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  • 1
    Electronic Resource
    Electronic Resource
    Strukturuntersuchungen an PF/cellulosepapier-verbunden mittels dynamisch-mechanischer analyse (1990)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 174 (1990), S. 151-164 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: This paper tries to connect the structure of tung oil and tricresyl phosphate modified phenolic paper-base laminates used for printed circuit boards in a large scale, with properties of these laminates by means of dynamic-mechanical analysis and dielectric measurements. The internal plasticization of tung oil is discussed. The modification of phenolic resin with tung oil causes in addition to flexibilisation, that a higher conversion of functional groups during the resit formation is attained by removal of steric hindrances, in this way the degree of cross-linkage is increased in comparison to the unmodified laminate. The measurements show that tricresyl phosphate is an external plasticizer which reduces the intermolecular interactions.
    Notes: Es wird versucht, für Verbunde aus mit Holzöl sowie Tricresylphosphat modifizierten Phenol-Formaldehyd-Polykondensaten und Cellulosepapier, die als Leiterplattenbasismaterial technisch in großem Umfang genutzt werden, mittels Torsionsschwingungs- und dielektrischer Messungen einen Zusammenhang zwischen dem strukturellen Aufbau und den Verbundeigenschaften herzustellen. Die innere Weichmacherwirkung von Holzöl wird diskutiert. Die Holzölmodifizierung bewirkt neben einer Flexibilisierung, daß durch Beseitigung sterischer Behinderungen ein größerer Umsatz der funktionellen Gruppen bei der Resitbildung erreicht und der Vernetzungsgrad im Vergleich zu einem unmodifizierten PF-Hartpapier erhöht wird. Die Messungen zeigen, daß Tricresylphosphat als äußerer Weichmacher wirkt, der die zwischenmolekularen Wechselwirkungen herabsetzt.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1990.051740113
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    Paper (German National Licenses)
    Fulltext
  • 2
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    The Arctic Cloud Puzzle: Using ACLOUD/PASCAL Multiplatform Observations to Unravel the Role of Clouds and Aerosol Particles in Arctic Amplification (2019)
    AMER METEOROLOGICAL SOC
    In:  EPIC3Bulletin of the American Meteorological Society, AMER METEOROLOGICAL SOC, 100(5), pp. 841-871, ISSN: 0003-0007
    Details
    Publication Date: 2019-06-17
    Description: Clouds play an important role in Arctic amplification. This term represents the recently observed enhanced warming of the Arctic relative to the global increase of near-surface air temperature. However, there are still important knowledge gaps regarding the interplay between Arctic clouds and aerosol particles, and surface properties, as well as turbulent and radiative fluxes that inhibit accurate model simulations of clouds in the Arctic climate system. In an attempt to resolve this so-called Arctic cloud puzzle, two comprehensive and closely coordinated field studies were conducted: the Arctic Cloud Observations Using Airborne Measurements during Polar Day (ACLOUD) aircraft campaign and the Physical Feedbacks of Arctic Boundary Layer, Sea Ice, Cloud and Aerosol (PASCAL) ice breaker expedition. Both observational studies were performed in the framework of the German Arctic Amplification: Climate Relevant Atmospheric and Surface Processes, and Feedback Mechanisms (AC)3 project. They took place in the vicinity of Svalbard, Norway, in May and June 2017. ACLOUD and PASCAL explored four pieces of the Arctic cloud puzzle: cloud properties, aerosol impact on clouds, atmospheric radiation, and turbulent dynamical processes. The two instrumented Polar 5 and Polar 6 aircraft; the icebreaker Research Vessel (R/V) Polarstern; an ice floe camp including an instrumented tethered balloon; and the permanent ground-based measurement station at Ny-Ålesund, Svalbard, were employed to observe Arctic low- and mid-level mixed-phase clouds and to investigate related atmospheric and surface processes. The Polar 5 aircraft served as a remote sensing observatory examining the clouds from above by downward-looking sensors; the Polar 6 aircraft operated as a flying in situ measurement laboratory sampling inside and below the clouds. Most of the collocated Polar 5/6 flights were conducted either above the R/V Polarstern or over the Ny-Ålesund station, both of which monitored the clouds from below using similar but upward-looking remote sensing techniques as the Polar 5 aircraft. Several of the flights were carried out underneath collocated satellite tracks. The paper motivates the scientific objectives of the ACLOUD/PASCAL observations and describes the measured quantities, retrieved parameters, and the applied complementary instrumentation. Furthermore, it discusses selected measurement results and poses critical research questions to be answered in future papers analyzing the data from the two field campaigns.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 3
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    Combining atmospheric and snow radiative transfer models to assess the solar radiative effects of black carbon in the Arctic (2020)
    Copernicus Publications on behalf of the European Geosciences Union.
