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- ItemRegional 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, ManfredThe 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.
- ItemProfiling of Saharan dust and biomass-burning smoke with multiwavelength polarization Raman lidar at Cape Verde(Milton Park : Taylor & Francis, 2017) Tesche, Matthias; Gross, Silke; Ansmann, Albert; Müller, Detlef; Althausen, Dietrich; Freudenthaler, Volker; Esselborn, MichaelExtensive lidar measurements of Saharan dust and biomass-burning smoke were performed with one airborne and three ground-based instruments in the framework of the second part of the SAharan Mineral dUst experiMent (SAMUM-2a) during January and February of 2008 at Cape Verde. Further lidar observations with one system only were conducted duringMay and June of 2008 (SAMUM-2b). The active measurements were supported by Sun photometer observations. During winter, layers of mineral dust from the Sahara and biomass-burning smoke from southern West Africa pass Cape Verde on their way to South America while pure dust layers cross the Atlantic on their way to the Caribbean during summer. The mean 500-nm aerosol optical thickness (AOT) observed during SAMUM-2a was 0.35 ± 0.18. SAMUM-2a observations showed transport of pure dust within the lowermost 1.5 km of the atmospheric column. In the height range from 1.5 to 5.0 km, mixed dust/smoke layers with mean lidar ratios of 67 ± 14 sr at 355 and 532 nm, respectively, prevailed. Within these layers, wavelength-independent linear particle depolarization ratios of 0.12–0.18 at 355, 532, and 710 nm indicate a large contribution (30–70%) of mineral dust to the measured optical properties. Ångstr¨om exponents for backscatter and extinction of around 0.7 support this finding. Mean extinction coefficients in the height range between 2 and 4 km were 66 ± 6 Mm−1 at 355 nm and 48 ± 5 Mm−1 at 532 nm. Comparisons with airborne high-spectral-resolution lidar observations show good agreement within the elevated layers. 3–5 km deep dust layers where observed during SAMUM-2b. These layers showed optical properties similar to the ones of SAMUM-1 in Morocco with a mean 500-nm AOT of 0.4 ± 0.2. Dust extinction coefficients were about 80 ± 6 Mm−1 at 355 and 532 nm. Dust lidar ratios were 53 ± 10 sr at 355 and 532 nm, respectively. Dust depolarization ratios showed an increase with wavelength from 0.31 ± 0.10 at 532 nm to 0.37 ± 0.07 at 710 nm.
- ItemSaharan 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, JostTwo 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.
- ItemOptical properties of aerosol mixtures derived from sun-sky radiometry during SAMUM-2(Milton Park : Taylor & Francis, 2017) Toledano, C.; Wiegner, M.; Groß, S.; Freudenthaler, V.; Gasteiger, J.; Müller, D.; Müller, T.; Schladitz, A.; Weinzierl, B.; Torres, B.; O’neill, N.T.The SAMUM-2 experiment took place in the Cape Verde is lands in January–February 2008. The colocated ground-based and airborne instruments allow the study of desert dust optical and microphysical properties in a closure experiment. The Meteorological Institute of the University of Munich deployed one sun-sky photometer and two tropospheric lidar systems. A travelling AERONET-Cimel sun-sky radiometer was also deployed. During the measurement period the aerosol scenario over Cape Verde mostly consisted of a dust layer below 2 km and a smoke-dust layer above 2–4 km a.s.l. The Saharan dust arrived at the site from the NE, whereas the smoke originated in the African equatorial region. This paper describes the main results of the Sun photometer observations, supported by lidar information. An analysis of the variations in the aerosol optical depth (AOD) in the range 340–1550 nm, the Ångström exponent, volume size distributions and single scattering albedo is presented. The aerosol mixtures are analysed by means of the fine mode fraction of the AOD provided by the sun-sky inversion data and the Spectral Deconvolution Algorithm. The mean AOD (500 nm) was 0.31, with associated low ångström exponent of 0.46. Several types of events were detected within the data set, with prevalence of dust or mixtures as characterized by the Ångstr¨om exponents of extinction and absorption and the fine mode fraction. Aerosol properties derived from sunphotometry were compared to in situ measurements of size distribution, effective radius and single scattering albedo.
