Cloud information for FIRE from surface weather reports

Surface weather observations of clouds were analyzed to obtain a global cloud climatology (Warren et al, 1986; 1988). The form of the synoptic weather code limits the types of cloud information which are available from these reports. Comparison of surface weather reports with instrumental observations during the FIRE field experiments can help to clarify the operational definitions which were made in the climatology because of the nature of the synoptic code. The long-term climatology from surface weather observations is also useful background for planning the location and timing of intensive field experiments

Optical properties of CO2 ice and CO2 snow from ultraviolet to infrared: Application to frost deposits and clouds on Mars

Researchers found that it is possible to grow large clear samples of CO2 ice at Mars-like temperatures of 150-170K if a temperature controlled refrigerator is connected to an isolated two-phase pure CO2 system. They designed a chamber for transmission measurements whose optical path between the 13mm diameter window is adjustable from 1.6mm to 107mm. This will allow measurements of linear absorption down to less than 0.01 cm (exp -1). A preliminary transmission spectrum of a thick sample of CO2 ice in the near infrared was obtained. Once revised optical constants have been determined as a function of wavelength and temperature, they can be applied to spectral reflectance/emissivity models for CO2 snow surfaces, both pure and contaminated with dust and water ice, using previously established approaches. It will be useful, also, to develop an infrared scattering-emission cloud radiance model (especially as viewed from near the limb) in order to develop a strategy for the identification of CO2 cloud layers by the atmospheric infrared radiometer instrument on the Mars Observer

Light-Absorbing Impurities in Snow: A Personal and Historical Account

The ability of light-absorbing impurities (LAI) to darken snow had been known for decades, even inspiring practical applications, but quantification of the radiative forcing awaited radiative-transfer modeling in 1980 and measurement of soot in Arctic snow in 1983-4. Climate-modeling interest in this forcing began in 2004, spurring a modern explosion of research on several topics: methods to measure black carbon (BC) and other LAI, Arctic air pollution, measurement of BC mixing ratio in snow over large areas, and radiative transfer modeling of this forcing and its climatic and hydrological effects. The BC-content of snow in large remote regions of the northern hemisphere is on the order of 20 parts per billion, causing albedo reductions of ∼1–2%. This reduction is climatically significant but difficult to detect by remote sensing, so quantification requires fieldwork to collect and analyze snow samples. This review is a personal account of early research at the National Center for Atmospheric Research and the University of Washington, followed by a brief summary of recent work by the author and his colleagues

Measurements of the light-absorbing material inside cloud droplets and its effect on cloud albedo

Most of the measurements of light-absorbing aerosol particles made previously have been in non-cloudy air and therefore provide no insight into aerosol effects on cloud properties. Here, researchers describe an experiment designed to measure light absorption exclusively due to substances inside cloud droplets, compare the results to related light absorption measurements, and evaluate possible effects on the albedo of clouds. The results of this study validate those of Twomey and Cocks and show that the measured levels of light-absorbing material are negligible for the radiative properties of realistic clouds. For the measured clouds, which appear to have been moderately polluted, the amount of elemental carbon (EC) present was insufficient to affect albedo. Much higher contaminant levels or much larger droplets than those measured would be necessary to significantly alter the radiative properties. The effect of the concentrations of EC actually measured on the albedo of snow, however, would be much more pronounced since, in contrast to clouds, snowpacks are usually optically semi-infinite and have large particle sizes

Representation Of A Nonspherical Ice Particle By A Collection Of Independent Spheres For Scattering And Absorption Of Radiation: 3. Hollow Columns And Plates

The ability of an assembly of spheres to represent scattering and absorption by a nonspherical ice crystal of the same volume-to-area (V/A) ratio was previously evaluated for convex shapes (circular cylinders and hexagonal prisms). Here we extend the comparison to indented and hollow prisms, which are common in ice clouds. In the equivalent-sphere representation, the crystal mass and surface area are both conserved. Internal surfaces as well as external surfaces contribute to the total surface area; in the model representation both become external surfaces of spheres. The optical depth tau of the model cloud is thus greater than that of the real cloud by the ratio A/4P, where A is the total area of the nonspherical particle and P is the orientation-averaged projected area. This ratio, which we call fluffiness,\u27\u27 is unity for convex shapes but may exceed 2 for clusters of hollow bullets. In effect, the scattering at interior surfaces of a hollow crystal becomes classified as multiple scattering in the model of ice spheres. Therefore, rather than directly comparing the asymmetry factor (g) and single-scattering albedo (omega(o)) of the hollow crystal to those of the equal-V/A sphere, it is more appropriate to compare the product tau(1 - g)omega(o), because this quantity largely determines the bulk radiative properties of the cloud. Errors in albedo, absorptance, and transmittance of ice clouds, caused by the equal-V/A representation, are presented for a range of aspect ratios, indentation depths, and ice-water paths at visible and near-infrared wavelengths