    In:  EPIC3Atmos. Chem. Phys.,, Copernicus Publications on behalf of the European Geosciences Union., 20, pp. 8139-8156
    Details
    Publication Date: 2020-10-12
    Description: The magnitude of solar radiative effects (cooling or warming) of black carbon (BC) particles embedded in the Arctic atmosphere and surface snow layer was explored on the basis of case studies. For this purpose, combined at- mospheric and snow radiative transfer simulations were per- formed for cloudless and cloudy conditions on the basis of BC mass concentrations measured in pristine early summer and more polluted early spring conditions. The area of inter- est is the remote sea-ice-covered Arctic Ocean in the vicin- ity of Spitsbergen, northern Greenland, and northern Alaska typically not affected by local pollution. To account for the radiative interactions between the black-carbon-containing snow surface layer and the atmosphere, an atmospheric and snow radiative transfer model were coupled iteratively. For pristine summer conditions (no atmospheric BC, minimum solar zenith angles of 55◦) and a representative BC particle mass concentration of 5 ng g−1 in the surface snow layer, a positive daily mean solar radiative forcing of +0.2Wm−2 was calculated for the surface radiative budget. A higher load of atmospheric BC representing early springtime conditions results in a slightly negative mean radiative forcing at the surface of about −0.05 W m−2, even when the low BC mass concentration measured in the pristine early summer condi- tions was embedded in the surface snow layer. The total net surface radiative forcing combining the effects of BC em- bedded in the atmosphere and in the snow layer strongly de- pends on the snow optical properties (snow specific surface area and snow density). For the conditions over the Arctic Ocean analyzed in the simulations, it was found that the at- mospheric heating rate by water vapor or clouds is 1 to 2 or-ders of magnitude larger than that by atmospheric BC. Sim- ilarly, the daily mean total heating rate (6 K d−1) within a snowpack due to absorption by the ice was more than 1 order of magnitude larger than that of atmospheric BC (0.2 K d−1). Also, it was shown that the cooling by atmospheric BC of the near-surface air and the warming effect by BC embedded in snow are reduced in the presence of clouds.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 4
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    Reassessment of shortwave surface cloud radiative forcing in the Arctic: consideration of surface-albedo–cloud interactions (2020)
    In:  EPIC3Atmos. Chem. Phys., 20, pp. 9895-9914
    Details
    Publication Date: 2020-09-14
    Description: The concept of cloud radiative forcing (CRF)is commonly applied to quantify the impact of clouds onthe surface radiative energy budget (REB). In the Arctic,specific radiative interactions between microphysical andmacrophysical properties of clouds and the surface stronglymodify the warming or cooling effect of clouds, complicat-ing the estimate of CRF obtained from observations or mod-els. Clouds tend to increase the broadband surface albedoover snow or sea ice surfaces compared to cloud-free con-ditions. However, this effect is not adequately consideredin the derivation of CRF in the Arctic so far. Therefore,we have quantified the effects caused by surface-albedo–cloud interactions over highly reflective snow or sea ice sur-faces on the CRF using radiative transfer simulations andbelow-cloud airborne observations above the heterogeneousspringtime marginal sea ice zone (MIZ) during the ArcticCLoud Observations Using airborne measurements duringpolar Day (ACLOUD) campaign. The impact of a modi-fied surface albedo in the presence of clouds, as comparedto cloud-free conditions, and its dependence on cloud opti-cal thickness is found to be relevant for the estimation of theshortwave CRF. A method is proposed to consider this sur-face albedo effect on CRF estimates by continuously retriev-ing the cloud-free surface albedo from observations undercloudy conditions, using an available snow and ice