- ItemRegional modelling of Saharan dust and biomass-burning smoke, Part I: Model description and evaluation(Milton Park : Taylor & Francis, 2017) Heinold, Bernd; Tegen, Ina; Schepanski, Kerstin; Tesche, Matthias; Esselborn, Michael; Freudenthaler, Volker; Gross, Silke; Kandler, Konrad; Knippertz, Peter; Müller, Detlef; Schladitz, Alexander; Toledano, Carlos; Weinzierl, Bernadett; Ansmann, Albert; Althausen, Dietrich; Müller, Thomas; Petzold, Andreas; Wiedensohler, AlfredThe spatio-temporal evolution of the Saharan dust and biomass-burning plume during the SAMUM-2 field campaign in January and February 2008 is simulated at 28 km horizontal resolution with the regional model-system COSMOMUSCAT. The model performance is thoroughly tested using routine ground-based and space-borne remote sensing and local field measurements. Good agreement with the observations is found in many cases regarding transport patterns, aerosol optical thicknesses and the ratio of dust to smoke aerosol. The model also captures major features of the complex aerosol layering. Nevertheless, discrepancies in the modelled aerosol distribution occur, which are analysed in detail. The dry synoptic dynamics controlling dust uplift and transport during the dry season are well described by the model, but surface wind peaks associated with the breakdown of nocturnal low-level jets are not always reproduced. Thus, a strong dust outbreak is underestimated. While dust emission modelling is a priori more challenging, since strength and placement of dust sources depend on on-line computed winds, considerable inaccuracies also arise in observation-based estimates of biomass-burning emissions. They are caused by cloud and spatial errors of satellite fire products and uncertainties in fire emission parameters, and can lead to unrealistic model results of smoke transport.
- ItemProfiling of fine and coarse particle mass: Case studies of Saharan dust and Eyjafjallajökull/Grimsvötn volcanic plumes(München : European Geopyhsical Union, 2012) Ansmann, A.; Seifert, P.; Tesche, M.; Wandinger, U.The polarization lidar photometer networking (POLIPHON) method introduced to separate coarse-mode and fine-mode particle properties of Eyjafjallajökull volcanic aerosols in 2010 is extended to cover Saharan dust events as well. Furthermore, new volcanic dust observations performed after the Grimsvötn volcanic eruptions in 2011 are presented. The retrieval of particle mass concentrations requires mass-specific extinction coefficients. Therefore, a review of recently published mass-specific extinction coefficients for Saharan dust and volcanic dust is given. Case studies of four different scenarios corroborate the applicability of the profiling technique: (a) Saharan dust outbreak to central Europe, (b) Saharan dust plume mixed with biomass-burning smoke over Cape Verde, and volcanic aerosol layers originating from (c) the Eyjafjallajökull eruptions in 2010 and (d) the Grimsvötn eruptions in 2011. Strong differences in the vertical aerosol layering, aerosol mixing, and optical properties are observed for the different volcanic events.
