bluuebunny/crossref_metadata_2025 huggingface dataset:
Are sedimentary salt layers always impermeable?
Authors: Yechieli Yoseph , Ronen Daniel , Berkowitz Brain
Published: February 2004

We report here, for the first time, the finding of a 24 to 31 m deep, 10,000 y old, water‐saturated and highly hydraulically conductive salt layer composed of idiomorphic halite crystals in the coastal area of the Dead Sea. The high hydraulic conductivity of the layer was evidenced by laboratory and field tests and by the rapid fluctuations of the water table, in a well penetrating the layer, following variations in the water level of the Dead Sea. Such layers may lead to intensive and rapid flow of water and non‐polar liquids.
Temporal variability of summer‐time ozone and aerosols in the free troposphere over the eastern North Atlantic
Authors: Prospero J. M. , Schmitt R. , Cuevas E. , Savoie D. L. , Graustein W. C. , Turekian K. K. , Volz‐Thomas A. , Díaz A. , Oltmans S. J. , Levy H.
Published: February 2004

In the free troposphere over Tenerife in the summer, O3 concentrations are anti‐correlated with major pollutant aerosols (nss‐SO = 4 and NO−3) and with 210Pb, a tracer for boundary layer sources. In contrast, O3 is highly correlated with 7Be, a product of cosmic ray interactions in the upper troposphere and stratosphere. This suggests that natural O3 sources (i.e. the stratosphere) might be playing an important role. Nonetheless our results do not preclude the possibility that substantial amounts of pollution‐related O3 could be transported in the free troposphere. However, to be consistent with our results, the transport mechanisms would have to incorporate efficient processes for the removal of pollutant aerosol species and 210Pb.
Observations of 2‐dimensional airglow structure and Na density from the ALOHA, October 9, 1993 ‘storm flight’
Authors: Swenson G. R. , Espy P. J.
Published: February 2004

On October 9, 1993, observations were made from the NCAR Electra aircraft during a 7 hour flight towards a tropospheric low pressure system NW of Maui. A very bright (>50% intensity amplitude) OH wave (∼200 km horizontal wavelength) was encountered ∼900 km NW of Maui. The OH volume weighted Na column density measured by the lidar increased 4‐fold at the same location. OH imagery showed the wave phase front was aligned NE‐SW, similar to the tropospheric airmass boundary which was located ∼2000 km NW of Maui. This ‘wall’ wave had an apparent phase velocity (vϕ) of 75 ms−1 toward the SE and was observed overhead Haleakala, Maui ∼3 1/4 hours later. The ‘wall’ appeared to represent the southern boundary for an extensive short horizontal wavelength structure, with a similar phase front alignment. This structure had weak amplitudes initially but was fully developed ∼1 hour after encountering the wall. The details of OH imagery, intensity, and Na structure associated with this event are summarized.
Frictional heating and the stability of rate and state dependent frictional sliding
Authors: Sleep Norman H.
Published: February 2004

Numerous laboratory experiments have found that the coefficient of friction of simulated faults depends both on the instantaneous sliding velocity and on a state variable that represents the previous sliding history. The coefficient of friction is typically given as μ = μ0+a1n( V/V0) + b1n( ψ/ψ0) where μ0, V0, ψ0, a, and b are constants, V is the sliding velocity and ψ is the state variable. The time derivative of the state variable is often given by an expression of the form 1/t0‐ψV/Dc where t0 is a constant with dimensions of time and Dc is a critical displacement. The stiffness of a one‐dimensional system must be less than the effective normal traction times (b‐a)/Dc for instability to occur. Temperature increase from frictional heating expands pore fluid, increasing its pressure and decreasing the effective stress on a sealed fault plane. The amount of temperature change depends on heat conduction into the country rock from the planar heat source of the fault zone. The apparent value of the coefficient a is decreased by an amount that depends on the square root of elapsed time of an oscillation from steady‐state. Systems which are close to the stability limit and/or have large characteristic times Dc/Vp, where Vp is the long term slip velocity, exhibit slow evolution in the absence of frictional heating and thus are significantly affected by frictional heating. In real faults, the effects of frictional heating at slow creep rates may conceivably be overwhelmed by those of compaction, dilation, hydrofracture, and fluid flow.
Increase in the atmospheric nitrous oxide concentration during the last 250 years
Authors: Machida T. , Nakazawa T. , Fujii Y. , Aoki S. , Watanabe O.
Published: February 2004

In order to estimate the concentrations of atmospheric nitrous oxide (N2O) during the last 250 years, air samples were extracted from an Antarctic ice core, H15, using a dry extraction system and were then analyzed with a precision of ±2 ppbv. The results obtained were clearly less scattered and much tighter than those of the previous studies. Our data showed that the concentrations of atmospheric N2O in the 18th century were about 276 ppbv on average. It was also obvious that the N2O concentration began to increase in the mid‐19th century and reached approximately 293 ppbv around 1965, the trend of the concentration increase correlating quite well with the direct atmospheric measurements at the South Pole. Such an increase in the atmospheric N2O concentration is thought to be of anthropogenic origin.
Comparing ground‐level spectrally resolved solar UV measurements using various instruments: A technique resolving effects of wavelength shift and slit width
Authors: Slaper H. , Reinen H. A. J. M. , Blumthaler M. , Huber M. , Kuik F.
Published: February 2004

