bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.
Oxygen‐18 and carbon‐13 records for the last 14,000 years from Lacustrine carbonates of Siling‐Co (Lake) in the Qinghai‐Tibetan Plateau
Authors: Morinaga H. , Itota C. , Isezaki N. , Goto H. , Yaskawa K. , Kusakabe M. , Liu J. , Gu Z. , Yuan B. , Cong S. 
Published: February 2008

To understand paleoenvironmental changes for the central Qinghai‐Tibetan plateau, we analyzed stable isotopes of oxygen and carbon from calcium carbonates in a bottom sediment core collected from Siling‐Co (lake). Five conventional and two TAMS 14C dates indicate that the core recovered sediments of the last 14,000 years. Calcium carbonates in the sediments seem to be primary carbonates precipitated chemically in the lake, and not clastic particles from limestones distributed around the lake, because of large variation of isotopic ratios, isotopic covariance since 6,000 yr BP and similarity between dates from total calcium carbonates and organic carbon. Their isotopic composition therefore reflects that of the lake water. We present the following paleoenvironmental history over the last 14,000 years in the central part of the plateau, from secular variations of δ18O, δ13C and CaCO3 content throughout the core: (1) Desiccation was dominant during the latter part of the Last Glacial stage (14,000 to 11,000 yr BP). (2) The Last Glacial stage abruptly terminated at 11,000 yr BP. (3) A temperate and stable climate was dominant from 11,000 to 5,000 yr BP. (4)Climatic conditions fluctuated from 5,000 to the present, including two strong desiccation periods (5,000 to 4,000 yr BP and 3,000 to 2,000 yr BP) and an intermediate period of heavy rainfall (4,000 to 3,000 yr BP). This period is also characterized by a covariant O and C isotopic trend.
Amine nitrogen in the atmospheric environment over the North Atlantic Ocean
Authors: Gorzelska Krystyna , Galloway James N. 
Published: February 2008

During the course of the Global Change Expedition/Coordinated Air‐Sea Experiment/Western Atlantic Ocean Experiment, we collected 77 aerosol and 20 precipitation samples over the North Atlantic Ocean; we speciated and quantified the organic nitrogen in these samples in the form of 18 different water‐soluble primary amine compounds. We calculated the nitrogen contribution from these 18 amine species as the total amine nitrogen (TAN). Concentrations of TAN in aerosol samples ranged from 0.3 to 1630 pmol N m−3. Serine, glycine, arginine, alanine, ethanolamine, and methylamine contributed approximately 90% of TAN. Highest concentrations were in the samples collected near North America, Bermuda, the Azores, and in the Arctic Circle; low concentrations were in the samples collected in the Gulf Stream and in the equatorial North Atlantic. Radon concentrations, trajectory analyses, and correlations between different amine species provided clues to the origin and atmospheric history of these compounds. The long‐range transport of terrestrial materials and oceanic inputs contributed to TAN. At low background concentrations, there was a statistically significant linear correlation between TAN and ammonium (NH4+) that persisted over the entire ocean area. Although their deposition flux may approach 10% of ammonium flux, relative to NH4+ the aerosol concentrations of the water‐soluble primary amines were small (average=2%). The TAN in rain samples ranged from <5 to727 nM (average=164 nM). Generally, the amine species in precipitation paralleled those in aerosol. The scavenging ratio for individual species ranged from 200 to 3000.Supplemental table is available with entire article on microfiche. Order from American Geophysical Union, 2000 Florida Avenue, N.W., Washington, D.C. 20009. Document G90‐001; $2.50. Payment must accompany order.
Large‐scale eddies in the Somali Current
Authors: Düing Walter 
Published: February 2008

