Global Change Abstracts The Swiss Contribution - SCNAT

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56 08.1-52 Counterflow virtual impact or based collection of small ice particles in mixed-phase clouds for the physico-chemical characterization of tropospheric ice nuclei : Sampler description and first case study Mertes S, Verheggen B, Walter S, Connolly P, Ebert M, Schneider J, Bower K N, Cozic J, Weinbruch S, Baltensperger U, Weingartner E Germany, Switzerland, England Meteorology & Atmospheric Sciences A ground-based sampling system named Ice-CVI is introduced that is able to extract small ice particles with sizes between 5 and 20 µm out of mixed-phase clouds. The instrument is based on a counterflow virtual impactor (CVI) removing interstitial particles and is supplemented by additional modules that pre-segregate other constituents of mixed-phase clouds. Ice particles of 20 µm and smaller are expected to grow only by water vapor diffusion and there is a negligible probability that they scavenge aerosol particles by impaction and riming. Thus, their residuals which are released by the Ice-CVI can be interpreted as the original ice nuclei (IN). In a first field test within the Cloud and Aerosol Characterization Experiment (CLACE-3) at the high alpine research station Jungfraujoch, the collection behavior of the single components and the complete system was evaluated under atmospheric sampling conditions. By comparing parameters measured by the Ice-CVI with corresponding results obtained from other inlets or with in-situ instrumentation it is verified that the small ice particles are representatively collected whereas all other mixed phase cloud constituents are effectively suppressed. In a case study it is observed that supermicrometer particles preferentially serve as IN although in absolute terms the IN concentration is dominated by sub- micrometer particles. Mineral dust (Si), nonvolatile organic matter and black carbon could be identified as IN components by means of different chemical analyses. The latter suggests an anthropogenic influence on the heterogeneous ice nucleation in supercooled, tropospheric clouds. Aerosol Science and Technology, 2007, V41, N9, pp 848-864. 08.1-53 A one-dimensional ensemble forecast and assimilation system for fog prediction Müller M D, Schmutz C, Parlow E Switzerland Modelling , Meteorology & Atmospheric Sciences A probabilistic fog forecast system was designed based on two high resolution numerical 1-D mod- Global Change Abstracts – The Swiss Contribution | Atmosphere els called COBEL and PAFOG. The 1-D models are coupled to several 3-D numerical weather prediction models and thus are able to consider the effects of advection. To deal with the large uncertainty inherent to fog forecasts, a whole ensemble of 1-D runs is computed using the two different numerical models and a set of different initial conditions in combination with distinct boundary conditions. Initial conditions are obtained from variational data assimilation, which optimally combines observations with a first guess taken from operational 3-D models. The design of the ensemble scheme computes members that should fairly well represent the uncertainty of the current meteorological regime. Verification for an entire fog season reveals the importance of advection in complex terrain. The skill of 1-D fog forecasts is significantly improved if advection is considered. Thus the probabilistic forecast system has the potential to support the forecaster and therefore to provide more accurate fog forecasts. Pure and Applied Geophysics, 2007, V164, N6-7, JUN, pp 1241-1264. 08.1-54 Ozone air pollution effects on tree-ring growth, delta C-13, visible foliar injury and leaf gas exchange in three ozone-sensitive woody plant species Novak K, Cherubini P, Saurer M, Fuhrer J, Skelly J M, Kräuchi N, Schaub M Switzerland, USA Meteorology & Atmospheric Sciences , Plant Sciences , Forestry We assessed the effects of ambient tropospheric ozone on annual tree- ring growth, delta C-13 in the rings, leaf gas exchange and visible injury in three ozone-sensitive woody plant species in southern Switzerland. Seedlings of Populus nigra L., Viburnum lantana L. and Fraxinus excelsior L. were exposed to charcoal-filtered air (CF) and nonfiltered air (NF) in open-top chambers, and to ambient air (AA) in open plots during the 2001 and 2002 growing seasons. Ambient ozone exposures in the region were sufficient to cause visible foliar injury, early leaf senescence and premature leaf loss in all species. Ozone had significant negative effects on net photosynthesis and stomatal conductance in all species in 2002 and in V. lantana and F. excelsior in 2001. Water-use efficiency decreased and intercellular CO 2 concentrations increased in all species in response to ozone in 2002 only. The width and delta C-13 of the 2001 and 2002 growth rings were measured for all species at the end of the 2002 growing season. Compared with CF seedlings, mean ring width in the AA and
