bluuebunny/crossref_metadata_2025 huggingface dataset:
Martian aeolian features and deposits: Comparisons with general circulation model results
Authors: Greeley Ronald , Skypeck Andrew , Pollack James B.
Published: February 2008

The development of a general circulation model (GCM) of Mars' atmosphere allows questions to be addressed concerning the relationships between near‐surface winds and the distribution of wind‐related features and deposits. Predictions of wind surface stress as a function of season and dust optical depth are used to investigate the distribution and orientation of wind streaks, yardangs, and rock abundance on the surface. The occurrence and orientation of bright streaks are well accounted for by the GCM. Results suggest that bright streaks form during southern hemisphere summer by Hadley cell circulation, in which dust is raised in the southern hemisphere, carried northward at high altitudes, then deposited in the wake of craters and other topographic obstacles by the descending Hadley cell. The reduction in the number of bright streaks southward from 30°N is interpreted to reflect the depletion of dust by near‐surface winds blowing to the south. Although the winds responsible for the formation of the dark streaks are not well reproduced in all areas by GCM simulations, a band of high wind surface stresses in the southern subtropics corresponding to the latitude band where most of the dark streaks are found are predicted at the height of the dust storm season (southern hemisphere summer). Yardang orientations do not match the GCM simulations for any season; their orientation is attributed to either structural control in the rocks (such as joint patterns) or to a change in wind patterns from the time when the yardangs formed. The global distribution of rocks on the surface is correlated well with predicted wind stress, particularly during dust storm season; the rocky areas are sites of strong winds, suggesting that fine material is swept away by the wind, leaving rocks and coarser material behind.
Excitation of positive ions by low‐energy electrons: Relevance to the Io torus
Authors: Smith Steven J. , Chutjian A. , Mawhorter R. J. , Williams I. D. , Shemansky D. E.
Published: February 2008

The importance of measuring electron‐ion excitation cross sections in singly and multiply charged positive ions is outlined, and recent results for Mg II and O II ions are given using the Jet Propulsion Laboratory's electron energy‐loss merged‐beams apparatus. For Mg II, collision strengths are presented for the 3s 2S → 3p 2P(h, k) resonance transition at electron energies from threshold to approximately 9 × threshold (40 eV). Theoretical comparisons are also given with two five‐state close‐coupling calculations. The energy variation of the collision strength is fitted with a semiempirical analytic function which includes approximations to polarization, resonance, and exchange contributions. In O II, first spectra anywhere of electron excitation of the optically allowed 2s22p3 4S0 → 2s2p4 4P (14.88 eV) and → 2p23s 4P (22.98 eV) transitions are presented. In addition, excitations of the two low lying, optically forbidden transitions 4S° → 2p3 2D0 (3.33 eV) and → 2p3 2P0 (5.02 eV) are detected for the first time.
The ultraviolet absorption spectrum of CO: Applications to planetary atmospheres
Authors: White H. Peter , Hua Xin‐Min , Caldwell J. , Chen F. Z. , Judge D. L. , Wu C. Y. Robert
Published: February 2008

Laboratory gas‐phase photoabsorption cross sections of the CO Cameron 0–0 band and the underlying pseudo‐continuum have been measured at a temperature of 147K and pressures ∼ 200 mbar, conditions similar to ambient in various planetary and satellite stratospheres in the solar system. A theoretical modeling program has also been used to calculate the band's spectrum. Agreement between the theoretical and the experimental spectra is very good. Models suggest that the observations of the CO Cameron band using the Hubble Space Telescope will be straightforward for Mars, but marginal for Titan.
Opportunities to improve hydrologic data
Authors: Dozier Jeff
Published: February 2008

Hydrologic data collection over scales from centimeters to continents, from minutes to years is difficult and expensive, so hydrologic models usually conceptualize processes based on simple, often homogeneous, views of nature. This forced oversimplification impedes scientific understanding and management of water resources. As the focus of hydrologic research shifts to larger regional and global scales, the collection, management, distribution, and analysis of data will improve so that models and data can each drive and direct the other. Better models illuminate the type and quantity of data needed to test hypotheses. Better data permit development and validation of more complete models and new hypotheses. Coordinated hydrologic experiments (such as the Global Energy and Water Cycle Experiment) and remote sensing of hydrologic parameters examine hydrologic variables at these larger scales, and isotope geochemistry, paleohydrology, and biological methods allow analysis and retrieval of new kinds of information. Improvements in the management and accessibility of data will make them more easily available to hydrologic scientists.
Dispersive distortions of transionospheric broadband VHF signals
Authors: Kretov Nikolai Vladimirovich , Ryshkina Tatjana Yevgenjevna , Fedorova Ludmila Valentinovna
Published: February 2008

The dispersive distortions of broadband signals propagating through the Earth's ionosphere are examined in relation to their influence on the range resolution of radars with frequencies from 100 MHz to 30 GHz. Polarization dispersion is taken into account in addition to phase dispersion, but scattering effects are neglected. Analytical expressions are deduced for the envelope and the frequency modulation of the convolution of the received and transmitted signals. The envelope and the frequency modulation of the convolution depend on the polarization, the Earth's magnetic field, and the total electron content of the ionosphere. The magnetic field does not affect the convolution if the carrier frequency of the broadband signal is more than 600–800 MHz. The distortion of the convolution envelope limits the range resolution of radars. The minimum resolution varies from 270 m to 3 cm when the carrier frequency increases from 100 MHz to 30 GHz.
Analysis of model simulations of spaced antenna/radar interferometer measurements
Authors: Sheppard E. L. , Larsen M. F.
Published: February 2008

