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search.filters.applied.f.access: openAccess × Author: Wendisch, Manfred × DDC: 550 × Has files: Yes × Publisher: Milton Park : Taylor & Francis × Subject: aerosol ×

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Now showing 1 - 6 of 6
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    Thermal IR radiative properties of mixed mineral dust and biomass aerosol during SAMUM-2
    (Milton Park : Taylor & Francis, 2011) Köhler, Claas H.; Trautmann, Thomas; Lindermeir, Erwin; Vreeling, Willem; Lieke, Kirsten; Kandler, Konrad; Weinzierl, Bernadett; Groß, Silke; Tesche, Matthias; Wendisch, Manfred
    Ground-based high spectral resolution measurements of downwelling radiances from 800 to 1200 cm−1 were conducted between 20 January and 6 February 2008 within the scope of the SAMUM-2 field experiment. We infer the spectral signature of mixed biomass burning/mineral dust aerosols at the surface from these measurements and at top of the atmosphere from IASI observations. In a case study for a day characterized by the presence of high loads of both dust and biomass we attempt a closure with radiative transfer simulations assuming spherical particles. A detailed sensitivity analysis is performed to investigate the effect of uncertainties in the measurements ingested into the simulation on the simulated radiances. Distinct deviations between modelled and observed radiances are limited to a spectral region characterized by resonance bands in the refractive index. A comparison with results obtained during recent laboratory studies and field experiments reveals, that the deviations could be caused by the aerosol particles’ non-sphericity, although an unequivocal discrimination from measurement uncertainties is not possible. Based on radiative transfer simulations we estimate the aerosol’s direct radiative effect in the atmospheric window region to be 8 W m−2 at the surface and 1 W m−2 at top of the atmosphere.
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    Desert dust aerosol air mass mapping in the western Sahara, using particle properties derived from space-based multi-angle imaging
    (Milton Park : Taylor & Francis, 2017) Kahn, Ralph; Petzold, Andreas; Wendisch, Manfred; Bierwirth, Eike; Dinter, Tilman; Esselborn, Michael; Fiebig, Marcus; Heese, Birgit; Knippertz, Peter; Müller, Detlef; Schladitz, Alexander; Von Hoyningen-HUENE, Wolfgang
    Coincident observations made over the Moroccan desert during the Sahara mineral dust experiment (SAMUM) 2006 field campaign are used both to validate aerosol amount and type retrieved from multi-angle imaging spectroradiometer (MISR) observations, and to place the suborbital aerosol measurements into the satellite’s larger regional context. On three moderately dusty days during which coincident observations were made, MISR mid-visible aerosol optical thickness (AOT) agrees with field measurements point-by-point to within 0.05–0.1. This is about as well as can be expected given spatial sampling differences; the space-based observations capture AOT trends and variability over an extended region. The field data also validate MISR’s ability to distinguish and to map aerosol air masses, from the combination of retrieved constraints on particle size, shape and single-scattering albedo. For the three study days, the satellite observations (1) highlight regional gradients in the mix of dust and background spherical particles, (2) identify a dust plume most likely part of a density flow and (3) show an aerosol air mass containing a higher proportion of small, spherical particles than the surroundings, that appears to be aerosol pollution transported from several thousand kilometres away.
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    Retrieval of aerosol optical thickness for desert conditions using MERIS observations during the SAMUM campaign
    (Milton Park : Taylor & Francis, 2017) Dinter, Tilman; Von Hoyningen-Huene, Wolfgang; Burrows, John P.; Kokhanovsky, Alexander; Bierwirth, Eike; Wendisch, Manfred; Schladitz, Alexander; Wendisch, Manfred; MüLLER, Detlef; Kahn, Ralph; Diouri, Mohammed
    Approximately 30% of the land surface is arid, having desert or semi-desert conditions. Aerosol originating from these regions plays a significant role in climate and atmospheric chemistry of the atmosphere. Retrieving aerosol properties from space-borne platforms above desert conditions, where the surface reflectance is usually very bright, is a challenging task. The proportion of the surface to top of atmosphere (TOA) reflectance can reach values over 90%, especially for wavelength above 500 nm. For these reasons detailed knowledge of aerosol and surface optical properties from these regions is required to separate atmosphere from intrinsically bright surfaces. An approach to retrieve aerosol properties over arid and semi-arid regions based on the Bremen Aerosol Retrieval (BAER) has been developed and validated within the Dust Aerosol Retrievals from Space-Born Instruments (DREAMS) Project, which is part of the Saharan Mineral Dust Experiment (SAMUM, 2006). Combining measurements of the backscattered radiation from the Medium Resolution Imaging Spectrometer (MERIS) instrument aboard Environmental Satellite (ENVISAT) and ground-based measurements in Morocco in radiation closure experiments yields the aerosol optical properties of mineral dust at selected locations.
