bluuebunny/crossref_metadata_2025 huggingface dataset:
Complementary roles of orbital insolation and North Atlantic Deep Water during Late Pleistocene interglacials
Authors: Crowley Thomas J. , Kim Kwang‐Yul
Published: February 2008

A long‐standing dilemma of the Milankovitch hypothesis involves the observation that the Holocene deglaciation was comparable in extent to previous late Pleistocene interglacials even though insolation forcing was less. In this paper we propose an explanation that is based on an observed complementary relationship between eccentricity and North Atlantic Deep Water (NADW) production rates. A δ13C record from the South Atlantic indicates that NADW production rates are high when eccentricity is low (stages 1, 11), and vice versa. For the Holocene, the inferred stronger thermohaline circulation injects approximately the same heat into the high latitude North Atlantic (∼9 W/m²) as the insolation differences between the early Holocene and last interglacial peak. We utilize an energy balance model to calculate that the excess heat from the Holocene thermohaline increase can explain at least 50–65% and 100% of the energy budget “shortfall” from Milankovitch forcing over the Laurentide and Fennoscandian ice sheets, respectively. We suggest that the observed complementary relationship between Milankovitch and NADW reflects a coupling due to a “reverse monsoonal” effect over the North Atlantic. During times of high eccentricity and strong land‐sea contrast, enhanced heating over land results in increased subsidence over the ocean, which causes circulation and precipitation changes. These processes could lower ocean salinities and decrease thermohaline circulation. Thus deglaciation can progress through either mechanism, with the total heat balance for each interglacial being approximately the same. However, the combined effect of increased insolation and reduced thermohaline circulation for the last interglacial yields slightly warmer (∼1.0°C) temperatures in mid‐ and high‐latitude northern hemisphere land areas than in the Holocene. This result is approximately in line with geologic data from these regions.
River Fluxes of Dissolved Silica to the Ocean Were Higher during Glacials: Ge/Si In Diatoms, Rivers, and Oceans
Authors: Froelich P. N. , Blanc V. , Mortlock R. A. , Chillrud S. N. , Dunstan W. , Udomkit A. , Peng T.‐H.
Published: February 2008

Two centric marine diatom species,Thalassiosira oceanicaandThalassiosira antarctica, were grown in batch cultures to determine the incorporation of germanium (Ge) and silicon (Si) into siliceous shells (opal). The results were modeled as Ge/Si “isotope” fractionation. During exponential growth, diatoms take up and incorporate Ge/Si from solution without major discrimination against Ge. During stationary phase growth near silica limitation, the Antarctic species (T. antarctica) discriminates slightly against Ge but integrated (Ge/Si)opalproduced over the latter portion of the growth cycle is indistinguishable from the initial solution ratio. These results confirm experiments using radioactive68Ge that showed absence of fractionation during diatom silica uptake (Azam and Volcani, 1981), in contrast to two‐box ocean models that invoke 50% Ge discrimination by diatoms to explain the observed “excess” surface ocean germanium concentration (Murnane and Stallard, 1988; Froelich et al., 1989) and late Pleistocene ocean sediment (Ge/Si)opalrecords (Mortlock et al., 1991). Runs of a 10‐box ocean Ge and Si model (PANDORA) with 50% discrimination reproduce the excess surface ocean Ge but introduces curvature into the deep ocean Ge versus Si relationship that is not observed in the oceans. Thus 50% fractionation is not supported by either cultures or models. If diatoms do not fractionate Ge/Si, then late Pleistocene (Ge/Si)opalvariations in piston cores are caused not by changes in local biosiliceous production and silica utilization (Mortlock et al, 1991) but rather by whole ocean changes in (Ge/Si)seawater. The marine (Ge/Si)opalrecord of the last 450 kyr can be modeled as transient oceanic responses to instantaneous continental climate transitions consistent with the chemical weathering model of Murnane and Stallard (1990). Glacial periods are characterized by lower continental weathering intensity, lower (Ge/Si)riv, and two fold higher dissolved silica river fluxes. Marine (Ge/Si)opalrecords thus contain a history of ocean silica chemistry that reflect rapid global changes in continental weathering.
The Cenozoic Record of Continental Mineral Deposition on Broken and Ninetyeast Ridges, Indian Ocean: Southern African Aridity and Sediment Delivery from the Himalayas
Authors: Hovan Steven A. , Rea David K.
Published: February 2008

The mineral component of pelagic sediments recovered from the Indian Ocean provides both a history of eolian deposition related to climatic changes in southern Africa and a record of terrigenous input related to sediment delivery from the Himalayas. A composite Cenozoic dust flux record from four sites in the central Indian Ocean is used to define the evolution of the Kalahari and Namib desert source regions. The overall record of dust input is one of very low flux for much of the Cenozoic indicating a long history of climate stability and regional hyperaridity. The most significant reduction in dust flux occurred near the Paleocene/Eocene boundary and is interpreted as a shift from semiarid climates during the Paleocene to more arid conditions in the early Eocene. Further aridification is recorded as stepwise reductions in the input of dust material which occur from about 35 to 40 Ma, 27 to 32 Ma, and 13 to 15 Ma and correlate to significant enrichments in benthic foraminifer δ18O values. The mineral flux in sediments from the northern Indian Ocean, site 758, records changes in the terrigenous input apparently related to the erosion of the Himalayas and indicates a rapid late Cenozoic uplift history. Three major pulses of increased terrigeneous sediment flux are inferred from the depositional record. The initial increase began at about 9.5 Ma and continued for roughly 1.0 million years. A second pulse with approximately the same magnitude occurred from about 7.0 to 5.6 Ma. The largest pulse of enhanced terrigenous influx occurred during the Pliocene from about 3.9 to 2.0 Ma when average flux values were severalfold greater than at any other time in the Cenozoic.
Determination of δ18O of Seawater in the Deep Ocean during the Last Glacial Maximum
Authors: Schrag D. P. , DePaolo D. J.
Published: February 2008

