bluuebunny/crossref_metadata_2025 huggingface dataset:
Reconstruction of oceanic flow characteristics from quasi‐Lagrangian data: 1. Approach and mathematical methods
Authors: Eremeev V. N. , Ivanov L. M. , Kirwan A. D.
Published: February 2008

We describe a nontraditional method for processing data derived from quasi‐Lagrangian tracers. The approach relies on a representation of the thermohydrodynamic field as a set of a finite number of functions (modes) with the subsequent computation of mode amplitudes from quasi‐Lagrangian data. This requires special methods for calculating mode components of the thermohydrodynamic field from Lagrangian observations. Also, because of the quasi‐Lagrangian nature of the data there are special problems caused by the need to filter in both space and time and to account for motions unresolved by such observations. The former problem is addressed by a filtering procedure based on a variational criteria and Pontryagin's principle. To handle the latter problem, a subgrid parameterization scheme appropriate for Lagrangian data is proposed.
Characteristics of suspended particles at an 11‐hour anchor station in San Francisco Bay, California
Authors: Kranck Kate , Milligan T. G.
Published: February 2008

Hourly measurements of suspended sediment in situ floc size distributions, constituent grain size distributions, total concentrations, and average particle densities are presented for five depths from an 11‐hour anchor station in San Francisco Bay. The flocs formed well‐sorted distributions with modal sizes between 100 and 500 μm, whereas the disaggregated sediment was poorly sorted with about the same volume of material in all size classes and relatively little material coarser than 100 μm. For both types of size spectra, concentrations at the coarse end of the size distribution fall off rapidly at a size range which varied with bottom shear stress. The settling rates corresponding to the modal floc diameters were generally related to the maximum disaggregated diameters by a square relationship, but turbulence appeared to limit floc size in the coarsest samples. Both the floc and disaggregated grain size vary with total concentration, suggesting that flocs are relatively stable entities which do not change during alternating settling and resuspension.
A view of the Canary Basin thermocline circulation in winter
Authors: Fiekas Volker , Elken Jüri , Müller Thomas J. , Aitsam Ain , Zenk Walter
Published: February 2008

During January and February 1989 the recirculation of the subtropical gyre in the eastern North Atlantic was surveyed with a three‐ship experiment. The analysis of hydrographic measurements and velocity data from a shipboard acoustic Doppler current profiler reveals the synoptic‐scale circulation patterns and water mass distributions in the Canary Basin. The geostrophic transport stream function estimated with a horizontally varying reference level of no motion highlights the major currents in three layers representing the vertical structure of the horizontal circulation. The classical circulation scheme is shown by the stream function in the upper 200 m: the Azores, Canary, and North Equatorial currents. Unlike the deep‐penetrating Azores Current, the Canary Current and the North Equatorial Current are restricted to the upper 200 m. Both carry North Atlantic Central Water along the water mass boundary with South Atlantic Central Water. South Atlantic Central Water flows through the passage between the Cape Verde archipelago and Africa via narrow currents into the area north of 14.5°N. At the southern edge of the subtropical gyre we identify an eastward flow of Antarctic Intermediate Water between 700 and 1200 m.
Airborne synthetic aperture radar imagery of atmospheric gravity waves
Authors: Thomson Richard E. , Vachon Paris W. , Borstad Gary A.
Published: February 2008

We analyze the oceanic “imprints” of atmospheric internal gravity waves detected in airborne synthetic aperture radar (SAR) images collected off the west coast of Vancouver Island, British Columbia, in June 1990. A sequence of SAR images taken over a period of 2.5 hours reveals that the waves traveled with group velocities of 3–6 m s−1 toward the northwest, counter to the 10 m s−1 surface winds. Wave crests were oriented normal to the coast and had lateral extents of several tens of kilometers. Observed wavelengths ranged from 1.2 to 2.3 km, while calculated wave periods ranged from 3 to 8 min. A comparison of the observed wave properties with values derived from a simple three‐layer density model of the troposphere suggest that the waves were low‐mode oscillations trapped within a 0.75‐km‐thick temperature inversion overlying a 1‐km‐thick weakly stratified marine boundary layer. Wave propagation was counter to the wind shear within the inversion layer. Generation of the internal wave groups appears to have occurred near the southern boundary of the stable marine air mass, where it bordered a convectively active air mass that was intruding northward along the coast.
World ocean circulation diagnostically derived from hydrographic and wind stress fields: 2. The water movement
Authors: Fujio Shinzou , Kadowaki Toshimitsu , Imasato Norihisa
Published: February 2008

The water movement in the world ocean is examined using a velocity field diagnostically derived from hydrographic and wind stress data. The movement of water is calculated numerically by tracking its constituent particles, and the attention is focused on where the water originates. The particle tracking indicates that deep water is formed not only in the North Atlantic and the Weddell Sea but also in the Ross Sea. The North Atlantic Deep Water contributes considerable volume to all the deep basins of the world ocean, while the Weddell Sea Deep Water (WSDW) tends to be confined to the southern region of the southern ocean. Similarly, the Ross Sea Deep Water (RSDW) does not flow northward in the present model because the Antarctic circumpolar current (ACC) penetrates sufficiently deep to carry the RSDW away to the South Atlantic. It is also found that the WSDW does not mix directly with the circumpolar Water because of the South Scotia Ridge, but rather mixes with the water recirculating in the Weddell Gyre, which is supplied by the middepth water of the ACC in the Atlantic‐Indian Basin. Water composition in 16 basins is summarized in the form of box diagrams of deep water exchange.
Volume flux induced by wind and waves in a saturated sea
Authors: Weber Jan Erik , Melsom Arne
Published: February 2008

