Impacts of aerosol chemical composition on microphysics and precipitation in deep convection

Aerosols affect precipitation by modifying cloud properties such as cloud droplet number concentration (CDNC). Aerosol effects on CDNC depend on aerosol properties such as number concentration, size spectrum, and chemical composition. This study focuses on the effects of aerosol chemical composition on CDNC and, thereby, precipitation in a mesoscale cloud ensemble (MCE) driven by deep convective clouds. The MCE was observed during the 1997 department of energy's Atmospheric Radiation Measurement (ARM) summer experiment. Double-moment microphysics with explicit nucleation parameterization, able to take into account those three properties of aerosols, is used to investigate the effects of aerosol chemical composition on CDNC and precipitation. The effects of aerosol chemical compositions are investigated for both soluble and insoluble substances in aerosol particles. The effects of soluble substances are examined by varying mass fractions of two representative soluble components of aerosols in the continental air mass: sulfate and organics. The increase in organics with decreasing sulfate lowers critical supersaturation (S_c) and leads to higher CDNC. Higher CDNC results in smaller autoconversion of cloud liquid to rain. This provides more abundant cloud liquid as a source of evaporative cooling, leading to more intense downdrafts, low-level convergence, and updrafts. The resultant stronger updrafts produce more condensation and thus precipitation, as compared to the case of 100% sulfate aerosols. The conventional assumption of sulfate aerosol as a surrogate for the whole aerosol mass can be inapplicable for the case with the strong sources of organics. The less precipitation is simulated when an insoluble substance replaces organics as compared to when it replaces sulfate. When the effects of organics on the surface tension of droplet and solution term in the Köhler curve are deactivated by the insoluble substance, S_c is raised more than when the effects of sulfate on the solution term are deactivated by the insoluble substance. This leads to lower CDNC and, thus, larger autoconversion of cloud liquid to rain, providing less abundant cloud liquid as a source of evaporative cooling. The resultant less evaporative cooling produces less intense downdrafts, weaker low-level convergence, updrafts, condensation and, thereby, less precipitation in the case where organics is replaced by the insoluble substance than in the case where sulfate is replaced by the insoluble substance. The variation of precipitation caused by the change in the mass fraction between the soluble and insoluble substances is larger than that caused by the change in the mass fraction between the soluble substances.     

Fallout radionuclides in the Pacific Ocean: Vertical and horizontal distributions,largely from GEOSECS stations

From GEOSECS stations, largely, the 1974 distributions of Pu and of¹³⁷Cs are described in the Pacific Ocean north of about 20°S latitude. Changes in some of these distributions are described from 1978 cruises by the authors.The Pacific exhibited, everywhere, a shallow subsurface layer of Pu-rich water with its concentration maximum at about 465 m in 1974; over a large portion of the central North Pacific a second layer of Pu-labelled water, less concentrated than the shallow layer, lay just above the bottom. Similar features were not observed in the case of¹³⁷Cs.The inventories of both Pu and¹³⁷Cs in the water column at most 1974 stations are substantially greater than those to be expected from world-wide fallout alone; these inventory excesses appear to be attributable to close-in fallout, but only if the ratio Pu/¹³⁷Cs in this source was much higher than in world-wide fallout. The North Pacific mean ratio of the inventories is 2.2 times that observed in world-wide fallout.Resolubilization of Pu both from sinking particles and from sediments explains peculiarities of its depth distributions.There is little evidence for tracer movement by sliding downward along density surfaces;¹³⁷Cs appears to have moved to depth by downmixing at the edge of the Kuroshio, and then moved horizontally and upward alongσ_t contours. The shallow Pu-rich layer shows no coordination with density, salinity or O₂ isopleths. The deep Pu-rich layer is restricted to a narrow range of O₂ concentrations that confirm its origin in the Aleutian Trench and rapid spread southward and laterally. Near-bottom circulation processes have been much more active than here-to-fore described.     

