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通过定义一个能客观定量描述大气环流四维时空变化的风向改变指数WI,用以研究大气环流的时空演变规律和季节转换。在对纬向平均的WI做了经验正交函数(EOF)分析后,得到了其前四个模态。第一模态揭示的是全年平均的WI空间分布的基态。第二模态反映的是WI场的偏差中呈现准调和变化的部分,热带、副热带、温寒带季风区在该模态中均有明显体现。第三模态反映的是WI场的偏差中呈现非调和变化的部分,该部分揭示了因南北半球海陆分布的差异和因大气、海洋流体的非线性效应,其所造成的从春到秋与从秋到春的季节变化的不对称性以及平流层的二月突变现象。第四模态反映的是全球各层盛行风反向区域从春到夏的北进和从夏到秋南撤的现象。 相似文献
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In this paper, a Wind Direction Change Index (WI), which can describe four-dimensional spatiotemporal changes of the atmospheric circulation objectively and quantitatively, is defined to study its evolution and seasonal variation. The first four modes can be obtained by EOF expansion of the zonally averaged WI. The first mode reveals the basic spatial distribution of the annually averaged WI. The second mode reflects the quasi-harmonic parts of the WI deviations. Tropical, subtropical and extratropical monsoon areas can be clearly reflected by this mode. The third mode reflects the non-harmonic parts of the WI deviations. It shows the so-called February reverse in stratospheric atmosphere as well as the asymmetric seasonal changes from spring to fall and from fall to spring due to both the land-sea distribution contrast between the Northern and Southern Hemispheres and the nonlinear effect of atmospheric and ocean fluids. The fourth mode reveals the northward advancing of the global reversed wind fields from spring to summer and their southward withdrawal from summer to autumn. 相似文献
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Five large earthquakes shook southern Calabria in February–March 1783. We focused on the first shock (Me 6.9), which occurred on 5 February in the Gioia Tauro Plain. Most investigators attribute the event to a W-dipping, high-angle fault running at the base of the Aspromonte crystalline bedrock on the ESE side of the Plain (Aspromonte Fault). Other workers contend that the earthquake was generated by an E-dipping, low-angle blind fault (Gioia Tauro Fault) similar to the adjacent Messina Straits Fault. In 1999–2000 we carried out four geochemical surveys in the Gioia Tauro Plain with the aim of contributing to this debate with an independent line of evidence. We sampled 240 groundwater sites and measured a suite of in-situ physical and chemical parameters. Our goal was to gain new insight into the seismogenic source by identifying geochemical anomalies associated with the deepening of the hydrological circuits due to the presence of enhanced faulting/fracturing. The deep-fluid signatures are mainly represented by temperature, salinity, total carbon and radon anomalies. We identified three zones of dominant deep fluid discharge: the Nicotera-Galatro area (along the Nicotera-Galatro portion of the NW-trending Nicotera-Gioiosa Jonica lineament), a small NW-SE trending area between Gioia Tauro and Seminara, and the coastline between Rosarno and Palmi. This latter sector locates just above the upper edge of the hypothesised Gioia Tauro Fault. Most of the geochemical anomalies are recorded around Rosarno, at the intersection between the Gioia Tauro Fault and the Nicotera-Gioiosa Jonica lineament. In contrast, no evidence of groundwater deepening and active fracturing was found along the Aspromonte Fault. Based on our new findings we updated the concepts of Geochemically Active Fault Zone and Geochemical Interaction Fault Zone in view of the modern understanding of the hydro-mechanical properties of fault zones and the faulting mechanisms promoting fracture permeability in the crust. 相似文献
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首先介绍了2014年2月12日新疆于田MS7.3地震的区域构造背景与断裂活动情况;然后分析了此次MS7.3地震震中位置以及周边历史地震震源机制特征,认为2014年2月12日于田MS7.3地震发生在阿什库勒断裂东支上,2014年MS7.3地震和2008年MS7.3地震是阿尔金断裂带南端尾部向西南方向延伸,由左旋走滑为主逐渐转变为拉张作用过程中,在阿什库勒断裂带不同位置发生的2次地震,2次地震存在着相同的力源关系,2008年MS7.3地震对2014年MS7.3地震的发生有促进作用;最后利用分层地壳模型计算了2008年MS7.3地震对2014年MS7.3地震的库仑应力作用,结果同样显示2008年MS7.3地震促进了2014年MS7.3地震的发生。 相似文献
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2020年西藏改则3次5级以上地震总结 总被引：1，自引：1，他引：0