We present a method for determining the δ18O of seawater in the deep ocean during the last glacial maximum from the measured δ18O values of deep sea pore fluids. Using data from Deep Sea Drilling Project (DSDP) site 576 in the Western Pacific, this method yields a glacial to interglacial change in δ18Osw of 1.0±0.25‰. This value for Δδ18Osw is the first direct measurement of deep ocean δ18O for the last glacial maximum and avoids the problems of spatial and temporal variability of the δ18O of surface water implicit in previous determinations. More precise, higher‐resolution pore fluid measurements are required to improve this determination.
Derivation of phase statistics from the Mueller matrix
Authors: Sarabandi K.
Published: February 2008

To answer the question of what radar polarimetry has to offer to the remote sensing of random media, statistics of the phase difference of the scattering matrix elements must be studied. Recent polarimetric measurements of rough surfaces have indicated that the statistical parameters of the phase difference (mean, standard deviation, etc.) are very sensitive to some of the physical parameters. In this paper the probability density function of the phase differences is derived from the Mueller matrix, assuming that the elements of the scattering matrix are jointly Gaussian. It is shown that the probability density functions of the copolarized and cross‐polarized phase differences are similar in form, and each can be determined by two parameters (α and ς) completely. The expressions for the probability density functions are verified by comparing the histograms, the mean, and the standard deviations of phase differences derived directly from polarimetric measurements of a variety of rough surfaces to the probability density function, its mean, and standard deviation derived from the Mueller matrices of the same data. The expressions for the probability density functions are of special interest for noncoherent polarimetric radars and noncoherent polarimetric models for random media such as vector radiative transfer.
A numerical assessment of rough surface scattering theories: Horizontal polarization
Authors: Rodríguez Ernesto , Kim Yunjin , Durden Stephen L.
Published: February 2008

We present a numerical evaluation of the regime of validity for various rough surface scattering theories against numerical results obtained by using the method of moments. The theories are the small perturbation method, the Kirchhoff approximation, the momentum transfer expansion, the two‐scale expansion, and a new theory, which we call the unified perturbation method. Both the field and phase perturbation expansions for these theories are examined. It is outlined how all these theories can be derived in a unified manner starting with the extinction theorem. We consider the contribution of each theory up to second order in the perturbation expansion for the surface current. The rough surfaces considered are oceanlike surfaces, which exhibit height power law spectra.
Scattering from a conducting cylinder above a lossy medium of sinusoidal interface
Authors: Vazouras C. N. , Cottis P. G. , Kanellopoulos J. D.
Published: February 2008

The problem of scattering from a conducting cylinder above a lossy medium having a sinusoidal profile interface is investigated by combining an integral equation approach with the extended boundary condition method. The incident transverse magnetic electric field and the Green function of the problem are determined by applying the extended boundary condition method. The application of the method of moments to the integral equation over the cross section of the scatterer results in an infinite linear set of equations for the unknown expansion coefficients of the electric field inside the scatterer. This infinite set is truncated and solved numerically. Finally, the far field scattered in free space is evaluated by employing the steepest descent approximation, and several interesting conclusions concerning the influence of the sinusoidal profile on the scattered field are deduced.
Coherent radar interferometry of vertical irregularity structures in the auroral E region
Authors: Ierkic H. M. , Haldoupis C. , Moorcroft D. R. , Nielsen E.
Published: February 2008

In a new experiment a coherent radar has been operated as an interferometer in order to measure the vertical variations of electron density fluctuations in the auroral E region. This was accomplished by placing an outrigger array of yagis in front of the permanent receiving array at the Scandinavian Twin Auroral Radar Experiment radar site in Malvik, Norway. The radar was operated in a mode that allowed the measurement of cross‐correlation coefficients between the outrigger antenna and several beams of the receiving array for 25 consecutive backscatter ranges. This provided, for the first time, the capability of studying the backscatter altitude and the dynamic height variations of 1‐m auroral irregularities in the E region. In addition, autocorrelations for a number of lags in each of the beams were determined. In this paper we discuss the technique and several experimental details and present results obtained in both the westward and eastward electrojets. We conclude that useful information on relative backscatter altitudes can be obtained from midradar ranges during spatially homogeneous electrojet conditions. Preliminary results show the mean backscatter layer altitude and width undergoing regular variations which often are closely related to concurrent changes observed in the echo intensity and irregularity phase velocity.
C and L band transionospheric scintillation experiment: Some results for applications to satellite radio systems
Authors: Banerjee P. K. , Dabas R. S. , Reddy B. M.
Published: February 2008

