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本文根据多年的天气图、卫星云图以及1980～1990年的NCEP再分析资料,通过统计分析和合成分析等方法建立了能够在南印度洋特定海区引起12m/s以上大风天气的高纬低压系统概念模型,并对主要的南印度洋西部副高型、南印度洋倒"品"字型作了详细的阐述。该天气概念模型主要发生在南半球的冬、春季。(1)南印度洋西部副高天气过程多由高纬度低压系统发展引起。在这一过程中,副高与高纬低压系统由纬向型向经向型转变,海平面气压槽和850hPa高度槽受到槽后冷平流的驱动不断向东北方向移动,并扫过南印度洋东部。(2)南印度洋倒"品"字天气模型中,低压槽受斜压系统的驱动东移并发展加深,与南印度洋东部的副高中心之间形成大风带。该天气概念模型的建立对南印度洋海区大风的预报可起到一定指导作用。 相似文献
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一、前 言 1988年7月16日～18日,出现了一次河套气旋进入渤海的天气过程。这次锋面气旋的形成主要是因为蒙古气旋向东南方向移动,移到河套地区的锋面扰动加强,并在河套地区形成新的锋面气旋。该气旋在发展和移动过程中,伴有强烈的降水、雷暴、大风等恶劣天气,受其影响,华北部分地区出现降水天气,渤、黄海北部出现了6～7级偏东大风,秦皇岛海区出现了波高达2.1m的中浪和风暴潮。本文利用传真图分析了此次过程及其对秦皇岛海区的影响。 二、气旋的发生、发展及移动情况 1.气旋形成的天气形势 16日08时500hPa高空图上,中西伯利亚地区有一低槽,并有冷气团与之配合。中纬度地区西风环流势力较强,自蒙古到渤海一带有一低槽,也有冷气团配合（见图1）。 相似文献
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浙江沿海大风的天气气候概况 总被引：5，自引：0，他引：5
用嵊泗站和大陈站资料对浙江省沿海大风的天气气候概况进行分析,结果表明浙北沿海平均每3d有1d出现大风,多于浙中南沿海(平均每7d有2d出现大风).浙北沿海以SSW大风最多,N大风次之;其中NNW—NE大风占46%,SSE—SW大风占43%;浙中南沿海以NNE大风最多,NE大风次之;其中N—ENE大风占77%,S—WSW占18%.浙北沿海大风以4月份最多,9月份最少;浙中南沿海大风以1月份最多,5月份最少;浙北沿海大风日数的月变化比浙中南小.浙江沿海大风的季风特征明显.浙江沿海冬半年大风多为冷空气大风,春季及初夏大风多为低压、倒槽引起,夏季大风主要是受热带气旋影响产生. 相似文献
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本文论述了青岛沿海主要灾害性天气暴雨、大风和形成暴雨、大风的各种天气系统。青岛沿海暴雨强度的分布由南向北递减,该区暴雨多起于7月上旬止于8月下旬。暴雨中心在青岛以南,其特点是:暴雨开始早、结束晚、暴雨次数多,强度也大。影响本区暴雨的主要天气系统有:气旋、冷锋、台风、高压后部、静止锋和暖切变。大风是该区最常见的一种重要的灾害性天气,它对渔业、养殖、港工建筑及海上交通运输影响很大。本区大风的分布特点是:由海岛向陆地风力逐渐减小。全年以北向大风日数为多,尤以冬季最盛,南向大风主要出现在春季.引起本区域大风的天气系统主要有寒潮(冷锋)、蒙古(东北)低压、气旋、台风及雷雨。 相似文献
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气旋波浪的个例分析 总被引：2，自引：0，他引：2
一、前言 强烈发展的入海气旋,是产生大风生成大浪的一种重要海上天气系统。特别是春秋季节移入我国北部海区的气旋与南下的冷空气相配合,常造成大风和降水天气,海面常出现大浪与巨浪。1979年11月25日“渤海二号”石油平台翻沉和1983年4月26日“107浮吊船”在渤海翻沉等海难事件,均为这种天气系统所致。 1983年 4月 25日 08时至28日 08时发生的一次强气旋天气过程,使渤海海区出现阵风达 11级和6.7米的巨浪(H_(1/10)=6.7米)。渔船受损,死伤渔民数人,经济损失严重。气旋带来的强风、暴雨、巨浪严重地威胁着人民生命财产的安全。因此,摸清气旋浪的分布规律有着十分重要的实用意义。 相似文献
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利用美国联合台风预警中心的热带气旋最佳路径数据集、美国国家海洋和大气管理局的扩展重构海表温度数据、全球海洋数据同化系统的温度、盐度数据及美国国家环境预报中心/国家大气研究中心的再分析资料, 分析了1981—2019年南印度洋热带气旋快速增强事件的气候特征和年际变率。结果表明, 南印度洋热带气旋快速增强事件产生频率呈现单峰分布, 主要产生在每年的12月至次年4月。南印度洋热带气旋增强事件的产生位置呈带状分布, 其中3个高值中心分别位于马达加斯加岛东北海域、南印度洋中部海域和澳大利亚西北海域, 这主要是由于热带气旋热潜和垂直风切变两个大尺度环境变量决定的。年际变率方面, 厄尔尼诺-南方涛动对南印度洋热带气旋增强事件产生频率的调制作用是不对称的, 厄尔尼诺年与拉尼娜年南印度洋热带气旋快速增强事件均减少, 但使其减少的物理机制不同。厄尔尼诺年, 热带气旋快速增强事件减少主要是较高的垂直风切变造成的; 拉尼娜年, 热带气旋快速增强事件减少主要是由于热带气旋热潜的降低, 而海表温度、垂直风切变和相对湿度也存在一定贡献。 相似文献
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长城站极地气旋与暴风雪天气 总被引：2，自引：0，他引：2
西南极极地气旋是造成长城站暴风雪的主要天气系统。夏季每月侵入长城站气旋有6～8个,平均3～4d就有气旋侵入南极半岛乔治王岛地区．冬季每月5～7个,且强度比夏季大。极地气旋移动路径在夏季稍有南移,冬季气旋路径向北扩展。西南极极地气旋东移靠近南极半岛,气旋有阻滞现象,气旋受阻气流上升使高空扰动,低压和低压槽强烈斜压发展,在锋区后伴有向北移动极地冷空气入侵,是形成长城站强暴风雪天气重要原因。极地气旋给长城站带来大风降雨降雪天气,长城站95％以上的暴风雪天气是由极地气旋引起的。而长城站暴风雪天气有二种类型：一种由极地气旋前部与锋面影响,吹北风或西北风暴风雪;另一种是由极地气旋南部或高压脊前影响,吹南风或东南风暴风雪天气。而后一种则是风速猛、气温低、危害最大。 相似文献
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Chandralata Raghukumar G. Sheelu P. A. Loka Bharathi Shanta Nair C. Mohandass 《Marine Georesources & Geotechnology》2001,19(1):1-16
In order to assess the impact of deep-sea mining on the in situ benthic life, we measured the microbial standing stock and concentration of organic nutrients in the deep-sea sediments of the Central Indian Ocean Basin in the Indian pioneer area. Sediments were collected using box core and grab samples during September 1996. The total bacterial numbers ranged from 10 10 -10 11 cells per g -1 dry weight sediment. There was a marginal decrease in the number of bacteria from surface to 30 cm depth, though the subsurface section registered a higher number than did the surface. The highest numbers were encountered at depths of 4-8 cm. The retrievable number of bacteria were two orders less in comparison with the direct total counts of bacteria. An almost homogeneous distribution of bacteria, total organic carbon, living biomass, and lipids throughout the depth of cores indicates active microbial and benthic processes in the deep sea sediments. On the other hand, a uniform distribution of total counts of bacteria, carbohydrates, and total organic carbon in all the cores indicates their stable nature and suggests that they can serve as useful parameters for long-term monitoring of the area after the benthic disturbance. Further studies on temporal variability in this region would not only verify the observed norms of distribution of these variables but would also help to understand restabilization processes after the simulated benthic disturbance. 相似文献
