bluuebunny/crossref_metadata_2025 huggingface dataset:
Climate model comparison of Gondwanan and Laurentide glaciations
Authors: Crowley Thomas J. , Baum Steven K. , Hyde William T.
Published: February 2008

Geologic studies indicate that the Carboniferous glaciation on Gondwanaland was approximately as extensive as the ice sheets during the Pleistocene. However, there is one major difference between the climate boundary conditions for the two ice sheets: the Gondwanan ice sheet was located on a supercontinent. Three different levels of sensitivity experiments were conducted to examine the effect of the large landmass on the magnitude of summer warming over the ice sheets: (1) simulations with present solar luminosity and present orbital forcing resulted in summer temperatures over the Gondwanan Ice Sheet 12°–17°C greater than over the Pleistocene Laurentide Ice Sheet; (2) lowering the solar constant 3% or modifying the seasonal insolation cycle to a “cold summer orbit” reduced the warming but still led to significant differences between Gondwanan and Pleistocene simulations; and (3) the combined effect of lowering the solar constant and modifying the seasonal insolation cycle to a cold summer orbit resulted in temperature patterns over the Gondwanan Ice Sheet similar to the Pleistocene. Model simulations also predict tropical sea surface temperatures about 4°C less than at present as a result of reduced solar luminosity. These results suggest that conditions necessary to explain Gondwanan ice sheet stability may be known, but required boundary conditions would be more extreme than in the Pleistocene. Although a number of uncertainties remain in these calculations, they help to better define critical conditions for glaciation for one of the most prolonged periods of continuous glaciation in Earth history.
The Earth's radiation budget and its relation to atmospheric hydrology: 1. Observations of the clear sky greenhouse effect
Authors: Stephens Graeme L. , Greenwald Thomas J.
Published: February 2008

This paper describes an observational study of the clear sky components of the Earth's radiation budget (ERB), the relationship of these components to the sea surface temperature (SST), and the microwave‐derived water vapor amount using observations that are coincident in both space and time. This study uses two sets of ERB data; the Nimbus 7 narrow field‐of‐view, broadband scanning radiometer data from June 1979 to May 1980 and the Earth Radiation Budget Experiment (ERBE) broadband scanning data from March 1985 to February 1986. Clear sky fluxes derived from Nimbus 7 data are compared to the ERBE data. Globally averaged Nimbus 7 clear sky longwave (LW) fluxes are lower than the equivalent ERBE fluxes by about 5 W m−2, whereas clear sky reflected fluxes are higher by about 3 W m−2. These biases are consistent with the possibility of slight cloud contamination of the Nimbus 7 clear sky fluxes, although biases in ERBE fluxes also may partly explain the differences. Comparisons of the global distributions of these clear sky fluxes reveal a cloud contamination in the Nimbus 7 fluxes over the regions of the storm tracks poleward of about 50° latitude. Despite these effects, the comparison of the two data sets generally agree within the uncertainty of the flux measurements and reproduce the gross features of clear sky ERB fluxes reported previously. A strategy for analyzing the emitted clear sky LW flux over the oceans is described using the simple arguments of gray body radiative equilibrium. A greenhouse parameter G, defined in terms of the SST and the emitted flux I, is introduced and a linear relationship between G and the precipitable water w is established from the observations. Using a simple nongray one‐dimensional climate model, we demonstrate how both the observations and the model differ from the simple ideas of gray body radiative equilibrium in significant ways. We demonstrate how the relationships between G and w and G and SST are affected by the assumed vertical profiles of water vapor and temperature. Although it is not possible to observe feedback processes directly, it is argued that the results of the paper are consistent with conventional ideas about the operation of a positive feedback on Earth between the greenhouse effect, SST and w.
Ozone budget over the Amazon: Regional effects from biomass‐burning emissions
Authors: Richardson Jennifer L. , Fishman Jack , Gregory Gerald L.
Published: February 2008

A one‐dimensional, time‐dependent, photochemical model is used in conjunction with data obtained during the dry‐season portion of NASA's Global Tropospheric Experiment and Brazil's Instituto Nacional de Pesquisas Espaciais (INPE) (National Institute for Space Research) Amazon Boundary Layer Experiment (ABLE 2A) to simulate the chemistry of the dry‐season Amazon troposphere. The background atmosphere, unperturbed by the presence of emissions from biomass burning, is simulated with inputs of surface sources and deposition of various species measured during ABLE 2A. The presence of haze layers over a region is simulated by the imposition of profiles of species characteristic of haze within the model for 12 hours. The inclusion of hydrocarbons within the modeled haze is found to approximately double the calculated in situ ozone production rate. The difference between the calculated total column ozone production rates in the haze simulation and the background simulation is the model‐predicted enhancement of the in situ ozone production due to regionally transported haze layers (up to 1000 km transport distance). The predicted enhancement of ozone is between 0.3 and 2.9 × 1011molecules O3cm−2s−1, near the range of observed rates of ozone increase over the Amazon Basin during the dry season. This suggests that the regional transport of haze during the southern tropical burning season is an important factor in explaining the increase of ozone observed annually during this period.
Relationships between CH4 emission, biomass, and CO2 exchange in a subtropical grassland
Authors: Whiting Gary J. , Chanton Jeffrey P. , Bartlett David S. , Happell James D.
Published: February 2008