On the basis of a Eulerian analysis in a rotating, homogeneous ocean, the Lagrangian mean volume fluxes induced by wind and wind‐generated gravity waves are obtained. Since only fluxes are considered, i.e., vertically integrated equations, no particular form of the vertical variation of the turbulent Reynolds stress has to be assessed. The effects of friction and turbulence are neglected in computing the primary wave field in the ocean. The wave growth, due to instability at the air‐water interface under the action of the wind, is not specifically computed. Observational values for the growth rate are used when discussing the results. The effect of wave breaking is modeled in a very simple way. It is shown that the Lagrangian momentum transfer to mean ocean currents due to growing/breaking waves in the saturation range is comparable to that obtained by the joint action of viscous and turbulent stresses.
Estimation of nitrate flux in a tidal front from satellite‐derived temperature data
Authors: Morin P. , Wafar M. V. M. , Le Corre P.
Published: February 2008

Regressional relations between sea surface temperature and NOAA satellite advanced very high resolution radiometer radiometric data, and between in situ temperature and nitrate concentrations in the surface and subsurface waters of the Ushant tidal front were significant. Nitrate images constructed from satellite‐derived temperature data agreed well with sea truth data. Nitrate transport into the euphotic zone in a spring‐neap tidal cycle, as deduced from satellite images, agreed with nitrate uptake rate and phytoplankton productivity. It is suggested that satellite‐derived nitrate images can be useful tools for assessing nitrate‐based productivity over large geographical areas in short time intervals.
Modeling mixed‐layer photochemistry of H2O2: Physical and chemical modeling of distribution
Authors: Sikorski Richard J. , Zika R. G.
Published: February 2008

We have combined a one‐dimensional mixing model with chemical parameters to model distribution of H2O2 in the surface ocean. The shape of the modeled H2O2 depth profile and the shape of the surface‐concentration diel were controlled by mixing dynamics. The model reproduced measured mixed‐layer H2O2 concentrations, within 20% at six of 14 stations, and within 40% at four other stations. This strongly supported the model's identification of photoproduction, mixing, and removal as the major processes controlling H2O2 distribution in the surface ocean. The key to this performance was identification of two classes of photoproductive waters, based on the ratio of UV absorption (c330 nm m−1) to visible absorption(c460 nm).
The δ18O of dissolved O2 in the surface waters of the subarctic Pacific: A tracer of biological productivity
Authors: Quay P. D. , Emerson S. , Wilbur D. O. , Stump C. , Knox M.
Published: February 2008

The 18O/16O of dissolved oxygen was measured in the upper ocean of the subarctic Pacific in 1988. In May and August, at stations Papa (50°N, 145°W) and R (53°N, 145°W), the mean δ18O in the mixed layer was 23.84±0.20 and 24.00±0.24 ‰ (versus standard mean ocean water) consistently more depleted than atmospheric saturation levels by about 0.4 ‰. This relative depletion is caused by input of photosynthetically produced O2. A value for the isotopic fractionation effect during respiration (αT) of 0.978±0.006 was determined from the time rate of change of the concentration and δ18O of O2 in the mixed layer measured during August 1988. Below the mixed layer (100–280 m) the O2 concentration decreased with a corresponding increase in δ18O. Model derived values for αT over this depth region ranged from 0.980 to 0.988 and depended on the mixing model. The difference between αT determinations for the surface layer versus upper thermocline likely results from mixing model inaccuracies or different isotope fractionation effects during plankton and bacterial respiration. If the calculated mixed layer αT values apply oceanwide, then photosynthesis and respiration by the marine biota have a similar effect to land plants in maintaining the δ18O of atmospheric O2 at 23.5 ‰.
Nitric oxide in the equatorial Pacific boundary layer: SAGA 3 measurements
Authors: Torres A. L. , Thompson A. M.
Published: February 2008

As part of the Soviet‐American Gases and Aerosols (SAGA) experiment, mixing ratios of atmospheric nitric oxide were measured at the surface of the equatorial Pacific Ocean between Hawaii and American Samoa during February and March 1990. Overall, NO mixing ratios for measurements made between 0800 and 1600 LT averaged 2.9 ± 0.1 parts per trillion by volume (pptv), where the uncertainties represent 95% confidence limits in the mean. Concentrations were generally highest near the equator: NO mixing ratios obtained between 0800 and 1600 LT averaged 4.0 ± 0.2 pptv in the 5°S–5°N latitude band and 2.1 ± 0.2 pptv in the 5°–15° bands north and south of the equator. In the equatorial band the average diurnal behavior was a steady rise in NO from early morning until local noon, reaching a peak of about 4.5 pptv that remained until late afternoon before beginning a rapid decline. In the 5°–15° bands north and south of the equator the average diurnal curve for NO was flat (within experimental uncertainties) at about 2 pptv from 0800 to 1600. These findings are consistent with previous measurements of NO in both boundary layer and free tropospheric remote Pacific environments. They confirm a picture of the remote equatorial Pacific boundary layer as a region of low NO and net photochemical destruction of O3. The NO and O3 measured on SAGA 3 correspond to a loss rate of ozone of ∼1 parts per billion by volume (ppbv) O3/day in a region where mean surface O3 is 10 ppbv.
Aerosol variability in the vertical in the southwest Pacific
Authors: Kristament I. S. , Liley J. B. , Harvey M. J.
Published: February 2008

