bluuebunny/crossref_metadata_2025 huggingface dataset:
Dust measurements in the Jovian magnetosphere
Authors: Grün E. , Krüger H. , Dermott S. , Fechtig H. , Graps A. L. , Zook H. A. , Gustafson B. A. , Hamilton D. P. , Hanner M. S. , Heck A. , Horányi M. , Kissel J. , Lindblad B. A. , Linkert D. , Linkert G. , Mann I. , McDonnell J. A. M. , Morfill G. E. , Polanskey C. , Schwehm G. , Srama R.
Published: February 2004

Dust measurements have been obtained with the dust detector onboard the Galileo spacecraft inside a distance of about 60RJ from Jupiter (Jupiter radius, RJ = 71,492 km) during two periods of about 8 days around Galileo's closest approaches to Ganymede on 27 June and on 6 Sept 1996. The impact rate of submicrometer‐sized particles fluctuated by a factor of several hundred with a period of about 10 hours, implying that their trajectories are strongly affected by the interaction with the Jovian magnetic field. Concentrations of small dust impacts were detected at the times of Ganymede closest approaches that could be secondary ejecta particles generated upon impact of other particles onto Ganymede's surface. Micrometer‐sized dust particles, which could be on bound orbits about Jupiter, are concentrated in the inner Jovian system inside about 20RJ from Jupiter.
The crystal structure of calcite III
Authors: Smyth Joseph R. , Ahrens Thomas J.
Published: February 2004

The crystal structure of calcite III has been deduced from existing high pressure powder X‐ray diffraction patterns, based on the assumption that it is a displacive modification of the calcite I structure. The structure is monoclinic with space group C2 and a Z of 6. There are two Ca and two C positions, and five O positions, and atom coordinates have been refined by distance‐least‐squares methods to give reasonable octahedral coordination for Ca and parallel, planar CO3 groups. Unit cell parameters refined from a published powder diffraction pattern at 4.1 GPa are: a = 8.746(8)Å; b = 4.685(5)Å; c = 8.275(8)Å; and β= 94.4°. The structure has a calculated density of 2.949 Mg/m³ at 4.1 GPa which is less than that of aragonite at this pressure and consistent with early piston cylinder studies. This implies that calcite III is indeed a metastable intermediary between calcite I and aragonite.
Uncertainties in reactive uptake coefficients for solid stratospheric particles—2. Effect on ozone depletion
Authors: Carslaw Kenneth S. , Peter Thomas , Müller Rolf
Published: February 2004

Uncertainties in reactive uptake coefficients for reactions involving HCl, ClONO2 and HOCl on nitric acid trihydrate (NAT) and sulfuric acid tetrahydrate (SAT) are shown to affect modeled Arctic stratospheric ozone depletion in a photochemical box model. The main contribution to the difference arises from the reaction ClONO2 + HCl → Cl2 + HNO3 in early to mid‐winter. During this period, differences in predicted HCl and ClONO2 are more than 1 ppbv for several weeks when an upper limit for solid PSC existence is assumed. Ozone depletion is greater when liquid aerosols persist through the winter compared with cases where solid particles are assumed to form.
Mineralogy of the Mafic Anomaly in the South Pole‐Aitken Basin: Implications for excavation of the lunar mantle
Authors: Pieters C. M. , Tompkins S. , Head J. W. , Hess P. C.
Published: February 2004

The mineralogy of South Pole‐Aitken Basin [SPA] (the largest confirmed impact basin on the Moon) is evaluated using five‐color images from Clementine. Although olivine‐rich material as well as basalts rich in clinopyroxene are readily identified elsewhere on the farside, the dominant rock type observed across the interior of SPA is of a very noritic composition. This mineralogy suggests that lower crust rather than the mantle is the dominant source of the mafic component at SPA. The lack of variation in observed noritic composition is probably due to basin formation processes, during which extensive melting and mixing of target materials are likely to occur.
Source scaling of microearthquakes at Mt. Etna Volcano and in the Calabrian Arc (southern Italy)
Authors: Patanè D. , Ferrucci F. , Giampiccolo E. , Scaramuzzino L.
Published: February 2004

Microearthquake data recorded at Mt. Etna volcano and in the Calabrian Arc (Southern Italy) have been used to study the scaling of the main source parameters. After correction of the P‐wave displacement spectra for both path attenuation and the site amplification effects, an inverse method has been applied to compute spectral parameters (low frequency spectral level, corner frequency and high frequency roll‐off). Results show that seismic moments (M0) range from ca. 1016 to 1021 dyne‐cm at Mt. Etna and from ca 1017 to 1020 dyne‐cm in southern Calabria. Corner frequencies range from ca. 3 to 15 Hz. In both areas we found that the stress drop decreases (from ca. 100 to few bars) with decreasing seismic moment. A simple Brune source model is not able to explain the source scaling, because the typical fall‐off observed at higher frequencies (ω−3 as an average) is larger than that of Brune's theory. Furthermore, the relation between the seismic moment and the corner frequency points to a scaling law behaving as M0∝ωc−4.5 and M0∝ωc−3.6 on average, at Mt. Etna and in southern Calabria respectively, and higher for smaller events in both areas. Therefore, the cube law (M0 ∝ ω−3) generally accepted for large earthquakes does not hold true for the analysed microearthquakes, neither for those which occur along the tectonic structures of southern Calabria, or along those hosting the roots of the feeding system of the largest European volcano.
Variationally induced breathing equations of state of pyrope, grossular, and majorite garnets
Authors: Downs J. W. , Bukowinski M. S. T.
Published: February 2004

