Observations of extremely thin clouds in the tropical tropopause region by a ship based lidar.

During the cruises ANT XVII/4 (Punta Arenas Bremerhaven, 2000) and ANT XX1/1 (Bremerhaven - Cape Town, 2003) continuous measurements of clouds and aerosol have been performed by a Mobile Aerosol Raman Lidar (MARL). This system measures backscatter of light at 355 nm and 532 nm and is able to detect even extremely thin layers of particles in the atmosphere. Cloud base and top height, depolarisation optical depth and color index can be deduced from this data. During the Polarstern cruises very thin layers of ice particles have been observed frequently in the tropical tropopause layer (TTL). Cases of persistent cloud layers with an optical depth below 10^-3 are reported. Based on the data of radiosondes which were launched daily aboard the vessel, the conditions at which these type of clouds form are analysed. It is shown, that these clouds form in a layer below the cold point, but above the lapse rate tropopause. The relation between cloud occurrence and temperature and wind in the TTL as well as state of the QBO are discussed

Technical Note: VUV photodesorption rates from water ice in the 120-150 K temperature range - significance for Noctilucent Clouds

Laboratory studies have been carried out with the aim to improve our understanding of physicochemical processes which take place at the water ice/air interface initiated by solar irradiation with a wavelength of 121.6 nm. It was intended to mimic the processes of ice particles characteristic of Noctilucent Clouds (NLCs). The experimental set-up used includes a high-vacuum chamber, a gas handling system, a cryostat with temperature controller, an FTIR spectrometer, a vacuum ultraviolet hydrogen lamp, and a microwave generator. We report the first results of measurements of the absolute photodesorption rate (loss of substance due to the escape of photoproducts into gas phase) from thin (20–100 nm) water ice samples kept in the temperature range of 120–150 K. The obtained results show that a flow of photoproducts into the gas phase is considerably lower than presumed in the recent study by Murray and Plane (2005). The experiments indicate that almost all photoproducts remain in the solid phase, and the principal chemical reaction between them is the recombination reaction H + OH → H<sub>2</sub>O which is evidently very fast. This means that direct photolysis of mesospheric ice particles seems to have no significant impact on the gas phase chemistry of the upper mesosphere

Fluorescence from atmospheric aerosol detected by a lidar indicates biogenic particles in the stratosphere

International audienceWith a lidar system that was installed in Lindenberg/Germany, we observed in June 2003, an extended aerosol layer at 13 km altitude in the lowermost stratosphere. This layer created an inelastic backscatter signal which we interpret as laser induced fluorescence from aerosol particles. Also, we find evidence for inelastic scattering in a smoke plume from a forest fire that we observed in the troposphere. Fluorescence from ambient aerosol had not yet been considered detectable by lidar. However, organic compounds such as polycyclic aromatic hydrocarbons sticking to the aerosol particles, or bioaerosol such as bacteria, spores or pollen fluoresce when excited with UV-radiation in a way that is detectable by our lidar system. Therefore, we conclude that fluorescence from organic material released by biomass burning creates the inelastic backscatter signal that we measured with our instrument and thus demonstrate a new and powerful way to characterize aerosols by a remote sensing technique. The stratospheric aerosol layer that we have observed in Lindenberg for three consecutive days is likely to be a remnant from Siberian forest fire plumes lifted across the tropopause and transported around the globe

Recent Progress in Iridium-Catalyzed Enantioselective Hydrogenation: Tetrasubstituted Olefins and Polyenes

Iridium-catalyzed enantioselective hydrogenation has become the method of choice to convert prochiral unfunctionalized olefins to optically active compounds. Recently, we reported on applications giving access to more than one stereocenter in a single hydrogenation step. In this account we present recent developments in the hydrogenation of tetrasubstituted unfunctionalized olefins and isoprenoid polyenes, which allow the generation of two stereocenters in a single hydrogenation step

Cirrus clouds, contrails, and ice supersaturated regions: observations by lidar and radiosonde in Lindenberg/Germany

From April to October 2003 measurements have been performed with a mobile Aerosol Raman Lidar (MARL) at the Meteorological Observatory in Lindenberg(14.5 E, 52.5 N) . The aim of this extensive campaign was the investigation of tropospheric water vapour, cirrus clouds and contrails over a longer period of time. The lidar system detects aerosols and clouds in the troposphere and lower stratosphere. Cirrus clouds are detected by the large depolarisation of the backscattered laser beam. The lidar operates day and night, during daytime contrails may be identified with the help of a video camera. In the upper troposphere cirrus has been detected in 55% of the measured time. Radiosonde (Vaisala RS 80) data are available four times a day form the routine observational program at the site. They frequently detect ice supersaturatedregions (ISSR) in the upper troposphere. The comparison of the RS 80 andthe MARL data shows that the correlation between ISSR and the occurrence of cirrus and contrails is rather week. On the other hand there is a strong link between the occurrence of subvisual cirrus and contrails in the upper troposphere

NeoPHOX - a structurally tunable ligand system for asymmetric catalysis

A synthesis of new NeoPHOX ligands derived from serine or threonine has been developed. The central intermediate is a NeoPHOX derivative bearing a methoxycarbonyl group at the stereogenic center next to the oxazoline N atom. The addition of methylmagnesium chloride leads to a tertiary alcohol, which can be acylated or silylated to produce NeoPHOX ligands with different sterical demand. The new NeoPHOX ligands were tested in the iridium-catalyzed asymmetric hydrogenation and palladium-catalyzed allylic substitution. In both reactions high enantioselectivities were achieved, that were comparable to the enantioselectivities obtained with the up to now best NeoPHOX ligand derived from expensive tert-leucine

Bewegtes Schreiben : Das Entwickeln einer Fragestellung ist (k)ein Spaziergang

Viele Schriftsteller*innen sind begeisterte Spaziergänger*innen, diese Passion könnte auch für wissenschaftliches Schreiben produktiv eingesetzt werden. Wir wollen herausfinden, ob Gehen einen Effekt auf den Schreibprozess hat. Im Rahmen dieser empirischen qualitativen Forschung haben wir untersucht, wie Studierende das Einbinden von Gehen bei einer Schreibübung zum Entwickeln einer Forschungsfrage empfinden. Im schulischen Kontext wurde dazu bereits geforscht, doch wie sieht dies im studentischen Kontext aus? Wir haben eine Einheit im Rahmen des Schreibmentoring-Programms der Universität Wien entwickelt und durchgeführt. Die Einheit setzte sich aus einer theoretischen Einführung, einem Freewriting, einem Themen-Spaziergang und der Drei-Schritt-Methode zur Entwicklung einer Fragestellung zusammen. Um die Erfahrungen der Teilnehmenden festzuhalten, wurde eine Gruppendiskussion durchgeführt, die mit einer qualitativen Inhaltsanalyse ausgewertet wurde. Die Ergebnisse zeigen, dass das Einbinden eines Spaziergangs zwischen zwei Schreibübungen positiv wahrgenommen wurde. Eine Erkenntnis ist, dass der Themen-Spaziergang als Möglichkeit zur Weiterentwicklung der im Freewriting ausformulierten Gedanken diente und als Pause empfunden wurde