Vertical variations of the tropospheric aerosol concentration and size distribution, for sizes between 0.12‐μm and 8‐μm diameter, in the Southwest Pacific have been examined. The data were obtained from flights by an instrumented aircraft over a period of more than 3 years. The data show that 44% of the variance in the concentration of the accumulation mode aerosol (0.12 μm to 0.5 μm) can be accounted for when it is modeled by an exponential decrease with height to 2400 m and a constant concentration above. The coarse mode aerosol concentration (greater than 0.5μm) also decreases exponentially with height to 2400 m (46% of the variance accounted for) at a rate only slightly greater than for the accumulation mode aerosol. More of the variance can be accounted for by fitting the exponential decrease multiplied by a different constant term to each vertical profile separately. This implies an improvement in the predictability of the aerosol concentration in the vertical if the column amount or the concentration at some height is known. Examination of the shape of the size distributions in the free troposphere shows no coarse mode, although the tail of the accumulation mode distribution extends to sizes greater than 0.5 μm. At low altitudes the concentration of accumulation mode particles is greater and a coarse mode is apparent. The shapes of the distributions, particularly above the boundary layer, are similar and independent of the particle concentration.
Determination of characteristic features of cloud liquid water from satellite microwave measurements
Authors: Liu Guosheng , Curry Judith A.
Published: February 2008

In this paper we present an algorithm for determining liquid water path (LWP) in clouds using satellite microwave measurements from the special sensor microwave/imager (SSM/I). This physically based algorithm is derived using the guidance of a 32‐stream plane‐parallel model of microwave radiative transfer in the cloudy atmosphere. Our investigation using both radiative transfer model and observed SSM/I data indicates that the retrieved LWP is sensitive to the emission temperature of the liquid water, to the presence of large hydrometeors, to the nonuniformity of the rainfall in the satellite field of view, and to the radiation from atmosphere and ocean. Therefore we have incorporated cloud temperature into our algorithm using ancillary infrared satellite data. To account for the effects of rainfall on the LWP retrievals, we use a threshold for the onset of precipitation to determine whether there is any precipitation in the satellite field of view. Two separate retrieval schemes are derived for non‐precipitating and precipitating clouds. A clear‐sky radiation scheme is developed to separate radiation of atmosphere and ocean from that of liquid water. This scheme could be easily tuned by observed microwave data so that the bias in LWP retrieval is minimized. This algorithm is indirectly validated by comparing retrieved values of LWP for clear versus cloudy situations. The retrievals are examined for regions in the tropical western Pacific Ocean, the North Atlantic Ocean, and the subtropical southeast Pacific Ocean. The retrievals obtained using our algorithm are also compared with simultaneous retrievals using other LWP algorithms described in the literature. The retrievals are compared for clear sky, liquid cloud only, cloud with ice, raining water cloud, and raining cloud with ice to assess and interpret the performance of the algorithms in each of these situations. The present algorithm is shown to perform consistently well in all three regions under all conditions. It is determined that features of our algorithm that results in more consistent global retrievals of LWP are inclusion of the tunable clear‐sky scheme, estimation of cloud temperature using satellite infrared radiances, and consideration of precipitation.
What Controls Opal Preservation in Tropical Deep‐Sea Sediments?
Authors: Archer D. , Lyle M. , Rodgers K. , Froelich P.
Published: February 2008

Measurements of opal preservation in deep sea sediment cores have been presented in three ways: the opal concentration as a fraction of total dry weight (%opaltot), the opal concentration normalized to calcite‐free dry weight (%opalcalcite‐free), and me opal accumulation rate (opal MAR). It is tempting to interpret changes in these indices as indicators of rates of biological production in past oceans. Based on theoretical constraints, we argue that in typical tropical and subtropical sediments, both %Opalcalcite‐free and opal MAR reflect a significant artifact of dilution by other phases. Thus the band of high %Opalcalcite‐free in the equatorial Pacific appears to be caused in large part by the high %Calcite in that region, rather than by high opal productivity. The best candidate for a reliable paleoproductivity proxy appears to be %Opaltot. Unfortunately, present‐day %Opaltot data from tropical and subtropical regions show little or no systematic trend with the rain rate of opal. Pore water silica concentration data reveal that the apparent pore water opal solubility is not constant but correlates regionally with the rain rate of opal to the seafloor. A model that treats opal as a single homogeneous phase with a single well‐defined solubility product predicts a strong dependence of opal concentration on rain rate (in stark contrast to the data), and a constant asymptotic pore water Si. Two models representing opal as multiple heterogeneous phases with different solubilities are able to reproduce the observed asymptotic pore water Si/rain rate relationship, but not the lack of rain rate trend in the opal concentration data. Only by assuming a systematic trend in the quality of opal (i.e., the solubility) as a function of opal production, can we reproduce the observed pattern of opal preservation. The implication of this study is that changes in opal preservation in the geologic record cannot simply be interpreted in terms of changes in surface ocean productivity until our understanding of opal diagenesis can be improved.
Analysis of the radio acoustic sounding system using a chirped acoustic wave
Authors: Masuda Yoshihisa , Awaka Jun , Nakamura Kenji , Adachi Tatsuhiro , Tsuda Toshitaka
Published: February 2008