A computer simulation of scattering from inhomogeneities in the refractive index is used to compare the spaced antenna and interferometer methods for measuring winds in clear air, both with and without turbulent fading. The results show that the spaced antenna analysis which is carried out in the time domain and the interferometer analysis which is carried out in the frequency domain are equivalent in terms of the information that the two methods yield. A data analysis method, equivalent to full correlation analysis, which can be carried out in the frequency domain is presented. The method is applied to model‐generated, simulated data in order to extract the typical full correlation analysis output parameters such as the apparent and true velocity. The results obtained are consistent with the model input parameters.
Transverse magnetic diffraction from tapered resistive junctions
Authors: Kempel Leo C. , Volakis John L. , Senior Thomas B. A.
Published: February 2008

In this paper we investigate the transverse magnetic (TM) scattering by a junction formed by two tapered resistive sheets whose resistivity increases away from the join. In particular, the exact diffraction coefficient for the junction formed by two coplanar linearly tapered resistive sheets is found by application of the Kontorovich‐Lebedev transform. In addition, a physical optics (PO) diffraction coefficient is presented for either linearly or quadratically tapered resistive junctions. All diffraction coefficients are compared to numerical results, and the validity range of the PO approximation is discussed.
Backarc thrust faulting and tectonic uplift along the Caribbean Sea Coast during the April 22, 1991 Costa Rica earthquake
Authors: Plafker George , Ward Steven N.
Published: February 2008

Surface deformation and a tsunami accompanied the destructive April 22, 1991, Costa Rica‐Panamá earthquake (Ms = 7.5). Along a 135 km stretch of Caribbean coast, coseismic uplift was measured between the lower and upper limits of sessile intertidal organisms stranded on coral reefs, the preearthquake and postearthquake high tide levels located from driftwood lines on beaches, and the preearthquake and postearthquake tide levels as pointed out by local residents. The nature and distribution of offshore vertical displacements were further constrained from analysis of measured run‐up heights and reported arrival times of the tsunami. Uplift detected along the coast jumped, within 4 km, from zero to 157 cm near Limón and generally decreased over a distance of 70 km southward to the border with Panamá. These data map an axis of uplift that intersects the coastal beach ridge just north of the port of Moín and runs offshore to the east and south roughly parallel to the coast. No surface faulting was found. The earthquake and tsunami were generated by backarc thrusting along faults that bound the north Panamá deformed belt and dip from the Caribbean Sea beneath Costa Rica and northern Panamá. Combined geodetic and seismological data indicate that the main rupture dips landward at an angle of about 30° and is approximately 40 km wide and 80 km long. Dislocation models suggest 2.2 m of slip on a causative thrust fault striking between 105° and 120°. We estimate that the repeat time for this type of earthquake is 200 to 1100 years. The historical record and new isotopic data favor the middle of the range.
Detrital blueschist‐Facies metamorphic mineral assemblages in Early Cretaceous sediments of the foreland basin of the Brooks Range, Alaska, and implications for orogenic evolution
Authors: Till Alison B.
Published: February 2008

Detrital metamorphic minerals found in the foreland basin of the Brooks Range were derived from blueschist‐facies rocks that now occupy the range's metamorphic core. The metamorphic minerals occur in the Torok Formation and the Nanushuk Group; they are contained in sediments at least as old as middle Albian in age, and may have arrived earlier. The source of the minerals is the blueschist‐facies schist belt, the structurally highest, more internal of two structurally and metamorphically distinct belts that occupy the metamorphic core of the Brooks Range. The blueschist facies rocks of the schist belt were exhumed between Late Jurassic and middle Albian time, during the major pulse of contractional deformation in the Brooks Range orogeny, rather than during late stage extensional collapse or postcontractional isostatic rebound, as suggested by other workers. The processes by which the blueschist‐facies rocks were uplifted and denuded must have operated during contractional tectonism. Post peak metamorphic structures in the blueschist‐facies rocks support their uplift by thrust systems; their unroofing apparently occurred by erosion and possibly by small‐scale extensional faulting.
Palinspastic reconstruction of southeastern California and southwestern Arizona for the Middle Miocene
Authors: Richard Stephen M.
Published: February 2008

