The spatial structure of the dayside ionospheric trough     

S. E. Pryse  L. Kersley  M. J. Williams  I. K. Walker 《Annales Geophysicae》1998,16(10):1169-1179

Tomographic imaging provides a powerful technique for obtaining images of the spatial distribution of ionospheric electron density at polar latitudes. The method, which involves monitoring radio transmissions from the Navy Navigation Satellite System at a meridional chain of ground receivers, has particular potential for complementing temporal measurements by other observing techniques such as the EISCAT incoherent-scatter radar facility. Tomographic reconstructions are presented here from a two-week campaign in November 1995 that show large-scale structuring of the polar ionosphere. Measurements by the EISCAT radar confirm the authenticity of the technique and provide additional information of the plasma electron and ion temperatures. The dayside trough, persistently observed at high latitudes during a geomagnetically quiet period but migrating to lower latitudes with increasing activity, is discussed in relationship to the pattern of the polarcap convection.  相似文献   

The plain man's guide to plate tectonics     

E.R. Oxburgh 《Proceedings of the Geologists' Association. Geologists' Association》1974,85(3):299-357

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The Belt and Road: Geographical pattern and regional risks     

Wu  Shaohong  Liu  Lulu  Liu  Yanhua  Gao  Jiangbo  Dai  Erfu  Feng  Aiqing  Wang  Wentao 《地理学报(英文版)》2019,29(4):483-495

Journal of Geographical Sciences - Building the Belt and Road is initiatives of China to promote win-win international cooperation in the new era, aiming at green, health, intellect and peace and...  相似文献   

Relationship of Arctic sea ice and Northern Hemispheric 500 hPa Polar vortices     

References： 《极地研究(英文版)》2007,18(1):73-83

Using the NCEP/NCAR reanalysis monthly 500 hPa height data on a 2.5 latitude-longitude grid and 1°×1° sea ice data,the polar vortex area,intensity index and arctic sea ice area index are calculated respectively,and the meridional distribution,period variation and the abrupts in the long range trend are analyzed to study their relationship.The results show that the meridional distribution of sea ice and polar vortex h-ave distinctive difference,the relative positions of them are different in the eastern and western hemispheres,and exept they have periods of 4 months,quasi half year,quasi year,4-5 years and 10 years commonly,and each of them has its own respective variation as well.The sea ice area is decreasing apparently since 1980's,so is the polar vortex area,but their abrupt changge time are different totally.The area of sea ice and polar vortex has prominent positive correlation,but the relationship of sea ice intensity,polar vortex intensity,polar vortex area is complicated.  相似文献   

海洋科技在21世纪海上丝绸之路建设中的作用     

韩鹏  钱洪宝 《海洋技术学报》2015,34(3):122-124

21世纪海上丝绸之路建设在海洋经济活动、海上综合保障等方面对海洋科技领域提出了新命题。在分析我国海洋技术优势领域的基础上,围绕科技创新政策伙伴关系、培育创新品牌、推进海洋经济和产业发展等方面,深入阐述了海洋科技领域在21世纪海上丝绸之路建设中的支撑作用,同时提出具体工作思路。  相似文献   

基于傅里叶变换质谱的烃源岩成熟度评价方法及地质意义     

韩双彪  谢林丰  唐致远  李剑  王成善  Brian HORSFIELD 《地质学报》2023,97(5):1717-1721

<正>伴随非常规油气资源的勘探开发,油气资源开采的广度和深度进一步扩大,一定程度上缓解了我国油气供需矛盾、保障了我国能源安全,同时有力推动了能源结构战略转型。但同时也对能源地质研究工作提出了新的挑战。有机质成熟度是油气评价的重要参数之一,不同成熟阶段的有机质会对应产出不同成因、不同性质、不同质量的油气,如何准确评价沉积有机质成熟度是当前油气资源勘探开发工作的关键问题之一。前人在科研实践工作中从光学、化学、谱学等角度提出了适用条件各异的成熟度评价方法,在部分地质环境中获得了良好的应用效果,但已有的成熟度指标多受测定方法原理的制约导致其适用性不同程度受限(肖贤明等,2020),制约了油气资源的高质量勘探开发。  相似文献   

