bluuebunny/crossref_metadata_2025 huggingface dataset:
Archean oceanic flake tectonics
Authors: Hoffman Paul F. , Ranalli Giorgio
Published: February 2008

Assuming that the Archean mantle was hotter and the oceanic crust thicker than at present, we estimate that the Archean oceanic lithosphere had a "sandwich" rheology, with the lower crust behaving as a soft, ductile layer. Accordingly, the Archean oceanic lithosphere had a rheological structure similar to present‐day continental lithosphere but unlike present‐day oceanic lithosphere. The thickness of the ductile layer is a decreasing function of age, while its strength is an increasing function of age. The buoyancy problem in Archean subduction could be overcome by delamination of oceanic upper crust, but mass balance calculation indicates that most Archean oceanic crust must have been recycled. Where the right dynamic conditions existed for delamination, oceanic flake tectonics may have been an important process leading to the preservation of oceanic upper crust in "greenstone belts" that are characteristic of Archean terrains.
Sensitivity of tropospheric hydrogen peroxide to global chemical and climate change
Authors: Thompson Anne M. , Owens Melody A. , Stewart Richard W.
Published: February 2008

The sensitivities of tropospheric HO2 and hydrogen peroxide (H2O2) levels to increases in CH4, CO and NO emissions and to changes in stratospheric O3 and tropospheric O3 and H2O have been evaluated with a one‐dimensional photochemical model. Specific scenarios of CH4‐CO‐NOx emissions and global climate changes are used to predict HO2 and H2O2 changes between 1980 and 2030. Calculations are made for urban and nonurban continental conditions and for low latitudes. Generally, CO and CH4 emissions will enhance H2O2 (as OH is converted to HO2); NO emissions will suppress H2O2 except in very low NOx regions. A global warming (with increased H2O vapor) or stratospheric O3 depletion will add to H2O2. Hydrogen peroxide increases from 1980 to 2030 could be 100% or more in the urban boundary layer.

Increases in CH4, CO and O3 that have occurred in the industrial era (since 1800) have probably produced temporal increases in background HO2 and H2O2. It might be possible to use H2O2 in ice cores to track these changes. Where formation of sulfuric acid in cloudwater and precipitation is oxidant limited, H2O2 and HO2 increases could be contributing to increases in acid precipitation.
Can remanent magnetization in the deep crust contribute to long wavelength magnetic anomalies?
Authors: Shive Peter N.
Published: February 2008

Long wavelength aeromagnetic anomalies require sources in the deep crust that are far more magnetic than the measured induced magnetization of lower crustal rocks. Several scientists have suggested that remanence in the deep crust may provide the missing magnetization. This is not likely, either through stable and/or viscous remanence. Bodies large enough to contribute to surface anomalies and carrying stable remanence probably cooled slowly enough that they are subdivided into zones of alternating polarity. This subdivision sharply reduces the power in the long wavelength portion of the anomaly spectrum. On the other hand, if such a body carries a viscous remanence, the viscous component will be acquired in such a way as to bring the total magnetization of the body into equilibrium with the earth's field. This equilibrium total magnetization is only about 25% greater than the induced magnetization, not enough to explain the discrepancy.
Doppler shift of auroral Lyman α observed from a satellite
Authors: Ishimoto M. , Meng C.‐I. , Romick G. R. , Huffman R. E.
Published: February 2008

The first documentation of Doppler shifted auroral Lyman α emission resulting from incident energetic protons in the auroral regions has been made using nadir VUV satellite spectral observations. The auroral Lyman α emission from high‐velocity protons is expected to show a red shifted wavelength displacement based on ground‐based observations of Balmer lines. VUV spectra (1100–1900Å) taken over five sample auroral oval crossings by a nadir‐viewing satellite in 1978 consistently show the Lyman α emission displaced toward longer wavelengths with a larger line width. The intensity peaks were shifted up to 4 Å when the geocoronal Lyman α emission profile was subtracted from the Lyman α emission profile observed over the auroral regions. The optical observations infer the auroral proton precipitation with average energies of 34 keV and an energy flux of 0.1 erg cm−1s−1 sr−1 when interpreted according to available model calculations. These values agree reasonably well with the average values for the characteristics of nightside incident auroral protons based on previous statistical satellite particle precipitation observations.
Attenuation in western Nevada: Preliminary results from earthquake and explosion sources
Authors: Hough S. E. , Anderson J. G. , Patton H. J.
Published: February 2008

We present preliminary results from a study of the attenuation of regional seismic waves at frequencies between 1 and 15 Hz and distances up to 250 km in Western Nevada. Following the methods of Anderson and Hough (1984) and Hough et al. (1988), we parameterize the asymptote of the high frequency acceleration spectrum by a two‐parameter model. We relate the model parameters to a two‐layer model for Qi and Qd, the frequency‐independent and the frequency dependent components of the quality factor. We comparing our results to previously published Q studies in the Basin and Range and find that our estimate of total Q, Qt, in the shallow crust is consistent with shear wave Q at close distances as determined by Chavez and Priestley (1985). For depths greater than 5 km, we obtain a Qt which is consistent with previous estimates of coda Q (Singh and Herrmann, 1983) and LgQ (Chavez and Priestley, 1986), suggesting that both coda Q and LgQ are insensitive to near‐surface contributions to attenuation.

