bluuebunny/crossref_metadata_2025 huggingface dataset:
Interannual variability of planet‐encircling dust storms on Mars
Authors: Zurek Richard W. , Martin Leonard J.
Published: February 2008

Interannual variability of the atmosphere of Mars is dominated by the occurence, or absence, of planet‐encircling dust storms. In this paper we use a recent review of Earth‐based telescopic observations of Mars together with Viking orbiter and lander data to estimate the frequency of occurrence of planet‐encircling dust storms over the past century and to test whether the period spanned by the Mariner 9 and Viking missions to Mars is representative of the decades prior to 1950. In doing so, we take into account the practical limitations imposed on Earth‐based coverage of Mars by the orbital geometries of the two planets. Both spacecraft and Earth‐based observations suggest that planet‐encircling dust storms on Mars occur during a so‐called “dust storm season” in southern spring and summer. Viking data demonstrate decidedly that planet‐encircling dust storms could have occurred in the past on Mars without being detected from Earth during years in which Mars was far from Earth during the dust storm season and thus difficult to observe. However, the same historical record indicates that planet‐encircling storms were absent during the dust storm seasons monitored during several favorable oppositions prior to 1956 and after 1986. Overall, the chance of a planet‐encircling dust storm occurring in any arbitrary Mars year is estimated to be approximately one in three (18–55% at the 95% level of confidence), if such occurrence is random from year‐to‐year and yet restricted seasonally to southern spring and summer.
The Mn‐Fe negative correlation in olivines in ALHA 77257 ureilite
Authors: Miyamoto M. , Furuta T. , Fujii N. , McKay D. S. , Lofgren G. E. , Duke M. B.
Published: February 2008

Mn, Fe, and oxygen zoning profiles of olivines in the ALHA 77257 ureilite were measured by an electron probe microanalyzer to study the effects of reduction on the Mn‐Fe value, because ureilite olivines exhibit thin reduced rims. The Mn content gradually increases toward the rim of ureilite olivines as the Fa (=100 × Fe/(Mg + Fe), mol %) component decreases, which suggests that the Mn‐Fe content of olivine is related to redox conditions. A calculated diffusional cooling rate of 1–2°C/h gives the best fit to both the observed MnO and Fa chemical zoning profiles of ALHA 77257. The results of melting experiments suggest that the negative correlation of Mn‐Fe in olivine and low‐Ca pyroxene is related to reduction and that the Mn‐Fe positive correlation is related to temperature. The Fe/Mn‐Fe/Mg trend of olivine cores in ureilites may be established by the reduction process at about 1275°C.
Paleocene to Eocene benthic foraminiferal isotopes and assemblages: Implications for deepwater circulation
Authors: Pak Dorothy K. , Miller Kenneth G.
Published: February 2008

Early Paleogene warm climates may have been linked to different modes and sources of deepwater formation. Warm polar temperatures of the Paleocene and Eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters. The possibility of increasing ocean heat transport through the production of warm saline deep waters (WSDW) in the Tethyan region has generated considerable interest. In addition, General Circulation Model results indicate that deepwater source regions may be highly sensitive to changing basin configurations. To decipher deepwater changes, we examined detailed benthic foraminiferal faunal and isotopic records of the late Paleocene through the early Eocene (∼60 to 50 Ma) from two critical regions: the North Atlantic (Bay of Biscay Site 401) and the Pacific (Shatsky Rise Site 577). These records are compared with published data from the Southern Ocean (Maud Rise Site 690, Islas Orcadas Rise Site 702). During the late Paleocene, similar benthic foraminiferal δ18O values were recorded at all four sites. This indicates uniform deepwater temperatures, consistent with a single source of deep water. The highest δ13C values were recorded in the Southern Ocean and were 0.5‰ more positive than those of the Pacific. We infer that the Southern Ocean was proximal to a source of nutrient‐depleted deep water during the late Paleocene. Upper Paleocene Reflector Ab was cut on the western Bermuda Rise by cyclonically circulating bottom water, also suggesting a vigorous source of bottom water in the Southern Ocean. A dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest Paleocene in the Southern Ocean. This is a short‐term (<100 kyr), globally synchronous event which also is apparent in both the Atlantic and Pacific records as a carbon isotopic excursion of approximately 1‰. Faunal analyses from the North Atlantic and Pacific sites indicate that the largest benthic foraminiferal faunal turnover of the Cenozoic was synchronous with the isotopic excursion, lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation. We speculate that the Southern Ocean deepwater source was reduced or eliminated at the time of the excursion. During the early Eocene, Southern Ocean δ13C values remained enriched relative to the North Atlantic and Pacific. However, the Southern Ocean was also enriched in δ18O relative to these basins. We interpret that these patterns indicate that although the Southern Ocean was proximal to a source of cool, nutrient‐depleted water, the intermediate to upper deep water sites of the North Atlantic and Pacific were ventilated by a different source that probably originated in low latitudes, i.e., WSDW.
Late Pleistocene Paleoceanography of the South Atlantic Sector of the Southern Ocean: Ocean Drilling Program Hole 704A
Authors: Hodell David A.
Published: February 2008