Methane flux was linearly correlated with plant biomass (r = 0.97, n = 6 and r = 0.95, n = 8) at two locations in a Florida Everglades Cladium marsh. One location, which had burned 4 months previously, exhibited a greater increase in methane flux as a function of biomass relative to sites at an unburned location. However, methane flux data from both sites fit a single regression (r = 0.94, n = 14) when plotted against net CO2 exchange suggesting that either methanogenesis in Everglades marl sediments is fueled by belowground root exudation or else factors which enhance photosynthetic production and plant growth are also correlated with methane production and flux in this oligotrophic environment. These data are the first to show a direct relationship between spatial variability in plant biomass, net ecosystem production, and methane emission in a natural wetland.
Lightning flashes from a prescribed fire‐induced cloud
Authors: Latham Don
Published: February 2008

A prescribed fire was ignited near Chapleau, western Ontario, Canada, on the afternoon of August 10, 1989. The fire, covering approximately 400 ha, burned vigorously over a period of 3 hours, from 1400 to 1700 EDT, generating a plume cloud structure including a portion resembling an anvil. During the period 1500–1630, 21 ground flashes lowering positive charge from the plume cloud were observed simultaneously by an electric field mill near the fire and a lightning location system. Four negative flashes that occurred at the beginning of the time period were not recognized as ground flashes by the location system. These four flashes out of a total of 37 flashes exceeding 90 V/m at the electric field meter were the only flashes perceived as lowering negative charge; all the others lowered positive Charge, whether recognized by the locating system as ground flashes or not. The median current of the positive flashes to ground as calculated from the location system output was 36 KA. Application of simple models of charge distribution to the plume structure indicate that the plume and associated cloud had a monopolar charge distribution, with positive charge at altitude and that the fire was most probably the source of this charge. A charge generation rate of 2 nC/m2/s by the fire could generate enough charge to satisfy the flash discharge rate and amount using the simplest model. The locations for the ground termini of the flashes are downwind of the fire location, some by as much as 30 km. They seem to be associated with the anvillike structure of the plume, although it is known that positive ground flashes commonly occur at considerable horizontal distances from their origin. There is no time organization to the distances of the termini from the fire.
Sensitivity of calculated odd nitrogen distributions to the diabatic wind fields
Authors: Boughner R. E. , Callis L. B. , Natarajan M.
Published: February 2008

Two‐dimensional and three‐dimensional model calculations are known to give stratospheric total odd nitrogen (NOy= N + NO + NO2+ 2 × N2O5+ HNO3+ HNO4+ ClONO2) mixing ratios which are significantly smaller than values inferred using measurements obtained from the limb infrared monitor of the stratosphere (LIMS) instrument. We examine NOydistributions calculated with two different advective transport fields, one derived from reported climatological data and one derived from LIMS T, O3, and H2O data. Specifically, it is of interest to see if the use of the advective fields derived from the LIMS data leads to a reconciliation of the inferred and calculated NOydistributions. Calculations with the advective field derived from climatological data show stronger poleward and downward motion in the winter season compared to the advective field derived from LIMS data. This leads to NOymixing ratios in the lower stratosphere that are about 20% larger in the polar regions of both hemispheres and approximately 40% higher in the equatorial region for climatological transport fields compared to those derived from LIMS data. As a consequence, the NOydistributions calculated in the present model with the LIMS advective field show worse agreement with NOyvalues inferred from the LIMS measurements than similar results obtained with the climatological wind field. Ozone levels in the lower stratosphere calculated with the climatological wind field are smaller than those computed with the LIMS wind field, which is most likely an indirect chemical effect associated with the larger NOyvalues.
Aerosol chemical components in Alaska air masses: 2. Sea salt and marine product
Authors: Shaw Glenn E.
Published: February 2008

The inhomogeneity of the aerosol chemistry for a 4‐year data set from the geographic central region of Alaska expressed through loading of principal components provides provisional multivariate statistical identification for components of nonanthropogenic (apparently natural) sources of particles. Besides an Al‐rich dust which is generally present but is slightly elevated in summer months, a marine sea‐salt component of aerosol is detectable as well as a Br component. The marine sea‐salt component was most evident when air over the ocean flowed behind the Alaska mountain range barrier from the Bering Sea and entered into the flat river floodplain of interior Alaska, undergoing little or no orographic lifting in the process. During such flow patterns, marine components such as sodium, chlorine, potassium, arid selenium are enhanced by up to a factor of 10 from average, but these very components are also attenuated strongly during forced overmountain “chinook” flow. We hypothesize that the sea‐salt deficiency for the latter flow is due to nucleation and rainout on the windward side of the Alaska mountain range and calculate that this is plausible. Chlorine in sea salt is evidently volatilized and released from the particulate phase, leading to a severalfold depletion relative to sodium aerosol during incursions of acid‐rich pollution aerosol from the Arctic. Bromine in aerosol in the central geographic region in Alaska undergoes a large (×10) enhancement each year in late March to early April in affiliation with flow of air from the Arctic.
Laboratory studies of large protonated water clusters under the conditions of formation of noctilucent clouds in the summer mesopause
Authors: Yang X. , Castleman A. W.
Published: February 2008