We have completed the first non‐empirical fully optimized calculations of the equations of state for pyrope, grossular, and MgSiO3 majorite garnets. The static Gibbs free energy of the 160‐atom unit cell was minimized relative to all 27 structural parameters for the tetragonal structure. Zero point vibration and thermal effects were estimated with a Debye‐like model and Debye temperatures obtained from the equations of state. Calculated zero‐pressure densities differ from experimental values by less than 1%, while the bulk‐moduli are systematically larger than those obtained spectroscopically. Nevertheless, the calculations strongly support experimental evidence that the bulk modulus of MgSiO3 majorite is close to that of pyrope and further indicate that its (∂KT/∂P)o is not distinctly larger than that of other silicate garnets. If these properties are close to those of real majorite, the steep gradient of the bulk modulus in the transition zone is at best marginally consistent with a Iherzolitic composition.
High resolution simulation of the severe precipitation event over the Saguenay, Quebec Region in July 1996
Authors: Yu Wei , Lin Charles A. , Benoit Robert
Published: February 2004

A high resolution regional simulation of the severe precipitation episode which gave rise to the floods in the Saguenay, Quebec region during July 19–21, 1996 was performed using the Mesoscale Compressible Community Model (MC2). The model is first calibrated by comparing the simulated precipitation field with radar observations for an earlier precipitation event. The model is then applied without further tuning to the Saguenay episode. This simulation is initialized with the Canadian Meteorological Center (CMC) analyses at a resolution of 35 km. A one‐way nested integration is next performed with a resolution of 10 km. The simulated precipitation field compares well with available station observations.
Surface UV from ERS‐2/GOME and NOAA/AVHRR data: A case study
Authors: Meerkoetter R. , Wissinger B. , Seckmeyer G.
Published: February 2004

A satellite based method for deriving spatial distributions of erythemally weighted UV irradiance at the surface has been developed. The effects of ozone column amount and cloud optical thickness on UV were taken into account by the combined usage of the new European‐Space‐Agency's GOME (Global‐Ozone‐Monitoring‐Experiment) sensor onboard the European‐Research‐Satellite‐2 (ERS‐2) and the NOAA/AVHRR instrument, respectively. As an example for application, horizontal distributions of surface UV irradiances are derived in a region covering the area of Southern Germany on two days 22. July and 13. August 1996. These two days represent clear and cloudy conditions, respectively. For the cloud free day 22. July 1996 the surface UV measurements at Garmisch‐Partenkirchen and Hohenpeissenberg (Southern Germany) were about 4.5% lower than those derived from satellite measurements. In addition, the accuracy of the method in case of the cloudy day is discussed.
Readjustment of the Krafla Spreading Segment to crustal rifting measured by satellite radar interferometry
Authors: Sigmundsson Freysteinn , Vadon Hélène , Massonnet Didier
Published: February 2004

Readjustment of the Krafla spreading segment on the Mid‐Atlantic Ridge in Iceland, after a rifting episode from 1975 to 1984, is detected by radar interferometry. Crustal deformation from 1992 to 1995 is dominated by ∼24 mm/year subsidence above a shallow magma chamber at Krafla, superimposed on ∼7 mm/year along‐axis subsidence of the spreading segment relative to its flanks. The deformation is caused by cooling contraction at ∼3 km depth and ductile flow of material away from the spreading axis, at a rate decreasing with time.
Observations of unstable atmospheric shear layers in the lower E region in the post‐midnight auroral oval
Authors: Larsen M. F. , Christensen A. B. , Odom C. D.
Published: February 2004

Observations of the neutral wind profiles in the post‐midnight sector of the auroral oval show the development of a narrow jet near 110–120 km altitude during disturbed conditions. The shears on the bottom side of the jet are highly unstable with Richardson numbers near or below the critical value of 0.25. The unstable shears imply that turbulence and, consequently, the eddy diffusivity will be enhanced in that part of the atmosphere.
Heat flow across the East African Plateau
Authors: Nyblade Andrew A.
Published: February 2004

Four new heat flow measurements from western Tanzania are combined with existing data from non‐rifted areas of East Africa to determine if there is a broad heat flow anomaly associated with the East African Plateau. Three of the new data sites lie in the Kibaran Belt and yield heat flows of 60, 68, and 74 mW m−2. The fourth new site is in the interior of the Tanzania Craton and gives a heat flow of 33 mW m−2. The ensemble of heat flow data from the interior of East Africa, when compared to the global distribution of heat flow in tectonically undisturbed Precambrian terrains of similar age, indicates that heat flow from the center of the Plateau is not elevated. This finding suggests that if the lithosphere beneath the interior of the Plateau lithosphere has been thermally perturbed, as proposed previously by many investigators, then the thermal anomaly must be of insufficient magnitude and/or has not existed for an adequate length of time to affect surface heat flow.
Block scale dispersivity for heterogeneous porous media characterized by stochastic fractals
Authors: Liu H. H. , Molz F. J.
Published: February 2004