A paleogeographic reconstruction of southeastern California and southwestern Arizona at 10 Ma has been made based on available geologic and geophysical data. Clockwise rotation of 39° has been reconstructed in the eastern Transverse Ranges, consistent with paleomagnetic data from late Miocene volcanic rocks, and with slip estimates for left‐lateral faults within the eastern Transverse Ranges and NW‐trending right‐lateral faults in the Mojave Desert. This domain of rotated rocks is bounded by the Pinto Mountain fault on the north. The model requires that the western part of the late Miocene Pinto Mountain fault was a thrust fault, which gained displacement to the west, because of the absence of evidence for rotation of the San Bernardino Mountains or for significant right slip faults within the San Bernardino Mountains. The Squaw Peak thrust system of Meisling and Weldon (1989) may be a western continuation of this fault system. The Sheep Hole fault bounds the rotating domain on the east. East of this fault an array of NW‐trending right slip faults and south‐trending extensional transfer zones has produced a basin and range physiography while accumulating up to 16 km of right slip. This maximum is significantly less than the 37.5 km of right slip required in this region by a recent reconstruction of the central Mojave Desert (Dokka and Travis, 1990a). Geologic relations along the southern boundary of the rotating domain are poorly known, but this boundary is interpreted to involve a series of curved strike slip faults and linking normal faults that accommodated noncoaxial extension. Quaternary movement on the Pinto Mountain and nearby faults is unrelated to the rotation of the eastern Transverse Ranges, and a hiatus during part of Pliocene time followed the deformation which produced the rotation. The reconstructed Clemens Well fault in the Orocopia Mountains, proposed as a major early Miocene strand of the San Andreas fault, projects eastward towards Arizona, where early Miocene rocks and structures are continuous across its trace, making large displacements on this structure unlikely. The model predicts a 14° clockwise rotation and 32% extension during late Miocene and early Pliocene time along a NW‐trending line parallel to the present trace of the San Andreas fault. Palinspastic reconstructions of the San Andreas system based on this proposed reconstruction may be significantly modified from current models.
Carbon sources and sinks in forest biomes of the former Soviet Union
Authors: Kolchugina Tatyana P. , Vinson Ted S.
Published: February 2008

The carbon budget of the forest biomes of the former Soviet Union (FSU) and their sequestration potential were assessed by considering (1) net ecosystem productivity (NEP) of different age forest stands and actual forest coverage, (2) carbon flux related to forest fires, (3) the rate of peat accumulation, and (4) anthropogenic influences. The area of forest biomes in the FSU was estimated at 1426.1 million hectares (Mha); forest ecosystems comprised 799.9 Mha, nonforest ecosystems and arable land comprised 506.3 and 119.9 Mha, respectively. The vegetation pool (phytomass and coarse woody debris) was 68.7 Gt C (carbon). The litter and soil carbon pools were 12.2 and 319.1 Gt C, respectively. The net primary productivity (NPP) of forest biomes ecosystems was 5.6 Gt C/yr, the rate of foliage formation was 2.3 Gt C/yr, the rate of humus formation was 161 Mt C/yr with 73 Mt C/yr in the stable form. The NEP of the forest biomes was assessed from the data on NEP of young, middle‐age, and premature forest stands. The NEP of the forest biomes was 825 Mt C/yr. Peat was accumulating at an average rate of 23 Mt C/yr. Carbon effluxes from mortmass, litter, and soil organic matter decomposition were calculated from the NPP, NEP, foliage, and humus formation rates. The efflux from mortmass decomposition was 2.6 Gt C/yr, from litter decomposition 2.1 Gt C/yr, and from soil organic matter decomposition 61 Mt C/yr. Peat combustion represented a carbon efflux of 30 Mt C/yr. The carbon efflux from forest fires and agricultural activities was 199 and 10 Mt C/yr, respectively. Carbon efflux from wood harvesting (carbon sequestration in regrowing vegetation was excluded) was 152 Mt C/yr. Considering all components of the natural carbon cycle and the anthropogenic influences, FSU forest biomes were a net sink of 485 Mt C/yr of atmospheric carbon. The Siberian and Far East forests represent approximately 82% of the net sink. The total carbon sink in FSU forests was equivalent to one half of the annual CO2fossil fuel emissions in the FSU or one half the carbon released from deforestation in subtropical regions.
Evaluation of the 13C constraint on the uptake of fossil fuel CO2 by the ocean
Authors: Broecker Wallace S. , Peng Tsung‐Hung
Published: February 2008

The proposal by Quay et al. [1992] that the time histories of 13C in atmospheric CO2 and oceanic ∑CO2 provide a constraint on the magnitude of uptake of fossil fuel CO2 by the ocean is examined. Our analysis suggests that, while the potential is there, the data base is too inaccurate to permit a distinction to be made among the carbon budgets currently on the table. Examples are given to demonstrate that the twenty or so percent uncertainties in the size of the effective exchange reservoir and in the magnitudes of the temporal changes in the 13C/12C ratio in atmospheric CO2 and ocean ∑CO2 are just too large to permit a reliable estimate of oceanic uptake of fossil fuel CO2. We conclude that tracer‐verified ocean general circulation models offer much better estimates than that based on the 13C budget.
Methane and nitrous oxide flux in a Wyoming subalpine meadow
Authors: Mosier A. R. , Klemedtsson L. K. , Sommerfeld R. A. , Musselman R. C.
Published: February 2008

The atmospheric concentrations of the greenhouse gases nitrous oxide and methane continue to increase. Since both gases are derived primarily from the soil, soil source/sink relationships in a variety of ecosystems must be understood before complete global source/sink budgets can be accurately made. Little information exists about soil/atmosphere exchange of nitrous oxide and methane from subalpine forests and forest meadows. A transect of flux measurement sites was established across a subalpine meadow and adjacent forest in southeastern Wyoming, and CH4 and N2O fluxes were measured at least weekly from snow melt in June until the winter snow covered the meadow in October during 1991 and 1992. Nitrous oxide emissions from the meadow were small both years, averaging only 2.5 and 1.3 ug N m−2 h−1 in 1991 and 1992, respectively. Fluxes were larger during the wetter year and varied from point to point, generally in response to soil moisture conditions. Methane flux varied across the meadow and over the season, also in response to changing soil moisture conditions. During the time of rapid snow melt when water was flowing freely across the meadow, the meadow acted as a net source of CH4.After snow melt was completed and the soil dried, the entire meadow became a sink for CH4.The mean snow‐free seasonal CH4 flux for the meadow was −3.5 and −21.4 ug C m−2 h−1 during 1991 and 1992, respectively. As a whole, the meadow served as a sink for atmospheric methane, but sites within the meadow served as a net source of CH4 during the snow‐free part of the year.
Generation of ELF and VLF waves by HF Heater‐modulated polar electrojet via a thermal instability process
Authors: Kuo S. P. , Lee M. C.
Published: February 2008