Spectrally resolved UV measurements are important for the study of biologically relevant UV in relation to changes in atmospheric parameters. The inter‐comparison of spectral instruments is essential as measurement techniques and calibrations are not standardized. The differences in slit functions cause large spectral variations when comparing the spectral readings directly. The method described, which compares spectral readings using different instruments, corrects for differences of wavelength calibrations and slit functions, and does not require knowledge of additional atmospheric parameters and UV‐transfer model calculations. The wavelength alignment has an accuracy of 0.02 nm over the wavelength interval from 300–400 nm, and a reproducibility of 0.01 nm. The robustness of the methods and reproducibility of results are shown in the evaluation of a seven day intercomparison campaign with three different scanning spectroradiometers.
Steepening of Alfvén waves and its effect on the structure of slow shocks
Authors: Karimabadi H.
Published: February 2004

The interaction between Alfvén/ion cyclotron (A/IC) waves and a slow shock is examined by means of hybrid simulations. It is shown that for a rather general set of parameters, slow shocks can generate A/IC waves which become group standing within the shock transition layer, and steepen into thin structures (∼4 ion inertial lengths). Each front is shocklike with finite jumps in the plasma parameters across it. In such cases, the transition from upstream to downstream conditions across the slow shock occurs over a number of layers. Following the jumps over the steepened front(s), the final transition to downstream is made over a much broader region more typical of slow shocks (≳60 ion inertial lengths). Other important effects of the steepened front are the local trapping of the plasma, generation of a coherent wavetrain and changes in the polarization of the slow shock. In particular, the first simulations of slow shocks with a right‐handed polarization and an upstream wavetrain are shown. Due to the unusually complicated structures of these slow shocks much care must be taken in the search and identification of slow shocks in the observations.
Artifact peroxides produced during cryogenic sampling of ambient air
Authors: Staffelbach Thomas , Neftel Albrecht , Dasgupta Purnendu K.
Published: February 2004

Peroxides were found to be produced as artifacts during cryogenic sampling with Horibe traps. Cryogenic trap sampling was compared to collection with a wet effluent diffusion denuder and a Nafion membrane diffusion denuder. Hydrogen peroxide and hydroxymethyl hydroperoxide measured in the cryogenic trap samples were significantly higher. In comparison, no evidence of artifact methyl hydroperoxide production was found. The amount of artifact H2O2 and HMHP produced increased with decreasing trap temperature. Spiking ambient air with ethene or isoprene showed that these hydrocarbons, in the presence of ozone, can be responsible for the artifact production of peroxides. Our results clearly suggest that the peroxide data obtained by cryogenic sampling and reported in the literature should be interpreted with caution.
Heliolatitude dependence of interplanetary heavy ions
Authors: Maclennan C. G. , Lanzerotti L. J. , Simnett G. M. , Sayle K. A.
Published: February 2004

In its rapid traversal of 80° of heliolatitude from the southern solar pole to the equator, the HI‐SCALE instrument on the Ulysses spacecraft measured the composition of ions accelerated at the co‐rotating interaction regions (CIRs) that it crossed. We compare ion composition measurements as a function of heliolatitude during this traversal to those made on the ascent to the southern solar pole. The C/O ratio (∼1) in the fast traverse at ∼1.4 AU is found to be about twice the value (∼0.5) found previously in the ecliptic as well as at intermediate latitudes beyond ∼2 AU. For the CIR‐associated events in the southerly high speed solar wind stream, the ion intensity enhancements are found to decrease monotonically with increasing heliolatitude once Ulysses crossed ∼20°S. Thus, the optimum region for CIR‐related particle acceleration in solar minimum conditions occurs near the boundary of the current sheet at distances between the orbits of Mars and Jupiter. These results, together with HI‐SCALE results on the heliolatitude dependence of anomalous oxygen suggest that the lower value of the C/O ratio arises from the enhanced (relative to 1 AU) abundance of low energy anomalous O at heliolatitudes beyond the current sheet and distances beyond ∼2 AU.
Heat flux observations in the mesopause region above Haleakala
Authors: Tao Xin , Gardner Chester S.
Published: February 2004

Horizontal and vertical heat fluxes between 85 and 100 km were computed using temperature and wind profiles observed on 21 October 1993 by the Na Wind/Temperature lidar operated at Haleakala during the ALOHA‐93 Campaign. On this night a warm layer developed between 85 and 90 km. The temperature increased by almost 40 K near 88 km, reaching a maximum of approximately 235 K at 1030 UT before decreasing throughout the remainder of the 5 h observation period. This substantial temperature increase was associated with a large amplitude wave, possibly the diurnal tide, and with a sporadic Na layer. The meridional wind field exhibited a strong vertical shear zone within the warm layer and sporadic Na layer which briefly exceeded the shear instability limit of ≈ 42 m/s/km at the time the temperature reached maximum. The vertical heat flux was directed upward within the warm layer reaching maximum at 88 km and downward above resulting in strong flux convergence. The average heat fluxes between 85 and 100 km were 2.5±2.4 K m/s (vertical), 77±25 K m/s (zonal), and −19±20 K m/s (meridional). The maximum heating rate associated with the convergence of vertical heat flux was 11±4.1 K/h at 91 km. The average heating rate between 85 and 100 km was 1.9±0.8 K/h.
A wavelet based methodology for scale‐space anisotropic analysis
Authors: Kumar Praveen
Published: February 2004