In addition to our attenuation results, we compare the high frequency content of explosions with that of earthquakes. Our results from S waves are similar to results for Pg waves by Chael et al. (1987), and Chael (1988), who find that the Pg wave spectra from explosions are depleted in high frequency energy with respect to earthquake spectra. Taylor et al. (1988) look at spectral energy at 1–2 Hz compared to energy at 6–8 Hz for earthquakes and explosions and find, especially for Lg waves, relative depletion of the higher frequencies for explosion sources. This result is also consistent with the results from this study.
Lower‐crustal porosity from electrical measurements and inferences about composition from seismic velocities
Authors: Hyndman R. D. , Klemperer S. L.
Published: February 2008

Seismic refraction velocities provide an important constraint on the composition of the lower continental crust. However, valid inferences on the composition may require allowance for the effect of porosity. Many refraction velocities obtained for the lower crust are characteristic of laboratory values for intermediate composition rocks, in disagreement with other estimates of a primarily mafic lower crust composition. The discrepancy is particularly large in Phanerozoic areas where most velocities are less than 7.0 km s−1, and where non‐seismic estimates such as from xenoliths are almost exclusively mafic. A mafic composition can be reconciled with the refraction data if the insitu velocities are reduced by porosity of a few percent. Support for the model is given by magnetotelluric measurements which have shown the lower crust to be commonly very electrically conductive. Lower crustal porosities of up to several percent are inferred, particularly in areas where the resistivity is less than 100 ohm‐m.
A comparison of current‐voltage relationships of collectors in the Earth's ionosphere with and without electron beam emission
Authors: Myers Neil B. , Raitt W. John , Gilchrist Brian E. , Banks Peter M. , Neubert Torsten , Williamson P. Roger , Sasaki Susumu
Published: February 2008

The CHARGE‐2 sounding rocket flight was designed primarily to measure the vehicle potential of an electron‐emitting payload in the mid‐latitude ionosphere. The experiment was separated into two sections, the larger section carried a 1 keV electron gun and was referred to as the mother vehicle. The smaller section, referred to as the daughter, was connected to the mother by an insulated, conducting tether, and was deployed to a distance of up to 426 m across the geomagnetic field. In addition to performing electron beam experiments, the mother vehicle contained a high voltage power supply capable of applying up to 450 V and 28 mA to the daughter through the tether. Steady state potentials of up to 560 V were measured for the mother vehicle during beam emissions of up to 36 mA. The daughter collected currents up to 6.5 mA and attained potentials of up to 1000 V relative to the background ionosphere. The CHARGE‐2 experiment was unique in that for the first time a comparison can be made of the current collection between an electron beam‐emitting vehicle and a non‐emitting vehicle at high potentials (400 V to 1000 V). The daughter current collection agreed well with the Parker‐Murphy model, while the mother current collection always exceeded the Parker‐Murphy limit and even exceeded the Langmuir‐Blodgett predicted current below 240 km. The additional current collection of the mother is attributed to beam‐plasma interactions. This additional source of collected current may be very important for successful electron beam emission at altitudes below 240 km.
Temporal variations in low degree zonal harmonics from Starlette orbit analysis
Authors: Cheng M. K. , Eanes R. J. , Shum C. K. , Schutz B. E. , Tapley B. D.
Published: February 2008

The dynamical effect of temporal variations in the zonal harmonics of the Earth's gravitational potential due to tidal and meteorological mass redistribution has been observed using satellite laser ranging (SLR) measurements to Starlette. The secular variations in the Earth's zonal harmonics,
, and the year‐to‐year fluctuation of the even degree annual and semi‐annual tides (Sa and Ssa) have been determined from a continuous Starlette orbit spanning from 1983 through 1985. When variations in higher degree zonals are assumed to be zero and the 18.6‐year tide is fixed to an equilibrium value, the results are:
,
,
, in units of 10−11 yr−1. The Starlette‐derived
is in good agreement with the value observed from Lageos and values predicted from postglacial rebound. The mean values for Sa and Ssa tides are in good agreement with other tide solutions. The year‐to‐year fluctuations of the even degree Sa, deduced from Starlette node variations, are about 25% of the mean value obtained during the three‐year Starlette orbit span.
A temperature profile of the mantle transition zone
Authors: Ito Eiji , Katsura Tomoo
Published: February 2008

The temperature distribution across the transition zone has been determined on the high‐pressure phase equilibria in the system Mg2SiO4‐Fe2SiO4 recently determined by Katsura and Ito [1988] and Ito and Takahashi [1988]. The temperature at the base of the transition zone (655 km depth) is estimated to be about 1600°C, assuming that the spinel dissociation is responsible for the sharp seismic discontinuity implied by study of reflected waves. This estimation would be little modified for the chemically stratified mantle models, since the lower mantle is characterized by the stability of perovskite. The temperatures in the region from 350 km to 655 km depth are calculated for a peridotitic mantle model, assuming an adiabatic temperature gradient. The α‐β and β‐γ transformations in (Mg,Fe)2SiO4 make the temperature profile steep in the depth regions of 390–415 km and 500–530 km, respectively. The temperature would increase from about 1400°C to 1600°C over the depths interval 350 between 655 km.
The proximity of hotspots to convergent and divergent plate boundaries
Authors: Weinstein Stuart A. , Olson Peter L.
Published: February 2008

