bluuebunny/crossref_metadata_2025 huggingface dataset:
The emission of nitrous oxide upon wetting a rice soil following a dry season fallow
Authors: Byrnes B. H. , Holt L. S. , Austin E. R.
Published: February 2008

A greenhouse experiment was conducted to measure nitrous oxide (N2O) emissions from a soil, which had been planted to flooded transplanted rice, as it was rewetted to simulate the end of a dry season fallow period. The pots of soil had been cropped to transplanted rice with two commonly used nitrogen (N) fertilizer treatments and a control, and the soil had been puddled before transplanting. Large amounts of nitrate N accumulated in the soils during the dry season fallow, and the N fertilizers applied to the previous crop had little effect on nitrate accumulation. There was little N2O emission during the nitrification period. With water additions meant to simulate rainfall events at the beginning of a wet season, the soil redox dropped slightly, and large amounts of N2O began to be emitted. Large emissions began 5 days after each of the two simulated rainy season watering events and stopped abruptly at soil saturation, even though considerable amounts of nitrate still remained in the soil after saturation. Total measured emissions amounted to 6 to 7 kg N2O‐N ha−1 for the period. Although these measurements were made in a system which may have favored nitrate accumulation, they are the first known measurements of N2O made from a rice soil as it is wetted. Nitrous oxide emitted from the flooding of rice soils that have accumulated nitrate during a dry season fallow may be a major source of N2O additions to the atmosphere.
Henry's law constants for aqueous solutions of hydrogen peroxide and hydroxymethyl hydroperoxide
Authors: Staffelbach Thomas A. , Kok Gregory L.
Published: February 2008

The Henry's law constants for aqueous solutions of hydrogen peroxide (H2O2) and hydroxymethyl hydroperoxide (HMHP) were measured for temperatures from 278 to 293 K at a pH of 2.1 to 2.4. A lower limit for the Henry's law constant of bis(hydroxymethyl)peroxide was obtained. At 288 K the Henry's law constant was determined for pH values from 2.2 to 6.4. The gas‐phase peroxides were generated by passing humidified zero air through a porous tube immersed in a thermostated hydroperoxide solution. The temperature dependence of the Henry's law constant can be expressed as HL[M atm−1]=exp(A/T[K]−B). The values of A are 7,514 ± 519 for H2O2 and 10,240 ± 913 for HMHP, and the values of B are 13.63 ± 0.11 for H2O2 and 20.03 ± 0.20 for HMHP. The dependence of the Henry's law constants as a function of pH was studied.
A retrieval method for atmospheric composition from limb emission measurements
Authors: Marks Crispin J. , Rodgers Clive D.
Published: February 2008

Efficient and flexible algorithms for the retrieval of atmospheric constituent and aerosol profiles from a limb‐sounding satellite radiometer are presented. The radiative transfer scheme ( “forward model”) has been generalized to cope with departures from local thermodynamic equilibrium (LTE), modelling emission from fundamental bands as well as hot bands. Its formulation makes possible a fast method of accurately calculating the radiance derivatives (“weighting functions”) required for the nonlinear optimal estimation algorithms. The retrieval schemes can be used with a wide variety of signal to noise ratios and with measurements from more than one wavelength. Multiple retrieval products are possible. A complete error analysis method emerges naturally from the theory, permitting an extensive prelaunch characterization of the retrieval products. The algorithms have been implemented for the improved stratospheric and mesospheric sounder (ISAMS), an infrared limb sounder on the Upper Atmosphere Research Satellite. The retrieval algorithms and error analysis are illustrated with some of the prelaunch tests performed for ISAMS. The O3 retrieval exemplifies those using measurements with a very high signal to noise ratio for which the quality of the retrieved product will be limited by spectroscopic and other forward model deficiencies. Preliminary calculations indicate that it should be possible to perform retrievals of daytime CO in the mesosphere and lower thermosphere because of rather than in spite of the strong non‐LTE emission in that region due to solar pumping at 4.6 μm. The “optimal onion‐peeling” algorithm used in the joint retrieval of CH4 and N2O is a very accurate means of solving strong cross contamination problems and proves to be much quicker than any iterative sequence of single‐product retrievals.
The impact of U.S. continental outflow on ozone and aerosol distributions over the western Atlantic
Authors: Anderson B. E. , Gregory G. L. , Barrick J. D. W. , Collins J. E. , Sachse G. W. , Bagwell D. , Shipham M. C. , Bradshaw J. D. , Sandholm S. T.
Published: February 2008

