A world without Greenland: impacts on the Northern Hemisphere winter circulation in low- and high-resolution models

To investigate the effect of Greenlands orography on the northern hemisphere winter circulation experiments with an atmospheric GCM are conducted: a perturbed integration where standard orography is reduced to sea level in the Greenland area is compared to a standard orography control integration. The outcome of these experiments suggests that the existence of high mountains at Greenland causes a reinforcement of the stationary wave field in the Atlantic sector, colder temperatures to the west of Greenland and warmer temperatures to the east and south, over the North Atlantic. The impact on the flow field cannot be understood in the framework of standing Rossby waves, but it indicates a resonance between remotely forced stationary waves and local (thermo-) dynamics. The pattern of the North Atlantic Oscillation (NAO), in particular the northern centre, lies further to the east in the flat-Greenland experiment compared to the control run and the observations. Together with the fact that the climatological low-pressure system around Iceland hardly shifts, this suggests that the location of the NAO is not necessarily tied to the time mean pressure distributions. Considering the model resolution as a parameter, experiments with a high resolution (T106) suggest that the near-field changes are represented sufficiently by a T42 resolution, a standard resolution used in state-of-the-art coupled climate models. In contrast, far-field changes depend critically on model resolution. Hemispheric circulation and temperature changes differ substantially from low to high resolution, and generalized statements about the impact of Greenlands orography cannot be made.     

Photometric and spectrophotometric observations of the classical symbiotic star YY Her during its return to quiescence

We present new photometric UBVRI and spectroscopic observations of the symbiotic star YY Her during its return to quiescence after a strong outburst in 1993. High-resolution spectra of YY Her at similar phases at outburst maximum ?=0.48) and in quiescence ?=0.37) are presented for the first time. The ephemeris of YY Her has been refined P=586^d). The last two observed minima (in 1999 and 2000) differed radically in shape from the 1997 minimum described previously. Both were sharp and deep $(\Delta U \sim 1\mathop .\limits^m 6, \Delta V \sim 0\mathop .\limits^m 9)$ . To explain this shape of the V light curve, which is only slightly affected by nebular emission, it should be assumed that the cool component of YY Her fills much of its Roche lobe and has a hot spot on the hemisphere facing the hot component. The emission spectrum rich in Fe II lines, which is characteristic of symbiotic stars, was observed during the outburst, but high-ionization lines (He II λ4686) were also observed. The He I λλ5876, 7065 lines exhibit distinct P Cyg profiles; the centers of the absorption components are shifted from the emission ones by V _r≈100 km s^?1, suggesting moderate outflow velocities.     

High Acetone Concentrations throughout the 0–12 km Altitude Range over the Tropical Rainforest in Surinam

Airborne measurements of acetone were performed overthe tropical rainforest in Surinam(2°–7° N, 54°–58° W, 0–12 kmaltitude) during the LBA-CLAIRE campaign in March1998, using a novel proton transfer reaction massspectrometer (PTR-MS) that enables the on-linemonitoring of volatile organic compounds (VOC) with ahigher proton affinity than water. The measuredacetone volume mixing ratios ranged from 0.1 nmol/molup to 8 nmol/mol with an overall average of 2.6nmol/mol and a standard deviation of 1.0 nmol/mol. Theobserved altitude profile and correlations with CO,acetonitrile, propane and wind direction are discussedwith respect to potential acetone sources. No linearcorrelation between acetone and CO mixing ratios wasobserved, at variance with results of previousmeasurement campaigns. The mean acetone/CO ratio(0.022) was substantially higher than typical valuesfound before. The abundance of acetone appears to beinfluenced, but not dominated, by biomass burning,thus suggesting large emissions of acetone and/oracetone precursors, such as possibly 2-propanol, fromliving plants or decaying litter in the rainforest.     

The 1997/1998 mass mortality of corals: effects on fish communities on a Tanzanian coral reef

The abnormally high surface temperatures in the world's oceans during 1997/1998 resulted in widespread coral bleaching and subsequent coral mortality. An experiment was performed to study the effects of this coral mortality as well as the influence of the structural complexity on fish communities on a Tanzanian coral reef. Changes in fish communities were investigated on plots of transplanted corals after 88% of these corals had died. A distinct shift in fish community composition was found, although diversity was not affected. Fish abundance rose by 39% mostly due to an increase in herbivores, which seemed to benefit from enhanced algal growth on the dead corals. Fish abundance, species diversity and community composition were also strongly influenced by the structural complexity provided by the live and dead corals. This suggests that a coral reef can support abundant and diverse fish populations also after the corals have died as long as the reef structure is sustained.     

