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  • Articles  (257)
  • Wiley-Blackwell  (257)
  • Geosciences  (257)
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  • Articles  (257)
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  • 1
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    Impacts of recent warming and the 2015/16 El Niño on tropical Peruvian ice fields (2017)
    Wiley-Blackwell
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    Publication Date: 2017-09-19
    Description: Data collected between 1974 and 2016 from snow pits and core samples from two Peruvian ice fields demonstrate the effect of the recent warming over the tropical Andes, augmented by El Niño, on the preservation of the climate record. As the 0 o C isotherm is approaching the summit of the Quelccaya ice cap in the Andes of southern Peru (5670 masl), the distinctive seasonal δ 18 O oscillations in the fresh snow deposited within each thermal year are attenuated at depth due to melting and percolation through the firn. This has become increasingly pronounced over 43 years. In the Andes of northern Peru, the ice field on the col of Nevado Huascarán (6050 masl) has retained its seasonal δ 18 O variations at depth due to its higher elevation. During the 2015/16 El Niño, snow on Quelccaya and Huascarán was isotopically (δ 18 O) enriched and the net sum of accumulation over the previous year (NSA) was below the mean for non-El Niño years, particularly on Quelccaya (up to 64% below the mean) which was more pronounced than the NSA decrease during the comparable 1982/83 El Niño. Interannual large-scale oceanic and middle to upper level atmospheric temperatures influence δ 18 O in precipitation on both ice fields, although the influences are variably affected by strong El Niño-Southern Oscillation events, especially on Quelccaya. The rate of ice wastage along Quelccaya's margin was dramatically higher during 2015/16 compared with that of the previous 15 years, suggesting that warming from future El Niños may accelerate mass loss on Peruvian glaciers.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 2
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    Investigating the preservation of nitrate isotopic composition in a tropical ice core from the Quelccaya Ice Cap, Peru (2014)
    Wiley-Blackwell
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    Publication Date: 2014-01-31
    Description: [1]  The nitrogen and oxygen isotopic composition of nitrate in ice cores offers unique potential for examining reactive nitrogen oxide (NO x ) budgets and oxidation chemistry of past atmospheres. A low-latitude record is of particular interest given that the dominant natural sources of NO x and production of hydroxyl radical are most prevalent in the Tropics. Any interpretation of nitrate in ice cores, however, must first consider that nitrate in snow is vulnerable to post-depositional loss and isotopic alteration. We report and assess the integrity of nitrate–δ 15 N, –δ 18 O and –Δ 17 O in a 30 m ice core from a high-elevation site in the central Andes. Clear seasonality in δ 15 N, δ 18 O and nitrate concentration exists throughout most of the record and cannot be explained by photolysis or evaporation based on our current understanding of these processes. In contrast, nitrate in the upper ~12 m of the core and in a snowpit shows very different behavior. This may reflect alteration facilitated by recent melting at the surface. The relationships between δ 15 N, δ 18 O, Δ 17 O and concentration in the unaltered sections can be interpreted in terms of mixing of nitrate from discrete sources. Transport effects and an englacial contribution from nitrification cannot be ruled out at this time, but the observed isotopic compositions are consistent with expected signatures of known NO x sources and atmospheric oxidation pathways. Specifically, nitrate deposited during the wet season reflects biogenic soil emissions and hydroxyl/peroxy radical chemistry in the Amazon while dry season deposition reflects a lightning source and ozone chemistry at higher levels in the Troposphere.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 3
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    The impact of high-frequency current variability on dispersion off the eastern Antarctic Peninsula (2011)
    Wiley-Blackwell
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    Publication Date: 2011-11-17
    Description: We present observations of high-frequency current variability on the continental shelf and the slope of the Antarctic Peninsula using Lagrangian surface drifters deployed as part of the Antarctic Drifter Experiment: Links to Isobaths and Ecosystems (ADELIE) project. Here we focus on high-frequency processes such as tides and inertial oscillations that are typically smoothed out of large-scale spatially averaged, and/or temporally averaged, observed current fields. We investigate the role that this class of motion plays in the transport of physical or biogeochemical properties. Lateral displacements on the shelf and slope are found to be larger than displacements in deeper waters where tidal currents are negligible. We apply this result in a parameterization of the lateral dispersion during an off-line drifter modeling study. The outcome is an improvement on the modeling of Lagrangian drifting particles compared with a standard random walk scheme.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 4