It is well known that several geophysical fields exhibit characteristic features at different scales. For some such fields scale‐space anisotropy is also present, that is, features contributing significant fraction of energy are oriented in different directions at different scales. Examples of such fields include clouds, rainfall, hurricanes etc. A technique based on wavelet transforms (with two‐dimensional directionally oriented Morlet wavelet) is developed to analyze such random fields. This methodology has significant advantage over Fourier transform based techniques and is demonstrated using the analysis of a spatial rainfall field.
Growth, sudden enhancement, and relaxation of current sheets in the magnetotail: Two‐dimensional substorm dynamics
Authors: Ma Z. W. , Wang Xiaogang , Bhattacharjee A.
Published: February 2004

A two‐dimensional, low‐dissipation magnetohydrodynamic simulation is used as a model for magnetospheric substorm dynamics. The simulation begins from a Grad‐Shafranov equilibrium of the magnetotail including the Earth's dipole field. This initial configuration is driven by a continuous electric field (of IMF origin) which induces equatorward flows. A thin current sheet develops algebraically in time, spanning Y‐points that stretch from the mid‐tail region (∼30 RE) to the near‐Earth region (∼10 RE). In the late growth phase, rapid thinning of the sheet and near‐explosive intensification of the current density are observed. The onset of a partial current disruption results from the formation of small islands in the near‐Earth region. Numerical results are compared with observations.
New evidence for the stratospheric dehydration mechanism in the equatorial Pacific
Authors: Vömel H. , Oltmans S. J. , Kley D. , Crutzen P. J.
Published: February 2004

Water vapor profile measurements obtained in the western and central Pacific during the Central Equatorial Pacific Experiment (CEPEX) show a strong connection between the water vapor content near the tropopause and areas of deep convection. We show that air ascending within deep convective towers can be dried to mixing ratios below 1 part per million by volume (ppmv), which is much lower than the average mixing ratio observed in the stratosphere. A sharp increase of water vapor mixing ratio above the tropopause is an indication of the evaporation of ice particles at the top of deep convective cells. A mixed layer of up to around 1 km thickness above the tropopause in the regions of deep convection is indicated by the vertical profiles of ozone, water vapor, and potential temperature. Furthermore, a local maximum was observed at 20 km, which is an indication for the seasonal cycle of the tropopause temperature.
An investigation of intrinsic gravity wave signatures using coordinated lidar and nightglow image measurements
Authors: Taylor M. J. , Gu Y. Y. , Tao X. , Gardner C. S. , Bishop M. B.
Published: February 2004

Simultaneous observations of gravity waves using an Na wind/temperature lidar and a multi‐wavelength all‐sky nightglow imager were obtained, for the first time, during the ALOHA‐93 campaign. A novel investigation of intrinsic wave parameters has been made by combining measurements of the horizontal wave components imaged in four nightglow emissions (height range ∼80–100 km) with Na lidar soundings of the horizontal wind field and temperature profiles over the same height interval. On October 19 both instruments registered marked monochromatic wave motions. The intrinsic periods of several of these waves have been determined and were found to vary considerably with altitude, often resulting in a significant increase over their observed wave periods. It is shown that these two instrumental techniques generally sampled different regions of the gravity wave spectrum: the lidar exhibiting most sensitivity to short vertical wavelength waves (less than about 10 km) while the imager was most responsive to larger vertical wavelength waves. This study illustrates the significant advantages of combining wind/temperature lidar and multi‐wavelength image observations for intrinsic gravity wave measurements.
Summer solstice solar radiation, the 100 kyr Ice Age cycle, and the next Ice Age
Authors: Ledley Tamara Shapiro
Published: February 2004

Modeling studies suggest that the summer solstice solar radiation is more important than the caloric half‐year solar radiation in producing glacial/interglacial cycles because it is more representative of the energy available to melt ice during the short melt season. Here it is shown that the correlation between the summer solstice solar radiation and the rate of change of the oxygen isotope record is generally greater than that between the caloric half‐year radiation and the rate of change of the oxygen isotope record. These results also suggest that the sawtoothed nature of the 100 kyr cycle may be produced by periods of relatively slow changes in ice volume, punctuated by periods of rapid growth that are initiated at times of extremely low summer solstice radiation; and that it is unlikely that an ice age will begin in the next 70 kyr.
Measurements of water vapor in the tropical lower stratosphere during the CEPEX Campaign: Results and interpretation
Authors: Weinstock E. M. , Hintsa E. J. , Dessler A. E. , Anderson J. G.
Published: February 2004

We present measurements of water vapor taken using a fast‐response Lyman‐alpha hygrometer mounted on the NASA ER‐2 for the Central Equatorial Pacific Experiment (CEPEX) during March and April 1993. The flights originated from Fiji (17°S, 178°E) and covered a range of potential temperatures up to 470 K. Concurrent ozone measurements and a 1‐D model are used to convert potential temperature to effective age of the air in the stratosphere. This analysis provides insight into measured water vapor profiles in the lower tropical stratosphere taken during different seasons on previous aircraft campaigns. It yields a picture of a seasonal cycle consistent with the variation of the average tropical tropopause temperature and an annually averaged mixing ratio of water in air entering the tropical stratosphere of about 4.45 ppmv.
Electric field patterns as seismic precursors
Authors: Yépez E. , Angulo‐Brown F. , Peralta J. A. , Pavía C. G. , González‐Santos G.
Published: February 2004