We investigated radio acoustic sounding system (RASS) echoes backscattered from refractive index fluctuations produced by an acoustic pulse linearly modulated in frequency (a chirped acoustic pulse). We have numerically simulated errors of the Doppler frequency shift which are caused by the fact that the widths of the acoustic and radar pulse are finite. We analytically showed that a RASS with a chirped acoustic pulse can correctly measure a wide range of Doppler shifts. The error of the Doppler shift measurement is found to be a function of the radar range resolution, the rate at which acoustic frequency is swept, and the width of the acoustic pulse. The error is also shown to be almost independent of the radar frequency and the lapse rates of the atmospheric temperatures. We have also numerically showed that when the chirped acoustic wave frequency is 50 Hz/s, errors are within 0.018°C when the radar frequency is 1357.5 MHz and the range resolution is 75 m. At the chirped wave frequency, errors are within 0.055°C for a 46.5‐MHz radar with a 150‐m range resolution. We also propose a method for designing a chirped acoustic pulse to measure atmospheric temperature.
Electromagnetic dyadic Green's function for multilayered symmetric gyroelectric media
Authors: Barkeshli S.
Published: February 2008

A complete, plane wave spectral, vector wave function expansion of the electromagnetic, electric, and magnetic, dyadic Green's function for electric, as well as magnetic, point currents for a planar, multilayered, symmetric gyroelectric medium, where the gyroelectric anisotropy is confined in the plane parallel to planar interfaces is presented. It is given in terms of z‐propagating, source‐free vector wave functions, where
is normal to the interfaces. It is shown that, because of the reflection symmetry of the electric permittivity tensor, where the modes are decoupled, an efficient representation of the field within each of the layers is possible. Some salient features of the Green's dyadic, along with a physical interpretation, are also described.
Mesozoic deformation in the Nevada Test Site and vicinity: Implications for the structural framework of the Cordilleran Fold and thrust belt and tertiary extension north of Las Vegas Valley
Authors: Caskey S. John , Schweickert Richard A.
Published: February 2008

Detailed studies in the CP Hills and Mine Mountain area of the Nevada Test Site (NTS), together with analysis of published maps and cross sections and a reconnaissance of regional structural relations, indicate that the CP thrust of Barnes and Poole [1968] actually comprises two separate, oppositely verging Mesozoic thrust systems: (1) the west vergent CP thrust, which is well exposed in the CP Hills and at Mine Mountain, and (2) the east vergent Belted Range thrust located northwest of Yucca Flat. Regional structural relations indicate that the CP thrust forms part of a narrow sigmoidal belt of west vergent folding and thrusting traceable for over 180 km along strike. The Belted Range thrust represents earlier Mesozoic deformation that was probably related to the Last Chance thrust system in southeastern California, as suggested by earlier workers. A reconstruction of the pre‐Tertiary geometry of the Cordilleran fold and thrust belt in the region between the NTS and the Las Vegas Range bears a close resemblance to other regions of the Cordillera and suggests that west vergent deformation developed in the hinterland of a part of the Sevier fold and thrust belt characterized by substantial structural relief. Reconstruction of the fold and thrust belt also suggests that previous estimates of upper crustal Tertiary extension north of the Las Vegas Valley shear zone (e.g., 80% [Guth, 1981]) are 2 or 3 times too large.
Seismic and tectono‐metamorphic characters of the lower continental crust in Phanerozoic areas: A consequence of post‐thickening extension
Authors: Rey Patrice
Published: February 2008

Deep seismic profiles of Phanerozoic continental crust commonly show a highly reflective lower crust. Rheological considerations suggest that the seismic fabric of the lower crust can be attributed to the tectonic transposition of various petrological heterogeneities in the main flow plane. The Variscan provinces of western Europe have been affected, during Phanerozoic times, by several extensional and compressional events. The geometrical relationships between seismic and geological structures indicate that the layering of the lower crust was acquired during the Late Carboniferous to Permian when the thickened Variscan crust was affected by gravitational collapse. Petrological and geochronological analyses of deep crustal rocks (xenoliths and exposed sections) indicate that the lower crust has recorded a major high‐T / medium‐P granulite facies metamorphism during the late Variscan extension, whereas on the surface Upper Carboniferous to Permian basins were being deposited. A similar scenario characterizes other Phanerozoic orogenic belts. In the Caledonian provinces of the British Islands, the lower crust is seismically reflective; it has undergone medium‐P granulitic metamorphism during the deposition of Devonian sedimentary basins, at the end of the Caledonian orogeny. In the same way, collapse of the Mesozoic belt in the western part of North America is responsible, during the Cenozoic, for pervasive crustal extension whose consequence is a seismic layering of the lower crust accompanied by a low‐P granulite grade metamorphic event, while in the mid‐ and upper crusts, low‐angle, ductile, normal faults give rise to the Basin and Range Province. Therefore, it is proposed that there is a genetic relationship between (1) post‐thickening crustal extension, (2) low‐ to medium‐P granulite facies metamorphism of the lower crust and (3) seismic layering of the lower crust.
Genesis and evolution of a Permian‐Jurassic magmatic arc/accretionary wedge, and reevaluation of terranes in the central Klamath Mountains
Authors: Hacker Bradley R. , Ernst W. G. , McWilliams Michael O.
Published: February 2008