An analysis of four different hotspot distributions, ranging from Morgan's [1972] original list of 19 to Vogt's [1981] list of 117 reveals that the hotspots are preferentially located near divergent plate boundaries. The probability of this proximity occurring by chance alone is quite remote, less than 0.01 for all four hotspot distributions. The same analysis also reveals that the hotspots are preferentially excluded from regions near convergent plate boundaries. The probability of this exclusion occurring by chance alone is 0.1 or less for three out of the four distributions examined. We interpret this behavior as being a consequence of the effects of large scale convective circulation on ascending mantle plumes. Mantle thermal plumes, the most probable source of hotspots, arise from instabilities in a basal thermal boundary layer. Plumes are suppressed from regions beneath convergent boundaries by descending flow and are entrained into the upwelling flow beneath spreading centers. Plate‐scale convective circulation driven by subduction may also advect mantle thermal plumes toward spreading centers.
Focused mantle upwelling below mid‐ocean ridges due to feedback between viscosity and melting
Authors: Buck W. Roger , Su Wusi
Published: February 2008

We present the first internally consistent calculation which leads to a narrow ‘conduit’ of rapid vertical advection and melting of mantle under a spreading center. In this model, mantle flow is driven by plate separation and compositional buoyancy. Melt segregation is described as flow through a permeable media. The major new feature is that the viscosity of the mantle is considered to be a strong function of the amount of partial melt present. Experiments show that the bulk viscosity of a partially molten rock is sharply reduced when the melt fraction exceeds a critical value. In the model, the viscosity is reduced as the critical melt fraction is approached. Whether or not a critical melt fraction can be reached under a spreading center depends on the mantle permeability for melt flow. The width of the upwelling area is controlled by the magnitude of the melt related viscosity reduction. Crust should be formed above the focused upwelling. Seismic observations show that the region of crustal accretion is only a few kilometers wide at fast spreading centers. With a viscosity reduction of three orders of magnitude the model predicts a zone of crustal accretion of this width.
Detection of multiply deuterated methane in the atmosphere
Authors: Mroz Eugene J. , Alei Mohammed , Cappis John H. , Guthals Paul R. , Mason Allen S. , Rokop Donald J.
Published: February 2008

Measurements of the isotopic composition of methane in the Antarctic atmosphere have indicated the presence of either 12CD4 or 13CHD3. The concentration is about 1.3 × 10−16(v/v). This concentration is at least 500 times higher than expected from the statistical combination of the natural isotopic abundances of H, D, 12C and 13C. There are no known sources of these species large enough to explain these concentrations. It is possible that these species have accumulated in the atmosphere by virtue of having atmospheric residence times that are substantially longer than the residence time of CH4.
Determination of vertical deflections using the Global Positioning System and geodetic leveling
Authors: Soler Tomás , Carlson Archie E. , Evans Alan G.
Published: February 2008

The capabilities of the Global Positioning System (GPS) for accurately determining geodetic quantities are well established. Nevertheless, no comparison between deflections of the vertical as determined through GPS with leveling and values conventionally computed by astrogeodetic methods has yet been published. This investigation demonstrates that accurate deflections of the vertical components (η,ξ) can be obtained independently of classical astronomic observations by combining geodetic leveling with satellite GPS positioning. The approach uses a radial configuration of baselines to determine the “best” (in a least squares sense) values of (η,ξ) at the central station.
Non‐WKB evolution of solar wind fluctuations: A turbulence modeling approach
Authors: Zhou Ye , Matthaeus William H.
Published: February 2008

Recent observations indicate systematic changes in the interplanetary inertial range velocity‐magnetic field correlation with increasing heliocentric distance. Here, we outline a multiple length scale model for the evolution of the small scale fluctuations due to local nonlinear couplings as well as couplings to large scale gradients, an approach similar to that used in turbulence modeling of inhomogeneous shear flows. A simple special case solution is given, indicating that couplings to large scale flow gradients can cause radial evolution of the type seen in observations. The strongest couplings of this type are linear and do not appear in the usual WKB orderings. The relationship of our approach to WKB theory is not fully understood at present.
On field line resonances of hydromagnetic Alfvén waves in dipole magnetic field
Authors: Chen Liu , Cowley Steven C.
Published: February 2008

Using the dipole magnetic field model, we have developed the theory of field line resonances of hydromagnetic Alfvén waves in general magnetic field geometries. In this model, the Alfvén speed thus varies both perpendicular and parallel to the magnetic field. Specifically, it is found that field line resonances do persist in the dipole model. The corresponding singular solutions near the resonant field lines as well as the natural definition of standing shear Alfvén eigenfunctions have also been systematically derived.
The thermal structure of Triton's atmosphere: Pre‐Voyager models
Authors: McKay Christopher P. , Pollack James B. , Zent Aaron P. , Cruikshank Dale P. , Courtin Régis
Published: February 2008