额济纳绿洲夏末典型晴天小气候特征分析

绿洲系统特有的地理地貌形成了绿洲特殊的小气候特征。利用额济纳绿洲2003年9月8～10日小气候观测资料，分析了绿洲柽柳林的小气候特征。在柽柳林内，地表和近地层大气温度有明显的日变化，日间地表给大气加热，大气温度呈超绝热递减率随高度递减；夜间大气给地表加热，大气为稳定层结。近地层空气湿度的日变化与温度相反。林内空气温度的垂直分布主要取决于冠层与地表吸收太阳辐射状况。在林冠顶层，白天以上升气流为主，夜间以下沉气流为主，绿洲荒漠环流效应已经不明显。绿洲上空大气浑浊度小，对太阳辐射的削减较少，绿洲具有很好的光资源背景。     

Petroleum inclusions and residual oils: constraints for deciphering petroleum migration

The analysis of petroleum inclusions (PI) in parallel to residual oils (=bitumens) provided specific constraints for petroleum migration processes in the Prague Basin. Whereas organic geochemical information from bitumens is limited due to alteration, additional high quality information was obtained from C_1–14-range compounds inside crystals. This was obtained by the application of a closed system for the decrepitation and thermal extraction of PI with subsequent gas chromatography (GC) and gas chromatography–mass spectrometry (GC–MS). The resulting data not only show pristine live oils, gases, residual and precipitated bitumens and a broad variation of mixtures of the groups above, but also show that gas migration and fractionation processes played a major role in the Prague Basin.     

Spectral features of RZ Psc, a cool star with Algol-like brightness minima

We have determined the physical (T _eff, logg, ζ) and kinematic (V _e sini,V _r ) parameters and abundances for 14 chemical elements in the atmosphere of the “antiflare” variable RZ Psc, using medium-resolution spectra obtained with the Coudé spectrographs of the 6-m telescope of the Special Astrophysical Observatory and the Crimean Astrophysical Observatory 2.6-m Shain telescope. The chemical composition of the star is characterized by a slight metal deficiency; however, the iron and calcium abundances are consistent with the solar values within the errors. We also detected a peculiar dip (depression) of the continuum level near the H_α line. Assuming that this depression and the photospheric H_α line have independent origins, we calculated the hydrogen abundance X in the atmosphere of RZ Psc. The resulting value X=0.70 (of the solar value) implies a relative deficiency of hydrogen. Together with the spatial location of the star, these properties provide evidence that RZ Psc is an evolved star, most likely belonging to population II.     

Early Variscan magmatism in the Western Carpathians: U–Pb zircon data from granitoids and orthogneisses of the Tatra Mountains (Slovakia)

This study presents the first U–Pb zircon data on granitoid basement rocks of the Tatra Mountains, part of the Western Carpathians (Slovakia). The Western Carpathians belong to the Alpine Carpathian belt and constitute the eastern continuation of the Variscides. The new age data thus provide important time constraints for the regional geology of the Carpathians as well as for their linkage to the Variscides. U–Pb single zircon analyses with vapour digestion and cathodoluminescence controlled dating (CLC-method) were obtained from two distinct granitoid suites of the Western Tatra Mountains. The resulting data indicate a Proterozoic crustal source for both rock suites. The igneous precursors of the orthogneisses (older granites) intruded in Lower Devonian (405 Ma) and were generated by partial melting of reworked crustal material during subduction realated processes. In the Upper Devonian (365 Ma), at the beginning of continent–continent collision, the older granites were affected by high-grade metamorphism including partial melting, which caused recrystallisation and new zircon growth. A continental collision was also responsible for the generation of the younger granites (350–360 Ma). The presented data suggest multi-stage granitoid magmatism in the Western Carpathians, related to a complex subduction and collision scenario during the Devonian and Carboniferous. Received: 19 February 1999 / Accepted: 3 December 1999     

Experimental generation of shock‐induced pseudotachylites along lithological interfaces

Abstract— To understand the mechanism of formation of shock‐induced pseudotachylites and particularly the role that rock heterogeneities and interfaces play in their formation, shock recovery experiments were carried out on samples consisting of two distinct lithologies (dunite and quartzite). It was possible to generate melt veins of 1–6 μm width along lithological interfaces at moderate shock pressures (6 to 34 GPa). The magnitudes of displacement along the interface, strain rate, and the kinetic heat production indicate that friction is an important heat source that largely contributes to the energy budget of the melt veins. The experimentally produced veins resemble natural S‐type pseudotachylites. The geometry of the veins depends on the orientation of the interface with respect to the shock front and includes strong variations in thickness, formation of melt pockets and injection veins, sudden changes in vein orientation, and sharp vein margins. Two types of melt were observed: vesicle‐free and vesicular melts. Dense vesicle‐free melt rock is likely to represent high‐pressure melts. Vesicular melts were also generated during shock compression, but they remained in a molten state during pressure release and continued shearing. Intermingling of comminuted olivine and melt suggests that ultracataclasis of olivine induced by a dynamic tensile failure is a precursor stage to frictional melting. Shock wave interferences at the lithological interface provide the necessary stress conditions to start dynamic failure of olivine. The composition of the frictional melts ranges from olivine‐normative to enstatite‐normative and is, thus, largely determined by olivine melting. The validity of the sequence of friction melting susceptibilities of rock‐forming minerals inferred from tectonically‐produced pseudotachylites is confirmed and can now be applied to ultra‐high strain rates during shock compression.