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31.
Recent high-resolution observations from the Solar Dynamics Observatory (SDO) have reawakened interest in the old and fascinating phenomenon of solar tornado-like prominences. This class of prominences was first introduced by Pettit (Astrophys. J. 76, 9, 1932), who studied them over many years. Observations of tornado prominences similar to the ones seen by SDO had already been documented by Secchi (Le Soleil, 1877). High-resolution and high-cadence multiwavelength data obtained by SDO reveal that the tornado-like appearance of these prominences is mainly an illusion due to projection effects. We discuss two different cases where prominences on the limb might appear to have a tornado-like behavior. One case of apparent vortical motions in prominence spines and barbs arises from the (mostly) 2D counterstreaming plasma motion along the prominence spine and barbs together with oscillations along individual threads. The other case of apparent rotational motion is observed in a prominence cavity and results from the 3D plasma motion along the writhed magnetic fields inside and along the prominence cavity as seen projected on the limb. Thus, the “tornado” impression results either from counterstreaming and oscillations or from the projection on the plane of the sky of plasma motion along magnetic-field lines, rather than from a true vortical motion around an (apparent) vertical or horizontal axis. We discuss the link between tornado-like prominences, filament barbs, and photospheric vortices at their base. 相似文献
32.
Olga V. Sidorova Matthias Saurer Vladimir S. Myglan Anja Eichler Margit Schwikowski Aleksander V. Kirdyanov Marina V. Bryukhanova Oksana V. Gerasimova Ivan A. Kalugin Andrey V. Daryin Rolf T. W. Siegwolf 《Climate Dynamics》2012,38(1-2):175-188
For the first time we present a multi-proxy data set for the Russian Altai, consisting of Siberian larch tree-ring width (TRW), latewood density (MXD), δ13C and δ18O in cellulose chronologies obtained for the period 1779–2007 and cell wall thickness (CWT) for 1900–2008. All of these parameters agree well between each other in the high-frequency variability, while the low-frequency climate information shows systematic differences. The correlation analysis with temperature and precipitation data from the closest weather station and gridded data revealed that annual TRW, MXD, CWT, and δ13C data contain a strong summer temperature signal, while δ18O in cellulose represents a mixed summer and winter temperature and precipitation signal. The temperature and precipitation reconstructions from the Belukha ice core and Teletskoe lake sediments were used to investigate the correspondence of different independent proxies. Low frequency patterns in TRW and δ13C chronologies are consistent with temperature reconstructions from nearby Belukha ice core and Teletskoe lake sediments showing a pronounced warming trend in the last century. Their combination could be used for the regional temperature reconstruction. The long-term δ18O trend agrees with the precipitation reconstruction from the Teletskoe lake sediment indicating more humid conditions during the twentieth century. Therefore, these two proxies could be combined for the precipitation reconstruction. 相似文献
33.
Spatial and temporal variability of the frequency of extreme daily rainfall regime in the La Plata Basin during the 20th century 总被引:1,自引:1,他引:0
We analyzed trends, interdecadal variability, and the quantification of the changes in the frequency of daily rainfall for two thresholds: 0.1 mm and percentile 75th, using high quality daily series from 52 stations in the La Plata Basin (LPB). We observed increases in the annual frequencies in spatially coherent areas. This coherence was more marked in austral summer, autumn, and spring, during which the greatest increases occurred in southern Brazil, especially during extreme events. In winter, the low and middle basins of the Río Uruguay and Río Paraná showed negative trends, some of which were significant. Interdecadal variability is well defined in the region with more pronounced positive jumps west of the basin between 1950 and 2000. This variability was particularly more marked during periods of extreme rainfall in summer, autumn, and spring, unlike in winter when extreme daily rainfall in the lower Rio Paraná basin decreased by up to 60%. The changes in the past century during extreme rainfall produced modifications in the annual rainfall cycle. The annual cycle of both indices was broader during the last period which is mainly explained by the strong decreases in winter. 相似文献
34.