We predict the existence of a relatively thick (several tens of mbar) N2‐CH4 atmosphere on Triton. As on Titan, we find that the organic haze produced by chemical reactions is the most significant factor affecting solar energy deposition. The production of haze material (∼ 10−15 g cm−2 s−1) is obtained by scaling from the Titan value. Collision induced absorption, primarily N2‐N2, is the dominant source of thermal infrared opacity. The troposphere is characterized by moist convection and the temperature lapse rate is determined by the saturation vapor relationship of N2 (about 0.25 K km−1). Given Triton's present orbital parameters, one polar cap is receiving sunlight while the other cap is in darkness. Following Trafton (1984) we assume the sublimating pole extends poleward of 35° and treat volatile transport as an isobaric process. For nominal values of the surface albedo and emissivity of 0.3 and 0.4, respectively, we find the surface temperature is 59 K (pressure = 51 mb). There is a hot stratosphere (T ≃ 130 K) similar to that on Titan due to absorption by the haze. The total opacity of the organic haze (or haze plus N2 cloud) is ≤ 1.
A Doppler lidar for measuring winds in the middle atmosphere
Authors: Chanin M. L. , Garnier A. , Hauchecorne A. , Porteneuve J.
Published: February 2008

The possibility to measure winds in the middle atmosphere with a Doppler lidar has just been demonstrated. It is aimed to study the wave‐mean flow interaction, when used in association with the Rayleigh lidar providing density and temperature profiles and their fluctuations. The new Doppler lidar relies on the Rayleigh scattering from air molecules and is designed to cover the height range 25‐60 km, a region where radars cannot operate. The Doppler shift of the backscattered echo is measured by inter‐comparing the signal detected through each of two high‐resolution, narrow band‐pass, Fabry‐Perot interferometers tuned on either side of the emitted laser line.
Hydrolytic weakening of quartz aggregates: The effects of water and pressure on recovery
Authors: Tullis Jan , Yund Richard A.
Published: February 2008

In order to test the effect of ‘water‧ at high pressure on the rate of dislocation climb in quartz, we have performed annealing experiments on portions of a quartzite sample previously deformed at 700°C, 10−5 sec−1, and 1500 MPa which had a high dislocation density but few subgrain boundaries. Portions of the deformed sample were annealed at 1500 MPa and 800°C for 1 and 4 days; samples with 0.17 wt % water added have a lower average dislocation density and a greater number of subgrain boundaries than those without water added. Annealing at 800°C for 4 days at 1500 MPa after vacuum drying at 800°C, or at 550 MPa with 0.17 wt % water added, produces no significant change in the dislocation microstructure. These results indicate that: (1) the presence of a water‐related defect in quartz accomplishes hydrolytic weakening by making the climb of dislocations easier, thus increasing the rate of recovery at a given imposed strain rate, and (2) for laboratory times this weakening requires a pressure >550 MPa.
Indications for ionospheric participation in the substorm process from AMPTE/CCE observations
Authors: Daglis I. A. , Sarris E. T. , Kremser G.
Published: February 2008

We present and discuss observations with the AMPTE/CCE spacecraft in the near‐earth nightside magnetosphere, which show a significant enhancement of ionospheric particle presence (mainly O+) at the beginning of the substorm growth phase. Such an enhancement indicates not only an ionospheric participation in the substorm initiation, but also an active role in the substorm growth phase.
Smoothness priors modeling of seafloor bathymetric data
Authors: Gersch Will
Published: February 2008

Multibeam bathymetric data is modeled from a Bayesian “smoothness priors” framework. Smoothness priors is a penalized likelihood‐nonparametric linear regression form of modeling and the bathymetry data are modeled one beam at‐a‐time. The method is applied to data previously analyzed in Goff and Jordan (1988) and Gilbert and Malinverno (1988). The results contrast nonparametric and parametric modeling, dispute the almost conventional removal of “deterministic” components prior to stochastic modeling and reveal new evidence about mid‐ocean ridge spreading processes.
Central and South America GPS geodesy ‐ CASA Uno
Authors: Kellogg James N. , Dixon Timothy H.
Published: February 2008

In January 1988, scientists from over 25 organizations in 13 countries and territories cooperated in the largest Global Positioning System (GPS) campaign in the world to date (Table 1). 43 GPS receivers collected approximately 590 station‐days of data in American Samoa, Australia, Canada, Colombia, Costa Rica, Ecuador, New Zealand, Norway, Panama, Sweden, United States, West Germany, and Venezuela. The experiment was entitled CASA UNO, an acronym for Central and South America – and uno is the Spanish word for one, designating first epoch measurements. The CASA UNO experiment was the first civilian effort implementing a global GPS satellite tracking network.