In this paper we report the results of two and a half years of measurements of the ground electric field at the Pacific coast of Mexico. The analysis of the voltage itself does not show any distinguishable feature that could be correlated to earthquakes. Fourier analysis, however gives clear patterns of the electric field prior to the four Ms,w > 6 earthquakes that occurred in the zone during the time interval considered.
Critical role of the equatorial topside F region on the evolutionary characteristics of the plasma bubbles
Authors: Sekar R. , Raghavarao R.
Published: February 2004

An investigation was carried out by means of a nonlinear numerical simulation of equatorial spread F (ESF) to understand the characteristics of the evolutionary pattern of plasma bubbles with different background topside plasma density distributions above the same bottomside distribution in the equatorial F region at the postsunset times. The investigation revealed that the upward drift of the plasma bubble significantly depends on fractional depletion which is controlled by the background topside electron density distribution. This in turn modifies the zonal and vertical extents of the plasma bubble. It is shown that the observed differences in the zonal widths and vertical extents of plasma bubbles over Kwajalein and Jicamarca regions are due to the differences in the plasma density distributions in the topside ionosphere over those regions.
On the purpose of toroidal motion in a convecting mantle
Authors: Bercovici David
Published: February 2004

The purpose of toroidal flow, i.e., strike‐slip motion and plate spin, in the plate‐tectonic style of mantle convection is enigmatic. It is a purely horizontal, dissipative flow field that makes no apparent contribution to the release of heat. However, when plate‐like toroidal motion is allowed to arise as a phenomenon of non‐Newtonian mantle dynamics, it in fact acts to reduce the net amount of viscous dissipation. We show that for a non‐Newtonian flow driven by an existing poloidal field (a source‐sink field), the generation of toroidal motion interacts with the nonlinear rheology to cause less viscous dissipation than if there were no toroidal motion. With power‐law rheologies, the generation of toroidal motion causes up to a 25% reduction in viscous dissipation. With a self‐lubricating rheology, which has been shown to induce the most plate‐like behavior, toroidal motion causes as much as an 80% reduction in viscous dissipation. Thus, basic non‐Newtonian fluid dynamical theory of the formation of plate tectonics shows that toroidal motion is far from superfluous but in fact facilitates the efficiency of convective flow at the surface.
Growth and evolution of a plasmoid associated with a small, isolated substorm: IMP 8 and GEOTAIL measurements in the magnetotail
Authors: Angelopoulos V. , Mitchell D. G. , Williams D. J. , McEntire R. W. , Lui A. T. Y. , Decker R. B. , Krimigis S. M. , Roelof E. C. , Christon S. P. , Kokubun S. , Yamamoto T. , Hughes W. J. , Samson J. C. , Friis‐Christensen E. , Hayashi K.
Published: February 2004

A tailward‐moving plasmoid was observed at the GEOTAIL satellite at a GSM position (−73.3, 18.1, −1.1) RE on September 16, 1993, at 0417 UT, when the IMP 8 satellite was at (−37.5, −2.5, 1.7) RE at the midnight plasma sheet/lobe interface. The first indication of the plasmoid formation a few minutes after the negative bay onset of a small, localized auroral substorm was the onset of tailward beams of energetic ions and electrons at GEOTAIL well within the plasma sheet. Earthward‐streaming energetic ions observed at IMP 8 a few minutes later suggest that the plasmoid evolved from within the plasma sheet to encompass the flux of nearly the entire thickness of the plasma sheet. The opposite direction of the anisotropies at IMP 8 and GEOTAIL suggest that the particle acceleration region was between X=−37.5 and −73 RE at that time. The isolated substorm associated with this plasmoid started equatorward of 67° latitude at a location which we map to near‐Earth nightside plasma sheet (|X| < 15 RE) based on ground observations of a field line resonance. The active electrojet did not expand poleward until at least 10 min after the detection of the acceleration region tailward of IMP 8 and at least several minutes after the core of the plasmoid had moved tailward of GEOTAIL. These observations reinforce by means of in situ, concurrent, multipoint measurements the attitude expressed recently by several researchers that the locations of lobe reconnection and equatorial projection of electrojet intensification during substorm expansion are distinctly different from each other.
Aerosol emissions by tropical forest and savanna biomass burning: Characteristic trace elements and fluxes
Authors: Echalar F. , Gaudichet A. , Cachier H. , Artaxo P.
Published: February 2004

Aerosol particles were collected during the dry season in the amazonian forest and in African and Brazilian savannas. Sampling was performed inside the plumes of vegetation fires and in the local background atmosphere. Samples were analysed for their elemental composition by Particle Induced X‐Ray Emission (PIXE). Enrichment factors relative to the local background were calculated. Savanna fire aerosols are characterised by enrichments in elements like K, P, Cl, Zn, and Br, whereas forest fire emissions are enriched in Si and Ca. The unexpected low potassium enrichment factor for the forest fires could be due to the prevailing smoldering conditions, whereas the high values of potassium enrichment factor during savanna fires could be associated with the predominant flaming conditions. This result indicates that potassium may be considered a good tracer of the flaming phase of fires only. Emission factors of P, S, Cl, K, Ca, Mn, Zn, Br and total particulate matter were calculated for African savanna fires. Our estimates of the annual potassium and zinc emissions by tropical savanna fires indicate that the contribution of this source should be taken into account to understand the biogeochemical cycle of these elements.
Pressure induced coordination change of Al in silicate melts from Al K edge XANES of high pressure NaAlSi2O6‐NaAlSi3O8 glasses
Authors: Li Dien , Secco R. A. , Bancroft G. M. , Fleet M. E.
Published: February 2004

