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  • 1
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    Simultaneous influences of thermodynamics and aerosols on deep convection and lightning in the tropics (2015)
    Wiley
    Details
    Publication Date: 2015-06-05
    Description: Convective features (CFs) observed by the Tropical Rainfall Measuring Mission (TRMM) satellite between 2004 and 2011 are analyzed to determine the relative roles of thermodynamics and aerosols as they modulate radar reflectivity and lightning. We studied the simultaneous impacts of normalized convective available potential energy (NCAPE) and warm cloud depth (WCD) as well as cloud condensation nuclei concentrations (D ≥ 40 nm; N40) on total lightning density (TLD), average height of 30 dBZ echoes (AVGHT30), and vertical profiles of radar reflectivity (VPRR) within individual CFs. The results show that TLD increases by up to 600% and AVGHT30 increases by up to 2–3 km with increasing NCAPE and N40 for fixed WCD. The partial sensitivity of TLD/AVGHT30 to NCAPE and N40 separately were comparable in magnitude, but account for a fraction of the total range of variability (i.e., when the influences of NCAPE and N40 are considered simultaneously). Both TLD and AVGHT30 vary inversely with WCD such that maxima of TLD and AVGHT30 are found for the combination of high NCAPE , high N40 , and shallower WCD . The relationship between lightning and radar reflectivity was shown to vary as a function of N40 for a fixed thermodynamic environment. Analysis of VPRRs shows that reflectivity in the mixed phase region is up to 5.0-5.6 dB greater for CFs in polluted environments compared to CFs in pristine environments (holding thermodynamics fixed). This analysis favors a merged hypothesis for the simultaneous roles of thermodynamics and aerosols as they influence deep convective clouds in the Tropics.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Burgess bounds for short mixed character sums (2015)
    Oxford University Press
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    Publication Date: 2015-05-20
    Description: This paper proves non-trivial bounds for short mixed character sums by introducing estimates for Vinogradov's mean value theorem into a version of the Burgess method.
    Print ISSN: 0024-6107
    Electronic ISSN: 1469-7750
    Topics: Mathematics
    Published by Oxford University Press
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  • 3
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    Environmental controls on storm intensity and charge structure in multiple regions of the continental United States (2015)
    Wiley
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    Publication Date: 2015-06-14
    Description: A database consisting of approximately 4000 storm observations has been objectively analyzed to determine environmental characteristics that produce high radar reflectivities above the freezing level, large total lightning flash rates on the order of 10 flashes min −1 and anomalous vertical charge structures (most notably, dominant mid-level positive charge). The storm database is drawn from four regions of the United States featuring distinct environments, each with coinciding Lightning Mapping Array (LMA) network data. LMAs are able to infer total lightning flash rates using flash clustering algorithms, such as the one implemented in this study. Results show that anomalous charge structures inferred from LMA data, significant lightning flash rates and increased radar reflectivities above the freezing level tend to be associated with environments that have high cloud base heights (approximately 3 km above ground level) and large atmospheric instability, quantified by normalized convective available potential energy (NCAPE) near 0.2 m s −2 . Additionally, we infer that aerosols may affect storm intensity. Maximum flash rates were observed in storms with attributed aerosol concentrations near 1000 cm −3 while total flash rates decrease when aerosol concentrations exceed 1500 cm −3 , consistent with previous studies. However, this effect is more pronounced in regions where the NCAPE and cloud base height are low. The dearth of storms with estimated aerosol concentrations less than 700 cm −3 (approximately 1% of total sample) does not provide a complete depiction of aerosol invigoration.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Relating atmospheric and oceanic DMS levels to particle nucleation events in the Canadian Arctic (2011)
    Wiley
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    Publication Date: 2011-11-01
    Description: Measurements of ocean surface and atmospheric dimethyl sulfide (DMS) and particle size distributions were made in the Canadian Arctic Archipelago during the fall of 2007 and the late summer of 2008 aboard the Canadian Coast Guard Ship Amundsen. Nucleation-mode particles were observed during the 2008 cruise, which took place in the eastern Arctic from August to September when the atmosphere and ocean were more photo-active as compared to the October 2007 transit in the Beaufort Sea during which no nucleation/growth events were observed. The observed nucleation periods in 2008 coincided with high atmospheric and ocean surface DMS concentrations, suggesting that the particles originated from marine biogenic sources. An aerosol microphysics box model was used to simulate nucleation given the measured conditions in the marine boundary layer. Although other sources may have contributed, we find that the newly formed particles can be accounted for by a marine biogenic DMS source for combinations of the following parameters: [OH] ≥ 3 × 105 molecules cm−3, DMS mixing ratio is ≥ 100 pptv, the activation coefficient is ≤ 10−7 and the background particle concentration is ≤ 100 cm−3.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
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    Theoretical constraints on pure vapor-pressure driven condensation of organics to ultrafine particles (2011)
    Wiley
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    Publication Date: 2011-08-16
    Description: Organic condensation to freshly nucleated particles contributes substantially to their growth. Here we explore a range of constraints on this process, under the assumption that gas-phase oxidation of organic vapors by hydroxy radical is forming organics with a sufficiently low volatility to condense onto particles in the 2–20 nm size range. To condense but not homogeneously nucleate, vapors need to have saturation concentrations (C*) in the 10−3 − 10−2 μg m−3 range, and this is exactly the range that gas-phase chemistry is likely to produce. At least half of the observed growth rate of ultrafine particles can be explained by these simple considerations and constraints.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    A Simple Way to Improve the Diurnal Cycle in Convective Rainfall over Land in Climate Models (2014)