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Arne Schnack-Friedrichsen Angela M. Davis Jim D. Bennell Dei G. Huws 《Marine Georesources & Geotechnology》2001,19(4):221-243
The interdependence between the seismo-acoustic properties of a marine sediment and its geotechnical/physical parameters has been known for many years, and it has been postulated that this should allow the extraction of geotechnical information from seismic data. Though in the literature many correlations have been published for the surficial layer, there is a lack of information for greater sediment depths. In this article, a desktop study on a synthetic seafloor model illustrates how the application of published near-surface prediction equations to subsurface sediments (up to several tens of meters burial depth) can lead to spurious predictions. To test this further, acoustic and geotechnical properties were measured on a number of sediment core samples, some of which were subjected to loading in acoustically-equipped consolidation cells (oedometers) to simulate greater burial depth conditions. For low effective pressures (representing small burial depths extending to around 10 meters subsurface), the general applicability of established relationships was confirmed: the prediction of porosity, bulk density, and mean grain size from acoustic velocity and impedance appears generally possible for the investigated sedimentary environments. As effective pressure increases through, the observed relationships deviate more and more from the established ones for the near-surface area. For the samples tested in this study, in some instances increasing pressure even resulted in decreasing velocities. There are several possible explanations for this abnormal behavior, including the presence of gas, overconsolidation, or bimodal grain size distribution. The results indicate that an appropriate depth correction must be introduced into the published prediction equations in order to obtain reliable estimates of physical sediment properties for greater subsurface depths. 相似文献
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Derek V. Ellis 《Marine Georesources & Geotechnology》2001,19(1):51-63
This article reviews information recently available from existing marine and coastal mining for responses to environmental issues affecting marine mining at different depths. It is particularly but not exclusively concerned with those issues affecting seabed biodiversity impact and recovery. Much information has been gathered in the past 10 years from shallow mining operations for construction aggregate, diamonds, and gold, from coastal mines discharging tailings to shallow and deep water, and from experimental deep mining tests. The responses to issues identified are summarized in a series of eight tables intended to facilitate site-specific consideration. Since impacts can spread widely in the surface mixing layer SML, and can affect the biologically productive euphotic zone, the main issues considered arise from the depth of mining relative to the SML of the sea. Where mining is below the SML, the issue is whether it is environmentally better to bring the extraction products to the surface vessel for processing (and waste discharge), or to process the extraction products as much as possible on the seabed. Responses to the issues need to be sitespecific, and dependent on adequate preoperational environmental impact and recovery prediction. For deep tailings disposal from a surface vessel, there are four important environmental unknowns: (1) the possible growth of "marine snow" (bacterial flocs) utilizing the enormous quantities of fine tailings particles (hundreds or thousands of metric tons per day) as nuclei for growth, (2) the possibility that local keystone plankton and nekton species may migrate diurnally down to and beyond the depth of deep discharge and hence be subjected to tailings impact at depth, (3) the burrow-up capability of deep benthos and their ability to survive high rates of tailings deposition, and (4) the pattern and rate of dispersion of a tailings density current through the deep water column from discharge point to seabed. Actions to obtain relevant information in general and site-specifically are suggested. 相似文献
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G. Parthiban 《Marine Georesources & Geotechnology》2000,18(3):223-235
