particles in the troposphere. This causes a relatively longer path through tropospheric than through stratospheric ozone. Analyses using calculated, as well as observed ozone profiles at the station Hohenpeißenberg in Bavaria, FRG, show, that decreases of UV‐B radiation at the earth's surface are possible even when total ozone declines.