Aluminum K‐edge XANES spectra of high pressure and high temperature (4.4 GPa and 1575°C) glasses along the NaAlSi2O6 (Jd)‐NaAlSi3O8 (Ab) join are reported using synchrotron radiation, and shown to provide direct experimental evidence for the pressure‐induced coordination change of Al. Five‐ and six‐fold coordinated Al (5Al and 6Al), characterized by Al K‐edge positions at 1567.8 and 1568.7 eV, respectively, first appear in glass of composition Jd60Ab40 and increase in proportion progressively with increasing Jd content. The end‐member jadeite glass contains about 6% of each of 5Al and 6Al. The present direct measurements confirm literature suggestions for the important role of Al in controlling viscosity and diffusion in mantle melts.
The elastic response of the Earth to interannual variations in Antarctic precipitation
Authors: Conrad Clinton P. , Hager Bradford H.
Published: February 2004

Measurements of elastic displacements of the bedrock surrounding large ice sheets have been proposed as a means to detect mass changes in these ice sheets. However, accumulation of glacial mass on the ice sheets is a noisy process, subject to large spatial and temporal variations in precipitation. We simulated the response of the Antarctic continent to a stochastic model of interannual precipitation variations and found that interannual variations in the elastic response of the earth are large when compared to the long‐term mean of displacements produced by an assumed average ice mass imbalance of 10%. If, as some scientists predict, Antarctic ice mass changes in the future become dramatic, the long‐term signal should be large enough to be detected by a few years of geodetic measurements, despite climatic noise.
Chemical sputtering could produce sodium vapor and ice on Mercury
Authors: Potter A. E.
Published: February 2004

It is suggested that chemical sputtering of surface rocks by protons from the Mercury magnetosphere can yield sodium vapor more efficiently than physical sputtering, thus lowering the required sodium concentration in surface rocks. Chemical sputtering can also yield sodium vapor having a relatively low kinetic temperature, in agreement with observation. Water vapor is produced in addition to sodium vapor. It could be produced in sufficient amounts to explain the observation of ice in Mercury polar craters.
A simple model to estimate atmospheric concentrations of aerosol chemical species based on snow core chemistry at Summit, Greenland
Authors: Bergin M. H. , Davidson C. I. , Dibb J. E. , Jaffrezo J. L. , Kuhns H. D. , Pandis S. N.
Published: February 2004

A simple model is presented to estimate atmospheric concentrations of chemical species that exist primarily as aerosols based on snow core/ice core chemistry at Summit, Greenland. The model considers the processes of snow, fog, and dry deposition. The deposition parameters for each of the processes are estimated for SO42− and Ca2+ and are based on experiments conducted during the 1993 and 1994 summer field seasons. The seasonal mean atmospheric concentrations are estimated based on the deposition parameters and snow cores obtained during the field seasons. The ratios of the estimated seasonal mean airborne concentration divided by the measured mean concentration (
) for SO42− over the 1993 and 1994 field seasons are 0.85 and 0.95, respectively. The
ratios for Ca2+ are 0.45 and 0.90 for the 1993 and 1994 field seasons. The uncertainties in the estimated atmospheric concentrations range from 30% to 40% and are due to variability in the input parameters. The model estimates the seasonal mean atmospheric SO42− and Ca2+ concentrations to within 15% and 55%, respectively. Although the model is not directly applied to ice cores, the application of the model to ice core chemical signals is briefly discussed.
Impact of lunar phase on the timing of global and latitudinal tropospheric temperature maxima
Authors: Balling Robert C. , Cerveny Randall S.
Published: February 2004

Daily global and latitudinal‐band lower‐tropospheric temperatures are examined with respect to lunar phase. Over the past 16 years, global temperature data show that the warmest time of the synodic cycle generally occurs five to eight days before the full moon. This global pattern appears strongly in the polar and subtropical regions, however, the mid‐latitudes of both hemispheres are inversely related to the global pattern. These empirical findings discount the possibility that variations in radiant energy directly control lower‐tropospheric temperatures through the synodic month, and suggest a more indirect lunar modulation related to atmospheric circulation, specifically mid‐latitude Rossby wave variations.
210Po and 210Pb disequilibrium in the hydrothermal vent fluids and chimney deposits from Juan de Fuca Ridge
Authors: Hussain N. , Church T. M. , Luther G. W. , Moore W. S.
Published: February 2004

Significantly deficient 210Po/210Pb activity ratios (0.14±0.14) are measured in the hydrothermal vent fluids collected from Juan de Fuca Ridge. Chimney deposits generally showed <5 dpm of excess 210Po. However, one sample from the outermost layer of a sealed spire yielded >1200 dpm g−1 of excess 210Po.