Satellite radio systems suffer loss of information in a wide band of frequencies during periods of intense ionospheric scintillation activity when the received signal undergoes rapid and deep fading. In order to assess the problem and to determine a proper fade margin for an Earth‐space link, system engineers require information on signal statistics as well as on the morphological aspects of scintillations. Our observations near the northern boundary of the equatorial scintillation belt at (18.9° N geomagnetic) within the Indian zone show that the signal at 4/1.5 Ghz has faded often beyond 10 dB pp, and at times beyond 24 dB pp at 4 Ghz during equinoctial months of high solar activity during the years of 1989–1990. In addition to the morphology at 4 Ghz, information on signal statistics, such as cumulative amplitude distribution function, fade rate distribution, and signal reliability for different message lengths for some events of scintillations, both at C and L band, has been presented. The theoretical Nakagami m distribution has been found to be the best for describing various levels of fade. Autocorrelation and power‐spectrum analysis have been used to estimate average fade rates and ground correlation distances. Performance evaluation of satellite Earth terminals using small antennas has been carried out to show the vulnerability of the system in the hostile ionospheric environment notwithstanding the advanced modulation systems being employed.
Whispering gallery effects in the troposphere
Authors: Hitney Herbert V.
Published: February 2008

Experimental data that recorded higher‐than‐expected signals at 3087.7 MHz far beyond the horizon in the presence of an elevated duct are examined and compared to results from the radio physical optics (RPO) propagation model. RPO is a range‐dependent hybrid model that combines ray optics and parabolic equation methods. Previous modeling of this same case study using waveguide methods for both the measured elevated duct and hypothetical evaporation ducts has been disappointing. However, when the elevated duct is allowed to rise slowly with increasing range, the RPO results closely match the observed signal levels, indicating that weakly attenuated Earth‐detached, or whispering gallery, modes were the dominant propagation mechanism.
Acceleration methods for the iterative solution of electromagnetic scattering problems
Authors: Murphy W. D. , Rokhlin V. , Vassiliou M. S.
Published: February 2008

We present a simple but effective technique for accelerating the convergence of iterative methods in the solution of electromagnetic scattering problems described by a second‐kind integral equation (SKIE). We call the technique “complexification and extrapolation,” or simply “complexification.” It is based on the mathematical principle of limiting absorption, and it alleviates the difficulties arising from the interior resonances of this SKIE, thus allowing the efficient solution of scattering from electrically large objects. The technique involves introducing an imaginary part to the real wavenumber and solving the problem, then repeating with a different imaginary part and extrapolating the solutions linearly back to the real axis. For higher‐order extrapolations we use additional complex wavenumbers. We have tested the method on a number of closed two‐dimensional conducting scatterers, using this SKIE discretized by Nyström's method and solved by the fast multipole method. We use a variant of the conjugate gradient (CG) method that we call the pseudoconjugate gradient (PCG) method. The PCG method as we employ it performs only 1.2 matrix vector products on average per iteration, as opposed to two for the standard CG. Complexification gives excellent results. Solutions are fast and accurate. The condition number of the discrete matrix is asymptotically bounded for a given problem as the number of points per wavelength increases. The empirical evidence we have gathered thus far also suggests that the condition number is essentially asymptotically bounded as the electrical size of the scatterer increases, holding the number of points per wavelength fixed. Thus the technique has great potential in the solution of scattering from electrically large objects. Note that the technique of complexification is not limited to the fast multipole method and should be of broad applicability in the numerical solution of scattering problems.
Distribution of underdense meteor trail durations and duty cycle and applications to meteor scatter communication system design
Authors: Ralston W. T. , Weitzen J. A. , Ostergaard J. C.
Published: February 2008

Analysis of data from recent experiments leads to the observation that the distribution of underdense meteor trail durations differs from classical predictions. A new theory for the distribution of underdense meteor trail durations has been developed based upon the assumption of a normal height distribution and lognormal amplitude distribution which leads to a lognormal distribution of the trail durations. It is shown that this model provides a better fit to observed data than the classic model. This model, applied in conjunction with previously reported work, can be used to provide improved predictions of the performance of meteor scatter communications systems.
Nappe tectonics, extension, and metamorphic evolution in the Indian Tethys Himalaya (Higher HImalaya, SE Zanskar and NW Lahul)
Authors: Spring Laurent , Crespo‐Blanc Anne
Published: February 2008

In the southern part of the Indian Tethys Himalaya between SE Zanskar and NW Lahul, nappe tectonics with transport toward the WSW during the main deformation phase has been ascertained. If the stratigraphy of the different units considered as nappes is combined, it results in a composite section ranging from lower Cambrian to Middle Cretaceous. A metamorphism of amphibolite facies in the lowest unit is associated with the nappe stacking. The Lower Miocene cooling ages of metamorphic biotite and muscovite suggest that the nappe emplacement starts at the Oligocene, or at the Oligocene‐Eocene boundary. After the compressional phases, an extension provokes the reactivation of older main thrusts as normal fault and the formation of a steeply dipping normal fault. This interpretation is based on detailed mapping.
Geology of the western flank of the Coast Mountains between Cape Fanshaw and Taku Inlet, southeastern Alaska
Authors: Gehrels George E. , McClelland William C. , Samson Scott D. , Patchett P. Jonathan , Orchard Michael J.
Published: February 2008