Orientation and motion of water molecules in cordierite: A proton nuclear magnetic resonance study

Conventional and solid state proton nuclear magnetic resonance (NMR) techniques have been used to examine water molecules in the channels of a single crystal of cordierite, (Mg, Fe)₂Al₄Si₅O₁₈, as a function of temperature, magnetic field, and orientation. Only one type of water was found rather than water in two distinct rigid orientations which were indicated by earlier infrared spectral studies. However, the measured dipolar splittings indicate that this water is in rapid motion. Shifts in the dipolar doublet due to Fe²⁺ impurities indicate that the water molecules are not moving among adjacent channel sites along a channel cavity. A two-site hopping model is proposed involving the major residence time spent with the hydrogen-hydrogen vector parallel to the channels, a minor residence time spent with the hydrogen-hydrogen vector perpendicular to the channels, and a short time (<1 μs) in transit. This model fits both the present NMR data and previously reported infrared absorption data and is compared to previously reported neutron diffraction data.     

The geochemistry of iron in Recent tidal-flat sediments of the Wash area,England: a mineralogical,Mössbauer,and magnetic study

Undisturbed core samples of Recent sediments from the Wash tidal flats, East Anglia, England, obtained using a Delft corer, were studied with special reference to the diagenesis and geochemical behaviour of iron. The Mössbauer effect in ⁵⁷Fe was used to monitor the distribution of Fe between different phases as a function of depth, together with the magnetic mineralogy and palaeomagnetic properties.The cores consist of, successively downwards: 0.36 m brown clay; 1.5 m finely laminated silts and fine sands, and 7.14 m homogeneous fine sands. The dominant minerals are quartz, feldspar, calcite and clay minerals, and chemical analysis for Al, Si, Mg, Mn, Ca, Fe, Na, K showed variations closely linked to lithological changes. Illite is the most abundant clay mineral (mean 48%), followed by mixed layer illite-montmorillonite and montmorillonite, kaolinite and chlorite. Chlorite is the major iron-bearing clay mineral and represents 4 to 10% of the <2 μm fraction throughout the core. Sulphide minerals are present throughout the core, including framboidal pyrite.Computer fit analysis of the Mössbauer spectra of best quality showed contributions from Fe²⁺ and Fe³⁺ in clay minerals (essentially chlorite), low-spin Fe²⁺ in pyrite, and magnetically ordered iron in greigite (Fe₃S₄). Systematic variations, as a function of sample depth, indicate a relative increase in the amount of Fe in pyrite at the expense of the clay minerals.Magnetite and titanium-bearing magnetite are the carriers of natural magnetic remanence in these sediments.The direction and intensity of natural remanence in the samples compare well with the known secular variation of the Earth's magnetic field derived from the historic-archaeomagnetic record and this enables the samples to be dated and sedimentation rates to be determined (1.5 mm yr^?1 for the upper 2 m and ~7.7 mm yr^?1 for the lower 7 m).     

Conditions of ore mineral formation in certain Zambian Copperbelt deposits with special reference to the role of cobalt

Studies of the compositions of coexisting sulphide assemblages from certain Zambian Copperbelt deposits and of their textural relations and host rock environments have been undertaken by routine microscopy and using electron microprobe analysis. Special attention has been paid to sulphide assemblages containing cobalt. Using experimental data on the systems Cu-Co-S, Cu-Fe-Co-S and on sulphidation equilibria, together with the available information on equilibria involving gangue minerals and some new calculations, an attempt has been made to define the chemical conditions of ore formation and/or re-equilibration in several deposits (Baluba, Chibuluma West and Chibuluma, Chambeshi S.E.). If a re-equilibration temperature of 300°C is assumed the range of aS₂ prevailing during final formation of the assemblages was of the order 10^–7 – 10^–9 atm, more rarely dropping to 10^–11 – 10^–12 atm. If magnetite is present, and this is considered very unlikely in most cases, aO₂ may have reached as high as 10^–35 atm but it is generally likely to have been around 10^–50 atm or even lower. Values of aCO₂ are assumed to have been of the order of 10^–0.5 atm. Detailed studies of drill hole samples from the Chambeshi S.E. deposit suggest an important link between the petrology of the host rocks and the sulphide mineral chemistry. In particular, the control exerted on sulphide composition by aS₂ may have been related to the availability of sulphate in the form of diagenetic anhydrite or in sulphate-rich interstitial waters. The distinctive distribution of cobalt in the ores appears related to the distribution of amphibolite bodies and in turn to rift fault systems in the Basement which allowed upward movement of fluids enriched in magmatically derived cobalt.     