- ItemLong term measurements of aerosol optical properties at a primary forest site in Amazonia(München : European Geopyhsical Union, 2013) Rizzo, L.V.; Artaxo, P.; Müller, T.; Wiedensohler, A.; Paixão, M.; Cirino, G.G.; Arana, A.; Swietlicki, E.; Roldin, P.; Fors, E.O.; Wiedemann, K.T.; Leal, L.S.M.; Kulmala, M.A long term experiment was conducted in a primary forest area in Amazonia, with continuous in-situ measurements of aerosol optical properties between February 2008 and April 2011, comprising, to our knowledge, the longest database ever in the Amazon Basin. Two major classes of aerosol particles, with significantly different optical properties were identified: coarse mode predominant biogenic aerosols in the wet season (January–June), naturally released by the forest metabolism, and fine mode dominated biomass burning aerosols in the dry season (July–December), transported from regional fires. Dry particle median scattering coefficients at the wavelength of 550 nm increased from 6.3 Mm−1 to 22 Mm−1, whereas absorption at 637 nm increased from 0.5 Mm−1 to 2.8 Mm−1 from wet to dry season. Most of the scattering in the dry season was attributed to the predominance of fine mode (PM2) particles (40–80% of PM10 mass), while the enhanced absorption coefficients are attributed to the presence of light absorbing aerosols from biomass burning. As both scattering and absorption increased in the dry season, the single scattering albedo (SSA) did not show a significant seasonal variability, in average 0.86 ± 0.08 at 637 nm for dry aerosols. Measured particle optical properties were used to estimate the aerosol forcing efficiency at the top of the atmosphere. Results indicate that in this primary forest site the radiative balance was dominated by the cloud cover, particularly in the wet season. Due to the high cloud fractions, the aerosol forcing efficiency absolute values were below −3.5 W m−2 in 70% of the wet season days and in 46% of the dry season days. Besides the seasonal variation, the influence of out-of-Basin aerosol sources was observed occasionally. Periods of influence of the Manaus urban plume were detected, characterized by a consistent increase on particle scattering (factor 2.5) and absorption coefficients (factor 5). Episodes of biomass burning and mineral dust particles advected from Africa were observed between January and April, characterized by enhanced concentrations of crustal elements (Al, Si, Ti, Fe) and potassium in the fine mode. During these episodes, median particle absorption coefficients increased by a factor of 2, whereas median SSA values decreased by 7%, in comparison to wet season conditions.
- ItemSeparation of the optical and mass features of particle components in different aerosol mixtures by using POLIPHON retrievals in synergy with continuous polarized Micro-Pulse Lidar (P-MPL) measurements(Katlenburg-Lindau : Copernicus, 2018) Córdoba-Jabonero, Carmen; Sicard, Michaël; Ansmann, Albert; del Águila, Ana; Baars, HolgerThe application of the POLIPHON (POlarization-LIdar PHOtometer Networking) method is presented for the first time in synergy with continuous 24/7 polarized Micro-Pulse Lidar (P-MPL) measurements to derive the vertical separation of two or three particle components in different aerosol mixtures, and the retrieval of their particular optical properties. The procedure of extinction-to-mass conversion, together with an analysis of the mass extinction efficiency (MEE) parameter, is described, and the relative mass contribution of each aerosol component is also derived in a further step. The general POLIPHON algorithm is based on the specific particle linear depolarization ratio given for different types of aerosols and can be run in either 1-step (POL-1) or 2 steps (POL-2) versions with dependence on either the 2- or 3-component separation. In order to illustrate this procedure, aerosol mixing cases observed over Barcelona (NE Spain) are selected: a dust event on 5 July 2016, smoke plumes detected on 23 May 2016 and a pollination episode observed on 23 March 2016. In particular, the 3-component separation is just applied for the dust case: a combined POL-1 with POL-2 procedure (POL-1/2) is used, and additionally the fine-dust contribution to the total fine mode (fine dust plus non-dust aerosols) is estimated. The high dust impact before 12:00 UTC yields a mean mass loading of 0.6±0.1 g m'2 due to the prevalence of Saharan coarse-dust particles. After that time, the mean