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  • Articles  (7)
  • American Meteorological Society  (4)
  • Wiley  (2)
  • Elsevier  (1)
  • Geography  (7)
  • 1
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    Aerodynamic Contrails: Microphysics and Optical Properties (2009)
    American Meteorological Society
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    Publication Date: 2009-02-01
    Description: Aerodynamic contrails form when air flows across the wings of subsonic aircraft in cruise. During a short adiabatic expansion phase, high supersaturations trigger burstlike homogeneous ice formation on ambient liquid aerosol particles within a wing depth. Small particles freeze first because they equilibrate most rapidly. Ambient temperature is the key determinant of nascent aerodynamic contrail properties. Only above ∼232 K do they become visible (but optically thin). These temperatures are at the high end of those prevailing at tropical upper tropospheric flight levels of subsonic aircraft. In colder midlatitude conditions, aerodynamic contrails stay invisible and the very small ice particles formed quickly evaporate when exposed to small subsaturations, explaining why the formation of these contrails is rarely observed. After formation, aerodynamic contrails develop into contrail cirrus if air is supersaturated with respect to ice. This type of anthropogenic ice cloud adds to contrail cirrus derived from jet exhaust contrails and may become particularly important in the future because air traffic is projected to increase significantly in tropical and subtropical regions. Regardless of whether aerodynamically induced ice formation leads to persistent contrail cirrus, cruising aircraft may act as sources of potent heterogeneous ice nuclei by preactivating the insoluble fraction in atmospheric particle populations. Aerodynamic contrails and aerodynamically induced preactivation should therefore be studied experimentally and with global models to explore their potential to induce climate change.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 2
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    Effective Radius of Ice Particles in Cirrus and Contrails (2011)
    American Meteorological Society
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    Publication Date: 2011-02-01
    Description: This paper discusses the ratio C between the volume mean radius and the effective radius of ice particles in cirrus and contrails. The volume mean radius is proportional to the third root of the ratio between ice water content and number of ice particles, and the effective radius measures the ratio between ice particle volume and projected cross-sectional area. For given ice water content and number concentration of ice particles, the optical depth scales linearly with C. Hence, C is an important input parameter for radiative forcing estimates. The ratio C in general depends strongly on the particle size distribution (PSD) and on the particle habits. For constant habits, C can be factored into a PSD and a habit factor. The PSD factor is generally less than one, while the habit factor is larger than one for convex or concave ice particles with random orientation. The value of C may get very small for power-law PSDs with exponent n between −4 and 0, which is often observed. For such PSDs, most of the particle volume is controlled by a few large particles, while most of the cross-sectional area is controlled by the many small particles. A new particle habit mix for contrail cirrus including small droxtal-shape particles is suggested. For measured cirrus and contrails, the dependence of C on volume mean particle radius, ambient humidity, and contrail age is determined. For cirrus, C varies typically between 0.4 and 1.1. In contrails, C = 0.7 ± 0.3, with uncertainty ranges increasing with the volume radius and contrail age. For the small particles in young contrails, the extinction efficiency in the solar range deviates considerably from the geometric optics limit.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 3
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    Aerodynamic Contrails: Phenomenology and Flow Physics (2009)
    American Meteorological Society
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    Publication Date: 2009-02-01
    Description: Aerodynamic contrails have been recognized for a long time although they appear sporadically. Usually one observes them under humid conditions near the ground, where they are short-lived phenomena. Aerodynamic contrails appear also at cruise levels where they may persist when the ambient atmosphere is ice-supersaturated. The present paper presents a theoretical investigation of aerodynamic contrails in the upper troposphere. The required flow physics are explained and applied to a case study. Results show that the flow over aircraft wings leads to large variations of pressure and temperature. Average pressure differences between the upper and lower sides of a wing are on the order of 50 hPa, which is a quite substantial fraction of cruise-level atmospheric pressures. Adiabatic cooling exceeds 20 K about 2 m above the wing in a case study shown here. Accordingly, extremely high supersaturations (exceeding 1000%) occur for a fraction of a second. The potential consequences for the ice microphysics are discussed. Because aerodynamic contrails are independent of the formation conditions of jet contrails, they form an additional class of contrails that might be complementary because they form predominantly in layers that are too warm for jet contrail formation.