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    Regional modelling of Saharan dust and biomass-burning smoke, Part 2: Direct radiative forcing and atmospheric dynamic response
    (Milton Park : Taylor & Francis, 2017) Heinold, Bernd; Tegen, Ina; Bauer, Stefan; Wendisch, Manfred
    The direct radiative forcing and dynamic atmospheric response due to Saharan dust and biomass-burning aerosol particles are presented for a case study during the SAMUM-2 field campaign in January and February 2008. The regional model system COSMO-MUSCAT is used. It allows online interaction of the computed dust and smoke load with the solar and terrestrial radiation and with the model dynamics. Model results of upward solar irradiances are evaluated against airborne radiation measurements in the Cape Verde region. The comparison shows a good agreement for the case of dust and smoke mixture. Dust and smoke particles influence the atmospheric dynamics by changing the radiative heating rates. The related pressure perturbations modify local and synoptic scale air-flow patterns. In the radiative feedback simulations, the Hadley circulation is enhanced and convergence zones occur along the Guinea coast. Thus, the smoke particles spread more than 5◦ further north and the equatorward transport is reduced. Within the convergence zones, Saharan dust and biomass-burning material are more effectively advected towards the Cape Verdes. Given the model uncertainties, the agreement between the modelled and observed aerosol distribution is locally improved when aerosol–radiation interaction is considered.
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    Arctic haze over Central Europe
    (Milton Park : Taylor & Francis, 2017) Heintzenberg, Jost; Tuch, Thomas; Wehner, Birgit; Wiedensohler, Alfred; Wex, Heike; Ansmann, Albert; Mattis, Ina; Müller, Detlef; Wendisch, Manfred; Eckhardt, Sabine; Stohl, Andreas
    An extraordinary aerosol situation over Leipzig, Germany in April 2002 was investigated with a comprehensive set of ground-based volumetric and columnar aerosol data, combined with aerosol profiles from lidar, meteorological data from radiosondes and air mass trajectory calculations. Air masses were identified to stem from the Arctic, partly influenced by the greater Moscow region. An evaluation of ground-based measurements of aerosol size distributions during these periods showed that the number concentrations below about 70 nm in diameter were below respective long-term average data, while number, surface and volume concentrations of the particles larger than about 70 nm in diameter were higher than the long-term averages. The lidar aerosol profiles showed that the imported aerosol particles were present up to about 3 km altitude. The particle optical depth was up to 0.45 at 550 nm wavelength. With a one-dimensional spectral radiative transfer model top of the atmosphere (TOA) radiative forcing of the aerosol layer was estimated for a period with detailed vertical information. Solar aerosol radiative forcing values between −23 and −38 W m−2 were calculated, which are comparable to values that have been reported in heavily polluted continental plumes outside the respective source regions. The present report adds weight to previous findings of aerosol import to Europe, pointing to the need for attributing the three-dimensional aerosol burden to natural and anthropogenic sources as well as to aerosol imports from adjacent or distant source regions. In the present case, the transport situation is further complicated by forward trajectories, indicating that some of the observed Arctic haze may have originated in Central Europe. This aerosolwas transported to the European Arctic before being re-imported in the modified and augmented form to its initial source region.
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    Saharan Mineral Dust Experiments SAMUM-1 and SAMUM-2: What have we learned?
    (Milton Park : Taylor & Francis, 2011) Ansmann, Albert; Petzold, Andreas; Kandler, Konrad; Tegen, Ina; Wendisch, Manfred; Müller, Detlef; Weinzierl, Bernadett; Müller, Thomas; Heintzenberg, Jost
    Two comprehensive field campaigns were conducted in 2006 and 2008 in the framework of the Saharan Mineral Dust Experiment (SAMUM) project. The relationship between chemical composition, shape morphology, size distribution and optical effects of the dust particles was investigated. The impact of Saharan dust on radiative transfer and the feedback of radiative effects upon dust emission and aerosol transport were studied. Field observations (ground-based, airborne and remote sensing) and modelling results were compared within a variety of dust closure experiments with a strong focus on vertical profiling. For the first time, multiwavelength Raman/polarization lidars and an airborne high spectral resolution lidar were involved in major dust field campaigns and provided profiles of the volume extinction coefficient of the particles at ambient conditions (for the full dust size distribution), of particle-shape-sensitive optical properties at several wavelengths, and a clear separation of dust and smoke profiles allowing for an estimation of the single-scattering albedo of the biomass-burning aerosol. SAMUM–1 took place in southern Morocco close to the Saharan desert in the summer of 2006, whereas SAMUM–2 was conducted in Cape Verde in the outflow region of desert dust and biomass-burning smoke from western Africa in the winter of 2008. This paper gives an overview of the SAMUM concept, strategy and goals, provides snapshots (highlights) of SAMUM–2 observations and modelling efforts, summarizes main findings of SAMUM–1 and SAMUM–2 and finally presents a list of remaining problems and unsolved questions.