Scientific goals of the project include measurement of strain in the northern Andes, measurement of subduction rates for the Cocos and Nazca plates beneath Central and South America, and measurement of relative motion between the Caribbean plate and South America. A second set of measurements are planned in 1991 (CASA DOS), and should provide preliminary estimates of crustal deformation and plate motion rates in the region. The CASA series of experiments are intended to be carried out over at least one decade.
Towards GPS orbit accuracy of tens of centimeters
Authors: Lichten Stephen M.
Published: February 2008

The Global Positioning System (GPS) will be used in the coming decade for mm‐level measurements of crustal motion and for sub‐decimeter earth orbiter positioning and navigation. GPS orbits for these applications will be required accurate to 10–20 cm. Although sub‐meter GPS orbit precision has been previously demonstrated with a regional tracking network, several factors are expected to play a role in further improvement to the several decimeter level. These include the use of worldwide ground tracking networks and improved orbit modeling. In this paper, CASA UNO orbit results are presented utilizing data from four continents. Refinements in orbit modeling, combined with the availability oft worldwide tracking network and the dense distribution of tracking sites in North and South America, have improved orbit determination precision to about 60 cm (per component) for four of the seven GPS satellites tracked in CASA UNO. The orbit results are consistent with California baseline repeatabilities, which are at the few mm level in horizontal and length, and 1–2 cm in the vertical. Baseline comparisons with VLBI provide a measure of orbit accuracy, showing sub‐cm agreement in length and 1.5 cm agreement in the horizontal.
SAM II and lidar aerosol profile comparisons during AASE
Authors: Osborn M. T. , Poole L. R. , Wang Pi‐Huan
Published: February 2008

The NASA Langley Research Center (LaRC) aerosol lidar system was one of several instruments that flew aboard a DC‐8 during the Airborne Arctic Stratospheric Expedition (AASE). Several of the Stratospheric Aerosol Measurement II (SAM II) altitude profiles of aerosol extinction were close enough in time and space to allow for intercomparison with the lidar measurements of aerosol backscatter. Comparisons between three SAM II 1.0 μm aerosol extinction profiles and analogous profiles inferred from nearly simultaneous airborne lidar measurements are discussed. As expected, the comparison made during homogeneous background aerosol conditions was excellent, with agreement within error bars. The other two comparisons show the first near‐simultaneous SAM II/lidar measurements of a polar stratospheric cloud (PSC). The comparison made well within the edge of a relatively homogeneous PSC layer was also good, especially using an extinction‐to‐backscatter model derived from in situ PSC particle size measurements. The comparison made near the edge of a PSC showing considerable spatial and temporal variability was poor, likely due to rapid changes which may occur near the cloud edge.
Plate‐mantle coupling and continental flooding
Authors: Gurnis Michael
Published: February 2008

The flooding records of continents have been computed in dynamically self‐consistent models of plates and convection. Platforms flood following rapid translation of continental plates as may occur following supercontinent breakup. In these models, continental flooding is primarily controlled by deep mantle sources and continental hypsometry is strongly influenced by dynamic topography. Some models, especially bottom heated ones, predict more extensive flooding than has been observed during the Phanerozoic. However, the computed flooding can be made consistent with the observations if: the viscosity of the upper regions of the convecting system are significantly reduced compared to the deep regions, the fluid is driven predominantly by internal heating, or the convection is confined to a depth appreciably less than the width of the non‐subducting plate.
Seasonal variation of momentum flux in the mesosphere observed with the MU radar
Authors: Tsuda Toshitaka , Murayama Yasuhiro , Yamamoto Mamoru , Kato Susumu , Fukao Shoichiro
Published: February 2008

We have regularly monitored mesospheric winds at 60–85km for three years with the MU radar (35°N, 136°E), and have found that the variance of wind velocity fluctuations for periods from 5 min to 2 hr shows a semi‐annual variation with a significant peak in summer centered in July and irregular enhancements in winter. The zonal momentum flux induced by gravity waves shows eastward and westward maxima in July–August and December–February, respectively. Typical eastward accelerations at the 70km altitude range from 7 to 13 m/s/day and from −8 to −11 m/s/day in summer and winter, respectively, which agree fairly well with theoretical predictions.
Radon fluxes from soils to the atmosphere measured by 210Pb–226Ra disequilibrium in soils
Authors: Graustein William C. , Turekian Karl K.
Published: February 2008

Measurements of the activities of the parent (226Ra) and progeny (210Pb) of 222Rn in 119 core samples of North American soils reveal that the mean fraction of the 222Rn produced in the upper 50 cm that escapes to the atmosphere equals or exceeds 25%. The flux derived from the upper 50 cm is 0.48 atoms cm−2 s−1. Measurement of 210Pb–226Ra disequilibrium at greater depths in 12 cores indicates a mean depth of 222Rn escape of ∼218 cm, slightly greater than commonly reported values of ∼175 cm. Using these mean depths to extrapolate the flux measurements from the upper 50 cm yields a total radon flux of from 1.9 to 2.3 atoms cm−2 s−1.
Radon and helium in soil gases in the Phlegraean Fields, central Italy
Authors: Lombardi S. , Reimer G. M.
Published: February 2008

The distribution and migration of radon and soil‐gas concentrations in the Phlegraean Fields, Italy, are controlled by the tectonic features of the area. Radon is supplied from surficial sources and helium has both surficial and deep origins. There is no direct correlation between the two noble gases on a point‐to‐point basis but the areal distribution of both gases is similar, suggesting that the distribution is controlled primarily by fractures and movement of geothermal fluids.
Plasma composition measurements of the Martian magnetosphere morphology
Authors: Lundin R. , Zakharov A. , Pellinen R. , Borg H. , Hultqvist B. , Pissarenko N. , Dubinin E. M. , Barabasj S. W. , Liede I. , Koskinen H.
Published: February 2008