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    Comparison of high-resolution wind fields extracted from TerraSAR-X SAR imagery with predictions from the WRF mesoscale model (2012)
    Wiley-Blackwell
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    Publication Date: 2012-02-28
    Description: We discuss the status of our efforts to determine a suitable Geophysical Model Function (GMF) that relates X-band normalized radar cross section (NRCS) to the near surface wind vector over the ocean. Development of an X-band GMF has become particularly relevant due to the recent launches of several X-band satellite synthetic aperture radar (SAR) systems. We concentrate here on SAR data collected by the TerraSAR-X satellite launched by the German Space Agency in 2007. Inversion of TerraSAR-X NRCS imagery to wind speed is accomplished using both a simple physics-based GMF as well as an empirical GMF derived by interpolating more accurately tested C- and Ku-band GMFs to X-band. We compare the retrieved wind speeds from three TerraSAR-X scenes with in situ data when available and also with predictions from the Weather Research and Forecast (WRF) model. At vertical polarization, these comparisons show reasonable agreement with in situ data for both the physics-based and empirical GMFs. At horizontal polarization however, the NRCS from the physics-based GMF is generally too low, resulting in an under prediction results of the corresponding retrieved wind speeds. An unexpected result from the WRF comparisons is the similarity between the small-scale structure (on scales ≈ 5–10 km) observed in the SAR imagery and the corresponding WRF output. We believe that this similarity may allow TerraSAR-X imagery to provide a quantitative measure of the quality of the WRF boundary-layer parameterization schemes.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 5
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    Surface ozone at a coastal suburban site in 2009 and 2010: Relationships to chemical and meteorological processes (2012)
    Wiley-Blackwell
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    Publication Date: 2012-03-07
    Description: Air quality and meteorological measurements were conducted at the Chemistry and Physics of the Atmospheric Boundary Layer Experiment (CAPABLE) site during the summers of 2009 and 2010 in Hampton, Virginia. Significant differences in surface ozone mixing ratios were observed between the two years and are correlated with meteorological parameters such as temperature, humidity, and cloud cover. The number of exceedance days for ozone set by the U.S. Environmental Protection Agency within this region has been decreasing for the past decade, especially in urban areas. There were no exceedance days with respect to ozone in 2009, and there were four exceedance days in 2010. The four highest ozone daily maxima and the two exceedance days observed during the 2010 measurement period were coincident with sea breeze phenomena. In one case, surface ozone increased at a rate of 14.6 ppb h−1 with the passage of a sea breeze front. A comprehensive multilinear regression model as well as an operational forecast was unable to resolve the high ozone observed during sea breeze events. As the number of exceedance days per year within this region continues to decrease, accurately forecasting sea breezes may become more important for the forecasting of pollution events.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 6
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    Alkyl-chain disorder in tetraisohexylammonium bromide (2012)
    Wiley-Blackwell
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    Publication Date: 2012-04-24
    Description: Tetraisohexylammonium bromide [systematic name: tetrakis(4-methylpentyl)azanium bromide], C 24 H 52 N + ·Br − , is a powerful structure II clathrate hydrate crystal-growth inhibitor. The crystal structure, in the space group P 3 2 21, contains one ammonium cation and one bromide anion in the asymmetric unit, both on general positions. At 100 K, the ammonium cation exhibits one ordered isohexyl chain and three disordered isohexyl chains. At 250 K, all four isohexyl chains are disordered. In an effort to reduce the disorder in the alkyl chains, the crystal was thermally cycled, but the disorder remained, indicating that it is dynamic in nature.
    Print ISSN: 0108-2701
    Electronic ISSN: 1600-5759
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley-Blackwell on behalf of International Union of Crystallography (IUCr).
