A mid-winter, tropical extreme flood-producing storm in southern Israel: Synoptic scale analysis

Summary An exceptional rainstorm affected the Negev Desert, the southern part of Israel, during 20–23 December 1993 as a result of an active Red Sea trough (ARST). The latter refers to a low pressure trough that extends from eastern Africa northward, along the Red Sea, accompanied by an upper-level cyclonic system. Rainfall totals in certain parts exceeded December averages by a factor of 5. Major precipitating systems had a typical Meso-scale Convective System structure accompanied by showers, with peak intensities of 60–80mmh^–1, and by hail and flash floods, resulting in loss of life and heavy damage.The origin of rainfall systems and of the moisture at lower latitudes, as well as the type of precipitation involved, indicate its tropical nature. The timing of the storm around the winter solstice is unusual, since these tropical-like storms are most frequent in the region in October–November.Unusual synoptic circumstances explain the development and intensity of this storm and this exceptional timing. In contrast to the normal situation in December the mid-level subtropical high over the Sahara was replaced by a cyclone, while the persistent high over the Arabian Peninsula intensified. As a result, a southerly flow persisted over the Red Sea several days prior to the storm initiation and transported tropical moisture and heat northward. The ascending air motion observed along the Red Sea enhanced convection there, which transported lower-level moisture from the water surface and transported it to the surrounding regions. Finally, a moving upper-trough that approached the region from the west transported the tropical moisture further to the Negev and supplied the lifting that transformed this moisture and instability into heavy showers.     

极端天气下三峡库区土地利用对河流水质的多时空尺度影响

为探究极端天气下流域内水质对土地利用的响应关系,本研究基于不同空间尺度(1000 m河段缓冲区、500 m河岸带缓冲区及子流域)的土地利用指数以及旱季(2019年11月)、雨季-洪水期(2020年7月)和雨季-干旱期(2022年8月)的水质数据,探究流域内土地利用对水质的多时空尺度影响,从而得到保护流域水质和规划流域内土地利用格局的最佳时空尺度和对水质影响最显著的预测因子。研究表明:(1)流域水质受极端天气影响,降雨会增强水体的稀释能力,高温会加快水中微生物反应速率,具体表现为雨季-洪水期的水质较好,雨季-干旱期次之,旱季较差。(2)土地利用对水质指标的影响存在时空尺度效应,土地利用在子流域和旱季尺度下对河流水质影响最显著。(3)不同土地利用指数对流域水质影响存在差异,耕地、林地、斑块密度、最大斑块指数和边缘密度是影响水质指标最显著的解释变量。其中林地与多数水质指标具有负相关关系,建设用地、耕地、斑块密度与较多水质指标存在正相关关系。本研究结果为合理规划土地利用格局以及保护河流水质提供科学依据,对三峡库区环境可持续发展及生态保护具有一定意义。     

Subduction, collision and initiation of hominin dispersal

Subduction is the main driving force of plate tectonics controlling the physiography of the Earth. The northward subduction of the Sinai plate was interrupted during the Early Pleistocene when the Eratosthenes Seamount began to collide with the Cyprian arc. A series of synchronous structural deformations was triggered across the entire eastern Mediterranean, and local topography was drastically accentuation along the Levantine corridor – one of the main pathways of hominin dispersal out of Africa. However, the choice of this preferred pathway and timing of dispersal has not been resolved. Though causes for dispersal out of Africa are in debate, we show that the transition from subduction to collision in the eastern Mediterranean set the route.     

青藏粉土单向冻结冻胀率变化特性研究

开展了饱和青藏粉土在开放系统不同温度梯度条件下的单向冻结试验,对冻结过程中冻结深度和冻胀速率的发展变化过程进行了研究.结果表明：不同顶板温度下,土样均在25 h左右达到冻结稳定状态,之后冻结深度基本不再发生变化.土样冻结过程中,冻胀速率表现为快速减小、较小值保持稳定、快速增大、较大值保持稳定四个阶段.基于以上试验结果,对土样冻结过程中冻胀率的变化过程进行了研究,发现冻胀率随冻结深度的增加先减小后增加,冻胀率从减小变为增大的时刻就是冻结深度趋于稳定的时刻,而冻胀率快速增大的时刻为冻胀速率进入较大值保持阶段的时刻.冻胀率变化的内在机理为土样冻结过程中由冰透镜体分凝所导致的未冻区固结和已冻区冻胀共同作用的结果.     

