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    Increasing the spatial resolution of cloud property retrievals from Meteosat SEVIRI by use of its high-resolution visible channel: Evaluation of candidate approaches with MODIS observations
    (Katlenburg-Lindau : Copernicus, 2020) Werner, Frank; Deneke, Hartwig
    This study presents and evaluates several candidate approaches for downscaling observations from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) in order to increase the horizontal resolution of subsequent cloud optical thickness (τ) and effective droplet radius (reff) retrievals from the native ≈ 3km×3km spatial resolution of the narrowband channels to ≈ 1km×1km. These methods make use of SEVIRI's coincident broadband high-resolution visible (HRV) channel. For four example cloud fields, the reliability of each downscaling algorithm is evaluated by means of collocated 1km×1km MODIS radiances, which are reprojected to the horizontal grid of the HRV channel and serve as reference for the evaluation. By using these radiances, smoothed with the modulation transfer function of the native SEVIRI channels, as retrieval input, the accuracy at the SEVIRI standard resolution can be evaluated and an objective comparison of the accuracy of the different downscaling algorithms can be made. For the example scenes considered in this study, it is shown that neglecting high-frequency variations below the SEVIRI standard resolution results in significant random absolute deviations of the retrieved τ and reff of up to ≈ 14 and ≈ 6μm, respectively, as well as biases. By error propagation, this also negatively impacts the reliability of the subsequent calculation of liquid water path (WL) and cloud droplet number concentration (ND), which exhibit deviations of up to ≈ 89gm-2 and ≈ 177cm-3, respectively. For τ , these deviations can be almost completely mitigated by the use of the HRV channel as a physical constraint and by applying most of the presented downscaling schemes. Uncertainties in retrieved reff at the native SEVIRI resolution are smaller, and the improvements from downscaling the observations are less obvious than for τ. Nonetheless, the right choice of downscaling scheme yields noticeable improvements in the retrieved reff. Furthermore, the improved reliability in retrieved cloud products results in significantly reduced uncertainties in derived WL and ND. In particular, one downscaling approach provides clear improvements for all cloud products compared to those obtained from SEVIRI's standard resolution and is recommended for future downscaling endeavors. This work advances efforts to mitigate impacts of scale mismatches among channels of multiresolution instruments on cloud retrievals. © Author(s) 2020.
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    Modelling mineral dust emissions and atmospheric dispersion with MADE3 in EMAC v2.54
    (Katlenburg-Lindau : Copernicus, 2020) Beer, Christof G.; Hendricks, Johannes; Righi, Mattia; Heinold, Bernd; Tegen, Ina; Groß, Silke; Sauer, Daniel; Walser, Adrian; Weinzierl, Bernadett
    It was hypothesized that using mineral dust emission climatologies in global chemistry climate models (GCCMs), i.e. prescribed monthly-mean dust emissions representative of a specific year, may lead to misrepresentations of strong dust burst events. This could result in a negative bias of model dust concentrations compared to observations for these episodes. Here, we apply the aerosol microphysics submodel MADE3 (Modal Aerosol Dynamics model for Europe, adapted for global applications, third generation) as part of the ECHAM/MESSy Atmospheric Chemistry (EMAC) general circulation model. We employ two different representations of mineral dust emissions for our model simulations: (i) a prescribed monthly-mean climatology of dust emissions representative of the year 2000 and (ii) an online dust parametrization which calculates wind-driven mineral dust emissions at every model time step. We evaluate model results for these two dust representations by comparison with observations of aerosol optical depth from ground-based station data. The model results show a better agreement with the observations for strong dust burst events when using the online dust representation compared to the prescribed dust emissions setup. Furthermore, we analyse the effect of increasing the vertical and horizontal model resolution on the mineral dust properties in our model. We compare results from simulations with T42L31 and T63L31 model resolution (2.8∘×2.8∘ and 1.9∘×1.9∘ in latitude and longitude, respectively; 31 vertical levels) with the reference setup (T42L19). The different model versions are evaluated against airborne in situ measurements performed during the SALTRACE mineral dust campaign (Saharan Aerosol Long-range Transport and Aerosol-Cloud Interaction Experiment, June–July 2013), i.e. observations of dust transported from the Sahara to the Caribbean. Results show that an increased horizontal and vertical model resolution is able to better represent the spatial distribution of airborne mineral dust, especially in the upper troposphere (above 400 hPa). Additionally, we analyse the effect of varying assumptions for the size distribution of emitted dust but find only a weak sensitivity concerning these changes. The results of this study will help to identify the model setup best suited for future studies and to further improve the representation of mineral dust particles in EMAC-MADE3.
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    GARRLiC and LIRIC: Strengths and limitations for the characterization of dust and marine particles along with their mixtures
    (Katlenburg-Lindau : Copernicus, 2017) Tsekeri, Alexandra; Lopatin, Anton; Amiridis, Vassilis; Marinou, Eleni; Igloffstein, Julia; Siomos, Nikolaos; Solomos, Stavros; Kokkalis, Panagiotis; Engelmann, Ronny; Baars, Holger; Gratsea, Myrto; Raptis, Panagiotis I.; Binietoglou, Ioannis; Mihalopoulos, Nikolaos; Kalivitis, Nikolaos; Kouvarakis, Giorgos; Bartsotas, Nikolaos; Kallos, George; Basart, Sara; Schuettemeyer, Dirk; Wandinger, Ulla; Ansmann, Albert; Chaikovsky, Anatoli P.; Dubovik, Oleg
    The Generalized Aerosol Retrieval from Radiometer and Lidar Combined data algorithm (GARRLiC) and the LIdar-Radiometer Inversion Code (LIRIC) provide the opportunity to study the aerosol vertical distribution by combining ground-based lidar and sun-photometric measurements. Here, we utilize the capabilities of both algorithms for the characterization of Saharan dust and marine particles, along with their mixtures, in the south-eastern Mediterranean during the CHARacterization of Aerosol mixtures of Dust and Marine origin Experiment (CHARADMExp). Three case studies are presented, focusing on dust-dominated, marinedominated and dust-marine mixing conditions. GARRLiC and LIRIC achieve a satisfactory characterization for the dust-dominated case in terms of particle microphysical properties and concentration profiles. The marine-dominated and the mixture cases are more challenging for both algorithms, although GARRLiC manages to provide more detailed microphysical retrievals compared to AERONET, while LIRIC effectively discriminates dust and marine particles in its concentration profile retrievals. The results are also compared with modelled dust and marine concentration profiles and surface in situ measurements.