Isotopic and sedimentologic data from Ocean Drilling Program hole 704A suggest that isotopic stages 7, 9, and 11 were marked by unusually strong interglacial conditions in surface waters of the southern ocean. During interglacial stages 9 and 11, warm surface waters penetrated far poleward and may have led to destabilization of the West Antarctic Ice Sheet. In contrast, the strongest glacial conditions in surface waters of the subantarctic South Atlantic occurred during oxygen isotopic stage 12. Comparisons of benthic carbon isotopic gradients between sites located in the North Atlantic, southern ocean, and Pacific indicate that the production of upper North Atlantic Deep Water (uNADW) was strongest during stages 7,9, and 11 and weakest during stage 12, These results suggest a possible link between the flux of uNADW and paleoceanographic change in the southern ocean and support the traditional NADW‐Antarctic connection whereby increased NADW leads to warming of the southern ocean.
Global magnetospheric imaging
Authors: Williams D. J. , Roelof E. C. , Mitchell D. G.
Published: February 2008

Understanding the formation and behavior of the Earth's vast high‐altitude environment, its magnetosphere, requires both local in situ measurements and global observations. The in situ observations performed over the past decades have provided both a completely new perspective of this environment and an understanding of many localized processes operating in it. The observations have been further synthesized to provide a valuable first impression of the global nature of the magnetosphere. This initial global construction has been very beneficial in summarizing past results and guiding future work in the field, yet many fundamental questions remain unresolved. This is because, until recently, the global magnetosphere has not been observed, even in part; it has remained invisible, and its actual shape and large‐scale dynamics remain mysteries. Now new developments and results have demonstrated the feasibility of obtaining such global images. These techniques include the detection of photons at X ray, extreme ultraviolet, ultraviolet, and visible wavelengths, radio emissions, and energetic neutral atoms. Taken together, such emissions can be used to form images of most of the magnetosphere proper: the aurora, plasmasphere, boundary regions, ring current, and plasma sheet. This paper describes the demonstrated and developing techniques for global magnetospheric imaging and discusses the scientific expectations of having global observations in conjunction with local measurements.
The Sudbury Structure as a terrestrial mare basin
Authors: Lowman Paul D.
Published: February 2008

This paper reviews the origin, development, and present status of the hypothesis that the Sudbury Structure of Ontario, Canada, is a deformed Precambrian impact crater analogous to the circular lunar maria. The petrologic similarity of the maria and terrestrial lopoliths, such as the Bushveld, Duluth, and Sudbury igneous complexes, was suggested in 1961, assuming these to be extrusive features roofed by their own silicic differentiates. This led to the proposal by R. S. Dietz in 1962 that the Sudbury Structure was a tectonically deformed impact basin, occupied by an extrusive lopolith, and analogous to the small lunar maria. He then searched for and found shatter cones at Sudbury. Discovery of shock metamorphic features in the Onaping Formation by B. M. French in 1967 showed that this formation was a fallback breccia. Detailed studies since the 1970s have further strengthened the impact theory. Isotopic and impact modeling investigations have shown that the Sudbury Igneous Complex may be largely impact melt rather than internally generated magma. The shape and size of the original impact crater are not well known. The absence of compressional deformation of the North Range supports an originally elliptical shape, which has been shown to be similar to those of impact craters on the Moon and Mars. However, field mapping and reflection profiling suggest that much of the present ellipticity may have been produced by northwest directed ductile thrusting concentrated on the South Range and interior of the complex. The size of the original structure is also uncertain. Recent investigations indicate that the present igneous complex is only the central part of a much larger and perhaps multiring structure. The analogy between the Sudbury Structure and lunar maria, though petrologically wrong, is valid to the extent that both classes of structure were initially formed by impact. However, the size and shape of the original crater and the degree to which the Sudbury Intrusive Complex and its ore deposits are impact‐generated are still open to debate.
Arctic ice shelves and ice islands: Origin, growth and disintegration, physical characteristics, structural‐stratigraphic variability, and dynamics
Authors: Jeffries Martin O.
Published: February 2008

Ice shelves are thick, floating ice masses most often associated with Antarctica where they are seaward extensions of the grounded Antarctic ice sheet and sources of many icebergs. However, there are also ice shelves in the Arctic, primarily located along the north coast of Ellesmere Island in the Canadian High Arctic. The only ice shelves in North America and the most extensive in the north polar region, the Ellesmere ice shelves originate from glaciers and from sea ice and are the source of ice islands, the tabular icebergs of the Arctic Ocean. The present state of knowledge and understanding of these ice features is summarized in this paper. It includes historical background to the discovery and early study of ice shelves and ice islands, including the use of ice islands as floating laboratories for polar geophysical research. Growth mechanisms and age, the former extent and the twentieth century disintegration of the Ellesmere ice shelves, and the processes and mechanisms of ice island calving are summarized. Surface features, thickness, thermal regime, and the size, shape, and numbers of ice islands are discussed. The structural‐stratigraphic variability of ice islands and ice shelves and the complex nature of their growth and development are described. Large‐scale and small‐scale dynamics of ice islands are described, and the results of modeling their drift and recurrence intervals are presented. The conclusion identifies some unanswered questions and future research opportunities and needs.
Intensity scintillation index and mean apparent radar cross section on monostatic and bistatic paths
Authors: Fremouw E. J. , Ishimaru Akira
Published: February 2008