Aircraft measurements of selected trace gas species, aerosols, and meteorological parameters were performed in the lower troposphere off the U.S. east coast during August and September 1989 as part of the NASA Global Tropospheric Experiment (GTE) Chemical Instrumentation Test and Evaluation (CITE 3) expedition. In this paper, we examine these data to assess the impact of continental outflow on western Atlantic O3 and small aerosol budgets. Results show that mixed layer (ML) O3 concentrations and small aerosol number densities (Np) were enhanced by factors of 3 and 6, respectively, within air masses of predominantly continental origin compared with clean maritime background air. These enhancements exhibited a marked altitude dependence, declining rapidly above the ML to the point where only slight to moderate differences in O3 and Np, respectively, were notable above 2.4 km. Within continentally influenced ML's, both O3 and Np were correlated with CO, exhibiting linear regression slopes averaging 0.4 ppbv(O3)/ppbv(CO) for O3 and 7.7 (particles cm−3)/ppbv(CO) for Np and indicating a primarily anthropogenic origin for the observed enhancement of these species. Comparisons between profiles in continental and background maritime air masses suggest that photochemical production below 1.4‐km altitude adds over 10% to western Atlantic tropospheric column O3 abundance in continental outflow regimes. For aerosols, eastward advection of low‐level continental air contributes an average net flux of 2.8 metric tons of submicron (accumulation mode) particles per kilometer of shoreline per day to the western Atlantic troposphere.
Effect of decreased solar luminosity on late Precambrian ice extent
Authors: Crowley Thomas J. , Baum Steven K.
Published: February 2008

The latest Precambrian (∼0.57 Ga) was marked by extensive glaciation on a supercontinent. Ice cover may have been in lower latitudes than during the Pleistocene. Deglaciation and breakup of the supercontinent were followed by the first appearance/expansion of metazoans. Herein we report results from a seasonal climate model that clarify some of the processes operating during this important time interval. We demonstrate that, because solar luminosity was about 6% less than present, the modeled snowline was approximately 15° equatorward of its modeled Pleistocene limit. The significance of this response depends on choice of paleogeographic reconstruction. If the supercontinent was located entirely in low latitudes, the freezing line changes would not be enough to trigger glaciation on land. However, the luminosity changes are much more important if the supercontinent extended into midlatitudes (∼50° paleolatitude). Such a configuration has extensive summer snowcover and would provide a “seed” area for ice growth into lower latitudes. We postulate that if the large snowline changes we simulate were coupled to an ice sheet model, the ice margin could have reached to within 25° of the equator. Such a response could reconcile models and geologic data, but the reconciliation would critically depend on a more precise definition of low latitude glaciation, that is, whether the ice was at 25–30° or 0° latitude. Additional simulations for one Precambrian/Cambrian boundary reconstruction (∼0.54 Ga) suggest that reduction in late Precambrian snow cover might simply reflect movement of a midlatitude supercontinent into lower latitudes. The deglaciation could have been associated with a sea level rise of as much as 250–300 m, creating a much larger area for habitat occupation by benthic biota. Although more work is required on this topic, our results could explain both glaciation and deglaciation, with the explanation critically dependent on choice of paleogeographic reconstruction and more precise descriptions of late Precambrian ice sheet locations.
Light scattering and cloud condensation nucleus activity of sulfate aerosol measured over the northeast Atlantic Ocean
Authors: Hegg Dean A. , Ferek Ronald J. , Hobbs Peter V.
Published: February 2008

Measurements on the relationship between sulfate mass and light scattering coefficient and sulfate cloud condensation nucleus efficiency over the Northeast Atlantic Ocean suggest lower values for these parameters than have been used in recent estimates of the climatic impact of sulfate aerosols. Analysis suggests an important role in both processes for nonsulfate aerosol.
Effects of surface area and volume on the rate of isotopic exchange between water and water vapor
Authors: Ingraham Neil L. , Criss Robert E.
Published: February 2008

The effects of surface area and volume on the rate of isotopic exchange between water and water vapor were quantified by allowing beakers containing waters with differing D, 18O, and tritium contents to equilibrate under controlled conditions in a closed system. Over a 2‐month period the waters shifted by as much as 80‰ in δD, 13‰ in δ18O, and 57,000 tritium unit (TU), sometimes in opposite directions (either toward being more enriched or more depleted) depending upon initial compositions of the juxtaposed waters. Over time the concentrations of the stable and radioactive isotopes approach a common value, which in an ideal closed system represents the mean composition on a volumetric basis. The exchange rate is represented by dRX/dt = −(RX − RM)ksx/vx where RX represents the actual isotopic ratio of the water at time t, RM is equal to αeq * Rv and represents the isotopic ratio of the water that would at any instant be in equilibrium with ambient vapor with an isotopic ratio of Rv, and sX and vX refer to the surface area and volume of the water, respectively. In our 20°C experiments the constant k ranged from 0.12 to 0.18 cm/d and was identical for D/H, T/H, and 18O/16O exchange for a given set of conditions. In cases where RM is constant, as, for example, occurs if the atmospheric reservoir is infinite or if water samples having identical surface areas and volumes undergo exchange, the isotopic ratio of the vapor is constant and the exchange equation is (δx − δ∞)/(δi − δ∞) = e−ks xt/v x where δi, δ∞ and δx refer to the δ value of the water at the initiation of the experiment, at equilibrium, and any time. In the case of exchange between samples having different surface areas and/or volumes, the isotopic ratio of the vapor is variable and the value for RM is RM = (sX(RX) + sY(RY) + (sZ(RZ) + …)/(sX + sY + sZ …). In the case of identical surface areas and volumes the composition of the waters may change, but the vapor to which the waters respond remains the same during the exchange process. In the case of differing surface areas, or differing volumes, the composition of the vapor and RM will both change. In any case, after complete exchange, all waters will attain the same equilibrium isotopic ratio.
Reaction of ClONO2 with HCl on NAT, NAD, and frozen sulfuric acid and hydrolysis of N2O5 and ClONO2 on frozen sulfuric acid
Authors: Hanson D. R. , Ravishankara A. R.
Published: February 2008