冻土静力学室内试验研究进展

冻土力学是冻土工程学的理论基础,以解决冻土工程问题为归宿。冻土力学分为冻土静力学和冻土动力学两个方面,而冻土静力学是冻土力学的重要部分。为此,对常规冻土静力学室内试验的研究进展进行了总结,系统地阐述了其在冻土的强度特性、变形特性及理论模型等方面所取得的重要研究成果,并指出研究中存在的一些不足之处。最后结合冻土静力学研究的特点及实际冻土工程建设的需要,对冻土静力学研究的未来发展进行了展望。     

What feeds shelf-edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil

In southeastern Brazil, the Serra do Mar coastal mountain range blocks the sediment influx from arriving at a ca. 1,500 km long continental margin comprising Santos and Pelotas basins. Despite this deprivation, the margin accumulated a ca. 1 km thick sedimentary succession since the Mid-Miocene. Examination of seismic reflection and oceanographic data indicates that shelf-margin clinoform formation exhibits a regional variability, with major sigmoidal clinoforms developed in the transitional area between both basins. Laterally, poorly developed oblique clinoforms constitute isolated depocenters along the shelf margin. The continuous clinoform development in the transitional area is attributed to the major influence on sediment transport patterns of several ocean bottom currents flowing along the margin, such as the Brazil Coastal Current, the Brazil Current and the Intermediate Water Brazil Current. These currents erode, transport and distribute sediments across the shelf break and upper slope from distant sediment sources located either north or south of the study area. The progressive southward strengthening of the Brazil Current could be responsible for a major southward sediment redistribution from the northern Campos Basin, and/or for sediment entrainment from northward-induced transport by the Brazil Coastal Current, originally derived from the De la Plata Estuary. In the transition between Santos and Pelotas basins, the Intermediate Water Brazil Current splits forming the Santos Bifurcation, allowing for a continuous depositional process and clinoform generation. We suggest that ocean bottom currents may shape other shelf-edge ‘contouritic clinoforms’ in continental margins mainly constructed by along-strike sediment transport largely driven by long-term geostrophic currents.     

Decadal and long-term sea level variability in the tropical Indo-Pacific Ocean

In this study, we analysed decadal and long-term steric sea level variations over 1966–2007 period in the Indo-Pacific sector, using an ocean general circulation model forced by reanalysis winds. The simulated steric sea level compares favourably with sea level from satellite altimetry and tide gauges at interannual and decadal timescales. The amplitude of decadal sea level variability (up to ~5 cm standard deviation) is typically nearly half of the interannual variations (up to ~10 cm) and two to three times larger than long-term sea level variations (up to 2 cm). Zonal wind stress varies at decadal timescales in the western Pacific and in the southern Indian Ocean, with coherent signals in ERA-40 (from which the model forcing is derived), NCEP, twentieth century and WASWind products. Contrary to the variability at interannual timescale, for which there is a tendency of El Niño and Indian Ocean Dipole events to co-occur, decadal wind stress variations are relatively independent in the two basins. In the Pacific, those wind stress variations drive Ekman pumping on either side of the equator, and induce low frequency sea level variations in the western Pacific through planetary wave propagation. The equatorial signal from the western Pacific travels southward to the west Australian coast through equatorial and coastal wave guides. In the Indian Ocean, decadal zonal wind stress variations induce sea level fluctuations in the eastern equatorial Indian Ocean and the Bay of Bengal, through equatorial and coastal wave-guides. Wind stress curl in the southern Indian Ocean drives decadal variability in the south-western Indian Ocean through planetary waves. Decadal sea level variations in the south–western Indian Ocean, in the eastern equatorial Indian Ocean and in the Bay of Bengal are weakly correlated to variability in the Pacific Ocean. Even though the wind variability is coherent among various wind products at decadal timescales, they show a large contrast in long-term wind stress changes, suggesting that long-term sea level changes from forced ocean models need to be interpreted with caution.