Elena D. Kireeva Olga B. Popovicheva Natalia M. Persiantseva Mikhail A. Timofeyev Natalia K. Shonija 《Journal of Atmospheric Chemistry》2009,64(2-3):129-147
Combustion-derived particles emitted by various transport engines are analyzed with respect to their morphology and composition. Soot particles collected behind an aircraft gas turbine engine combustor, in the diesel engine exhaust pipe, and at the end of ship pipe demonstrate heterogeneous morphological structures and different chemical identities. Individual particle analysis allows the characterization of emitted soot particles into three fractions, namely C-O, C-O-S, and Fe-C-O, with the dominant presence of chain soot agglomerates, irregular internally mixed soot, and particles of distinct morphology, respectively. The influence of oxygen and sulfur concentrations on the ability of soot to uptake water is proposed as a method for categorizing transport engine-generated particles. Categories of hydrophobic and hydrophilic particles within non-hygroscopic soots can be defined based on the amount of water uptake relative to several reference laboratory-made soots comparable to transport engine emissions. This method of characterizing hydrophobic/hydrophilic and hygroscopic soots in combustion emissions will help to determine the potential impacts of the combustion emissions on CCN/IN formation in the atmosphere. 相似文献
35.
Holger Steffen Olga Gitlein Heiner Denker Jürgen Müller Ludger Timmen 《Tectonophysics》2009,474(1-2):69
Fennoscandia is a key region for studying effects of glacial isostatic adjustment. The associated mass variations can be detected by the Gravity Recovery and Climate Experiment (GRACE) satellite mission, which observes the Earth's gravity field since April 2002, as well as by absolute gravimetry field campaigns. Since 2003, annual absolute gravity (AG) measurements have been performed in Fennoscandia by the Institut für Erdmessung (IfE, Institute of Geodesy) of the Leibniz Universität Hannover, Germany, within a multi-national cooperation. This offers a unique opportunity for validation and evaluation of the GRACE results. In this preliminary study, the GRACE results are compared to secular gravity changes based on the surveys from 2004 to 2007 with the FG5-220 gravimeter of the IfE.The results from GRACE monthly solutions provided by different analysis centres show temporal gravity variations in Fennoscandia. The included secular variations are in good agreement with former studies. The uplift centre is located west of the Bothnian Bay, the whole uplift area comprises Northern Europe. Nevertheless, the differences between the GRACE solutions are larger than expected and the different centre-specific processing techniques have a very strong effect on possible interpretations of GRACE results. The comparison of GRACE to the AG measurements reveals that the determined trends fit well with results from GRACE at selected stations, especially for the solution provided by the GFZ. Variations of land hydrology clearly influence results from GRACE and the AG measurements. 相似文献
36.
随着旅游活动的全球化,跨文化旅游者的消费行为成为学界关注的热点问题。本文以地处丝绸之路黄金节点的乌兹别克斯坦为案例地,通过深入调研,分析了不同文化类别国家的旅游者在乌兹别克斯坦的旅游行为和感知差异,并借用霍夫斯泰德的文化差异理论对其进行解释。研究发现:(1)乌兹别克入境旅游者普遍年龄比较大,受教育水平高,停留时间长,更愿意花钱,并想获得真正的深度体验,寻找真实性;(2)不同文化类别游客在旅游目的、旅行方式、停留时间、游览空间等方面具有不同特征;(3)西方游客以精神性体验为主,关注文化体验和建筑,并希望在旅途中找到快乐;俄罗斯游客以世俗体验为主,追求休闲和美食;亚洲游客则两者兼而有之,表现为重视与本族群的关系、景点的文化价值和关心服务质量。研究对于了解丝绸之路旅游者的消费特征,推动中乌旅游合作和丝绸之路旅游发展具有重要意义。 相似文献
37.
