共查询到20条相似文献，搜索用时 31 毫秒
1.
利用连续小波分析和经验模态分解方法,对我国北方地区(33°～41°N,108°～115°E)1470 ～2002年每年夏季降水量指数的时间序列进行了周期成分分析,探索全球气候变暖下的该地区降水量的多尺度变化特征.小波分析表明,降水量指数的可能周期有2.57a,4.83a,10.65a,23.25a,48.56a,68.30a和105.90a的周期,在95％置信水平有统计意义的周期是2.57a和23.25a的周期.这些周期和自然因素导致的周期相联系,不仅包含了气候系统内部(平流层准2a振荡和厄尔尼诺/南方涛动)的非线性作用,还包含了气候系统外(主要是太阳活动)受强迫的周期变化,且二者在原始降水量中所在比重相当,共同反映了原始降水量的绝大部分变化.降水量不只是在百年尺度上受太阳活动的驱动,在数十年尺度上也受到太阳活动的影响.我国北方地区的夏季降水量指数和夏季温度指数同相位反相关,全球增温并没有明显地改变二者之间的反相关关系.近百年来全球变暖期间,夏季降水量出现明显的新特征:短周期成分(小于30a的周期)的振幅比以往要显著大,而长周期成分的振幅比以往要显著小,同时呈现降水量逐年减少的长期变化趋势. 相似文献
2.
Dhammika A. Tantrigoda M. M. P. M. Fernando 《Journal of the Geological Society of India》2013,82(4):430-434
Satellite free air gravity anomalies over the Indian ocean region 79°E–86°E, 2°S–8°S were obtained from the website http://topex.ucsd.edu and a contour map was compiled. Five profiles of the anomaly have been interpreted in terms of two-dimensional structures in the ocean. Thickness of sediments lying on the oceanic crust determined from the interpretation of gravity profiles were used to compile an isopach map of the region 79°E–86°E, 2°S–8°S. This map in combination with one of the isopach maps compiled by previous workers, provides information regarding the thickness of sediments up to 6° S. According to this map sediment thickness varies from ～600 m over the middle part of the region to ～800 m further south, indicating that thinning of sediments in the middle part of the region is only localized. Information provided by this gravity study may be useful in planning detailed seismological studies to delimit the outer edge of the continental margin of Sri Lanka, defined according to the United Nations Convention of the Law of the Sea (UNCLOS). 相似文献
3.
E. V. Sharkov K. N. Shatagin I. S. Krassivskaya I. V. Chernyshev N. S. Bortnikov A. V. Chistyakov N. V. Trubkin A. Yu. Kramchaninov 《Petrology》2008,16(4):335-352
Based on detailed petrological, geochemical, and isotope-geochemical study, fragments of fresh pillow lavas with chilled glass margins dredged at the Sierra-Leone test site in the axial MAR rift zone between 5° and 7°N correspond to MORB tholeiites, which are not primitive mantle melts but were differentiated in intermediate magmatic (intrusive) chambers. Small-scale geochemical and Sr-Nd isotope heterogeneities were established for the first time in the basalts and their glasses. It was shown that some samples show significant nonsystematic differences in the 87Sr/86Sr ratio between the basalts and their chilled glasses and less significant difference in ?Nd; higher Sr ratios can be observed both in the glasses and basalts of the same lava fragments. No significant correlation is observed between the isotope characteristics of the samples and their geochemistry; it was also shown that seawater did not affect the Sr and Nd isotope composition of the chilled glasses of the studied pillow lavas. It is suggested that such differences in isotope ratios are related to a small-scale heterogeneity of the melts owing to incomplete homogenization during their rapid ascent to the surface. The heterogeneity of the basaltic melts is explained by their partial contamination by the older plutonic rocks (especially gabbroids) of the lower oceanic crust, through which they ascended to the ocean floor surface. The wider scatter of the Sr isotopic ratios relative to Nd is related to the presence of xenocrysts of calcic plagioclase; correspondingly, the absence of a Nd mineral carrier in the rocks results in less distinct Nd isotope variations. It was shown that all of the studied basalts define a single trend along the mantle correlation array in the Sr-Nd isotope diagram. The causes of this phenomenon remain unclear. 相似文献
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To characterize the hydrothermal processes of East Pacific rise at 9o-10oN, sulfide mineral compositions, textural, and geochemical features of chimney ores were studied using ore microscope, scanning electron microscope, X-ray diffraction analysis, and electron microprobe techniques. Results show that there are three mineral assemblages for the hydrothermal chimney ores, namely: (i) anhydrite marcasite pyrite, (ii) pyrite sphalerite chalcopyrite, and (iii) chalcopyrite bornite digenite covellite. Mineral assemblages, zonational features, and geochemical characteristics of the ore minerals indicate that ore fluid temperature changed from low to high then to low with a maximum temperature up to 400 ℃. The chimney is a typical black smoker. The initial structure of the chimney was formed by the precipitation of anhydrites, and later the sulfides began to precipitate in the inner wall. 相似文献
6.