The reaction of ClONO2 with HCl on the nitric acid trihydrate (NAT) and dihydrate (NAD) and on frozen sulfuric acid solutions was studied as functions of reactant concentration and temperature representative of the stratosphere. A flow tube reactor equipped with a chemical ionization mass spectrometer detector was used. The measured reactive uptake coefficient shows a strong dependence on temperature at constant H2O partial pressure. Our results for NAT are qualitatively similar to but quantitatively different from those of Abbatt and Molina [1992a]. The hydrolysis of N2O5 and ClONO2 on frozen sulfuric acid were measured to be far less efficient than that in liquid solutions. The implications of these results to the heterogeneous chemistry of the stratosphere are discussed.
A general circulation model study of the effects of faster rotation rate, enhanced CO2 concentration, and reduced solar forcing: Implications for the faint young sun paradox
Authors: Jenkins Gregory S.
Published: February 2008

Solar energy at the top of the atmosphere (solar constant), rotation rate, and carbon dioxide (CO2) may have varied significantly over Earth's history, especially during the earliest times. The sensitivity of a general circulation model to faster rotation, enhanced CO2 concentration, and reduced solar constant is presented. The control simulation of this study has a solar constant reduced by 10% the present amount, zero land fraction using a swamp ocean surface, CO2 concentrations of 330 ppmv, present‐day rotation rate, and is integrated under mean diurnal and seasonal solar forcing. Four sensitivity test are performed under zero land fraction and reduced solar constant conditions: (1) increased rotation rate, (2) 8 times present CO2, (3) a combination of 1 and 2, and (4) 3 with a 15% reduction in the solar constant. Results indicate the following changes in the global mean sea surface temperatures (SSTs) compared to the control simulation: (1) + 6.6 K, (2) + 12 K, (3) + 18.5 K, and (4) + 6.6 K relative to the control's global mean temperature of 264.7 K. Sea ice is confined to higher latitudes in each experiment compared to the control, with ice‐free areas equatorward of the subtropics. The warm SSTs are associated with a 20% reduction in clouds for the rotation rate experiments and higher CO2 concentrations in the other experiments. These results are in contrast to previous studies that have used energy balance and radiative convective models. Previous studies required a much larger atmospheric CO2 increase to prevent an ice‐covered Earth. The results of the study, suggest that because of its possible feedback with clouds, the general circulation of the atmosphere should be taken into account in understanding the climate of early Earth. While higher CO2 concentrations are likely in view of the results, very large atmospheric CO2 concentrations may not be necessary to counterbalance the lower solar constant that existed early in Earth's history.
Mars dust storms: Interannual variability and chaos
Authors: Ingersoll Andrew P. , Lyons James R.
Published: February 2008

The hypothesis is that the global climate system, consisting of atmospheric dust interacting with the circulation, produces its own interannual variability when forced at the annual frequency. The model has two time‐dependent variables representing the amount of atmospheric dust in the northern and southern hemispheres, respectively. Absorption of sunlight by the dust drives a cross‐equatorial Hadley cell that brings more dust into the heated hemisphere. The circulation decays when the dust storm covers the globe. Interannual variability manifests itself either as a periodic solution in which the period is a multiple of the Martian year, or as an aperiodic (chaotic) solution that never repeats. Both kinds of solution are found in the model, lending support to the idea that interannual variability is an intrinsic property of the global climate system. The next step is to develop a hierarchy of dust‐circulation models capable of being integrated for many years.
Galileo observations of post‐imbrium lunar craters during the first Eearth‐Moon flyby
Authors: McEwen Alfred S. , Gaddis Lisa R. , Neukum Gerhard , Hoffman Harald , Pieters Carle M. , Head James W.
Published: February 2008

Copernican‐age craters are among the most conspicuous features seen on the far side and western limb of the Moon in the Galileo multispectral images acquired in December 1990. Among the new morphologic observations of far‐side craters are bright rays, continuous ejecta deposits, and dark rings associated with probable impact‐melt veneers. These observations suggest that the mapped age assignments of several large far‐side craters (Ohm, Robertson, and possibly Lowell and Lenz) need revision. New crater size‐frequency measurements on Lunar Orbiter images suggest the following age reassignments: Hausen (170 km diameter), Pythagoras (120 km), and Bullialdus (61 km) from Eratosthenian to Upper Imbrian, and Carpenter (60 km) and Harpalus (39 km) from Copernican to Eratosthenian. Colors and albedos of craters (away from impact‐melt veneers) are correlated with their geologic emplacement ages as determined from counts of superposed craters; these age‐color relations are used to estimate the emplacement age (time since impact event) for other Copernican‐age craters. These age‐color relations indicate a probable Copernican age for 27 far‐side or western limb craters larger than 10 km diameter that were not previously mapped as Copernican. The apparent deficiency of Copernican craters on the far side compared with the near side in published geologic maps is not present in our data. Age‐color trends differ between mare and highland regions and between the interiors and continuous ejecta of the craters. Similar trends are established for color and albedo versus soil‐maturity indices for the returned lunar samples, with distinct trends for mare and highland soils. However, the mare versus highland offsets are reversed in the two comparisons. These relations can be explained by variations in regolith thicknesses and rates of mixing with relatively fresh, crystalline ejecta. Therefore, the soil‐maturity trends represent longer geologic time periods in regions with thinner regoliths, such as the maria.
He, Ne, and Ar from the solar wind and solar energetic particles in lunar ilmenites and pyroxenes
Authors: Benkert Jean‐Paul , Baur Heinrich , Signer Peter , Wieler Rainer
Published: February 2008

