Primary vs. secondary curved fold axes: Deciphering the origin of the Aït Attab syncline (Moroccan High Atlas) using paleomagnetic data     

《Journal of Structural Geology》2015

The Aït Attab syncline, located in the Central High Atlas, displays a curved geometry in plan view, and is considered as one of the most spectacular fold shapes in the Central High Atlasic belt. We conducted a paleomagnetic study in Jurassic-Cretaceous red beds to investigate the origin of this geometry. The Natural Remanent Magnetization (NRM) is dominated by a secondary magnetization carried by haematite with unvarying normal polarity that has been dated at about 100 Ma. The regional fold test performed in both limbs of the syncline is positive and the paleomagnetic vectors (after tectonic correction) are parallel throughout the curvature, indicating a negative oroclinal bending test. These results are inconsistent with previous works that consider the bent geometry of this syncline to result from subsequent distortion of originally NE–SW trending structures by rotation about a vertical axis. We interpret the NRM data to demonstrate that the changing trend of the Aït Attab syncline is a primary feature, resulting from the influence of pre-existing, NE–SW and E-W-striking extensional faults that developed during a strike-slip regime. Paleomagnetic results also reveal that the tilting observed in the sampled red beds is post Albian, probably linked to the Cenozoic inversion of the High Atlasic belt.  相似文献   

1960～2018年中国高温热浪的线性趋势分析方法与变化趋势     

张嘉仪  钱诚 《气候与环境研究》2020,25(3):225-239

高温热浪直接影响人体健康和作物生长。研究全球变暖背景下我国高温热浪发生率的趋势是气候变化研究的基本问题之一,可为人们的生产生活等提供重要的科学信息。目前对于高温热浪趋势的研究大都使用最小二乘（Ordinary Least Squares,OLS）方法估计趋势,结合学生t检验判断趋势的统计显著性。本文审视了以往常用方法在研究我国高温热浪发生率的线性趋势时的适用性。首先,以2018年东北局部地区因当年高温日数异常多而形成离群值的例子展开,说明OLS方法估计趋势时对离群值非常敏感,造成虚假趋势。进一步,通过正态分布检验和自相关计算,发现1960~2018年中国至少有91.14%站点、90.06%格点的高温日数和92.18%站点、87.74%格点的热浪次数的序列不服从正态分布,而且多数存在自相关。采用一种不易受离群值影响并考虑自相关的非参数方法,本文对1960～2018年中国站点和格点、4个典型区域以及全国平均的高温日数和热浪次数的线性趋势做出了更为准确的估计。研究发现,高温日数显著增多的站点主要出现在华南和西北地区,热浪次数呈显著增多趋势的站点目前几乎仅限于华南地区和新疆的个别站点;区域平均而言,仅有华南区域和西北区域的高温日数和热浪次数是显著增多的,华北区域和东北区域趋势并不显著;全国平均的高温日数和热浪次数都是显著增多的。本文对高温热浪的趋势及其显著性估计、统计预测的方法选择上有重要参考价值。  相似文献   

气候系统模式FGOALS-s2对南半球气候的模拟和预估   总被引：1，自引：0，他引：1  

周天军  孙丹  薛峰 《大气科学》2013,37(2):499-517

针对参加“国际耦合模式比较计划”(CMIP5)的IAP/LASG气候系统模式FGOALS-s2,评估了其对南半球气候平均态的模拟能力,在此基础上,预估了未来不同“典型浓度路径”(RCPs)情景下南半球气候的变化特征.对20世纪历史气候模拟结果的分析表明,模式能够合理再现南半球大气环流气候态分布特征,包括6～8月平均(JJA)南半球双西风急流现象,只是模拟的北支急流偏弱、南支急流偏强.未来气候预估试验中,不同RCPs情景下南半球温度变化以增暖为主要特征,陆地增温大于海洋,只有南大西洋—印度洋海盆存在局部变冷.综合四种不同情景,未来随着温室气体浓度的增加,南半球中纬度高压带将显著加强,绕极低压带将加深.降水呈现出增多的特征,12月到来年2月平均(DJF)强于JJA,海洋强于陆地,只有南印度洋和南太平洋中部局部降水减少.未来不同RCPs情景下,马斯克林高压表现出先减弱后增强的特征,而澳大利亚高压则呈现出先增强后减弱的特征.南极涛动(AAO)的变化表现为:RCP2.6和RCP4.5情景下AAO都表现为先增强后减弱,RCP6.0和RCP8.5情景下都为一致的增强趋势,这主要与四种情景中模拟的未来温度变化结构不同有关.例如在RCP6.0和RCP8.5情景下,南半球高纬高层温度增暖趋势小于中纬地区,使得经向温度梯度增大,中纬度西风加强,60°S以南位势高度减小,最终令AAO增强.  相似文献   

吉林省主汛期典型多雨年和少雨年成因对比分析     

纪玲玲  杨雪艳  张婷  姜红霞  马树庆 《气象与环境学报》2013,29(3):42-47

将1951-2011年吉林省主汛期降水量排名的前、后6位分别定义为多、少雨年,利用NCEP（2.5°×2.5°）再分析资料计算主汛期平均高度场、温度场、风场及比湿、涡度等物理量场;根据天气学原理和常规天气预报经验,对比分析主汛期典型多雨与少雨天气系统结构形态、分布位置、中心强度等特征。结果表明：500 hPa多雨年568等高线较少雨年平均偏南3个纬度,副热带高压588等高线较少雨年平均偏西7个经度偏北1个纬度;低层辐合高层辐散是多雨年的重要特征;850 hPa和700 hPa平均水汽含量多雨年明显多于少雨年;典型多雨年850 hPa风场贝加尔湖附近为单辐合中心,少雨年为双辐合中心。  相似文献   