The western flank of the Coast Mountains batholith between Cape Fanshaw and Taku Inlet is underlain primarily by Jura‐Cretaceous strata of the Gravina belt; pre‐Permian(?), Permian, and Triassic strata of the Taku terrane; and mid‐Proterozoic(?) to upper Paleozoic rocks of continental margin affinity. The continental margin rocks include mid‐Proterozoic(?) to lower Paleozoic(?) quartzite and marble of the Tracy Arm assemblage; mid‐Paleozoic metavolcanic and subordinate metasedimentary rocks of the Endicott Arm assemblage; and upper Paleozoic quartz‐rich metaturbidites and metaconglomerate of the Port Houghton assemblage. We suggest that these three assemblages are correlative with components of the Yukon‐Tanana terrane, which underlies a large region of Yukon and eastern Alaska. Rocks of the Gravina belt, Taku terrane, and Yukon‐Tanana terrane are juxtaposed along west‐vergent thrust faults of mid‐Cretaceous age and are internally deformed and disrupted along latest Cretaceous to early Eocene dip‐slip and possibly strike‐slip shear zones. These rocks and structures, together with mid‐Cretaceous to Eocene plutons of the Coast Mountains batholith, separate rocks of the Alexander‐Wrangellia terrane to the west from rocks of the Stikine terrane to the east. Mid‐Cretaceous thrust faults in the area belong to a system of thrusts that form the inboard margin of the Alexander‐Wrangellia terrane from central Alaska to northwestern Washington. The continental margin rocks in the northern Coast Mountains may be part of the in situ North American margin that has been overthrust by the Stikine and adjacent terranes. Alternatively, these rocks may have (1) rifted from and then returned to the North American margin, (2) moved >800 km along left‐lateral or right‐lateral faults from elsewhere along the North American margin, or (3) originated near a continent other than North America.
Geochemical cycles in an ocean general circulation model. Preindustrial tracer distributions
Authors: Maier‐Reimer Ernst
Published: February 2008

A state‐of‐the‐art report is given of the Hamburg model of the oceanic carbon cycle. The model advects geochemical tracers important to the carbon cycle by the currents of a general circulation model. The geochemical cycling is driven by a Michaelis‐Menten type production kinetics. The model is an extension of the Bacastow and Maier‐Reimer (1990) model. It is based on a more realistic current field and includes a mechanism of lysocline‐sediment interaction. Principal variables are ∑CO2, alkalinity, phosphate, oxygen, and silicate. The carbon variables are defined for 12C, 13C, and 14C separately. In addition to these carbon isotopes, 39A and δ18O of dissolved oxygen are predicted. The model predicts realistic global patterns of tracer distribution. In the equatorial eastern Pacific, however, the structures are exaggerated due to a strong upwelling which is a common feature of coarse resolution models of the general circulation of the ocean.
Methane consumption and carbon dioxide emission in tallgrass prairie: Effects of biomass burning and conversion to agriculture
Authors: Tate Cathy M. , Striegl Robert G.
Published: February 2008

Consumption of atmospheric methane and emission of carbon dioxide by soils were measured on unburned and annually burned tallgrass prairie and on adjacent wheat and sorghum agricultural plots in Kansas. Profiles of CH4 and CO2 concentration with soil depth were also measured. Overall patterns of CH4 consumption by soils varied temporally, with soil depth and land use. Mean CH4 consumption for the 200‐day sampling period was −1.02 mg CH4 m−2 d−1 (SE=0.13, n=41) for burned prairie, −0.63 (SE=0.09, n=45) for unburned prairie, −0.85 (SE=0.20, n=36) for wheat, and −0.45 (SE=0.08, n=40) for sorghum. Less than 20 % of the variance in CH4 consumption was explained by soil temperature and/or moisture content. Overall patterns of CO2 emission from prairie and agricultural soils varied temporally, but not among land use. Mean CO2 emission for the 200‐day sampling period was 15.7 g CO2 m−2 d−1 (SE=1.8, n=41) for burned prairie, 14.5 (SE=1.3, n=45) for unburned prairie, 13.9 (SE=2.1, n=36) for wheat, and 10.3 (SE=2.1, n=40) for sorghum. More than 70% of the variance in prairie CO2 emission rate was explained by soil temperature and moisture. Crop management practices influenced the timing of CO2 emission from agricultural plots but not the net annual rate of emission. Methane concentrations generally decreased and CO2 concentrations increased with soil depth, and the magnitude of CH4 and CO2 flux generally increased with increased magnitude of the soil gas concentration gradient. Fertilization of agricultural fields had no measured effect on CH4 or CO2 flux or on soil gas concentrations.
Temporal variations of the Earth's gravitational field from satellite laser ranging to Lageos
Authors: Nerem R. S. , Chao B. F. , Au A. Y. , Chan J. C. , Klosko S. M. , Pavlis N. K. , Williamson R. G.
Published: February 2008