He, Ne, and Ar in ilmenite and pyroxene separates from two lunar regolith samples exposed to the solar corpuscular radiation at widely different epochs were analyzed by the closed system stepped etching technique. This method avoids element or isotope fractionation due to diffusion during the experiment and thus depth profiles of element and isotopic composition of implanted solar noble gases can be determined. Ilmenites from a relatively recently irradiated soil release in the first steps He and Ne with isotopic compositions identical to modern solar wind values. We conclude that ilmenite retains isotopically unfractionated He, Ne, and Ar from the solar wind (SW) in the outermost grain layers. The isotopic composition of SW noble gases has remained constant over the last 100 Ma but there is some evidence for a slight change over a Ga timescale. The ratio 36Ar/38Ar in the solar wind is 2–3% larger than that in the terrestrial atmosphere. We give further evidence for the identification of a solar energetic particle component (SEP), which was implanted with energies exceeding those in the solar wind. All ilmenites and pyroxenes contain SEP‐Ne with 20Ne/22Ne = 11.2±0.2, in agreement with SEP‐Ne found earlier in lunar plagioclase. (21Ne/22Ne)SEP is consistent with SEP‐Ne being derived from SW‐Ne by mass dependent fractionation. In addition, the new data reveal SEP‐He and SEP‐Ar, both isotopically heavier than the SW components. The isotopic fractionation factors required to relate SW and SEP gases are approximately equal to the square of the mass ratios. Element ratios in the SEP dominated steps are similar (He: Ar) or identical (Ne: Ar) to present‐day solar wind values, indicating little or no element fractionation in the SEP reservoir.
Radar polarization properties of volcanic and playa surfaces: Applications to terrestrial remote sensing and Venus data interpretation
Authors: Campbell Bruce A. , Arvidson Raymond E. , Shepard Michael K.
Published: February 2008

The radar polarization properties of lava flows in Hawaii (Kilauea) and Arizona (SP flow), and two play a surfaces (Lunar Lake, Nevada and Lavic Lake, California), are compared to the predicted behaviors of theoretical scattering models. At 5.7 cm and 24 cm wavelengths, Kilauea lava flows can be modeled by a combination of facet and diffuse (dipole‐like) scattering. Scattering by rock faces on the scale of the radar wavelength is proposed to account for much of the facet return. The radar echoes at 24‐cm wavelength from SP flow are, on average, consistent with entirely diffuse scattering, but there are regions within the flow where circular polarization ratios exceed unity, suggesting a coherent scattering effect. 68 cm data for the lava flows show evidence of radar penetration and volume scattering. The playa surfaces are characterized by polarization properties which in some cases are qualitatively consistent with the first‐order small‐perturbation model, but the echoes do not closely match the predictions of this model for any reasonable dielectric constant value. These results show that it may be difficult to construct invertible models for the polarization behavior of some surfaces (the playas), whereas for others (the Kilauea lava flows) the scattering properties can be successfully modeled. The first‐order small‐perturbation model is not appropriate for inverse modeling of most terrestrial lava flows, though very smooth surfaces on Venus may be amenable to the use of this model. High circular polarization ratios observed for SP flow, tentatively attributed here to coherent backscatter, may be analogous to Arecibo observations of high‐reflectivity areas on Venus.
The kinetics of the formation of nitrile compounds in the atmospheres of Titan and Neptune
Authors: Monks P. S. , Romani P. N. , Nesbitt F. L. , Scanlon M. , Stief L. J.
Published: February 2008

The nitrile compounds HCN and C2HCN (cyanoacetylene) were detected on Titan by Voyager 1. The ethylene‐analog nitrile to cyanoacetylene C2H3CN (acrylonitrile) remains undetected. More recently, ground‐based observers have detected HCN on Neptune and placed an upper limit on C2HCN. Kinetic aspects of the formation of acrylonitrile have been studied in a discharge‐flow mass spectrometric system at T = 298 K. The fractional yield for the formation of acrylonitrile from the fast gas phase reaction CN + C2H4 → C2H3CN + H has been determined to be (0.2 ± 0.1). The other possible gas phase reaction leading to the formation of acrylonitrile, HCN + C2H3 → C2H3CN + H, has been determined to be slow under planetary conditions at k(T = 298 K) = 2–7 × 10−14 cm3 molecule−1 s−1, but remains an important chemical sink for HCN. The planetary implications of the results are discussed in terms of the ratio of acrylonitrile to cyanoacetylene on Titan and Neptune.
A study of low‐latitude VHF scintillations in relation to electric fields during magnetic storms
Authors: Lakshmi D. R. , Dabas R. S. , Rao B. C. N. , Reddy B. M.
Published: February 2008