Studies of the formation and growth of large protonated water clusters in a fast flow tube reactor at temperatures equivalent to those under which NLC are known to form offer, for the first time, the possibility to experimentally investigate some of the mechanisms of NLC formation at the molecular level. Importantly, bimodal cluster distributions obtained in the laboratory experiments are similar to those found in situ and also are in accordance with predictions based on ion‐induced nucleation theories. The experiments show a strong dependence of temperature and water partial pressure on the production of large protonated water clusters of sizes similar to those observed during NLC displays. A consideration of the thermodynamics of the clustering reactions and their unimolecular dissociation kinetics provides a further understanding of the conditions necessary for the observation of the protonated water clusters both in the laboratory and in situ. Investigations of chemical reactions of the protonated water clusters with a variety of neutral reactants were also made, and the findings enable an assessment to be made of the chemical environment existing during NLC formation.
Simultaneous measurements of the charge, size, and shape of hydrometeors in an electrified cloud
Authors: Weinheimer A. J. , Dye J. E. , Breed D. W. , Spowart M. P. , Parrish J. L. , Hoglin T. L. , Marshall T. C.
Published: February 2008

With the use of an induction cylinder in conjunction with an optical array probe, simultaneous measurements were obtained of the size, shape, and charge of hydrometeors in a New Mexico thunderstorm, The particles with detectable charges (greater than 1–3 pC) were primarily graupel particles, and their charges are generally consistent with laboratory measurements of ice‐ice collisional charging. The fraction with detectable charge increases with size, as does the magnitude of the mean charge. Also, the positively charged particles occur primarily at higher temperatures (> −22°C), and the degree of negative charging increases with decreasing temperature (down to −35°C).
Extratropical aspects of the 40–50 day oscillation in length‐of‐day and atmospheric angular momentum
Authors: Dickey J. O. , Ghil M. , Marcus S. L.
Published: February 2008

Fluctuations in Earth rotation over time scales of 2 years or less are dominated by atmospheric effects; spectral analyses of length‐of‐day (LOD) and atmospheric angular momentum (AAM) data show significantly increased variability in the 40–50 day band. LOD and AAM fluctuations on the 40–50 day time scale have previously been linked to tropical, convectively driven waves of the type first described by Madden and Julian (1971) (referred to as MJ hereinafter). A significant spectral peak centered at 42 days has also been found, however, in the AAM of a 3‐year (1120‐day) perpetual‐January simulation of the global atmosphere, performed using a version of the University of California at Los Angeles (UCLA) general circulation model (GCM) which does not give rise to MJ oscillations in the tropics. In the present work the 40–50 day oscillation is studied using the 12‐year overlap between two records: (1) AAM data, compiled from the National Meteorological Center (NMC); and (2) LOD variation from the Jet Propulsion Laboratory Kalman‐filtered Earth rotation series. We analyze the NMC records by latitude belts, in light of the UCLA GCM results, in order to identify possibly distinct sources of the AAM oscillation in the mid‐latitudes and the tropics. Results suggest that two intraseasonal oscillations exist in the Earth‐atmosphere system: a tropical, 50‐day oscillation associated with the convectively driven MJ wave and a mid‐latitude, 40‐day oscillation associated with the interaction of nonzonal flow with topography.
Induced magnetic fields at the surface of Venus inferred from pioneer Venus orbiter near‐periapsis measurements
Authors: Luhmann Janet G.
Published: February 2008

Although magnetic field measurements have not been made on the surface of Venus or, for that matter, below the Pioneer Venus Orbiter (PVO) periapsis altitude of ∼150 km, the theory of the large‐scale ionospheric magnetization that results from the solar wind interaction can be used in concert with the available data to infer the existence of nonzero fields down to the surface. Here it is argued that magnetometer measurements in the upper part of the “diffusion region” of the ionosphere can be extrapolated to lower altitudes because of the particularly simple physics that determines the altitude profile of the large‐scale magnetic field in this region. The magnetic field at the bottom of the ionosphere inferred by this method using the PVO data is up to tens of nanoteslas when large‐scale ionospheric fields are present, suggesting the likely presence of fields of similar strength below. Given the negligible intrinsic field of Venus inferred from the PVO measurements, these fields must result from the solar wind interaction. The implications for Mars, which may have an analogous solar wind interaction, is that magnetometers on the surface could regularly observe varying fields of similar magnitude and origin.
The Influence of CaCO3 Dissolution on Core Top Radiocarbon Ages for Deep‐Sea Sediments
Authors: Broecker Wallace S. , Klas Mieczyslawa , Clark Elizabeth , Bonani Georges , Ivy Susan , Wolfli Willy
Published: February 2008

Radiocarbon ages on CaCO3 from deep‐sea cores offer constraints on the nature of the CaCO3 dissolution process. The idea is that the toll taken by dissolution on grains within the core top bioturbation zone should be in proportion to their time of residence in this zone. If so, dissolution would shift the mass distribution in favor of younger grains, thereby reducing the mean radiocarbon age for the grain ensemble. We have searched in vain for evidence supporting the existence of such an age reduction. Instead, we find that for water depths of more than 4 km in the tropical Pacific the radiocarbon age increases with the extent of dissolution. We can find no satisfactory steady state explanation and are forced to conclude that this increase must be the result of chemical erosion. The idea is that during the Holocene the rate of dissolution of CaCO3 has exceeded the rain rate of CaCO3. In this circumstance, bioturbation exhumes CaCO3 from the underlying glacial sediment and mixes it with CaCO3 raining from the sea surface.
Carbonate Dissolution Fluctuations in the Western Equatorial Pacific During the Late Quaternary
Authors: Le Jianning , Shackleton N. J.
Published: February 2008

