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  • 1
    Electronic Resource
    Electronic Resource
    Early-season river entry of adult Atlantic salmon: its dependency on environmental factors (2003)
    Oxford, UK : Blackwell Science Ltd
    Journal of fish biology 62 (2003), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: River entry of adult Atlantic salmon Salmo salar into the River Tornionjoki, monitored during three migration seasons (1997–1999) by horizontal split-beam hydroacoustics, started early in June when water temperature was c. 9° C and when the discharge varied between 1700 and 2000 m3 s−1. In 1997 and 1999, migration peaked during the latter half of June, 17 days after the peak flood, at water temperatures ranging from 11· 5 to 18·2° C. Few statistically significant correlations were observed between river entry and six measured environmental factors and those that were significant were not persistent over the years. The strongest correlation ( r = −0·60) was between the number of upstream migrants and seawater level, with a time lag of 1 day in 1998. In 1998 and 1999, no clear diurnal migration pattern was observed, although in 1997 the intensity of midday migration was higher than that of the midnight migration. It is concluded that environmental factors have little effect on river entry of Atlantic salmon in a large pristine river located at high latitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1095-8649.2003.00005.x
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    Paper (German National Licenses)
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  • 2
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    Sensitivity of a continental nighttime stratocumulus-topped boundary layer to varying environmental conditions (2016)
    Wiley
    Details
    Publication Date: 2016-07-21
    Description: Large-eddy simulation of a nocturnal stratocumulus-topped boundary layer in a continental mid-latitude environment has been performed to examine the sensitivity of the cloud to a number of different environmental parameters. The simulations showed that the stratocumulus cloud was strongly affected by the presence of an overlying free tropospheric cirrus cloud (FTC), in agreement with previous studies of marine nighttime stratocumulus. When introducing an FTC with an optical thickness of 2, stratocumulus liquid water path decreased by 30%. Enhancing the optical thickness of the FTC to 8 further decreased the liquid water path by almost 10%. The presence of an FTC decreased the cloud-top radiative cooling which decreased the turbulent mixing in the boundary layer so that the liquid water content and cloud depth were reduced. The sensitivity of the stratocumulus cloud to an overlying FTC was found to be affected by the moisture content in the free troposphere. When a clear positive or negative moisture gradient above the inversion was imposed, and an overlying FTC with an optical thickness of 8 was introduced, the stratocumulus cloud LWP decreased by more than 40%. Furthermore, the effect of changes in free tropospheric moisture content and an overlying FTC on the stratocumulus cloud properties was found to be non-linear, the combined response was in general weaker than the two responses added together. The modeled response to changes in cloud condensation nuclei (CCN) concentrations was found to be non-significant, unless the CCN concentrations were so low that drizzle was induced (r 50 cm −3 ).
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 3
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    Aerosol Effect on the Cloud Phase of Low‐Level Clouds Over the Arctic (2019)
    Wiley
    Details
    Publication Date: 2019
    Description: Abstract Three years of nighttime Cloud‐Aerosol Lidar and Infrared Pathfinder Satellite Observation data was used in synergy with CloudSat measurements to quantify how strongly aerosol type and aerosol load affect the cloud phase in low‐level clouds over the Arctic. Supercooled liquid layers were present in the majority of observed low‐level clouds (0.75 ≤ z ≤ 3.5 km) between −10 and −25 °C. Furthermore, based on the subset (6%) of data with high quality assurance for aerosol typing, ice formation is more common in the presence of dust or continental aerosols as opposed to marine or elevated smoke aerosols. With the first aerosol group, glaciated clouds were found at cloud top temperatures of 2 to 4 °C warmer than with the latter aerosol types. Further association of the aerosol concentration with the cloud phase showed that the aerosol concentration outweighs the aerosol type effect. Depending on the aerosol load, the temperature at which a cloud completely glaciates can vary by up to 6–10 °C. However, this behavior was most pronounced in stable atmospheric conditions and absent over open ocean with lower tropospheric stability values and probably less stratified clouds. Finally, more mixed‐phase clouds were associated with high aerosol load, suggesting that mixed‐phase clouds have an extended lifetime in the Arctic under high cloud condensation nuclei concentrations. This implies that in a pristine environment, with few or no local aerosol sources, and under the investigated conditions the amount of aerosol particles affects the cloud phase more than the aerosol type does.