We have estimated monthly values of the J2 and J3 Earth gravitational coefficients using LAGEOS satellite laser ranging (SLR) data collected between 1980 and 1989. For the same time period, we have also computed corresponding estimates of the variations in these coefficients caused by atmospheric mass redistribution using surface atmospheric pressure estimates from the European Center for Medium Range Weather Forecasts (ECMWF). These data were processed both with and without a correction for the “inverted barometer effect,” the ocean's isostatic response to atmospheric loading. While the estimated zonal harmonics in the orbit analysis accommodate gravitational changes at a reduced level arising from all other higher degree zonal effects, the LAGEOS and atmospheric time series for J2 compare quite well and it appears that the non‐secular variation in J2 can be largely attributed to the redistribution of the atmospheric mass. While the observed changes in the “effective” J3 parameters are not well predicted by the third degree zonal harmonic changes in the atmosphere, both odd zonal time series display strong seasonality. The LAGEOS J3 estimates are very sensitive to as yet unmodeled forces acting on the satellite and these effects must be better understood before determining the dominant geophysical signals contributing to the estimate of this time series.
Chlorine catalyzed destruction of ozone: Implications for ozone variability in the upper stratosphere
Authors: Chandra Sushil , Jackman Charles H. , Douglass Anne R. , Fleming Eric L. , Considine David B.
Published: February 2008

The annual mean and the annual amplitude of ozone have been derived from ozone measurements from the SBUV and SBUV/2 spectrometers on board the Nimbus‐7 and NOAA‐11 satellites. These values differ significantly from values calculated using a two‐dimensional model of stratospheric photochemistry and dynamics with standard chemistry. We have found that the differences between the calculated and data‐derived values are considerably improved by changing the partitioning in the Cly family to create a larger reservoir of HCl and reducing ClO. This is accomplished by including a channel for the products HCl+O2 from the reaction ClO+OH in addition to the products Cl+HO2. This partitioning also improves the agreement between the calculated and measured values of ClO/HCl ratio.
Interatomic potentials calculated from equations of state: Limitation of finite strain to moderate K′
Authors: Hofmeister Anne M.
Published: February 2008

Conditions under which equations of state (EOS) are valid are investigated by calculating implicit interatomic potentials for fixed structures. Third‐order Eularian finite strain yields physically realistic potentials only for ∼3.8 < K′o < B. The upper limit B depends on the size of the long range attractive potential relative to that of the repulsive potential, and is ∼6 for neutral solids or incompressible materials (e.g., argon or MgO), or ∼8 for ionic or soft solids (e.g., NaCl). Thus, 3rd order yields reasonable interatomic potentials for the range K′o commonly occupies. Potentials for 4th order are unrealistic if K″o varies by more than a few % from the 3rd order value. Vinet, Ferrante, Rose and Smith's EOS should be used instead for materials with high K′o (e.g., gases or liquids) because it yields valid potentials for all values of the elastic parameters.
Non‐Newtonian flow (through porous media): A lattice‐Boltzmann method
Authors: Aharonov Einat , Rothman Daniel H.
Published: February 2008

We introduce a new two‐dimensional microscopic model for the simulation of non‐Newtonian fluids. The model is based on the recently introduced lattice‐gas and lattice‐Boltzmann models of fluid dynamics, which simulate Newtonian fluids by simple interactions on the particle level. The model has the advantage of easy treatment of complex boundaries and multiphase fluids. We use the new model to study non‐Newtonian flow in porous media, and find that flux is related to force by a simple scaling law.
Observations of wavelength and convection of electron cyclotron harmonics
Authors: Paranicas Christopher
Published: February 2008

In this report we will discuss recent determinations of wavelength and convection of Electron Cyclotron Harmonic (ECH) emissions as observed by the CRRES Plasma Wave Experiment (PWE). One motivation for this study is that these emissions may power the keV electron precipitation generating the diffuse aurora and so it is important to establish typical wave intensities. Problems encountered in doing this include wave attenuation because ECH wavelengths are typically close to the antenna length and the fact that it is difficult to study the effect of these waves on local electrons because of wave convection near the geomagnetic equator. We will also discuss a technique for approximating the emission wavelength with only one two‐element electric dipole antenna.
Latitudinal distributions of methane in the upper troposphere and marine boundary air over the Pacific in 1990
Authors: Matsueda Hidekazu , Inoue Hisayuki , Ishii Masao
Published: February 2008

Measurements of atmospheric methane at 11–13 km were made over the Pacific from 65°N to 65°S by two research flights (INSTAC II, February – March, 1990, and III, October, 1990). Relatively low concentrations were observed in the high latitudes, indicating intrusion of stratospheric methane at 11–13 km. Methane distributions in the tropical and subtropical regions showed north to south gradients and longitudinal gradients from west to central Pacific.

During almost the same period of the INSTAC III flight, atmospheric methane in the marine boundary air was measured on boad a research vessel in the Pacific from 35°N to 20°S. In the Northern Hemisphere, methane concentrations in the marine boundary air showed relatively higher values compared with those at 11–13 km. However, the relative methane levels between lower and upper air were reversed between 10°N and the equator, where the Intertropical Convergence Zone (ITCZ) was located. Such positive vertical gradient appearing around the ITCZ was maintained to the mid‐latitudes of the Southern Hemisphere. These results strongly suggests that methane‐rich air in the Northern Hemisphere was actively transported upward at the ITCZ and then meridionally transported through the upper troposphere into the Southern Hemisphere.
Source characteristics of the Nicaraguan Tsunami Earthquake of September 2, 1992
Authors: Ide Satoshi , Imamura Fumihiko , Yoshida Yasuhiro , Abe Katsuyuki
Published: February 2008