Leonhard Gantner Vera Maurer Norbert Kalthoff Olga Kiseleva 《Boundary-Layer Meteorology》2017,162(3):475-502
A method to simulate characteristics of wind speed in the boundary layer of tropical cyclones in an idealized manner is developed and evaluated. The method can be used in a single-column modelling set-up with a planetary boundary-layer parametrization, or within large-eddy simulations (LES). The key step is to include terms in the horizontal velocity equations representing advection and centrifugal acceleration in tropical cyclones that occurs on scales larger than the domain size. Compared to other recently developed methods, which require two input parameters (a reference wind speed, and radius from the centre of a tropical cyclone) this new method also requires a third input parameter: the radial gradient of reference wind speed. With the new method, simulated wind profiles are similar to composite profiles from dropsonde observations; in contrast, a classic Ekman-type method tends to overpredict inflow-layer depth and magnitude, and two recently developed methods for tropical cyclone environments tend to overpredict near-surface wind speed. When used in LES, the new technique produces vertical profiles of total turbulent stress and estimated eddy viscosity that are similar to values determined from low-level aircraft flights in tropical cyclones. Temporal spectra from LES produce an inertial subrange for frequencies \(\gtrsim \)0.1 Hz, but only when the horizontal grid spacing \(\lesssim \)20 m. 相似文献
38.
Nino MATESHVILI Giuli MATESHVILI Iuri MATESHVILI Lev GHEONDJIAN Olga AVSAJANISHVILI 《Meteoritics & planetary science》1999,34(6):969-973
Abstract— Photometric observations of the twilight sky were carried out during Leonids 1998. The obtained vertical distributions of aerosol between 20 and 140 km demonstrate the processes of the intrusion of fine meteor dust and its subsequent intra-atmospheric dynamics. The characteristic radii of two fractions of the meteor dust particles were estimated by their sedimentation velocities. They varied within rp = 0.006–0.06 μm and rp = 19–81 μm limits depending on an assumed particle density within ρp = 0.4–4.0 g cm?3. The assumption of ρp = 2.0 g cm?3 gave radii of the two fractions to be 0.01 and 30 μm, respectively. 相似文献
39.
We have investigated the frustule ultrastructure of Baikalian Aulacoseira: A.baicalensis (K.Meyer) Sim. and of thin-wall, spore-producing Aulacoseira which has long been designated as A. islandica (O.Muller) Sim. or A.islandica ssp. helvetica (O.Muller) Sim. (now A.skvortzowii Edlund, Stoermer,Taylor). It was found that the disagreement on the name of spore-forming Aulacoseira is due to the destruction of its vegetative frustules in the process of breaking free of the organic content, while ultrastructure data on A.islandica from different Russia''s regions can reflect signatures of different species.A. baicalensis is characterized by great polymorphism. A. baicalensis starts its development from the initial cell (auxospore). The morphological characteristics of the frustule undergo the drastic changes in the course of the life cycle. It sequentially changes the morphology and structure of its valves. Its cells evolve through several stages of development:from cyclotella-like cells to narrow and short reproducing cells. In the influence zone of the Baikalsky Pulp-and-Paper Plant (BPPP), waste waters, disturbances in the frustule structure both in vegetative and generative cells have been detected. 相似文献
40.
Upper Cambrian to Middle Ordovician radiolarian chert successions from Kazakhstan were studied to clarify the history of the emergence of benthic animals in ocean floor sediments. Radiolarian tests and clay were deposited for a period of 30 Myr without experiencing an influx of continent-derived coarse clastic materials. Red, grey and black cherts of the Upper Cambrian to the upper mid-Darriwilian are thinly laminated, and no trace of benthic animal activity is recognized in that time interval. Bioturbation structures and burrow traces in mid-Darriwilian stage red chert in Kazakhstan suggest that benthic animals colonized the location where radiolarian chert formed, but that there was a significant delay in colonization when compared with similar reported occurrences in Australia and Canada. 相似文献