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The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution spectra of reflected sunlight in three near-infrared bands centered around 0.76, 1.6, and 2.3 mu m and to deliver simultaneous retrie...
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The Geostationary Fourier Transform Spectrometer (GeoFTS) is designed to measure high-resolution spectra of reflected sunlight in three near-infrared bands centered around 0.76, 1.6, and 2.3 mu m and to deliver simultaneous retrievals of column-averaged dry air mole fractions of CO2, CH4, CO, and H2O (denoted XCO2, XCH4, XCO, and XH2O, respectively) at different times of day over North America. In this study, we perform radiative transfer simulations over both clear-sky and all-sky scenes expected to be observed by GeoFTS and estimate the prospective performance of retrievals based on results from Bayesian error analysis and characterization.
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Understanding the mechanism of formation of solid-electrolyte interphases (SEI) is key to the prospects of lithium metal batteries (LMB). Here, we investigate via cyclic voltammetry, impedance spectroscopy and chronoamperometry th...
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Understanding the mechanism of formation of solid-electrolyte interphases (SEI) is key to the prospects of lithium metal batteries (LMB). Here, we investigate via cyclic voltammetry, impedance spectroscopy and chronoamperometry the role of kinetics in controlling the properties of the SEI generated from the reduction of propylene carbonate (PC, a typical solvent in LMB). Our observations are consistent with the operation of a radical chain PC electropolymerization into polymer units whose complexity increases at lower initiation rates. As proof-of-concept, we show that slow initiation rates via one-electron PC reduction at underpotentials consistently yields compact, electronically insulating, Li+-conducting, PC impermeable SEI films. (C) 2016 The Author(s). Published by Elsevier B.V.
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Understanding and predicting precipitation characteristics on seasonal and longer timescales can help California prepare for long-term droughts and precipitation extremes. We find that interannual variations in total precipitation...
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Understanding and predicting precipitation characteristics on seasonal and longer timescales can help California prepare for long-term droughts and precipitation extremes. We find that interannual variations in total precipitation across California are primarily determined by precipitation frequency. As was shown previously for total precipitation, the precipitation frequency is linked to the North Pacific jet stream location. This indicates that California precipitation frequency is primarily controlled by where the jet guides precipitate weather systems rather than how moist or energetic the systems are. The jet's position, in turn, depends on the states of the El Nino-Southern Oscillation (ENSO) and of the Pacific Decadal Oscillation (PDO). We use this to construct a regression model that predicts variations in California's annual total precipitation and precipitation frequency. Up to 20% of the wintertime precipitation variance in Southern California is predictable using decorrelated ENSO and PDO indices in the previous summer.
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The ocean is the largest solar energy collector on Earth. The amount of heat it can store is modulated by its complex circulation, which spans a broad range of spatial scales, from metres to thousands of kilometres. In the classic...
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The ocean is the largest solar energy collector on Earth. The amount of heat it can store is modulated by its complex circulation, which spans a broad range of spatial scales, from metres to thousands of kilometres. In the classical paradigm, fine oceanic scales, less than 20 km in size, are thought to drive a significant downward heat transport from the surface to the ocean interior, which increases oceanic heat uptake. Here we use a combination of satellite and in situ observations in the Antarctic Circumpolar Current to diagnose oceanic vertical heat transport. The results explicitly demonstrate how deep-reaching submesoscale fronts, with a size smaller than 20 km, are generated by mesoscale eddies of size 50-300 km. In contrast to the classical paradigm, these submesoscale fronts are shown to drive an anomalous upward heat transport from the ocean interior back to the surface that is larger than other contributions to vertical heat transport and of comparable magnitude to air-sea fluxes. This effect can remarkably alter the oceanic heat uptake and will be strongest in eddy-rich regions, such as the Antarctic Circumpolar Current, the Kuroshio Extension and the Gulf Stream, all of which are key players in the climate system.
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We introduce an objective definition for onset and withdrawal of the South Asian summer monsoon (SASM), based on the large-scale atmospheric moisture budget. The change point (CHP) index allows precise characterization of the diff...