A large, Ms = 7.2, shallow earthquake took place off the Pacific coast of Nicaragua on September 2, 1992, and set off large tsunamis. The ground motion of the main shock was very weak along the whole Nicaraguan coast. A tsunami as high as 10 m was observed at El Transito, whereas a height of about 2 m is empirically expected for an earthquake of Ms 7.2. The tsunami magnitude Mt is estimated to be 7.9 from tide gage data. The Nicaraguan event is a tsunami earthquake which generates unusually large tsunamis for its earthquake magnitude. The source mechanism is studied in detail by using waveforms of body waves and surface waves recorded on global broadband seismographs. The possibility of single force source is ruled out from radiation patterns and the amplitude ratio of Rayleigh and Love waves. The main shock is interpreted as a low‐angle thrust fault with strike = 302°, dip = 16° and slip = 87°, the Cocos plate underthrusting beneath the Caribbean plate. The seismic moment from surface wave analysis is 3.0 × 1020 Nm (Mw = 7.6). The source dimension is estimated to be 200 km × 100 km from the aftershock area. The inversion results of body waves suggest bilateral rupture with rupture velocity as low as 1.5 km/s and duration time of about 100 s. The source process time is unusually long, indicating that the associated crustal deformation has a long time constant.
A combined parametric and conversion mechanism for upshifted stimulated electromagnetic emissions
Authors: Goodman Simon , Thidé Bo , Erukhimov Lev
Published: February 2008

We study the combined process of a three‐wave parametric decay of an oscillating electric pump field into an electron Bernstein and a lower hybrid wave, and a conversion of the pump wave off slowly growing field aligned irregularities into an upper hybrid wave which merges with the lower hybrid wave. It is found that slowly growing, upshifted stimulated electromagnetic emissions, observed experimentally for pump frequencies slightly above electron cyclotron harmonics, are well explained within this model. In the radiation spectrum there is a lower cutoff frequency which increases linearly with the cyclotron harmonic.
Geophysical inferences of thermal‐chemical structures in the lower mantle
Authors: Yuen D. A. , Cadek O. , Chopelas A. , Matyska C.
Published: February 2008

Lateral variations of the temperature field in the lower mantle have been reconstructed using new results in mineral physics and seismic tomographic data. We show that, with the application of high‐pressure experimental values of thermal expansivity and of sound velocities, the slow seismic anomalies in the lower mantle under the Pacific and Africa can be converted into realistically looking plume structures with large dimensions of 0(10³ km). The outer fringes of the plumes have an excess temperature of around 400 K. In the core of the plumes are found tongue‐like structures with extremely high thermal anomalies. These values can exceed 1200 K and are too high to be explained on the basis of thermal anomalies alone. We suggest that these major plumes in the deep mantle may be driven by both thermal and chemical buoyancies or that enhanced conductive heat‐transfer may be important there.
Estimation of seafloor roughness spectral parameters from multi‐beam sonar acoustic backscatter data: Axial Seamount, Juan De Fuca Ridge
Authors: Dziak Robert P. , Matsumoto Haruyoshi , Fox Christopher G.
Published: February 2008

A new method to estimate seafloor roughness spectra applies the surface backscatter model of Jackson et al. [1986] to multi‐beam sonar backscatter data. The use of principal components analysis, following spectral estimation, derives a single mappable index from correlated spectral parameters. This index can be mapped as a continuous field corresponding to geological observations in the area. This method allows for quantitative delineation of the neovolcanic zone and other zones of volcanic and tectonic activity from hull‐mounted sonar systems.
Most recent fall deposits of Ksudach Volcano, Kamchatka, Russia
Authors: Bursik M. , Melekestsev I. V. , Braitseva O. A.
Published: February 2008

Three of four Plinian eruptions from Ksudach Volcano are among the four largest explosive eruptions in southern Kamchatka during the past 2000 years. The earliest of the eruptions was voluminous and was accompanied by an ignimbrite and the fifth and most recent caldera collapse event at Ksudach. The isopach pattern is consistent with a column height of 23 km. The three more recent and smaller eruptions were from the Shtyubel' Cone, within the fifth caldera. Using isopach and grain size isopleth patterns, column heights ranged from ≥ 10 to 22 km. Although the oldest eruption may have produced a large acidity peak in the Greenland ice, the three Shtyubel' events may not be related to major acid deposition. Thus it is possible that few if any of the uncorrelated acidity peaks of the past 2000 years in Greenland ice cores result from eruptions in southern Kamchatka.
The abundance of sulfur dioxide below the clouds of Venus
Authors: Bézard Bruno , de Bergh Catherine , Fegley Bruce , Maillard Jean‐Pierre , Crisp David , Owen Tobias , Pollack James B. , Grinspoon David
Published: February 2008

We present a new method for determining the abundance of sulfur dioxide below the clouds of Venus. Absorption by the 3ν3 band of SO2 near 2.45 µm has been detected in high‐resolution spectra of the night side of Venus recorded at the Canada‐France‐Hawaii telescope in 1989 and 1991. The inferred SO2 abundance is 130±40 ppm at all observed locations and pertains to the 35–45 km region. These values are comparable to those measured by the Pioneer Venus and Venera 11/12 entry probes in 1978. This stability stands in contrast to the apparent massive decrease in SO2 observed at the cloud tops since these space missions. These results are consistent with laboratory and modelling studies of the SO2 destruction rates in the lower atmosphere of Venus. The new spectroscopic technique presented here allows a remote monitoring of the SO2 abundance below the clouds, a likely tracer of Venusian volcanism.
Relationships between dynamically recrystallized grain size and deformation conditions in experimentally deformed olivine rocks
Authors: Van der Wal Dirk , Chopra Prame , Drury Martyn , Gerald John Fitz
Published: February 2008