It is well known that subsurface contaminant transport is significantly influenced by heterogeneous distributions of the relevant hydraulic properties. A practical scheme to deal with these heterogeneous distributions may be the combination of the two commonly used approaches, the so‐called equivalent homogeneous and heterogeneous approaches. As an important step to establish such a hybrid approach, this brief communication is devoted to determining block scale dispersivity in porous media characterized by Gaussian stochastic fractals. Sensitivity analyses indicate that block scale dispersivity is a strong function of block size and anisotropy in K.
Mantle involvement in lithospheric collision: Seismic evidence from the Trans‐Hudson Orogen, western Canada
Authors: Hajnal Z. , Nemeth B. , Clowes R. M. , Ellis R. M. , Spence G. D. , Burianyk M. J. A. , Asudeh I. , White D. J. , Forsyth D. A.
Published: February 2004

Three seismic refraction/wide‐angle reflection profiles were recorded over the Trans‐Hudson Orogen. The profiles display high quality coherent seismic signals associated with the Moho and lithospheric mantle to depths in excess of 160 km. As outlined by wide‐angle reflections, depth to Moho varies between 40–54 km with a number of well‐defined structural reliefs. Immediately beneath the Moho, in the central part of the orogen, an anomalous high‐velocity zone (∼8.45 km/s) with lateral dimensions of 100 km (north‐south) by 130 km (east‐west) and maximum thickness of 50 km was delineated by mantle refraction arrivals. This zone may represent a locally preserved remnant of older mantle from micro‐continental collisions. Mantle discontinuities with some structural relief are interpreted at average depths of 75 and 158 km. Based on wide‐angle reflections at offsets beyond 400 km, they bound a layered zone with variable velocities, probably representing imbricated sequences of peridotite and eclogite. We postulate that these unusual features of the upper mantle are the result of lithospheric convergence of bounding Archean cratons and closure of the intervening ocean basin.
El Niño: A coupled response to radiative heating?
Authors: Sun De‐Zheng
Published: February 2004

The very existence of El Niño— the oscillatory behavior of the tropical Pacific climate—may be due to the warmth of the tropics (relative to the coldness of the high latitudes). This is elucidated by subjecting a mathematical model for the coupled tropical ocean‐atmosphere system to a varying radiative heating. The temperature of the deep ocean is kept fixed. In response to an increasing radiative heating, the coupled system first experiences a pitch‐fork bifurcation that breaks the zonal symmetry imposed by the solar radiation. The resulting zonal sea surface temperature (SST) gradients increase with increases in the radiative heating. When the zonal SST gradients exceed a critical value, a Hopf bifurcation takes place which brings this system to an oscillatory state, a state that closely resembles the observed tropical Pacific climate. Further increases in the radiative heating result in increases in the magnitude of the oscillation. The results shed new light on the physics of El Niño and suggest that climate change due to anthropogenic forcing may occur through the same dynamic modes that sustain natural variability.
Rossby wave propagation into the tropical stratosphere observed by the high resolution Doppler imager
Authors: Ortland D. A.
Published: February 2004

Stratospheric wind observations by the High Resolution Doppler Imager on the Upper Atmosphere Research Satellite show that quasi‐stationary Rossby waves propagate into the tropics. Rossby wave breaking and dissipation causes meridional transport and direct deposition of momentum, and has a significant influence on the evolution of the mean tropical winds in the upper stratosphere. Deeper penetration into the tropics occurs when the quasi‐biennial oscillation is in its westerly phase above 30 km. During northern winter, subtropical momentum deposition by Rossby waves occurs only in late November through December, while during southern winter this occurs primarily in August and September.
Effect of diurnal convection on trapped thermal plasma in the outer plasmasphere
Authors: Reynolds M. A. , Ganguli G. , Fedder J. A. , Meléndez‐Alvira D. J.
Published: February 2004

A kinetic, multi‐species model of the plasmasphere is constructed that includes the effect of convection and corotation electric fields on trapped particles in drifting flux tubes. The resulting morphology of the outer plasmasphere is significantly different from the morphology obtained using the assumption of diffusive equilibrium. The difference is due primarily to the contraction and expansion of the region of velocity space accessible to the trapped particles, and has implications for the interpretation of remote sensing experiments.
Direct comparison of astronomical and 40Ar/39Ar ages of ash beds: Potential implications for the age of mineral dating standards
Authors: Hilgen F. J. , Krijgsman W. , Wijbrans J. R.
Published: February 2004

We present first results of 40Ar/39Ar multiple single fusion datings on biotites and feldspars from two volcanic ash beds found on Crete, Gavdos and Koufonisi (Greece). Preferred 40Ar/39Ar ages—calculated against TCR sanidine with an age of 27.92 Ma, intercalibrated to an age of 28.09 ± 0.10 Ma (1σ) for FCT‐3 biotite and an age of 24.99 ± 0.07 Ma for DRA sanidine—are slightly but consistently younger than astronomical ages obtained independently for the same ash beds. The best fit to the astronomical ages is obtained when the age of TCR sanidine is increased slightly to 27.98 ± 0.19 Ma, the age of FCT‐3 biotite to 28.15 ± 0.19 Ma and the age of DRA sanidine to 25.05 ± 0.17 Ma. The ages for the standards arrive slightly younger if the 40Ar/39Ar age ‐ of 6.936 ± 0.006 Ma (1σ)—for a single pure sanidine separate of the lower ash—dated astronomically at 6.941 Ma—is considered most reliable.
Evidence for a relationship between spring snow cover in North America and summer rainfall in New Mexico
Authors: Gutzler David S. , Preston Jessica W.
Published: February 2004