Generation of ELF and VLF waves via a thermal instability process in a HF‐modulated polar electrojet has been investigated. It is shown that a positive feedback through the electron‐neutral collisional heating process can cause the transient response of the plasma to the modulated HF heater to grow exponentially. The threshold fields of the instability under normal electrojet conditions are found to be about 2.25 V / m and 1.13 V / m for the operation of the o‐mode and x‐mode heaters with a 50% duty cycle, respectively. For a heater wave field of, e.g., 1.5 V/m, the instability can be excited by the x‐mode heater within a few tens of millisecond. The predicted dependence of the ELF/VLF radiation amplitude on the percentage of the duty cycle of the HF modulation is identical to that of the recent observational results of Barr and Stubbe [1991b].
Tailward propagating cross‐tail current disruption and dynamics of near‐Earth Tail: A multi‐point measurement analysis
Authors: Jacquey C. , Sauvaud J. A. , Dandouras J. , Korth A.
Published: February 2008

Plasma and magnetic field data taken simultaneously in the near‐Earth plasma sheet (6.6–13 RE) aboard three satellites, GEOS‐2, ISEE‐1, and ISEE‐2, are used to infer directly the location and tailward propagation velocity of the partial cross‐tail current disruption associated with a well‐defined substorm. This study shows that the disruption starts at 6–9 RE and propagates down the tail with a velocity of the order of 150 to 250 km/s over tens of earth radii during the substorm expansion phase. Moreover, magnetic variations measured aboard GEOS‐2 suggest that the partial current disruption also propagates longitudinally. After a time delay of about 2 minutes after the disruption onset, an injection front of accelerated particles is measured at geostationary orbit. This time delay is interpreted as indicating that the front propagates earthward with a velocity of the order of 20 to 160 km/s and also eastward. The overall post‐onset magnetic signatures measured at geostationary orbit are shown to be mainly due to an expansion (thickening) of the current sheet in the close vicinity of GEOS‐2 during the expansion phase.
The soliton transform and a possible application to nonlinear Alfvén waves in space
Authors: Hada T. , Hamilton R. L. , Kennel C. F.
Published: February 2008

We apply the inverse scattering transform (IST) based upon the Derivative Nonlinear Schrödinger (DNLS) equation to a complex time series of nonlinear Alfvén wave data generated by numerical simulation. The IST describes the long‐time evolution of quasi‐parallel Alfvén waves more efficiently than the Fourier transform, which is adapted to linear, not nonlinear, problems. When we add dissipation, so the conditions for the validity of the DNLS are not strictly satisfied, the IST continues to provide a compact description of the wave‐field in terms of a small number of decaying envelope solitons. Since large amplitude Alfvén waves and other nonlinear waves play essential roles in various space environments—the solar wind is one obvious example—we suggest that it may be of interest to investigate how inverse scattering transforms can be developed into practical tools for the analysis of space data.
Seismic efficiency of decoupled nuclear explosions
Authors: Adushkin Vitaly V. , Kitov Ivan O. , Kuznetsov O. P. , Sultanov Djamil D.
Published: February 2008

Experimental observations of the seismic efficiency of a decoupled nuclear explosion in a salt dome are presented. The energy decoupling factor was calculated from local, regional and teleseismic data using the ratio of the amplitudes of the tamped (well coupled) explosion that had created the cavity and that of the decoupled one. To calculate the amplitudes of the seismic waves of a well coupled explosion of the same yield as the decoupled one, a scaling law for explosions fired within the same region was used. An energy decoupling factor near 30 is consistent with local, regional and teleseismic data. It is concluded that decoupling was only partial for the event described. Numerical calculations of partial decoupling showed that the seismic wave spectrum at an epicentral distance of 2.3 km is consistent with an amplitude decoupling factor of 20, which is consistent with the energy decoupling factor 30.
The polar heliospheric magnetic field
Authors: Suess S. T. , Nerney Steven
Published: February 2008

We describe the large‐scale magnetic field morphology in the heliosheath. A simple argument, which depends only on the interstellar wind flowing nearly in the solar equatorial plane, shows that polar heliospheric magnetic fieldlines never approach the heliopause and therefore are accessible to galactic cosmic rays only through perpendicular diffusion. The same argument implies reconnection, at fine scales (ca. 0.2 AU), on the nose of the heliopause, between the interplanetary magnetic field and the magnetic field in the local interstellar medium (LISM). Galactic cosmic rays therefore have direct access across the heliopause to fieldlines connected to equatorial regions of the inner solar system.
One‐year observations of Mount‐Pinatubo aerosol with an advanced Raman lidar over Germany at 53.5° N
Authors: Ansmann Albert , Wandinger Ulla , Weitkamp Claus
Published: February 2008