The results of 0.97, 2.3, 3.9, 7.7, 11.1, and 21.7 GHz observations of a complete sample of radio sources obtained on the RATAN-600 radio telescope are presented. The sample is comprised of sources from the 4.85-GHz MGB survey, and contains all sources at declinations 10°–12°30′ (J2000) with Galactic latitudes |b|>15° and flux densities S4.85>200 mJy. Optical identifications have been obtained for about 86% of the radio sources with flat spectra and 59% of those with steep spectra. The spectra of the flat-spectrum sources have been decomposed into extended and compact components. 相似文献
7.
Conditions of the formation of plagiogranite from the Markov trough,Mid-Atlantic Ridge, 5°52′-6°02′N
Aranovich L. Ya. Bortnikov N. S. Serebryakov N. S. Sharkov E. V. 《Doklady Earth Sciences》2010,434(1):1257-1262
Doklady Earth Sciences - 相似文献
8.
I. F. Gablina I. G. Dobretsova V. E. Beltenev A. D. Lyutkevich E. V. Narkevskii A. N. Gustaitis 《Doklady Earth Sciences》2012,442(2):163-167
Based on studies conducted on the 33rd cruise of the R/V Professor Logachev in 2010, a new type of sulfide mineralization of the mid-oceanic ridges has been established. It was formed in the present-day
organic sediments due to diffuse penetration of hydrothermal fluids that emanated along the fractures in basalts on the slopes
of the Mid-Atlantic Ridge. 相似文献
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The results of observations on the Large Phased Array of the Lebedev Physical Institute made as part of a survey of the northern sky at 102.5 MHz are reported. Survey source lists for the declination ranges 27.5°–33.5° and 67.5°–70.5° are given, together with their coordinates, flux densities, and identifications with 4C objects. In total, there are 920 sources with flux densities S 102.5≥3.0 Jy in the two zones, which cover 0.73 star. The observing and data-reduction methods are described, and the reliability and completeness of the catalog are estimated. 相似文献
11.
V. Yu. Rusakov V. V. Shilov B. N. Ryzhenko I. F. Gablina I. A. Roshchina T. G. Kuz’mina N. N. Kononkova I. G. Dobretsova 《Geochemistry International》2013,51(8):646-669
New material from eight columns recovered during Cruise 32 of the R/V Professor Logachev in 2009 was used to explore the lithological facies, biostratigraphy, mineralogy, and geochemistry of sediments from the northwestern (active) and eastern (inactive) hydrothermal vent fields of the Semenov cluster. Mineral types of sediments were distinguished, and a general scheme was proposed for the vertical structure of the hydrothermal-sedimentary sequence overlying massive sulfide ores. It was found that the ore-bearing sediments exhibit a vertical zoning in the distribution of mineral assemblages, which are controlled by oxygen activity. The mechanisms of the formation of atacamite, CuCl2 · 3Cu(OH)2, which is a widespread mineral in red iron-oxide bodies replacing sulfides (gossans), were evaluated. 相似文献
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A search for extended radio sources with peak flux densities higher than 10 Jy at 110.6 MHz has been carried out, and two giant radio-galaxy candidates found. Data from a 24-hour survey in an area spanning ～8° in declination were used for the search. 相似文献
14.
D. Bala Subrahamanyam Radhika Ramachandran S. Indira Rani S. Sijikumar T. J. Anurose Asish Kumar Ghosh 《Natural Hazards》2012,61(3):893-910
Accurate knowledge of different meteorological parameters over a launch site is very crucial for efficient management of satellite
launch operations. Local weather over the Indian satellite launch site located at Sriharikota High Altitude Range (SHAR: 13.72°N,
80.22°E) is very much dependent on the atmospheric circulation prevailing over the Bay of Bengal oceanic region and topography-induced
convective activities. With a view to providing severe weather threat prediction in terms of launch commit criteria (LCC),
two numerical atmospheric models namely high-resolution regional model (HRM) and advanced regional prediction system (ARPS)
are made operational over SHAR in a synoptic and mesoscale domain, respectively. In the present research article, two launch
campaigns through Polar Satellite Launch Vehicle (PSLV-C11 and PSLV-C12) when contrasting weather conditions prevailed over
the launch site are chosen for demonstration of potential of two models in providing location-specific short-to-medium-range
weather predictions meeting the needs of LCC. In the case of PSLV-C11 campaign, when the launch site underwent frequent thundershower-associated
rainfall, ARPS model–derived meteorological fields were effectively used in prediction of probability of the wet spells. On
the other hand, Bay of Bengal underwent severe cyclonic storm during PSLV-C12 campaign, and its formation was reasonable captured
through HRM simulations. It is concluded that a combination of HRM and ARPS provide reliable short-to-medium-range weather
prediction over SHAR, which has got profound importance in launch-related activities. 相似文献
15.