Nighttime VHF scintillations observed at Lunping (magnetic latitude 14.7°N) during four specific seasonal storms showed four different types of behaviour: Scintillation activity was found to be either inhibited or triggered during magnetic storms depending on the phase of the storm and its local time. A qualitative explanation for this behaviour is attempted in terms of storm time electric fields. The triggering of postmidnight scintillation activity during the recovery phase seems to be a result of penetration of the dusk‐dawn electric fields due to shielding charges developed in the ring current region,while inhibition of usual premidnight scintillation activity seems to be related to the ionospheric disturbance dynamo electric fields acting opposite to normal fields. One case where postsunset scintillation activity was triggered seems to be a result of penetration of dawn‐dusk convection electric field which developed following the main phase onset.
Comparison of predicted and measured detection rates of meteor signals
Authors: Mawrey R. S. , Broadhurst A. D.
Published: February 2008

Comparisons of monthly‐averaged daily cycles of measured and predicted detection rates of meteor signals for a midpath and an endpath meteor link are used to reveal the validity and limitations of published radiant distributions of meteors. A new method is used to aid in determining the validity and limitations of the nonuniform distributions. Discrepancies in the published, predicted, and measured annual variations in the detection rate of meteor signals are investigated. Contrary to recently published information, predicted annual variations in the detection rate of meteor signals that are caused by meteor radiants close to the ecliptic are shown to be comparable to measured results.
Propagation of a low‐frequency rectangular pulse in seawater
Authors: King Ronold W. P.
Published: February 2008

As a necessary preliminary to the determination of the electromagnetic field scattered by a metal cylinder submerged in the ocean, the propagation of a low frequency pulse with a rectangular envelope is evaluated numerically as a function of the distance of travel. Graphs of the three component terms and their sum are shown for four distances. The very significant changes in shape and amplitude of the pulse are discussed.
Generation of HF sidebands in the ionosphere during oblique heating: First results
Authors: Noble S. T. , Gordon W. E.
Published: February 2008

Results from the first high‐power two‐frequency heating experiment to employ obliquely incident modifying waves are presented. Diagnostic instruments measuring the effects at HF and ULF were deployed in the skip zone of the modifying waves to investigate aspects related to HF sidebands. Although occurring far less frequently than with vertically incident heating, HF sidebands were observed on a number of occasions. Two categories of sideband excitation mechanisms are currently recognized (phase modulation and downconversion) and could be responsible for the observed sidebands. Theoretical initiatives are needed to help sort out the contributions of these processes during oblique heating.
Time domain Green function technique for a point source over a dissipative stratified half‐space
Authors: He Sailing , Karlsson Anders
Published: February 2008

In this paper the time domain scattering problem of a stratified dissipative half‐space excited by a point source is considered. Both the direct and inverse scattering problem are treated. The dissipative wave equation is reduced to an equation in one spatial dimension by spatial Fourier series and a Hankel transform. The transformed wave equation is then solved by a combination of a time domain wave‐splitting technique and a Green function technique. The Green functions represent the internal fields inside the stratified medium. The splitting is expressed in terms of a Neumann operator K which has an explicit expression as a convolution integral with a Bessel function kernel. Based upon this wave splitting, Green functions can be defined and a set of first order partial differential equations for Green functions are derived. The equations are well suited for a numerical treatment and a number of numerical examples for both the direct and inverse problems are presented. A brief discussion of the invariant imbedding method applied to the direct and inverse scattering problem is also given. It is shown that one‐sided reflection data are sufficient to reconstruct the phase velocity and the dissipation coefficient simultaneously by using two different values of the Hankel transform parameter.
Closely spaced monopoles for mobile communications
Authors: Vaughan Rodney G. , Scott Neil L.
Published: February 2008

The spatial cross‐correlation function for antenna signals in multipath environments depends on the mutual coupling between the antennas. In general, this function is different from the spatial autocorrelation coefficient function of the multipath, fading field. This difference influences the design criteria for the element spacing of compact (that is, closely spaced elements) antennas. The relationship between the spatial autocorrelation function and the cross‐correlation function is presented and used for practical, compact diversity antenna design.
Structure of the near zone electric field and the power radiated from a VLF antenna in the ionosphere
Authors: Sotnikov V. I. , Solovyev G. I. , Ashour‐Abdalla M. , Schriver D. , Fiala V.
Published: February 2008

In this paper we examine the electric field and radiated power produced in the near zone of a ring VLF antenna whose loop plane is aligned parallel to the external magnetic field. In this case there exist two resonance surfaces, one inside the other, which can be given in parametric form. The electric field singularity on the resonance surfaces is of a logarithmic type, but there are also curves and points (focuses) where the field displays a more severe singularity (branch pole type). The asymptotes of the field close to the resonance surfaces are given. Using the expression for the Fourier component of the antenna generated magnetic current, the radiated power and the percentage of the power that goes into the whistler mode are calculated for different values of the angle between the antenna loop and the external magnetic field. The results show that only a small portion of the radiated power is transferred to the whistler mode. Suggestions as to how to increase the portion of the radiated power that goes into whistler waves are discussed.
An analysis of transverse electric scattering from a rectangular channel in a conducting plane
Authors: Park Tah J. , Eom Hyo J. , Yoshitomi Kuniaki
Published: February 2008

