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- ItemThe Pagami Creek smoke plume after long-range transport to the upper troposphere over Europe – Aerosol properties and black carbon mixing state(München : European Geopyhsical Union, 2014) Dahlkötter, F.; Gysel, M.; Sauer, D.; Minikin, A.; Baumann, R.; Seifert, P.; Ansmann, A.; Fromm, M.; Voigt, C.; Weinzierl, B.During the CONCERT 2011 field experiment with the DLR research aircraft Falcon, an enhanced aerosol layer with particle linear depolarization ratios of 6–8% at 532 nm was observed at altitudes above 10 km over northeast Germany on 16 September 2011. Dispersion simulations with HYSPILT suggest that the elevated aerosol layer originated from the Pagami Creek forest fire in Minnesota, USA, which caused pyro-convective uplift of particles and gases. The 3–4 day-old smoke plume had high total refractory black carbon (rBC) mass concentrations of 0.03–0.35 μg m−3 at standard temperature and pressure (STP) with rBC mass equivalent diameter predominantly smaller than 130 nm. Assuming a core-shell particle structure, the BC cores exhibit very thick (median: 105–136 nm) BC-free coatings. A large fraction of the BC-containing particles disintegrated into a BC-free fragment and a BC fragment while passing through the laser beam of the Single Particle Soot Photometer (SP2). In this study, the disintegration is a result of very thick coatings around the BC cores. This is in contrast to a previous study in a forest-fire plume, where it was hypothesized to be a result of BC cores being attached to a BC-free particle. For the high-altitude forest-fire aerosol layer observed in this study, increased mass specific light-absorption cross sections of BC can be expected due to the very thick coatings around the BC cores, while this would not be the case for the attached-type morphology. We estimate the BC mass import from the Pagami Creek forest fire into the upper troposphere/lower stratosphere (UTLS) region (best estimate: 25 Mg rBC). A comparison to black carbon emission rates from aviation underlines the importance of pyro-convection on the BC load in the UTLS region. Our study provides detailed information on the microphysics and the mixing state of BC in the forest-fire aerosol layer in the upper troposphere that can be used to better understand and investigate the radiative impact of such upper tropospheric aerosol layers.
- ItemAirborne observations of the Eyjafjalla volcano ash cloud over Europe during air space closure in April and May 2010(München : European Geopyhsical Union, 2011) Schumann, U.; Weinzierl, B.; Reitebuch, O.; Schlager, H.; Minikin, A.; Forster, C.; Baumann, R.; Sailer, T.; Graf, K.; Mannstein, H.; Voigt, C.; Rahm, S.; Simmet, R.; Scheibe, M.; Lichtenstern, M.; Stock, P.; Rüba, H.; Schäuble, D.; Tafferner, A.; Rautenhaus, M.; Gerz, T.; Ziereis, H.; Krautstrunk, M.; Mallaun, C.; Gayet, J.-F.; Lieke, K.; Kandler, K.; Ebert, M.; Weinbruch, S.; Stohl, A.; Gasteiger, J.; Groß, S.; Freudenthaler, V.; Wiegner, M.; Ansmann, A.; Tesche, M.; Olafsson, H.; Sturm, K.Airborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with lidar directly over the volcano and up to a distance of 2700 km downwind, and up to 120 h plume ages. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm−3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m−3. The Falcon flew in ash clouds up to about 0.8 mg m−3 for a few minutes and in an ash cloud with approximately 0.2 mg m−3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m−3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 μm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240–1600) kg s−1. The volcano induced about 10 (2.5–50) Tg of distal ash mass and about 3 (0.6–23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.
- ItemThe impact of mineral dust on cloud formation during the Saharan dust event in April 2014 over Europe(Göttingen : Copernicus GmbH, 2018) Weger, M.; Heinold, B.; Engler, C.; Schumann, U.; Seifert, A.; Fößig, R.; Voigt, C.; Baars, H.; Blahak, U.; Borrmann, S.; Hoose, C.; Kaufmann, S.; Krämer, M.; Seifert, P.; Senf, F.; Schneider, J.; Tegen, I.A regional modeling study on the impact of desert dust on cloud formation is presented for a major Saharan dust outbreak over Europe from 2 to 5 April 2014. The dust event coincided with an extensive and dense cirrus cloud layer, suggesting an influence of dust on atmospheric ice nucleation. Using interactive simulation with the regional dust model COSMO-MUSCAT, we investigate cloud and precipitation representation in the model and test the sensitivity of cloud parameters to dust-cloud and dust-radiation interactions of the simulated dust plume. We evaluate model results with ground-based and spaceborne remote sensing measurements of aerosol and cloud properties, as well as the in situ measurements obtained during the ML-CIRRUS aircraft campaign. A run of the model with single-moment bulk microphysics without online dust feedback considerably underestimated cirrus cloud cover over Germany in the comparison with infrared satellite imagery. This was also reflected in simulated upper-Tropospheric ice water content (IWC), which accounted for only 20 % of the observed values. The interactive dust simulation with COSMO-MUSCAT, including a two-moment bulk microphysics scheme and dust-cloud as well as dust-radiation feedback, in contrast, led to significant improvements. The modeled cirrus cloud cover and IWC were by at least a factor of 2 higher in the relevant altitudes compared to the noninteractive model run. We attributed these improvements mainly to enhanced deposition freezing in response to the high mineral dust concentrations. This was corroborated further in a significant decrease in ice particle radii towards more realistic values, compared to in situ measurements from the ML-CIRRUS aircraft campaign. By testing different empirical ice nucleation parameterizations, we further demonstrate that remaining uncertainties in the ice-nucleating properties of mineral dust affect the model performance at least as significantly as including the online representation of the mineral dust distribution. Dust-radiation interactions played a secondary role for cirrus cloud formation, but contributed to a more realistic representation of precipitation by suppressing moist convection in southern Germany. In addition, a too-low specific humidity in the 7 to 10 km altitude range in the boundary conditions was identified as one of the main reasons for misrepresentation of cirrus clouds in this model study.