Planktonic foraminiferal test fragmentation in three cores along a depth transect from the western equatorial Pacific (ERDC‐93P, 1619 m; RC17‐177, 2600 m; V28‐238, 3120 m [Thompson, 1976]) were examined for the last 500 kyr at sample intervals from 2.5 to 5 kyr to study the fluctuations of dissolution in the western equatorial Pacific. The age models were constructed by correlating the δ18O records with the SPECMAP stack [Imbrie et al., 1984]. Results showed that intermediate and deep waters experienced the same patterns of dissolution through climatic cycles. Fragmentation varied with a greater amplitude, and the carbonate ion concentration changed less, in the deep than in the intermediate water. Dissolution has significant variance distributions and coherencies with δ18O over the 100, 41, and 23 kyr periods of orbital variations; dissolution maxima lag ice volume minima by 6 to 20 kyr. The dissolution variability was consistent with recent geochemical models which seek to explain the reduction of atmospheric CO2 concentration at the last glacial maximum [Broecker, 1982; Boyle, 1988].
The Small‐Comet Hypothesis
Authors: Dessler A. J.
Published: February 2008

According to the small‐comet hypothesis, small comets strike the Earth approximately 20 times per minute, each small comet nominally containing 100 tons (105 kg) of water‐ice. The primary observations interpreted as evidence for these small comets are dark spots in the Earth's atomic‐oxygen UV dayglow seen by the UV imager on the Dynamics Explorer (DE) satellite. These small comets must disintegrate near Earth and then sublimate within a few seconds, the water vapor expanding to form clouds of water vapor, nominally 50 km in diameter, that temporarily block the spacecraft's view of the dayglow, thus producing the dark spots. In this review we examine problems in basic mechanisms underlying the small‐comet hypothesis. These include inconsistencies with known geophysical phenomena, conflicting results from independent searches for evidence of the presence of small comets, and inconsistencies within the small‐comet hypothesis itself. No other geophysical interpretation that can account for the DE dark spots has been advanced. The only viable alternative in the literature is a nongeophysical one—the instrument‐artifact hypothesis—in which it is proposed that the dark spots appear randomly in the DE pictures. Tests of this hypothesis, both qualitative and statistical, show that it, neatly and economically, explains the DE dark‐spot data. Owing to the weight of accumulated evidence against the small‐comet hypothesis, the lack of credible supporting evidence, and the plausibility of the instrument‐artifact hypothesis, it is unlikely that the small‐comet hypothesis is valid.
Experimental characterization of isotropic chiral composites in circular waveguides
Authors: Hollinger R. D. , Varadan V. V. , Ghodgaonkar D. K. , Varadan V. K.
Published: February 2008

This paper reports the first experimental characterization of microwave chiral composites in circular waveguides and the associated calibration that is required for accurate measurements. The experimental setup, sample preparation, calibration, measurement technique, and data analysis are discussed. Results are presented in the form of rotary dispersion and axial ratio and compared with that obtained from free space measurements. It is demonstrated that an effect similar to the Cotton effect can be observed at microwave frequencies also.
Implications of paleomagnetic data on Miocene extension near a major accommodation zone in the Basin and Range Province, northwestern Arizona and southern Nevada
Authors: Faulds James E. , Geissman John W. , Shafiqullah Muhammad
Published: February 2008

Paleomagnetic data from volcanic and crystalline rocks elucidate the evolution of a major Miocene accommodation zone in the northern Colorado River extensional corridor. The accommodation zone is a 10‐km‐wide belt of intermeshing conjugate normal faults that facilitates reversals in the dominant tilt direction of fault blocks and dip direction of major normal fault systems. Tilt‐corrected means (e.g., N = 28 sites, D = 353.4°, I = 61.3°, α95= 6.7°, k = 17.4) from Miocene volcanic strata overlap expected Miocene directions at the 95% confidence level. These data and geologic relations suggest that at exposed structural levels the accommodation zone did not facilitate distributed strike‐slip displacement between opposing tilt block domains. Vertical axis rotations are probably negligible in most of the corridor, as the Miocene structural grain generally mimics that in the zone. Discrepancies between characteristic remanent magnetizations (ChRM) in crystalline rocks and expected directions are therefore attributed to rotations about horizontal (i.e., tilting or flexing) axes. ChRMs from Cretaceous and Miocene intrusions suggest 50°–90° of tilting of large crystalline terranes on either side of the accommodation zone. The magnitude of tilting inferred from the paleomagnetic data is similar to that of Tertiary strata in nearby fault blocks, implying that these crystalline terranes are parts of highly tilted fault blocks rather than flexed lower plate rocks. Major low‐angle normal faults that bound highly tilted parts of these crystalline terranes probably nucleated at steep dips and were rotated to gentle dips by block tilting. Paleomagnetic data indicative of negligible tilting (e.g., Miocene intrusions, northern Black Mountains crystalline terrane, N = 13 sites, D = 359°, I = 55°, α95= 9°, k = 24) and geologic relations imply that lower plate rocks may surface in both the east and west tilted domains 35–50 km away from the zone. The trend toward shallower structural levels, with respect to Miocene extension, and tapering of highly extended terrane toward the accommodation zone imply that the magnitude of upper crustal extension decreases toward the zone. Temporal patterns of major extension, especially an apparently continuous northward younging across both the east and west tilted domains, further suggest that the accommodation zone served as a long‐lived rupture barrier between conjugate normal fault systems rather than as a short‐term boundary between opposing systems that propagated toward and converged at the zone.
Kinematic evidence for extensional unroofing of the Franciscan Complex along the Coast Range Fault, Northern Diablo Range, California
Authors: Harms T. A. , Jayko A. S. , Blake M. C.
Published: February 2008