    Print ISSN: 2169-897X
    Electronic ISSN: 2169-8996
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Adsorptive uptake of water by semisolid secondary organic aerosols (2015)
    Wiley
    Details
    Publication Date: 2015-03-28
    Description: Aerosol climate effects are intimately tied to interactions with water. Here we combine hygroscopicity measurements with direct observations about the phase of secondary organic aerosol (SOA) particles to show that water uptake by slightly oxygenated SOA is an adsorption-dominated process under subsaturated conditions, where low solubility inhibits water uptake until the humidity is high enough for dissolution to occur. This reconciles reported discrepancies in previous hygroscopicity closure studies. We demonstrate that the difference in SOA hygroscopic behavior in sub- and supersaturated conditions can lead to an effect up to about 30% in the direct aerosol forcing – highlighting the need to implement correct descriptions of these processes in atmospheric models. Obtaining closure across the water saturation point is therefore a critical issue for accurate climate modeling.
    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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  • 5
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    Aerosol Chemical Composition in Cloud Events by High Resolution Time-of-Flight Aerosol Mass Spectrometry (2013)
    American Chemical Society (ACS)
    Details
    Publication Date: 2013-03-01
    Description: Environmental Science & Technology DOI: 10.1021/es302889w
    Print ISSN: 0013-936X
    Electronic ISSN: 1520-5851
    Topics: Chemistry and Pharmacology , Energy, Environment Protection, Nuclear Power Engineering
    Published by American Chemical Society (ACS)
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  • 6
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    From nuclear power to coal power: Aerosol induced health and radiative effects (2015)
    Wiley
    Details
    Publication Date: 2015-11-28
    Description: We have investigated what would be the climate and PM-induced air quality consequences if all nuclear reactors worldwide were closed down and replaced by coal combustion. In a way, this presents a “worst-case scenario” since less polluting energy sources are available. We studied simultaneously the radiative and health effects from coal power emissions using a global 3D aerosol-climate model (ECHAM-HAMMOZ). This approach allowed us to estimate the effects of a major global energy production change from low-carbon source to a high-carbon one using detailed spatially resolved population density information. We included the radiative effects of both CO 2 and PM 2.5 , but limited the study of health effects to PM 2.5 only. Our results show that the replacement of nuclear power with coal power would have globally caused an average of 150 000 premature deaths per year during the period 2005–2009 with two-thirds of them in Europe. For 37 years the aerosol emissions from the additional coal power plants would cool the climate but after that the accumulating CO 2 emissions would accelerate the warming of the climate.
    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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    Surfactant effects in global simulations of cloud droplet activation (2012)
    Wiley
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    Publication Date: 2012-03-02
    Description: Atmospheric aerosols often contain surface active organics. We study the influence of these surfactants on predictions of particle cloud activation potential and aerosol indirect climate effects, by implementing different parametrizations of surfactant effects in the global circulation model ECHAM5.5–HAM2. A parametrization based only on droplet surface tension reduction produces significantly larger effects on predicted cloud droplet numbers than novel parametrizations based on detailed considerations of organic surface activity. It seems better to disregard surfactant effects altogether than employing parametrizations accounting only for effects on surface tension. We strongly recommend not using only the surface tension reduction to represent the surfactant effects in climate models.
    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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  • 8
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    Partitioning of semivolatile surface-active compounds between bulk, surface and gas phase (2011)
    Wiley
    Details
    Publication Date: 2011-02-05
    Description: We present a model study demonstrating that surface partitioning of volatile surfactants enhances their uptake by submicron liquid droplets. In submicron-sized droplets, surface partitioning of a surface-active volatile species may significantly decrease its equilibrium partial pressure, thus increasing the total flux of the surfactant from gas phase to aqueous phase. Such uptake of volatile organic species into aqueous aerosols can be followed by aqueous-phase chemistry to form low-volatility secondary organic aerosol material, leading to increased aerosol mass. In the study, we used an air parcel model that includes simplified aqueous- and gas-phase chemistry, condensation/evaporation, and a model of aqueous-phase thermodynamics that takes into account the partitioning of surfactants between the bulk and surface phases. We modeled the uptake and aqueous-phase chemical reactions of methylglyoxal, as it is a moderate surfactant that forms less volatile secondary organic material via aqueous-phase chemical reactions with the hydroxyl radical as well as hydronium and ammonium ions. Our model simulations show an order of magnitude higher uptake of methylglyoxal in aqueous aerosols of cloud condensation nuclei sizes (less than 200 nm in radius) when surface partitioning is taken into account, compared to when surface partitioning is neglected. As a consequence, the production of SOA through the aqueous-phase chemical processing of methylglyoxal is also enhanced, but to a lesser degree, because condensation of the hydroxyl radical from gas phase limits the production.