Representation Of A Nonspherical Ice Particle By A Collection Of Independent Spheres For Scattering And Absorption Of Radiation: 2. Hexagonal Columns And Plates

[1] A cloud of nonspherical ice particles may be represented in radiation models by a collection of spheres, in which the model cloud contains the same total volume of ice and the same total surface area as the real cloud but not the same number of particles. The spheres then have the same volume-to-area (V/A) ratio as the nonspherical particle. In previous work this approach was shown to work well to represent randomly oriented infinitely long circular cylinders for computation of hemispherical reflectance, transmittance, and absorptance. In this paper the results have been extended to hexagonal columns and plates using a geometric optics technique for large particles and finite-difference-time-domain theory (FDTD) for small particles. The extinction efficiency and single-scattering coalbedo for these prisms are closely approximated by the values for equal-V/A spheres across the ultraviolet, visible, and infrared from 0.2 to 25 mum wavelength. Errors in the asymmetry factor can be significant where ice absorptance is weak, at visible wavelengths for example. These errors are greatest for prisms with aspect ratios close to 1. Errors in hemispheric reflectance, absorptance, and transmittance are calculated for horizontally homogeneous clouds with ice water paths from 0.4 to 200,000 g m(-2) and crystal thicknesses of 1 to 400 mum, to cover the range of crystal sizes and optical depths from polar stratospheric clouds (PSCs) through cirrus clouds to surface snow. The errors are less than 0.05 over most of these ranges at all wavelengths but can be larger at visible wavelengths because of the ideal shapes of the prisms. The method was not tested for, and is not expected to be accurate for, angle-dependent radiances

Sources of light-absorbing aerosol in arctic snow and their seasonal variation

Two data sets consisting of measurements of light absorbing aerosols (LAA) in arctic snow together with suites of other corresponding chemical constituents are presented; the first from Siberia, Greenland and near the North Pole obtained in 2008, and the second from the Canadian arctic obtained in 2009. A preliminary differentiation of the LAA into black carbon (BC) and non-BC LAA is done. Source attribution of the light absorbing aerosols was done using a positive matrix factorization (PMF) model. Four sources were found for each data set (crop and grass burning, boreal biomass burning, pollution and marine). For both data sets, the crops and grass biomass burning was the main source of both LAA species, suggesting the non-BC LAA was brown carbon. Depth profiles at most of the sites allowed assessment of the seasonal variation in the source strengths. The biomass burning sources dominated in the spring but pollution played a more significant (though rarely dominant) role in the fall, winter and, for Greenland, summer. The PMF analysis is consistent with trajectory analysis and satellite fire maps

The Effect of DNA Structure on the Catalytic Efficiency and Fidelity of Human DNA Polymerase β on Templates with Platinum-DNA Adducts

DNA adducts formed by platinum-based anticancer drugs interfere with DNA replication. The carrier ligand of the platinum compound is likely to affect the conformation of the Pt-DNA adducts. In addition, the conformation of the adduct can also change upon binding of damaged DNA to the active site of DNA polymerase. From the crystal structures of pol beta ternary complexes it is evident that undamaged gapped and primed single-stranded (non-gapped) DNA templates exist in very different conformations when bound to pol beta. Therefore, one might expect that the constraints imposed on the damaged templates by binding to the polymerase active site should also affect the conformation of the Pt-DNA adducts and their ability to inhibit DNA replication. In support of this hypothesis we have found that the efficiency, carrier ligand specificity, site of discrimination (3'-G versus 5'-G of the Pt-GG adducts), and fidelity of translesion synthesis past Pt-DNA adducts by pol beta are strongly affected by the structure of the DNA template. Previous studies have suggested that the conformation of Pt-DNA adducts may be affected by the sequence context of the adduct. In support of this hypothesis, our data show that sequence context affects the efficiency, fidelity, and pattern of misincorporation by pol beta