We develop an expression herein for the intensity scintillation index on a two‐way (radar) path, in terms of the one‐way index and the correlation between scintillations produced on the uplink and downlink. The expression is appropriate for monostatic (fully correlated) and bistatic (totally or partially uncorrelated, or anticorrelated) paths whose links are statistically similar and obey Nakagami m statistics. A companion expression for the mean apparent radar cross section (RCS) in the presence of scintillation describes enhancement on monostatic paths and energy‐conserving depletion of mean apparent RCS on small‐angle bistatic paths. The companion expression, which does not depend upon Nakagami m statistics nor require statistical similarity, is consistent with more detailed calculations by previous authors. Special cases of both expressions are consistent with recent monostatic measurements.
Statistical analysis of the spatial relationship between the radio and optical aurora: Further evidence for refraction
Authors: Prikryl P. , Cogger L. L.
Published: February 2008

Recent studies have found strong evidence that ionospheric refraction can explain some of the large aspect angle VHF radio aurora observations. The spatial relationship between such observations made with the Bistatic Auroral Radar System (BARS) and simultaneous 557.7‐nm emissions detected by an All‐Sky Imager (ASI) has been found consistent with the above idea (Hall et al., 1990). In this paper, further results of a cross‐correlation analysis of the BARS and ASI intensities are presented. Two‐dimensional as well as one‐dimensional (along radar beam direction) cross‐correlation functions are computed for a large statistical sample of 4 months of data. It is found that for all levels of ASI intensity and/or BARS power, stronger radar echoes predominantly occur on the remote side of the optical aurorae. The results are in agreement with the model calculation of refraction by Watermann (1990). In the premidnight sector, some of the brightest aurorae are found coincident with the strongest radar echoes, and a significant fraction of weaker radar echoes occur equatorward of fainter auroral forms.
Electromagnetic fields in an inhomogeneous plasma from obliquely incident transient plane waves
Authors: Karlsson Anders , Otterheim Henrik , Stewart Rodney
Published: February 2008

In this paper, transient fields inside gyrotropic media are studied by a time domain Green function technique based upon a wave‐splitting method. The medium is stratified in one spatial direction and the incident field is a plane electromagnetic pulse of arbitrary waveform at oblique incidence. Green operators are introduced which map the incident field to the internal fields. The relation between the Green operators and the scattering operators used in the invariant imbedding method are discussed. By introducing a complementary medium, a reciprocity relation is derived from which useful relations for the Green operators are obtained.
Comparison of Kalman filter estimates of zenith atmospheric path delays using the Global Positioning System and very long baseline interferometry
Authors: Tralli David M. , Lichten Stephen M. , Herring Thomas A.
Published: February 2008

Kalman filter estimates of zenith nondispersive atmospheric path delays at Westford, Massachusetts, Fort Davis, Texas, and Mojave, California, were obtained from independent analyses of data collected during January and February 1988 using the Global Positioning System (GPS) and very long baseline interferometry (VLBI). The apparent accuracy of the path delays is inferred by examining the estimates and covariances from both sets of data. The ability of the geodetic data to resolve zenith path delay fluctuations is determined by comparing further the GPS Kalman filter estimates with corresponding wet path delays derived from water vapor radiometric (WVR) data available at Mojave over two 8‐hour data spans within the comparison period. GPS and VLBI zenith path delay estimates agree well within one standard deviation formal uncertainties (from 10–20 mm for GPS and 3–15 mm for VLBI) in four out of the five possible comparisons, with maximum differences of 5 and 21 mm over 8‐ to 12‐hour data spans. For one comparison, the maximum difference between GPS and VLBI is 50 ± 20 mm and clearly shows an unexplained systematic difference which is probably related to poor elevation angle coverage in the VLBI data at the time, GPS fiducial network sensitivity, and poor azimuthal coverage. The root‐mean‐square differences between GPS estimates of the total path delays and WVR measurements added to the hydrostatic delay component determined from surface barometric pressure data are between 9 and 15 mm, however, with biases of 10–15 mm.
Systematic Errors in Radar Wind Estimation: Implications for Comparative Measurements
Authors: Kudeki Erhan , Rastogi Prabhat K. , Sürücü Fahri
Published: February 2008

SA, IDI, and DBS horizontal wind estimators are examined and demonstrated to share common biases under inhomogeneous flow field conditions. The biases can reach magnitudes of several tens of meters per second at mesospheric heights, contaminate gravity wave flow field measurements, cause distortions in measured flow field spectra, and possibly account for large wind measurement errors evidenced in recent experimental studies including the AIDA'89 effort. However, being a linear response to gravity wave flow field fluctuations, the biases are expected to cancel out in long‐term wind and tidal statistics compiled with radar wind data.
Generation and obduction of ophiolites: Constraints from the Bay of Islands Complex, western Newfoundland
Authors: Cawood Peter A. , Suhr Günter
Published: February 2008