    Wiley
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    Publication Date: 2014-02-06
    Description: [1]  Within the tropics, and during the summer months in mid-latitudes, most of the rainfall reaching the surface is generated by moist convection. Over land, the diurnal cycle in moist convective rainfall usually peaks in the late afternoon. In most climate models, the diurnal peak in convective rainfall occurs several hours too early, and is often near local solar noon. We argue that this bias partly originates from the methods used in convective parameterizations to calculate the cloud base mass flux. In most convective parameterizations, the initial convective mass flux is determined from the Convective Available Potential Energy (CAPE) of an updraft parcel originating from the model layer closest to the surface. In models, the rapid increase in the CAPE of this near surface layer following sunrise contributes to a rapid increase in convective precipitation. However, the mass weighted CAPE of the boundary layer as a whole responds much more slowly to the increase in downward solar radiation at the surface. Using a recently developed convective parameterization in version 4 of the Community Atmosphere Model (CAM4), we show that the overall accuracy in the diurnal simulation of convective precipitation increases as the number of near surface layers from which convective air parcels are permitted to originate increases from one to four. We also show that the simulation of the diurnal cycle in convective precipitation over land can be improved through the introduction of variables which attempt to represent the persistence of subgridscale convective organization within a grid column across model timesteps.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Policy must recognize drug impact on different sectors (2008)
    Nature Publishing Group (NPG)
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    Publication Date: 2008-02-01
    Description: 〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Pierce, Robin -- Illes, Judy -- England -- Nature. 2008 Jan 31;451(7178):521. doi: 10.1038/451521c.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18235479" target="_blank"〉PubMed〈/a〉
    Keywords: Biomedical Enhancement/*ethics/standards ; Cognition/*drug effects ; Humans ; Legislation, Drug ; Pharmaceutical Preparations/economics/supply & distribution
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 8
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    Ice nucleating particle emissions from photochemically-aged diesel and biodiesel exhaust (2016)
    Wiley
    Details
    Publication Date: 2016-05-19
    Description: Immersion-mode ice-nucleating particle (INP) concentrations from an off-road diesel engine were measured using a continuous-flow diffusion chamber at -30 °C. Both petro-diesel and biodiesel were utilized, and the exhaust was aged up to 1.5 photochemically equivalent days using an oxidative flow reactor. We found that aged and unaged diesel exhaust of both fuels is not likely to contribute to atmospheric INP concentrations at mixed-phase cloud conditions. To explore this further, a new limit-of-detection parameterization for ice nucleation on diesel exhaust was developed. Using a global chemical-transport model, potential black carbon INP (INP BC ) concentrations were determined using a current-literature INP BC parameterization and the limit-of-detection parameterization. Model outputs indicate that the current-literature parameterization likely overemphasizes INP BC concentrations, especially in the Northern Hemisphere. These results highlight the need to integrate new INP BC parameterizations into global climate models as generalized INP BC parameterizations are not valid for diesel exhaust.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    Large contribution of natural aerosols to uncertainty in indirect forcing (2013)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2013-11-10
    Description: The effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Carslaw, K S -- Lee, L A -- Reddington, C L -- Pringle, K J -- Rap, A -- Forster, P M -- Mann, G W -- Spracklen, D V -- Woodhouse, M T -- Regayre, L A -- Pierce, J R -- England -- Nature. 2013 Nov 7;503(7474):67-71. doi: 10.1038/nature12674.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, UK.〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/24201280" target="_blank"〉PubMed〈/a〉
    Keywords: Aerosols/*analysis ; *Climate ; Greenhouse Effect ; History, 18th Century ; History, 19th Century ; History, 20th Century ; History, 21st Century ; Human Activities/history ; *Models, Theoretical ; Sulfides/analysis ; Sulfur Dioxide/analysis ; *Uncertainty ; Volcanic Eruptions/history
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 10
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    Rethinking organic aerosols: semivolatile emissions and photochemical aging (2007)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2007-03-03
    Description: Most primary organic-particulate emissions are semivolatile; thus, they partially evaporate with atmospheric dilution, creating substantial amounts of low-volatility gas-phase material. Laboratory experiments show that photo-oxidation of diesel emissions rapidly generates organic aerosol, greatly exceeding the contribution from known secondary organic-aerosol precursors. We attribute this unexplained secondary organic-aerosol production to the oxidation of low-volatility gas-phase species. Accounting for partitioning and photochemical processing of primary emissions creates a more regionally distributed aerosol and brings model predictions into better agreement with observations. Controlling organic particulate-matter concentrations will require substantial changes in the approaches that are currently used to measure and regulate emissions.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Robinson, Allen L -- Donahue, Neil M -- Shrivastava, Manish K -- Weitkamp, Emily A -- Sage, Amy M -- Grieshop, Andrew P -- Lane, Timothy E -- Pierce, Jeffrey R -- Pandis, Spyros N -- New York, N.Y. -- Science. 2007 Mar 2;315(5816):1259-62.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA 15213, USA. alr@andrew.cmu.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/17332409" target="_blank"〉PubMed〈/a〉
    Keywords: Aerosols ; Air Pollutants/*chemistry ; Computer Simulation ; Hydrocarbons/chemistry ; Mathematics ; Models, Chemical ; Organic Chemicals/*chemistry ; Oxidation-Reduction ; Particulate Matter/*chemistry ; Phase Transition ; Photochemistry ; Ultraviolet Rays ; Vehicle Emissions/*analysis ; Volatilization
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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