Physical conditions in the convective envelope of stars

Summary The mechanical flux originating in the convective envelope of stars is shown to depend critically by the treatment of convection. In particular, in the framework of the mixing-length theory, in passing from a mixing lengthl=H _P to a mixing lengthl=H the presence of mechanical fluxes shifts from being a marginal phenomenon to a dominant one.Possible implications concerning atmospheric microturbulence in Main Sequence stars, as so asA _p andA _m stars, several types of variables and mass loss are briefly discussed.

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Sommario Si mostra come il flusso cinetico originato negli inviluppi convettivi di una stella dipenda criticamente dalle assunzioni fatte nel trattamento della convezione superadiabatica. In particolare, sulla base della teoria della lunghezza di rimescolamento, a seconda che si assumal=H _P o l=H i flussi cinetici passano dall'essere un fenomeno marginale a contributi determinanti.E' discussa una serie di possibili implicazioni riguardanti la microturbolenza atmosferica in stelle di sequenza principale, le stelleA _p eA _m, diversi tipi di variabili e la perdita di massa in fase di gigante.

     

Petrogenesis of Cenezoic volcanic rocks from the Aegean island arc

The Aegean volcanic arc formed in response to northeasterly subduction of the Mediterranean sea floor beneath the Aegean Sea. The active arc lies over 250 km from the Hellenic Trench in a region which has suffered considerable extension and subsidence since the mid-Tertiary. Suites of samples from the different volcanic centres making up the arc have been studied geochemically in order to assess lateral variations and to constrain the contribution of crustal contamination and sediment subduction in their petrogenesis.Lavas from all the major volcanic centres exhibit typical calc-alkaline major-element characteristics, and show enrichment in light REE and LIL elements but low contents of HFS elements. The enrichment in light REE is greater in the eastern (Nisyros, Kos) and western (Milos, Poros, Methana, Aegina) sectors of the arc (Ce_n/Yb_n=4) than in the central Santorini sector (Ce_n/Yb_n=2). All lavas have significant negative Eu anomalies and many have slight negative Ce anomalies. Less coherence is observed in the abundances and ratios of the other LIL elements, compared with the REE, along the island chain.Whereas the effects of crystal fractionation are evident in the trace-element patterns of lavas from individual islands, and are particularly well marked for Santorini, it is clear that there are consistent differences in trace-element abundances and ratios in the lavas of the various islands which reflect compositional differences in the mantle source and/or in melting conditions. Lavas from the eastern and western sectors have much higher levels of Ba and Sr but relatively lower Th, K and Rb than those from Santorini. Although some geochemical features could be explained through involvement of a component of subducted sediment in the source regions of the volcanoes, other element abundances and ratios indicate that this component must be very small. Detailed consideration of the inter-island geochemical variations suggests a complex make-up of the underlying lithosphere, resulting from a long history of subduction. In the region of Santorini, where crustal stretching is greatest, the underlying asthenosphere may be involved in magma production.     

Influence of North Atlantic Oscillation on Moscow Climate Continentality

Izvestiya, Atmospheric and Oceanic Physics - The natural variability of regional climatic conditions poses certain difficulties in detecting global climate change at a local scale. The question...     

Atmospheric temperature sounding with the Fourier spectrometer

Preliminary results of a space experiment using the IKFS-2 infrared sounder (Meteor-M2 satellite) showed high-quality of measurements of spectra of the outgoing thermal radiation of the atmosphere–surface system and the adequacy of developed IR radiation atmospheric models in the 15-μm carbon gas absorption band used to recover the vertical profiles of the atmospheric temperature. Outgoing radiation spectra measured by IKFS-2 instruments make it possible to restore vertical temperature profiles with errors close to 1K in most of the 0–30 km high-altitude region, except for the lower troposphere and altitudes above 30 km, where these errors are close to 2–3K.     

Application of the coral health chart to determine bleaching status of <Emphasis Type="Italic">Acropora downingi</Emphasis> in a subtropical coral reef

The ‘Coral Health Chart’ has become a popular tool for monitoring coral bleaching worldwide. The scleractinian coral Acropora downingi (Wallace 1999) is highly vulnerable to temperature anomalies in the Persian Gulf. Our study tested the reliability of Coral Health Chart scores for the assessment of bleaching-related changes in the mitotic index (MI) and density of zooxanthellae cells in A. downingi in Qeshm Island, the Persian Gulf. The results revealed that, at least under severe conditions, it can be used as an effective proxy for detecting changes in the density of normal, transparent, or degraded zooxanthellae and MI. However, its ability to discern changes in pigment concentration and total zooxanthellae density should be viewed with some caution in the Gulf region, probably because the high levels of environmental variability in this region result in inherent variations in the characteristics of zooxanthellae among “healthy” looking corals.     