A combined Raman elastic‐backscatter lidar is utilized to observe the development of the stratospheric perturbation after the strong eruptions of Mount Pinatubo in June 1991. Height profiles of the particle extinction and backscatter coefficients are determined simultaneously and independently of each other. From these data the area‐weighted mean particle radius and the aerosol surface area and mass are determined. The lidar measurements are taken at Geesthacht in northern Germany (53.5° N, 10.5° E). The Pinatubo aerosol layer is located between the tropopause and about 24km height. Traces of stratospheric aerosol were frequently found down to 5 km height. The optical depth of the stratospheric aerosol layer has been of the order of 0.15 in 1992. The ratio of optical depth to column‐integrated backscatter varied between about 15 and 60 sr. Most values were found between 20 and 30 sr. Extinction‐to‐backscatter ratios > 50, between 20 and 30, and < 15 sr indicate effective particle radii < 0.2, between 0.2 and 0.75, and >0.75 µm, respectively, as Mie scattering calculations show. Variations of the extinction‐to‐to‐backscatter ratio with height between about 10 and 90 sr were observed. Column aerosol mass and surface area were of the order of 0.05 gm−2 and 2.5 × 1011 µm² m−2 in the first half of 1992.
Extrusion tectonics of the Okhotsk Plate, northeast Asia
Authors: Riegel Steven A. , Fujita Kazuya , Koz'min Boris M. , Imaev Valery S. , Cook David B.
Published: February 2008

Based on focal mechanism, geologic, and lineament data, faulting in the Chersky Range, northeast Asia, changes from right‐lateral transpression between North America and Eurasia to left‐lateral strike‐slip between North America and the Okhotsk plate. The location of the Okhotsk‐Eurasia boundary is poorly constrained; available data suggest this boundary is right‐lateral. The Okhotsk plate is being compressed and extruded from between North America and Eurasia resulting in high levels of microseismic activity along the southern flanks of the Chersky Range.
GPS measurements of crustal deformation associated with the 22 April 1991, Valle de la Estrella, Costa Rica Earthquake
Authors: Lundgren Paul R. , Kornreich Wolf Susan , Protti Marino , Hurst Kenneth J.
Published: February 2008

We present analysis results for Global Positioning System (GPS) measurements made at sites in Costa Rica during two campaigns in February and July 1991. GPS solutions for 5 sites (Limon, Liberia, Bratsi, ETCG, and Vueltas) reveal significant horizontal and vertical displacements relative to their February positions. Horizontal displacements relative to Liberia, measured 244.7 ± 0.8, 89.2 ± 0.9, 12.4 ± 1.3, and 1.9 ± 0.9 cm at Limon, Bratsi, Vueltas, and ETCG respectively. Vertical displacements relative to Liberia measured 163 ± 2.1, 15.3 ± 3.0, −10.5 ± 4.4, and −0.6 ±2.1 cm at Limon, Bratsi, Vueltas, and ETCG respectively. We find differences in the GPS derived vertical and horizontal displacements compared to other types of geodetic measurements of uplift in the coastal region and their associated models. To address these differences we compute a dislocation model which fits the GPS measured displacements. A simple uniform planar slip model can not reconcile the differences between the coastal uplift data or the seismic moment, suggesting considerable complexity of the earthquake source.
On the spatial range of validity of the gas dynamic model in the magnetosheath of Venus
Authors: Zhang T. L. , Russell C. T. , Luhmann J. G. , Spreiter J. R. , Stahara S. S.
Published: February 2008

In the past the global solar wind interaction with Venus has been treated principally with gas dynamic models. While this gas dynamic treatment has proven successful in modeling some of the global characteristics of the interaction, this model does not include the magnetic barrier in a self‐consistent manner. This magnetic barrier is formed in the inner magnetosheath where it transfers solar wind momentum flux to the obstacle via magnetic pressure. In this study we examine the extent to which the gas dynamic fluid approximation describes the magnetic field in the dayside Venus magnetosheath by comparing with two gas dynamic models, one which matches the observed ionopause location and one which matches the bow shock location. We find that each model predicts the field profile reasonably well in the vicinity of the matched bow shock or ionopause but neither model provides an adequate model over the entire range from the ionopause to the bow shock.
Magnetic field properties of the intermediate transition of the Venus ionosheath
Authors: Perez‐de‐Tejada H. , Intriligator D. S. , Strangeway R. J.
Published: February 2008

We report new results of a statistical analysis of the electric and magnetic field data of the Pioneer Venus Orbiter (PVO) on the intermediate transition of the Venus ionosheath. This transition marks the outer boundary of an expansion region along the flanks of the inner ionosheath, and is identified by simultaneous observations of weak plasma fluxes and characteristic 30 kHz electric field bursts measured, respectively, with the plasma analyzer and the electric field detector. In many cases, the magnetic field signature across the intermediate transition is characterized by a sudden decrease in intensity and an abrupt rotation so that the direction is more nearly aligned with the Sun‐Venus line. In other cases the 30 kHz bursts occur outside a region of enhanced magnetic field reminiscent of the magnetic barrier external to the Venus dayside ionopause. In these cases there is also a rotation of the magnetic field toward the Sun‐Venus line associated with the 30 kHz bursts, but, in general, the conditions change more gradually. These variations may result from the expansion of the shocked solar wind at and near the magnetic polar regions of the Venus ionopause around which the draped interplanetary magnetic field lines slip over the planet. The expansion of the ionosheath plasma may result from local heating processes associated with a friction‐like interaction between the shocked solar wind and the topside ionospheric plasma.
Unfolding the subducting plate in the central New Hebrides Island ARC: Geometrical argument for detachment of part of the downgoing slab
Authors: Chatelain Jean‐Luc , Guillier Bertrand , Gratier Jean‐Pierre
Published: February 2008