Franciscan metagraywacke immediately below the Del Puerto ophiolite, an outlier of the Coast Range ophiolite in the northern Diablo Range, was sheared during top‐to‐the‐east displacement on the Coast Range fault. This represents normal faulting and extensional offset. It was accompanied by attenuation of the Coast Range ophiolite and Great Valley sequence in the hanging wall along layer‐parallel normal faults that sole into the Coast Range fault. Extension occurred as the Franciscan Complex moved relatively west, out from under North American lithosphere and across the subducting ocean plate below. This effected a lengthening and thinning in the wedge of material above the down‐going plate, presumably in response to instability brought about by subduction shallowing (Krueger and Jones, 1989) and accretion of the Franciscan Central belt in the latest Cretaceous to early Paleocene. As a result, blueschist facies terranes of the uppermost part of the Franciscan Complex are now juxtaposed directly against hanging wall units that bear only low‐grade metamorphism.
A Middle Jurassic to Early Tertiary Andean‐Sierran Arc Model for the Coast Belt of British Columbia
Authors: van der Heyden P.
Published: February 2008

Regional tectonic features of the western Canadian Cordillera can be interpreted in terms of Middle Jurassic accretion of a single composite superterrane (Stikinia + Wrangellia + Alexander) to ancestral North America. Closure of the intervening Cache Creek‐Bridge River ocean moved the continental edge to a new position west of the accreted superterrane. The Coast Belt is primarily a succession of superimposed Middle Jurassic to early Tertiary magmatic arcs related to prolonged subduction of Pacific Ocean lithosphere beneath the new North American margin. Discrete magmatic pulses, separated by lulls or periods of relative quiescence, successively overprinted the new margin. The Insular and Intermontane superterranes, previously viewed as widely separate entities prior to mid‐Cretaceous time, were already amalgamated before an initial Middle Jurassic overprint produced an ancestral Coast Belt. Late Jurassic to Early Cretaceous rift‐related(?) marine basins, mid to Late Cretaceous compressional structures, and early Tertiary extensional features coincident with the Coast Belt are subsidiary intraplate attributes that reflect external adjustments in plate motions within a primary, subduction‐related Andean magmatic arc.
Isostatic rebound due to tectonic denudation: A viscous flow model of a layered lithosphere
Authors: Wdowinski Shimon , Axen Gary J.
Published: February 2008

A four‐layer model of the upper 150 km of the Earth is used to calculate the viscous response of continental crust and the underlying mantle to tectonic denudation. The model comprises a strong upper crustal layer, a weak lower crustal layer, a very strong mantle lithosphere layer, and a weak mantle asthenosphere layer, which is in accord with experimental constraints on strength‐depth profiles for continental lithosphere. The strength of each layer is represented by its effective viscosity. Flow in the crust and mantle is driven by buoyancy forces, which arise from the unloading of an allochthon along a detachment fault by a series of instantaneous displacements (earthquakes or rapid creep events). Numerical solutions, obtained by using a finite element technique, predict footwall uplift, Moho deflection, and surface topography that are consistent with observations from the Basin and Range province of the western United States. The calculated curvature of the footwall uplift is also similar to that observed and is sensitive to the geometry of the detachment fault. Such bending need not be elastically controlled; hence the curvatures of footwall domes do not clearly place limits on the effective elastic thickness of the extending crust. The upward deflection of the Moho and the surface topography are sensitive to the viscosity structure and enable us to bound the range of the various viscosities. By matching observations from the Basin and Range province, which indicate no Moho deflection and low magnitude of surface topography (≤3–5 km), we estimate the upper crustal, lower crustal, and mantle lithospheric viscosities in the ranges 1021–1023Pa s, 1019–1021Pa s, and 1021–1023Pa s, respectively.
Ecosystem behavior at Bermuda Station “S” and ocean weather station “India”: A general circulation model and observational analysis
Authors: Fasham M. J. R. , Sarmiento J. L. , Slater R. D. , Ducklow H. W. , Williams R.
Published: February 2008