Estimation of physical efficiency of hail protection accounting for changes in hail climatology

Results are considered of study of climate global warming effects on hail climatology and on technique of estimation of physical efficiency of hail protection taking account of the region hail danger trend. It is found that during last 30 years, occurrence frequency of hail and the number of heavy hailstorms in the mountainous areas of the Northern Caucasus decreased, on average, by a factor of 1.5–2, and in the foothill areas increased by 15–20%. It is shown that efficiency of hail protection works should be estimated taking into account the hail danger trend for each region.     

An Intercomparison of Large-Eddy Simulations of the Stable Boundary Layer

Results are presented from the first intercomparison of large-eddy simulation (LES) models for the stable boundary layer (SBL), as part of the Global Energy and Water Cycle Experiment Atmospheric Boundary Layer Study initiative. A moderately stable case is used, based on Arctic observations. All models produce successful simulations, in as much as they generate resolved turbulence and reflect many of the results from local scaling theory and observations. Simulations performed at 1-m and 2-m resolution show only small changes in the mean profiles compared to coarser resolutions. Also, sensitivity to subgrid models for individual models highlights their importance in SBL simulation at moderate resolution (6.25 m). Stability functions are derived from the LES using typical mixing lengths used in numerical weather prediction (NWP) and climate models. The functions have smaller values than those used in NWP. There is also support for the use of K-profile similarity in parametrizations. Thus, the results provide improved understanding and motivate future developments of the parametrization of the SBL.     

评估空间—发生率—震级地震预测的基于似然的检验

区域地震似然模型(RELM)工作组的5年实验是设计用来比较预测加州及附近各纬度-经度-震级单元地震发生率的若干有希望的方法。这种预测模式被作为世界范围内其他地震可预测性试验的蓝本,因此考虑如何评估这种预测的性能是很重要的。最近采用的两个试验都基于给定预测情况下观测到的地震分布的概率,一个测试比较了空间-发生率-震级单元的观测值和预测值,另一个测试仅仅比较了预测的发生率和观测地震的数目。在本文中,我们讨论了目前关于发生率预测的微小的缺陷,我们建议采用另外两个测试分别进行空间-发生率-震级预测的空间和震级分量的预测。为了更好地说明问题,我们考虑了区域地震似然模型预测和进行区域地震似然模型实验的前半期观测到的地震分布。我们得出空间—发生率—震级预测好像是和观测地震的分布相一致,尽管空间预测和观测地震的空间分布是不一致的,我们建议这些新的测试应该被用于提供更详细的地震预测评估。我们也讨论了每个基于似然测试的统计学功效以及基于似然测试的结果的稳定性(相对于地震目录的不确定性)。     

Geological interpretation of a deep seismic‐reflection transect across the boundary between the Delamerian and Lachlan Orogens,in the vicinity of the Grampians,western Victoria

A deep seismic‐reflection transect in western Victoria was designed to provide insights into the structural relationship between the Lachlan and the Delamerian Orogens. Three seismic lines were acquired to provide images of the subsurface from west of the Grampians Range to east of the Stawell‐Ararat Fault Zone. The boundary between the Delamerian and Lachlan Orogens is now generally considered to be the Moyston Fault. In the vicinity of the seismic survey, this fault is intruded by a near‐surface granite, but at depth the fault dips to the east, confirming recent field mapping. East of the Moyston Fault, the uppermost crust is very weakly reflective, consisting of short, non‐continuous, west‐dipping reflections. These weak reflections represent rocks of the Lachlan Orogen and are typical of the reflective character seen on other seismic images from elsewhere in the Lachlan Orogen. Within the Lachlan Orogen, the Pleasant Creek Fault is also east dipping and approximately parallel to the Moyston Fault in the plane of the seismic section. Rocks of the Delamerian Orogen in the vicinity of the seismic line occur below surficial cover to the west of the Moyston Fault. Generally, the upper crust is only weakly reflective, but subhorizontal reflections at shallow depths (up to 3 km) represent the Grampians Group. The Escondida Fault appears to stop below the Grampians Group, and has an apparent gentle dip to the east. Farther east, the Golton and Mehuse Faults are also east dipping. The middle to lower crust below the Delamerian Orogen is strongly reflective, with several major antiformal structures in the middle crust. The Moho is a slightly undulating horizon at the base of the highly reflective middle to lower crust at 11–12 s TWT (approximately 35 km depth). Tectonically, the western margin of the Lachlan Orogen has been thrust over the Delamerian Orogen for a distance of at least 25 km, and possibly over 40 km.