Velocity records from a subsurface mooring in the Somali Current exhibit direction reversals during a time when the SW Monsoon is still steadily blowing. The records are interpreted in terms of large‐scale eddies which seem to be generated near the equator and propagate slowly northward along the coast of Somalia.The Somali Current constitutes the most important branch of the complex East African Current System. It is generated by the Summer Monsoon and flows along the coast of East Africa, from the latitude of Mombasa to the island of Socotra, corresponding to a distance of about 2200 km. Translated to the path of the Gulf Stream, this corresponds to the distance between Yucatan and Cape Hatteras. Despite the fact that this current has been immensely important to seafarers for nearly 2000 years, it is one of the least explored boundary current systems in the Northern Hemisphere. In contrast to the Gulf Stream, which shows only insignificant seasonal variations, the Somali Current reverses its direction following the seasonal change of the monsoon winds. A first long‐term current meter record from the region indicates that the classical picture of a straightforward oceanic response to the forcing of the windstress may be greatly oversimplified. It is shown that some of the key features of the record are not related to fluctuations of the wind field, but more likely to large‐scale eddies propagating northward along the coast.
High strain rate studies in rock
Authors: Grady Dennis 
Published: February 2008

Dynamic compression studies using high velocity impact are usually considered to involve a catastrophic process of indeterminate loading rate by which a material is brought to a shock compressed state. Although this is frequently the case, methods are also available to control the rate of strain during the shock compression process. One of the most accurate of these methods makes use of the anomalous nonlinear elastic property of glass to transform an initial shock or step wave input into a ramp wave of known amplitude and duration. Fused silica is the most carefully calibrated material for this purpose and, when placed between the test specimen and the impact projectile, can provide loading strain rates in the range of 104/s to 106/s for final stress states of approximately 3.9 GPa or less.Ramp wave compression experiments have been conducted on dolomite at strain rates of 3 × 104/s. Both initial yielding and subsequent deformation at this strain rate agrees well with previous shock wave studies (⋵ ∼ 106/s) and differs substantially from quasi‐static measurements (⋵ ∼ 10−4/s). The ramp wave studies have also uncovered a pressure‐induced phase transition in dolomite initiating at 4.0 GPa.
The Earth hydrogen exobase near a solar minimum
Authors: Vidal‐Madjar A. 
Published: February 2008

Measurements of the solar Lyman alpha flux and of the exobase hydrogen density distribution were made by the University of Paris experiment aboard the Orbiting Solar Observatory (OSO‐5) during the period August 1974 to August 1975. These data were obtained near the end of the solar cycle # 20, at a time of nearly minimum solar activity. To compare most accurately solar minimum and solar maximum conditions, these data were subjected to the same analysis procedures used for OSO‐5 data from 1969‐1972 (Vidal‐Madjar et al., 1973).The results are presented individually and the average exobase hydrogen density is observed to reach 3.5 × 105 atoms cm−3 (at 500 km) for an average exospheric temperature as low as 725 K. This result shows that the non‐thermal escape mechanism increases even more than previously observed. For low solar activity conditions, the non‐thermal escape flux can be more than a factor seven larger than the Jeans escape flux.The non‐thermal mechanisms become increasingly important at low solar activity; the minimum‐to‐maximum density ratio deduced from only dayside measurements is also observed to increase at solar minimum and may reach values as high as 3.7, although the average value is of the order of 2.1.Finally, the dayside, latitudinal sub‐solar bulge monitored from 1969 to 1972 is still observed at solar minimum and presents the same amplitude as during solar maximum conditions.
New evidence for tectonic uplift in the Diablo Plateau Region, West Texas
Authors: Reilinger Robert , Brown Larry , Powers Dennis 
Published: February 2008