    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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    Long-term measurements of cloud droplet concentrations and aerosol-cloud interactions in continental boundary layer clouds (2013)
    Co-Action Publishing
    In: Tellus B
    Details
    Publication Date: 2013-10-12
    Description: The effects of aerosol on cloud droplet effective radius ( R eff ), cloud optical thickness and cloud droplet number concentration ( N d ) are analysed both from long-term direct ground-based in situ measurements conducted at the Puijo measurement station in Eastern Finland and from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Terra and Aqua satellites. The mean in situ N d during the period of study was 217 cm −3 , while the MODIS-based N d was 171 cm −3 . The absolute values, and the dependence of both N d observations on the measured aerosol number concentration in the accumulation mode ( N acc ), are quite similar. In both data sets N d is clearly dependent on N acc , for N acc values lower than approximately 450 cm −3 . Also, the values of the aerosol–cloud-interaction parameter [ACI=(1/3)* d ln( N d )/ d ln( N acc )] are quite similar for N acc 〈400 cm −3 with values of 0.16 and 0.14 from in situ and MODIS measurements, respectively. With higher N acc (〉450 cm −3 ) N d increases only slowly. Similarly, the effect of aerosol on MODIS-retrieved R eff is visible only at low N acc values. In a sub set of data, the cloud and aerosol properties were measured simultaneously. For that data the comparison between MODIS-derived N d and directly measured N d , or the cloud droplet number concentration estimated from N acc values ( N d,p ), shows a correlation, which is greatly improved after careful screening using a ceilometer to make sure that only single cloud layers existed. This suggests that such determination of the number of cloud layers is very important when trying to match ground-based measurements to MODIS measurements. Keywords: aerosol–cloud interaction, cloud droplet number concentration, aerosol, cloud droplet effective radius (Published: 11 October 2013) Citation: Tellus B 2013, 65 , 20138, http://dx.doi.org/10.3402/tellusb.v65i0.20138
    Print ISSN: 0280-6509
    Electronic ISSN: 1600-0889
    Topics: Geography , Physics
    Published by Co-Action Publishing on behalf of The International Meteorological Institute in Stockholm.
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  • 10
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    Direct and indirect effects of sea spray geoengineering and the role of injected particle size (2012)
    Wiley
    Details
    Publication Date: 2012-01-25
    Description: Climate-aerosol model ECHAM5.5-HAM2 was used to investigate how geoengineering with artificial sea salt emissions would affect marine clouds and the Earth's radiative balance. Prognostic cloud droplet number concentration and interaction of aerosol particles with clouds and radiation were calculated explicitly, thus making this the first time that aerosol direct effects of sea spray geoengineering are considered. When a wind speed dependent baseline geoengineering flux was applied over all oceans (total annual emissions 443.9 Tg), we predicted a radiative flux perturbation (RFP) of −5.1 W m−2, which is enough to counteract warming from doubled CO2 concentration. When the baseline flux was limited to three persistent stratocumulus regions (3.3% of Earth's surface, total annual emissions 20.6 Tg), the RFP was −0.8 Wm−2 resulting mainly from a 74–80% increase in cloud droplet number concentration and a 2.5–4.4 percentage point increase in cloud cover. Multiplying the baseline mass flux by 5 or reducing the injected particle size from 250 to 100 nm had comparable effects on the geoengineering efficiency with RFPs −2.2 and −2.1 Wm−2, respectively. Within regions characterized with persistent stratocumulus decks, practically all of the radiative effect originated from aerosol indirect effects. However, when all oceanic regions were seeded, the direct effect with the baseline flux was globally about 29% of the total radiative effect. Together with previous studies, our results indicate that there are still large uncertainties associated with the sea spray geoengineering efficiency due to variations in e.g., background aerosol concentration, updraft velocity, cloud altitude and onset of precipitation.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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