前期春季北太平洋海温异常与冬季北半球极涡的关系     

张婧雯  李栋梁  柳艳菊 《气象科学》2015,35(1):52-59

利用NCEP/NCAR再分析资料和NOAA海温资料,用EOF、相关分析等方法,分析了1960—2010年500 hPa和100 hPa等压面上北半球后冬(2月)极涡面积和前春(4月)北太平洋(20~60 °N,120 °E~120 °W)海表温度(SST)的变化特征,揭示了二者的时空联系。结果表明:近50 a来,(1)冬季北半球500 hPa和100 hPa极涡面积整体经历了先扩张后收缩的变化。春季北太平洋SST经历了先降低后升高的变化。其突变时间与500 hPa极涡面积的突变时间相近,均出现在1987年,且与后冬500 hPa大西洋欧洲大陆区(Ⅳ区)极涡面积相关更好。(2)春季北太平洋SST的EOF第一模态空间型表现为PDO,第二模态表现为三极子型,突变分别出现在1980s初期和中期。(3)北太平洋SST与500 hPa Ⅳ区极涡面积相关的空间分布表现为:当前期春季北太平洋中部海温异常偏高(低),南部和北部海温异常偏低(高),使得下一个冬季500 hPa Ⅳ区极涡面积的扩大(缩小),这种空间遥相关型对应着海温的第二模态。北太平洋海温异常以第一模态空间型居多,但是对后冬北半球极涡面积影响大的却是第二模态。(4)当前春北太平洋SST呈第二模态时,对应次年冬季中高纬度对流层温度"上冷下暖",极地东风和绕极西风环流加强,极涡面积偏大。  相似文献   

Preservation of layered paleodeposits in high-latitude pedestal craters on Mars     

Seth J. Kadish  James W. Head 《Icarus》2011,213(2):443-450

An outstanding question in Mars’ climate history is whether or not pedestal craters represent the armored remnants of ice-rich paleodeposits. We address this question using new high-resolution images; in a survey of several hundred high-latitude pedestal craters, we have identified 12 examples in which visible and/or topographically expressed layers are exposed on the marginal scarp of the pedestal. One example, located on the south polar layered deposits, preserves ice-rich layers that have otherwise been completely removed from the polar cap. These observations provide empirical evidence that the pedestal crater formation mechanism is capable of armoring and preserving ice-rich layered paleodeposits. Although layered exposures have not yet been observed in mid-latitude pedestal craters, high-latitude instances of discontinuous, partially covered layers suggest that layers can be readily concealed, likely through mantling and/or mass wasting processes along the marginal scarp. This interpretation is supported by the observation that high-latitude pedestals with exposed layers along their margins are, on average, taller than mid-latitude examples, and have larger, steeper marginal scarps, which may help to maintain layer exposures. These observations favor the interpretation that mid- to high-latitude pedestal craters represent the armored remnants of ice- and dust-rich paleodeposits, which occurred transiently due to changes in the climate regime. Preservation of fine-scale layering of ice and dust at these latitudes implies that the climate change did not involve regional melting conditions.  相似文献   

Thermal contraction crack polygons on Mars: A synthesis from HiRISE, Phoenix, and terrestrial analog studies     

Joseph S. Levy  David R. Marchant 《Icarus》2010,206(1):229-216

Thermal contraction crack polygons are complex landforms that have begun to be deciphered on Earth and Mars by the combined investigative efforts of geomorphology, environmental monitoring, physical models, paleoclimate reconstruction, and geochemistry. Thermal contraction crack polygons are excellent indicators of the current or past presence of ground ice, ranging in ice content from weakly cemented soils to debris-covered massive ice. Relative to larger topographic features, polygons may form rapidly, and reflect climate conditions at the time of formation—preserving climate information as relict landforms in the geological record. Polygon morphology and internal textural characteristics can be used to distinguish surfaces modified by the seasonal presence of a wet active layer or dry active layer, and to delimit subsurface ice conditions. Analysis of martian polygon morphology and distribution indicates that geologically-recent thermal contraction crack polygons on Mars form predominantly in an ice-rich latitude-dependent mantle, more likely composed of massive ice deposited by precipitation than by cyclical vapor diffusion into regolith. Regional and local heterogeneities in polygon morphology can be used to distinguish variations in ice content, deposition and modification history, and to assess microclimate variation on timescales of ka to Ma. Analyses of martian polygon morphology, guided by investigations of terrestrial analog thermal contraction crack polygons, strongly suggest the importance of excess ice in the formation and development of many martian thermal contraction crack polygons—implying the presence of an ice-rich substrate that was fractured during and subsequent to obliquity-driven depositional periods and continually modified by ongoing vapor equilibration processes.  相似文献   

Viscous liquid film flow on dune slopes of Mars     

Diedrich Möhlmann  Akos Kereszturi 《Icarus》2010,207(2):654-658

It is shown that viscous liquid film flow (VLF-flow) on the surfaces of slopes of martian dunes can be a low-temperature rheological phenomenon active today on high latitudes. A quantitative model indicates that the VLF-flows are consistent with the flow of liquid brines similar to that observed by imaging at the Phoenix landing site. VLF-flows depend on the viscosity, dynamics, and energetics of temporary darkened liquid brines. The darkening of the flowing brine is possibly, at least partially, attributed to non-volatile ingredients of the liquid brines. Evidence of previous VLF-flows can also be seen on the dunes, suggesting that it is an ongoing process that also occurred in the recent past.  相似文献