Validation of Ground-Based Visible Measurements of Total Ozone by Comparison with Dobson and Brewer Spectrophotometers

Comparisons of total column ozone measurements from Dobson, Brewer and SAOZ instruments are presented for the period 1990 to 1995 at seven stations covering the mid- and the high northern latitudes, as well as the Antarctic region. The main purpose of these comparisons is to assess, by reference to the well established Dobson network, the accuracy of the zenith-sky visible spectroscopy for the measurement of total ozone. The strengths and present limitations of this latter technique are investigated. As a general result, the different instruments are found to agree within a few percent at all stations, the best agreement being obtained at mid-latitudes. On average, for the mid-latitudes, SAOZ O₃ measurements are approximately 2% higher than Dobson ones, with a scatter of about 5%. At higher latitudes, both scatter and systematic deviation tend to increase. In all cases, the relative differences between SAOZ and Dobson or Brewer column ozone are characterised by a significant seasonal signal, the amplitude of which increases from about 2.5% at mid-latitude to a maximum of 7.5% at Faraday, Antarctica. Although it introduces a significant contribution to the seasonality at high latitude, the temperature sensitivity of the O₃ absorption coefficients of the Dobson and Brewer instruments is shown to be too small to account for the observed SAOZ/Dobson differences. Except for Faraday, these differences can however be largely reduced if SAOZ AMFs are calculated with realistic climatological profiles of ozone, pressure and temperature. Other sources of uncertainties that might affect the comparison are investigated. Evidence is found that the differences in the air masses sampled by the SAOZ and the other instruments contribute significantly to the scatter, and the impact of the tropospheric clouds on SAOZ measurements is displayed.     

Fish population responses to chronic and acute pollution: The influence of life history strategies

We have developed a simulation model to estimate pollution effects on economically important estuarine-dependent fish populations. Traditionally, pollution studies have focused upon impacts on individual organisms; however, wise management of marine resources depends upon an understanding of dynamics at the population level. As a required first step toward conducting relevant pollution studies, we have compiled available life history data on eight species (14 spatial-temporal stocks), concentrating on age-specific rates of growth, survival, and fecundity. Leslie matrix models of species population dynamics were used to predict pollutant impacts—mediate through changes in 1st-year survival. On average, and without compensation, these modelled stocks respond to a one-time-50% reduction in first-year survival by taking ten years to equilibrate at 88% of their preimpact abundance. Our synthesis of the data included a search for derived (standardized) population parameters to evaluate differences in susceptibility among and within fish populations to pollutant stresses. We demonstrated that knowledge of a species’ age-specific fecundity pattern provides additional predictive power of its response to pollution perturbation.     

Plutonium oxidation state distributions in the Pacific Ocean during 1980–1981

The concentration of plutonium and its oxidation state distribution have been measured as a function of depth at three locations in the North Pacific Ocean. Concentration profiles were similar to those observed in the same area during 1974 with primary maxima at depths of a few hundred meters below the surface and secondary maxima near the bottom. Oxidation state distribution profiles were similar at the three locations with plutonium about equally divided between the reduced and oxidized forms except near the bottom. There the oxidized form was more abundant and comprised ～ 90% of the total plutonium. No major change in oxidation state occurred at the depths of the shallow concentration maxima suggesting that their formation and persistence were not dependent upon a redox change. The concentration maxima near the bottom coincided with the enhanced abundance of the poorly sorbed oxidized form suggesting that they resulted from the loss of oxidized plutonium from the sediments.     

Vertical profile of artificial radionuclide concentrations in the Central Arctic Ocean

The artificial radionuclides ⁹⁰Sr, ¹³⁷Cs, ²³⁸Pu, ^239,240Pu and ²⁴¹Am have been measured in eight water samples collected in 1979, at intervals from surface to bottom, through the ice at the LOREX satellite camp SS near the North Pole. Differences in the concentrations and ratios of these nuclides, compared with values measured, over time, in the various water masses that flow into the Arctic Ocean, can be used as semi-independent checks on rates of flow to the LOREX stations and on residence times in the Arctic Ocean. An unexpected finding was that water labelled with low-level liquid waste from the Windscale plant on the Irish Sea is a major component of the 1500 m LOREX sample, and has reached there in no more than eight to ten years. Even from this one station in the Polar Ocean, estimation of the inventories of the various radionuclides is good enough to emphasize the importance of horizontal advection of the various supply terms to the Arctic.