Investigation of key areas of the central Klamath Mountains demonstrates that genetic relationships connect several regionally significant lithologic units that were previously considered to be separate tectonostratigraphic terranes. The rocks embody an intraoceanic tholeiitic to alkaline magmatic arc and contiguous accretionary wedge formed in Permian to Middle Jurassic time. The Eastern Hayfork and St Claire Creek units comprise Permian‐Jurassic oceanic sedimentary rocks deposited nearby and coeval with eruption of the North Fork‐Salmon River volcanoplutonic arc. The more inboard St Claire Creek unit consists of stratigraphically coherent chert and minor argillite probably deposited in a back‐arc setting, whereas the more outboard Eastern Hayfork sedimentary rocks were disrupted during formation of an accretionary wedge. The volcanoplutonic North Fork‐Salmon River arc extends for 200 km in the central Klamath Mountains and was active episodically or continuously from Permian through Middle Jurassic time. Alkalic members of the mafic igneous suite may have erupted following subduction of a spreading center. A varied heating history has produced an amalgam of submarine and regional low‐pressure, moderate‐temperature metamorphism, overprinted locally by contact metamorphism. Geochronology of weakly metamorphosed mafic dikes/sills (10 new 40Ar/39Ar analyses) suggests that significant heat was retained regionally into Early Cretaceous time.
Production mechanism of C2‐C4 hydrocarbons in seawater: Field measurements and experiments
Authors: Ratte M. , Plass‐Dülmer C. , Koppmann R. , Rudolph J. , Denga J.
Published: February 2008

The production mechanism of light nonmethane hydrocarbons (NMHC) in seawater was investigated during the North Atlantic atmospheric chemistry program (NATAC) in April and May 1991 in the European coastal seas and the North Atlantic. A significant alkene production occurred in the presence of light only. Under conditions of negligible NMHC emissions (low wind velocity) increasing hydrocarbon concentrations were observed during daytime, whereas the concentrations remained constant during night. NMHC formation experiments were carried out with seawater filled in quartz glass bottles and showed the same dependence of light. Experiments with differently pretreated seawater samples indicated that the presence of dissolved organic material (DOM) is also necessary for alkene production. We suggest a two‐step production mechanism for alkenes: first DOM is released, probably from algae, then part of this material is photochemically transformed into alkenes. The production rates in the quartz glass bottles were comparable to the production rates in the ocean surface. This indicates that the processes occurring in the experimental setups represent the processes occurring in the field. Since the production ‐ and emission rates were in the same range it can be concluded that the budget of light alkenes in the remote marine environment is determined by the production in seawater as the dominant source and the flux into the atmosphere as the main loss process.
Observations of atomic deuterium in the mesosphere from ATLAS 1 with ALAE Instrument
Authors: Bertaux Jean‐Loup , Quémerais Eric , Goutail Florence , Kockarts Gaston , Sandel Bill
Published: February 2008

During the first ATLAS mission, the ALAE Lyman α spectrophotometer collected various measurements of hydrogen and deuterium atoms, from the mesosphere, the thermosphere, the exosphere and the interplanetary medium. In this paper is presented a preliminary analysis of some observations of atomic deuterium, which Lyman α emission is excited by resonance scattering of solar photons. Nadir measurements along the sunlit Earth part of the orbit show that the emission changes as a function of solar zenith angle. Comparison with a simple model shows that, from the shuttle altitude of 300 km and at low solar zenith angles, the line‐of‐sight probes atomic deuterium down to 80 km of altitude (where O2 absorption is complete), whereas at angles from 60° to 90°, the mesospheric part of the emission progressively vanishes. Then, the remaining emission mainly consist of the thermospheric part (z ≥ 100 km). This type of observations provides a sounding of atomic deuterium at its peak production and concentration, and D atoms can be used as a proxy to H atoms (which cannot be observed from a satellite) in this particularly active region of the mesosphere.
Mean winds and tidal components during counter electrojet events
Authors: Somayajulu V. V. , Cherian Ligi , Rajeev K. , Ramkumar Geetha , Reddi C. Raghava
Published: February 2008

The first observations of mean winds and the amplitude and phases of the tidal components measured with a meteor wind radar located at Trivandrum (8.5°N, 77°E) during five consecutive days of counter electrojet events identified in the horizontal component of the earth's magnetic field from January 27–31, 1987 are described. The mean zonal winds in the altitude region of 90–105 km are in general westward during counter electrojet days and eastward during no counter electrojet days. The amplitudes and phases of the tidal components on the counter electrojet days are found to be substantially different from those on the no counter electrojet days.
2. Morphology and dynamics of the Pinatubo aerosol layer in the northern hemisphere as detected from a ship‐borne lidar
Authors: Nardi B. , Chanin M. ‐L. , Hauchecorne A. , Avdyushin S. I. , Tulinov G. F. , Ivanov M. S. , Kuzmenko B. N. , Mezhuev I. R.
Published: February 2008