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We introduce an objective definition for onset and withdrawal of the South Asian summer monsoon (SASM), based on the large-scale atmospheric moisture budget. The change point (CHP) index allows precise characterization of the different stages and timescales of the large-scale SASM and is highly correlated with the local operational index, the monsoon onset over Kerala. The CHP-based onset and withdrawal dates, which capture the expected seasonal transitions in rainfall and winds, correspond with regime changes in the SASM moisture budget between negative and positive net precipitation. Climatological composites reveal that the seasonal transitions in SASM sector mean precipitation and circulation closely resemble those of the zonal mean Hadley circulation. The CHP index at grid points within the SASM domain yields a robust definition of local onset and withdrawal dates, which are well correlated with the large-scale index on interannual timescales, providing insight into the regional variability of the SASM.
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Manganese (Mn) toxicity in humans has been observed as manganism, a disease that resembles Parkinson's disease. The mechanism of Mn toxicity and the chemical forms that may be responsible for its neurotoxicity are not well underst...
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Manganese (Mn) toxicity in humans has been observed as manganism, a disease that resembles Parkinson's disease. The mechanism of Mn toxicity and the chemical forms that may be responsible for its neurotoxicity are not well understood. We examined the toxicity of Mn oxide nanomaterials in a neuronal precursor cell model, using the MTS assay to evaluate mitochondrial function in living cells and the LDH assay to quantify the release of the enzyme lactate dehydrogenase as a result of damage to the cell membrane. Both assays show that the toxicity of Mn is dependent on the type of Mn oxide nanomaterial and its concentration as well as on the state of cell differentiation. Following exposure to Mn oxide nanomaterials, reactive oxygen species (ROS) are generated, and flow cytometry experiments suggest that cell death occurred through apoptosis. During exposure to Mn oxide nanomaterials, increased levels of the transcription factor NF-kappa B (which mediates the cellular inflammatory response) were observed.
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The complex export pathways that connect the surface waters of the Weddell Sea with the Antarctic Circumpolar Current influence water mass modification, nutrient fluxes, and ecosystem dynamics. To study this exchange, 40 surface d...
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The complex export pathways that connect the surface waters of the Weddell Sea with the Antarctic Circumpolar Current influence water mass modification, nutrient fluxes, and ecosystem dynamics. To study this exchange, 40 surface drifters, equipped with temperature sensors, were released into the northwestern Weddell Sea's continental shelf and slope frontal systemin late January 2012. Comparison of the drifter trajectories with a similar deployment in early February 2007 provides insight into the interannual variability of the surface circulation in this region. Observed differences in the 2007 and 2012 drifter trajectories are related to a variable surface circulation responding to changes in wind stress curl over the Weddell Gyre. Differences between northwestern Weddell Sea properties in 2007 and 2012 include 1) an enhanced cyclonic wind stress forcing over the Weddell Gyre in 2012; 2) an acceleration of the Antarctic Slope Current (ASC) and an offshore shift of the primary drifter export pathway in 2012; and 3) a strengthening of the Coastal Current (CC) over the continental shelf in 2007. The relationship between wind stress forcing and surface circulation is reproduced over a longer time period in virtual drifter deployments advected by a remotely sensed surface velocity product. The mean offshore position and speed of the drifter trajectories are correlated with the wind stress curl over the Weddell Gyre, although with different temporal lags. The drifter observations are consistent with recent modeling studies suggesting that Weddell Sea boundary current variability can significantly impact the rate and source of exported surface waters to the Scotia Sea, a process that determines regional chlorophyll distributions.
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The subpolar gyres of the Southern Ocean form an important dynamical link between the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. Despite their key involvement in the production and export of bottom water ...