Constraints provided by the Bay of Islands ophiolite complex (BOIC), western Newfoundland, suggest that its generation, as well as its obduction, is related to collision of the Dunnage Zone island arc system with the irregular continental margin of eastern North America. The constraints include the supra‐subduction zone setting of the BOIC; its extensional environment of generation; the synchronous occurrence of ophiolite generation with initiation of drowning and deformation of the North American continental margin; and the restriction of the BOIC, as well as other Appalachian ophiolites and associated Taconian allochthons, to reentrants in the North American margin. During the early phases of collision of the Dunnage arc with the North American margin, subduction of old oceanic lithosphere trapped in reentrants will continue and allow the development of two potential sites of ophiolite generation. The first develops through trench rollback, leading to ophiolite generation in the overriding arc plate outboard of the reentrant, whereas the second develops in a transtensional environment with spreading centers offset by strike‐slip faults which propagate through the overriding plate away from the indenter promontory. The configuration of the BOIC spreading ridge normal to the continental margin, and the direction of initial obduction parallel to the margin, favor generation of the ophiolite in an overall strike‐slip regime. With complete subduction of the oceanic remnant, extension in the overriding plate ceases, and the buoyant newly formed oceanic lithosphere is obducted onto the continental margin. Diachronous collision of the arc with the irregular continental margin accounts for the range of ages for ophiolite generation and obduction observed within the Dunnage Zone, and for termination of arc volcanism along the North American margin.
Oblique‐slip deformation in extensional terrains: A case study of the lakes Tanganyika and Malawi Rift Zones
Authors: Scott Deborah L. , Etheridge Michael A. , Rosendahl Bruce R.
Published: February 2008

The East African Rift system (EAR) is the archetypal continental rift and a widely proposed analogue for the early stages of evolution of passive continental margins. The three‐dimensional structure of parts of the EAR has been recently elucidated by a multifold seismic (MFS) survey of Lakes Tanganyika and Malawi (Project PROBE). Analysis of fault geometries displayed on the PROBE MFS data coupled with the more extensive 28‐kHz echosounder data has improved understanding of the geometry and kinematics of the linked fault systems that underlie the lakes. In particular, it has been recognized that profiles across (i.e., at high angles to) the rift elongation commonly display fault geometries that are not readily retrodeformable. There must therefore be significant displacement out of the plane of what would conventionally be regarded as “dip” lines, that is, perpendicular to rift elongation and parallel to the tectonic transport or extension direction. Careful determination of fault plane dip and the dip of synrift reflectors in the hanging wall demonstrates that the dip directions of the shallowest faults and the steepest hanging wall sediment dips are oriented either NW or SE. This defines the direction of maximum fault block rotation and therefore the direction of extension or tectonic transport as NW/SE, oblique to the trend of the regional rift axis and to the apparent strike of many of the major border faults in the survey area. The border faults and many other faults imaged on the PROBE MFS data must therefore have significant components of strike‐slip motion and the Tanganyika and Malawi rift zones have undergone extension oblique to and not perpendicular to their axes. Near dip‐slip normal faults, steeply dipping oblique‐slip faults and subvertical strike‐slip or transfer faults have all been recognized in a complex, linked fault system that accomplishes the extension. The overall orientation of the rift lakes and their internal segmentation are influenced by major, preexisting, subvertical fault zones within the basement. Complex accommodation zones act principally as transfer zones that allow switches in gross polarity of the border fault system. The detailed geometries of the accommodation zones result from the specific relations between juxtaposed half‐graben and the strike and internal geometry of the influencing basement structure. The variations in fault geometry, subsidence, water depth and basin or rift morphology can be better explained by an oblique‐slip extensional model influenced by basement structures than by a simple orthogonal extensional model.
Jurassic (Tithonian) radiolaria from La Désirade (Lesser Antilles): Preliminary paleontological and tectonic implications
Authors: Montgomery Homer , Pessagno Emile A. , Muñoz Ivette M.
Published: February 2008

Jurassic (upper Tithonian) Radiolaria recovered from bedded, red ribbon cherts on La Désirade, Guadeloupe, are the oldest fossils yet discovered in the Lesser Antilles. This age not only corroborates contested isotopic ages for the igneous basement of La Désirade but also demonstrates that previously reported differences in basement ages for the central and eastern end of the island are invalid. In addition, La Désirade chert yielded a higher‐latitude, Northern Tethyan to Southern Boreal Realm radiolarian assemblage (indicating deposition at a minimum of 22° north or south of the Jurassic paleoequator). Because Northern Tethyan or Boreal Jurassic oceanic crust did not exist in the spreading gap between North and South America, or east to Eurasia, we conclude that La Désirade oceanic crust formed in the Pacific. The fact that no Upper Jurassic red ribbon chert has been found in the Atlantic Ocean or in the Caribbean aside from in displaced oceanic fragments in Puerto Rico and the Dominican Republic lends additional support to a Pacific origin for the oldest crustal fragment in the Lesser Antilles.
Tectonic implications of out‐of‐sequence faults in an Accretionary Prism, Prince William Sound, Alaska
Authors: Bol Alan J. , Gibbons Helen
Published: February 2008