Scattering ratios of the Pinatubo aerosol layer obtained by the ship‐borne lidar of the Roscomhydromet of Russia on‐board PROFESSOR ZUBOV are presented. During a campaign primarily in the low‐latitude (8°N–43°N) Atlantic Ocean, 48 days of data were obtained within the 73 day period spanning 11‐July and 21‐September of 1991 [Avdyushin et al., 1992]. These data show the aerosol cloud to be primarily in the 16–27 km altitude region, with a high degree of variability in the vertical structure and in the longitudinal structure, and to a lesser degree, in the latitudinal structure. Scattering ratios of up to 50 were recorded in the multi‐layered structure which was often observed. These are the first lidar observations showing a high degree of zonal variability of the vertical structure of the aerosol layer. We show the latitudinal range of the Pinatubo aerosol cloud in the northern hemisphere over a 2 month period and estimate the latitudinal dispersion rate for the months of the measurements to be approximately 5° latitude per month. A clear periodic variability was observed in the altitude structure during the entire data‐set primarily within 8°N–22°N latitude and within the altitude region of the layer, from which a mean zonal wind profile was produced by a spectral analysis of the aerosol profiles.
Age determination of recent cave deposits using excess 210Pb ‐ A new technique
Authors: Baskaran M. , Iliffe Thomas M.
Published: February 2008

Cave deposits have been widely used as proxy recorders in deciphering palaeoclimate during the last glacial/interglacial maxima (∼ 120 ka) [Harmon et al., 1975; Atkinson et al., 1978; Goede and Harmon, 1983; Ayliffe and Veeh, 1989]. Palaeoclimatic studies of cave deposits for the past 1–1000 yr time scale require a precise dating technique, that until now has been lacking. Due to the multiple sources of carbon in speleothems, 14C dates obtained for recently deposited calcite are highly variable and thus, 14C dating techniques are not suitable to obtain speleothem ages for the past 1–1000 years.

Here, we show for the first time that speleothems contain high concentrations of excess 210Pb and that this 210Pb excess can be successfully employed to obtain growth rates of speleothems deposited during the last 100 years. Of two specimens analyzed, a tubular “soda straw” stalactite yielded a longitudinal growth rate of 1.1 mm/yr, while a normal icicle‐shaped stalactite had a lateral growth rate of 0.028 mm/yr. The mass growth rates of these two speleothems (149 and 78 mg/yr respectively) are comparable within a factor of two. Studies of fine‐scale variations in the isotopic composition of recent speleothems will help to corroborate the validity of palaeoclimate records obtained using longer lived isotopes and extending back into Pleistocene.
Retrieval of thermospheric atomic oxygen, nitrogen and temperature from the 732 NM emission measured by the ISO on ATLAS 1
Authors: Fennelly Judy A. , Torr Douglas. G. , Torr Marsha R. , Richards Phillip G. , Yung SoPo
Published: February 2008

The Imaging Spectrometric Observatory (ISO) was a part of the ATLAS 1 Mission flown on the shuttle Atlantis from March 24 to April 2, 1992. During limb scanning operations, the ISO measured the O+(2P) ion emission at 732 nm. We have used a numerical inversion technique to retrieve thermospheric atomic oxygen, molecular nitrogen and temperature profiles. These preliminary results indicate a lower thermospheric temperature cooler than that predicted by MSIS for the solar conditions during the mission. Although the densities agree at low altitudes, the reduced scale height produces O and N2 densities 25% lower than the MSIS at 300 km.
The first Greenland ice core record of methanesulfonate and sulfate over a full glacial cycle
Authors: Hansson Margareta E. , Saltzman Eric S.
Published: February 2008

Methanesulfonate (MSA) in ice cores has attracted attention as a possible tracer of past oceanic emissions of dimethylsulfide (DMS). After sulfate MSA is the second most prevalent aerosol oxidation product of DMS, but in contrast to sulfate, DMS oxidation is the only known source of MSA. The hypothesis by Charlson et al., [1987] of a climate feedback mechanism with sulfur emissions from marine phytoplankton influencing the cloud albedo adds to the interest in establishing long records of MSA and non‐seasalt sulfate spanning large climatic changes. Records of MSA and non‐seasalt sulfate covering time periods from a few years to thousands of year have been extracted from antarctic ice cores [Ivey et al., 1986; Saigne and Legrand, 1987; Legrand and Feniet‐Saigne, 1991; Mulvaney et al., 1992] but only the record from the Vostok ice core [Legrand et al., 1991] covers a full glacial cycle. The concentrations of MSA and non‐seasalt sulfate in Antarctica have been found to increase under glacial conditions. Here we present the first Northern Hemisphere record of MSA, and the first continuous record of non‐seasalt sulfate, both extracted from the Renland ice core, East Greenland. The records are extending from the Holocene to the Eem interglacial 130,000 years B.P. The contrast to the Southern Hemisphere records is striking, with a decreasing concentration of MSA with the advance of glaciation but an increasing concentration of non‐seasalt sulfate. A strong linear relationship is found in the Renland ice core between the ratio of MSA to non‐seasalt sulfate and the temperature, with higher ratios associated with warmer climatic stages, while the opposite relationship to temperature is found in the Vostok ice core. A more complicated picture is emerging of the use of MSA in ice cores as a quantitative tracer which suggests that previous interpretations can have been overly simplistic.
Multi‐isotope study of ozone: Implications for the heavy ozone anomaly
Authors: Mauersberger K. , Morton J. , Schueler B. , Stehr J. , Anderson S. M.
Published: February 2008