Plasma composition measurements from the Phobos‐2 spacecraft have revealed new data on the dynamics and composition of plasmas in the Martian magnetosphere—a magnetosphere being significantly wider and more dynamic than was anticipated before. The tail width is some 6–9 Mars radii at antisolar distances greater than ten Martian radii and it contains some features that are similar to those observed in the Geotail. The strong dominance of plasma of Martian origin implies a modest access of solar wind particles into the central tail. Heavy ions like O+ are in fact up to ten times more abundant then H+. Some plasma properties, such as the characteristics of the ionospheric ion outflow, the presence of a distinct plasma sheet and the overall width of the tail are arguments for a weak intrinsic magnetic field on Mars. However, yet other plasma characteristics, such as strong ion pick‐up processes, indicates a Venus‐like interaction. Thus, our present view based on primarily plasma measurements is that Mars constitutes a hybrid obstacle to the solar wind.

The observation of two distinctly different plasma boundaries suggests that the magnetosphere of Mars is contained whithin an exterior / composition boundary—termed the Mass‐Loading Boundary (MLB), and an interior boundary—a “magnetopause”. MLB marks the boundary for a cometary‐like interaction and the “magnetopause” the limit of solar wind plasma entry—possibly also constituting the boundary for an intrinsic magnetic field.
The magnetotail of Mars: Phobos observations
Authors: Yeroshenko Ye. , Riedler W. , Schwingenschuh K. , Luhmann J. G. , Ong M. , Russell C. T.
Published: February 2008

Magnetic measurements obtained by the Phobos spacecraft in circular orbit at 2.86 Mars radii show a 2‐lobed magnetic tail. The peak solar‐antisolar component of the magnetic field in these lobes is about 14 nT. The polarity of the tail lobes is sensitive to the direction of the interplanetary magnetic field as expected for a magnetic field induced by the solar wind interaction. The ratio of the cross‐tail component of the tail field is over twice that in the solar wind, or about a factor of 4 larger than the ratio observed in the Venus tail at greater distances. Since the ratio is observed to decrease with increasing distance in the Venus tail, we conclude that the Mars and Venus magnetotails are in fact similar. If there is an influence of an intrinsic planetary magnetic field on the magnetotail of Mars that influence is weak.
An interplanetary planar magnetic structure oriented at a large (∼ 80 deg) angle to the Parker spiral
Authors: Farrugia C. J. , Dunlop M. W. , Geurts F. , Balogh A. , Southwood D. J. , Bryant D. A. , Neugebauer M. , Etemadi A.
Published: February 2008

Magnetic field structures in the solar wind, characterised by a variation of the field vectors within a plane inclined to the ecliptic (‘Planar Magnetic Structures’, PMS's), were reported recenty (Nakagawa et al., 1989). These PMS's have the property that the plane of variation of the field also contains the nominal Parker spiral direction. We report here an observation of a PMS where the direction of the line of intersection of the plane of field variation with the ecliptic plane makes a large (∼80 deg) angle to the Parker spiral direction. Furthermore, the angular variables of the field, θB(elevation) and φB (azimuth) (a) vary over a restricted range, and (b) are linearly related. We show the latter property to be related to the former. We argue that currently proposed models for the origin of PMS's, in as much as they require field configurations which retain strict alignment with the Parker spiral direction from formation to observation, are probably incomplete.
The Darwin Rise: A Cretaceous superswell?
Authors: McNutt M. K. , Winterer E. L. , Sager W. W. , Natland J. H. , Ito G.
Published: February 2008

The Japanese Guyots, Wake Guyots, and Mid‐Pacific Mountains are part of a broad area of Cretaceous volcanism in the western Pacific termed the “Darwin Rise.” Based on Seabeam bathymetric data we classify these drowned volcanic islands as: type “A,” those that advanced to the atoll stage before final submergence; type “B,” those that drowned at the barrier reef stage; and type “V,” those with little or no reef material on their volcanic summits. Widespread evidence for karst topography extending to depths of 200 m on the summits of A and B guyots sheds new light on events leading to the synchronous extinction of reefs on the Darwin Rise in the mid‐Cretaceous. We propose that after the formation of the reefs on the A and B guyots, the entire region was elevated at approximately the Aptian‐Albian boundary (113 Ma) to form a superswell similar to that existing now in French Polynesia. The type V guyots formed on this anomalously shallow lithosphere. The demise of the reefs was the direct result of the rise of this superswell, although climate factors may have prevented reef recolonization following its later subsidence.
δs at high pressure and dlnVs/dlnVp in the lower mantle
Authors: Agnon A. , Bukowinski M. S. T.
Published: February 2008

δs, a measure of the sensitivity of the adiabatic bulk‐modulus to isobaric density changes, controls lateral variations of P‐wave velocities. To estimate the effect of pressure on δs, we have performed lattice dynamic calculations of the cubic alkaline earth oxides. We used a many‐body parametric Hamiltonian that reproduces the available laboratory data on thermoelastic properties. The calculations were carried out for P‐T conditions that correspond to those of the lower mantle. We find that δs decreases from 4±1 at standard conditions to ≤ 2 at lower mantle conditions. The latter value is consistent with D.L. Anderson's estimates based on geophysical data.