albedoparameterization. Using ACLOUD data reveals that the esti-mated average shortwave cooling by clouds almost doublesover snow- and ice-covered surfaces (−62 W m−2instead of−32 W m−2), if surface-albedo–cloud interactions are con-sidered. As a result, the observed total (shortwave plus long-wave) CRF shifted from a warming effect to an almost neu-tral one. Concerning the seasonal cycle of the surface albedo, it is demonstrated that this effect enhances shortwave cool-ing in periods when snow dominates the surface and poten-tially weakens the cooling by optically thin clouds duringthe summertime melting season. These findings suggest thatthe surface-albedo–cloud interaction should be considered inglobal climate models and in long-term studies to obtain arealistic estimate of the shortwave CRF to quantify the roleof clouds in Arctic amplification.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 5
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    Wintertime Airborne Measurements of Ice Nucleating Particles in the High Arctic: A Hint to a Marine, Biogenic Source for Ice Nucleating Particles (2020)
    Wiley
    In:  EPIC3Geophysical Research Letters, Wiley, 47, pp. 1-11, ISSN: 0094-8276
    Details
    Publication Date: 2020-09-14
    Description: Ice nucleating particles (INPs) affect the radiative properties of cold clouds. Knowledge concerning their concentration above ground level and their potential sources is scarce. Here we present the first highly temperature resolved ice nucleation spectra of airborne samples from an aircraft campaign during late winter in 2018. Most INP spectra featured low concentration levels (〈3 · 10−4 L−1 at −15°C). −2 −1 However, we also found INP concentrations of up to 1.8·10 L at −15°C and freezing onsets as high as −7.5°C for samples mainly from the marine boundary layer. Shape and onset temperature of the ice nucleation spectra of those samples as well as heat sensitivity hint at biogenic INP. Colocated measurements additionally indicate a local marine influence rather than long‐range transport. Our results suggest that even in late winter above 80°N a local marine source for biogenic INP, which can efficiently nucleate ice at high temperatures, is present. Clouds are a key factor in the energy budget of the Arctic atmosphere. Ice nucleating particles (INPs) can modify the radiation properties and lifetime of clouds by affecting the relative abundance of liquid and frozen droplets in a cloud. Despite this important ability, knowledge about the INP concentration above ground level is limited as airborne INP measurements are very scarce in the Arctic. Here we present results from an aircraft campaign, which took place during the late winter of 2018 in latitudes above 80°N. We found INP concentrations at above −15°C, which are similar to those found in midlatitudes. These INPs also initiate freezing already at high temperatures. We found indications that the INPs are biogenic and originate from a local, marine source, rather than being transported from midlatitudes into the Arctic. Due to the presence of numerous cracks, open leads and polynyas in the sea ice in the investigation area, the ocean may provide a source for these biogenic INP in an environment, where sources on land are still shrouded in snow and ice. However, in a warming Arctic contributions from different sources might change, making the characterization of the current state important.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 6
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    Validation of the sea ice surface albedo scheme of the regional climate model HIRHAM–NAOSIM using aircraft measurements during the ACLOUD/PASCAL campaigns (2019)
    In:  EPIC3The Cryosphere, 13(6), pp. 1695-1708, ISSN: 1994-0424
    Details
    Publication Date: 2020-07-07
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    Measurements and Modeling of Optical-Equivalent Snow Grain Sizes under Arctic Low-Sun Conditions (2021)
    MDPI
    In:  EPIC3Remote Sensing, MDPI, 13
    Details
    Publication Date: 2022-03-14