    Print ISSN: 0022-4928
    Electronic ISSN: 1520-0469
    Topics: Geography , Geosciences , Physics
    Published by American Meteorological Society
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  • 4
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    Evidence for influence of mineral weathering on stream water sulphate in Vermont and New Hampshire(USA) (2004)
    Wiley
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    Publication Date: 2004-06-08
    Description: Mass balance studies in forested catchments in the northeastern USA show that S losses via streamwater SO42- exceed measured atmospheric S inputs. Possible sources of the excess S loss include underestimated dry deposition, mineralization of organic S in soils, desorption of soil sulphate, oxidation of recently formed sulphides and mineral weathering. Evaluating the relative contribution of these sources and processes to SO42- export is important to our understanding of S cycling as well as to policy makers in their evaluation of the efficacy of S emission controls. In order to evaluate the potential for mineral weathering contributions to SO42- export, we measured concentration and isotopic composition (δ34S and δ18O) of SO42- in stream water, and concentration and δ34S values of four S fractions in bedrock and soil parent material in catchments of varying geological composition. Geological substrates with low S concentrations were represented by catchments underlain by quartzite and granite, whereas geological substrates with high S concentrations were represented by catchments underlain by sulphidic slate, schist and metavolcanic rocks. Catchments with S-poor bedrock had stream-water SO42- concentrations 〈100 μeq L-1 and isotopic values consistent with those of atmospheric SO42- that had been cycled through the organic soil pool. Catchments with S-rich bedrock had stream-water SO42- concentrations ranging from 56 to 229 μeq L-1. Isotopic values deviated from those of SO42- in atmospheric deposition, clearly indicating a mineral weathering source in some cases, whereas in others spatial variability of mineral δ34S values precluded the isotopic detection of a weathering contribution. These results, along with evidence suggesting formation of secondary sulphate minerals in bedrock weathering rinds, indicate that mineral weathering may be an important source of S in the surface waters of some forested catchments in the northeastern USA. © 2004 John Wiley and Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 5
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    Evaluating nitrate uptake in a Rocky Mountain stream using labelled 15N and ambient nitrate chemistry (2010)
    Wiley
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    Publication Date: 2010-06-11
    Description: Background aqueous chemistry and 15Nnitrate tracer injection methods were used to calculate in-stream nitrate uptake metrics at Red Canyon Creek, a third-order stream in the Rocky Mountains in the state of Wyoming, United States. 'Net' nitrate uptake lengths, which reflect both nitrate uptake and regeneration, and 'gross' nitrate uptake lengths, which exclude re-mineralization, were quantified separately from background nitrate chemistry and 15N labelling tracer data, respectively. Gross nitrate uptake lengths, from tracer injections of 15N labelled nitrate, ranged from 502 to 3140 m. Net nitrate uptake lengths, from background nitrate chemistry downstream of a point source, ranged from 1170 to 4330 m. Diurnal changes in uptake lengths suggest the importance of nitrate utilization by autotrophs in the stream and benthic zone. The differences between net and gross nitrate uptake lengths along lower reaches of Red Canyon Creek allowed us to estimate the nitrate regeneration rate, which was 0.056-0.080 μmol m-2 s-1 during the day and 0.0062-0.0083 μmol m-2 s-1 at night. Spatial patterns of streambed pore water chemistry indicate those areas of the hyporheic zone where denitrification was likely occurring. Permanent log dams generated stronger redox gradients in the hyporheic zone than areas with transient beaver dams. By combining isotopically labelled nitrate additions, estimates of uptake from background aqueous nitrate chemistry and characterization of redox conditions in the hyporheic zone, we were able to determine the nitrate regeneration rate and the redox processes responsible for nitrogen cycling in the hyporheic zone. © 2010 John Wiley & Sons, Ltd.
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 6
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    A Parametric Radiative Forcing Model for Contrail Cirrus (2012)
    American Meteorological Society
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    Publication Date: 2012-07-01
    Description: A new parameterized analytical model is presented to compute the instantaneous radiative forcing (RF) at the top of the atmosphere (TOA) produced by an additional thin contrail cirrus layer (called “contrail” below). The model calculates the RF using as input the outgoing longwave radiation and reflected solar radiation values at TOA for a contrail-free atmosphere, so that the model is applicable for both cloud-free and cloudy ambient atmospheres. Additional input includes the contrail temperature, contrail optical depth (at 550 nm), effective particle radius, particle habit, solar zenith angle, and the optical depth of cirrus above the contrail layer. The model parameters (5 for longwave and 10 for shortwave) are determined from least squares fits to calculations from the “libRadtran” radiative transfer model over a wide range of atmospheric and surface conditions. The correlation coefficient between model and calculations is larger than 98%. The analytical model is compared with published results, including a 1-yr simulation of global RF, and is found to agree well with previous studies. The fast analytical model is part of a larger modeling system to simulate contrail life cycles (“CoCiP”) and can allow for the rapid simulation of contrail cirrus RF over a wide range of meteorological conditions and for a given size-dependent habit mixture. Ambient clouds are shown to have large local impact on the net RF of contrails. Net RF of contrails may both increase and decrease and even change sign in the presence of higher-level cirrus, depending on solar zenith angle.
    Print ISSN: 1558-8424
    Electronic ISSN: 1558-8432
    Topics: Geography , Physics
    Published by American Meteorological Society
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  • 7
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    An uncoupled dynamical downscaling for the North Sea: Method and evaluation (2013)
    Elsevier
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    Publication Date: 2013-12-01
    Print ISSN: 1463-5003
    Electronic ISSN: 1463-5011
    Topics: Geography , Geosciences , Physics
    Published by Elsevier
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