Aerosol characterization and optical thickness retrievalsusing GOME and METEOSAT satellite data

Summary ?Retrievals of atmospheric aerosol optical thickness are highly dependent on the choice of the class describing the aerosol properties leading to significant errors while using classes available in the literature. High spectral resolution measurements from GOME (Global Ozone Monitoring Experiment) between the ultraviolet and the near infrared can be used for an accurate characterization of the aerosol optical properties. The radiometer MVIRI (METEOSAT Visible and Infrared Imager) on board the geostationary satellite METEOSAT, while being equipped only with broadband VIS channel, ensures an adequate half-hourly monitoring of the atmospheric conditions over a large portion of the Earth. The present algorithm is based on a combination of data from both sensors for the retrieval of the aerosol optical thickness at the reference wavelength of 0.55 μm (AOT). A case of a desert dust outbreak from the African continent over the Atlantic Ocean is examined. AOT values obtained using a priori fixed classes taken from the literature are compared with those retrieved with this algorithm using the GOME-derived classes. Systematic differences of the order of a few tenths on average are found which remain significant also after considering the measurement errors. This represents a novelty introduced by the synergetic use of both sensors. Received March 13, 2002     

Particle size dependent response of aerosol counters

During an international workshop at the Institute for Experimental Physics of the University of Vienna, Austria, which was coordinated within the Committee on Nucleation and Atmospheric Aerosols (IAMAS-IUGG), 10 instruments for aerosol number concentration measurement were studied, covering a wide range of methods based on various different measuring principles. In order to investigate the detection limits of the instruments considered with respect to particle size, simultaneous number concentration measurements were performed for monodispersed aerosols with particle sizes ranging from 1.5 to 50 nm diameter and various compositions.The instruments considered show quite different response characteristics, apparently related to the different vapors used in the various counters to enlarge the particles to an optically detectable size. A strong dependence of the 50% cutoff diameter on the particle composition in correlation with the type of vapor used in the specific instrument was found. An enhanced detection efficiency for ultrafine hygroscopic sodium chloride aerosols was observed with water operated systems, an analogous trend was found for n-butanol operated systems with nonhygroscopic silver and tungsten oxide particles.     

Aerosol climatology for the planetary boundary layer derived from regular lidar measurements

Regular aerosol extinction and backscatter measurements using a UV Raman Lidar have been performed for almost 3 years in Hamburg in the frame of the German Lidar Network. A set of 92 aerosol extinction and 164 aerosol backscatter profiles has been used for statistical investigations. Mean values and variances of the aerosol extinction and backscatter in the boundary layer have been calculated. Large fluctuations during the whole year have been found. The measured aerosol extinction over Hamburg shows a seasonal cycle with highest values in early fall and a second less prominent peak in spring.An analysis of the data using back trajectories showed a dependence of the aerosol extinction on the origin of the air mass. The residence time of the air mass over industrialized areas was found to be an important parameter for the measured aerosol extinction at Hamburg. However, only a small part of the total variability could be explained by the air mass origin.For 75 cases of aerosol extinction measurements under cloud-free conditions, the aerosol backscatter profile and therefore, the lidar ratio as a function of altitude could be determined. Winter measurements of the lidar ratio are often close to model results for maritime aerosol, the summer measurements are close to the model results for urban or continental aerosols.The high quality of the data has been proven by intercomparisons with other lidar systems and with star photometer measurements of the aerosol optical depth during the Lindenberg Aerosol Characterization Experiment (LACE'98) field campaign.     