    Description: The size and shape of snow grains directly impacts the reflection by a snowpack. In this article, different approaches to retrieve the optical-equivalent snow grain size (ropt) or, alternatively, the specific surface area (SSA) using satellite, airborne, and ground-based observations are compared and used to evaluate ICON-ART (ICOsahedral Nonhydrostatic—Aerosols and Reactive Trace gases) simulations. The retrieval methods are based on optical measurements and rely on the ropt-dependent absorption of solar radiation in snow. The measurement data were taken during a three-week campaign that was conducted in the North of Greenland in March/April 2018, such that the retrieval methods and radiation measurements are affected by enhanced uncertainties under these low-Sun conditions. An adjusted airborne retrieval method is applied which uses the albedo at 1700 nm wavelength and combines an atmospheric and snow radiative transfer model to account for the direct-to-global fraction of the solar radiation incident on the snow. From this approach, we achieved a significantly improved uncertainty (〈25%) and a reduced effect of atmospheric masking compared to the previous method. Ground-based in situ measurements indicated an increase of ropt of 15 μm within a five-day period after a snowfall event which is small compared to previous observations under similar temperature regimes. ICON-ART captured the observed change of ropt during snowfall events, but systematically overestimated the subsequent snow grain growth by about 100%. Adjusting the growth rate factor to 0.012 μm2 s�1 minimized the difference between model and observations. Satellite-based and airborne retrieval methods showed higher ropt over sea ice (〈300 μm) than over land surfaces (〈100 μm) which was reduced by data filtering of surface roughness features. Moderate- Resolution Imaging Spectroradiometer (MODIS) retrievals revealed a large spread within a series of subsequent individual overpasses, indicating their limitations in observing the snow grain size evolution in early spring conditions with low Sun.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    A comprehensive in situ and remote sensing data set from the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) campaign (2019)
    In:  EPIC3Earth Syst. Sci. Data, 11, pp. 1853-1881
    Details
    Publication Date: 2019-12-13
    Description: The Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) cam- paign was carried out north-west of Svalbard (Norway) between 23 May and 6 June 2017. The objective of ACLOUD was to study Arctic boundary layer and mid-level clouds and their role in Arctic amplification. Two research aircraft (Polar 5 and 6) jointly performed 22 research flights over the transition zone between open ocean and closed sea ice. Both aircraft were equipped with identical instrumentation for measurements of basic meteorological parameters, as well as for turbulent and radiative energy fluxes. In addition, on Polar 5 active and passive remote sensing instruments were installed, while Polar 6 operated in situ instruments to characterize cloud and aerosol particles as well as trace gases. A detailed overview of the specifications, data processing, and data quality is provided here. It is shown that the scientific analysis of the ACLOUD data benefits from the coordinated operation of both aircraft. By combining the cloud remote sensing techniques operated on Polar 5, the synergy of multi-instrument cloud retrieval is illustrated. The remote sensing methods were validated us- ing truly collocated in situ and remote sensing observations. The data of identical instruments operated on both aircraft were merged to extend the spatial coverage of mean atmospheric quantities and turbulent and radiative flux measurement. Therefore, the data set of the ACLOUD campaign provides comprehensive in situ and remote sensing observations characterizing the cloudy Arctic atmosphere. All processed, calibrated, and validated data are published in the World Data Center PANGAEA as instrument-separated data subsets (Ehrlich et al., 2019b, https://doi.org/10.1594/PANGAEA.902603).