In the central part of the New Hebrides island arc a sizable gap exists in the seismic activity. Seismic observations in the zone of the gap have been previously interpreted as either related to a detachment of part of the downgoing slab or associated with a continuous slab. We give a geometrical argument which, added the seismic observations from these previous studies, adds one step in favor of the detachment hypothesis. After unfolding the downgoing plate and restoring it to its initial state, using a 3D balance technique, we show that the gap can be filled with three pieces. Two of these pieces are seismic zones located beneath the seismic gap and the third one is a deep (550 – 650 km) seismic zone located about 200 km north‐east of the arc. These three pieces could be detached parts of the subducting plate.
Fluid reservoir (?) beneath the KTB drillbit indicated by seismic shear‐wave observations
Authors: Lüschen Ewald , Sobolev Stephen , Werner Ulrich , Söllner Walter , Fuchs Karl , Gurevich Boris , Hubral Peter
Published: February 2008

Indications for the possible presence of a fluid accumulation below the drillbit of the KTB (German Continental Deep Drilling Project)‐Hauptbohrung are provided by comparisons of seismic P‐wave and S‐wave reflection sections. A bright reflection with negative polarity at approx. 8 km depth is seen only on P‐wave sections. It is absent on S‐wave sections in contrast to deeper reflections. This observation can be explained by the following geological models or combinations of them: (1) brine accumulation within a strongly fractured rock reservoir, (2) liquid/gas interface within strongly fractured rocks, (3) rock composition with increased quartz content and corresponding low Poisson's ratio, and (4) varying symmetry system of seismic anisotropy due to rock foliation. Predictions concerning the nature and location of this reflector are expected to be verified by drilling and direct probing in spring‐summer, 1993.
Spatial correlations of interdecadal variation in global surface temperatures
Authors: Mann Michael E. , Park Jeffrey
Published: February 2008

We have analyzed spatial correlation patterns of interdecadal global surface temperature variability from an empirical perspective. Using multi‐taper coherence estimates from 140‐yr records, we find that correlations between hemispheres are significant at ≳95% confidence for non‐randomness for most of the frequency band 0.06 <f <0.24 cyc/yr. Coherence estimates of pairs of 100‐yr grid‐point temperature data series near 5‐yr period reveal teleconnection patterns consistent with known patterns of ENSO variability. Significant correlated variability is observed near 15 year period, with the dominant tele‐connection pattern largely confined to the Northern Hemisphere. Peak‐to‐peak ΔT ≈0.5°, with simultaneous warming and cooling of discrete patches on the earth's surface. A global average of this pattern would largely cancel.
Global tropospheric distribution and calibration scale of HCFC‐22
Authors: Montzka S. A. , Myers R. C. , Butler J. H. , Elkins J. W. , Cummings S. O.
Published: February 2008

Measurements of atmospheric chlorodifluoro‐methane (HCFC‐22), based upon a new calibration scale developed in this laboratory, suggest a global tropospheric mean that is ∼28% lower than determined previously from surface‐based measurements. A global mean of 101.8 (±1.2, 1 s.d.) ppt and interhemispheric difference of 13 (±1) ppt were determined for HCFC‐22 in 1992 from air collected in flasks from seven remote sites located between 82° N and 90° S. These results are consistent with mixing ratios predicted from recent emission estimates and a lifetime for HCFC‐22 of 13.6 (+1.9, −1.5) yr. Based upon the analysis of flasks and archived air samples from mid‐1987 through 1992, a mean growth rate for HCFC‐22 of 7.3 (±0.3)% yr−1 was estimated for this period.
Global mesospheric tidal winds observed by the high resolution Doppler imager on board the Upper Atmosphere Research Satellite
Authors: Morton Y. T. , Lieberman R. S. , Hays P. B. , Ortland D. A. , Marshall A. R. , Wu D. , Skinner W. R. , Burrage M. D. , Gell D. A. , Yee J.‐H.
Published: February 2008

This paper presents preliminary results of a study of mesospheric and lower thermospheric diurnal tidal winds obtained with the High Resolution Doppler Imager (HRDI) on the Upper Atmosphere Research Satellite (UARS). Zonal averages of the meridional and zonal wind fields are performed at fixed local times. These analyses reveal tidal structures in the mean meridional wind field during the months of February and March 1992. Results are presented for a typical day in February 1992. The observed maximum amplitude of meridional wind is approximately 75 m s−1. The observed vertical wavelength is about 20 km, with amplitudes increasing linearly with height. In addition to the tides, the zonal wind field reveals many features of the mesospheric climatological mean zonal wind.
Spacecraft glows and laboratory luminescence: Evidence for a common reaction mechanism
Authors: Greer W. A. D. , Pratt N. H. , Stark J. P. W.
Published: February 2008

Surface‐mediated O + NO recombination, a key reaction in spacecraft glow, has been investigated in the laboratory and the results used to provide a re‐evaluation of Atmosphere Explorer glow. A value for the rate coefficient is determined. The luminescence of the desorbed NO2*, lifetime 134 ± 27 µs is first order in both O and NO flux and is independent of O‐atom translational energy in the range 0.2 – 0.9 eV. Using this data and three identified processes contributing to NO formation in orbit, our remodelling removes earlier ambiguity in the interpretation of Explorer glow and provides the first reported correlation of orbital glow data in respect of altitude, ram angle dependence and absolute photon flux. We hypothesise that a single, common, reaction is predominantly responsible for laboratory, spacecraft and shuttle luminescence.
Aureol‐3 observations of new boundaries in the auroral ion precipitation
Authors: Bosqued Jean M. , Ashour‐Abdalla Maha , El Alaoui Mostafa , Zelenyi Lev M. , Berthelier Annick
Published: February 2008