Two possible mechanisms for interannual modulation of precipitation anomalies in the Southwest U.S. are examined. The association between El Niño/Southern Oscillation (ENSO) fluctuations and New Mexico precipitation anomalies is found to vary with season: positive Pacific Ocean surface temperature anomalies are associated with positive winter‐spring precipitation anomalies in New Mexico but negative summer anomalies. We propose that the spring snow extent across the west‐central U.S. acts to enhance or suppress the subsequent summer monsoon circulation affecting the American Southwest, such that excessive snow leads to deficient summer rain, and deficient snow leads to abundant rain. This mechanism is consistent with the observed seasonal variation in the ENSO—precipitation relationship.
Absorption cross sections for water vapor from 183 to 193 nm
Authors: Cantrell Christopher A. , Zimmer Audrey , Tyndall Geoffrey S.
Published: February 2004

Absorption cross sections for water vapor at 184.9 nm were measured using a standard low‐pressure mercury lamp light source, optically filtered to isolate the spectral region near the emission line. The light from the source was detected using a solar‐blind phototube. Experiments were performed over a wide range of water column amounts, using neat water vapor and water vapor/nitrogen mixtures, with four methods to determine the water vapor concentration in the cell. Absorption cross sections were measured between 0 and 80°C. The results from these experiments yield a cross section of 7.14 (± 0.2) × 10−20 cm² molecule−1 at 25°C with a small positive temperature dependence (about 4% between 0 and 80°C). This result is about 30% greater than current recommendations. The absorption spectrum was also measured at discrete wavelengths between 183 and 193 nm using a scanning double monochromator system. The cross section of deuterated water vapor was determined at 184.9 nm. The implications of the changes in the H2O cross section for the calibration of atmospheric OH and HO2 measurements using the 184.9 nm photolysis of water vapor are discussed.
Crustal structure at Nanga Parbat, northern Pakistan, from magnetotelluric soundings
Authors: Park Stephen K. , Mackie Randall J.
Published: February 2004

A magnetotelluric survey in northern Pakistan contains effects from both 2‐D and 3‐D structure. Identification of the effects of the sediments along the Indus River valley using 3‐D modeling permitted the selection of modes that could be accurately inverted with 2‐D inversions. The resulting 2‐D model reveals generally resistive (> 500 ohm‐m) upper crust (0–8 km), a more conductive (30–50 ohm‐m) middle to lower crust (8–40 km), and a resistive (> 300 ohm‐m) upper mantle. Shallow crustal (< 10 km) conductors correlate with a hydrothermally altered fault zone and/or carbonaceous metamorphic rocks near the Raikot fault. A prominent midcrustal conductor located beneath Nanga Parbat is required to fit the data, but its depth, dimensions, and conductivity are poorly constrained by existing data.
O2 continuum: A possible explanation for the discrepancies between measured and modeled shortwave surface irradiances
Authors: Murcray F. J. , Goldman A. , Landry J. C. , Stephen T. M.
Published: February 2004

Ground based solar spectra between 1 and 5µm (10,000 and 2000 cm−1) have been obtained with a new, absolutely calibrated spectrometer. These spectra have sufficient spectral resolution (2 cm−1) to allow atmospheric absorption lines to be distinguished from underlying continuum absorption. Continuum absorption due to O2 has been identified around 1.06µm (9366 cm−1), 1.27µm (7882 cm−1), and 1.6µm (6326 cm−1). These continuum absorptions are not included in the HITRAN database. Similar continuum absorption should be present around the 0.762µm (13121 cm−1) and 0.688µm (14525 cm−1) bands of O2.
Coupling the plasma interaction at Io to Jupiter
Authors: Crary F. J. , Bagenal F.
Published: February 2004

Io's interaction with the jovian magnetosphere causes auroral and radio emissions. This interaction can not be modeled as either an Alfvén wave or a steady current loop alone. Given the Galileo measurement of low flow velocities in Io's wake, we argue that the interaction begins as an Alfvénic disturbance but as the disturbance is convected downstream it has time to evolve into a steady current loop. We associate high latitude phenomena with different phases of the interaction.
Dielectric properties of ice at millimeter wavelengths
Authors: Koh Gary
Published: February 2004

The use of radars to study the geophysical features in a polar environment requires reliable information about the relative complex dielectric permittivity, ε = ε′ + iε″, of ice at microwave and millimeter‐wave frequencies. To address this requirement, ε of ice at millimeter wavelengths was obtained using an interference technique. The interference pattern was produced by measuring the transmittance through bubble‐free ice slabs at normal incident angle as the frequency was swept from 75 to 110 GHz. From the resulting interference patterns, ε′ was determined to be 3.17±0.05 and virtually independent of frequency. Frequency‐dependent absorption loss was observed such that ε″ increased from approximately 2.4 ± 0.2 × 10−3 to 4.0 ± 0.2 × 10−3 over the swept frequencies.
Temperature and area constraints of the South Volund Volcano on Io from the NIMS and SSI instruments during the Galileo G1 orbit
Authors: Davies Ashley Gerald , McEwen Alfred S. , Lopes‐Gautier Rosaly M. C. , Keszthelyi Laszlo , Carlson Robert W. , Smythe William D.
Published: February 2004

