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291.
Subramaniam S. Ravindra Babu Y. Rabindranath Bera Basheerullah Baig G. Viswanath P. V. Bajpai O. P. 《Journal of the Indian Society of Remote Sensing》2003,31(3):187-196
Journal of the Indian Society of Remote Sensing - A stationary, compact, spatially modulated Fourier Transform spectro-radiometer based on triangular, common path Sagnac interferometer has been... 相似文献
292.
A. Chakraborty H. C. Upadhyaya O. P. Sharma S. K. Deb 《Meteorology and Atmospheric Physics》2003,83(3-4):221-236
Summary ?A newly developed ocean general circulation model has been tested and verified with some idealized experiments. Generally
two types of idealized experiments have been done here. First types are called as “symmetric experiments” and second types
are called as “transport experiments”. The first types of experiment help to correct the model core and any deficiency from
boundary conditions. The second types of experiment are the type of validation experiment. In both the experiments there are
no continents, so in the first type of experiments where symmetric forcings are provided one can expect that model should
maintain the symmetric nature. In the second type of experiments one can expect that model should respond correctly to the
wind forcings, if no wind curl is present in the wind forcing there will be no circulation in the extratropics and if there
is no wind the equator there will be no circulation. The model reproduces the possible envisaged results of these experiments
and gives the confidence for performing the realistic integration.
Received February 20, 2002; accepted July 7, 2002
Published online: February 20, 2003 相似文献
293.
Vulnerability Assessment of the Maize and Sorghum Crops to Climate Change in Botswana 总被引:1,自引:0,他引:1
This study examines the sensitivity of maize and sorghum crops to global warming in Botswana, a country with arid climatic conditions and shortfalls in locally produced grain. The vulnerability of the maize and sorghum crops to climate change were studied using crop simulation models while climate change scenarios were generated from Global Circulation Models. Simulated yields indicated that rain-fed crop production under the observed climate was a small fraction of what could be produced under optimal conditions. The gap was attributed to both physical (especially lack of rain) and socio-economic constraints. Using the southern African core climate change scenario, simulated yields declined by 36% in the case of maize and 31% for sorghum in the sand veldt region. Yield reductions from thehard veldt region were in the order of 10% for both maize and sorghum. The growing season became shorter, the average reduction in days in the sand veldt region being 5 and 8 days for maize and sorghum respectively, and correspondingly, 3 and 4 days over the hard veldt region. The food security option currently followed in Botswana was found to be a good adaptive strategy under a changed climate. 相似文献
294.
S. Solberg T. Krognes F. Stordal OØ Hov H. J. Beine D. A. Jaffe K. C. Clemitshaw S. A. Penkett 《Journal of Atmospheric Chemistry》1997,28(1-3):209-225
Simultaneousindependent measurements of NOy and NOx(NOx= NO + NO2) by high-sensitivitychemiluminescence systems and of PAN (peroxyacetylnitrate) and PPN (peroxypropionyl nitrate) by GC-ECDwere made at Spitsbergen in the Norwegian Arcticduring the first half year of 1994. The average mixingratio of the sum of PAN and PPN (denoted PANs)increased from around 150 pptv in early winter to amaximum of around 500 pptv in late March, whereasepisodic peak values reached 800 pptv. This occurredsimultaneously with a maximum in ozone which increasedto 45–50 ppbv in March–April. The average NOxmixing ratio was 27 pptv and did not show any cyclethrough the period. The NOy mixing ratio showeda maximum in late March, while the difference betweenNOy and PAN decreased during spring. This is anindication of the dominance of PAN in the NOybudget in the Arctic, but possible changes in theefficiency of the NOy converter could alsocontribute to this. Although most PAN in theArctic is believed to be due to long range transport,the observations indicate local loss and formationrates of up to 1–2 pptv h-1 in April–May.Measurements of carbonyl compounds suggest thatacetaldehyde was the dominant, local precursor ofPAN.Now at 1. 相似文献
295.
296.
Late summer hypoxia (<3 ppm oxygen) in western Long Island Sound (WLIS) is a persistent environmental and management issue whose controlling processes are poorly understood. Measured rates of sediment and water-column oxygen consumption in the bottom water suggest that a condition of no oxygen should be attained on the time scale of 13–30 d. Observations, however, indicate the onset of hypoxia is of the order 150 d. Therefore, horizontal and/or vertical transport of oxygen into the area of hypoxia must play an important role. Hypoxia decreases benthic activity and the sediment flux of222Rn. The resulting horizontal gradient in bottom water222Rn was measured and used to estimate the effective horizontal transport rate (>5–50 m2 s?1), which is considerably slower than previous estimates. Scale analysis of the hypoxia process indicates that horizontal transport rates alone can explain the slow progression of hypoxia in XLIS but that vertical processes may also be capable of delaying the onset of hypoxia especially under conditions of weak stratification or weak intermediate layer oxygen consumption. This scale analysis indicates a delicately balanced process that is sensitive to both climatologically-driven variability in the rates of horizontal and vertical transport as well as the biologically-driven rates of oxygen consumption. An improved ability to predict and/or control hypoxia must be based on a better understanding of temporal and spacial variations in circulation, mixing, and stratification as well as the biological processes in the water column and the sediments. 相似文献
297.