Recent releveling measurements conducted by the National Geodetic Survey in West Texas and southeastern New Mexico indicate uplift of the Diablo Plateau‐Salt Basin region relative to benchmarks to the northeast in the Great Plains. These new measurements confirm and enhance the previously reported interpretation of releveling data in this area. Total relative uplift measured between 1934 and 1977 reaches 19 ± 3 cm. Combining this new information with leveling data from 1934, 1943 and 1958 along this same route indicates that: (1) the uplifted area extends 120 km in the east‐west direction (there is presently no control on any north‐south component of tilting), with maximum relative uplift occurring approximately 12 km west of the boundary between the Diablo Plateau and Salt Basin graben; and (2) on the time scale between measurements (∼20 yrs), uplift appears to be occurring more or less continuously, although not at a constant rate. The progressive deformation indicated by the releveling measurements, the large magnitude relative to possible leveling errors, and the spatial dimensions of the uplift rule out systematic errors or near‐surface effects (water table variations, sediment compaction, etc.) as an explanation and favor a tectonic origin. Intracrustal magmatic activity or some form of preseismic deformation (dilatancy, fault creep at depth, etc.) appear to be the most reasonable explanations in view of presently available geologic and geophysical information.The pattern of uparching is perturbed at the Salt Basin graben, indicating 4.2 ± 0.3 cm of subsidence relative to its margins between 1958 and 1977. This subsidence could be related to the regional tectonic uparching, although near‐surface, non‐tectonic effects cannot be excluded.
Vertical winds as a plausible cause for equatorial counter electrojet
Authors: Raghavarao R. , Anandarao B. G. 
Published: February 2008

The signatures of the counter‐electrojet that occurs in the afternoon hours as recorded on the ground and satellite‐borne magnetometers during the magnetically quiet days, clearly indicate reversal of the jet current in a narrow latitude region centered around the dip equator. The latitudinal variation of the vertical (Z) and northward (H) components of the earth's magnetic field reveal that the decrease and reversal of the eastward toroidal current of the jet is maximum around the dip equator.By numerically solving the equations governing the electrojet including the terms due to local winds it is shown that vertically upward winds of 15 ‐ 20 m/s are most effective in producing the counter‐electrojet. The profile of vertical winds adopted in the model calculations was actually measured during twilight hours. It is shown that the latitudinal variations of H and Z observed during the counter‐electrojet can be reproduced satisfactorily by the vertical wind hypothesis. A rocket experiment is suggested to verify the presence of vertical winds during the counter‐electrojet.
Oxygen isotopic anomalies in Allende Inclusion Hal
Authors: Lee Typhoon , Mayeda Toshiko K. , Clayton Robert N. 
Published: February 2008

The oxygen isotopic composition has been measured on the constituent phases of Allende inclusion HAL, which has unusual mineralogical, chemical, and calcium isotopic compositions. The oxygen in HAL is heterogeneous, with the rim showing more “normal” composition and the hibonite core showing large deviation from both the terrestrial material and the usual inclusions. The observed pattern indicates that HAL is a bona fide and more devious member of the rare “FUN” family, whose isotopic composition is characterized by correlated nuclear effects and extreme mass fractionation. The data imply that HAL has suffered a large oxygen mass fractionation of 25‰ per mass unit, followed by exchange with oxygen in a second reservoir. The present experiment supports the identification of two distinct reservoirs from which all refractory inclusions in carbonaceous meteorites derived their oxygen. The required fractionation process seems to operate according to the volatility of various elements and could have been caused by evaporation during a heating event. Nuclear anomalies can be produced in the same heating event if the progenitors of the refractory inclusions were macroscopic aggregates of tiny pre‐solar intersteller dust grains and if these grains were destroyed differentially during the evaporation.Primitive meteoritic samples showing correlated isotopic abundance anomalies due to nuclear processes are important to the understanding of the origin of solar system material, since their correlated patterns may be identifiable with nucleosynthetic signatures of astrophysical sources. Only two such samples are well established, Cl and EKl‐4‐1, both Ca‐Al‐rich inclusions from the Allende meteorite. These rare objects are almost indistinguishable from the usual Ca‐Al inclusions in their mineralogical and chemical compositions and are thus difficult to recognize. The most striking signposts for them are the pronounced isotopic anomalies in O, Mg, and Si which apparently resulted from extreme mass‐dependent fractionation processes [Clayton and Mayeda 1977, Clayton et al. 1978, Wasserburg et al. 1977, Yeh and Epstein 1978]. Because of this intriguing coupling between the Fractionation and Unknown Nuclear effects, this type of anomaly has been dubbed “FUN.”Allende inclusion HAL, which showed large Ca fractionation favoring heavy isotopes with additional superposed nuclear effects [Lee et al. 1979] is a potential FUN sample. However, HAL is different from previous FUN samples in three respects: (1) HAL has a highly unusual mineralogical composition [Allen et al., 1979, 1980]; (2) neither Cl nor EKl‐4‐1 shows Ca fractionation favoring heavy isotopes; (3) the Mg in HAL is not fractionated [Lee et al., 1979]. In this paper we report an oxygen isotopic study which demonstrates that HAL is indeed a FUN object.
Photodissociation quantum yields for the NO3 free radical
Authors: Magnotta Frank , Johnston Harold S. 
Published: February 2008