With δs ≤ 2, and a corresponding parameter for shear modulus not decreasing with compression, no partial melting is required to account for the observation that ΔlnVs/ΔlnVp ≥ 2 in the lower mantle. Although more data and calculations on additional minerals are needed to draw any firm conclusions, our results indicate that the relatively small lateral variations of lnVp, when compared to lnVs, are due entirely to compressional effects.
Magnetic asymmetries of unmagnetized planets
Authors: Brecht Stephen H.
Published: February 2008

This letter discusses the results produced by 3‐D hybrid particle code simulations of the solar wind interaction with unmagnetized planets such as Venus and Mars. The solar wind velocity is perpendicular to the IMF in the cases studied. It is found that there are asymmetries in both the magnetic structure and shock location for spherical obstacles ranging in radius from 1000 km to 6000 km. The asymmetries found are due to differences in the electron and ion currents paths (diamagnetic behavior). Mass loading of 0+ was not included in these simulations.
Mantle convection and crustal evolution on Venus
Authors: Kaula William M.
Published: February 2008

Venus is probably similar to the Earth in that recycling of basaltic crust has been induced by the development of cratons: combinations of siliceous crust with high Mg:Fe mantle. Venus has less remaining energy sources at depth, but still enough to to support the great plateaus, and to deliver appreciable heat close to the surface by convection. The main differences of Venus from the Earth arise from its lack of water, rather than higher temperatures. Lack of water (plus lower stress levels due to lesser energy) makes the upper mantle more viscous, and hence Venus tectonics more driven by bulk mantle, rather than boundary layer, characteristics. Making tectonics difficult to infer from Magellan imagery will be shallower and more widespread layers of weakness in crustal rocks obscuring the mantle‐driven patterns.
Comparisons between GEOSAT and SEASAT tracking over non‐ocean surfaces
Authors: Brenner A. C. , Frey H. V. , Zwally H. J.
Published: February 2008

Comparisons between GEOSAT and SEASAT altimeter tracking over non‐ocean surfaces are presented. The GEOSAT tracker shows more agility over the rougher surfaces and therefore is able to maintain lock better than SEASAT. For repeat groundtracks over the Greenland ice sheet, GEOSAT provided twice as many usable height measurements as SEASAT. Large off‐nadir attitude excursions caused differences in GEOSAT tracking between repeat cycles. The increased GEOSAT pulse width caused an acquisition problem mostly over the quickly‐varying land surfaces. The GEOSAT altimeter was sometimes able to track over surfaces SEASAT could not but at times the acquisition problem was worse. The effect of all the modifications is that the GEOSAT measurements give more detailed along track information of the small‐scale topography. Over the ice sheets GEOSAT yields denser coverage, but over land SEASAT measurements give a better overall picture of the general topography. These results suggest that the GEOSAT elevation data set over land can best be used to augment the information obtained from the SEASAT data and is most valuable when investigating topography at scales less than 100 km.
Ozone measurements from the NOAA‐9 and the NIMBUS‐7 satellites: Implications of short and long term variabilities
Authors: Chandra S. , McPeters R. D. , Hudson R. D. , Planet W.
Published: February 2008

This paper gives an overview of the measurements of total ozone and ozone profiles by the SBUV/2 instrument on the NOAA‐9 spacecraft relative to similar measurements from the SBUV and TOMS instruments on Nimbus‐7. It is shown that during the three year period from March 14, 1985, to February 28, 1988, when these data sets overlap, there have been significant changes in the calibrations of the three instruments that may be attributed to diffuser plate degradation (for SBUV/TOMS) and to the drift of the NOAA‐9 orbit to later equator crossing times (for SBUV/2). These changes in instrument characteristics have affected the absolute values of the trends derived from the three instruments, but their geophysical characteristics and response to short term variations are accurate and correlate well among the three instruments. For example, the total column ozone measured by the three instruments shows excellent agreement with respect to its day to day, seasonal, and latitudinal variabilities. At high latitudes, the day to day fluctuations in total ozone show a strong positive correlation with temperature in the lower stratosphere, as one might expect from the dynamical coupling of the two parameters at these latitudes.
Evidence of very early aftershock activity along the northwest portion of the 18 October 1989 earthquake rupture zone
Authors: Simila G. W. , McNally K. C. , Nava E. , Protti‐Quesada M. , Yeliln J.
Published: February 2008

We find evidence that at least 24 significant aftershocks, ∼ M ≥ 4, occurred within the first 34 minutes following the onset of rupture in the 18 October 1989 earthquake. Only six of these very early aftershocks are contained in current listings of aftershock locations. Here we provide preliminary locations for 18 of these events. Sixteen of the 18 locations are found in the northwest portion of the mainshock rupture zone, with greatest concentration near the intersection of the San Andreas and Sargent faults.
Simultaneous, in situ measurements of OH and HO2 in the stratosphere
Authors: Stimpfle R. M. , Wennberg P. O. , Lapson L. B. , Anderson J. G.
Published: February 2008