Analysis of data from darkside and eclipse observations of Io by the NIMS and SSI instruments show that the South Volund hot spot is a manifestation of high temperature active silicate volcanism. The NIMS data are fitted with a two temperature model (developed from modelling terrestrial lavas) which yields a better fit to the data than a single temperature fit. The multispectral color temperatures obtained from NIMS are compared with the brightness temperatures obtained from the SSI instrument, and show excellent agreement for the hotter of the two components fitted to the NIMS data. The two components might correspond to a cooled crust which has formed on the surface of an active flow or lava lake, at a temperature of approximately 450 K, and covering an area of about 50 km², and a hotter and much smaller component, at a temperature of approximately 1100 K and an area of less than 0.1 km². The hot component implies the existence of cracks in the surface crust of a flow or lake through which the hot interior radiates, a hot vent area, or breakouts of lava forming new flow lobes. The ratio of these areas is consistent with the crack‐to‐crust ratio of some lava flows and lava lakes on Earth.
Quasi‐static dislocations in three dimensional inhomogeneous media
Authors: Du Yijun , Segall Paul , Gao Huajian
Published: February 2004

We present an approximate (perturbation) method for computing surface displacement fields due to quasi‐static dislocations in inhomogeneous elastic half‐spaces, extending the work of Du et al. [1994] to three dimensions. Three dimensional methods are required to model geodetic observations. The perturbation method allows one to include more realistic earth structure in the analysis of surface deformation measurements, and is computationally efficient enough to be used in inversions for source properties. As an example, we investigate the effect of material inhomogeneity on the location of the fault plane for the 1989 Kalapana, Hawaii, earthquake. Inversion of coseismic elevation changes assuming a homogeneous half‐space yielded a finite source depth markedly shallower than the mainshock and principal aftershocks [Árnadóttir et al., 1991]. Incorporation of lateral and vertical variations in shear modulus, consistent with velocity and density data, yields a source depth more consistent with the seismic results. Failure to account for variations in elastic properties can bias estimates of source depth and moment.
Magnetotail flow bursts: Association to global magnetospheric circulation, relationship to ionospheric activity and direct evidence for localization
Authors: Angelopoulos V. , Phan T. D. , Larson D. E. , Mozer F. S. , Lin R. P. , Tsuruda K. , Hayakawa H. , Mukai T. , Kokubun S. , Yamamoto T. , Williams D. J. , McEntire R. W. , Lepping R. P. , Parks G. K. , Brittnacher M. , Germany G. , Spann J. , Singer H. J. , Yumoto K.
Published: February 2004

A series of bursty bulk flow events (BBFs) were observed by GEOTAIL and WIND in the geomagnetotail. IMP8 at the solar wind showed significant energy coupling into the magnetosphere, while the UVI instrument on POLAR evidenced significant energy transfer to the ionosphere during two substorms. There was good correlation between BBFs and ionospheric activity observed by UVI even when ground magnetic signatures were absent, suggesting that low ionospheric conductivity at the active sector may be responsible for this observation. During the second substorm no significant flux transport was evidenced past WIND in stark contrast to GEOTAIL and despite the small intersatellite separation ((3.54, 2.88, −0.06) RE). Throughout the intervals studied there were significant differences in the individual flow bursts at the two satellites, even during longitudinally extended ionospheric activations. We conclude that the half‐scale‐size of transport‐bearing flow bursts is less than 3 RE.
Model‐validated parametrization for air‐sea gas transfer in the North Indian Ocean
Authors: Haines Meredith A. , Luther Mark E. , Fine Rana A.
Published: February 2004

Mixed‐layer CFC‐11 saturations measured in the northwestern Indian Ocean during the 1995 World Ocean Circulation Experiment (WOCE) along I7N are compared to those from a numerical model using three alternative parametrizations for the air‐sea flux of CFC‐11. The Wanninkhof [1992] gas flux parametrization for climatological winds gives gas saturations which agree best with those observed. The observed and model mixed‐layers are in equilibrium with the contemporary atmosphere to within 1% (the experimental error) in the summer of 1995, excluding cold coastal upwelled waters. When the model is used to extend the space and time scales of the observations in the Arabian Sea, widespread supersaturations of 5% due to weak winds and warming are predicted in the spring and fall, and under saturations of 5% due to mixing in the winter. The model validation of CFC‐11 transfer parametrization and investigation of temporal and spatial variability in saturation are applicable to the physically‐forced saturation variations of carbon dioxide and other gases of interest.
Simultaneous observations of transient decreases of Earth's far‐ultraviolet dayglow with two cameras
Authors: Frank L. A. , Sigwarth J. B.
Published: February 2004

The Polar spacecraft carries two cameras which are capable of viewing Earth's far‐ultraviolet dayglow. One of these two cameras was programmed into a special operating mode during 12 April and 30 July 1996 in order to obtain simultaneous images of transient decreases of dayglow emissions from atomic oxygen at 130.4 nm. During the 76 minutes of usable imaging the two cameras acquired five sets of frames for which a transient decrease was detected by each camera, and the transient decrease occurred at the same geographical position in the dayglow. These series of observations provide strong evidence for the identification of atmospheric holes as a geophysical phenomenon.
Trails of OH emissions from small comets near Earth
Authors: Frank L. A. , Sigwarth J. B.
Published: February 2004