Laboratory experiments have been performed with O and O2 in their ground electronic states to study the distribution of all possible ozone isotopes formed. Results show that with respect to 48O3 the two symmetric molecules 17O17O17O and 18O18O18O are depleted, in good agreement with standard recombination theory. A large enrichment of about 18% is found in the asymmetric molecule 16O17O18O, while all others carry about 2/3 of that. A comparison with past laboratory and stratospheric ozone isotope measurements leads to the following conclusion: There is a standard enrichment which resides in asymmetric molecules only. It will lead to an enrichment of stratospheric 49O3 and 50O3 of 8 to 9%; this has been actually observed in recent balloon experiments. Occasionally, the enrichments in the stratosphere are larger, reaching 40% at certain altitudes. Only when ozone was formed in an electric discharge process have larger enrichments been measured in laboratory experiments, affecting both symmetric and asymmetric molecules. The results provide an important connection between numerous laboratory studies and stratospheric measurements.
Observations of shear wave splitting on the southeast flank of Mauna Loa Volcano, Hawaii
Authors: Munson Clifford G. , Thurber Clifford H. , Li Yingping
Published: February 2008

We use a combination of particle motion covariance matrix decomposition, particle motion plots, and cross correlation to estimate the polarization and split times of shear wave arrivals from local earthquakes in the Kaoiki and Hilea regions of southern Hawaii. Consistent leading shear wave polarizations and identifiable fast and slow shear wave arrivals were frequently observed. Average delay times for the four arrays vary from 100 to 230 ms. The leading shear wave polarizations at stations in the Kaoiki region agree with the direction of the local maximum horizontal compressive stress, σH, determined from focal mechanism studies and field observations of ground rupture. For the Bird Park (BP) array, in the Kaoiki region, the relationship between delay time and event depth shows evidence for both dominant shallow and weaker pervasive anisotropy. The correlation between delays and event depth is much weaker for the Ainapo (AN) array than for BP, however a smaller slope is apparent. Conservative estimates of the crack densities for the BP and AN arrays are e=12% and e=6%, respectively. In the Hilea region, the leading shear wave polarization for the Punaluu Gulch (PG) array differs by approximately 30° from the direction of σH determined from focal mechanism studies, while the Waihaka Gulch (WG) array shows no predominant polarization direction. No correlation between delay time and event depth was observed for either of the two Hilea arrays.
Refinement of enthalpy measurement of MgSiO3 perovskite and negative pressure‐temperature slopes for Perovskite‐forming reactions
Authors: Akaogi Masaki , Ito Eiji
Published: February 2008

Enthalpy for MgSiO3 orthopyroxene‐perovskite transition at 298 K was measured by differential drop‐solution calorimetry. Based on four measurements of MgSiO3 perovskite, the ΔH°298 of 102.2±2.5 kJ/mol was more precisely determined than that in the previous study. The enthalpies of transitions from MgSiO3 ilmenite to perovskite and from Mg2SiO4 spinel to perovskite + periclase were calculated to be 43.2±5.0 and 86.1±3.6 kJ/mol, respectively. The boundaries of these transitions were calculated using the above data together with physical properties of relevant phases, including recently determined properties of perovskite: heat capacity, entropy, and temperature dependence of bulk modulus. The calculated P‐T slopes for the ilmenite‐perovskite transition and the spinel dissociation are −3.4±2 and −3±1 MPa/K, respectively. The latter slope may suggest that the upper and lower mantle convect separately but intermittent mixing occurs between them.
Time dependence in atmospheric carbon inputs from drainage of organic soils
Authors: Rojstaczer Stuart , Deverel Steven J.
Published: February 2008

Historical and contemporary subsidence in the San Joaquin‐Sacramento Delta, California indicates that subsidence rates associated with drainage of organic soils have declined over time. Contemporary measurements of carbon flux into the atmosphere can be used to predict contemporary rates of permanent subsidence. This correspondence indicates that most subsidence is caused by carbon oxidation. The current contribution of atmospheric carbon from the Delta is 2×1012 gm C/yr. This estimate is a factor of 3–4 less than previous estimates and reflects the declining rate of CO2 production in the Delta over the last several decades. Estimates of current production of CO2 from other drained agricultural lands that are based upon time‐averaged historical rates of subsidence are also likely to be too large.
Regional distribution of monsoon and desert dust signals recorded in Asian glaciers
Authors: Wake Cameron P. , Mayewski Paul A. , Zichu Xie , Ping Wang , Zhongqin Li
Published: February 2008

Short‐term (6 months to 17 years) glaciochemical records have been collected from glacier basins throughout the mountains of central Asia. The spatial distribution of snow chemistry in central Asia is controlled predominantly by the influx of dust from the arid and semi‐arid regions in central Asia. The glaciochemical data suggests that glaciers which are removed from large source areas of mineral aerosol, such as those in the Himalaya, the Karakoram, and the southeastern Tibetan Plateau, are the ones most likely to contain longer‐term glaciochemical records which detail annual to decadal variation in the strength of the Asian monsoon and long‐range transport of Asian dust.
Magma in layering at the Moho of the Basin and Range of Nevada
Authors: Suetnova Elena , Carbonell Ramon , Smithson Scott B.
Published: February 2008