Seismic facies and architecture of ice-contact submarine fans in high-relief fjords, Troms, Northern Norway 总被引:1,自引:0,他引:1
ASTRID LYSÅ TORE O. VORREN 《Boreas: An International Journal of Quaternary Research》1997,26(4):309-328
During the Late Weichselian, large marginal moraines were deposited in the Norwegian fjords. In Troms County these features are termed the Skarpnes and Tromsø-Lyngen moraines, respectively, and have been mapped from land into the marine environment where they were formed as ice-contact submarine fans. High-resolution seismic data from several fjords have been studied and reveal a typical sediment thickness of 150–320 m for these ice-contact systems. All of the ice-contact submarine fans were formed under similar climatic conditions, but display wide variation in geometry, architecture and seismic pattern. This variation is related to differences in sediment supply, the nature of the subsurface of the fan (e.g. position of thresholds), basin geometry and basin depth. Based on interpretation of the different seismic facies and the architecture of the fans, former ice-front positions have been suggested and a model has been presented for the formation of different types of ice-contact submarine fans dependent upon variation in local basin condition. 相似文献
298.
R. Melamed R.C. Villas Bas G.O. Gonalves E.C. Paiva 《Journal of Geochemical Exploration》1997,58(2-3)
Mercury accumulation in the food chain, as a consequence of gold recovery in Brazil, has been an issue of concern. Reactions of Hg in the environment are quite complex, and can involve various Hg chemical species. Laboratory experiments were carried out on Hg0 solubility, Hg complexation and sorption on river sediments from a gold mining region in Brazil. The reactivity and the mobility of Hg species were considered. Results indicate that methyl mercury is more mobile than ionic mercury, and that the presence of humic acid enhances drastically the solubility of Hg0. The soluble complex formed has a relatively lower interaction at the sediment/water interface and is more prone to spread through the aquatic environment. 相似文献
299.
Paul J. Lechler Jerry R. Miller Liang-Chi Hsu Mario O. Desilets 《Journal of Geochemical Exploration》1997,58(2-3)
The Carson River Superfund Site in west-central Nevada is an area of Hg-contaminated soil, sediment, water, air, and biola resulting from the amalgamation milling of Ag-Au ores of the Comstock lode worked approximately a century ago. In order to develop an understanding of the behavior, transport, and fate of Hg at this site, a technique was developed to estimate the proportions of total, elemental, exchangeable, organic, and sulfide Hg in soils, sediments, and tailings.Results of this analysis performed on active Carson River sediments indicate that Hg is selectively dissolved out of Hg-Au amalgam particles and subsequently adsorbed to fine-grained sediments which are then deposited in downstream, low-energy reaches of the Carson River and Labontan Reservoir. In the relatively more-reducing environment of the reservoir Hg appears to be converted, in large part, to relatively-insoluble HgS.The original elemental form of Hg released to the environment is the chemical form which is still dominant in most highly-contaminated soils, sediments, and tailings. Deeper, more-reducing soil horizons, however, appear to fix a significant portion of the Hg as HgS, analogous to the Lahontan Reservoir example described above. This fixation as HgS is documented to be largely limited to higher-sulfur areas where sulfide minerals from the Comstock ores increase the total sulfur concentrations of contaminated soils, sediments, and tailings. 相似文献
300.
John O. Solem Thyra Solem Kaare Aagaard Oddvar Hanssen 《Journal of Paleolimnology》1997,18(3):269-281
Invertebrate colonization of lakes following the uplift of land from the sea was studied in four lakes, currently situated between 39 and 24 m a.s.l., on the central Norwegian coast. The lakes were isolated from the sea between 9500 and 7700 years B.P. Animal and algal remains picked from core samples showed that the first colonizers preserved as fossils were usually members of the Chironomidae, Daphnidae/Chydoridae, Acarina, Porifera (Ephydatia mülleri and Spongilla lacustris), Bryozoa (Cristatella mucedo and Plumatella spp.) and Charophyta (Chara sp.). Of the chironomids, the genus Chironomus was present in the oldest lacustrine layers of all four lakes, but other genera recorded at the marine/lacustrine boundary were Dicrotendipes, Procladius (?), Einfeldia, Microtendipes, and Glyptotendipes. Remains of the caddis fly family Limnephilidae were also present in the earliest lacustrine sediments in Kvennavatnet and Kvernavatnet. The oldest invertebrate fauna is typical for mesotrophic lakes. However, chironomids and mites have been present in this area from at least about 10?500 years B.P. A diverse chironomid community was established between 300 and 800 years after isolation from the sea at Kvernavatnet on the island of Hitra, while only between 80 and 120 years passed before a comparably diverse community developed at Kvennavatnet on the mainland coast. A similar development of the invertebrate fauna occurred in Kvennavatnet, Kvernavatnet and Storkuvatnet. However, Litjvatnet deviates greatly from the ‘normal’ pattern because a tsunami disturbed the bottom sediments and fauna. The tsunami, a gigantic sea wave, was caused by a submarine slide from the Norwegian continental slope. It reached Litjvatnet, today located 24 m a.s.l., but was not traced in Storkuvatnet at 30 m a.s.l. This event happened about 7200 years B.P. 相似文献