The Chugach and Prince William terranes constitute a Mesozoic through Tertiary accretionary complex bordering the Gulf of Alaska. Faults of the Contact fault system juxtapose the two terranes. Across the previously mapped trace of the Contact fault in western Prince William Sound, we studied three belts of alternately higher and lower deformation intensity and metamorphism. Out‐of‐sequence reverse faults separate these belts. Until recently, researchers assumed that the Prince William terrane was accreted to the Chugach terrane along the Contact fault. However, our work supports an emerging view that the Chugach and Prince William terranes represent older and younger parts of a continuously evolved accretionary prism, best considered a single terrane. We found that we cannot distinguish the Chugach from the Prince William terrane on the basis of lithology, deformation, or metamorphism; therefore, we cannot precisely identify the local strand of the Contact fault system. Furthermore, the major faults in the study area are relatively late‐stage features, related not to initial accretion but rather to internal deformation of the prism. West‐northwest shortening characterizes the deformation along the Contact fault system in western Prince William Sound, whereas dextral‐slip faulting characterizes the deformation along the Contact fault system in eastern Prince William Sound. We ascribe this difference to development of the Alaska orocline coeval with changes in plate motions during Eocene time, which resulted in convergence in western Prince William Sound remaining relatively orthogonal while convergence in eastern Prince William Sound became increasingly oblique.
Thermochronologic data from Tobago, West Indies: Constraints on the cooling and accretion history of Mesozoic oceanic‐arc rocks in the southern Caribbean
Authors: Cerveny P. F. , Snoke A. W.
Published: February 2008

Fission‐track thermochronologic studies on mid‐Cretaceous dioritic and tonalitic rocks from Tobago, West Indies, provide important temporal constraints on post magmatic Mesozoic cooling as well as the final phase of accretion of these oceanic‐arc plutonic rocks onto the continental margin of northern South America. Zircon fission track data indicate that the plutonic rocks of Tobago cooled through the zircon closure isotherm (250° – 200°C) at about 103 Ma. Apatite ages and track length analysis suggest rapid cooling through the apatite annealing zone (120° – 60°C) at about 45 Ma. Furthermore, the track lengths in apatites from these plutonic rocks are all greater than 14 microns, which implies that these rocks have not been above 50°C since 45 Ma. If a geothermal gradient of 25°C/km is inferred, the analyzed samples have been at depths of less than 2 km since 45 Ma. Tobago has occupied an upper crustal structural position since the mid‐Cretaceous, and significant final uplift of these Mesozoic oceanic‐arc rocks occurred in the mid‐Eocene. The tectonothermal history of Tobago since the mid‐Eocene has not involved deep burial or a high‐temperature thermal flux. This history apparently has chiefly involved translation of the Tobago terrane along the Caribbean ‐ South America Plate Boundary Zone at upper crustal levels.
Structural evidence for extensional exhumation of blueschist‐bearing serpentinite matrix melange, New England Orogen, southeast Queensland, Australia
Authors: Little T. A. , Holcombe R. J. , Sliwa R.
Published: February 2008

The footwall of a normal fault in the North D'Aguilar block in eastern Australia contains blueschist blocks within a serpentinite matrix melange. The melange contains mass‐flow deposits and was derived by erosion and redeposition of oceanic lithosphere exposed on the ocean floor by faulting. In mid‐Carboniferous time, the melange was metamorphosed in the epidote‐blueschist facies, mylonitized, and underplated to the hanging‐wall of a subduction zone. An S‐type granitoid, intruded at ∼306–307 Ma, was probably derived by partial melting of subducted metasediments during the peak of a greenschist facies overprint that accompanied transposition of an early high‐P/low‐T fabric. Mylonitic rocks below the normal fault absorbed a component of top‐to‐the‐west simple shear related to movement on that originally west dipping fault, and resulted in juxtaposition of very low‐grade accretionary sequences above polydeformed blueschists in a metamorphic core complex. At deeper levels in the footwall of the fault, bulk deformation was approximately irrotational. Later, the low‐angle fault was folded, and its displacement was transferred westward into a more planar fault splay. The juxtaposition of high‐P serpentinite melange against upper plate rocks probably reflects the mechanical weakness of serpentinite in deformed oceanic sequences, and the role serpentinite plays in strain softening that concentrates deformation along major extensional shear zones.
Global analysis of the potential for N2O production in natural soils
Authors: Bouwman A. F. , Fung I. , Matthews E. , John J.
Published: February 2008

A simple global model of the production potential of nitrous oxide (N2O) in natural soils is developed to analyze the relative importance, both geographically and seasonally, of the different controls on N2O production at the global scale. Five major controls on N2O production are included: (1) input of organic matter, (2) soil fertility, (3) soil moisture status, (4) temperature, and (5) soil oxygen status. Indices for the controls are derived from global gridded (1°×1° resolution) data bases of soil type, soil texture, NDVI and climate. The model explains close to 60% of the variability found in measurements reported at about 30 sites in six different ecosystems throughout the world. Although this result is reasonable for global analyses, the correlation is considered insufficient to make global estimates of nitrous oxide emission with confidence. The model confirms conclusions from earlier studies that the major source regions of nitrous oxide are in the tropics.
Analysis of short‐period P waves from the 1989 Macquarie Ridge Earthquake using a broadband array in Japan
Authors: Tada Taku , Shimazaki Kunihiko , Tsuboi Seiji
Published: February 2008