Layering at the Moho as determined from seismic reflection data is a commonly observed phenomenon in the Basin and Range for which we propose a porous‐flow melt model. Analysis of seismic reflection data from the 1986 PASSCAL Nevada experiment indicates that the Moho in the Nevada Basin and Range is layered and has unusually high reflectivity. This reflectivity is difficult to explain in terms of a velocity contrast caused by different rock types, and, in fact, a lower velocity of less than 6.5 km/s suggests the presence of partially molten material at the Moho in a zone containing 20% to 25% of low‐velocity layers. To explain the seismic observations, we have developed a viscous, porous‐flow model for basaltic melt ascent. Such a model produces systematic variations in volumetric melt flow with depth and close correspondence between seismic interpretation and modeling of partial melt ascent. This suggests that such layering involving viscous, porous flow of partial melt is a plausible explanation of the layering of the Moho in the Basin and Range and may have more general application.
A general solution for stochastic radiative transfer
Authors: Evans K. Franklin
Published: February 2008

The three‐dimensional variability of clouds has an important impact on the transfer of radiation in the Earth's atmosphere, and thus the current practice in climate modeling of assuming clouds are horizontally homogeneous entails significant errors. A new method, based on the backward Monte Carlo technique, has been developed for computing the mean outgoing radiation field from any type of stochastic ensemble of cloud structure. The accuracy of the technique has been verified by comparison with many realizations of deterministic radiative transfer. The method illustrates how spatial variability should be defined, and should lead to improved representations of the radiative effects of clouds in climate models.
Is the magnetosphere a lens for MHD waves?
Authors: Papadopoulos K. , Sharma A. S. , Valdivia J. A.
Published: February 2008

A novel viewpoint of the magnetosphere as a lens for MHD waves is presented. Using a simple model of the variation of the Alfven speed as proportional to the local magnetic field value given by the Earth's dipole field and that due to the magnetopause currents represented by a current loop, it is found that the near‐Earth magnetotail, in the range 8–16 RE, is the focus of the magnetospheric lens. This location is found to be quite insensitive to a wide variation of parameters. By using simple diffraction theory analysis it is found that the focal region extends about 1 RE about the neutral sheet in the north‐south plane and 0.2–0.5 RE along the Sun‐Earth line. Compressive MHD waves carried by the solar wind or created by the interaction of the wind with the magnetopause can be amplified by a factor of about 100 in the focal region and this has potentially important implications to substorm activity.
Effects of water and melt on seismic velocities and their application to characterization of seismic reflectors
Authors: Watanabe Tohru
Published: February 2008

The effects of a silicate melt and water on seismic velocities are compared at relatively small fluid fraction (less than 20 vol.%) on the basis of a theoretical model of composite materials, to show that the two fluids are clearly characterized by the velocity ratio Vp/Vs. For a silicate melt, Vp/Vs increases with increasing fluid fraction. When a significant reflection is expected, Vp/Vs becomes much larger than 2. For water, Vp/Vs decreases as the fluid fraction increases to 10 vol.% then it increases. But it remains similar to a solid state value (about 1.8), unless the amount of water exceeds 15 vol.%. This will be a good measure to distinguish between two candidates for seismic reflectors: partially molten rocks and rocks containing free water. If a reflector can be treated as a thin low velocity layer, the velocity ratio in it can be estimated from the frequency dependence of reflection coefficient.
On the nonlinear response of airglow to atmospheric gravity waves
Authors: Hines Colin O. , Tarasick David W.
Published: February 2008

An attempt is made to clarify the role that may be played by nonlinearities in airglow fluctuations induced by atmospheric gravity waves.
Spectral evidence for stirring scales and two‐dimensional turbulence in the auroral ionosphere
Authors: Earle G. D. , Kelley M. C.
Published: February 2008

Electric field power spectra from two auroral sounding rocket flights show evidence of a distinct scale size regime for injection of energy into the auroral oval. The signature of this process is a broad plateau in the spectrum, with power law dependences at both shorter and longer scale sizes. We argue that the spectral properties at high k are dominated by processes occurring near the edges of inverted‐V electron precipitation regions (auroral arcs) We see no compelling reason to conclude that a linear local plasma instability is occurring but rather, that nonlinear mixing and forward cascade yield the observed velocity field. The spectra of simultaneously observed density irregularities are quite different from those of the electric field, implying that the plasma density does not behave as a passive scalar in the auroral zone during active conditions. At low‐k values we show that the rocket spectra are consistent with the power spectra of magnetospheric electric fields measured by the DE, AE‐C, and Hilat stallites.
On the ion‐tearing instability of forced current sheets
Authors: Lakhina G. S.
Published: February 2008

The ion‐tearing mode instability is studied in a magnetotail configuration, with an embedded thin current sheet at the center of the plasma sheet, taking into account the effects due to electron dynamics and perturbed electrostatic potential. It is found that the presence of trapped electrons in the forced current sheet has a strong stabilizing effect on thinner current sheets. The ion‐tearing instability can exist provided the trapped electron population density is less than about 10‐20% of the total electron number density. This can be achieved either by the background turbulence present in the plasma sheet or by the high ‐ frequency plasma instabilities excited by the strong current of the inner current sheet itself. Under such a situation, the configuration becomes progressively more ion‐tearing unstable as the forced current sheet becomes thinner. This eventually could lead to the disruption of the current sheet and to the onset of substorm expansion phase.