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排序方式: 共有266条查询结果,搜索用时 15 毫秒
31.
32.
BO Husφy 《极地研究(英文版)》2002,13(1)
1 IntroductionAtlatitudesaround 80°Nandinthemesosphere /lowerthermosphere (MLT) ,therehavebeenfewmeasurementsofneutraldynamics.ArequirementwasseenforlongtermcontinualmonitoringandaVHFmeteorradarwasidentifiedasbeingamostsuitableinstrument.RadarsliketheEISCA… 相似文献
33.
Solar Physics - A curved filament in a decaying active region (AR&;nbsp;8329) was observed on 9 September 1998 with a combination of several instruments. The main data base is a 4-hour long time... 相似文献
34.
Lakes perched on hill-tops have very small catchments. Their water chemistry is largely influenced by the chemical composition of precipitation and by the underlying bedrock geology. They are ideal sites for testing the hypothesis that land-use and associated soil changes are a major cause of recent lake acidification. On this hypothesis, hill-top lakes in SW Norway are predicted not to show any recent lake acidification because, by their very nature, the chemistry of such lakes is little influenced by land-use or soil changes.Palaeolimnological analyses of diatoms and chrysophytes show that prior to ca. 1914 the two hill-top lakes investigated were naturally acid with reconstructed lake-pH values of at least 4.8–5.1. Since ca. 1914 lake pH values declined to ca. 4.5–4.7. These results contradict the land-use hypothesis. All the available palaeolimnological evidence (diatoms, chrysophytes, pollen, sediment geochemistry, carbonaceous particles) is consistent with the acid-deposition hypothesis.In the absence of any evidence to support the land-use hypothesis as a primary cause of recent lake acidification and in the light of several independent refutations, it is perhaps time to put the land-use hypothesis for recent lake acidification to rest. 相似文献
35.
36.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
37.
A novel downscaling approach of the ERA40 (ECMWF 40-years reanalysis) data set has been taken and results for comparison with
observations in Norway are shown. The method applies a nudging technique in a stretched global model, focused in the Norwegian
Sea (67°N, 5°W). The effective resolution is three times the one of the ERA40, equivalent to about 30 km grid spacing in the
area of focus. Longer waves (<T42) in the downscaled solution are nudged towards the ERA40 solution, and thus the large-scale
circulation is similar in the two data sets. The shorter waves are free to evolve, and produce high intensities of winds and
precipitation. The comparison to observations incorporate numerous station data points of (1) precipitation (#357), (2) temperature
(#98) and (3) wind (#10), and for the period 1961–1990, the downscaled data set shows large improvements over ERA40. The daily
precipitation shows considerable reduction in bias (from 50 to 11%), and twofold reduction at the 99.9 percentile (from −59
to −29%). The daily temperature showed a bias reduction of about a degree in most areas, and relative large RMSE reduction
(from 7.5 to 5.0°C except winter). The wind comparison showed a slight improvement in bias, and significant improvements in
RMSE. 相似文献
38.
Till Kuhlbrodt Stefan Rahmstorf Kirsten Zickfeld Frode Bendiksen Vikebø Svein Sundby Matthias Hofmann Peter Michael Link Alberte Bondeau Wolfgang Cramer Carlo Jaeger 《Climatic change》2009,96(4):489-537
This paper discusses the risks of a shutdown of the thermohaline circulation (THC) for the climate system, for ecosystems
in and around the North Atlantic as well as for fisheries and agriculture by way of an Integrated Assessment. The climate
model simulations are based on greenhouse gas scenarios for the 21st century and beyond. A shutdown of the THC, complete by
2150, is triggered if increased freshwater input from inland ice melt or enhanced runoff is assumed. The shutdown retards
the greenhouse gas-induced atmospheric warming trend in the Northern Hemisphere, but does not lead to a persistent net cooling.
Due to the simulated THC shutdown the sea level at the North Atlantic shores rises by up to 80 cm by 2150, in addition to
the global sea level rise. This could potentially be a serious impact that requires expensive coastal protection measures.