Particle fluxes were measured 7 m above the sea bottom during the predisturbance, disturbance, and postdisturbance periods by using time series sediment traps attached to seven deep-sea moorings deployed in the INDEX experiment site in the Central Indian Basin. The predisturbance particle fluxes varied between 22.3 to 55.1 mg m -2 day -1 . Increased and variable particle fluxes were recorded by the sediment traps during the disturbance period. The increase observed was 0.5 to 4 times more than the background predisturbance fluxes. The increases in particle fluxes (~4 times) recorded by the sediment trap located in the southwestern direction (DMS-1) were the greatest, which could be the result of preferential movement of resuspended particles generated during the deep-sea benthic disturbance along the general current direction prevailing in this area during the experimental period. Also, the traps located closer to the disturbance area recorded greater fluxes than did the traps far away, across the Deep Sea Sediment Resuspension System path. This variability in recorded particle fluxes by the traps around the disturbance area clearly indicates that physical characteristics such as grain size and density of the resuspended particles produced during the disturbance had an important effect on particle movement. The postdisturbance measurements during ~5 days showed a reduction in particle fluxes of ~50%, indicating rapid particle settlement. 相似文献
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海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。 相似文献
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Geoacoustic Inversion via Genetic Algorithm and Its Application to Manganese Sediment Identification
An acoustic inversion method using a wide-band signal and two near field receivers is proposed and applied to multiple layered seabed models including a manganese sediment. The inversion problem can be formulated into a probabilistic model comprised of signals, a forward model, and additive noise. The forward model simulates wide-band signals, such as chirp signals, and is chosen to be the source-waveletconvolution plane wave modeling method. The wavelet matching technique, using weighted least-squares fitting, estimates the sediment sound-speed and thickness on which determination of the possible numerical ranges for a priori uniform distribution is based. The genetic algorithm is applied to a global optimization problem to find a maximum a posteriori solution for determined a priori search space. Here the object function is defined by an L 2 norm of the difference between measured and modeled signals. Not only the marginal pdf but also its statistics are calculated by numerical evaluation of integrals using the samples selected during importance sampling process of the genetic algorithm. 相似文献
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The advanced piston corer (APC) has been used by the Ocean Drilling Program since 1985 for recovering soft sediments from the ocean floor. The pullout force measured on extracting the core barrel from the sediment is shown to correlate with the average shear strength of the sediment core measured in the ship's laboratory. A simple rule of thumb is derived relating the shear strength of the sediment to the pullout force. Multiple APC holes at individual sites allow the consistency of the pullout measurements to be assessed. The effects of different operational procedures during APC coring are also explored. Although generally applicable, the correlation between pullout force and laboratory measurements of shear strength breaks down for some APC holes, possibly because of the disturbance of some sediment types during the APC coring process. A better understanding of the physical process of APC coring, and its effect on the properties of the sediment both inside and immediately outside the core barrel, would indicate what confidence can be put on the measurement of pullout force as a way of evaluating the in situ shear strength of deep sea sediments. 相似文献
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Shigehisa Nakamura 《Marine Geodesy》2000,23(1):55-61
Specific properties of the interannual sea level variations and annual tides in the Northwestern Pacific were studied. Several tide stations were monitored. The monthly mean sea level for the year of 1995 was analyzed at each tide station. A seismic event in 1995, some tectonic activity around the subject area, and the Kuroshio (the oceanic western boundary current) may possibly contaminate results which would have occurred from the astronomical annual tide alone. 相似文献
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