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    Small-scale structure of thermodynamic phase in Arctic mixed-phase clouds observed by airborne remote sensing during a cold air outbreak and a warm air advection event (2019)
    COPERNICUS GESELLSCHAFT MBH
    In:  EPIC3Atmospheric Chemistry and Physics, COPERNICUS GESELLSCHAFT MBH, ISSN: 1680-7316
    Details
    Publication Date: 2020-04-02
    Description: The synergy between airborne lidar, radar, passive microwave, and passive imaging spectrometer measurements was used to characterize the vertical and small-scale (down to 10 m) horizontal distribution of the cloud thermodynamic phase. Two case studies of low-level Arctic clouds in a cold air outbreak and a warm air advection observed during the Arctic CLoud Observations Using airborne measurements during polar Day (ACLOUD) were investigated. Both clouds exhibited the typical vertical mixed-phase structure with mostly liquid water droplets at cloud top and ice crystals in lower layers. The cloud top horizontal small-scale variability observed during the cold air outbreak is dominated by the liquid water close to the cloud top and shows no indication of ice in lower cloud layers. Contrastingly, the cloud top variability of the case observed during a warm air advection showed some ice in areas of low reflectivity or cloud holes. Radiative transfer simulations considering homogeneous mixtures of liquid water droplets and ice crystals were able to reproduce the horizontal variability of this warm air advection. To account for more realistic vertical distributions of the thermodynamic phase, large eddy simulations (LES) were performed to reconstruct the observed cloud properties and were used as input for radiative transfer simulations. The simulations of the cloud observed during the cold air outbreak, with mostly liquid water at cloud top, realistically reproduced the observations. For the warm air advection case, the simulated cloud field underestimated the ice water content (IWC). Nevertheless, it revealed the presence of ice particles close to the cloud top and confirmed the observed horizontal variability of the cloud field. It is concluded that the cloud top small-scale horizontal variability reacts to changes in the vertical distribution of the cloud thermodynamic phase. Passive satellite-borne imaging spectrometer observations with pixel sizes larger than 100 m miss the small-scale cloud top structures, which limits their capabilities to provide indications about the cloud vertical structure.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Effects of variable ice–ocean surface properties and air mass transformation on the Arctic radiative energy budget (2023)
    Copernicus Publications
    In:  EPIC3Atmospheric Chemistry and Physics, Copernicus Publications, 23(17), pp. 9647-9667, ISSN: 1680-7316
    Details
    Publication Date: 2023-10-24
    Description: Low-level airborne observations of the Arctic surface radiative energy budget are discussed. We fo- cus on the terrestrial part of the budget, quantified by the thermal-infrared net irradiance (TNI). The data were collected in cloudy and cloud-free conditions over and in the vicinity of the marginal sea ice zone (MIZ) close to Svalbard during two aircraft campaigns conducted in the spring of 2019 and in the early summer of 2017. The measurements, complemented by ground-based observations available from the literature and radiative transfer simulations, are used to evaluate the influence of surface type (sea ice, open ocean, MIZ), seasonal characteris- tics, and synoptically driven meridional air mass transports into and out of the Arctic on the near-surface TNI. The analysis reveals a typical four-mode structure of the frequency distribution of the TNI as a function of sur- face albedo, the sea ice fraction, and surface brightness temperature. Two modes prevail over sea ice and another two over open ocean, each representing cloud-free and cloudy radiative states. Characteristic shifts and modifi- cations of the TNI modes during the transition from winter to spring and early summer conditions are discussed. Furthermore, the influence of warm air intrusions (WAIs) and marine cold-air outbreaks (MCAOs) on the near- surface downward thermal-infrared irradiances and the TNI is highlighted for several case studies. It is concluded that during WAIs the surface warming depends on cloud properties and evolution. Lifted clouds embedded in warmer air masses over a colder sea ice surface, decoupled from the ground by a surface-based temperature inversion, have the potential to warm the surface more strongly than near-surface fog or thin low-level boundary layer clouds because of a higher cloud base temperature. For MCAOs it is found that the thermodynamic profile of the southward-moving air mass adapts only slowly to the warmer ocean surface.
    Repository Name: EPIC Alfred Wegener Institut
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