A reduction of marine net primary productivity is associated with the impacts of warming rather than a THC shutdown. Regional
shifts in the currents in the Nordic Seas could strongly deteriorate survival chances for cod larvae and juveniles. This could
lead to cod fisheries becoming unprofitable by the end of the 21st century. While regional socioeconomic impacts might be
large, damages would be probably small in relation to the respective gross national products. Terrestrial ecosystem productivity
is affected much more by the fertilization from the increasing CO2 concentration than by a THC shutdown. In addition, the level of warming in the 22nd to 24th century favours crop production
in northern Europe a lot, no matter whether the THC shuts down or not. CO2 emissions corridors aimed at limiting the risk of a THC breakdown to 10% or less are narrow, requiring departure from business-as-usual
in the next few decades. The uncertainty about THC risks is still high. This is seen in model analyses as well as in the experts’
views that were elicited. The overview of results presented here is the outcome of the Integrated Assessment project INTEGRATION. 相似文献
39.
Christian Wolf Alfonso Aragón-Salamanca Michael Balogh Marco Barden Eric F. Bell Meghan E. Gray Chien Y. Peng David Bacon Fabio D. Barazza Asmus Böhm John A. R. Caldwell Anna Gallazzi Boris Häußler Catherine Heymans Knud Jahnke Shardha Jogee Eelco van Kampen Kyle Lane Daniel H. McIntosh Klaus Meisenheimer Casey Papovich Sebastian F. Sánchez y Taylor Lutz Wisotzki Xianzhong Zheng 《Monthly notices of the Royal Astronomical Society》2009,393(4):1302-1323
We investigate the properties of optically passive spirals and dusty red galaxies in the A901/2 cluster complex at redshift ∼0.17 using rest-frame near-ultraviolet–optical spectral energy distributions, 24-μm infrared data and Hubble Space Telescope morphologies from the STAGES data set. The cluster sample is based on COMBO-17 redshifts with an rms precision of σ cz ≈ 2000 km s−1 . We find that 'dusty red galaxies' and 'optically passive spirals' in A901/2 are largely the same phenomenon, and that they form stars at a substantial rate, which is only four times lower than that in blue spirals at fixed mass. This star formation is more obscured than in blue galaxies and its optical signatures are weak. They appear predominantly in the stellar mass range of log M * /M⊙ =[10, 11] where they constitute over half of the star-forming galaxies in the cluster; they are thus a vital ingredient for understanding the overall picture of star formation quenching in clusters. We find that the mean specific star formation rate (SFR) of star-forming galaxies in the cluster is clearly lower than in the field, in contrast to the specific SFR properties of blue galaxies alone, which appear similar in cluster and field. Such a rich red spiral population is best explained if quenching is a slow process and morphological transformation is delayed even more. At log M * /M⊙ < 10 , such galaxies are rare, suggesting that their quenching is fast and accompanied by morphological change. We note that edge-on spirals play a minor role; despite being dust reddened they form only a small fraction of spirals independent of environment. 相似文献
40.
超声提取-固相萃取小柱净化-气相色谱法测定土壤中14种有机氯农药 总被引:7,自引:7,他引:0
对土壤中14种有机氯农药的超声提取技术和磺化、固相萃取小柱两种净化方法进行系统研究。结果表明,超声提取节省提取时间,提高分析效率;磺化法和固相萃取小柱法都有净化作用,但磺化法使样品中的艾氏剂、狄氏剂和异狄氏剂全部损失;固相萃取小柱净化当丙酮-正己烷淋洗液体积比为1∶9、淋洗液收集8 mL时回收率>90%,干扰最小。方法检出限为0.63~2.59μg/kg,精密度(RSD,n=7)为1.17%~14.66%,基体加标平均回收率为82.78%~106.94%。方法用于生态地球化学调查评价批量土壤样品的实际分析,检测结果满足评价工作需要。 相似文献