The nitrate free radical was photolyzed by a pulsed tunable dye laser between 470 and 685 nm, at 296 K, and in the presence of 10 torr N2. The two product channels, NO + O2 and NO2 + O, were measured by resonance fluorescence of NO or of O. Absolute calibration of the method was achieved by in situ ultraviolet photolysis of NO2, which yields both NO and O. With these data on photochemical yields, the photolysis coefficients for the two product channels at the surface of the earth with an overhead sun over wavelengths 470‐700 nm are calculated to bej1(NO + O2) = 0.022 ± 0.007 s−1j2(NO2 + O) = 0.18 ± 0.06 s−1
Design criteria for laboratory measurements of low permeability rocks
Authors: Trimmer Donald A. 
Published: February 2008

The advantages and limitations of two versions of the pulse technique for laboratory measurements of low permeabilities (10−16 to 10−24 m²) are discussed. The transient pulse technique developed by Brace et al. [1968] is the preferred method because of the ease of data reduction. The modified transient pulse technique developed by Trimmer et al. [1980] can be used when the assumptions inherent in the transient pulse technique are invalid.The systematic error associated with the transient pulse technique is a function of the ratio of the effective sample pore volume to the reservoir volumes. If this ratio is less than 0.25, then the error associated with the transient technique is less than 10%. The modified transient pulse technique does not suffer from this systematic error. Criteria are also presented for optimizing the experimental configuration for measurement durations as well as ease of data reduction.
Frozen‐flux upper limits to the magnitudes of geomagnetic Gauss coefficients, based on MAGSAT observations
Authors: Benton Edward R. , Coulter Margaret C. 
Published: February 2008

If the earth's core is regarded as a perfect conductor and the surrounding mantle as an insulator, then the unsigned magnetic flux, Po, crossing the core‐mantle boundary remains constant in time. In practice this constancy is limited by the core's finite conductivity, but it is expected to hold for at least millenia. For such time spans an upper limit Gnm or Hnm may be derived for the magnitude of any geomagnetic Gauss coefficient gnm or hnm, by assuming that the entire value of Po is attributed to that coefficient alone. Such upper limits are evaluated here for n = 1 ‐ 4, using a value of Po derived from Magsat data.The ratio |gnm/Gnm|, |hnm/Hnm| between the observed magnitude of a coefficient and its upper limit defines a "relative multipole index" for the present value of that coefficient. Using the Magsat model MGST 6/80 it is found that for the dipole term this ratio is about 0.72, suggesting that |g10| is presently only about 28% lower than the maximum value during the past few millenia. Also, the largest of the other multipole indices calculated (|g3¹/G3¹| ≃ 0.23) is a factor of over 3 smaller, so presumably a dramatic change in field configuration outside the core is required before the next polarity reversal is completed.
Aerosol minima
Authors: Hogan A. W. , Barnard S. C. , Winters W. 
Published: February 2008