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    Vertical profiles of aerosol mass concentration derived by unmanned airborne in situ and remote sensing instruments during dust events
    (Katlenburg-Lindau : Copernicus, 2018) Mamali, Dimitra; Marinou, Eleni; Sciare, Jean; Pikridas, Michael; Kokkalis, Panagiotis; Kottas, Michael; Binietoglou, Ioannis; Tsekeri, Alexandra; Keleshis, Christos; Engelmann, Ronny; Baars, Holger; Ansmann, Albert; Amiridis, Vassilis; Russchenberg, Herman; Biskos, George
    In situ measurements using unmanned aerial vehicles (UAVs) and remote sensing observations can independently provide dense vertically resolved measurements of atmospheric aerosols, information which is strongly required in climate models. In both cases, inverting the recorded signals to useful information requires assumptions and constraints, and this can make the comparison of the results difficult. Here we compare, for the first time, vertical profiles of the aerosol mass concentration derived from light detection and ranging (lidar) observations and in situ measurements using an optical particle counter on board a UAV during moderate and weak Saharan dust episodes. Agreement between the two measurement methods was within experimental uncertainty for the coarse mode (i.e. particles having radii > 0.5 μm), where the properties of dust particles can be assumed with good accuracy. This result proves that the two techniques can be used interchangeably for determining the vertical profiles of aerosol concentrations, bringing them a step closer towards their systematic exploitation in climate models.
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    Optimizing the detection, ablation, and ion extraction efficiency of a single-particle laser ablation mass spectrometer for application in environments with low aerosol particle concentrations
    (Katlenburg-Lindau : Copernicus, 2020) Clemen, Hans-Christian; Schneider, Johannes; Klimach, Thomas; Helleis, Frank; Köllner, Franziska; Hünig, Andreas; Rubach, Florian; Mertes, Stephan; Wex, Heike; Stratmann, Frank; Welti, André; Kohl, Rebecca; Frank, Fabian; Borrmann, Stephan
    The aim of this study is to show how a newly developed aerodynamic lens system (ALS), a delayed ion extraction (DIE), and better electric shielding improve the efficiency of the Aircraft-based Laser ABlation Aerosol MAss spectrometer (ALABAMA). These improvements are applicable to single-particle laser ablation mass spectrometers in general. To characterize the modifications, extensive sizeresolved measurements with spherical polystyrene latex particles (PSL; 150-6000 nm) and cubic sodium chloride particles (NaCl; 400-1700 nm) were performed. Measurements at a fixed ALS position show an improved detectable particle size range of the new ALS compared to the previously used Liu-type ALS, especially for supermicron particles. At a lens pressure of 2.4 hPa, the new ALS achieves a PSL particle size range from 230 to 3240 nm with 50% detection efficiency and between 350 and 2000 nm with 95% detection efficiency. The particle beam divergence was determined by measuring the detection efficiency at variable ALS positions along the laser cross sections and found to be minimal for PSL at about 800 nm. Compared to measurements by singleparticle mass spectrometry (SPMS) instruments using Liutype ALSs, the minimum particle beam divergence is shifted towards larger particle sizes. However, there are no disadvantages compared to the Liu-type lenses for particle sizes down to 200 nm. Improvements achieved by using the DIE and an additional electric shielding could be evaluated by size-resolved measurements of the hit rate, which is the ratio of laser pulses yielding a detectable amount of ions to the total number of emitted laser pulses. In particular, the hit rate for multiply charged particles smaller than 500 nm is significantly improved by preventing an undesired deflection of these particles in the ion extraction field. Moreover, it was found that by using the DIE the ion yield of the ablation, ionization, and ion extraction process could be increased, resulting in up to 7 times higher signal intensities of the cation spectra. The enhanced ion yield results in a larger effective width of the ablation laser beam, which in turn leads to a hit rate of almost 100% for PSL particles in the size range from 350 to 2000 nm. Regarding cubic NaCl particles the modifications of the ALABAMA result in an up to 2 times increased detection efficiency and an up to 5 times increased hit rate. The need for such instrument modifications arises in particular for measurements of particles that are present in low number concentrations such as ice-nucleating particles (INPs) in general, but also aerosol particles at high altitudes or in pristine environments. Especially for these low particle number concentrations, improved efficiencies help to overcome the statistical limitations of single-particle mass spectrometer measurements. As an example, laboratory INP measurements carried out in this study show that the appli- cation of the DIE alone increases the number of INP mass spectra per time unit by a factor of 2 to 3 for the sampled substances. Overall, the combination of instrument modifications presented here resulted in an increased measurement efficiency of the ALABAMA for different particle types and particles shape as well as for highly charged particles. © 2020 Copernicus GmbH. All rights reserved.