mass loading is reduced by two-thirds, showing a rather weak dust incidence. In the smoke case, the arrival of fine biomass-burning particles is detected at altitudes as high as 7 km. The smoke particles, probably mixed with less depolarizing non-smoke aerosols, are observed in air masses, having their origin from either North American fires or the Arctic area, as reported by HYSPLIT back-trajectory analysis. The particle linear depolarization ratio for smoke shows values in the 0.10-0.15 range and even higher at given times, and the daily mean smoke mass loading is 0.017±0.008 g m'2, around 3 % of that found for the dust event. Pollen particles are detected up to 1.5 km in height from 10:00 UTC during an intense pollination event with a particle linear depolarization ratio ranging between 0.10 and 0.15. The maximal mass loading of Platanus pollen particles is 0.011±0.003 g m'2, representing around 2 % of the dust loading during the higher dust incidence. Regarding the MEE derived for each aerosol component, their values are in agreement with others referenced in the literature for the specific aerosol types examined in this work: 0.5±0.1 and 1.7±0.2 m2 g'1 are found for coarse and fine dust particles, 4.5±1.4 m2 g'1 is derived for smoke and 2.4±0.5 m2 g'1 for non-smoke aerosols with Arctic origin, and a MEE of 2.4±0.8 m2 g'1 is obtained for pollen particles, though it can reach higher or lower values depending on predominantly smaller or larger pollen grain sizes. Results reveal the high potential of the P-MPL system, a simple polarization-sensitive elastic backscatter lidar working in a 24/7 operation mode, to retrieve the relative optical and mass contributions of each aerosol component throughout the day, reflecting the daily variability of their properties. In fact, this procedure can be simply implemented in other P-MPLs that also operate within the worldwide Micro-Pulse Lidar Network (MPLNET), thus extending the aerosol discrimination at a global scale. Moreover, the method has the advantage of also being relatively easily applicable to space-borne lidars with an equivalent configuration such as the ongoing Cloud-Aerosol LIdar with Orthogonal Polarization (CALIOP) on board NASA CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) and the forthcoming Atmospheric Lidar (ATLID) on board the ESA EarthCARE mission.
- ItemLong-term study on coarse mode aerosols in the Amazon rain forest with the frequent intrusion of Saharan dust plumes(Katlenburg-Lindau : EGU, 2018) Moran-Zuloaga, Daniel; Ditas, Florian; Walter, David; Saturno, Jorge; Brito, Joel; Carbone, Samara; Chi, Xuguang; Hrabě de Angelis, Isabella; Baars, Holger; Godoi, Ricardo H. M.; Heese, Birgit; Holanda, Bruna A.; Lavrič, Jošt V.; Martin, Scot T.; Ming, Jing; Pöhlker, Mira L.; Ruckteschler, Nina; Su, Hang; Wang, Yaqiang; Wang, Qiaoqiao; Wang, Zhibin; Weber, Bettina; Wolff, Stefan; Artaxo, Paulo; Pöschl, Ulrich; Andreae, Meinrat O.; Pöhlker, ChristopherIn the Amazonian atmosphere, the aerosol coarse mode comprises a complex, diverse, and variable mixture of bioaerosols emitted from the rain forest ecosystem, long-range transported Saharan dust (we use Sahara as shorthand for the dust source regions in Africa north of the Equator), marine aerosols from the Atlantic Ocean, and coarse smoke particles from deforestation fires. For the rain forest, the coarse mode particles are of significance with respect to biogeochemical and hydrological cycling, as well as ecology and biogeography. However, knowledge on the physicochemical and biological properties as well as the ecological role of the Amazonian coarse mode is still sparse. This study presents results from multi-year coarse mode measurements at the remote Amazon Tall Tower Observatory (ATTO) site. It combines online aerosol observations, selected remote sensing and modeling results, as well as dedicated coarse mode sampling and analysis. The focal points of this study are a systematic characterization of aerosol coarse mode abundance and properties in the Amazonian atmosphere as well as a detailed analysis of the frequent, pulse-wise intrusion of African long-range transport (LRT) aerosols (comprising Saharan dust and African biomass burning smoke) into the Amazon Basin.We find that, on a multi-year time scale, the Amazonian coarse mode maintains remarkably constant concentration levels (with 0.4 cmĝ'3 and 4.0 μg mĝ'3 in the wet vs. 1.2 cmĝ'3 and 6.5 μg mĝ'3 in the dry season) with rather weak