Photosynthetically available radiation (PAR; 400–700 nm, E m−2 d−1) is the fraction of the total solar energy (Mjoules m−2 d−1) that is used by organisms for photosynthesis and vision. We present a statistical summary of a 17-yr time series of PAR
data (1982–1998) collected near Chesapeake Bay as well as a second set of data on PAR and total solar energy gathered over
a shorter time span (1997–1998). The time series data (5,126 daily totals) varied between 1–67 E m−2 d−1 and were used to estimate the minimum and maximum values of PAR as a function of day of the year. In monthly frequency distributions
of the PAR data, three modes were observed corresponding to sunny, partly cloudy, and overcast days. The second set of PAR
and total solar energy data were used to examine the ratio of PAR to total solar energy, which was 2.04 E Mjoule−1 for PAR between 10 and 70 E m−2 d−1. On overcast days, the ratio increased to as high as 3 E Mjoule−1 as PAR increased in importance as a fraction of the total solar energy. These values were consistent with others in the literature,
and the relationships reported here can be used to predict the climatology of PAR and total solar energy within the Chesapeake
region. The PAR data were also combined with reported minimum values of PAR for net primary production in the surface mixed
layer of the water column of aquatic systems to estimate the combinations of mixed layer depth and diffuse attenuation coefficient
(number of optical depths) under which light limitation of phytoplankton primary production is expected to occur. 相似文献
16.
吉尔吉兹加盟共和国部长会议所属地质保矿管理局的地质勘探队1959年10月钻进90°—75°角的斜孔时,利用了由作者设计的金属轻便钻塔。 相似文献
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《地质科技情报》2016,(1)
为了深入了解西南印度洋中脊调查区表层沉积物的物质来源和沉积环境,对大洋第30航次在该区域获取的21个表层沉积物样品进行了物相鉴定和主量元素、微量元素及稀土元素含量测试,分析结果显示,样品可分为Si质沉积物和Ca质沉积物两类,其中Si质沉积物富含Si、Mg、Fe、Al,稀土元素含量特征、轻重稀土元素分馏特征,以及稀土元素的北美页岩归一化曲线均表明沉积物保留了N-MORB的特征,主要为基性岩、超基性岩的风化产物;而Ca质沉积物富Ca、LOI、Sr,稀土元素以及微量元素之间的分配均指示沉积物物源为生源主导;所有站位均显示了两类沉积物不同程度的混杂,表明物质来源具有一定的多样性,调查区总体为稳定的偏氧化环境。 相似文献
19.
Björn Lindberg Christian Berndt Jürgen Mienert 《International Journal of Earth Sciences》2007,96(1):201-213
This is the first in-depth study of a cluster of cold-water coral reefs, the Fugløy Reefs, found at 70°N on the Norwegian margin. Combining high-resolution seismic reflection data, side-scan sonar, video-images, and oceanographic measurements reveals the geologic, geomorphologic and oceanographic setting in which the reefs occur. The reefs consist mainly of the scleractinian ahermatypic Lophelia pertusa, and exist below the thermocline at water depths between 140 m and 190 m. The reefs appear as cone-shaped, acoustically transparent features on seismic reflection data, consistently located in places characterized by the availability of hard substrate, high relief, and periodical exposure to high tidal currents (>30 cm/s). These currents transport water of the Norwegian Atlantic Current to the reefs from an area with fluid expulsion-related pockmarks. The spatial relationship between reef, pockmark locations, and current directions suggests that seepage of biogenic gas might be a catalyst to reef growth. With a height of more than 40 m some of the Fugløy reefs are among the highest reported from the Norwegian Margin. This indicates highly favourable growth conditions, and conservative estimates indicate a net growth rate for the reefs of ~5 mm/year. We expect that cold-water reefs will be found further north along the Barents Sea margin as general awareness on the geophysical signature and appearance of the reefs increases, because all known factors involved in reef establishment and growth are within the required intervals also further north. 相似文献
20.
I. F. Gablina E. A. Popova T. A. Sadchikova T. A. Khusid N. S. Os’kina V. E. Bel’tenev V. V. Shilov 《Doklady Earth Sciences》2010,433(2):998-1002
For the first time detailed investigations of hydrothermal alterations on microbiota of ore-bearing sediments of the Ashadze-1
field (13° N, Mid-Atlantic Ridge) were carried out and local mineral-geochemical zoning was established. For the first time
for the region, enriching of Mg sediments related with hydrothermal activity was revealed. It was concluded that hydrotherms
affecting sediments are characterized with a high Mg content. 相似文献