If the observed 210Po‐210Pb disequilibrium in vent fluids is a result of 210Po removal by the precipitates, residence time of polonium with respect to its irreversible removal from hot fluids is estimated to be of the order of a few minutes. Alternatively, if the disequilibrium is a result of an insufficient growth of 210Po from in‐situ210Pb following heating, the residence time of hot fluids within the hydrothermal system can be shown to be less than 30 days, which is considerably lower than previously reported values.
Uptake of Hbr on Ice at Polar Atmospheric Conditions
Authors: Chu Liang T. , Heron James W.
Published: February 2004

The uptake of HBr in water ice has been investigated in a flow reactor under polar atmospheric conditions. The HBr uptake on ice films was determined in the range of 1.1±0.7 × 1014−7.7±1.1 × 1016 molecules/cm² at 188 and 195 K as HBr partial pressures varied from 3.7 × 10−8 to 6.4 × 10−6 Torr. This is the first report of a laboratory study at polar atmospheric conditions that shows HBr·3H2O to be formed during the uptake process. The HBr adsorption and uptake thermodynamics were also investigated. The implications of these new findings for the heterogeneous chemistry of the polar ozone depletion are briefly discussed.
Three‐dimensional seismic image of a geothermal reservoir: The Geysers, California
Authors: Julian B. R. , Ross A. , Foulger G. R. , Evans J. R.
Published: February 2004

Three‐dimensional seismic travel‐time tomography of The Geysers geothermal area, in the coast ranges of northern California, shows a strong (−9%) anomaly in VP/VS, the ratio of the compressional and shear wave speeds, that is not evident in VP alone and corresponds closely to the most intensively exploited part of the geothermal reservoir. This anomaly probably indicates low pore pressure and relatively dry conditions, caused partly by boiling of pore water as steam is extracted. Steam pressure decreases over the last decade have probably caused seismologically measurable changes in wave speeds. Tomographic measurement of VP/VS is a promising technique both for identifying geothermal resources and for monitoring them during exploitation.
Constraints from sea beam bathymetry on the development of normal faults on the East Pacific Rise
Authors: Lee Sang‐Mook , Solomon Sean C.
Published: February 2004

We address the question of the horizontal extent of active upper crustal extension near a fast‐spreading ridge by applying seafloor slope criteria for normal fault identification to twelve Sea Beam swaths that cross the axis of the East Pacific Rise between 9°10′ and 9°50′N. Both the density of and the total throw on identified fault system increase with axial distance to at least 30 km from the rise, indicating that the half width of the zone of active normal faulting is 30 km or more. The densities of inward‐ and outward‐facing normal fault scarps in this distance range appear to be similar. The distance from the rise to the nearest large‐throw fault zone is approximately axisymmetric to the north of 9°23′N, but the mid‐point between nearest large‐throw fault zones is offset 2–3 km to the west of the bathymetric axis south of 9°23′N and thus tracks the center of the axial magma chamber reflector and presumably the axis of most recent magmatic emplacement.
The stress state implied by dislocation models of subduction deformation
Authors: Douglass J. J. , Buffett B. A.
Published: February 2004

Dislocation models of the earthquake cycle are often employed to predict surface deformations above a subduction zone. However, these models, being based entirely on a kinematic formulation of subduction behaviour, place no constraints on the subsurface stress field. Here, the stress state predicted by an elastic dislocation model is shown to exhibit characteristics inconsistent with those anticipated based on physical models of subduction behaviour. In particular, the model predicts an unreasonable distribution of stress along the interface between the overriding and subducting plates. The net shear traction integrates to zero along the interface, so significant shear must act on the overriding plate in the updip direction, opposite to that of the relative direction of motion of the subducting slab. Quantitative calculations using an elastic half‐space representation of the Earth are employed to illustrate the inconsistencies inherent in the dislocation model. Analytic expressions for this case are extended to allow for calculation of the stress components over the entire half‐space.
Time resolved sprite imagery
Authors: Rairden R. L. , Mende S. B.
Published: February 2004

Fleeting columns of luminosity occurring above large thunderstorms at 50–90 km altitude, presently known as sprites, were imaged with an intensified video charge coupled device (CCD) camera during a July 1995 ground‐based campaign near Fort Collins, Colorado. These unfiltered intensified images reveal detailed spatial structure within the sprite envelope. The temporal resolution of standard interlaced video imagery is limited by the 60 fields per second acquisition rate (16 ms). The specific CCD used here, however, is subject to bright events leaking into the readout registers, allowing time‐resolution on the order of the linescan rate (63 µs). Typical sprite onset is found to follow the associated cloud lightning by 1.5 to 4 ms. The onsets of the individual sprites within a cluster are generally, but not always, simultaneous to within 1 ms. Sprites tend to have a bright localized core, less than 2 km in horizontal dimension, which rises to peak intensity within 0.3 ms and maintains this level for 5 to 10 ms before fading over an additional 10 ms.
LITE Validation Experiment along California's Coast: Preliminary results
Authors: Strawbridge K. B. , Hoff R. M.
Published: February 2004

The Lidar In‐Space Technology Experiment (LITE) was launched aboard the Space Shuttle Discovery on September 9, 1994. It employed a three‐wavelength Nd:YAG lidar system. The validation of LITE involved ground truth experiments which were carried out by over 50 international groups consisting of both airborne and ground‐based lidar platforms. Our experiment involved the operation of an airborne Nd:YAG lidar system, at the fundamental wavelength of 1064 nm, aboard National Research Council's Convair 580 (CV580) aircraft, operating in a nadir orientation. Two flight tracks aligned with orbital tracks over California's coast provided an interesting study. First, comparisons with preliminary LITE data and CV580 results will illustrate the transport of urban aerosols from Los Angeles and San Francisco. Secondly, a correlative study of cloud top heights, obtained from a marine stratus cloud deck off the coast of California showed agreement with the 10s averaged LITE data of ±50m.
Large‐scale hybrid simulations of the magnetotail during reconnection
Authors: Krauss‐Varban D. , Omidi N.
Published: February 2004

