Global Change Abstracts The Swiss Contribution - SCNAT

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62 resolution of the snow scheme, and autumnal runoff from the Mediterranean part of the Rh ne is sensitive to the spatial resolution of precipitation. Journal of Hydrometeorology, 2007, V8, N5, OCT, pp 1002-1015. 08.1-68 Direct assessment of international consistency of standards for ground-level ozone: strategy and implementation toward metrological traceability network in Asia Tanimoto H, Mukai H, Sawa Y, Matsueda H, Yonemura S, Wang T, Poon S, Wong A, Lee G, Jung J Y, Kim K R, Lee M H, Lin N H, Wang J L, Ou Yang C F, Wu C F, Akimoto H, Pochanart P, Tsuboi K, Doi H, Zellwegern C, Klausenn J Japan, Peoples R China, South Korea, Taiwan, Switzerland Meteorology & Atmospheric Sciences , International Relations An international exercise to directly assess consistency of standards for ground-level ozone in East Asia was conducted as part of the East Asian Regional Experiment 2005 (EAREX 2005) in the framework of the Atmospheric Brown Clouds (ABC) project. Ten organizations collaboratively participated in the intercomparison. Four groups representing Japan, Korea, Hong Kong, and Taiwan made comparisons at the Gosan super observatory, Jeju Island, Korea, in March 2005, with ozone instruments calibrated to their national standards, and four Japanese groups made off-site comparisons with laboratory-level standards. All comparisons generally indicated good agreement with the standard reference photometer (SRP) 35, built by the National Institute of Standards and Technology (USA) and maintained by the National Institute for Environmental Studies (Japan). The assessment was expanded to measurement networks contributing to the World Meteorological Organization’s Global Atmospheric Watch (WMO/ GAW) program as part of off-site comparisons, and excellent agreement was achieved. These efforts contribute to propagating traceability of the national metrology standards among the atmospheric science community, to ensuring comparability of the existing ozone measurements, and to establishing an integrated network of air quality monitoring in Asia. Journal of Environmental Monitoring, 2007, V9, N11, pp 1183-1193. Global Change Abstracts – The Swiss Contribution | Atmosphere 08.1-69 The influence of a weakening of the Atlantic meridional overturning circulation on ENSO Timmermann A, Okumura Y, An S I, Clement A, Dong B, Guilyardi E, Hu A, Jungclaus J H, Renold M, Stocker T F, Stouffer R J, Sutton R, Xie S P, Yin J USA, South Korea, England, France, Germany, Switzerland Oceanography , Meteorology & Atmospheric Sciences , Modelling The influences of a substantial weakening of the Atlantic meridional overturning circulation (AMOC) on the tropical Pacific climate mean state, the annual cycle, and ENSO variability are studied using five different coupled general circulation models (CGCMs). In the CGCMs, a substantial weakening of the AMOC is induced by adding freshwater flux forcing in the northern North Atlantic. In response, the well- known surface temperature dipole in the low- latitude Atlantic is established, which reorganizes the large- scale tropical atmospheric circulation by increasing the northeasterly trade winds. This leads to a southward shift of the intertropical convergence zone (ITCZ) in the tropical Atlantic and also the eastern tropical Pacific. Because of evaporative fluxes, mixing, and changes in Ekman divergence, a meridional temperature anomaly is generated in the northeastern tropical Pacific, which leads to the development of a meridionally symmetric thermal background state. In four out of five CGC- Ms this leads to a substantial weakening of the annual cycle in the eastern equatorial Pacific and a subsequent intensification of ENSO variability due to nonlinear interactions. In one of the CGCM simulations, an ENSO intensification occurs as a result of a zonal mean thermocline shoaling. Analysis suggests that the atmospheric circulation changes forced by tropical Atlantic SSTs can easily influence the large- scale atmospheric circulation and hence tropical eastern Pacific climate. Furthermore, it is concluded that the existence of the present- day tropical Pacific cold tongue complex and the annual cycle in the eastern equatorial Pacific are partly controlled by the strength of the AMOC. The results may have important implications for the interpretation of global multidecadal variability and paleo- proxy data. Journal of Climate, 2007, V20, N19, OCT, pp 4899-4919.