The total number concentration of atmospheric particles, as measured with a variety of Nolan‐Pollak derived photo electric nucleus counters, is often indistinguishable from the concentration measured in filtered air. These periods of near zero aerosol concentration persist for periods of a few minutes to tens of hours at many places.Near zero concentrations are frequently measured over calm seas following dissipation of fog, but aerosol generation by bubble mechanisms increase the aerosol concentration in a few minutes. Interesting cases of near zero surface aerosol concentration are found over the Arctic in summer when such concentrations persist at the surface for periods of time dependent on sky conditions, surface vegetation and near surface meteorological parameters. Size measurements of the reappearing aerosol indicate that it is formed in situ.
13C/12C ratios in CO2 extracted from Antarctic ice
Authors: Friedli H. , Moor E. , Oeschger H. , Siegenthaler U. , Stauffer B. 
Published: February 2008

Air is extracted from bubbles of polar ice samples by a dry extraction method, and the 13C/12C ratio is measured on CO2 separated from the air.Ice samples of typically 700 g are crushed at ca. −20°C, the evolving air is trapped cryogenically, and CO2 is frozen out from this air for mass‐spectrometric isotope analysis. First δ13C and δ 18O results of CO2 from Antarctic ice cores are presented, and δ13C is discussed in relation to atmospheric CO2 variations. δ13C of 400 to 800 year old ice is ca. 1.1 %o higher than the 1980 atmospheric value, which agrees well with model‐based estimations. The measurement of three ca. 50,000 yr old samples yielded astonishingly low values, but contamination cannot be excluded.
Evidence for the presence of 53Mn in the early solar system
Authors: Birck Jean‐Louis , Allègre Claude J. 
Published: February 2008

Chromium isotopic anomalies appear to be widespread in the Allende inclusions. Clear anomalies are shown in the 53Cr/52Cr isotopic ratio. Deviations from the terrestrial value are correlated with the Mn/Cr ratios indicating that 53Mn (half life T=3.7 × 106y) existed at the time of formation of the meteorite inclusions. The initial 53Cr/52Cr in the inclusions is lower than the terrestrial value.Recent results have shown that chromium isotopic anomalies are frequent on the 54Cr isotope (Birck and Allègre, 1984). At the same time our results suggested the possibility of some anomalies on the 53Cr isotope which can be produced by the decay of 53Mn.The present article presents improved precision measurements on the same inclusions of the Allende meteorite and an extension of the measurements to mineral separates. These results are the first evidence for live 53Mn in the early solar system (noted 53Mn* in the following).
Application of 36/40Ar Versus 39Ar/40Ar Correlation diagrams to the 40Ar/39Ar spectra of phlogopites from Southern African kimberlites
Authors: Phillips D. , Onstott T. C. 
Published: February 2008

40Ar/39Ar incremental heating analyses were performed on phlogopite mica from the DK‐7 kimberlite pipe in southern Botswana. No age plateau was obtained, as the spectrum yielded a step‐wise increase in age with increasing temperature. The ages appear to be anomalously high, suggesting the presence of excess radiogenic argon components that have been partially released by diffusion during cooling of the kimberlite.The pattern of data points on an 39Ar/40Ar vs. 39Ar/40Ar correlation plot, however, delineates two types of excess argon, one which is radiogenic‐rich, and one with a 40Ar/36Ar ratio of 366. The latter component may reflect the contamination of the kimberlite xenocrysts by fluid originating from an undegassed mantle source.
Equatorial counterelectrojet: Two distinct categories
Authors: Kane R. P. 
Published: February 2008

It is shown that among the equatorial counterelectrojets there are two distinct categories, the fast one and the slow one, having different characteristics.In a recent communication [Kane, 1978] it was shown that there is no clear‐cut relationship between equatorial counterelectrojet and interplanetary magnetic field (IMF). In the communications Rastogi and Patel [1975] and Patel [1978], sharp decreases in the equatorial H field during daytime (also termed as counterelectrojets by these authors) are shown to be associated with rapid fluctuations of the latitude θ of the IMF. From private conversations and correspondence, it seems that many people consider the latter results as contradiction of the former one. Contradictory opinions in scientific matters are neither uncommon nor unwelcome, as these aid the free spirit of scientific enquiry. However, in the present case, no contradiction whatsoever is involved, as is explained below. There are two distinct categories of equatorial counterelectrojets, and their characteristics are described in the sections that follow.