The results are reported for a successful search for the OH emissions associated with an influx of small comets into Earth's upper atmosphere with a camera on board the Polar spacecraft. The spatial distributions of the OH emissions are characterized by a bright core of intensities at or less than the spatial resolution of the camera which is surrounded by a larger dim region of luminosities. The Earth's shadow is employed in order to obtain a coarse determination of the altitudes of these OH trails, i.e., an altitude range < 3000 km.
Recording wind microstructure with a seismograph
Authors: Steeples Don W. , Schmeissner Chris , Macy Brian
Published: February 2004

In an effort to characterize the effects of atmospheric waves on seismic sensors at the surface of the earth, we used geophones to perform some simple experiments allowing us to “watch” the wind. By examining the wind noise on the resulting seismograms, we were able to characterize the microstructure of atmospheric wind gusts at a horizontal scale of 1 to 10 m. In a first experiment to detect the wind‐induced wave field, we placed 96 geophones on the ground in a straight line aligned parallel with the wind at intervals of 0.3 m. We recorded the resulting data using a 96‐channel exploration seismograph. In essence, the seismograph system served as a linear array of 96 ground‐level wind sensors. On a 1‐ to 2‐m scale, wind‐gust details became apparent after the seismograph had recorded for a period of 7.5 s. When wind‐gust speeds were between 4 and 7 m/s (as measured directly from the time‐and‐distance relationships obtained from the seismogram), the wavelength of the gusts was between 3 and 6 m. In a second experiment, we used an array consisting of three parallel lines of 32 geophones each and were able to detect the lateral components of wind motion and turbulence relative to the long axis of the array. We noted variations in both space and time in the effect of the wind gusts on the geophones. The sensing system we describe is preliminary; however, when further refined, it may be a useful way of looking at the microstructure of atmospheric motion near the ground. The data we obtained also suggest that when models are constructed and near‐ground atmospheric observations are made using grid spacings of more than 1 m, the results may be subject to serious spatial‐aliasing effects. The authors offer these results in the hope that they will stimulate new, cross‐disciplinary scientific inquiry. Moreover, applications of the technique might include the generation of data to support improved modeling of atmospheric turbulence at meter scales, which could be of interest to those requiring information about wind shear, wind‐induced soil erosion, the dispersion of pollutants and toxins, and other subjects of interest.
Acoustic mapping of diffuse flow at a seafloor hydrothermal site: Monolith Vent, Juan de Fuca Ridge
Authors: Rona P. A. , Jackson D. R. , Wen T. , Jones C. , Mitsuzawa K. , Bemis K. G. , Dworski J. G.
Published: February 2004

Diffuse flow of hydrothermal solutions commonly occurs in patchy areas up to tens of meters in diameter in seafloor hydrothermal fields. It is recognized as a quantitatively significant component of thermal and chemical fluxes, yet is elusive to map. We report a new acoustic method to detect and map areas of diffuse flow using phase‐coherent correlation techniques. The sonar system was modified to record phase information and mounted on DSV SEA CLIFF. The submersible occupied a stationary position on the seafloor and the transducer scanned the seafloor surrounding Monolith Vent, a sulfide edifice venting black smokers, at a nominal range of 17 m at a depth of 2249 m on the Juan de Fuca Ridge. Patchy areas of uncorrelated returns clearly stood out from a background of returns that exhibited ping‐to‐ping correlation. The areas of uncorrelated returns coincided with areas of diffuse flow as mapped by a video survey with the Navy's Advanced Tethered Vehicle (ATV). Correlated returns were backscattered from invariant seafloor. Uncorrelated returns were distorted by index of refraction inhomogeneities as they passed through diffuse flow between the seafloor and the transducer. The acoustic method presented can synoptically map areas of diffuse flow. When combined with standard in situ measurement and sampling methods the acoustic mapping will facilitate accurate determination of diffuse thermal and chemical fluxes in seafloor hydrothermal fields.
The solar cause of interplanetary disturbances observed in the distance range 0.24–1 AU
Authors: Manoharan P. K.
Published: February 2004

Interplanetary disturbances are an important aspect of the physics of the sun and heliosphere. They are identified as an increase in the density turbulence compared with the ambient solar wind. Here, we report the detection of a large number of interplanetary disturbances within the distance range 0.25–1 AU based on interplanetary scintillation measurements made between 1986 and 1991. For the first time, this yields the helio‐latitudinal distribution of interplanetary transients at different phases of the solar cycle, thereby providing insight into the physical processes influencing these phenomena. It is found that near solar minimum (1986–mid–1988), transients originate in the equatorial region of the Sun. As solar activity increases, they are observed at higher latitudes, and even in the polar regions at solar maximum (1989–1991). These disturbances also show a wide range of speeds, with a global average speed of ∼450 kms−1. More than 80% of the disturbances are associated with the active prominences on the Sun, which are suggested to be the source of coronal mass ejections.
Activation volume of silicon diffusion in San Carlos olivine
Authors: Béjina F. , Raterron P. , Zhang J. , Jaoul O. , Liebermann R. C.
Published: February 2004

The activation volume of silicon diffusion (Vsi) in olivine is reported for the first time. Specimens of San Carlos olivine single crystal were annealed at 1763 K and at pressures to 9 GPa in an uniaxial split‐sphere apparatus. 30Si was used as tracer and the diffusion profiles were analyzed using the resonant nuclear reaction 30Si(p,γ). We obtain Vsi = (−1.9 ± 2.4)×10−6 m³/mol with a more probable value close to zero.
Retrieving CCN column density from single‐channel measurements of reflected sunlight over the ocean: A sensitivity study
Authors: Mishchenko M. I. , Travis L. D. , Rossow W. B. , Cairns B. , Carlson B. E. , Han Q.
Published: February 2004