Large‐scale, 2‐D hybrid simulations are used to investigate the ion kinetic physics associated with quasi steady‐state reconnection in the magnetotail. The simulations encompass a significant portion (20 × 120 RE) of the tail. After formation of transient plasmoids, the results show the features of fast Petschek‐type reconnection. There are two pairs of thin transition layers attached to the x‐point which divert and accelerate the flow within a few ion inertial lengths. These transition layers do not quite conform to the properties of the expected slow shocks. The reason for this appears to be the fact that the ion dissipation scale is comparable to the thickness of the developing plasma sheet. As a result, we find signatures of only partially thermalized, counterstreaming ions in what resembles the plasma sheet boundary layer. A fast ion beam forms immediately upstream of the boundary layer. The results are consistent with the notion that slow shocks or similar transition layers are responsible for the heating and formation of the central plasma sheet and for the ion beams observed in the plasma sheet boundary layer.
Detection of a solar particle event at an heliolatitude of 73.8°S
Authors: Pick M. , Lanzerotti L. J. , Buttighoffer A. , Hoang S. , Forsyth R. J.
Published: February 2004

We report the observations of an electron event at a heliolatitude of 73.8°S, the highest latitude interplanetary solar event reported to date. This event was detectable because the interplanetary background was not obscured by electrons produced in co‐ rotating interaction regions. The event was associated with an interplanetary type III burst and a solar active region located at 6°S as detected by the Nancay radioheliograph. The origin of the electrons is discussed. The observations favor an acceleration process in the low or middle corona followed by coronal propagation from the solar source to the highest heliolatitudes. This high latitude electron event presents rather different characteristics from those detected at low heliolatitudes.
Inconsistency of Ulysses millisecond Langmuir spikes with wave collapse in type III radio sources
Authors: Cairns Iver H. , Robinson P. A.
Published: February 2004

Recent Ulysses observations of millisecond spikes superposed on broader Langmuir wave packets in type III radio sources are compared quantitatively with constraints from the theory of wave collapse. It is found that both the millisecond spikes and the wave packets have fields at least 10 times too small to be consistent with collapse, contrary to previous interpretations in terms of this process. Several alternative explanations are considered and it is argued that the spikes should be interpreted as either non‐collapse phenomena or observational artifacts. To the extent the observations are representative, this rules out theories for type III bursts at ∼ 1–4 AU that rely on collapse.
Constraints on solar wind acceleration mechanisms from Ulysses plasma observations: The first polar pass
Authors: Barnes Aaron , Gazis Paul R. , Phillips John L.
Published: February 2004

The mass flux density and velocity of the solar wind at polar latitudes can provide strong constraints on solar wind acceleration mechanisms. We use plasma observations from the first polar passage of the Ulysses spacecraft to investigate this question. We find that the mass flux density and velocity are too high to reconcile with acceleration of the solar wind by classical thermal conduction alone. Therefore acceleration of the high‐speed wind must involve extended deposition of energy by some other mechanism, either as heat or as a direct effective pressure, due possibly to waves and/or turbulence, or completely non‐classical heat transport.
Contrail observations by ground‐based scanning lidar: Cross‐sectional growth
Authors: Freudenthaler V. , Homburg F. , Jäger H.
Published: February 2004

The spatial growth of individual contrails of commercial aircrafts in the time range from 1 min to 60 min behind the aircraft is investigated by means of a ground‐based scanning backscatter lidar. The growth in width varies between 18 m/min and 140 m/min, and the growth of the cross‐section between 3500 m²/min and 25000 m²/min. These values cover the findings of model calculations and former investigations. The vertical growth is often limited by boundaries of the humid layer at flight level, but values up to 18 m/min were observed. In a single case a vertical growth of 4.5 m/s during the early vortex regime was derived from video images.
Observations of HFC‐134a in the remote troposphere
Authors: Montzka S. A. , Myers R. C. , Butler J. H. , Elkins J. W. , Lock L. T. , Clarke A. D. , Goldstein A. H.
Published: February 2004

Hydrofluorocarbon‐134a (CF3CH2F) has been detected and quantified in air samples collected at remote, globally dispersed locations. Using gas chromatography and mass spectrometry detection techniques, we have observed increases for HFC‐134a throughout the global troposphere from <50 fmol mol−1 (ppq) in the late 1980s to 1.6 pmol mol−1 (ppt) in mid‐1995. Results obtained from samples collected during two cruises in 1994 indicate that mixing ratios more than doubled during that year. Increases observed globally from early 1994 through mid‐1995 are consistent with exponential growth at ∼100% yr−1.
Multiple impact event in the Paleozoic: Collision with a string of comets or asteroids?
Authors: Rampino Michael R. , Volk Tyler
Published: February 2004

