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M. Voiculescu C. Haldoupis D. Pancheva M. Ignat K. Schlegel S. Shalimov 《Annales Geophysicae》2000,18(9):1182-1196
Measurements of midlatitude E region coherent backscatter obtained during four summers with SESCAT, a 50 MHz Doppler system operating in Crete, Greece, and concurrent ionosonde recordings from the same ionospheric volume obtained with a CADI for one of these summers, are used to analyse the long-term variability in echo and Es occurrence. Echo and Es layer occurrences, computed in percent of time over a 12-h nighttime interval, take the form of time sequences. Linear power spectrum analysis shows that there are dominant spectral peaks in the range of 2–9 days, the most commonly observed periods appearing in two preferential bands, of 2–3 days and 4–7 days. No connection with geomagnetic activity was found. The characteristics of these periodicities compare well with similar properties of planetary waves, which suggests the possibility that planetary waves are responsible for the observed long-term periodicities. These findings indicate also a likely close relation between planetary wave (PW) activity and the well known but not well understood seasonal Es dependence. To test the PW postulation, we used simultaneous neutral wind data from the mesopause region around 95 km, measured from Collm, Germany. Direct comparison of the long-term periodicities in echo and Es layer occurrence with those in the neutral wind show some reasonable agreement. This new evidence, although not fully conclusive, is the first direct indication in favour of a planetary wave role on the unstable midlatitude E region ionosphere. Our results suggest that planetary waves observation is a viable option and a new element into the physics of midlatitude Es layers that needs to be considered and investigated. 相似文献
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Mirela G. Tulbure Dana M. Ghioca-Robrecht Carol A. Johnston Dennis F. Whigham 《Estuaries and Coasts》2012,35(5):1353-1359
Nonnative Phragmites is among the most invasive plants in the U.S. Atlantic coast tidal wetlands, whereas the native Phragmites has declined. Native and nonnative patches growing side by side provided an ideal setting for studying mechanisms that enable nonnative Phragmites to be a successful invader. We conducted an inventory followed by genetic analysis and compared differences in growth patterns and ventilation efficiency between adjacent native and nonnative Phragmites stands. Genetic analysis of 212 patches revealed that only 14 were native suggesting that very few native Phragmites populations existed in the study area. Shoot density decreased towards the periphery of native patches, but not in nonnative patches. Ventilation efficiency was 300?% higher per unit area for nonnative than native Phragmites, likely resulting in increased oxidation of the rhizosphere and invasive behavior of nonnative Phragmites. Management of nonnative Phragmites stands should include mechanisms that inhibit pressurized ventilation of shoots. 相似文献
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Mircea Voiculescu 《Natural Hazards》2009,51(3):459-475
Snow avalanches represent an undeniable reality in the Southern Carpathians both as a geomorphic process and as a type of
hazard. Before the 1990s, few researchers focused on avalanches in Romania. However, after 1990, avalanches became an increasingly
important topic of Romanian research including research on their management implications. This study focuses on the Făgăraş
massif, a representative mountain unit in the Southern Carpathians that is dominant due to its glacial and periglacial relief,
high altitudes and high occurrence of avalanche hazards. Three main research issues are considered. First, types of avalanches
are delineated along with affected areas of the Balea glacial valley (on the northern slope) and the Capra glacial valley
(on the southern slope) using data from a research centre for snow and avalanche monitoring that was created in the Balea
glacial cirque in 2003. Second, the impact of avalanches on human activities is considered including transportation use of
the Transfăgărăşan Highway that traverses the highest elevations in Romania and winter recreation activities such as skiing,
snowboarding, climbing and hiking. The impacts on forests are also considered. Third, the needs and gaps of avalanche management
are considered, specifically in the Făgăraş massif and also more generally in the mountains of Romania. 相似文献
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Horia Mitrofan Constantin Marin Florina Chitea Nicoleta Cadicheanu Ioan Povar&#x; Alin Tudorache Daniela Elena Ioni&#x;&#x; Mirela‐Adriana Anghelache 《地学学报》2021,33(1):56-73