The Twomey effect is an increase of the cloud albedo with increasing concentration of tropospheric aerosols serving as cloud condensation nuclei (CCN). Confirmation and quantification of this effect on a global basis requires accurate satellite retrievals of CCN concentrations. We present a theoretical study of the ability of passive satellite remote sensing techniques to provide reliable estimates of tropospheric aerosol column densities over the ocean. We show that a retrieval algorithm based on single‐channel single‐viewing‐angle radiance measurements is incapable of accurately determining CCN column densities and that an algorithm based on multiangle radiance measurements provides much better retrievals. However, even for the latter algorithm the errors in the retrieved CCN column densities can exceed a factor of 5. The poor performance of single‐channel radiance‐only algorithms is explained by the strong dependence of the extinction cross section and weak dependence of the phase function on aerosol effective radius. In contrast, high‐precision multiangle polarization measurements, which are much more sensitive to aerosol microphysics, are capable of constraining CCN column densities to within a few tens of percent.
Water on early Mars: Possible subaqueous sedimentary deposits covering ancient cratered terrain in western Arabia and Sinus Meridiani
Authors: Edgett Kenneth S. , Parker Timothy J.
Published: February 2004

Western Arabia and northern Sinus Meridiani (30°N–10°S; 40°W–40°E) are almost entirely covered by wind‐eroded, horizontally‐bedded, sedimentary layers that lap against local topographic features. This portion of Mars' ancient cratered terrain is relatively low (< 1 km elevation) and flat (sloping westward 0.7 m/km over 3,000 km). The region lacks valley network channels. We propose that at some time in early Martian history, this region was under water. The water hypothesis is strengthened by the presence of (1) a shore‐like contact between smooth‐surfaced deposits and ancient cratered terrain in central Sinus Meridiani, (2) polygonal structures in northern Sinus Meridiani, and (3) sand (which cannot be from airfall), possibly reworked by wind from the underlying sedimentary units. The September 1997 arrival of Mars Global Surveyor's thermal emission spectrometer offers an opportunity to begin to test this hypothesis by searching for carbonate and evaporite minerals among the sediment covering the region.
The heterogeneous reaction of NO3 with NaCl and KBr: A nonphotolytic source of halogen atoms
Authors: Seisel Sabine , Caloz François , Fenter Frederick F. , van den Bergh Hubert , Rossi Michel J.
Published: February 2004

The heterogeneous reactions of NO3 on NaCl and KBr salt were studied at room temperature using a Knudsen reactor equipped with dual detection, namely Laser induced fluorescence (LIF) and mass spectrometry (MS). The uptake coefficients of NO3 were found to be γ = (4.9±3)·10−2 onto NaCl and γ = 0.16±0.08 onto KBr. In the case of NaCl, HCl was the sole product observed. However, there is indirect evidence that Cl atoms are the primary products. In the case of KBr we observed Br2 and Br to be the products of reaction. A first estimation of the atmospheric relevance of these reactions indicate that under certain conditions the heterogeneous loss of NO3 on seasalt aerosols may compete with removal by homogeneous gas phase reactions.
Cetacean distributions and oceanographic features near the Kerguelen Plateau
Authors: Tynan Cynthia T.
Published: February 2004

Cetacean surveys were conducted in the austral summer during World Ocean Circulation Experiment hydrolegs I8S and I9S in the southeastern Indian Ocean. The highest density of cetaceans occurred along the southern flank of the Kerguelen Plateau and northern edge of the Princess Elizabeth Trough, where the distribution of whales coincides with the mean positions of the Southern Front of the Antarctic Circumpolar Current (ACC) and southern water mass boundary (Southern Boundary) of the ACC. The topographic steerage of these features of the ACC around the southern edge of the Kerguelen Plateau brings shoaled, nutrient‐rich Upper Circumpolar Deep Water (UCDW) to higher latitude than in adjacent basins. The higher concentrations of cetaceans near the Kerguelen Plateau suggests that whales benefit from a cascade of trophic dynamics associated with the poleward extent of UCDW, the marginal ice edge zone, and the proximity of several oceanographic features: the high latitude penetration and close alignment of the Southern Front and Southern Boundary of the ACC; the unique poleward extent of the Southern Boundary as it is topographically steered around the plateau; the entrainment of macronutrients into the surface mixed layer near the Southern Boundary; isopycnal shoaling in cyclonic eddies; the presence of complex bathymetry; and the advection of a tongue of ice northward along the eastern side of the plateau. The association between these concurrent oceanographic features and whales suggests that the southeastern edge of the Kerguelen Plateau is a predictably productive foraging location for cetaceans and their prey.
A density‐tapering approach for modeling the seismic response of free‐surface topography
Authors: Schultz Craig A.
Published: February 2004