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  • 7
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    Integrating carbon emissions from lakes and streams in a subarctic catchment (2013)
    Wiley-Blackwell
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    Publication Date: 2013-07-17
    Description: [1]  Northern inland waters emit CO 2 and CH 4 to the atmosphere but the importance of these emissions is poorly understood due to a lack of integrated catchment scale estimates of carbon (C) emissions from lakes and streams. In this study we quantified the annual emission of CO 2 and CH 4 from 27 lakes and 23 stream segments in a 15 km 2 subarctic catchment in northern Sweden. All lakes and streams were net sources of C to the atmosphere on an annual basis. Streams dominated (96%) the aquatic CO 2 emission while lakes (61%) dominated the aquatic CH 4 emission. Total aquatic C emission from the catchment was estimated to be 9.1 g C m -2  yr -1 (98% as CO 2 ). Although streams only accounted for 4% of the aquatic area in the catchment, they accounted for 95% of the total emission. The C emissions from lakes and streams were considerably larger than previously reported downstream waterborne export of C from the catchment indicating that that the atmospheric losses of C in the aquatic systems is an important component in the catchment C balance.
    Print ISSN: 0148-0227
    Topics: Biology , Geosciences
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 8
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    Radiative constraints on the minimum atomic oxygen concentration in the mesopause region (2013)
    Wiley-Blackwell
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    Publication Date: 2013-07-12
    Description: [1]  Atomic oxygen [O] plays a fundamental role in the photochemistry and energy budget of the terrestrial mesopause region (80 to 100 km). [O] is difficult to measure directly and is typically inferred at night from measurements of hydroxyl [OH] or molecular oxygen [O 2 ] emissions. During the day measurements of ozone [O 3 ] concentration are used to infer [O]. These inferences carry significant uncertainties [ Mlynczak et al ., 2013a]. Recently Mlynczak et al ., [2013b] used energy balance principles to set an upper limit on the annual global mean [O] concentration in the mesopause region. In this paper we use night measurements of OH emission to set a lower limit on the global annual mean atomic oxygen concentration. These independent, radiatively constrained values of the maximum and minimum atomic oxygen concentration also place constraints on the magnitude of dynamical processes in the annual global mean energy budget of the mesopause region.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 9
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    Inter-annual variability in tropospheric nitrous oxide (2013)
    Wiley-Blackwell
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    Publication Date: 2013-07-07
    Description: [1]  Observations of tropospheric N 2 O mixing ratio show significant variability on inter-annual timescales (0.2 ppb, 1 standard deviation). We found that inter-annual variability in N 2 O is weakly correlated with that in CFC-12 and SF 6 for the northern extra-tropics and more strongly correlated in the southern extra-tropics suggesting that inter-annual variability in all these species is influenced by large-scale atmospheric circulation changes and, for SF 6 in particular, inter-hemispheric transport. N 2 O inter-annual variability was not, however, correlated with polar lower stratospheric temperature, which is used as a proxy for stratosphere to troposphere transport in the extra-tropics. This suggests that stratosphere to troposphere transport is not a dominant factor in year-to-year variations in N 2 O growth-rate. Instead, we found strong correlations of N 2 O inter-annual variability with the Multivariate ENSO Index. The climate variables, precipitation, soil moisture and temperature were also found to be significantly correlated with N 2 O inter-annual variability, suggesting that climate-driven changes in soil N 2 O flux may be important for variations in N 2 O growth rate.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 10
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    Low-temperature Debye–Scherrer powder diffraction on Beamline I11 at Diamond (2013)
    Wiley-Blackwell
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    Publication Date: 2013-05-16
    Description: A bespoke capillary sample holder is described that attaches to the cold head of a commercially manufactured (PheniX) closed-cycle helium cryostat originally intended for flat-plate geometry. The new holder allows high-resolution synchrotron powder diffraction data to be collected from samples in Debye–Scherrer geometry over the temperature range 11–295 K. To demonstrate that high-quality powder data can be obtained using this new sample holder, structural refinement (Rietveld) and thermal expansion results measured from reference samples (Si and Al) are presented.
    Print ISSN: 0021-8898
    Electronic ISSN: 1600-5767
    Topics: Geosciences , Physics
    Published by Wiley-Blackwell on behalf of International Union of Crystallography (IUCr).
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