Global Change Abstracts – The Swiss Contribution | Atmosphere 63 08.1-70 Aerosols in polar regions: A historical overview based on optical depth and in situ observations Tomasi C, Vitale V, Lupi A, Di Carmine C, Campanelli M, Herber A, Treffeisen R, Stone R S, Andrews E, Sharma S, Radionov V, von Hoyningen Huene W, Stebel K, Hansen G H, Myhre C L, Wehrli C, Aaltonen V, Lihavainen H, Virkkula A, Hillamo R, Stroem J, Toledano C, Cachorro V E, Ortiz P, de Frutos A M, Blindheim S, Frioud M, Gausa M, Zielinski T, Petelski T, Yamanouchi T Italy, Germany, USA, Canada, Russia, Norway, Switzerland, Finland, Sweden, Spain, Poland, Japan Meteorology & Atmospheric Sciences , Modelling Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and for different time periods. They were examined to estimate ensemble average, long-term trends of the summer background aerosol optical depth AOD(500 nm) in the polar regions (omitting the data influenced by Arctic haze and volcanic eruptions). The trend for the Arctic was estimated to be between -1.6% and -2.0% per year over 30 years, depending on location. No significant trend was observed for Antarctica. The time patterns of AOD(500 nm) and angstrom ngstrom’s parameters a and beta measured with Sun photometers during the last 20 years at various Arctic and Antarctic sites are also presented. They give a measure of the large variations of these parameters due to El Chichon, Pinatubo, and Cerro Hudson volcanic particles, Arctic haze episodes most frequent in winter and spring, and the transport of Asian dust and boreal smokes to the Arctic region. Evidence is also shown of marked differences between the aerosol optical parameters measured at coastal and high-altitude sites in Antarctica. In situ optical and chemical composition parameters of aerosol particles measured at Arctic and Antarctic sites are also examined to achieve more complete information on the multimodal size distribution shape parameters and their radiative properties. A characterization of aerosol radiative parameters is also defined by plotting the daily mean values of a as a function of AOD(500 nm), separately for the two polar regions, allowing the identification of different clusters related to fifteen aerosol classes, for which the spectral values of complex refractive index and single scattering albedo were evaluated. Journal of Geophysical Research Atmospheres, 2007, V112, ND16, AUG 21 ARTN: D16205. 08.1-71 Aerosol partitioning between the interstitial and the condensed phase in mixed-phase clouds Verheggen B, Cozic J, Weingartner E, Bower K, Mertes S, Connolly P, Gallagher M W, Flynn M, Choularton T, Baltensperger U Germany, England, Switzerland Meteorology & Atmospheric Sciences (1) The partitioning of aerosol particles between the cloud and the interstitial phase (i.e., unactivated aerosol) has been investigated during several Cloud and Aerosol Characterization Experiments (CLACE-3, CLACE-3 1/2 and CLACE-4) conducted in winter and summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580 m altitude, Switzerland). Ambient air was sampled using different inlets in order to determine the activated fraction of aerosol particles, F-N, defined as the fraction of the total aerosol number concentration (with particle diameter d(p) > 100 nm) that has been incorporated into cloud particles. The liquid and ice water content of mixedphase clouds were characterized by analyzing multiple cloud probes. The dependence of the activated fraction on several environmental factors is discussed on the basis of more than 900 h of incloud observations and parameterizations for key variables are given. FN is found to increase with increasing liquid water content and to decrease with increasing particle number concentration in liquid clouds. FN also decreases with increasing cloud ice mass fraction and with decreasing temperature from 0 to -25 degrees C. The Wegener- Bergeron-Findeisen process probably contributed to this trend, since the presence of ice crystals causes liquid droplets to evaporate, thus releasing the formerly activated particles back into the interstitial phase. Ice nucleation could also have prevented additional cloud condensation nuclei from activating. The observed activation behavior has significant implications for our understanding of the indirect effect of aerosols on climate. Journal of Geophysical Research Atmospheres, 2007, V112, ND23, DEC 13 ARTN: D23202. 08.1-72 Alpha-Pinene oxidation in the presence of seed aerosol: Estimates of nucleation rates, growth rates, and yield Verheggen B, Mozurkewich M, Caffrey P, Frick G, Hoppel W, Sullivan W Canada, Switzerland, USA Meteorology & Atmospheric Sciences , Modelling A recently developed inverse-modeling procedure has been applied to a case study of particle nucle-
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