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The subpolar gyres of the Southern Ocean form an important dynamical link between the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. Despite their key involvement in the production and export of bottom water and the poleward transport of oceanic heat, these gyres are rarely acknowledged in conceptual models of the Southern Ocean circulation, which tend to focus on the zonally averaged overturning across the ACC. To isolate the effect of these gyres on the regional circulation, we carried out a set of numerical simulations with idealized representations of theWeddell Sea sector in the Southern Ocean. A key result is that the zonally oriented submarine ridge along the northern periphery of the subpolar gyre plays a fundamental role in setting the stratification and circulation across the entire region. In addition to sharpening and strengthening the horizontal circulation of the gyre, the zonal ridge establishes a strong meridional density front that separates the weakly stratified subpolar gyre from the more stratified circumpolar flow. Critically, the formation of this front shifts the latitudinal outcrop position of certain deep isopycnals such that they experience different buoyancy forcing at the surface. Additionally, the zonal ridge modifies the mechanisms by which heat is transported poleward by the ocean, favoring heat transport by transient eddies while suppressing that by stationary eddies. This study highlights the need to characterize how bathymetry at the subpolar gyre-ACC boundary may constrain the transient response of the regional circulation to changes in surface forcing.SIGNIFICANCE STATEMENT: This study explores the impact of seafloor bathymetry on the dynamics of subpolar gyres in the Southern Ocean. The subpolar gyres are major circulation features that connect the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. This work provides deeper insight for how the submarine ridges that exist along the northern periphery of these gyres shape the vertical distribution of tracers and overturning circulation in these regions. These findings highlight an underappreciated yet fundamentally important topographical constraint on the three-dimensional cycling of heat and carbon in the Southern Ocean}processes that have far-reaching implications for the global climate. Future work should explore how the presence of these ridges affect the time-evolving response of the Southern Ocean to changes in surface conditions.
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We report that TiO2 coatings formed via atomic layer deposition (ALD) may tune the activity of IrO2, RuO2, and FTO for the oxygen-evolution and chlorine-evolution reactions (OER and CER). Electrocatalysts exposed to approximate to...
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We report that TiO2 coatings formed via atomic layer deposition (ALD) may tune the activity of IrO2, RuO2, and FTO for the oxygen-evolution and chlorine-evolution reactions (OER and CER). Electrocatalysts exposed to approximate to 3-30 ALD cycles of TiO2 exhibited overpotentials at 10 mA cm(-2) of geometric current density that were several hundred millivolts lower than uncoated catalysts, with correspondingly higher specific activities. For example, the deposition of TiO2 onto IrO2 yielded a 9-fold increase in the OER-specific activity in 1.0 M H2SO4 (0.1 to 0.9 mA cm(ECSA)(-2) at 350 mV overpotential). The oxidation state of titanium and the potential of zero charge were also a function of the number of ALD cycles, indicating a correlation between oxidation state, potential of zero charge, and activity of the tuned electrocatalysts.
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Oceanic boundary currents over the continental slope exhibit variability with a range of time scales. Numerical studies of steady, along-slope currents over a sloping bathymetry have shown that cross-slope Ekman transport can adve...
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Oceanic boundary currents over the continental slope exhibit variability with a range of time scales. Numerical studies of steady, along-slope currents over a sloping bathymetry have shown that cross-slope Ekman transport can advect buoyancy surfaces in a bottom boundary layer (BBL) so as to produce vertically sheared geostrophic flows that bring the total flow to rest: a process known as buoyancy shutdown of Ekman transport or Ekman arrest. This study considers the generation and evolution of near-bottom flows due to a barotropic, oscillating, and laterally sheared flow over a slope. The sensitivity of the boundary circulation to changes in oscillation frequency omega, background flow amplitude, bottom slope, and background stratification is explored. When omega/f << 1, where f is the Coriolis frequency, oscillations allow the system to escape from the steady buoyancy shutdown scenario. The BBL is responsible for generating a secondary overturning circulation that produces vertical velocities that, combined with the potential vorticity (PV) anomalies of the imposed barotropic flow, give rise to a time-mean, rectified, vertical eddy PV flux into the ocean interior: a "PV pump.'' In these idealized simulations, the PV anomalies in the BBL make a secondary contribution to the time-averaged PV flux. Numerical results show the domain-averaged eddy PV flux increases nonlinearly with omega with a peak near the inertial frequency, followed by a sharp decay for omega/f > 1. Different physical mechanisms are discussed that could give rise to the temporal variability of boundary currents.
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