大气对地球自转参数（ERP）的高频激发   总被引：4，自引：0，他引：4  

谢伯全  郑大伟 《天文学报》1996,37(2):113-123

本文采用１９８３—１９９２年期间由空间大地测量技术观测和归算的地球自转参数（ＥＲＰ）序列，以及由全球气象资料归算的大气角动量（ＡＡＭ）序列，分析和研究了大气对地球自转参数的日长变化（ＬＯＤ）和极移（ｘ和ｙ）在一个月时间尺度以内的高频激发作用，得到的主要结果如下：１大气对ＬＯＤ分量高频潮汐的估计值存在着影响，但是，潮汐形变参数ｋ／ｃ随时间和频率的变化却是受非大气因素的扰动引起的．２．大气可以解释３０天以下ＬＯＤ非潮汐的大部分变化．３．极移分量３０天以内的高频变化也主要由大气激发．ｘ分量与大气的相关性要强于ｙ分量，而且更为稳定，主要表现为平均时间尺度约为２７天的波动，大气对这个波动的贡献可达７０％．  相似文献   

东风盐场卤水中可溶性糖的研究Ⅱ、盐田卤水中可溶性糖的来源、消耗及其调控方法初探     

宫相忠  高尚德  李永祺 《海洋湖沼通报》1997,(3)

本文研究了东风盐场不同盐度的卤水中可溶性糖的变化及其与微藻优势种的组成和细胞数量之间的关系，卤虫对可溶性糖的调节作用及嗜盐菌对可溶性糖的消耗。结果表明，可溶性糖在低卤区和硅藻、甲藻等微藻密切相关，在中、高卤区与蓝藻和盐藻等密切相关，卤水中的卤虫能通过滤食微藻而有效地控制卤水中可溶性糖的浓度，在结晶卤水中接种嗜盐菌能有效地降解卤水中的可溶性糖，从而达到提高盐质的目的。  相似文献   

Future goals for imaging     

A. J. Dean 《Experimental Astronomy》1995,6(4):77-84

The demands imposed on the imaging system of an astronomical gamma-ray telescope are numerous; it must identify and resolve individual point sources, often in crowded regions of the sky; extended emission structures must be measured on angular dimensions which can extend up to the size scale of the Galactic plane; it must achieve these goals with high sensitivity for both the wide band continuum radiation as well a for discrete spectral line emissions, and ideally have as large a field of view as possible to enhance the probability of registering the unpredictable transient events which pervade the high energy sky. True imaging systems are currently under development for operation for energies up to about 100 keV, however the most practical tool for higher energies, for the time being, remains the coded mask. Some options are briefly reviewed.  相似文献   

Critical Approach to Methods of Glacier Reconstruction in High Asia and Discussion of the Probability of a Qinghai-Xizang （Tibetan） Inland Ice     

Matthias Kuhle 《山地科学学报》2007,4(2):91-124

This overview discusses old and new results as to the controversy on the past glacier extension in High Asia, which has been debated for 35 years now. This paper makes an attempt to come closer to a solution. H.v. Wissmann's interpretation (1959) of a small-scale glaciation contrasts with M. Kuhle's reconstruction (1974) of a large-scale glaciation with a 2.4 million km2 extended Qinghai-Xizang (Tibetan) inland glaciation and a Himalaya-Karakorum icestream network. Both opinions find support but also contradiction in the International and Chinese literature (Academia Sinica). The solution of this question is of supraregional importance because of the subtropical position of the concerned areas. In case of large albedo-intensive ice surfaces, a global cooling would be the energetical consequence and, furthermore, a breakdown of the summer monsoon. The current and interglacial heat-low above the very effective heating panel of the Qinghai-Xizang (Tibetan) Plateau exceeding 4000 m, which gives rise to this monsoon circulation, would be replaced by the cold-high of an inland ice. In addition, the plate-tectonically created Pleistocene history of the uplift of High Asia — should the occasion arise up to beyond the snowline (ELA) —would attain a paleoclimatically great, perhaps global importance. In case of a heavy superimposed ice load, the question would come up as to the glacio-isostatic interruption of this primary uplift. The production of the loesses sedimentated in NE-China and their very probable glacial genesis as well as an eustatic lowering of the sea-level by 5 to 7 m in the maximum case of glaciation are immediately tied up with the question of glaciation we want to discuss. Not the least, the problems of biotopes of the sanctuary-centres of flora and fauna, i.e., interglacial re-settlement, are also dependent on it. On the basis of this Quaternary- geomorphological-glaciological connection, future contributions are requested on the past glaciation, the current and glacial permafrost table and periglacial development, the history of uplift, and the development of Ice Age lakes and loess, but also on the development of vegetation and fauna in High Asia.  相似文献   

深层卤水自喷钻井若干特征的分析     

周训 《地球科学与环境学报》1992,(3)

本文以四川盆地中部的L_1井为例,讨论深层卤水自喷钻井卤水产出特征、水文地球化学特征和开采动态特征,并对钻井的测试资料进行分析,预测该钻井的卤水可采资源量。  相似文献   

长江三峡阶地的成因机制   总被引：15，自引：0，他引：15  

杨达源 《地理学报》1988,(2)

根据对长江三峡阶地堆积物进行的野外调查与室内分析发现三峡阶地的成因具有以下特点:构成阶地上部的河漫滩相堆积、中部的冲积砾石层与作为阶地基座的基岩平台是在不同时期形成的;阶地上部河漫滩相堆积是在中全新世气候温暖、长江三峡高水位条件下形成的.因此,长江三峡阶地是在构造上升的基础上由于气候及长江三峡流量及水位变化而形成的,并非一定是间歇性构造上升的标志.  相似文献