Global Change Abstracts – The Swiss Contribution | Atmosphere 57 NF P. nigra seedlings was reduced by 52 and 46%, respectively, in 2002, whereas in V lantana and F. excelsior ring width showed no significant reductions in either year. Although delta C-13 was usually more negative in CF seedlings than in AA and NF seedlings, with the exception of F. excelsior in 2001, ozone effects on delta C-13 were significant only for V lantana and P nigra in 2001. Among species, P. nigra exhibited the greatest response to ozone for the measured parameters as well as the most severe foliar injury and was the only species to show a significant reduction in ring width in response to ozone exposure, despite significant negative ozone effects on leaf gas exchange and the development of visible foliar injury in V lantana and F. excelsior. Thus, significant ozone-induced effects at the leaf level did not correspond to reduced tree-ring growth or increased delta C-13 in all species, indicating that the timing of ozone exposure and severity of leaf-level responses may be important in determining the sensitivity of tree productivity to ozone exposure. Tree Physiology, 2007, V27, N7, JUL, pp 941-949. 08.1-55 Perturbation of the European free troposphere aerosol by North American forest fire plumes during the ICARTT-ITOP experiment in summer 2004 Petzold A, Weinzierl B, Huntrieser H, Stohl A, Real E, Cozic J, Fiebig M, Hendricks J, Lauer A, Law K, Roiger A, Schlager H, Weingartner E Germany, Norway, France, Switzerland Meteorology & Atmospheric Sciences , Modelling , Forestry , Plant Sciences During the ICARTT-ITOP Experiment in summer 2004 plumes from large wildfires in North America were transported to Central Europe at 3 - 8 km altitude above sea level (a.s.l.). These plumes were studied with the DLR (Deutsches Zentrum fuer Luft- und Raumfahrt) research aircraft Falcon which was equipped with an extensive set of in situ aerosol and trace gas instruments. Analyses by the Lagrangian dispersion model FLEXPART provided source regions, transport times and horizontal extent of the fire plumes. Results from the general circulation model ECHAM/MADE and data from previous aerosol studies over Central Europe provided reference vertical profiles of black carbon (BC) mass concentrations for year 2000 conditions with forest fire activities below the long-term average. Smoke plume observations yielded a BC mass fraction of total aerosol mass with respect to PM 2.5 of 2 - 8%. The ratio of BC mass to excess CO was 3 - 7.5 mg BC (g CO)(-1). Even after up to 10 days of atmospheric transport, both characteristic properties were of the same order as for fresh emissions. This suggests an efficient lifting of BC from forest fires to higher altitudes with only minor scavenging removal of particulate matter. Maximum aerosol absorption coefficient values were 7 - 8Mm (-1) which is about two orders of magnitude above the average European free tropospheric background value. Forest fire aerosol size distributions were characterised by a strong internally mixed accumulation mode centred at modal diameters of 0.25 - 0.30 µm with an average distribution width of 1.30. Nucleation and small Aitken mode particles were almost completely depleted. Atmospheric Chemistry and Physics, 2007, V7, N19, pp 5105-5127. 08.1-56 Long-term variability of daily North Atlantic- European pressure patterns since 1850 classified by simulated annealing clustering Philipp A, Della Marta P M, Jacobeit J, Fereday D R, Jones P D, Moberg A, Wanner H Germany, Switzerland, England, Sweden Meteorology & Atmospheric Sciences Reconstructed daily mean sea level pressure patterns of the North Atlantic - European region are classified for the period 1850 to 2003 to explore long- term changes of the atmospheric circulation and its impact on long- term temperature variability in the central European region. Commonly used k- means clustering algorithms resulted in classifications of low quality because of methodological deficiencies leading to local optima by chance for complex datasets. In contrast, a newly implemented clustering scheme combining the concepts of simulated annealing and diversified randomization (SANDRA) is able to reduce substantially the influence of chance in the cluster assignment, leading to partitions that are noticeably nearer to the global optimum and more stable. The differences between conventional cluster analysis and the SANDRA scheme are significant for subsequent analyses of single clusters - in particular, for trend analysis. Conventional indices used to determine the appropriate number of clusters failed to provide clear guidance, indicating that no distinct separation between clusters of circulation types exists in the dataset. Therefore, the number of clusters is determined by an external indicator, the so- called dominance criteria for t- mode principal component analysis. Nevertheless, the resulting partitions are stable for certain numbers of clusters and provide meaningful and reproducible clusters. The resulting types of pressure patterns reveal pronounced long- term vari-
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