Interesting and well‐separated structures in the 1–20 keV ion precipitation pattern have been revealed by an analysis of more than 50 crossings of the nightside (21–03 MLT) auroral zone by the AUREOL‐3 satellite. First, velocity‐dispersed ion structures (VDIS) are crossed near the poleward edge of the oval, and are the best ionospheric signature of ion beams flowing along the plasma sheet boundary layer. Proceeding equatorward, a large majority of VDIS events are bounded by a new and interesting narrow band of strongly reduced precipitation, or a gap, which delineates VDIS from the diffuse precipitation region connected to the CPS. A statistical analysis shows that the gap has an extent of about 1–2 degrees, which is almost independent of magnetic activity; its location, ∼70° ILAT, shifts significantly equatorward with higher magnetic activity levels. Intense electron arcs are observed near the equatorward edge of the gap. An important result is that the overall sequence of VDIS‐gap‐CPS can be explained in terms of orbital dynamics in the tail. The gap in precipitation appears as the counterpart of the “wall” regime in the equatorial plane, in which a cross‐tail current carried by energetic ions is strongly enhanced between 8 and 12 RE. This region has important consequences for the development of substorms.
Plasma dynamics driven by finite‐width current filament and KV potential drops in ionosphere‐magnetosphere coupling
Authors: Ganguli Supriya B. , Mitchell H. G. , Palmadesso P. J.
Published: February 2008

We have simulated the plasma dynamics of a quasi‐two‐dimensional current filament in ionosphere‐magnetosphere coupling. The simulation consists of a set of one‐dimensional flux tube simulations with different imposed time‐dependent, field‐aligned currents. The dynamical interactions of the individual current filaments with the ionospheric and magnetospheric plasma generate kV field‐aligned potential drops along the field lines, and the side‐by‐side display exhibits the evolution of the implied potential structure in the horizontal direction. The primary cross‐field motion produced by the horizontal E‐field (E×B drift) is perpendicular to both of the significant spatial directions, and is thus ignorable in this geometry. The effects of other cross‐field drift processes are discussed. The simulation thus provides insight into the dynamical evolution of 2D potential structures driven by an imposed finite‐width field‐aligned current profile. Spatial and temporal variation of other plasma parameters (temperatures, density, etc.) that are determined primarily by parallel transport effects are also displayed.
Low and high frequency waves generated by gyrophase bunched ions at oblique shocks
Authors: Gurgiolo C. , Wong H. K. , Winske D.
Published: February 2008

The interaction of the solar wind with gyrophase bunched ions reflected at an oblique (ΘBn = 45°) shock ( MA=8) is simulated using a 1D hybrid code. These ions are unstable to low frequency hydromagnetic waves as well as whistler waves. At some point in the hydromagnetic wave growth ion trapping occurs which restricts the local distribution in gyrophase to a higher degree than the input distribution. Given the growth rate of the MHD waves, gyrophase mixing is ineffective in isotropising the ions, except at the leading edge of the injected distribution.
Comparing U.S. and Russian experience with cavity decoupling in salt
Authors: Glenn L. A.
Published: February 2008

Recently released Russian data on two underground nuclear explosions in an Azgir salt dome allow comparison for the first time with similar U. S. explosions. In both cases, highly tamped explosions were employed to form cavities and, after a period of several years, much smaller explosions were then carried out in these same cavities. The seismic decoupling factor obtained from the Russian tests appears to be a factor of 4 less than is predicted, based on the U. S. experience. However, the Russian data are found to be entirely consistent with smaller scale U. S. experiments with chemical explosives. These results can be explained by the extent of damage in the immediate vicinity of the cavity walls, but it remains unclear why the damage should exist at the Russian site, and not at the U. S.
Global and seasonal variations in middle atmosphere CO from UARS/ISAMS
Authors: López‐Valverde M. A. , López‐Puertas M. , Marks C. J. , Taylor F. W.
Published: February 2008

Carbon monoxide limb emissions at 4.6‐μm measured by the Improved Stratospheric And Mesospheric Sounder (ISAMS) on board the Upper Atmosphere Research Satellite (UARS) are presented. The main features observed in the radiance measurements are presented and discussed. These radiances are used to obtain the CO abundances in the middle atmosphere, using a special retrieval scheme which incorporates the non‐LTE nature of the CO emission at 4.6‐μm. The first global maps of the CO abundance in the middle atmosphere illustrating its latitudinal/seasonal variations are presented and briefly discussed. One of the most interesting results obtained is the increase in the CO relative abundance in the mesosphere towards the winter polar region, in accordance with previous predictions by 2D dynamical‐chemical models of the middle atmosphere.
A demonstration of the joint use of P wave polarization and travel‐time data in tomographic inversion: Crustal velocity structure near the South Iceland Lowland Network
Authors: Hu Ge , Menke William , Rognvaldsson Sigurdur
Published: February 2008