seasonality (in terms of abundance and size spectrum), which is in stark contrast to the pronounced biomass burning-driven seasonality of the submicron aerosol population and related parameters. For most of the time, bioaerosol particles from the forest biome account for a major fraction of the coarse mode background population. However, from December to April there are episodic intrusions of African LRT aerosols, comprising Saharan dust, sea salt particles from the transatlantic passage, and African biomass burning smoke. Remarkably, during the core period of this LRT season (i.e., February-March), the presence of LRT influence, occurring as a sequence of pulse-like plumes, appears to be the norm rather than an exception. The LRT pulses increase the coarse mode concentrations drastically (up to 100 μg mĝ'3) and alter the coarse mode composition as well as its size spectrum. Efficient transport of the LRT plumes into the Amazon Basin takes place in response to specific mesoscale circulation patterns in combination with the episodic absence of rain-related aerosol scavenging en route. Based on a modeling study, we estimated a dust deposition flux of 5-10 kg haĝ'1 aĝ'1 in the region of the ATTO site. Furthermore, a chemical analysis quantified the substantial increase of crustal and sea salt elements under LRT conditions in comparison to the background coarse mode composition. With these results, we estimated the deposition fluxes of various elements that are considered as nutrients for the rain forest ecosystem. These estimates range from few g haĝ'1 aĝ'1 up to several hundreds of g haĝ'1 aĝ'1 in the ATTO region.The long-term data presented here provide a statistically solid basis for future studies of the manifold aspects of the dynamic coarse mode aerosol cycling in the Amazon. Thus, it may help to understand its biogeochemical relevance in this ecosystem as well as to evaluate to what extent anthropogenic influences have altered the coarse mode cycling already.
- ItemShip-borne aerosol profiling with lidar over the Atlantic Ocean: From pure marine conditions to complex dust-smoke mixtures(Göttingen : Copernicus GmbH, 2018) Bohlmann, S.; Baars, H.; Radenz, M.; Engelmann, R.; Macke, A.The multi-wavelength Raman lidar PollyXT has been regularly operated aboard the research vessel Polarstern on expeditions across the Atlantic Ocean from north to south and vice versa. The lidar measurements of the RV Polarstern cruises PS95 from Bremerhaven, Germany, to Cape Town, Republic of South Africa (November 2015), and PS98 from Punta Arenas, Chile, to Bremerhaven, Germany (April/May 2016), are presented and analysed in detail. The latest set-up of PollyXT allows improved coverage of the marine boundary layer (MBL) due to an additional near-range receiver. Three case studies provide an overview of the aerosol detected over the Atlantic Ocean. In the first case, marine conditions were observed near South Africa on the autumn cruise PS95. Values of optical properties (depolarisation ratios close to zero, lidar ratios of 23 sr at 355 and 532 nm) within the MBL indicate pure marine aerosol. A layer of dried marine aerosol, indicated by an increase of the particle depolarisation ratio to about 10% at 355 nm (9% at 532 nm) and thus confirming the non-sphericity of these particles, could be detected on top of the MBL. On the same cruise, an almost pure Saharan dust plume was observed near the Canary Islands, presented in the second case. The third case deals with several layers of Saharan dust partly mixed with biomass-burning smoke measured on PS98 near the Cabo Verde islands. While the MBL was partly mixed with dust in the pure Saharan dust case, an almost marine MBL was observed in the third case. A statistical analysis showed latitudinal differences in the optical properties within the MBL, caused by the downmixing of dust in the tropics and anthropogenic influences in the northern latitudes, whereas the optical properties of the MBL in the Southern Hemisphere correlate with typical marine values. The particle depolarisation ratio of dried marine layers ranged between 4 and 9% at 532 nm. Night measurements from PS95 and PS98 were used to illustrate the potential of aerosol classification using lidar ratio, particle depolarisation ratio at 355 and 532 nm, and Angström exponent. Lidar ratio and particle depolarisation ratio have been found to be the main indicator for particle type, whereas the Ångström exponent is rather variable.