A model of biological production in the euphotic zone of the North Atlantic has been developed by coupling a seven‐compartment nitrogen‐based ecosystem model with a three‐dimensional seasonal general circulation model. The predicted seasonal cycles of phytoplankton, Zooplankton, bacteria, nitrate, ammonium, primary production, and particle flux have been compared to data from Bermuda Station “S” and Ocean Weather Station “India”. Bearing in mind the simplicity of the model and the paucity of data, the results are encouraging. However, deficiencies in the physical model lead to winter nitrate values at Bermuda being overestimated, and at both positions the predicted magnitude of the spring phytoplankton bloom was too high. Simulations were carried out with different detrital sinking rates and and it was found that a sinking rate of 10 m d−1 gave the best agreement with observations. The model was used to investigate the factors affecting the population growth of phytoplankton and it was found that the model supported the generally held theory that the spring bloom is initiated by the cessation of physical mixing. After the bloom, phytoplankton are controlled by Zooplankton grazing. At Ocean Weather Station “India” the model reproduced the observed high summer nitrate levels and suggested that these high values are caused by a combination of high vertical nitrate transport, ammonium inhibition of nitrate uptake, and Zooplankton grazing control. The model demonstrated the critical importance of Zooplankton in understanding ecosystem dynamics and highlights the need for more observational data on the seasonal cycles of Zooplankton biomass and growth rates.
Jovian Bremsstrahlung X rays: A Ulysses prediction
Authors: Waite J. H. , Boice D. C. , Hurley K. C. , Stern S. A. , Sommer M.
Published: February 2008

The Jovian aurora is the most powerful planetary aurora in the solar system; to date, however, it has not been possible to establish conclusively which mechanisms are involved in the excitation of the auroral emissions that have been observed at ultraviolet, infrared, and soft X ray wavelengths. Precipitation of Iogenic heavy sulfur and oxygen ions, downward acceleration of electrons along Birkeland currents, and a combination of both of these mechanisms have all been proposed to account for the observed auroral emissions. Modeling results reported here show that precipitating auroral electrons with sufficient energy to be consistent with the Voyager UVS observations will produce bremsstrahlung X rays with sufficient energy and intensity to be detected by the Solar Flare X Ray and Cosmic Ray Burst Instrument (GRB) on board the Ulysses spacecraft The detection of such bremsstrahlung X rays at Jupiter would provide strong evidence for the electron precipitation mechanism, although it would not rule out the possibility of some heavy ion involvement, and would thus make a significant contribution toward solving the mystery of the Jovian aurora.
Heat and fluid flux through sediment on the western flank of the Mid‐Atlantic Ridge: A hydrogeological study of North Pond
Authors: Langseth Marcus G. , Becker Keir , Von Herzen Richard P. , Schultheiss Peter
Published: February 2008

A comprehensive survey of heat flow, sediment thickness and bathymetry in a large intermontane sediment pond on the western flank of the Mid‐Atlantic Ridge (North Pond) shows that only 20 to 25% of the heat escaping from the lithosphere flows through the sediments in the pond even though they completely cover a 70 km2 area of the seafloor. Three in situ pore‐pressure gradient measurements gave values that were negative relative to hydrostatic, indicating that there is drawdown of water through the sediment at rates of 1 to 5 mm/yr. North Pond is a recharge zone for hydrothermal circulation that is probably driven by lateral pressure gradients produced by topographic relief.
Bursts of transverse ion acceleration at rocket altitudes
Authors: Arnoldy R. L. , Lynch K. A. , Kintner P. M. , Vago J. , Chesney S. , Moore T. E. , Pollock C. J.
Published: February 2008

High time resolution ion mass spectrometer distribution function measurements and wave data from a sounding rocket flight over an aurora have revealed the fine structure of the transverse ion acceleration mechanism in the upper ionosphere. The transversely accelerated ion (TAI) events can occur in a volume with a cross‐field dimension as small as several tens of meters and thus appear as 50–100 ms ion bursts due to the rocket payload motion. Bulk heating to a characteristic energy of several eV and tail heating in the direction perpendicular to B of a few percent of ambient ions to a characteristic energy the order of 10 eV occur for both hydrogen and oxygen ions. The TAI at 90° pitch angle occur in localized regions of intense lower hybrid waves and in regions of density depletion. On close examination of the correlation between the wave bursts and the TAI it is believed that the waves produce the ion acceleration. The TAI occur during periods of field‐aligned auroral electron bursts. Finally, near 1000 km altitude they occur about once every second. If the event presented here is considered average, the flux of TAI oxygen ions above 7 eV could account for the ion conic fluxes measured by the ISIS spacecraft.
Fractal analysis of fault systems in Japan and the Philippines
Authors: Matsumoto Naoko , Yomogida Kiyoshi , Honda Satoru
Published: February 2008

Complexity of fault systems in Japan and the Philippines is quantitatively measured using fractal dimension. The areas studied are the Median Tectonic Line, Izu, Unzen on the Japanese Islands, and the fault system yielded by the Philippine earthquake which occurred on July 16, 1990. Results are summarized as follows: Fractal dimensions along the Median Tectonic Line vary between 1 and 1.3. The Unzen area gives the highest fractal dimension (1.4) of all the areas studied, which implies that the fault system there is the most complex. Fractal dimension of the fault system associated with the Philippine earthquake is smaller than 1. It can be interpreted that this fault system is almost one‐dimensional, with truncated by numerous gaps of various sizes.
Postseismic coastal uplift in southern Chile
Authors: Barrientos Sergio E. , Plafker George , Lorca Emilio
Published: February 2008