The problem of transverse electric plane wave scattering from a rectangular channel which is engraved in a perfect conducting plane is investigated. A Fourier transform technique is employed to express the scattered field in the spectral domain in terms of parallel‐plate waveguide modes. The boundary conditions are enforced on the conducting surface and the channel aperture to obtain simultaneous equations for the transmitted field inside the channel. The simultaneous equations are solved to represent the transmitted field in a series form. By using the stationary phase approximation, the exact expression for the far‐zone scattered field is obtained and the echo width behavior is numerically studied in terms of the scattering angle, frequency, and channel size. It is found that the behavior of the echo width versus the channel depth exibits resonance irrespective of the size of the channel width. An approximate series expression (Kirchhoff solution) for the echo width is valid for high‐frequency scattering regimes (a > 2 λ). We also present an approximate closed form solution for nadir backscattering which is valid when a > 0.2λ.
One‐way wave propagation methods in direct and inverse scalar wave propagation modeling
Authors: Fishman Louis
Published: February 2008

Wave field splitting, invariant imbedding, and phase space methods reformulate the Helmholtz wave propagation problem in terms of an operator scattering matrix characteristic of the modeled environment. The subsequent equations for the reflection and transmission operators are of first‐order (one‐way) in range, nonlinear (Riccati‐like), and, in general, nonlocal. The reflection and transmission operator equations provide the framework for constructing inverse algorithms based on, in principle, exact solution methods.
Multiantenna scanning diversity system for mobile TV reception with independently optimized picture and sound quality
Authors: Lindenmeier H. K. , Reiter L. M. , Hopf J. F.
Published: February 2008

The presented mobile multiantenna scanning diversity system for terrestrial TV highly improves the reception in cars making use of four active broadband TV antennas. The diversity systems for picture and sound choose independently from each other the optimum antenna signal among the four TV antennas based upon different diversity criteria. An indicator sensitive to the RF level evaluates the picture quality at the end of each video line. The TV sound is optimized by application of a diversity processor originally designed for FM broadcasting and is available now as an integrated circuit. This processor is sensitive to noise, multipath distortions, and three types of interferences: cochannel, adjacent channel, and intermodulation interferences.
Magnetic stratigraphy of the Morales Formation: Late Neogene clockwise rotation and compression in the Cuyama Basin, California Coast Ranges
Authors: Ellis Barbara J. , Levi Shaul , Yeats Robert S.
Published: February 2008

The Cuyama basin in the southern Coast Ranges of California underwent a transition from strike‐slip to compressional faulting, synchronous with the deposition of the Pliocene‐Pleistocene Morales Formation. Paleomagnetic stratigraphy was used to date the Morales Formation and, by inference, the beginning of compressional tectonics. Sections sampled below the Whiterock and Morales thrusts in the western Cuyama basin are predominantly normal and are correlated with the Gauss chron (3.57–2.60 Ma). An abrupt appearance of clasts derived from the overlying thrust sheet in the section below the Whiterock thrust suggests uplift of the Caliente Range during the middle to late Gauss chron. Seismic reflection data indicate that the eastern sections were deposited earlier. In conjunction with fossil evidence, the eastern sections are correlated to a time between the late Gilbert and early Matuyama chrons. The presence of a crystalline boulder bed midway in an eastern Cuyama basin section indicates uplift of the Mount Pinos‐Frazier Mountain highlands during the Matuyama chron between 2.60 and 0.78 Ma. Paleomagnetic directions of the Morales Formation document approximately 23° clockwise rotation of the Cuyama basin.
Active tectonics in the Lesser Caucasus: Coexistence of compressive and extensional structures
Authors: Rebaï S. , Philip H. , Dorbath L. , Borissoff B. , Haessler H. , Cisternas A.
Published: February 2008

Detailed SPOT image analysis which completed field data and a microseismicity study was done on the central Caucasian mountain belt (Georgia, Armenia, and eastern Turkey), north of the front of the Arabian collision in order to clarify the relationships between compression, extension, and volcanism. In fact, this region is characterized by relatively complex active tectonics, associating both N‐S compressive (E‐W thrusts and folds) and E‐W extensional (N‐S normal faults and dikes) structures accompanied by considerable Neogene to Quaternary volcanism, and NE‐SW left‐lateral and NW‐SE right‐lateral strike‐slip faults. These different structures are all intricately imbricated and can be observed at different scales. The general layout implies an important variation in the stress state; for instance, this passes from a N‐S compression in the Spitak earthquake fault zone to an E‐W extension at the Aboul‐Samsar volcanic axis. These results agree well with the N‐S convergence between Arabia and Eurasia, and the E‐W lateral expulsion of the Anatolian and Iranian blocks. A detailed cartographic network of active structures was drawn and their kinematic relationships were specified. In places, recent offsets on strike‐slip faults were estimated at about 500 to 1000 m. Suitable sites for future determination of fault velocity displacements were also selected. This study shows that some strike‐slip faults behave partly like faults which transform the E‐W extension of the N‐S striking normal faults into a N‐S compression along the E‐W thrusts. One of the characteristics of this region is the continuous important volcanic activity at least from the Jurassic until now. This persistence evidences a lithospheric thinning, which remained in spite of the recent Arabian‐Eurasian collision because of the E‐W extension linked to the opposite lateral expulsion of the Anatolian and Iranian blocks. This geodynamic evolution can explain the juxtaposition and superimposition of volcanic structures and thrusts in a general compressive context.
Structural and tectonic evolution of the Humber Zone, western Newfoundland, 1. Implications of balanced cross sections through the Appalachian structural front, Port Au Port Peninsula
Authors: Stockmal Glen S. , Waldron John W. F.
Published: February 2008