We have developed a simple method of array analysis, enabling to find out apparent radiation centers of teleseismic waves. Applying this method to short‐period P waveforms from the 1989 Macquarie Ridge earthquake recorded at 7 stations of the Pre‐POSEIDON network in Japan, we obtained a pattern of apparent radiation center migration that is more compatible with a bilaterally propagating source model than with a unilateral one.
Evidence of inorganic chlorine gases other than hydrogen chloride in marine surface air
Authors: Pszenny A. A. P. , Keene W. C. , Jacob D. J. , Fan S. , Maben J. R. , Zetwo M. P. , Springer‐Young M. , Galloway J. N.
Published: February 2008

We report the first measurements of inorganic chlorine gases in the marine atmosphere using a new tandem mist chamber method. Surface air was sampled during four days including one diel cycle in January, 1992, at Virginia Key, Florida. Concentrations of HCl* (including HCl, ClNO3, ClNO2, and NOCl) were in the range 40 to 268 pptv and concentrations of Cl2* (including Cl2 and any HOCl not trapped in the acidic mist chamber) were in the range <26 to 254 pptv Cl. Concentrations of Cl2* increased during the night, and decreased after sunrise as HCl* concentrations increased by similar amounts. The measurements suggest an unknown source of either HOCl or Cl2 to the marine atmosphere. Photochemical model calculations indicate that photolysis of the observed Cl2* would yield a chlorine atom (Cl•) concentration of order 104–105 cm−3. Oxidation by Cl• would then represent a significant sink for alkanes and dimethylsulfide (DMS) in the marine boundary layer. The cycling of Cl• could provide either a source or a sink for O3, depending on NOX levels.
A multifractal equivalent of the Beaufort scale for sea‐state
Authors: Kerman Bryan R.
Published: February 2008

It is reported here that the ocean surface under a sufficiently high wind is a multi‐fractal process, consisting of breaking wave singularities. It has been argued elsewhere that the singularity strength associated with individual breaking waves implies a distinct energy state within a continuum of such states whose entropy is associated with a fractal dimension. When the multi‐fractal process is modelled in the simplest, non‐trivial multiplicative energy flux cascade – as a Besicovitch‐Cantor process – 3 independent variables are required for a full description. It is shown that when a closure assumption is invoked which relates the 2 sub‐process energy fluxes as a power‐law in their respective receiving areas (the process' support), the 2 exponents involved are remarkably constant within the experimental variation arising from different aircraft imaging sorties over different sea states. The result is a reduction of complexity from 3 to just 1 independent variable to describe any realization; this parameter is referred to as the multi‐fractal equivalent of the Beaufort scale.
Prediction of the heliospheric current sheet tilt: 1992 – 1996
Authors: Suess S. T. , McComas D. J. , Hoeksema J. T.
Published: February 2008

Heliospheric current sheet tilt evolves systematically over the solar cycle. Here we show that this evolution is different than the sunspot cycle and that tilt for the period 1992 – 1996 can be predicted using persistence. That is, the tilt over the coming cycle will be the same as for the past cycle. The Ulysses spacecraft has passed Jupiter and is moving out of the plane of the ecliptic, so we use the prediction of the changing heliospheric current sheet tilt to predict that Ulysses will pass beyond the envelope, or maximum latitude, of the heliospheric current sheet in November 1993.
ULF magnetic fields generated by electrical storms and their significance to geomagnetic pulsation generation
Authors: Fraser‐Smith A. C.
Published: February 2008

The STAR Laboratory has been operating two independent electromagnetic noise monitoring systems in the vicinity of Stanford University for several years, one covering the ULF range (0.01–10 Hz) and the other the ELF/VLF range (10 Hz – 32 kHz). These two systems were operating during the relatively rare occurrence of a large local electrical storm on 23 September 1990 and their measurements (which cover 25 narrow frequency bands in the more than five‐decade range 0.01 Hz – 32 kHz) provide a detailed picture of the ULF and ELF/VLF magnetic field fluctuations that accompanied the storm. As would be expected, considering the important role played by lightning in its generation, ELF/VLF radio noise is enhanced. However, the ELF/VLF enhancements are smaller than those that occur at ULF: the amplitude of the magnetic field fluctuations in a 100 Hz band centered on 2 kHz was approximately doubled, whereas in the range 0.2–0.5 Hz the amplitude was increased roughly 20 times, and the increase was about 50 times for the range 0.01–0.02 Hz. Some years ago I proposed that repetitive lightning in electrical storms could trigger Pc 1 geomagnetic pulsation events, but these new results suggest that there may exist a broader link between electrical storms and geomagnetic pulsations. Considering that there are perhaps 2000 electrical storms in progress around the world at any time, and that large ULF electrical current systems below the ionosphere can stimulate ULF hydromagnetic waves in the ionosphere, the new measurements suggest that the electrical currents associated with thunderstorms, taken as a whole, may be a source of ULF energy in the magnetosphere and thus influence the generation and amplification of some classes of geomagnetic pulsations.
Mantle viscosity stratification and flow geometry: Implications for surface motions on Earth and Venus
Authors: Kiefer Walter S.
Published: February 2008