Eight circular geologic structures ranging from ∼3 to 17 km in diameter, showing evidence of outward‐directed radial deformation and intensive brecciation, lie within a linear swath ∼15 km wide along a straight line stretching ∼700 km across the United States from southern Illinois through Missouri to eastern Kansas. Based on their similar geological characteristics and the presence of diagnostic and/or probable evidence of shock, these structures, once classified as ‘cryptovolcanic’ or ‘cryptoexplosion’ structures, are more confidently ascribed to hypervelocity impact. No other similar occurrence of aligned features is known, and we calculate the probability of a chance alignment to be <10−9. The unusual alignment suggests that the features are coeval and related to a multiple impact event, with a best‐constrained late Mississippian‐early Pennsylvanian (∼330–310 Myr) age. Calculations suggest that the proposed impact‐crater chain is unlikely to have been formed by an incoming impactor disrupted by terrestrial or lunar tidal effects, and may have been the result of a string of asteroidal or cometary objects produced by breakup within the inner Solar System.
Thermomechanical modeling of pulsation tectonics and consequences on lithospheric dynamics
Authors: Larsen Tine B. , Yuen David A. , Smedsmo Jamie L. , Malevsky Andrei V.
Published: February 2004

Pulsating phenomena can control continental breakup and the formation and closing of oceanic basins. Using a two‐dimensional time‐dependent convection model with a non‐linear, temperature‐ and depth‐dependent rheology, we have obtained self‐consistently such types of pulsating behavior. Very hot mantle plumes ascend to the surface, where they can quickly thin the lithosphere down to a few kilometers. An episode of intense shear heating then ensues, which is comparable to the length of the main episode for flood volcanism, lasting a couple of Myrs. The highest plate velocities occur during this period, when both the lithosphere and slab are profusely lubricated by the impingement of the hot plume.
Dicing with earthquakes
Authors: Burton Paul W.
Published: February 2004

The VAN group have been publicizing claims to be predicting earthquakes since 1981. Their predictions of two basic parameters of earthquakes, magnitude and location, are very loosely constrained. Most VAN magnitude predictions are below 5.7 Ms, with a tolerance of ±0.7 Ms. The uncertainty range spanned by a predicted magnitude is so enveloping that such forecasts cannot be viewed as plainly successful In terms of VAN's claims to spatial resolution, these, if successful, might constrain the linear dimension of the source region of a magnitude 8.0 Ms earthquake but do not adequately constrain a magnitude as large as 7.5 Ms.

Not only do VAN need to refine the tolerances in their magnitude and location predictions before careful judgements can be made, but it is also necessary to provide an unambiguous statement of the prediction hypothesis used in relation to a pre‐published and communally archived dataset of complete seismic electric signal occurrences similar to Seismological Station Bulletins.
Simulated annealing two‐point ray tracing
Authors: Velis Danilo R. , Ulrych Tadeusz J.
Published: February 2004

We present a new method for solving the two‐point seismic ray tracing problem based on Fermat's principle. The algorithm overcomes some well known difficulties that arise in standard ray shooting and bending methods. Problems related to: (1) the selection of new take‐off angles, and (2) local minima in multipathing cases, are overcome by using an efficient simulated annealing (SA) algorithm. At each iteration, the ray is propagated from the source by solving a standard initial value problem. The last portion of the raypath is then forced to pass through the receiver. Using SA, the total traveltime is then globally minimized by obtaining the initial conditions that produce the absolute minimum path.

The procedure is suitable for tracing rays through 2D complex structures, although it can be extended to deal with 3D velocity media. Not only direct waves, but also reflected and head‐waves can be incorporated in the scheme. One important advantage is its simplicity, in as much as any available or user‐preferred initial value solver system can be used. A number of clarifying examples of multipathing in 2D media are examined.
Coupling between middle and upper atmospheric NO: Constraints from HALOE observations
Authors: Siskind David E. , Russell James M.
Published: February 2004

Observations of NO, NO2, and CH4 from the HALOE instrument on the UARS satellite are used to investigate the transport of thermospheric NO into the middle atmosphere. By comparing the variation of NO and NO2 with simultaneous measurements of a long lived stratospheric tracer like CH4, regions of enhanced odd nitrogen can be quantified. Our results indicate substantial enhancement of NO in the high latitude winter mesosphere extending from thermospheric altitudes down to about 55–60 km. We also see evidence of substantial equator ward mixing of mesospheric NO. Occasional enhancements of NOx are seen extending down into the upper stratosphere in winter; however, they do not appear to persist. Observations by HALOE at latitudes up to 75–80 degrees in early spring show no evidence for enhanced NOx. This suggests that the effect of thermospheric NO on high latitude upper stratospheric O3 may be less than previously thought.
Evidence for critical level filtering of atmospheric gravity waves
Authors: Whiteway James A. , Duck Thomas J.
Published: February 2004

Radiosonde measurements were used to investigate gravity wave activity within the lower stratosphere above the Canadian High Arctic. The sondes were launched from the weather station at Eureka (80°N, 86°W) on Ellesmere Island. Gravity waves were detected by the fluctuations they induced in temperature and the associated perturbation potential energy density was used to gauge the amount of wave activity. It was found that, over a 15 month period, there were isolated episodes of enhanced wave activity rather than any distinct seasonal cycle. Profiles of wind velocity were also measured and used here to show that periods of high wave activity occurred only when there would be no (or very little) critical level filtering of the stationary waves generated by flow over the rough terrain in the vicinity of Eureka. It was also found that the potential energy spectral density was enhanced at all resolvable scales during the periods of high wave activity.