The Appalachian structural front in western Newfoundland, which is principally a submarine feature that comes ashore on Port au Port Peninsula, is interpreted to be a structural triangle zone, or tectonic wedge. Rocks within the triangle zone, which are therefore transported, include the Taconian (Middle Ordovician) Humber Arm Allochthon, Taconian foreland clastic sediments, and the Cambro‐Ordovician platform succession. The transported clastic sediments and platformal rocks, as well as structurally involved Grenville crystalline basement exposed east of the peninsula, compose the Acadian (Siluro‐Devonian) Port au Port Allochthon, which carried the Humber Arm Allochthon as a high structural slice; Acadian transport of tens of kilometers westward is suggested. This interpretation contrasts markedly with the traditional and widely accepted interpretation of the Taconian and Acadian orogenies in western Newfoundland. Here we reinforce our earlier arguments for an allochthonous interpretation by presenting a series of six closely spaced, balanced cross sections across the Port au Port Peninsula. These sections illustrate our interpretation of complex and noncylindrical structures within the triangle zone, as well as the envisioned structural linkage between exposures on Port au Port Peninsula and the geometry of the triangle zone interpreted from offshore seismic data 23 km along strike to the northeast. The southeast vergent Tea Cove thrust, which formed an early upper detachment to the triangle zone, is offset and overturned by the north‐northwest vergent Round Head thrust. The Round Head thrust is interpreted to flatten into a second southeast vergent thrust, the Red Brook detachment, which formed a late upper detachment to the triangle zone. Some map‐scale structures are interpreted as fault‐bend folds above oblique ramps on the Red Brook detachment. Allochthonous crystalline basement within the triangle zone, beneath its attached platformal cover, is interpreted as a result of thrust reactivation of a preexisting basement‐cutting normal fault, which may have formed during rifting of the early Paleozoic Iapetus Ocean. This interpretation is suggested by the stratigraphy and geometry of spatially restricted coarse conglomeratic units on Port au Port Peninsula, and is supported by the restored cross sections.
Magnetic reconnection in the presence of sheared flow and density asymmetry: Applications to the Earth's magnetopause
Authors: La Belle‐Hamer A. L. , Otto A. , Lee L. C.
Published: February 2008

Classical models of magnetic reconnection consist of a small diffusion region bounded by two symmetric slow shocks, across which the plasma is accelerated. Asymmetries often present in space plasmas are sheared plasma flow and dissimilar plasma densities on the two sides of current sheets. In this paper, we investigate magnetic reconnection in the presence of a shear flow and an asymmetric density across the current sheet using two‐dimensional magnetohydrodynamic (MHD) simulations. The results demonstrate that magnetic reconnection can occur only for a plasma flow velocity (in the frame of the X line) which is below the Alfvén speed in each inflow region. This limits the velocity of the X line to a certain range for a given flow shear and provides an upper limit to the total velocity shear at which reconnection ceases to operate. Depending on the direction of the flow in the adjacent inflow region, the effects from the sheared flow and from the density asymmetry will compete with or enhance each other in respect to the magnitude and location of the currents which bound the outflow regions. The results are applied to the dayside and flank regions of the magnetosphere. For the dayside region where the magnetosheath flow is slow, the magnetic field transition region is thin and the accelerated flow is earthward of the sharp current layer (magnetopause). At the flanks tailward of the X line, shear flow and density asymmetry effects compete making the magnetic field transition layer broad with the high‐speed flow contained within the transition region which explains corresponding observations. At the flanks sunward of the X line, shear flow and density asymmetry effects enhance each other and lead to a strong current sheet on the magnetosheath side of the accelerated flow. The total volume affected by magnetic reconnection is much larger than the steady state region. A large bulge region precedes the steady state region. Qualitatively, the bulge and the steady state region have similar signatures and both can explain observations. We provide criteria in order to distinguish between the bulge and the steady state region in observations.
Automatic Calibration of Conceptual Rainfall‐Runoff Models: Optimization Algorithms, Catchment Conditions, and Model Structure
Authors: Gan Thian Yew , Biftu Getu Fana
Published: February 2008