系统总结2020年2月—3月西藏改则3次5级以上地震发生前出现的地震活动性和地球物理观测异常，结果如下：①地震活动性：震前存在地震发生率异常；②地球物理观测：3次地震震中500 km范围内无观测台站分布，地球物理场观测能力较弱；③综合方法：识别出Wq值异常。3次改则地震均位于可可西里至唐古拉地区，其中2月21日5.0级地震位于羌塘地块北缘，而3月10日5.0级和3月12日5.1级地震位于羌塘地块南缘，且3月的2次地震相距约5 km，构成震群型序列。对3次5级以上地震序列的跟踪发现，2月21日改则5.0级地震序列主要分布在向阳湖—布若错断裂南侧发育的一条NNE走向的小断裂上，余震较少，震后40天内共发生8次ML 2.0以上地震，主震震源机制为张性破裂；3月10日5.0级和3月12日5.1级地震震源机制均为走滑型，余震序列丰富，主要分布在多条构造的延伸区域，计算得到序列h值为0.58，b值为0.88。综合分析认为，改则3次5级以上地震前地震活动异常较少，主要为具有中期意义的异常，综合方法的异常识别主要为后续强震的地点判定提供依据。 相似文献
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根据1961—2019年广东86个站点的降水和气温以及大气环流和海温资料,采用统计分析方法,研究广东2月降水和气温的时空分布特征及其相应的大气环流与海温特征。结果表明:近59年广东2月有两个年代际降水偏少时段,但对应的气温特征显著不同,分别是1961—1981年“冷干”和1999—2019年“暖干”,其对应的大气环流特征表明,第一时段1961—1981年（第二时段1999—2019年）500 hPa高度场以经向（纬向）环流为主,东亚大槽偏强（弱）,东亚冬季风偏强（弱）,低层受异常北（南）风控制,地面冷高压偏强（弱）,偏强的冷空气阻碍了来自海上的水汽输送（偏弱的冷空气不能南下至广东）,使得广东处于水汽辐散区（青藏高原表现为反气旋式环流,南支系统不活跃,对广东地区水汽输送不足）,最终导致广东2月低温少雨（高温少雨）。进一步的分析表明,热带东太平洋和北太平洋中部海温异常是影响广东2月降水的重要外强迫因子,其中第一时段1961—1981年（第二时段1999—2019年）是热带东太平洋（北太平洋中部）海温异常偏冷（暖）通过850 hPa经向风切变偏弱（北太平洋中部异常反气旋环流）来影响广东降水。热带印度洋全区一致型、西太平洋暖池区和北太平洋中部海温异常是影响广东2月气温的外强迫因子,其中前两者主要通过东亚大槽这一环流影响广东气温,而北太平洋中部海温仅影响“暖干”期下广东2月的气温。 相似文献
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J.-C. Thouret K. E. Abdurachman J.-L. Bourdier S. Bronto 《Bulletin of Volcanology》1998,59(7):460-480
In contrast to most twentieth-century eruptions of Kelud volcano (eastern Java), the 10 February 1990 plinian eruption was
not accompanied by lake-outburst lahars. However, at least 33 post-eruption lahars occurred between 15 February and 28 March
1990. They swept down 11 drainage systems and travelled as far as 24 km at an estimated mean peak velocity in the range of
4–11 m s–1. The deposits (volume ≥30 000 000 m3) were approximately 7 m thick 2 km from vent, and 3 m thick 10 km from vent, on the volcaniclastic apron surrounding the
volcano. Subtle but significant sedimentological differences in the deposits relate to four flow types: (a) Early, massive
deposits are coarse, poorly sorted, slightly cohesive, and commonly inversely graded. They are inferred to record hot lahars
that incorporated pumice and scoria from pyroclastic-flow deposits, probably by rapid remobilization of hot proximal pyroclastic
flow deposits by rainfall runoff. Sedimentary features, such as clasts subparallel to bedding and thick, reversely to ungraded
beds, suggest that these flows were laminar. (b) Abundant, very poorly sorted deposits include non-cohesive, clast-supported,
inversely graded beds and ungraded, finer-grained, and cohesive matrix-supported beds. These beds display layering and vertical
segregation/density stratification, suggesting unsteady properties of pulsing debris flows. They are interpreted as deposited
from segments of flow waves at a middle distance downstream that incorporated pre-eruption sediments. Sedimentological evidence
suggests unsteady flow properties during progressive aggradation. (c) Fine-grained, poorly sorted and ungraded deposits are
interpreted as recording late hyperconcentrated streamflows that formed in the waning stage of an overflow and transformed
downcurrent into streamflows. (d) Ungraded, crudely stratified deposits were emplaced by flows transitional between hyperconcentrated
flows and streamflows that traveled farther downvalley (as far as 27 km from the vent). At Kelud, the transformation of flow
and behavior occurs within only 10 km of the source, at the apex of the alluvial fans. The rapid change of flow behavior is
attributed to the low fines content and to the unsteady flow regime, which may be due to: (a) the rapid deposition of bedload,
owing to the break in channel gradient close to the vent and to changes in channel cross-section and roughness; and (b) the
very low silt+clay content in the non-cohesive deposits. These deposits mix with water to produce streamflows.
Received: 27 June 1997 / Accepted: 5 January 1998 相似文献
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为表彰一批在我国野外地勘一线工作中做出突出成绩 的 45 周岁以下的青年地质工作者,向中国地质学会成立百 年献礼,学会于 2022 年 2 月 22 日启动了第五届“野外青年 地质贡献奖---金罗盘奖”申报及推荐工作。 相似文献
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