Methane occurrences displaying signatures of a possible abiotic origin had previously been reported in the South‐West Carpathians (Romania). Such an accumulation, at Tisovi?a, was intercepted by a well drilled in an ophiolitic rocks massif, whereas in two other localities—situated tens of kilometres faraway—the concerned methane is released via thermal groundwater outflows that are apparently not associated with any ultramafic products. By using groundwater ionic compositions, corroborated with previously published isotopic (13C‐CH4, 2H‐CH4, 3He/4He) and molecular gas analyses, we assessed in more detail the conjectured abiotic provenance of methane, and quantitatively investigated the hypothesis of a progressive mixing between two, abiotic and thermogenic, methane end‐members. The corresponding geofluids behaviour was modelled by hypothesizing a “concealed” ophiolite serpentinization setting (largely similar to that at Tisovi?a), whose abiotic methane production was “diverted” towards remote discharges at ground surface, via a ~20‐km‐long flowpath supposedly generated by recently operating extensional tectonics. 相似文献
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Mirela Suteanu 《Pure and Applied Geophysics》2015,172(7):1865-1878
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I.G. Usoskin M. Voiculescu G.A. Kovaltsov K. Mursula 《Journal of Atmospheric and Solar》2006,68(18):2164-2172
Studies of the relation between cosmic rays (CR) (solar activity) and atmospheric cloudiness are mostly based on the satellite ISCCP cloud data. However, doubts have been cast that these relations can be an artifact of instrumental effects, i.e., of the masking/obscuring low clouds by higher clouds in the satellite view. If this is the case, most of the earlier results based on ISCCP data would be devaluated. Here, we reanalyze the ISCCP cloud coverage data and its relation with the cosmic ray-induced ionization, and show that the correlation between low clouds and CR is affected by higher clouds in some geographical regions, but not everywhere. In turn, our results show that low clouds also may affect the relation of higher clouds with CR in some regions. Accordingly, correlation analysis can be performed only when the strong relation between clouds of different types is taken into account. In particular, studies based on global or latitudinal (zonally averaged) cloud data should be revised. 相似文献
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Mirela Slukan Altić 《The Cartographic journal》2013,50(4):305-317
In this paper, we present the results of an original research study that was based on the analysis of British charts of the Adriatic produced during and immediately after military operations undertaken by British forces and their allies against Napoleon in the Adriatic. We analyse the creation and production of British charts of the Adriatic from the first charting campaign of the Hydrographic Office of 1800–1801 to charts produced in the period of British rule over the island of Lissa of 1811–1815 to the first systematic hydrographic surveying of the Adriatic of 1817–1819 under the leadership of William Henry Smyth that resulted in the first hydrographic atlas and pilot book of the Adriatic. At the same time, the paper evaluates the British contribution to the creation of some of the first reliable nautical charts of the Adriatic and to the development of the nautical cartography of the Adriatic in general. 相似文献
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Ferri J Topić Popović N Což-Rakovac R Beer-Ljubić B Strunjak-Perović I Skeljo F Jadan M Petrić M Barišić J Simpraga M Stanić R 《Marine environmental research》2011,71(3):218-224
Floating fish farms attract a great number of wild fish species, changing their behaviour and physiology. The saddled bream, Oblada melanura, sampled from populations aggregated around the Adriatic fish farm and from natural/control populations, were analysed for differences in eleven blood biochemistry parameters and liver histomorphology. The levels of lactate dehydrogenase (LDH), alkaline phosphatase (ALKP) and urea (URE) in cage-associated saddled bream (428.00±SD 321.56 U/L, 86.13±SD 39.87 U/L and 0.05±SD 0.16 mmol/L, respectively) were significantly lower than those observed in the control specimens (1047.06±SD 505.56 U/L, 125.75±SD 34.70 U/L and 1.99±SD 0.73 mmol/L, respectively). In contrast to that, concentrations of aspartate aminotransferase (AST) in cage-associated fish (87.63±SD 132.34 U/L) were higher than values noted for the control population (6.55±SD 5.90 U/L). URE and AST presented the main variables contributing to the discrimination between two analysed populations. One-way ANOSIM based on the blood parameters showed significant difference between saddled bream that fed around cages and those from the remote waters (R=0.697; P < 0.01). Hepatocytes of cage-associated fish contained large cytoplasmatic clear spaces indicating excessive accumulation of fat in the hepatocyte cytoplasm. All observed differences can be attributed to contrasting feeding behaviour of sampled populations but basic nutritional differences between them should be quantified in the future. Moreover, further research is necessary to detect their impact on the health status of the fish. 相似文献
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