From 32 CRR‐catchment cases (combinations from four conceptual rainfall‐runoff models (CRR) and eight catchments) calibrated with either two or three optimization methods, (1) the shuffle complex evolution method (SCE‐UA), (2) the multiple start Simplex (MSX), and (3) the local Simplex, it seems that all three methods produced parameter sets of comparable, local‐optimum quality. Even with comparable performance among the models, some parameter values derived by the three optimization methods for the same CRR‐catchment cases are surprisingly different from each other. In addition, parameter sets of SCE‐UA or MSX, which often produce marginally better results than the local Simplex at the calibration stage, could end up with worse results at the validation stage. Apparently, given the inherent limitations of calibration data, model inadequacies, and identifiability problems, it is impossible to achieve global convergence in the parameter search. However, other than those for dry catchments such as Ihimbu or Bird Creek, the parameter sets obtained are generally feasible. Both SCE‐UA and the local Simplex are viable optimization tools, while MSX is inefficient computationally. SCE‐UA can complete the parameter search in one run, while the local Simplex often requires multirun operations to get good results.
Aerosol and ozone distributions over the western North Atlantic during WATOX‐86
Authors: Bridgman H. A. , Schnell R. C. , Bodhaine B. A. , Oltmans S. J.
Published: February 2008

On January 4, 6, 8, and 9, 1986, a series of National Oceanic and Atmospheric Administration WP‐3D research flights was conducted over the western Atlantic Ocean 200‐300 km off the coast of North America from Nova Scotia to Georgia as part of the Western Atlantic Ocean Experiment (WATOX). Rights were made perpendicular to NW airflow to establish the flux of gas and aerosol emissions off the North American continent to the ocean. Representative condensation nucleus (CN) concentrations averaged 150‐250 cm−3 in the free troposphere in clean conditions, but in atmospheric layers containing anthropogenic air pollution transported from long distances, CN concentrations reached 6500 cm−3. In the marine boundary layer, CN concentrations averaged 500 to 750 cm−3 under relatively clean conditions, and 1500 to 3000 cm−3 in polluted air. Aerosol scattering extinction (bsp) ranged from 70 × 10−6 m−1 in the marine boundary layer to 20 × 10−6 m−1 in the free troposphere. Aerosol bsp was not as responsive to changes in atmospheric structure as CN although factor‐of‐2 changes across the marine boundary layer were observed. Aerosol size spectra in the marine boundary layer were an order of magnitude greater than those in the free troposphere. Consistent peaks in the volume spectra between 8 and 10 μm diameter established the importance of sea salt as a major aerosol component. Ozone profiles in the free troposphere, normally in the 30‐40 ppb range, exhibited laminae of enhanced concentrations (up to 70 ppb) at moisture boundaries, suggesting that active ozone production was occurring at these levels. Ozone concentrations within the marine boundary layer were generally lower than in the free troposphere.
Controls of CO2 sources and sinks in the Earth scale surface ocean: Temperature and nutrients
Authors: Volk Tyler , Liu Zhongze
Published: February 2008

The ocean has prominent regions where disequilibium persists on an annual average between CO2in the surface water and the overlying atmosphere. This paper examines several of these regions using models in which CO2 cycles in a steady state, where sources (ocean outgassing) and sinks (ingassing) are in balance. The relative strengths of surface temperatures and surface nutrients, the two main contributors to the source and/or sink properties, are quantified in each model. Models with two ocean surfaces indicate that the sink in the north Atlantic and the sources in the equatorial Atlantic and Pacific are all dominated by the global temperature patterns. Several ocean models with three surface zones explore alternatives for forming the earth's strongest source, in the equatorial Pacific, a particularly interesting region because temperature and nutrients clearly reinforce each other. Data show that a model to explain the control factors upon the equatorial Pacific source must extend to over 30% of the global ocean to reach the nearest counterbalancing sink between 40°S and 50°S. From the analyses of the equatorial Pacific, the conclusion is that temperature control is responsible for certainly more than 50%, and probably closer to 70%, of the CO2outgassing, with the balance coming from the Earth scale surface nutrient structure.
Causes of anoxia in the world ocean
Authors: Sarmiento Jorge L. , Herbert Timothy D. , Toggweiler J. R.
Published: February 2008

We examine the hypothesis that global scale episodes of anoxia such as occurred in the Cretaceous are due to high productivity and/or stagnation of the circulation. Two modes of ocean circulation are considered: a thermohaline overturning cell, essentially vertical, which involves global scale upwelling into the surface followed by sinking in deep water formation regions; and an approximately horizontal cell which connects the abyss directly with deeply convecting waters in deep water formation regions. Modern analogs for these processes are formation of North Atlantic Deep Water and Antarctic Bottom Water, respectively. Over most of the oceans the surface new production is nutrient limited and thus directly proportional to the supply of nutrients by the vertical overturning cell. A reduction in oxygen can only be brought about by increased vertical overturning associated with increased production. In addition, the model shows that as the deep ocean becomes lower in oxygen, the sensitivity of the oxygen levels to the meridional circulation decreases such that it becomes difficult or impossible to achieve complete anoxia. This relative insensitivity of deep ocean oxygen levels to the magnitude of the vertical overturning cell and associated surface production may explain why it has been difficult to establish a clear connection between high surface productivities in low and mid‐latitudes and anoxia. In deep water formation regions, on the other hand, new production is not nutrient limited. A reduction in abyssal oxygen can be brought about by high productivity in such regions and/or by stagnation of the horizontal circulation cell, in accordance with the stagnation hypothesis. Furthermore, the sensitivity of the deep ocean oxygen to the processes occurring in deep water formation regions increases as oxygen levels decrease. We therefore suggest that processes occurring in deep water formation regions may be the critical ones in determining deep ocean oxygen.