Modelled variability of the sea surface circulation in the North-western Mediterranean Sea and in the Gulf of Lions

A chain of three nested models, based on the MARS 3D code, is used to simulate the North-western Mediterranean Sea circulation with a finest grid of 1.2 km resolution and 30 vertical sigma levels. This modelling system allows to resolve the coastal dynamics taking into account the influence of the general basin circulation. The aim of this study is to assess the ability of the nested MARS-3D models to reproduce most of the circulation features observed in the North-western Mediterranean Basin and in the Gulf of Lions. Comparisons of modelled sea surface temperature and salinity with MEDAR/MEDATLAS climatology and NOAA/AVHRR satellite measurements show that the model accurately reproduces the large and coastal scale variability. Over the Northern Basin, the seasonal changes of the cyclonic gyre extension are correctly simulated, even though in summer, the modelled temperature of the surface layer remains in basin-average 1°C cooler than the satellite measured temperature. As soon as the stratification erodes, modelled and observed temperatures become closer. Over the Gulf of Lions, realistic coastal responses are obtained under different wind conditions. Upwellings are correctly located and their intensity and spatial extension were here improved by the use of Aladin wind fields (10 km spatial resolution) and the introduction of a drag coefficient fitted according to the stability of the planetary boundary layer. The dispersion of fresh Rhone water discharge and the mesoscale circulation simulated by MARS-3D also agree with satellite measurements.     

青藏高原积雪深度对延伸期预报技巧的影响

高原积雪是重要的陆面因子,其变化的时间尺度长于大气而短于海洋。本文利用国家气候中心第二代月动力延伸期预测模式（DERF2.0）历史回报资料与被动微波资料（SMMR）、被动微波成像专用传感器（SSM/I）数据反演的逐日雪深资料,分析了1983~2014年冬季和春季转换季节高原积雪对热带外地区延伸期尺度预测技巧的影响。结果表明,高原积雪异常年动力模式在高原积雪显著影响的青藏高原地区、贝加尔湖地区和北太平洋地区预报技巧明显高于正常年份。随着预报时效的延长,高原积雪偏多年的技巧衰减最慢、其次为积雪偏少年,积雪正常年最快,表明高原积雪异常年可预报时效更长,且高原积雪异常对预报技巧的改善在第1候的预报中就显现出来,尤其是积雪偏多年,其影响时段明显要早于海洋。结果显示高原积雪对延伸期预报技巧有重要贡献,暗示高原积雪异常为东亚延伸期预报的潜在可预报源。     

SW物候模型在北京樱花始花期预测中的应用

基于海淀气象站1981—2012年逐日平均气温资料和2014年3月逐日平均气温滚动预报资料,应用SW物候模型,进行了2014年北京玉渊潭公园杭州早樱始花期的预测试验,取得了较好的效果。试验结果表明:应用SW模型预测2014年杭州早樱的始花期,提前10天预测的结果(始花期为3月27日)和自然条件下的实况值偏差为3~4天,提前一周左右预测的结果(始花期为3月25日)和自然条件下的实况值,偏差为1~2天。研究结果进一步验证了SW物候模型用于观赏植物观赏期预测的适用性较高,可进行更广泛的业务试用。     

坡顶加载时黏性土坡土钉加固前后的离心模型试验比较研究

为研究坡顶加载条件下黏性土坡的承载特性和变形规律,进行了素土坡和土钉加固土坡的加载离心模型试验。测量了土坡的承载和变形过程。通过对比两种土坡的承载特性和变性规律,土钉的加固作用体现在：限制了土坡向坡面方向的位移,使土坡的承载能力得到了明显提高;在加固土坡内形成的土钉影响区域改善了加载底板边缘处的薄弱程度;增大了土坡中上部土体的竖向压缩变形,减小了剪切变形,增强了土坡的稳定性。土坡上部土钉的加固效果随着坡顶荷载的增大而越明显;土坡中下部土与土钉的相互作用越靠近坡面越强     

Kimmeridgian (Late Jurassic) ostracods from Highway A16 (NW Switzerland): taxonomy, stratigraphy, ecology, and biogeography

Ostracods are a common microfaunal element of the Kimmeridgian of the Jura Mountains in NW Switzerland. The stratigraphical subdivision within the Kimmeridgian can as clearly be inferred from ostracods as it is the case from the ammonite biozonation. This proves the utiliy of the ostracod biozonation, especially where ammonites are not available or rare. The ostracod-bearing layers of the sequence under study (middle part of the Reuchenette Formation = Banné Member, Courtedoux Member and Lower Virgula Marls) have been deposited in waters with highly brackish to marine salinities (high in the pliohaline range to—predominanttly—brachyhaline according to the Venice System, Oertli 1964). From the base of the section (base of the Banné Member, high brachyhaline in average), salinities slowly decreased, with lowest salinities in the lower dinosaur track levels of Courtedoux Member (high pliohaline on average). They then increased again to higher salinities (high brachyhaline on average) above the upper dinosaur track levels of the Courtedoux Member and the Lower Virgula Marls (lowermost A. eudoxus Zone). These trends perfectly correlate with the increased occurence of ammonites above the upper dinosaur track levels. In terms of Kimmeridgian ostracod palaeobiogeography, the fauna of the NW Swiss Jura Mountains described in this work is most similar to the Aquitan and Paris Basins, a little less to Northern Germany, and even less (with not even half of the species in common) to Southern Germany. The NW Swiss Jura Mountains still belong to a largely boreally influenced “Western and Central European subprovince”, whereas Southern Germany (though located more to the north) was subjected to an enhanced tethyan influence.     