This study investigates the accuracy of a density‐tapering approach for modeling the seismic response of free‐surface topography on a fourth‐order staggered finite‐difference grid. The accuracy of the boundary condition near the free‐surface and at‐depth is rigorously tested in 2D where noise artifacts are identified and characterized. This technique is then modified using spatial density filters, to reduce the noise artifacts while retaining the accuracy, stability, and computational efficiency of the original algorithm. The modified density‐ tapering boundary condition is accurate down to 15 points per wavelength (PPW) with noise levels below 5% in almost all instances. This multi‐step technique adjusts only the material properties near the taper zone allowing it to remain a preprocessing technique, applied prior to the finite‐difference calculation.
Approximate separation of volcanic and 11‐year signals in the SBUV‐SBUV/2 total ozone record over the 1979‐1995 Period
Authors: McCormack J. P. , Hood L. L. , Nagatani R. , Miller A. J. , Planet W. G. , McPeters R. D.
Published: February 2004

The combined Nimbus 7 SBUV, NOAA 11, and preliminary NOAA 9 SBUV/2 monthly zonal mean total ozone data set, extending from January 1979 to December 1995, is analyzed with a multiple regression statistical model that includes a term to describe the direct effect of volcanic aerosols on total ozone. Outside of polar regions, which are not included in this analysis, the volcanic regression coefficients in the northern hemisphere are negative (consistent with heterogeneous chemical losses of ozone on volcanic sulfate aerosols) and reach their maximum values between 40°N–60°N latitude. Although inclusion of the aerosol term in the statistical model introduces some additional uncertainty to the derived solar response, statistically significant values of the solar coefficients are found in northern and southern subtropical regions throughout the year, with maximum amplitudes of ∼2.5% at 30° latitude in both hemispheres during winter. We conclude that the 11‐year signal in the SBUV‐SBUV/2 total ozone record is approximately separable from volcanic aerosol effects.
Hemispheric asymmetry of surface temperature anomalies
Authors: Gordon Adrian H. , Bye John A. T.
Published: February 2004

In recent months there has been some controversy concerning the possible effect of suspended sulfate aerosols on warming trends predicted to occur in response to steadily increasing greenhouse gas concentrations in the troposphere. Evidence in the recent literature both supporting and doubting the theory that aerosols have suppressed warming in the Northern Hemisphere more than in the Southern Hemisphere has relied on analyses of radiosonde observations covering various periods between 1958 and 1995. In this letter the UK Met Office/University of East Anglia Climatic Research Unit (Parker/Jones) data sets of mean surface temperature anomalies over land and sea for the past 140 years serve as an independent data base to test earlier reported results obtained from radiosonde observations. The results suggest that there is no evidence of any systematic differences in temperature trends between the two hemispheres.
Real‐time single particle monitoring of a relative increase in marine aerosol concentration during winter rainstorms
Authors: Noble Christopher A. , Prather Kimberly A.
Published: February 2004

During the months of December 1996 and January 1997, aerosol characterization was performed in real‐time at Riverside, CA, an inland location approximately 100 km east of the Los Angeles coast. Analysis was performed on a single particle basis with measurements of both particle size and composition. Data were collected throughout the course of five rainstorms. Single particle mass spectra demonstrate that obvious composition changes occur in the aerosol systems as the marine air mass is transported inland. While precipitation scavenging of aerosols was observed, there was a significant relative increase of sea salt particles in the non‐scavenged aerosol. Compositionally‐resolved particle size distributions also demonstrate real‐time changes that occur in the atmospheric aerosol sample.
The heliosphere‐interstellar medium interaction: One shock or two?
Authors: Richardson John D.
Published: February 2004

The issue of whether a shock forms in the interstellar medium as it approaches the heliopause has not been settled. Observations generally show that the local interstellar medium is slightly supersonic with respect to a stationary (constant distance from the Sun) heliopause. The solar wind dynamic pressure varies over the solar cycle, causing the heliopause distance to move inward and outward. This work shows that the heliopause speeds may be large compared to the speed of the interstellar medium. This leads to the scenario where the interstellar medium is supersonic with respect to the heliopause when the heliopause moves outward (the declining phase of the solar cycle) and subsonic the rest of the time. A shock would form when the heliopause moves outwards and dissipate when the heliopause moves inwards. The heliospheric radio emission is shown to occur at times when the heliopause moves outwards and thus may be related to the formation of the shock in the interstellar medium. This work leads to two testable predictions: 1) that the heliospheric radio emissions will intensify when the solar wind pressure increases and 2) the temperature of the interstellar neutrals will fluctuate over a solar cycle with larger temperatures when there is a shock in the interstellar medium.
Calculated elastic constants and anisotropy of Mg2SiO4 spinel at high pressure
Authors: Kiefer Boris , Stixrude Lars , Wentzcovitch Renata M.
Published: February 2004

We calculated the elastic properties of Mg2SiO4 spinel, using the plane‐wave pseudopotential method. The athermal elastic constants were calculated directly from the stress‐strain relations up to 30 GPa, which encompasses the experimentally observed stability field of spinel. The calculated elastic constants are in very good agreement with Brillouin scattering data at zero pressure. We calculated the isotropically averaged elastic wave velocities and the anisotropy from our single crystal elastic constants. We find that the elastic anisotropy is weak (azimuthal and polarization anisotropy of S‐waves: 5%, azimuthal P‐wave anisotropy: 2.5%, at zero pressure) compared to other silicates and oxides. The anisotropy decreases initially with increasing pressure, changing sign at 17GPa before increasing in magnitude at higher pressures. At typical pressures of the earth's transition zone (20–25 GPa), the elastic anisotropy is 1% and 2% for P‐ and S‐waves respectively.