Stratospheric OH and HO2 radical densities have been measured between 36 and 23 km using a balloon‐borne, in situ instrument launched from Palestine, TX on August 25, 1989. OH is detected using the laser‐induced fluorescence technique (LIF) employing a Cu‐vapor‐laser pumped dye laser coupled with an enclosed‐flow detection chamber. HO2 is detected nearly simultaneously by adding No to the sample flow to convert ambient HO2 to OH. Observed OH and HO2 densities ranged from 8.0 ± 2.8 × 106 and 1.4 ± 0.5 × 107 molec cm−3, respectively, at 36 km, to 1.4± 0.5 × 106 and 3.0± 1.0 × 106 at 23 km, where the uncertainty is ±1σ. The HO2 density exhibits a maximum in the 34–30 km of 1.7±0.6 × 107. The data were obtained over a solar zenith angle variation of 51° at 36 km to 61° at 23 km. O3 and H2O densities also were measured simultaneously with separate instruments.
Lateral temperature variations at the core‐mantle boundary deduced from the magnetic field
Authors: Bloxham Jeremy , Jackson Andrew
Published: February 2008

Recent studies of the secular variation of the Earth's magnetic field over periods of a few centuries have suggested that the pattern of fluid motion near the surface of Earth's outer core may be strongly influenced by lateral temperature variations in the lowermost mantle. In this paper we introduce a self‐consistent method for finding the temperature variations near the core surface by assuming that the dynamical balance there is geostrophic and that lateral density variations there are thermal in origin. The calculation is accomplished by using the radial and horizontal components of the magnetic field at the core‐mantle boundary to calculate the fluid flow and its radial derivative near the core surface, which are related to the pattern of lateral temperature variations by the thermal wind equation. As expected, these lateral temperature variations are very small. We find some agreement between this pattern and the pattern of topography of the core‐mantle boundary, but are unable to answer conclusively to what extent core surface motions are controlled by the mantle, rather than being determined by processes in the core.
Intrinsic magnetic discontinuities and solar X‐ray emission
Authors: Parker E. N.
Published: February 2008

The fundamental theorem of magnetostatic equilibrium predicts that the bipolar magnetic fields of active regions on the Sun contain tangential discontinuities as an intrinsic part of their equilibrium. It appears that rapid reconnection at these many tangential discontinuities (nanoflares) is the primary source of heat that produces the X‐ray emitting corona. The X‐ray corona Is then a cloud of nanoflares.
Electromagnetic ion/ion cyclotron instability at slow shocks
Authors: Winske D. , Omidi N.
Published: February 2008

The linear and nonlinear properties of the obliquely propagating electromagnetic ion/ion cyclotron instability are investigated. The instability is driven by the relative, field‐aligned streaming of two ion beams and can exist at a lower velocity threshold than the more commonly studied, parallel propagating electromagnetic ion beam instabilities. It is shown that the instability plays an important role in the formation of, dissipation at, and waves upstream of slow mode shocks. Possible application of this instability to ion beams in the plasma sheet boundary layer is also briefly discussed.
The relationship between plate velocity and trench viscosity in Newtonian and power‐law subduction calculations
Authors: King Scott D. , Hager Bradford H.
Published: February 2008

Convection with a Newtonian temperature‐dependent rheology leads to little or no surface velocity unless zones of weakness are introduced. “Plate‐like” features are observed in calculations both with Newtonian rheology, employing imposed weak zones, and with power‐law (non‐Newtonian) rheology, where high stresses at the trench reduce the effective viscosity. Since deformation at subduction zones involves faulting, both of these parameterizations should be treated with some skepticism. It is important to understand how the parameterizations affect the model results. We study the relationship between trench viscosity and plate velocity using a Newtonian rheology by varying the viscosity at the trench. The plate velocity is a function of the trench viscosity for fixed Rayleigh number and plate/slab viscosity. Slab velocities for non‐Newtonian rheology calculations are significantly different from slab velocities from Newtonian rheology calculations at the same effective Rayleigh number. Both models give reasonable strain‐rates for the slab when compared with estimates of seismic strain‐rate. Non‐Newtonian rheology eliminates the need for imposed weak zones and provides a self‐consistent fluid dynamical mechanism for subduction in numerical convection models.
Vibrational populations of the excited states of N2 under auroral conditions
Authors: Cartwright David C.
Published: February 2008

The equations of statistical equilibrium for the population and depopulation of the electronic states of N2 have been solved for steady state normal auroral conditions. All vibrational levels for the seven lowest triplet electronic states (A, B, W, B′, C, E, D) and the three lowest excited singlet electronic states (a, a′, w) of N2 were included in the calculations. Recently measured auroral secondary electron spectra were employed to calculate the rates for electron impact excitation. The transition probabilities, electron impact excitation cross sections, and vibrationally dependent quenching rates used were a combination of the best available experimental and theoretical data. The results of these calculations are the absolute vibrational populations of all the electronic states. Intrasystem cascading and vibrationally dependent quenching were found to be important in determining the vibrational populations in the lower singlet and triplet excited electronic states. The predicted vibrational populations for the A and B triplet states agree well with the available experimental data. These calculations predict that a fairly large density of N2 in excited metastable states is produced under auroral conditions.