New biostratigraphical data for the Burdigalian Montchaibeux Member at the locality Courrendlin-Solé (Canton of Jura,Switzerland)

Geological surveys were carried out in the Miocene deposits at the place known as “En Solé” east of the village Courrendlin (Delémont Basin, Canton of Jura, Switzerland). This resulted in the discovery of new Miocene small mammal assemblages. The association of the rodents Megacricetodon aff. collongensis and Melissiodon sp. allows to biochronostratigraphically correlate for the first time the so-called “Rote Mergel des Mont Chaibeux” representing the lower part of the Montchaibeux Member of the Bois de Raube Formation to the regional M. collongensis–Keramidomys interval zone (MN 4; early Miocene).     

水位上升与荷载耦合作用下土坡稳定极限分析方法研究

边坡失稳产生的灾害不仅会给工农业生产带来巨大损失,也会对人民的生命财产安全造成巨大威胁。目前,滑坡灾害已与地震、火山并列成为全球3大地质灾害之一,其中由水库水位变化诱发的滑坡近来得到重视。因此,建立合理的边坡稳定性分析方法对预测以及防控滑坡灾害十分重要。实际中的边坡失稳过程往往在多种荷载因素的耦合作用下发生,但现有边坡极限分析等稳定性解析方法偏重于考虑单一荷载因素,难以合理考虑多类荷载耦合作用条件,缺乏对边坡稳定性依赖加载过程这一现象的合理解释。本文在极限分析原理的基础上,将水库区边坡所受荷载凝练为水位上升与坡顶加载的耦合作用。将水位荷载简化为水位线以下土体受到浮力以及黏聚力的减小,建立了一个土坡稳定性分析方法,编写了相应的数值计算程序,通过与离心模型试验结果进行对比验证了方法的有效性。该方法计算结果表明,边坡稳定性随坡顶荷载增加单调下降,而随水位上升表现出先降低后增加的非单调变化。因此,坡顶荷载与水位上升耦合加载过程中,边坡稳定性对于加载过程具有显著的依赖性。     

Mantle-driven geodynamo features – Effects of compositional and narrow D″ anomalies

Lower mantle heterogeneity could cause deviations from axial symmetry in geodynamo properties. Global tomography models are commonly used to infer the pattern of core–mantle boundary heat flux via a linear relation that corresponds to a purely thermal interpretation of lower mantle seismic anomalies, ignoring both non-thermal origins and non-resolved small scales. Here we study the possible impact on the geodynamo of narrow thermal anomalies in the base of the mantle, originating from either compositional heterogeneity or sharp margins of large-scale features. A heat flux boundary condition composed of a large-scale pattern and narrow ridges separating the large-scale positive and negative features is imposed on numerical dynamos. We find that hot ridges located to the west of a positive large-scale core–mantle boundary heat flux anomaly produce a time-average narrow elongated upwelling, a flow barrier at the top of the core and intensified low-latitudes magnetic flux patches. When the ridge is located to the east of a positive core–mantle boundary heat flux anomaly, the associated upwelling is weaker and the homogeneous dynamo westward drift leaks, precluding persistent intense low-latitudes magnetic flux patches. These signatures of the core–mantle boundary heat flux ridge are evident in the north–south component of the thermal wind balance. Based on the pattern of lower mantle seismic tomography (Masters et al., 2000), we hypothesize that hot narrow thermal ridges below central Asia and the Indian Ocean and below the American Pacific coast produce time-average fluid upwelling and a barrier for azimuthal flow at the top of the core. East of these ridges, below east Asia and Oceania and below the Americas, time-average intense geomagnetic flux patches are expected.     

离心场中土体图像采集与位移测量系统的研制与应用

以存储前移为主要思路,开发了离心场中高质量图像高速采集与位移非接触测量系统。该系统由图像采集、数据存储、通讯控制、分析处理和辅助制样5个子系统组成,能够克服高速旋转的离心场的干扰,在离心模型试验过程中高速采集高质量图像。该系统能够对多点同时进行测量,从而得到土体表面任意时刻、任意区域的位移场,并具有对土体无干扰、测量精度高、前期准备工作量小、自动化程度高等优点。使用该系统对土坡破坏离心模型试验中的土坡变形过程进行了测量,结果表明,土坡的破坏过程可分为均匀变形、应变局部化和破坏后变形3个阶段,加载过程中首先在坡顶和坡脚产生应变局部化。