Tide gage records at Puerto Montt, referenced to a mareograph in Talcahuano, indicate a large (at least 75 cm) postseismic uplift of the region following the 1960 Mw = 9.5 event. Field observations carried out in 1989 at the same locations of previous measurements in 1968 are consistent with tide gage records. The postseismic elevation changes are modeled as the result of propagating creep on the downdip extension of the coseismic fault. For a 30° E fault dip, minimum square error indicates a fault creep velocity of 4–6 km/yr and slip amplitude of 3–5 m.
Accelerating seismic moment release and outer‐rise compression: Possible precursors to the next great earthquake in the Alaska Peninsula region
Authors: Jaumé Steven C. , Estabrook Charles H.
Published: February 2008

The moment release rate in the Kodiak Island (KI) segment increased prior to the great 1964 Prince William Sound earthquake (MW = 9.2). Starting in 1983 the moment release rate in the Shumagin Island (SI) segment shows a similar increase. In July 1990, an outer‐rise reverse earthquake showed arc‐normal compression at a depth of 42 km seaward of the Alaska Peninsula (AP) segment. Because accelerating moment release and arc‐normal compression have both been proposed as precursors to large and great earthquakes, we suggest this is evidence that the SI‐AP region is nearing the end of the seismic cycle between large thrust earthquakes.
Interrelation between induced seismic instabilities and complex geological structure
Authors: Guyoton Fabrice , Grasso Jean‐Robert , Volant Philippe
Published: February 2008

From 1982 to 1989, more than 520 local seismic events were recorded by a permanent network of 9 telemetered stations over an active gas field (Lacq, France). The geological data of 46 boreholes coupled to several tens of kilometers of seismic profiles, concentrated in a small volume of 15 × 15 × 10 km3, allow the development of a very precise velocity structure, exhibiting a dome geometry limited by faulted strips. The discretized velocity model includes almost 20000 blocks with 500 m × 500 m × 250 m minimum dimensions. A relocation technique using this a priori detailed 3D velocity model allows precise locations of induced earthquakes. 351 relocated hypocenters show that of the seismic activity concentrated on geometrical discontinuities of the local dome structure. The locations of seismic events are correlated with geomechanical layers of the structure. Spatial and temporal migration of seismic ruptures mimics the different permeability rings of the reservoir which are progressively depleted by gas extraction. Most of these events are at present confined close to major thrust planes which limit the dome structure laterally, and in depth onto preexisting faults in the basement below the gas field. The occurence of these deep clusters demonstrates that fluid manipulation in the sedimentary covers can activate preexisting basement faults. This result changes previous assessments of local seismic risk and provides new insights into fault mechanisms in areas with complex geological structure.
Propagating rift pseudofaults ‐ Zones of crustal underplating imaged by multichannel seismic reflection data
Authors: Hasselgren E. , Clowes R. M. , Calvert A. J.
Published: February 2008

Two multichannel seismic reflection lines recorded over the northern Juan de Fuca plate off western Canada provide images of the crustal structure of three pseudofaults, the traces of propagating rifts. Anomalous reflectivity, including both subhorizontal and dipping events at times below the normal crust‐mantle transition, is prevalent in the region of the pseudofaults. Although the crustal thickness elsewhere on the lines varies by only about 10%, crust associated with the pseudofaults is as much as 30% thicker than average. This may be due to an increase in thickness of the interpreted oceanic crustal layer 3B or crustal underplating. The results indicate that magma supply at propagating rifts may at times be large, perhaps due to the effects of nearby hotspots or convective partial melting associated with the initiation of rifting.
Ulysses observations of escaping VLF emissions from Jupiter
Authors: Kaiser M. L. , Desch M. D. , Farrell W. M. , MacDowall R. J. , Stone R. G. , Lecacheux A. , Pedersen B.‐M. , Zarka P.
Published: February 2008

The Ulysses URAP experiment has detected Jovian radio emissions in the VLF range at distances from Jupiter in excess of 1.5 A.U. The URAP observations represent the first synoptic observations of Jupiter in the VLF band, 3 to 30 kHz. In this band lie the low‐frequency extent of the bKOM emission, the escaping continuum emission, and the Jovian type IIIs. Initial results indicate that the continuum varies in frequency with the solar wind ram pressure at Jupiter, whereas, the Jovian type IIIs appear to be controlled to some extent by the planetary rotation, often appearing when system III longitude 100° faces the spacecraft.
Polar cap convection for Bz northward
Authors: Crowley G. , Cannon P. S. , Dozois C. G. , Reinisch B. W. , Buchau J.
Published: February 2008

The Digisonde at Qanaq, Greenland (87°Λ) measures the ionospheric convection velocity in the central polar cap. The average local time variation of the velocity for Bz northward under various By conditions is presented. The nightside drifts for Bz northward tend to be antisunward, and resemble those which occur for southward IMF, as pointed out by Heppner and Maynard (1987). However, it is difficult to reconcile the observed diurnal drift variation with the Heppner‐Maynard distorted two‐cell model. Modified forms of the Potemra et al. (1984) four cell model offer a more plausible framework in which to understand the Qanaq data. The polar cap cells are relatively small, and are displaced towards the dayside.
IMF draping around the Geotail: IMP 8 observations
Authors: Kaymaz Zerefsan , Siscoe George , Luhmann Janet G.
Published: February 2008