New microstructural data on experimentally deformed “wet” and “dry” natural olivine rocks (Anita Bay and Åheim dunite), together with the other reliable experimental data, indicate that the experimental stress‐recrystallized grain size relationship in olivine‐rocks is largely independent of water content and temperature, and is only slightly dependent on the flow properties of the material. The experimental data cover a stress range of 30–300 MPa, water contents from <30 ppm to 300 ppm, and temperatures in the range 1100–1650°C. Local melt contents of up to 10 volume% cannot be demonstrated to have a significant effect on the stress—grain size relationship.
Mars volatile evolution: Implications of the recent measurement of 17O in water from the SNC meteorites
Authors: Jakosky Bruce M.
Published: February 2008

Escape of oxygen to space on Mars is capable of producing a fractionation of oxygen isotopes in the remaining oxygen which is off of the fractionation line produced by the usual mass‐dependent exchange processes. The magnitude of fractionation which can occur can be larger than that which was measured in oxygen in water derived from the SNC meteorites (thought to have come from Mars). In conjunction with the apparent lack of fractionation of 18O in the atmosphere, this result suggests that less than 25% of the oxygen in the martian climate system has been lost over geologic time. Other mechanisms also might be able to produce such a fractionation, so that this conclusion is not unique; however, it is consistent with other lines of evidence. There is no requirement for an initial volatile inventory with an isotopic composition different from that of the bulk planet (as might be the case for a late veneer of volatile‐rich material).
On slow‐mode waves in an anisotropic plasma
Authors: Hau L. ‐N. , Sonnerup B. U. Ö.
Published: February 2008

The properties of small‐amplitude waves propagating in a homogeneous anisotropic plasma are investigated using an MHD double‐polytropic model that incorporates the CGL double‐adiabatic model in one extreme and the isothermal model in the other. It is found that the properties of fast and intermediate mode waves remain qualitatively the same as in ordinary MHD but that, in certain parameter regimes, three inversions occur for slow‐mode waves: (1) their phase speed exceeds that of intermediate waves; (2) they behave like fast‐mode waves in that, across them, the plasma density and magnetic field increase or decrease together; (3) rarefaction waves rather than compression waves steepen.
NOY from sub‐sonic aircraft emissions: A Global three‐dimensional model study
Authors: Kasibhatla Prasad S.
Published: February 2008

The 11‐level Geophysical Fluid Dynamics Laboratory global chemical transport model (GCTM), which explicitly treats NOx, HNO3, PAN as transported species, has been used to assess the impact of sub‐sonic aircraft emissions on the distribution of reactive nitrogen compounds (NOy) in the atmosphere. A three ‐ dimensional aircraft source inventory compiled by Boeing and McDonnell Douglas [Wuebbles et al., 1993] has been used, in conjunction with previously compiled surface‐based fossil‐fuel combustion and stratospheric source inventories. Consistent with previous two‐dimensional model calculations, we find that aircraft emissions have a significant impact on upper tropospheric NOx and HNO3 budgets in the mid‐ and high latitudes of the Northern Hemisphere. Moreover, we find that the relative impact of the aircraft source on upper tropospheric NOx levels at mid‐ and high northern latitudes varies longitudinally, and that in certain regions the aircraft source dominates the total NOx budget. Aircraft emissions appear to only minimally impact the NOy budget in the Northern Hemisphere lower troposphere, and in much of the Southern Hemisphere. In contrast to a previous study with a simplified transport model [Ehhalt et al., 1992], we find that it is not necessary to invoke fast upward transport of surface emissions to explain the STRATOZ III measurements of NO in the upper troposphere of Northern Hemisphere mid‐latitudes in the GCTM. However, comparisons of model results with NOy measurements at Mauna Loa, Hawaii, and over western Alaska suggest that sources other than surface‐based fossil‐fuel combustion, stratospheric NOx production, and aircraft emissions, are significant in determining the free tropospheric NOy budget in these regions.
Melting of forsterite and spinel, with implications for the glass transition of Mg2SiO4 liquid
Authors: Richet Pascal , Leclerc Franck , Benoist Luc
Published: February 2008

As determined by quantitative differential thermal analysis, the enthalpies of fusion of forsterite and spinel, are ΔHf = 142 ± 14 and 107 ± 11 kJ/mol at 2174 and 2408 K, respectively. Significant premelting has been observed for forsterite, beginning about 100 K below the congruent melting point. When heated in graphite crucibles, forsterite reacts with carbon and the products of reaction vaporize with an overall enthalpy of reaction of the order of 1600 kJ/mol. The configurational entropy of Mg2SiO4 liquid decreases so rapidly with decreasing temperature that it would be almost zero at its nominal glass‐transition temperature as estimated by extrapolating viscosity data for magnesium aluminosilicate melts. Extreme cooling rates are thus needed in order to quench actual Mg2SiO4 glasses having significant configurational entropies.
Recurrent patterns in the spatial behaviour of Italian seismicity revealed by the fractal approach
Authors: De Rubeis V. , Dimitriu P. , Papadimitriou E. , Tosi P.
Published: February 2008