A joint inversion of both P‐wave travel‐time and polarization direction data is performed on a data set from the South Iceland Lowland network. The root mean square reduction of the polarization and travel‐time residuals are 72% and 76%, respectively. Furthermore, travel‐time residuals drop 45% even when they were given no weight in the inversion, indicating that the polarization measurements are related to the same regional‐scale velocity heterogeneities thought to cause the travel‐time anomalies. The results show two crustal low‐velocity zones trending NE across the study area, a direction that is sub‐parallel to the strike of the Western Volcanic Zone in south Iceland.
Towards a detailed knowledge of the world ocean tides: The example of the Kerguelen Plateau
Authors: Le Provost Christian , Lyard Florent
Published: February 2008

A zoom view of a solution of the M2 tide, computed over the whole Indian Ocean, and focusing on the Kerguelen Plateau, is presented to illustrate the extent of detail and accuracy which can be expected from solutions produced by a global ocean tide model based on Finite Element methods developed by the authors. The characteristics of the M2 tide as revealed by this solution are in good agreement with the observations available around Kerguelen island, and explain the phase differences of more than 40 degrees observed between the two sides of the western part of this island which, until now, has been unexplained. For the M2 tide, this results from the presence of a one‐node axisymetric standing wave, with a real amphidromic point on the north western side of the plateau, which is due to the combination of two waves, one coming directly from the ocean to the West, and the other propagating counterclockwise on the shelf around the island.
Double beam analysis of anomalies in the core‐mantle boundary region
Authors: Krüger Frank , Weber Michael , Scherbaum Frank , Schlittenhardt Jörg
Published: February 2008

Seismic P‐waves from nuclear explosions at the Kazakhstan test site in Eastern Kazakhstan (KTS) observed at the Yellowknife‐array (YKA, Canada) are used to analyze the structure at the base of the mantle under Severnaya Zemlya (Arctic Sea). 18 events at the Degelen subsite and 9 events at the Shagan River subsite of KTS are studied. The simple waveforms and well controlled source parameters of nuclear explosions allow the use of the events as source arrays in addition to the usual receiver array configuration. A new method (double‐beamforming) integrating both concepts is presented. This method increases the resolution considerably. For the Degelen⇔YKA path one anomalous arrival (1.9 s before PcP, slowness between P and PcP slowness) is observed. Smaller anomalous arrivals are found 6.5 s (Degelen⇔YKA) and 8.1 s before PcP (Shagan River⇔YKA). These anomalous phases cannot be explained with standard Earth models. They are produced by reflections from an inhomogeneity in the lowermost mantle at (82.3N, 107.5E) under the area north of Severnaya Zemlya. The strong variations between the wavefields for the two source‐receiver combinations indicate a heterogeneous structure in the lower mantle. The anomaly found here is located close to an anomaly in the lowermost mantle beneath the Nansen Basin.
Balloonborne measurements of Pinatubo aerosol during 1991 and 1992 at 41°N: Vertical profiles, size distribution, and volatility
Authors: Deshler Terry , Johnson Bryan J. , Rozier William R.
Published: February 2008

Vertical profiles of aerosol have been measured approximately biweekly since June 1991 at Laramie, Wyoming (41°N). Both the total number concentration and concentration of particles >0.15 to 10.0 µm were measured using balloonborne instruments. The aerosol size distributions were best represented when bimodal lognormal distributions were fit to the data. After an early short‐lived intense aerosol layer, the stratospheric maximum surface area and mass (40 µm² cm−3, 160 ppbm) was observed to occur approximately 180 days after the eruption. The aerosol was then observed to remain relatively homogeneous both in altitude and time during 1992, with the maximum surface area and mass remaining relatively constant between 20 to 30 µm² cm−3 and 30 to 60 ppbm.
A quantitative model of plasma in Neptune's magnetosphere
Authors: Richardson John D.
Published: February 2008

A model encompassing plasma transport and energy processes is applied to Neptune's magnetosphere. Starting with profiles of the neutral densities and the electron temperature, the model calculates the plasma density and ion temperature profiles. Good agreement between model results and observations is obtained for a neutral source of 5×1025s−1 if the diffusion coefficient is 10−8L³RN²s−1, plasma is lost at a rate 1/3 that of the strong diffusion rate, and plasma sub‐corotates in the region outside Triton.
A 3D simulation of the early winter distribution of reactive chlorine in the north polar vortex
Authors: Douglass A. , Rood R. , Waters J. , Froidevaux L. , Read W. , Elson L. , Geller M. , Chi Y. , Cerniglia M. , Steenrod S.
Published: February 2008

Early in December 1991, high values of ClO are seen by the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite at latitudes south of areas of temperatures cold enough to form polar stratospheric clouds (PSC's). A three dimensional simulation shows that the heterogeneous conversion of chlorine reservoirs to reactive chlorine on the surfaces of PSC's (processing) takes place at high latitudes. Often the “processed” air must be transported to lower latitudes, where the reactive chlorine is photochemically converted to ClO, to be observed by MLS. In this simulation, one incidence of cold temperatures is associated with an anticyclone, and a second with a cyclone. The transport of processed air associated with the anticyclone is marked by shearing; a decrease in the maximum of the processed air is accompanied by growth of the area influenced by the processing. In contrast, the air processed in the cyclonic event spreads more slowly. This shows that transport and shearing is a crucial element to the evolution of reactive chlorine associated with a processing event. In particular, transport and shearing, as well as photochemical processes, can cause variations in observed ClO.