Pseudodynamic tests on rubber base isolators with numerical substructuring of the superstructure and strain‐rate effect compensation

A pseudodynamic testing procedure has been applied by which the seismic response of a base‐isolated building is obtained by using as specimen the isolators, while the superstructure is numerically simulated. The procedure also takes advantage of the continuous pseudodynamic testing capabilities of the ELSA laboratory, which increase the accuracy of the results and reduce the strain‐rate effect of the rubber bearings. A simple proportional correction of the measured forces compensates the remaining strain‐rate effect due to the unrealistic speed of the test. The correction factor is obtained by means of a characterizing test on the specific rubber isolators. The developed method has been successfully applied to the prediction of the seismic response of a base‐isolated four‐storey building submitted to several specified accelerograms. The results for those earthquakes as well as the effects of some changes of the parameters of the system are discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Mobility of Phosphorus during the Weathering of Volcanic Ashes

Data are presented on phosphorus mobility during the weathering of rhyolite–dacite tephra of the modern and ancient eruptions. Distal tephra cannot be considered a phosphorus source, since phosphorous has low mobility during weathering both in subaerial and subaqueous sedimentation conditions. However, volcanic ashes exert a fertilization effect, providing the supply of nutrient elements into the ecosystem of internal basins and coastal zones.     

Chemical composition of stars in the galactic halo

The chemical compositions of the atmospheres of six metal-poor stars are analyzed. Spectra with signal-to-noise ratios of no less than 100 and a resolution of R≈17 000 were obtained using the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The abundances of Li, O, α-process elements (Mg, Si, Ca, Ti), Na, K, Sc, iron-peak elements (Cr, Mn, Fe, Ni, Cu, Zn), and s-process elements (Y, Ba) are derived. The star G251-54 ([Fe/H]=?1.55, T _eff=5541 K, logg=3.58) is deficient in some elements compared to both stars with similar metallicities and the Sun. The atmosphere of G251-54 has the following elemental abundances relative to iron: [O/Fe]=+0.47, [α/Fe]≈?0.3, [Na/Fe]=?0.60, [Sc/Fe]=?0.57, [Cr, Ni, Fe]≈0, [Zn/Fe]=+0.16, [Cu/Fe]=?0.66, [Y/Fe]=?0.70, and [Ba/Fe]=?1.35. The remaining five stars have metallicities in the range ?1.6<[Fe/H]相似文献   

Facies Associations of Riphean Sedimentary Sequences

Large-scale facies associations typical of intra- and pericratonic Riphean sections of the Volga–Ural region, western slope of the Urals, Timan–Pechora region, Kola Peninsula, outer and inner parts of the Siberian, North American, and Indian platforms are considered. The reconstruction of their lateral and vertical relationships makes it possible to reconstruct principal trends in the evolution of late Precambrian sedimentary basins. Recommended special studies aimed at the restoration of spatial architecture of associations retained in fragments of Riphean sedimentary basins could yield a substantially new information on the basin filling. Such approach has important implications for estimation of the potential of late Precambrian sedimentary basins with respect to the exploration for mineral resources including hydrocarbons.     

Specific Compositional Features of Sediments from the Haakon Mosby Mud Volcano,Southwestern Barents Sea

The submarine Haakon Mosby mud volcano was studied in detail during several cruises, resulting in the collection of an abundant and diverse lithological material. Comprehensive field and laboratory studies made it possible to identify different types of sediments with specific granulometric and pelite fraction (<0.005 mm) compositions, as well as the regularity of their spatial distribution relative to various morphostructural zones of the mud volcano.     

Seismic Hazard for Selected Sites in Greece: A Bayesian Estimate of Seismic Peak Ground Acceleration

A procedure for estimating maximum values of seismic peak ground accelerationat the examined site and quantiles of its probabilistic distribution in a future timeinterval of a given length is considered. The input information for the method areseismic catalog and regression relation between peak seismic acceleration at a givenpoint and magnitude and distance from the site to epicenter (seismic attenuation law).The method is based on Bayesian approach, which simply accounts for influenceof uncertainties of seismic acceleration values. The main assumptions for the method are Poissonian character of seismic events flow and distribution law of Gutenberg-Richter's type. The method is applied to seismic hazard estimation in six selected sitesin Greece.