This paper gives maps of magnetosheath magnetic field lines in a roughly 12RE thick annulus circling the tail approximately 30RE downwind from Earth. There are maps for northward and southward IMF and for quasi‐equatorial IMF (the usual case). The maps are based on IMP 8 data taken during the 127 orbits (four years) when ISEE 3 measured the upstream IMF. In these four years, IMP 8's orbit swept the mapped annulus eight times. The maps project the field onto a plane perpendicular to the sun‐earth line, after correcting for solar wind aberration and tail flaring. Each shows draping around the tail: The field enters from one side, bifurcates at the tail boundary, “flows” around in both directions, rejoins at the opposite side, and exits. A new finding is that, contrary to expectations, the draping pattern is rotated relative to the plane formed by the IMF and the aberrated x‐axis. For example, it is rotated relative to the equatorial plane when the IMF lies in the equatorial plane. The degree of rotation varies from essentially zero for strongly northward and southward IMF to a peak ∼17° for moderately southward IMF. The sense of rotation is clockwise for toward IMF sectors and counterclockwise for away IMF sectors—the same as the dayside merging line. We also find that the tail is fatter and the magnetosheath field less ordered for strongly southward IMF than for strongly northward IMF. The new findings are understandable in terms of dayside magnetic merging.
Electron temperatures determined by tristatic plasma‐line observations with the EISCAT UHF incoherent scatter radar
Authors: Kirkwood S. , Björnå N.
Published: February 2008

Tristatic observations of photoelectron‐enhanced plasma‐lines with the EISCAT UHF incoherent scatter radar are presented. It is shown that electron temperatures can be derived from these measurements with a time resolution of the order of a minute and a statistical accuracy of 50–100 K.
Sub‐daily resolution of Earth rotation variations wtth global positioning system measurements
Authors: Lichten Stephen M. , Marcus Steven L. , Dickey Jean O.
Published: February 2008

Data from a worldwide Global Positioning System (GPS) tracking experiment have been used to determine variations in Earth rotation (UT1‐UTC) over a time period of three weeks. Kalman filtering and smoothing enabled changes in UT1‐UTC over intervals of 2 to 24 hrs to be detected with the GPS data. Internal consistency checks and comparisons with other solutions from very long baseline interferometry (VLBI) and satellite laser ranging (SLR) indicate that the GPS UT1‐UTC estimates are accurate to about 2 cm. Comparison of GPS‐estimated variations in UT1‐UTC with 2‐hr time resolution over 4 days with predicted variations computed from diurnal and semi‐diurnal oceanic tidal contributions strongly suggests that the observed periodic sub‐daily variations ∼0.1 msec (5 cm) are largely of tidal origin.
Structure in the UV nightglow observed from low Earth orbit
Authors: Ross M. N. , Christensen A. B. , Meng C.‐I. , Carbary J. F.
Published: February 2008

Limb images of the low latitude UV O2 Herzberg I emission were obtained from a low Earth orbit spacecraft in early 1988. The layer displays patchy, sometimes horizontally periodic, spatial variability on scales of tens of km with amplitude up to 20%. We interpret periodic wavelike features in terms of perturbations associated with gravity wave propagation through the layer. The putative waves are shown to have horizontal wavelength about 15 km, similar vertical wavelength, and temperature oscillation roughly equal to or exceeding the observed emission perturbation.
The effect of the shock of 15:43 UT March 23, 1991 on 50 keV to 5 MeV ions at Ulysses
Authors: Armstrong T. P. , Choo T. H. , Roelof E. C. , Simnett G. M. , Sarris E. T.
Published: February 2008

The intensities, angular distributions, and energy spectra of 50 keV to 5 MeV ions are examined in the several hour time interval when an interplanetary shock passed the Ulysses spacecraft. The increase in intensity, evolution of pitch angle distribution from upstream flow away from the shock to a post‐shock “pancake” distribution, the earlier arrival of more energetic particles, and the presence of non‐gyrotropic effects at the time of shock passage all can be understood in terms of kinematical behavior of the particles crossing the shock.
Laser measurements of ozone absorption cross sections in the Chappuis Band
Authors: Anderson Stuart M. , Mauersberger Konrad
Published: February 2008

We have developed a sensitive spectrometer which exploits several He‐Ne laser transitions in the visible for precise, high resolution measurements of Chappuis band ozone absorption cross sections at room temperature. An overall, uncertainty of better than 1% has been achieved through a combination of transducer calibrations and an experimental procedure which unambiguously determines the impurity content of each ozone sample. The cross section near 602.5 nm is (5.16±0.03) × 10−21 cm2/molecule. Our results compare favorably with those from most previous studies in the visible range, although some are clearly lower than this consensus probably due to errors in ozone density measurements.
Modelling the influence of global sea surface temperatures on the variability and predictability of seasonal Sahel rainfall
Authors: Rowell David P. , Folland Chris K. , Maskell Kathy , Owen John A. , Ward M. Neil
Published: February 2008

An atmospheric general circulation model has been forced by observed global sea surface temperature data from ten individual years. The results support the idea that oceanic effects tend to dominate the forcing of both interannual and interdecadal variability of Sahel rainfall, with different local atmospheric mechanisms dominating in different years. Further experiments indicate that skillful predictions of July–September Sahel rainfall are possible using the persistence of June SST anomalies.