Three are the essential parameters needed to describe seismicity: the b‐value of the Gutenberg‐Richter relation and the spatial and temporal fractal dimensions (Ds and Dt). Several cases have been reported when a significant decrease in the b‐value or in the spatial fractal dimension preceded major earthquake sequences or aftershocks. Here we use the fractal method based on the correlation integral to study the temporal changes in the spatial (2‐D) distribution of earthquakes in three important seismic zones of Italy. In all three zones Ds shows significant variability, which correlates well with the major events and clearly marks the beginning and the end of an earthquake cycle. Finally, the nucleation of most major events is associated with a fractal dimension value which corresponds to the topological dimension of a plane.
Observations of a quasi‐static plasma sheet boundary
Authors: Angelopoulos V. , Kennel C. F. , Coroniti F. V. , Feldman W. C. , Gosling J. T. , Kivelson M. G. , Walker R. J. , Russell C. T.
Published: February 2008

No high‐speed flows or discernible counterstreaming ion beams were observed during a series of plasma sheet boundary encounters resulting from solar wind‐driven plasma sheet motions. We conclude that the boundary may be active primarily during plasma sheet “recovery”. A temporal onset of flows in the inner plasma sheet (IPS) was associated with the appearance of counterstreaming beams embedded in an already isotropic plasma sheet distribution, suggesting that high speed flows at the plasma sheet boundary and close to the neutral sheet may have a common generation mechanism.
High Rayleigh number regime of temperature‐dependent viscosity convection and the Earth's early thermal history
Authors: Hansen U. , Yuen D. A.
Published: February 2008

We have carried out steady‐state calculations of thermal convection with strongly temperature‐dependent viscosity, spanning six decades in surface Rayleigh number (Ras). The style of convection undergoes a transition from a stagnant‐lid regime to a constant‐viscosity‐like regime at sufficiently high Ras. For viscosity variations of 10³ this transition would occur at around Ras of O (107) with attendant Nusselt (Nu) numbers of around 50. This transition in the style of convection with Ra suggests that there might be a change in the style of convection and surface features in the very young Earth, when the surface Rayleigh number was much higher from greenhouse effects, which took place in the last part of the accretionary period.
Three views of two giant streams: Aligned observations at 1 AU, 4.6 AU, and 5.9 AU
Authors: Siscoe George , Intriligator Devrie
Published: February 2008

A close radial alignment of the IMP and Pioneers 10 and 11 spacecraft in 1974 allows a nearly unambiguous, empirical study of the radial evolution of the interaction regions of two contrasting weak and strong, giant streams. The study confirms the main aspects of the standard model of corotating interaction regions: an expanding and strengthening pair of forward‐reverse shocks sandwich a stream interface. It adds the following concepts: stream group speed — the speed at the stream interface tends to remain constant with distance; corotating stream complexes — interaction regions can include features like noncompressive density enhancements and streamer belts; secondary interfaces — a possible precursor to the reverse shock; and emerging stream interfaces — one emerged between 1 AU and 4.6 AU. The study uses the conservation specific entropy to correlate features between spacecraft.
Dynamic compliance from torsional creep and forced oscillation tests: An experimental demonstration of linear viscoelasticity
Authors: Jackson Ian
Published: February 2008

Recently developed forced torsional oscillation techniques provide new opportunities for the quantitative study at high temperature and pressure, and low frequency, of the shear mode viscoelasticity responsible for seismic wave dispersion and attenuation. Creep tests, in which the response is measured both during the period of application of a steady torque and following its removal, allow recoverable anelastic strains to be distinguished from the permanent strains of genuinely viscous deformation. The relative merits of these complementary approaches are highlighted through the conduct and analysis of some low‐strain high‐temperature experiments. Evidence of the linearity of the stress‐strain relationship is provided by the close consistency between the dynamic torsional compliance of an alumina‐iron test assembly computed by Fourier transformation of the creep function and that derived more directly from the forced oscillation experiments.
Surface melting on Antarctic Peninsula ice shelves detected by passive microwave sensors
Authors: Ridley Jeff
Published: February 2008

A 13 year time series of spaceborne passive microwave radiance measurements over the Antarctic Peninsula ice shelves, reveals a systematic increase in the duration of the summer melt season. Combined with data from meteorological stations on the Antarctic Peninsula, the annual motion and long‐term trends of the 0°C isotherm can be monitored.
The evolution of the interplanetary sector structure in 1992
Authors: Balogh A. , Erdös G. , Forsyth R. J. , Smith E. J.
Published: February 2008

The unique vantage point of the Ulysses spacecraft throughout 1992 and the beginning of 1993, at a close to constant heliocentric distance of about 5 AU and a slowly varying heliographic latitude from 5° to 30° south is used to describe and discuss the evolution of the sector structure of the interplanetary magnetic field during the declining phase of the solar cycle. From the end of 1990 to the beginning of 1992 the sector structure changed from a four sector to a two sector structure, but remained constant in solar longitude. From about June‐July 1992, the structure, matching the evolution in the computed coronal magnetic fields, drifted eastwards, with a recurrence period of about 28 days. This result may indicate a slower rotation rate for the dipolar component of the solar magnetic field which becomes dominant about this time in the solar cycle.