For a fixed heat flow, the surface flow velocity of a convecting layer is not strongly sensitive to the variation of viscosity as a function of depth. Thus, the inferred absence of a low viscosity asthenosphere on Venus can not account for the limited surface motions there. The surface velocity is dependent on the convective geometry. Cartesian geometry convection can produce large surface velocities if the high viscosity surface layer is broken in places by weak zones. On the other hand, a high viscosity surface layer may inhibit the development of large surface velocities in axisymmetric convection.
Cold Moho boundary beneath island arc systems: An example from the North Kamchatka Arc
Authors: Kepezhinskas Pavel
Published: February 2008

A suite of amphibole‐bearing ultramafic and mafic xenoliths representing the crust‐mantle boundary was sampled in the northern segment of the Kamchatka arc. These nodules exhibit low equilibration temperatures at elevated pressures suggesting relatively cold conditions at Moho depths, which are uncommon in modern island arcs. A model including successive stages of subduction initiation, subduction cessation resulting in cooling of the lithospheric wedge, followed by intra‐arc rifting due to upwelling of astenospheric diapirs is proposed to explain the observed textural, petrologic and chemical characteristics of sampled rock assemblage.
Pickup water group ions at comet Grigg‐Skjellerup
Authors: Coates A. J. , Johnstone A. D. , Huddleston D. E. , Wilken B. , Jockers K. , Borg H. , Amata E. , Formisano V. , Bavassano‐Cattaneo M. B. , Winningham J. D. , Gurgiolo C. , Neubauer F. M.
Published: February 2008

The density and velocity distribution of cometary water group ions was measured by the Giotto spacecraft in the regions upstream and downstream of the ‘bow shock’ at comet Grigg‐Skjellerup. The results show that the distributions of ions are ring‐like until quite close to the shock, the timescales for pitch angle and energy diffusion appear similar and the ion density follows a r−2 dependence.
Global biogeochemical cycling estimates with CZCS satellite data and general circulation models
Authors: Erickson David J. , Eaton Brian E.
Published: February 2008

Computed geophysical fields from a 3‐D general circulation model are coupled with the Coastal Zone Color Scanner (CZCS) satellite data on chlorophyll content of surface ocean waters. The CZCS satellite data on chlorophyll content of surface ocean waters are used to estimate the ‘photochemical lability’ of dissolved organic matter in the surface ocean. Monthly estimates are made of the global ocean to atmosphere flux of a biogeochemically important gas, carbonyl sulfide (OCS), with 2.8° × 2.8° latitude‐longitude spatial resolution. This novel technique provides a conceptual and computational method for integrating data collected as part of future satellite measurement campaigns, such as the Earth Observing System (EOS) and Sea‐viewing Wide‐field‐of view Sensor (Sea WiFS), with 3‐D chemistry‐climate prediction models.
Laboratory measurements of the loss of ClO on pyrex, ice and NAT at 183 K
Authors: Kenner R. D. , Plumb I. C. , Ryan K. R.
Published: February 2008

The rate of loss of ClO on Pyrex, water ice and nitric acid trihydrate, NAT, surfaces at 183 K has been measured in a flow reactor sampled by a mass spectrometer. Upper limits for the rates of loss of ClO on Pyrex at 295 K, Cl2 on ice at 183 K and O3 on Pyrex, ice and NAT surfaces at 183 K have also been determined. In all cases the probability of loss of the species from the gas‐phase upon collision with the surface is less than 10−4. These small values make it probable that heterogeneous reactions involving these species are unimportant in the winter polar stratosphere.
Dynamic surface topography: A new interpretation based upon mantle flow models derived from seismic tomography
Authors: Forte A. M. , Peltier W. R. , Dziewonski A. M. , Woodward R. L.
Published: February 2008

The very long wavelength (i.e. in the degree range ℓ = 1–8) dynamic topography at the Earth's surface, estimated by isostatic reduction of the observed topography, is shown to be in good agreement with the topography predicted by a model of viscous flow in the mantle. This flow model was previously derived by independent consideration of the observed nonhydrostatic geoid and is based upon a recent model of large‐scale seismic shear velocity heterogeneity in the mantle. Our estimate (and prediction) of the long wavelength dynamic surface topography reveals significant depressions (≈ 2–3 km) of the continental shields relative to their hydrostatic reference positions.
Linear array data gathering for microearthquake observation: Survey of mid‐crustal reflectors
Authors: Katsumata K. , Tsukada S. , Ogino I. , Mizoue M.
Published: February 2008

Linear Array Data Gathering (LADG) is a method for using microearthquake observations to investigate fine structure in the Earth. There are two types of LADG, multistation and multisource. In the multisource case, seismic wavefrom data from many sources recorded at one station are used. We apply the multisource geometry to survey reflectors in the deep portion of the crust at Nikko‐Ashio region, Central Honshu, Japan. We detect the PP and PS reflections as well as SS and SP from a partial melt zone located at 19.5 km in depth. No previous study has found the PP and PS reflections in this region. As a result of this study, we are confident that LADG for microearthquake observation is eminently useful for the survey of fine crustal structure.
Altitude variations of ionospheric currents at auroral latitudes
Authors: Kamide Y. , Brekke Asgeir
Published: February 2008

On the basis of updated EISCAT experiments, the first full derivation of the ionospheric current density of the auroral electrojets at six different altitudes are presented. It is found that current vectors at different altitudes are quite different, although the eastward and westward currents prevail in the evening and morning sectors, respectively, once the currents are integrated over altitude. The eastward electrojet becomes almost northward whilst the westward electrojet becomes almost southward, at the highest altitude, 125 km, in this study. The physical implications of these characteristics are discussed.
Coseismic displacements: 1992 Landers, California, Earthquake
Authors: Murray M. H. , Savage J. C. , Lisowski M. , Gross W. K.
Published: February 2008

The rupture associated with the 1992 Landers earthquake (Ms = 7.5) extended along the west edge of a 60 × 50 km trilateration network that had been surveyed two months before the earthquake and was resurveyed a month after it. The coseismic displacement field within the network was calculated from the changes observed in the trilateration network supplemented by the displacements measured at four GPS stations and other less timely trilateration measurements. Stations near the rupture were displaced by as much as 3 m. The observed changes are reproduced reasonably well by dislocation modeling in which the Landers rupture is represented by 8 vertical fault segments, each extending from the surface to 9 km depth. Two additional segments represent the Big Bear and Eureka Peak faults. The average modeled right‐lateral slip on the Landers rupture is about 5 m. However, the residuals for the best‐fit slip distribution are about four times greater than expected from measurement error. Given that uncertainty, a broad range of slip models furnish acceptable fits to the data. The large residuals are attributed to inelastic deformation (principally sympathetic slip on numerous unmodeled faults) within the fault blocks assumed to be elastic in the model.
1. Spatial and temporal evolution of the optical thickness of the Pinatubo aerosol cloud in the northern hemisphere from a network of ship‐borne and stationary lidars
Authors: Avdyushin S. I. , Tulinov G. F. , Ivanov M. S. , Kuzmenko B. N. , Mezhuev I. R. , Nardi B. , Hauchecorne A. , Chanin M. ‐L.
Published: February 2008

The vertical profiles of the extinction coefficient and the total optical thickness of the Pinatubo aerosol layer obtained from a network of 5 Rayleigh‐Mie lidars are presented here. Three ship‐borne lidars (PROFESSOR ZUBOV†, PROFESSOR VIZE†, HENRI POINCARE*) and two fixed lidar stations (OHP* and CEL*) are operated respectively by the Roscomhydromet†, of Russia and of the Service d'Aeronomie du CNRS* of France. The measurements presented are in the altitude range 15–35 km. They were obtained between July 1991 ‐ April 1992 and cover 8°S–60°N latitude and 80°W–6°E longitude. This represents extensive coverage of the western sector of the northern hemisphere, which is partly coincident with UARS satellite coverage. Optical depths of up to 0.2 were observed and maximum extinction coefficient values of 0.08 km−1 were obtained at 24 km and 18°N latitude.
Interaction of field‐aligned cold plasma flows with an equatorially‐trapped hot plasma: Electrostatic shock formation
Authors: Singh Nagendra
Published: February 2008

Effects of equatorially trapped hot plasma on the highly supersonic cold‐plasma flow occurring during early stage plasmaspheric refilling are studied by means of numerical simulations. It is shown that the equatorially trapped hot ions set up a potential barrier for the cold ion beams and facilitate formation of electrostatic shocks by reflecting them from the equatorial region. Simulations with and without the hot plasma show different flow properties; the formation of electrostatic shocks occur only in the former case. The simulation with the hot plasma also reveals that the magnetic trapping in conjunction with the evolution of the electrostatic potential barrier produces ion velocity distribution functions consisting of a cold core and a hot ring in the perpendicular velocity. Such a distribution function provides a source of free energy for equatorial waves. The corresponding electron population is warm and field aligned.
Northern hemisphere extratropical circulation anomalies and recent January land surface temperature trends
Authors: Palecki Michael A. , Leathers Daniel J.
Published: February 2008

This study demonstrates that long‐term January temperature trends in the Northern Hemisphere are strongly related to decadal‐scale variations in extratropical mid‐tropospheric circulation modes. Circulation indices derived from a rotated principal components analysis of 500‐mb geopotential heights explain 72% of the January Northern Hemisphere land surface air temperature variance. An analysis of the spatial characteristics of January temperature trends from 1966 through 1985 indicates a close correspondence between the observed trends and those obtained from consideration of the phase and strength of the major modes of low‐frequency mid‐tropospheric variation.
Stratospheric aerosol change in the early stage of volcanic disturbance by the Pinatubo Eruption observed over Tsukuba, Japan
Authors: Hayashida Sachiko , Sasano Yasuhiro
Published: February 2008

An increase in the amount of stratospheric aerosol due to the Pinatubo eruption (June 12 –15, 1991, 15.14° N, 120.35° E) was observed from the end of June by a lidar in NIES, Tsukuba (36° N, 140° E). The first arrival of volcanic aerosol layers was observed just above the tropopause on June 28, 1991, only two weeks after the eruption. Aerosol layers higher than 20 km appeared sporadically in July and August, reflecting the inhomogeneity of aerosol distribution.

After the change in the wind system from summer easterlies to winter westerlies, the main body of the volcanic aerosol layer made its appearance over Tsukuba. The integrated backscattering coefficient (IBC) increased in winter as a result of transportation of aerosols from the tropical region. The IBC, which can be converted to optical thickness, exceeded the level of the value observed after the El Chichon eruption.